field study of condensing heating in makeup-air and mixed ...field study of high efficiency heating...

Field Study of Condensing Heating in Makeup-air and

Mixed-air Rooftop Units (RTUs)

10/15/2017

Contract # 72633

Conservation Applied Research and Development (CARD) FINAL Report

Prepared for: Minnesota Department of Commerce, Division of Energy Resources Prepared by: Gas Technology Institute

Field Study of High Efficiency Heating & Cooling Mixed-air Rooftop Units (RTUs) Gas Technology Institute 1

Prepared by: Patricia Rowley Douglas Kosar Shawn Scott Alejandro Baez Guada Gas Technology Institute 1700 S. Mount Prospect Road Des Plaines, Illinois 60018 Phone: 647-768-0555 website: www.gastechnology.org Project Contact: Patricia Rowley ([email protected])

© 2017 Gas Technology Institute. All Rights Reserved.

Contract Number: 72633

Prepared for Minnesota Department of Commerce, Division of Energy Resources: Jessica Looman, Commissioner, Department of Commerce Bill Grant, Deputy Commissioner, Department of Commerce, Division of Energy Resources

Mark Garofano, Project Manager [email protected]

ACKNOWLEGEMENTS

This project was supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources, through the Conservation Applied Research and Development (CARD) program, which is funded by Minnesota ratepayers.

The authors would also like to acknowledge Heartland Seven Corners Hotel and the Blue Plate Restaurants Company for their participation, in addition to CenterPoint Energy, Reznor-Nortek Global, John J. Morgan Co., and the Center for Energy and Environment for their in-kind and technical contributions to this project. Thank you to all project partners for sharing your time and expertise.

DISCLAIMER

This report does not necessarily represent the view(s), opinion(s), or position(s) of the Minnesota Department of Commerce (Commerce), its employees or the State of Minnesota (State). When applicable, the State will evaluate the results of this research for inclusion in Conservation Improvement Program (CIP) portfolios and communicate its recommendations in separate document(s).

Commerce, the State, its employees, contractors, subcontractors, project participants, the organizations listed herein, or any person on behalf of any of the organizations mentioned herein make no warranty, express or implied, with respect to the use of any information, apparatus, method, or process disclosed in this document. Furthermore, the aforementioned parties assume no liability for the information in this report with respect to the use of, or damages resulting from the use of, any information, apparatus, method, or process disclosed in this document; nor does any party represent that the use of this information will not infringe upon privately owned rights.


Table of Contents

Table of Contents ...............................................................................................................................2

List of Figures .....................................................................................................................................5

List of Tables ......................................................................................................................................7

Definition of Terms and Acronyms......................................................................................................9

Executive Summary .......................................................................................................................... 11

Objective ................................................................................................................................................. 12

Field Sites ................................................................................................................................................. 12

Results ..................................................................................................................................................... 13

Summary ................................................................................................................................................. 14

Background ..................................................................................................................................... 16

Packaged Rooftop Units (RTUs) ............................................................................................................... 16

Condensing Heating Design ................................................................................................................ 16

Condensing RTU Market Challenges ................................................................................................... 17

Condensing RTU Products ................................................................................................................... 18

Methodology ................................................................................................................................... 20

Demonstration Site Selection .................................................................................................................. 20

Site Selection Criteria .......................................................................................................................... 20

Demonstration Plan ................................................................................................................................ 21

Data Collection Equipment ................................................................................................................. 21

Duplicate Sensors ................................................................................................................................ 23

RTU Data Comparison Methodologies ................................................................................................ 24

Results ............................................................................................................................................. 26

Field Site Identification ............................................................................................................................ 26

Courtyard Marriott Minneapolis Downtown ...................................................................................... 27

The Lowry Restaurant ......................................................................................................................... 28

Hotel Kitchen Makeup Air Unit (100% OA) ............................................................................................. 29

Baseline Equipment ............................................................................................................................ 29

Condensing MAU Equipment .............................................................................................................. 32


5-Ton Rooftop Unit (0% to 30% OA) ....................................................................................................... 46

Baseline Equipment ............................................................................................................................ 47

Condensing RTU Equipment ............................................................................................................... 51

Discussion of Results ........................................................................................................................ 67

Situational Analysis.................................................................................................................................. 68

Market Development and Economic Trends ...................................................................................... 68

Minnesota RTU Market ....................................................................................................................... 68

Condensing RTU Market ..................................................................................................................... 69

Energy Conservation Potential for Minnesota .................................................................................... 71

Transferability ..................................................................................................................................... 72

Non-Energy Impacts ............................................................................................................................ 73

Conclusions and Recommendations.................................................................................................. 74

Summary ................................................................................................................................................. 74

Recommendations .................................................................................................................................. 74

Next Steps................................................................................................................................................ 75

References ....................................................................................................................................... 77

Appendix A: Reznor RHH Select Installation Instructions ................................................................... 79

Appendix B: Condensate Management Best Practices ....................................................................... 81

Building Codes & Combustion Condensate Management ...................................................................... 81

International Mechanical Code (IMC) ................................................................................................. 82

Uniform Plumbing Code (UPC) ............................................................................................................ 83

Minnesota State Code (IMC/UPC) Summary ...................................................................................... 84

Condensate Management Best Practices ............................................................................................... 85

Reznor R8HE Condensate Installation Instructions ............................................................................ 86

Reznor RHH Condensate Installation Instructions .............................................................................. 88

Reznor RHH Installation at Hotel Site ................................................................................................. 88

Neutralizers ......................................................................................................................................... 90

Condensate Pumps ............................................................................................................................. 91

Appendix C: Energy Conservation Potential – Calculation Details ...................................................... 92

Step 1 – Determine Ventilation Air ......................................................................................................... 92


Step 2 – Minnesota Building Square Footage ......................................................................................... 92

Step 3 – Calculated Heat Load ................................................................................................................. 93

Step 4 – Building Operating Schedules.................................................................................................... 93

Step 5 – Market Penetration ................................................................................................................... 94

Appendix D: Emissions Reduction Potential Supporting Information ................................................ 95

Appendix E ...................................................................................................................................... 96

Overview ................................................................................................................................................. 97

New Measure Characterizations ............................................................................................................. 98

Description .......................................................................................................................................... 98

Definition of Efficient Equipment ....................................................................................................... 98

Definition of Baseline Equipment ....................................................................................................... 98

Deemed Lifetime of Efficient Equipment ............................................................................................ 99

Deemed Measure Cost ........................................................................................................................ 99

Loadshape ........................................................................................................................................... 99

Coincidence Factor .............................................................................................................................. 99

Algorithm .......................................................................................................................................... 100

Proposed Changes to Existing Measures............................................................................................... 109

References ............................................................................................................................................. 110


List of Figures

Figure 1. Schematic of a Condensing Heating Module ............................................................................... 16

Figure 2. Range of Outside Air Fraction for Condensing RTU Products ...................................................... 19

Figure 3. Baseline RTU Monitored Data Points ........................................................................................... 22

Figure 4. Current Switches and State Loggers ............................................................................................ 23

Figure 5. Minneapolis Hotel Demonstration Site........................................................................................ 27

Figure 6. Side-by-side Kitchen MAUs at the Hotel Field Site ...................................................................... 28

Figure 7. Restaurant Field Site for 5-ton RTU Demonstration .................................................................... 28

Figure 8. Baseline 5-ton RTU at Restaurant Site ......................................................................................... 29

Figure 9. Side-by-side Baseline Kitchen MAUs ............................................................................................ 29

Figure 10. MAU Heating Only Baseline Monitoring of Gas Use .................................................................. 31

Figure 11. MAU Heating Only Baseline Monitoring of Electric Use ............................................................ 32

Figure 12. Condensing MAU Installed October 2016 .................................................................................. 33

Figure 13. Incorrect MAU Condensate Installation at the Hotel Site ......................................................... 35

Figure 14. Corrected Installation of the MAU Condensate Drain ............................................................... 35

Figure 15. Condensing MAU Temps, Fan and Gas Valve Operation ........................................................... 36

Figure 16. Baseline MAU Temps, Fan and Gas Valve Operation ................................................................ 36

Figure 17. Normalized Gas Usage with respect to Heating Degree Days ................................................... 37

Figure 18. Baseline Normalized Gas Usage for 2015/2016 and 2016/2017 .............................................. 38

Figure 19. Equivalent Full Load Hours with respect to Heating Degree Days ............................................ 38

Figure 20. Measured Total Electricity Use of Baseline and Condensing MAUs .......................................... 39

Figure 21. Baseline 5-ton RTU Serving the Restaurant Dining Room ......................................................... 47

Figure 22. Multiple RTUs installed at the Restaurant Field Site ................................................................. 49

Figure 23. Comparison of RTU Heating Runtimes at Restaurant Site ......................................................... 50

Figure 24. Combined RTU Gas Usage with respect to Heating Degree Days .............................................. 50

Figure 25. Baseline RTU Gas Usage with respect to Heating Degree Days ................................................. 51

Figure 26. Installation of Condensing RTU and Fixed OA Damper .............................................................. 53

Figure 27. Electricity Usage with respect to Cooling Degree Days ............................................................ 54

Figure 28. Gas Usage with respect to Heating Degree Days ....................................................................... 57


Figure 29. Daily Equivalent Full Load Hours vs Heating Degree Days ......................................................... 58

Figure 30. Reznor R8HE Installation Schematic .......................................................................................... 86

Figure 31. Existing RTU Installed on “sleepers” Instead of a Roof Curb ..................................................... 87

Figure 32. Reznor R8HE Condensate Drain Installation .............................................................................. 87

Figure 33. Reznor RHH Condensate Drain Installation Instructions ........................................................... 88

Figure 34. MAU Condensate Drain at the Hotel Demonstration Site ......................................................... 89


List of Tables

Table 1. Baseline Data Acquisition System Equipment Specifications ....................................................... 22

Table 2. Duplicate Data Acquisition System Equipment Specifications ...................................................... 23

Table 3. Baseline Kitchen MAU Specification ............................................................................................. 30

Table 4. Parallel Kitchen MAU Specification ............................................................................................... 30

Table 5. Condensing Kitchen Makeup Air Unit Specification ...................................................................... 33

Table 6. Total Measured Energy Use Data for Condensing MAU and Baseline .......................................... 40

Table 7. Extrapolated Annual Gas Use for Condensing MAU and Baseline ................................................ 41

Table 8. Estimated Annual Energy Savings for Heating .............................................................................. 41

Table 9. Estimated Annual Net Energy Cost Savings................................................................................... 41

Table 10. Estimated Annual Net Energy Costs for Condensing vs Baseline MAU ...................................... 43

Table 11. Condensing MAU Installed Cost Premiums and Paybacks .......................................................... 45

Table 12. Net Energy Cost Savings with respect to Energy Prices .............................................................. 46

Table 13. Baseline RTU Specifications ........................................................................................................ 48

Table 14. Condensing RTU Specifications ................................................................................................... 52

Table 15. Cooling Energy and Cost Savings for Replacement vs Baseline RTU ........................................... 55

Table 16. Total Measured Energy Use for Condensing and Baseline RTUs ................................................ 56

Table 17. Annual Gas Use for Condensing and Baseline RTUs ................................................................... 59

Table 18. Estimated Annual Energy Savings for Heating ............................................................................ 59

Table 19. Net Energy Cost Savings for Condensing Heating ....................................................................... 59

Table 20. Low Runtime Annual Net Energy Costs for Condensing RTU ...................................................... 61

Table 21. Low Runtime Condensing RTU Paybacks .................................................................................... 62

Table 22. Low Runtime Net Energy Cost Savings ........................................................................................ 63

Table 23. High Runtime Net Energy Costs for Condensing Heating ........................................................... 64

Table 24. High Runtime Condensing RTU Paybacks .................................................................................... 65

Table 25. High Runtime Net Energy Cost Savings ....................................................................................... 66

Table 26. Condensing RTU Energy Conservation Potential for Natural Gas Only....................................... 72

Table 27. CBECs Total Floor Space for Target Market Building Types ........................................................ 93

Table 28. Energy Conservation Potential Calculations (Excerpt) ................................................................ 94


Table 29. Energy Conservation Potential Calculations ............................................................................... 95

Table 30. Emissions and Source Energy Savings with 2.5% Market Penetration ....................................... 95

Table 31. NCDC HDD Values for All Climate Zones ................................................................................... 100

Table 32. TMY3 HDD Values for Climate Zone 2 ....................................................................................... 101

Table 33. 8760 Hour Annual Operation Scenario for HDD45 ................................................................... 104













Definition of Terms and Acronyms

AFUE annual fuel utilization efficiency

AHJ Authority Having Jurisdiction

ASHRAE American Society of Heating, Refrigeration and Air-Conditioning Engineers

Btu British thermal unit

C&I commercial and industrial

cfm cubic foot/feet per minute

DCV demand control ventilation

DOAS dedicated outside air systems

DOE Department of Energy

DX direct expansion

EFLH equivalent full load hours

EIA Energy Information Administration

ERV energy recovery ventilation

EUI energy use intensity

F degrees Fahrenheit

GTI Gas Technology Institute

HDD heating degree day

HVAC heating, ventilating, and air conditioning

IAPMO International Association of Plumbing and Mechanical Officials

IAQ indoor air quality

ICC International Code Council

IFGC International Fuel Gas Code

IMC International Mechanical Code

IPC International Plumbing Code


MBH thousands of BTU per hour

MAU make-up air unit

NA not applicable

NCDC National Climatic Data Center

NFGC National Fuel Gas Code

NFPA National Fire Protection Association

OA outside air

OAT outside air temperature

RA return air

RTU rooftop unit

SA supply air

TE thermal efficiency

UMC Uniform Mechanical Code

UPC Uniform Plumbing Code

VAV variable air volume

VRF variable refrigerant flow

W.G. water gauge


Executive Summary

Packaged unitary heating, ventilation, and air conditioning (HVAC) systems or rooftop units (RTUs) are used in 40% of conditioned commercial floor space in the United States. As major energy consumers, the use of high efficiency RTU products offer significant potential for energy savings. While the majority of recent RTU efficiency improvements have focused on electric air-conditioning, the introduction of high efficiency heating has been limited. Emerging RTUs with condensing heating provide higher heating efficiencies (+90% thermal efficiencies (TE)), resulting in more than 10% gas savings over conventional, non-condensing efficiency levels. Given the high heating loads in Minnesota, condensing RTUs offer significant natural gas conservation potential, along with non-energy benefits such as the reduction of greenhouse gas emissions.

Condensing heating technology is commonly used in residential furnaces and boilers. However, the introduction of condensing furnaces in unitary packages for the commercial and industrial (C&I) market, especially weatherized systems like RTUs, has been slowed by certain economic and technical challenges. For example, current first cost premiums for condensing RTU equipment is high due to additional material costs and the initial lower volume, higher cost production of the current product offerings from non-major, second-tier HVAC manufacturers. Presently most contractors lack the experience necessary to make installation of condensing RTUs routine, which often leads to higher installation costs. On the technical side, best practices need to be developed for affordable combustion condensate systems that meet code requirements for condensate disposal, including neutralization of its acidic content where required. Condensate systems must also provide adequate freeze protection in outdoor installations. Emerging best practices for condensate management are based on a limited number of pilot studies, and additional field studies are needed to demonstrate reliable condensate disposal from rooftop locations.

The most cost-effective initial markets for condensing RTUs are applications with large heating loads and long runtimes. These applications must generate adequate energy savings to pay back the cost premium of the condensing equipment. The cost premium includes incremental equipment costs; material and installation costs for the condensate management system; and any additional maintenance costs for neutralization. The conditioning of OA for ventilation to maintain indoor air quality presents a large heating load, and some commercial and institutional buildings even utilize RTUs that are dedicated outside air systems (DOAS) to condition 100% OA for building ventilation. Other buildings use RTUs that are make-up air systems (MAUs) to supply 100% OA to compensate for exhaust and maintain neutral or slightly positive building pressurization. Many 100% OA systems operate continuously during occupied hours, up to 24/7 in some cases, offering long runtimes as well. While, the use of 100% OA systems appears to be gaining in popularity, especially DOAS for ventilation air treatment, it is still a fraction of the mass market. Conventional RTUs are typically selected based on first costs rather than energy efficiency.


Objective

The objective of this field study was to determine the energy savings and cost-effectiveness of the emerging condensing RTU products and to validate best practices in condensate management at two field sites in Minneapolis, Minnesota. The overall goal was to demonstrate condensing RTU technology in expanding market opportunities, from 100% OA to mixed-air applications, and to determine its viability for inclusion in the Minnesota Conservation Improvement Program (CIP).

Field Sites

This study was designed to provide real-world datasets on energy savings and economics across the range of applications, and to identify potential target costs required for a beneficial payback. The first site represented an application with 100%OA, which represent the early target market for condensing RTUs. A hotel commercial kitchen makeup air unit (MAU) was selected to demonstrate the performance and cost-effectiveness of condensing RTUs, expanding the initial niche market beyond dedicated outside air systems (DOAS) used for building ventilation. A conventional RTU installed over a dining area at a restaurant was selected for the second site to demonstrate condensing technology at lower capacities and lower OA fractions of 30% or less.

At the hotel demonstration site, two existing MAUs delivered makeup air to opposite sides of the same kitchen exhaust hood. Both MAUs were constant volume, heating-only units that provide conditioned 100% OA continuously to compensate for the kitchen exhaust air. When the OA temperature dropped below the setpoint (approximately 45F), the MAUs heated the makeup air to a preset supply temperature (approximately 70F). The first MAU was a 30-year-old unit with 77% thermal efficiency (TE) nameplate efficiency that would be replaced by the condensing MAU for the demonstration. The second MAU was a 5-year-old system (80% TE) that continued to operate during the baseline and demonstration monitoring. Both MAUs were monitored for baseline energy use, so the condensing MAU could be compared to an older replacement MAU as well as a newer standard efficiency unit.

For the second demonstration site, the project team identified a restaurant application with a five-ton conventional RTU (0-30% OA). Although condensing RTUs with smaller capacities may not be cost-effective at current equipment costs and/or fuel costs, condensing heating will likely be adopted across the range of capacities in the future. Five-ton conventional RTUs make up a significant share of the RTU market. The baseline RTU was one of four HVAC rooftop units serving a single-story restaurant. The selected 5-ton RTU (11% OA) provided heating and cooling to a portion of the dining room area. Runtime data was also recorded for the adjacent RTUs during baseline monitoring period.

At both sites, baseline monitoring was conducted from October 2015 to September 2016 to include the full range of seasonal variations to accurately predict annual baseline energy use. Condensing RTUs units were installed in October 2016 and monitored until September 2017. At the hotel site, the baseline 77% TE kitchen MAU was replaced with the Reznor RHH-260D with a nameplate efficiency of 91% TE. At the


restaurant site, the baseline 80% AFUE RTU was replaced with the Reznor R8HE with a nameplate efficiency of 95% AFUE.

A real-time data acquisition system recorded performance data from baseline and condensing RTUs, including the following parameters: gas consumption; gas valve operation to determine heating runtimes; supply fan electricity consumption; and temperatures of outdoor air, supply air, and return air. Energy consumption was normalized with respect to weather data, specifically heating degree days (HDD), to determine the energy savings of the condensing units relative to the baseline equipment.

Results

Based on this field study, condensing heating can generate gas savings up to 17%, compared to standard efficiency (80% TE) systems, across the range of capacities and applications. In both applications, 100%OA MAUs and conventional RTUs, natural gas cost savings more than offset the expected increase in electricity costs due to the fan energy penalty, resulting in a positive net energy cost savings.

Despite significant gas savings and annual cost savings, current installation and maintenance costs for condensate management systems present an economic challenge for cost effective application of condensing MAUs. Based on this field study, annual costs savings from the condensing MAU were sufficient to offset current equipment premiums, but with the additional cost of the condensate management system, simple paybacks exceeded the life of the equipment, assumed as fifteen years. Incremental costs for this study were for end-of-life replacement and based on a new condensing unit as compared to an equivalent standard-efficiency unit (80% TE) offered by the same manufacturer. Current historically low natural gas prices contribute to the challenging economics for many energy efficiency technologies, including condensing rooftop applications

As with most emerging technologies, condensing RTUs are presently manufactured in smaller production volumes and have higher first costs in comparison to the mature market pricing for competing established baseline technologies. For condensing RTUs (excluding the condensate management system and its installation), DOE projects the equipment cost premium in a mature market to be $4.40 per 1000 Btu/hr of output heating capacity.1 The installed cost of the condensate management systems can vary widely due to specific site configurations and local code. Assuming projected mature market prices for both equipment and condensate systems, condensing MAUs have potential to achieve simple paybacks of 4.0 years. Although local Minnesota codes do not require it, one of the two sites included a neutralizer in the condensate drain. Additional maintenance costs for annual neutralizer replacement, if included, extends the payback to 6-11 years for this MAU site, based on mature market pricing for total installed costs.

As expected, the economics were even more challenging for smaller capacity condensing RTUs in applications with lower OA fractions. For this demonstration, the target 5-ton RTU was found to have

1 DOE Notice of Proposal Rulemaking (NOPR) Commercial Warm Air Furnace (CWAF) technical documentation [DOE 2015].

https://www.regulations.gov/document?D=EERE-2013-BT-STD-0021-0012

https://www.regulations.gov/document?D=EERE-2013-BT-STD-0021-0012


low heating loads due to lower ventilation loads (11%OA) and lower runtime (<600 EFLH), in part due to the operation of adjacent RTUs. The condensing RTU did not generate adequate cost savings to offset the installed cost premiums, even with projected mature market prices. The use of condensing RTUs will not be cost effective in low runtime, low capacity applications. However, assuming mature market prices for condensing equipment and condensate systems, low-capacity condensing RTUs have potential to achieve 6-year paybacks in applications with longer runtimes (>1800 EFLH)2. Annual maintenance costs for the neutralizer replacement, if required, will lengthen paybacks to 9 years, based on mature market pricing for total installed costs.

In addition to energy and cost savings, this field study successfully demonstrated best practices for combustion condensate management to provide adequate freeze protection in colder climate rooftop environments. Existing codes for combustion condensate disposal allow for wide discretion by the installing contractor, subject to approval by the authority having jurisdiction (AHJ), regarding the drain connection and neutralizer requirements. For installation contractors unfamiliar with this technology, manufacturers must provide clear and detailed installation instructions to ensure proper condensate management to prevent condensate freezing. In this study, installation issues regarding condensate management occurred at both field sites.

Summary

The use of condensing heating in rooftop applications offers high efficiency heating (90% TE to 95% TE) generating significant gas savings compared to standard efficiency (80% TE) systems. At current prices, the cost effectiveness of condensing MAUs is dependent on the site-specific heating runtimes and costs of the condensate management system. With mature market pricing, condensing MAUs have potential to achieve simple paybacks of 4 years. Cost effective application of condensing heating in low capacity conventional, lower %OA RTUs is more challenging, and will require long runtimes as well as mature market pricing and/or equipment rebates to offset the higher cost premium.

This field study confirms 100% OA applications as the most promising initial market entry for condensing heating in commercial rooftop products. These applications, such as DOAS and MAU, provide the long, predictable runtimes and larger heating loads required to generate net energy savings large enough to offset the installed cost premium. Based on multiple pilot studies demonstrating the potential energy savings, a number of utility rebate programs are including condensing RTUs, either as general prescriptive rebates or custom rebates for specific applications, such as DOAS. Leveraging these datasets and experience, GTI drafted a work paper for a Minnesota utility to develop a new measure for the State of Minnesota’s Energy Conservation Improvement Program (Appendix E).

This report also includes a summary of best practices for condensate management, including manufacturer installation instructions and applicable codes. Clear and specific instructions will reduce confusion around installation requirements to prevent freezing or other operational issues, while still

2 Based on a previous study that measured runtimes of installed RTUs in a multiple applications; EFLHs ranged from 600 to a high of 1800 [Kosar 2014].


minimizing costs. Increasing the familiarity and uniformity of condensate management will be the first step in reducing installed costs.


Background

Packaged Rooftop Units (RTUs)

Packaged unitary heating, ventilation, and air conditioning (HVAC) systems or rooftop units (RTUs) are used in 40% of conditioned commercial floor space in the United States. RTUs are major energy consumers in the commercial building sector, and emerging high efficiency RTU products offer potential for significant energy savings. The majority of recent RTU efficiency improvements have focused on electric air-conditioning, while the introduction of high efficiency heating has been limited. Emerging RTUs with condensing heating can provide higher heating efficiencies (+90% thermal efficiencies (TE)), resulting in over 10% gas savings over conventional, non-condensing efficiency levels. Given the high heating loads in Minnesota, condensing RTUs offer significant natural gas conservation potential, along with providing non-energy benefits such as the reduction of greenhouse gas emissions.

Condensing Heating Design A condensing heating design incorporates a secondary heat exchanger that increases thermal efficiency up to 97% by condensing the water vapor in the hot exhaust gases. The return airflow initially passes over the secondary, condensing (lower temperature) in line heat exchanger, and then passes over the primary, tubular/clamshell (higher temperature) heat exchanger (Figure 1). As a result, supply air temperatures of a condensing furnace are consistent with non-condensing furnaces.

Figure 1. Schematic of a Condensing Heating Module


Since the secondary heat exchanger is located in the primary air stream, there is an incremental pressure drop for the supply fan that increases fan energy use whenever the fan is operating. In some applications, the supply fan operates continually during occupied hours or even 24/7 depending on the building type and application, which has a multiplying effect on this energy penalty. Therefore, the net annual cost savings calculated for this emerging technology must take into account natural gas savings as well as the level of increase in fan electric usage (“fan energy penalty”) and any additional maintenance costs for condensate management. With ongoing development, the fan energy penalty may be reduced through improvements in heat exchanger design as well as multi-stage or variable-speed supply fans.

Condensing RTU Market Challenges Condensing heating technology has achieved significant penetration of the residential furnace and boiler market. However, the introduction of condensing furnaces in unitary packages for the commercial and industrial (C&I) market, especially weatherized systems like RTUs, has been slowed by certain economic and technical challenges. For example, due to limited production, current first costs of condensing RTU equipment is quite high. In addition, most contractors do not have the experience necessary to make installation of condensing RTUs routine, which often leads to higher installation costs until that experience is gained. A challenge on the technical side is the development of affordable combustion condensate systems that meet code requirements for condensate disposal, including neutralization of its acidic content if required by local codes. Condensate systems must also provide adequate freeze protection for outdoor installations. While some best practices for condensate management have been developed based on a limited number of pilot studies, additional field studies are needed to demonstrate reliable condensate disposal from rooftop locations.

The most cost-effective initial markets for condensing RTUs are applications with large heating loads and long runtimes. These applications must generate adequate energy savings to pay back the cost premium of the condensing equipment. The cost premium includes: incremental equipment costs; material and installation of the condensate management system; and any additional maintenance costs for neutralization. Systems that condition 100% outside air (OA) to maintain indoor air quality or to provide make-up air are common applications with large heating loads. Many 100% OA systems operate continuously during occupied hours, up to 24/7 in some cases, offering extended runtimes.

Dedicated outside air systems (DOAS) are increasingly used to provide conditioned 100% OA to meet ventilation requirements in commercial buildings. Make-up air units (MAUs) deliver conditioned 100% OA in hotel/apartment buildings or restaurants, to compensate for exhaust air and maintain neutral or slightly positive building pressurization. Over the heating season, these systems warm cold outside air to its required supply air temperature. Previous field studies indicate that condensing heating in 100% OA applications can provide significant gas savings with promising economics [Kosar 2017].


Condensing RTU Products The vast majority of the product and market development to date has taken place with smaller HVAC manufacturers. Engineered Air, Modine, Reznor, ICE Western, and Munters have all been actively introducing condensing RTU product lines over the last few years. The marketplace is dynamic and manufacturers are now progressing their condensing RTU offerings from first generation 90% TE to second generation 93% TE and higher product lines. Current condensing products offer heating input capacities ranging from 60 to 3,000 MBH and modulating turndown ratios as high as 60:1. Product line airflows range from 650 to 44,000 cfm with cooling capacities of 1 to 120 tons.

It was not until late summer of 2014 that any of the larger HVAC manufacturers established a condensing RTU offering. However, those offerings have seen very limited in-house resource commitment and market exposure by the two engaged major HVAC manufacturers, Trane and York. In late summer 2014, Trane, began offering condensing RTUs as a retrofitted option, taking RTUs off their large volume production line and modifying the product at their Creative Solutions custom production facility. In early spring 2015, York began offering specialized condensing RTUs for dedicated outside air system (DOAS) application. That condensing DOAS offering is actually a rebranded product made by others, which in this case is one of the smaller aforementioned HVAC manufacturers.

Many manufacturers rely on the availability of condensing heating modules from commercial warm air (duct) furnace (CWAF) manufacturers, in particular from Beckett Gas and Heatco, that have been actively developing condensing heating modules and providing these high efficiency gas furnace components to small and large HVAC manufacturers that package RTUs. The condensing heating modules range from 90 to 1,650 MBH input capacities at up to 93% TE and up to 10:1 turndown, with airflows from 431 to 45,833 cfm, depending on temperature rise. Both Heatco and Beckett offer services to HVAC manufacturers that allow any HVAC packager to readily enter the marketplace with a condensing RTU. Those services start with the HVAC packager providing their RTU housings to the CWAF plant on a one-time basis for "best fit" of available heating modules to their RTUs. The CWAF manufacturer provides in plant testing for Intertek (ETL), Canadian Standards Association (CSA), and Underwriters Laboratories (UL) “satellite” certification of the furnace sections of those RTUs. Both CWAF manufacturers have designed their condensing heating modules to replace their equivalent output capacity, non-condensing heating modules within the same housing dimensions, so transitions from non-condensing to condensing heating modules can be readily accomplished. This design approach can, however, have even higher pressure drop consequences for the condensing heating module in a given RTU. Since larger HVAC manufacturers have tentatively entered the marketplace with condensing RTUs only in the last year or two, the continued early market development will rely predominately on the product offerings from the smaller HVAC manufacturers for the foreseeable future.

As with most emerging technologies, higher equipment and installation costs are a challenge for market entry. With small production volumes, it is difficult for new products to compete economically with established mass produced technologies with mature market pricing. This is especially true for RTUs which are usually selected based on first costs rather than energy efficiency. RTUs are typically


purchased by construction contractors and/or building owners, while the building tenants are the ones to financially benefit from the energy savings of higher efficiency products.

As shown in Figure 2, RTU products span the range of ventilation, from conventional units (0-30% OA), to higher mixed-air (between 30% and 100% OA), and then DOAS and 100% OA makeup air units. One of the smaller HVAC manufacturers, Reznor, has moved out ahead of the pack to introduce a line of condensing heating RTUs that cover the full spectrum of OA%, from 100% OA (DOAS) to fully recirculated or 0% OA, and everything in between. Reznor recently launched a new mixed-air RTU product line combining condensing heating with high efficiency cooling to address a much larger segment of the C&I market and expand the adoption of condensing heating in RTU applications. A field demonstration of this new RTU product line will determine the energy savings and cost-effectiveness of condensing RTU in multiple applications, and determine its viability for inclusion in the Minnesota Conservation Improvement Program (CIP).

Figure 2. Range of Outside Air Fraction for Condensing RTU Products

Source: Kosar, D., CEE 2015 Industry Partners Meeting, Bloomingdale, IL, September 17, 2015.


Methodology

The objective of this field study was to determine the energy savings of new high-efficiency condensing RTU products and to demonstrate best practices in condensate management from cold climate rooftop locations. This field study also investigated the potential cost-effectiveness of condensing units as compared to standard efficiency RTUs. The overall goal of this field study was to demonstrate condensing RTU technology in expanded market applications, and determine its viability for inclusion in the Minnesota Conservation Improvement Program (CIP).

For this project, GTI partnered with a local Minnesota utility, CenterPoint Energy, and the RTU manufacturer, Reznor, to demonstrate the newly commercialized, condensing RTUs at two Minnesota field sites. Existing equipment was monitored for a full year to establish the baseline energy use for each field site. Likewise, the performance of the new condensing RTUs was monitored the following year to determine annual energy savings across the full range of ambient conditions and seasonal variations. The field study also quantified the costs of installation, operation and maintenance, and payback projections for the condensing equipment and condensate management systems.

Demonstration Site Selection

Site Selection Criteria A previous field study, led by GTI, demonstrated the cost effectiveness of condensing heating in a DOAS application at a Minnesota “big-box” retail store. This early market entry was selected to provide the highest heating loads generating the greatest energy savings and the shortest paybacks for condensing equipment. For the current study, the initial site selection process targeted existing installations of mixed-air RTUs to demonstrate Reznor’s new mixed-air condensing product line to expand the initial DOAS niche market. Buildings with high occupancy and indoor air quality requirements typically require higher ventilation rates, such as auditoriums, theaters, restaurants, hotels, gymnasiums, nursing homes, healthcare, and schools. These applications typically use DOAS or mixed-air RTUs.

The initial approach for site selection focused on demonstrating the new mixed-air RTUs at two Minnesota demonstration sites. The site selection criteria included the following requirements:

• Utilize an existing, operating mixed-air RTU with 30-100% OA fraction • Accommodate three to four pre-arranged visits following installation and performance

monitoring • Located within the partner utility’s territory • Commit to the two year project and be willing to:

o Retain existing RTU during twelve months of baseline monitoring o Allow access for an additional twelve months monitoring of the demonstration

condensing RTU equipment o Allow equipment performance data to be published


The second approach used for site selection involved taking a long-term view of future markets for condensing RTUs by demonstrating RTU performance and economics at opposite ends of the mixed-air OA fraction. Under this approach, the first demonstration site targeted applications with high OA fraction, such as 100% OA make-up air units (MAUs) used in commercial kitchens or corridors in hotel, condominium, or apartments. Condensing heating in MAU applications is expected to be cost-effective in the near term. The second site demonstrated condensing RTU technology at lower capacities and lower ventilation rates. Although condensing RTUs in smaller capacities may not be cost-effective at current equipment costs and/or fuel costs, condensing heating is likely be adopted across the range of capacities in the future. Demonstration of condensing heating in standard RTUs determined the installed energy use and operating costs for the range of capacities, and provided cost targets required for a beneficial payback.

Demonstration Plan

The demonstration plan specified the data collection methods to monitor the performance of baseline existing equipment and new high efficiency demonstration units. The plan specified instrumentation and on-site DAS with remote communications for real-time monitoring of RTU performance. In addition, low-cost duplicate sensors were installed as backup to ensure continuous data collection.

The existing RTUs were monitored from October 2015 to September 2016 across the full range of ambient conditions and seasonal variations to accurately predict baseline energy use. The new condensing equipment was installed in October 2016. Performance data was analyzed, and reported for a year to determine annual energy use and operating costs as compared to baseline data. The same instrumentation was used to monitor baseline and demonstration units.

Data Collection Equipment Baseline characterization included monitoring gas and electricity use during heating operation (and cooling, if applicable) using a DAS with remote communications capability. Gas meters equipped with pulse counters were installed in the gas supply to accurately monitor gas consumption. A current switch was used to time stamp the opening and closing of single and two-stage gas valves. A compact watt-hour meter was installed to monitor the electricity consumption of the supply fan and a second watt-hour meter monitored electricity consumption of the total system, including the compressor. A current switch was used to monitor the runtime of the supply fan. Outdoor air, return air, and supply air temperatures were monitored using Type-T thermocouples. These data points are represented in Figure 3 along with an accompanying list of DAS specifications in Table 1. Meters were installed by a local contractor, while GTI installed the remaining sensors and commissioned the DAS at each site. The data logger has cellular communications capability for remote downloading of data. Real-time access of RTU performance monitoring was available as needed for diagnostics or troubleshooting. Data was recorded at 5-minute intervals and transmitted to a file server via cell phone modem.


Figure 3. Baseline RTU Monitored Data Points

Table 1. Baseline Data Acquisition System Equipment Specifications

Label Monitored Data Equipment Manufacturer/ Model Accuracy

GP Gas Use Gas Meter with pulser

American Meter 1) AC-250-TC-P (5-ton RTU) 2) AC-425-TC-P (MAU)

1) 40 pulses/cu.ft. 2) 20 pulses /cu.ft.

W1 RTU fan power Watthour meter; 20A current transformers

Continental Controls RWNB-3D-480-P ACT-0750-020 Opt C0.6

± 0.5%

W2 RTU total electricity use

Watthour meter; 50A current transformers

Continental Controls RWNB-3D-480-P ACT-0750-050 Opt C0.6

± 0.5%

T1 Return Air Temperature

Thermocouple Omega 5TC-TT-T-24-72 ± 1oF

T2 Outdoor Air Temperature


T3 Supply Air Temperature



Duplicate Sensors GTI used duplicate sensors as a backup to continuously collect data in the event of a failure in the DAS or primary sensors. This low cost technique, described in Table 2 and Figure 4, has been used extensively by GTI in past monitoring activities. The duplicate sensors utilize a low cost DAS to confirm key operating parameters, such as runtime, and establish baseline energy use. The duplicate DAS consist of current switches and battery-operated data loggers to record staged gas valves, staged compressor operation, and constant volume fan operation. Nameplate rating information for each unit can be used to translate runtimes into energy uses. Data collected for each RTU includes readings from current switches on staged gas valve operation to monitor heating run time (conventional efficiency RTUs). At the restaurant demonstration site, additional low-cost sensors were used to monitor runtimes of the adjacent RTUs installed in the building to provide data on the total heating and cooling loads. Baseline data from these sensors was downloaded manually when the demonstration units were installed.

Table 2. Duplicate Data Acquisition System Equipment Specifications

Data Label Monitored Data Point Equipment

CS-G1 CS-G2

Gas Valve Runtime (1st and 2nd stage)

Current Switch

CS-F Supply Fan Runtime Current Switch

CS-C1 Compressor Runtime (1st and 2nd stage)

Current Switch

Record current switch measurement of gas valves, compressors, fan, and economizer

HOBO State Loggers

Figure 4. Current Switches and State Loggers


RTU Data Comparison Methodologies The energy savings of the condensing RTUs at each field site was determine by two methodologies: 1) a direct comparison of measured data and 2) an analytical comparison based on nameplate efficiencies. Each method is explained in more detail below.

Method 1: Direct Comparison Methodology

A direct comparison of the baseline and condensing RTUs measured energy use was used to determine annual energy savings. At both demonstration sites, energy use was monitored to provide an opportunity for direct comparison; however site issues or significant equipment differences, such as multi-speed supply fan operation, limited the direct comparison of measured data. The direct comparison methodology follows these steps:

1. For condensing and baseline RTUs, measured gas use was adjusted to a common supply temperature of 70F, and then weather normalized based on the HDD of the monitoring period. Average annual gas use was calculated by multiply normalized gas use (therms/HDD) by the normal annual average HDD for the demonstration site, based on the National Climatic Data Center 30 year (1981 -2010) [NCDC 2016].

2. To compare annual RTU heating runtimes for different locations/applications, annual equivalent full load hours (EFLH) were calculated based on the ratio of measured gas use divided by the maximum rated gas input for the RTU.

3. Since different fan motor technologies were used in the baseline and condensing RTUs at both sites, the fan energy penalty (i.e. increase in electricity use) was calculated based on a representative additional pressure drop (0.20 inch W.G.) for the condensing RTU.

4. Net energy cost savings were based on the Department of Energy (DOE) Energy Information Administration (EIA) Minnesota State Annual Average Commercial Prices [DOE 2015]: natural gas: $0.696 per therm based on 1050 Btu/c.f.; electricity: $0.0944 per kWh

Method 2: Analytical Comparison Methodology

Given site issues or equipment differences that preclude direct comparisons, the analytical comparison methodology is the most valid approach to determine annual average energy savings and cost effectiveness. Using this methodology, annual gas savings was determined from an analytical comparison between monitored condensing RTU data and a projected baseline based on nameplate heating efficiencies.

The analytical comparison methodology follows these steps:

1. Natural gas use for the condensing RTUs was calculated based on the nameplate efficiency and capacity of the demonstration RTUs, using the runtime EFLH measured at the field sites. The linear correlation of EFLH relative to HDD, as determined from measured data at each site, was normalized to the regional normal annual average HDD [NCDC 2016] for Minnesota Zone 1


(Duluth), Zone 2 (St. Cloud), and Zone 3 (Minneapolis-St. Paul) to estimate average annual gas use for each region.

2. Baseline RTU gas use was determined by the product of the condensing RTU gas use multiplied by the ratio of condensing nameplate efficiency over the baseline nameplate efficiency.

3. Since different fan motor technologies were used in the baseline and condensing RTUs at both sites, the fan energy penalty (i.e. increase in electricity use) was calculated based on a representative additional pressure drop (0.20 inch W.G.) for the condensing RTU.

5. Net energy costs were based on EIA Minnesota State Annual Average Commercial Prices [DOE 2015]: natural gas: $0.696 per therm based on 1050 Btu/c.f.; electricity: $0.0944 per kWh

6. The cost premium for condensing RTU was based on the incremental equipment costs over equivalent standard efficiency (80%TE) non-condensing equipment offered by the same manufacturer, plus the added material and installation costs of the combustion condensate system. If a neutralizer was required in the condensate system, its added annual maintenance cost was included.

7. The simple payback of the condensing RTU was based on the cost premium of the condensing RTU divided by the annual net energy savings (minus any annual neutralizer maintenance costs)

8. To illustrate the impact of the various cost elements, the simple payback was calculated through the following progression:

a. gas cost savings only b. net energy savings, with added fan energy costs

i. without condensate system costs ii. with condensate system costs

c. plus any added neutralizer maintenance costs

Nameplate efficiencies for the existing baseline equipment were used in step 2: 80% thermal efficiency (TE) for the MAU and 80% rated annual fuel utilization efficiency (AFUE) for the 5-ton RTU. The current DOE federal minimum efficiency is 80% TE or 81% AFUE, depending on the input firing rate of the furnace equipment. Most state-enforced codes, including Minnesota, match these DOE federal minimum efficiency levels. The DOE federal minimum efficiency rulemaking for furnaces (the indirect-fired gas heating component in RTUs/DOAS/MAU) addresses the following two equipment categories:

1. The current federal minimum efficiency threshold for gas-fired commercial warm air furnaces (CWAFs) with 225,000 Btu/hour and greater input capacity is 80% TE. Based on recent final rulemaking, this will increase to 81% TE on January 1, 2023.

2. Gas-fired warm air furnaces less than 225,000 Btu/hour input capacity (“residential” WAFs), the current DOE federal minimum efficiency was recently increased, effective January 1, 2015, to 81% AFUE (up from 78% AFUE) for weatherized gas furnaces.


Results

Field Site Identification

The site selection process proved challenging in spite of planning, collaboration, and multiple approaches conducted over the course of one year. The project team, including local utility representatives, the manufacturer’s technical and marketing staff, local sales agents, and GTI staff, reached out to potential sites, trade allies, and contractors. The key challenge was finding older installed mixed-air RTUs with higher OA fractions.

GTI identified and solicited over 16 sites with existing mixed-air (30%-60% OA) RTUs, including school districts, nursing homes, national accounts, hotels, hospitality sites, and restaurants. These sites were not approved for a variety of reasons, such as the functionality of the existing RTU, cost of early replacement, perceived barriers to new technology, changes in stakeholders, delay in replacement needed for baseline monitoring, or lack of access to the final decision maker. One example of this was a condominium board that voted against the recommendation for pilot participation due to the perceived risk of introducing a new technology.

Over the course of this process, GTI discovered that mixed-air RTUs (30-100% OA), a relatively new product, are primarily used in new construction. Since the project required a measured baseline, new construction could not be considered as a potential site. Many applications (e.g. schools) satisfy ventilation requirements by using a 100%OA DOAS along with standard RTUs, rather than mixed-air RTUs with a higher OA fraction. Other potential sites seem to use standard RTUs that may be “grandfathered” by using like-for-like replacements, avoiding any permitting or code compliance issues.

To meet the overall project goal of expanding the market for RTUs with condensing heating, the project team selected two different types of applications for the demonstration sites. These sites demonstrate condensing RTU performance and economics at opposite ends of the mixed-air ventilation requirement, ranging from high ventilation rates (100% OA) at the first site, to a conventional RTU with lower capacities and lower ventilation rates (0-30% OA) at the second site.

Commercial kitchen and hotel corridor MAU with 100% OA are another promising market for condensing RTUs to expand the initial niche market beyond DOAS. These applications also have inherently high heating loads with potential to generate significant energy savings and are expected to be cost-effective in the near term. The project team identified a kitchen MAU serving a hotel commercial kitchen for the first demonstration site.

The second site demonstrated condensing RTU technology at lower capacities and lower ventilation rates. The project team identified a restaurant dining room application with a five-ton conventional RTU (11% OA). Although high efficiency condensing RTUs in smaller capacities may not be cost-effective at current equipment costs and/or fuel costs, condensing heating will likely be adopted across the range of capacities in the future. Five-ton conventional RTUs make up a significant share of the RTU market. This


demonstration of condensing heating in a conventional RTU provides real-world datasets on the energy savings across the range of capacities, and identifies the target costs required for a beneficial payback.

Courtyard Marriott Minneapolis Downtown The first site, selected to demonstrate a high ventilation application, was the hotel kitchen at Courtyard Marriott Minneapolis Downtown (Figure 5). At the hotel demonstration site, two existing side-by-side MAUs shown in Figure 6 delivered makeup air to opposite sides of the same kitchen exhaust hood. Both MAUs were constant volume, heating-only units that provide conditioned 100% OA continuously. The demonstration unit would replace the 30-year old gas-fired Trane MAU (77% TE), shown on the left in Figure 6. The newer standard efficiency Greenheck MAU (80% TE), shown on the right, was installed five years prior and remained in place during the baseline and demonstration periods. Both MAUs were monitored for baseline energy use, so the condensing MAU could be compared to an older replacement MAU as well as a newer standard efficiency unit.

Although these MAUs served the same exhaust hood, each MAU unit operates independently. Unlike RTUs, MAUs operate based on OA temperatures instead of the temperature of the conditions space. The MAUs deliver constant a volume of OA during occupied hours to offset the airflow from the kitchen exhaust. When the OA temperature drops below a setpoint (approximately 45F), the MAU heats the airflow to the supply setpoint (approximately 70F). If either MAU fails to operate, the conditioned space may experience slightly negative pressure during operation of the kitchen exhaust fan. If the MAUs cannot deliver the supply air temperature, the conditioned space may be cooler than design; however, this is not likely to impact occupant comfort as much as in other applications, due to the heat generated by cooking equipment in a commercial kitchen.

Figure 5. Minneapolis Hotel Demonstration Site


Figure 6. Side-by-side Kitchen MAUs at the Hotel Field Site

The Lowry Restaurant The second demonstration site represents a low capacity conventional RTU with lower ventilation rates. The Lowry is a single-story restaurant (Figure 7) with extended hours, open daily from 6:30 am until 2:00 am. The existing 5-ton baseline RTU, show in Figure 8, was one of three RTUs and a kitchen MUA installed at the restaurant. The baseline RTU provided heating and cooling to a portion of the restaurant dining room. The baseline RTU did not have an economizer and used a fixed 8x8 inch OA damper (1/4 open) installed in the return ductwork to provide OA ventilation. The demonstration unit selected was the 5-ton Reznor R8HE with condensing heating and high efficiency cooling. The 5-ton R8HE was the only available condensing RTU product in this capacity range.

Figure 7. Restaurant Field Site for 5-ton RTU Demonstration


Figure 8. Baseline 5-ton RTU at Restaurant Site

Hotel Kitchen Makeup Air Unit (100% OA)

Baseline Equipment

Specifications

As previously described, this site featured side-by-side existing kitchen MAUs: a 30 year-old Trane unit (shown left in Figure 9), and a five year-old Greenheck unit (shown right). Both 100% OA MAUs served the same hotel kitchen exhaust hood with single speed supply fans. Bothheating-only units included two burner modules with multi-stage gas valves and total input capacity of 600 MBH. Additional specifications are shown in Table 3 and Table 4.

Figure 9. Side-by-side Baseline Kitchen MAUs


Table 3. Baseline Kitchen MAU Specification

Baseline Kitchen MAU Specifications

RTU Manufacturer/ Model Number Trane GFNC030FFA26G1ACR

Thermal efficiency (%) 77%

Gas Input (Two burners) 1) 300,000 Btu/hr; 2-stage

2) 300,000 Btu/hr; 2-stage

Heat Output 1) 231,000 Btu/hr

2) 231,000 Btu/hr

Airflow Nominal 4800 cfm (Adjusted to approximately 2700 cfm for 80F temperature rise)

Table 4. Parallel Kitchen MAU Specification

Parallel Kitchen MAU Specifications

RTU Manufacturer/ Model Number Greenheck 1GX-115-H22-DB


Gas Input 1) 300,000 Btu/hr; 1-stage

2) 300,000 Btu/hr; 2-stage

Heat Output 1) 240,000 Btu/hr

2) 240,000 Btu/hr

Airflow Nominal 4000 cfm (Adjusted to approximately 2778 cfm for 80F temperature rise)

Baseline Energy Analysis

A full year of baseline data was collected for the older Trane unit, to be replaced by the demonstration condensing MAU, and the standard efficiency Greenheck MAU. For both MAUs, fan operation was 24/7 for the majority of the monitoring period. The site wanted the MAUs to have slightly different heating lockout setpoints. The Greenheck MAU heating operation turned on at 44F OA temperatures, and turned off at OA temperatures above 45F. The Trane unit turned on at 46F OA temperatures and turned off at OA temperatures above 48F, and as a result, operated longer than the Greenheck MAU. To provide an equivalent comparison, the analysis included only data for OA temperatures below 43F when both units are operating. Daily energy use for both units was adjusted to a common 70F supply temperature, and then weather normalized to daily HDDs, with a base temperature of 45F (HDD45).


As shown in Figure 10, daily gas consumption for both units had a strong linear relationship with respect to HDD45, as reflected in the R-squared (R2) correlation. As expected, the older less efficient Trane MAU (77% TE) had higher gas consumption for the same HDD45 compared to the more efficient (80% TE) Greenheck MAU. Baseline monitoring of the total electric usage is shown in Figure 11. Since these MAUs are heating only, electric consumption is predominately the supply fan energy use and was relatively constant during operation. Supply fan energy generally increases as OA temperatures decline and air becomes more dense. Decreasing OA temperatures from 40°F to 0°F are expected to increase fan power on the order of 7%. Electric consumption for the Greenheck MAU was lower than the Trane MAU, likely due to a more efficient fan and an improved heat exchanger design with a lower pressure drop.

Figure 10. MAU Heating Only Baseline Monitoring of Gas Use

y = 0.169x + 1.997R² = 0.974

y = 0.160x + 1.886R² = 0.870

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Baseline Trane MAU Baseline 2015/16 Greenheck MAU

Note: Gas use normalized to 70F supply temperature


Figure 11. MAU Heating Only Baseline Monitoring of Electric Use

y = 0.1342x + 43.692R² = 0.8197

y = 0.014x + 22.559R² = 0.2346

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Baseline Trane MAU Baseline Greenheck MAU

Condensing MAU Equipment

Specifications

In October 2016, the Trane MAU was replaced by the Reznor RHH-260D MAU with condensing heating, shown in Figure 12. The RHH-260D has a single modulating gas valve and a constant speed fan. The condensing design includes a secondary heat exchanger that increases thermal efficiency up to 91%. This secondary heat exchanger is located in the supply air stream, adding an incremental pressure drop for the supply fan that results in higher electric energy consumption whenever the fan is operating. For this site, the MAU fan operates continually, 24/7.

Table 5 lists the specifications for the RHH-260D. Although the condensing MAU heating capacity was less than the baseline, it was adequate to deliver the required 80F temperature rise at 2700 cfm for this application. Measured data infers that both the Trane and Greenheck MAUs were significantly oversized. This is a common practice to provide a factor of safety to deliver supply temperatures on the coldest days and to reduce recovery time, i.e., quickly reach setpoint temperatures following a thermostat setback period. A recent study by GTI found that many commercial buildings have excess heating capacity, more than double in some cases, so that some individual RTUs have minimal or no runtimes [Kosar 2014]. For condensing RTUs, oversizing results in shorter runtimes and longer paybacks


for the higher cost premium of oversized equipment. Condensing RTUs sized to more closely match design requirements will operate with higher EFLHs and lower first cost premiums minimizing the payback timeframes.

Figure 12. Condensing MAU Installed October 2016

Table 5. Condensing Kitchen Makeup Air Unit Specification

RTU Manufacturer/ Model Number Reznor RHH-260D


Gas Input 260,000 Btu/hr; Single 8:1 Modulating Gas Valve

Heat Output 236,600 Btu/hr

Airflow 2921-5440 cfm 3800 cfm (adjusted January 24, 2017) Adjusted to approximately 2700 cfm to achieve 80F temp rise (Oct 2017)

Fan 5 HP blower

Temperature Rise 40F to 100F


Installation

Two installation issues were discovered during operation of the condensing MAU. The first was discovered when the MAU shut down at outdoor ambient temperatures of 1.4F, still within normal winter temperatures for Minnesota. The MAU displayed an error message: “Alarm ID: 3 Low Discharge Temperature Alarm (Critical Shutdown Alarm)”. According to Reznor technical support, when the unit calls for heat, the low discharge temperature alarm is active. If the discharge air temperature falls below 33F/1C (Low Limit Alarm Setpoint) for more than 10 minutes, the controller shuts down the system. The unit will not restart until the alarm is acknowledged via the unit controller or remote display.

Upon reviewing the data collected just prior to this error, GTI found the condensing MAU was not able to maintain the supply air temperature when OA temperature dropped below 20F. With a simple calculation (BTUH/ (1.08 * cfm) = Delta-T), it was discovered the condensing MAU could not deliver the required 80F temperature rise at the nameplate supply air flow (4800 cfm), which was specified to match the baseline nameplate. Calculations using measured baseline data indicate the baseline unit was also operating at a lower fan speed than specified, approximately 2700 cfm, to maintain 70F supply temperatures at ambient temperatures as low as -10F. This example illustrates the need for independent calculations and on site measurements to verify the capacity requirement and installation setpoints for a given site. In order to increase the MAU temperature rise, the condensing MAU blower speed was adjusted to a lower airflow by the mechanical contractor per instructions provided in the installation manual, also shown in the appendices. Fan speed is usually adjusted during installation to deliver the required temperature rise at design temperatures.

The second issue involved installation of the condensate drain. Due to lack of familiarity with condensate management for a condensing RTU, the installing contractor installed the drain from the condensing heat exchanger and the non-condensing heat exchanger in a Y-configuration that ran horizontally across the cabinet before dropping vertically down inside the roof curb into the conditioned space (Figure 13). This allowed condensate to collect in the line and freeze at very low ambient temperatures (below 5F).

Best practices and applicable codes for combustion condensate disposal are described in detail in Appendix B. According to best practices, the condensate drain line must drop vertically through the inside of the roof curb, followed by a drain trap located inside the conditioned space. Installations must avoid any non-vertical drain lines outside the conditioned space where liquid can collect and freeze, such as those shown in Figure 13. Following feedback from GTI and Reznor, the MAU was lifted from the curb and the condensate line was installed correctly, as shown in Figure 14. In response to concerns by the site, the contractor added insulation to the line and heat tape (unplugged) to address any potential freezing incidents in the future. Previous field studies by GTI, in cold climates such as Minnesota, demonstrated that insulation and heat tape are not necessary to prevent freezing as long as best practices are followed.

Existing codes, subject to AHJ approval, provide for wide discretion by the installing contractor as to whether a sanitary sewer or storm drain connection is utilized for disposal, and whether or not a


neutralizer is installed. This site used a sanitary drain connection and a calcium carbonate neutralizer, located in the conditioned space, to counteract the acidic content of the combustion condensate.

Figure 13. Incorrect MAU Condensate Installation at the Hotel Site

Figure 14. Corrected Installation of the MAU Condensate Drain

Heating Analysis

Heating performance was analyzed using a direct comparison of the measured energy use of the condensing MAU and the non-condensing MAU. Due to the difference in heating lockout setpoints (OA temperature thresholds for heating operation), data was filtered to exclude OA temperatures below 43F and daily energy use under 23 hours runtime. This provides a conservative estimate of potential gas savings for MAU applications. The following figures display 5-minute interval data of MAU operation throughout a typical day. The non-condensing MAU supply air temperature (Figure 16) had significant variability compared to the condensing MAU (Figure 15). This is due to staged gas valve controls versus


the fully modulating gas valve control in the condensing unit, not related to the condensing technology itself. For a direct comparison between these MAUs, gas usage for the baseline and condensing MAU was normalized to a 70F supply temperature to account for the variation in supply air temperatures.

Figure 15. Condensing MAU Temps, Fan and Gas Valve Operation

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Daily gas use for the Reznor condensing MAU and both baseline MAUs (Greenheck and Trane) was normalized to HDD45 as shown in the graph in Figure 17. Measured gas consumption had a strong linear relationship with respect to HDD45 as reflected in the R-squared (R2) values. Based on this data, the Reznor condensing MAU had 23% lower gas consumption compared to the baseline Trane MAU that it replaced, and 17% savings in gas consumption compared to the standard efficiency non-condensing Greenheck MAU. Gas use for the Greenheck MAU had more variability due to brief periods of firing of its second heating module to meet the larger heating load at higher HDDs.

Figure 17. Normalized Gas Usage with respect to Heating Degree Days

Figure 18 presents the linear correlation for Greenheck gas usage based on data collected during baseline monitoring period 2015/2016 and the demonstration period 2016/2017. Data from 2016/2017 showed significantly higher energy use and additional scatter with a lower linear correlation. The Greenheck MAU included two heating modules, each with 300 MBH capacity. Upon starting, both modules fired and then only the first module operated the majority of the time. Data points with higher gas consumption included days when both modules operated for longer periods. It is unclear from the available dataset why this unit had higher energy use during the demonstration period. Both the facility manager and the mechanical contractor were not aware of any change in setpoints, controls, or other operating conditions. GTI will continue to investigate any potential issues with this unit through the mechanical contractor. Due to the stronger correlation and more conservative estimate, GTI used the Greenheck 2015/2016 dataset for the standard efficiency baseline.


Figure 18. Baseline Normalized Gas Usage for 2015/2016 and 2016/2017

y = 0.160x + 1.886R² = 0.870

y = 0.262x + 1.309R² = 0.847

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Baseline 2015/16 Greenheck MAU Greenheck MAU 2016/17

Note: Gas use normalized to 70F supply temperature

Figure 19. Equivalent Full Load Hours with respect to Heating Degree Days

y = 0.432x + 10.876R² = 0.9633

y = 0.271x + 3.707R² = 0.969

y = 0.271x + 2.731R² = 0.796

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Reznor Condensing MAU Baseline Trane MAU Greenheck 2015/2016


Figure 19 presents a graph comparing the EFLH of all three MAUs with respect to HDD45. EFLH was calculated based on measured gas use relative to total gas input capacity. Due to the lower heating capacity of the Reznor MAU compared to the Trane and Greenheck MAUs, the EFLH is proportionately higher for a given HDD. This includes data collected only after the supply fan was adjusted to a lower speed to increase the temperature rise, resulting in fewer days monitored during 2016/2017. Gas use data was not normalized for the slight differences in fan speed between the baseline and condensing MAUs. Note the condensing MAU reaches 24 EFLH at about 30 HDD, indicating the supply fan many require further adjustment to lower the fan speed in order to maintain supply temperatures at lower ambient temperatures.

Figure 20. Measured Total Electricity Use of Baseline and Condensing MAUs

y = 0.2979x + 72.659R² = 0.8165

y = 0.1342x + 43.692R² = 0.8197

y = 0.014x + 22.559R² = 0.2346

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Kitchen MAU Supply Fan Electricity Usev. Heating Degree Days

Reznor Condensing MAU Baseline Trane MAU Baseline Greenheck MAU

Figure 20 compares the daily total electricity usage for the three units. Since these are heating-only, total electricity use is comprised primarily of supply fan energy use. Fan energy use for the Greenheck MAU was lower than the Trane MAU, most likely due to a more efficient fan design as well as an improved heat exchanger design with lower pressure drop. As expected, the Reznor condensing MAU had higher electricity consumption compared to both non-condensing MAUs, due to the incremental pressure drop of the added condensing heat exchanger (fan energy penalty). The incremental fan energy may also be increased due to the higher pressure drop of a smaller housing for the given airflows of the Reznor MAU versus the larger housings of the Greenheck and Trane MAUs. The increase in fan energy occurs whenever the fan is operating, which at this site is 24/7. As a result, any calculations of net energy cost savings must include both the reduced gas use and increased electric use. This presents tradeoffs in right sizing condensing RTUs to maximize gas savings per unit of input capacity with higher


EFLHs and to reduce the fan energy penalty, in order to optimize the net energy savings for the shortest paybacks.

Table 6 summarizes the total measured energy use data for the baseline and condensing MAUs with 100% OA operation. Total gas use and runtime for the demonstration 2016/2017 heating season include only data from February 10, 2017 thru May 1, 2017. There were fewer days in the demonstration period due to issues with the fan speed and the condensate drain installation that occurred during January as described earlier. Even with a smaller data sample, measured gas use had a strong linear correlation with HDD, allowing gas use to be extrapolated for annual HDD for three Minnesota regions to estimate annual energy use and the net energy cost savings.

Table 6. Total Measured Energy Use Data for Condensing MAU and Baseline

Monitored Results Baseline 2015 / 2016

Baseline 2015 / 2016

Demonstration 2016 / 2017

Demonstration 2016 / 2017

Trane Greenheck Reznor Greenheck

Total Gas Input (therms) 4,802 4,990 1,497 1,897

Total Electric Input (kWh) 4,622 2,628 2,796 979

HDD (Base 45) 820 909 294 296

EFLH 818 811 578 296

Heating Energy Savings – Analytical Comparison

Table 7 presents the estimated annual average gas use for each MAU based measured gas use normalized to NOAA climate normals computed for the 30-year period from 1981 to 2010. Annual gas use was estimated for three regions in Minnesota: Minneapolis-St. Paul, the location of the demonstration site; and two colder regions, St. Cloud and Duluth. This represents the range of potential energy savings and economics for the state of Minnesota. As expected, the condensing MAU will generate higher gas savings in colder climates.

Table 7 forms the basis for predicted energy savings and operating cost savings shown in Table 8. Estimated gas savings generated by the condensing MAU ranged from 915 to 1206 therms/year (17%) compared to the standard efficiency MAU (80% TE). The baseline and condensing MAUs utilized different fan speeds and cabinet sizes, so a direct comparison of measured fan energy would not be valid. Fan energy penalties were calculated using an analytical projection for identical fan technologies (60% efficiency) with a representative additional pressure drop (0.20 inch W.G.) for the condensing MAU. For this demonstration site, since the MAU fan operates continuously, the increased electric use (“fan energy penalty”) was incurred over 8760 hours/year fan runtime.


Table 7. Extrapolated Annual Gas Use for Condensing MAU and Baseline3

Weather Data City Climate Zone

Normal Annual

HDD(45)

Estimate EFLH

Baseline 77% TE Therms

Baseline 80% TE Therms

Condensing 91% TE Therms

Duluth MN ZONE1 4327 1880 7,333 6,942 5,737

St. Cloud MN ZONE2 3908 1699 6,624 6,272 5,183

Minneapolis-St. Paul MN ZONE3 3291 1433 5,582 5,284 4,369

Table 8. Estimated Annual Energy Savings for Heating4


Estimated Gas Savings

Therms/yr

Percent Gas

Savings

Increased Peak

Electric KW

Increased Annual Electric

KW/yr

Duluth MN ZONE1 1206 17% 0.15 1302

St. Cloud MN ZONE2 1088 17% 0.15 1302

Minneapolis-St. Paul MN ZONE3 915 17% 0.15 1302

Table 9. Estimated Annual Net Energy Cost Savings5


Natural Gas Cost Savings

Electricity Cost Savings

Annual Maintenance

Net Cost Savings

Duluth MN ZONE1 $839 -$123 N/A $716

St. Cloud MN ZONE2 $758 -$123 N/A $635

Minneapolis-St. Paul MN ZONE3 $637 -$123 N/A $514

Annual energy costs for this demonstration site, shown in Table 9, are based on 2015 EIA Annual Average Commercial Prices: natural gas: $0.696 per therm based on 1050 Btu/c.f.; electricity: $0.0944 per kWh. Net cost savings includes annual savings in natural gas and any increased electricity consumption due to the fan energy penalty. Based on this field study, estimated net energy cost savings for the condensing MAU ranged from $514 in milder Minnesota climates to $716 in colder regions. This illustrates how cost-effective applications require high heating loads to generate the gas savings and cost savings adequate to offset the fan penalty and the first cost premium for condensing rooftop

3 NOAA climate normals computed for the 30 year period from 1981 to 2010 4 Estimate based on 8760 hrs/yr, 0.20 in.W.G incremental pressure drop, 60% fan & motor efficiency 5 Assumes no condensate neutralizer and no incremental maintenance required for condensing RTU


equipment. Replenishment of the condensate neutralizer, every 1-2 years, adds incremental maintenance costs, which significantly affects annual cost savings and corresponding paybacks. Since condensate neutralizer is not required by local codes, this additional maintenance cost was not included in the analysis.

There are some caveats regarding the validity of this direct comparison between the condensing MAU and non-condensing MAU. The difference in supply air flow and capacity of the Reznor condensing MAU prevents direct comparison to the older Trane MAU and the standard efficiency Greenheck MAU. Given the higher, unused heating capacity of the non-condensing MAUs, a portion of the measured energy savings may be due fewer cycling losses or part-load operation at this particular site, rather than improved efficiency due to condensing heating. As a more valid comparison of a condensing MAU and an equivalent non-condensing MAU, an analytical comparison is presented in the following sections based on EFLH determined from the measured data at the field site.

Economics

First Cost Premium

Equipment cost premiums for the condensing MAU, as reported by the distributor, were approximately $1,731 or $7.32 per 1000 Btu/hr of output heating capacity for the condensing MAU (236.6 MBH) relative to an equivalent standard efficiency MAU offered by the same manufacturer. As the market expands for condensing equipment, equipment and installation costs are expected to decrease due to larger production volumes, and as contractors become more familiar with installation requirements. DOE projects competitive mass market pricing of the equipment cost premium only for condensing RTUs (not including the condensate management system and its installation) in a mature market to be $4.40 per 1000 Btu/hr of output heating capacity. Personal communications [Kosar 2015] with a major HVAC company indicates that they anticipate a similar equipment cost premium of $4.50 per 1000 Btu/hr of output heating capacity for condensing RTU equipment.

The additional cost of the condensate management system is more difficult to generalize given specific site and local code needs. The installing contractor for this site estimated the incremental installation costs for the condensing MAU to include $1,840 labor plus $500 in material, for a total $2,340 ($9.89 per 1000 Btu/hr). This assumes the contractor is familiar with the installation and condensate management best practices, and excludes the installation issues experienced at this site during the demonstration. Another contractor estimated $2,600 to supply and install approximately 50 ft. of condensate drain, without neutralizer. Costs will vary depending on the building size and the accessibility of a drain for the condensate. In previous demonstrations by GTI, incremental costs for condensate management ranged from $1.45 per 1000 Btu/hr output heating capacity (sanitary drain with no neutralizer) to $6.08 per 1000 Btu/hr (storm drain with neutralizer). For another site, costs increased up to $12.06 per 1000 Btu/hr output heating for a site utilizing a sanitary drain with no neutralizer, but requiring a scissor lift and additional labor hours for a high ceiling drain line installation. Installation costs are expected to decrease as installation contractors become more familiar with condensing rooftop equipment.


The neutralizer is sized for the connected condensate load based typically on the gallons of condensate produced annually. The industry rule of thumb has been one gallon of condensate produced each hour for every 100,000 Btu per hour of input capacity that is firing for that hour. The cost of neutralizers generally range (uninstalled) from $50 to $250 for 2,000 gallons (100,000 Btu/hr input firing for 2,000 EFLHs) up to 40,000 gallons (400,000 Btu/hr input firing for 10,000 EFLHs). If neutralizers are used, annual maintenance is estimated at $65 to $130, which can be a costly added deduction from the net energy cost savings every year. Existing code language provides for wide discretion by the installing contractor, subject to AHJ approval, whether or not a neutralizer is required.

The following economic analysis presents paybacks based on the actual demonstration costs for this study, as well as mature market economic projections. Mature market assumptions used in the following analysis include:

• $4.40 per 1000 Btu/hr output heating capacity RTU equipment premium • $2.00 per 1000 Btu/hr output heating capacity installed condensate system premium • $100 annual maintenance for neutralizer

Economic Assumptions and Inputs

Table 10 presents estimated net energy costs savings based on nameplate efficiencies and measured EFLH adjusted to the Normal Annual HDD45 for three Minnesota zones: Duluth (MN ZONE 1), St. Cloud (MN ZONE 2), and Minneapolis-St. Paul (MN ZONE 3). Non-condensing RTU gas use is determined by the product of the condensing RTU gas use multiplied by the ratio of condensing nameplate efficiency (91% TE) over the non-condensing nameplate efficiency (80% TE). Utility rates were based on EIA 2015 state averages for commercial customers. As shown in Table 10, the resulting net energy cost savings for the condensing MAU compared to the standard efficiency unit ranged from $239 to $352.

Table 10. Estimated Annual Net Energy Costs for Condensing vs Baseline MAU

Net Energy Cost Assumptions MN ZONE1 MN ZONE2 MN ZONE3

Heating Module Assumptions

Capacity Btu/hr Out 240,000 240,000 240,000

Base AFUE/TE 80% 80% 80%

Base Btu/hr In 300,000 300,000 300,000

High Efficiency AFUE/TE 91% 91% 91%

High Efficiency Btu/hr In 263,736 263,736 263,736

Heat Equivalent Full Load Hours (EFLH)/Yr 1880 1699 1433

Base therms/yr 5,640 5,097 4,298



High Efficiency therms/yr 4,959 4,481 3,778

Site Gas Savings therms/yr 682 616 520

Gas Cost Savings ($0.696/therm) $475 $429 $362

Supply Fan Assumptions

Fan CFM 3,800 3,800 3,800

Added Fan DP, inch WG 0.2 0.2 0.2

Fan & Motor Efficiency 60% 60% 60%

Added kW 0.149 0.149 0.149

Fan Operating Hours/Yr 8,760 8,760 8,760

Site Added Fan kWh/yr 1,302 1,302 1,302

Electric Savings ($0.0944/kWh) -$123 -$123 -$123

Net Energy Cost Savings $352 $306 $239

Simple Paybacks

Based on the net energy cost savings for each region, Table 11 presents a progressive series of condensing MAU paybacks.

The projected simple paybacks for the 100% OA MAU range from 4.9- 7.3 years based on current cost premiums for condensing equipment alone, including the fan energy penalty. However, as you progress through the added cost of the condensate system installation, at current costs, paybacks increase to 11.6-17.1 years. Lastly, including annual maintenance of the neutralizer at $100/year, simple paybacks for current cost premiums exceeds the life of the equipment, assumed to be 15 years.

With projected mature market costs, paybacks are reduced to 3.0-4.4 years when looking at just condensing RTU equipment premiums and the net energy cost savings alone. The addition of the condensate system installation at mature market costs extends paybacks to 4.3-6.3 years. Annual maintenance costs for the neutralizer, for these cases, lengthen paybacks to 6-11 years.

While 100%OA applications, such as MAUs, offer economic benefits at current costs, reductions in equipment and condensate system costs have potential to achieve target paybacks from 4 to 6 years. Near-term cost reductions in condensate systems, installation, and annual maintenance are important for cost-effective applications of condensing RTUs.


Table 11. Condensing MAU Installed Cost Premiums and Paybacks

INSTALLED COSTS & PAYBACKS

Current Market Prices



Mature Market

Projection

Mature Market

Projection

Mature Market

Projection

ZONE1 ZONE2 ZONE3 ZONE1 ZONE2 ZONE3

with equipment cost premium only6

$1,731 $1,731 $1,731 $1,041 $1,041 $1,041

annual therm savings 614 1088 915 614 1088 915

annual gas cost savings $475 $429 $362 $475 $429 $362

simple payback (years) 3.6 4.0 4.8 2.2 2.4 2.9

with fan energy penalty

annual net energy cost savings

$352 $306 $239 $352 $306 $239


with added condensate system cost6

$2,340 $2,340 $2,340 $473 $473 $473

Total Incremental Installed Cost

$4,071 $4,071 $4,071 $1,514 $1,514 $1,514


with neutralizer maintenance

annual cost $100 $100 $100 $100 $100 $100

annual net O&M cost savings $252 $206 $139 $252 $206 $139


Table 12 illustrates the effect of natural gas and electricity rates on the net energy cost savings. Increases in natural gas prices, currently at historic lows, and/or decreased electricity prices lead to increased net energy cost savings and in turn, shorter paybacks.

6 Based on actual demonstration costs and projections per 2015 DOE NOPR Commercial Warm Air Furnace Technical Support Document


Table 12. Net Energy Cost Savings with respect to Energy Prices

5-Ton Rooftop Unit (0% to 30% OA)

The second field site demonstrates condensing heating in a conventional RTU application to determine the energy savings at lower capacities and lower ventilation rates (0 to 30% OA). The overall objective was to identify cost or performance targets for condensing heating to be cost-effective across the range of capacities and applications. The selected site was a restaurant located in Minneapolis, The Lowry. The building HVAC system included three RTUs and a kitchen MAU. A 10-ton RTU was located over the main dining area between the front and back entrances. A 5-ton RTU was located over a smaller dining area in the front of the restaurant and adjacent to the front door, and another 5-ton RTU served the office area in the back of the restaurant. At the time of the demonstration, Reznor had recently introduced a 5-ton condensing RTU, the first condensing product for low OA fraction applications. To demonstrate this newly introduced product, the existing 5-ton RTU serving the front dining area was selected for the baseline (Figure 21).


Figure 21. Baseline 5-ton RTU Serving the Restaurant Dining Room

Baseline Equipment

Specifications

Specifications for the baseline 5-ton RTU are shown in Table 13. The RTU had standard efficiency natural gas heating (80% AFUE) and 9.7 SEER cooling. A real-time DAS was installed on the baseline RTU to determine key operating parameters and to establish baseline energy use. Baseline monitoring of gas and electric usage, temperatures, and runtimes was conducted from October 2015 to September 2016.

In addition, a low-cost DAS was used to monitor runtimes of the remaining RTUs serving the building to provide information on the total building heating and cooling loads. This low-cost DAS consisted of current switches and battery-operated data loggers to record staged gas valve operation, staged compressor operation, and constant volume fan operation. Nameplate rating information for each unit could be used to translate runtimes into energy consumption. Data from these sensors was downloaded manually when the demonstration units were installed.


Table 13. Baseline RTU Specifications

Description Specification

RTU Manufacturer/ Model Number Carrier 48TJE004---611QE

Gas Input, Btu/hour 115,000

Temp rise 35-65F

Nameplate Efficiency, % 80% AFUE

Cooling Output 5 tons (57,000 btuh)

Cooling Efficiency 9.7 SEER/8.5 EER

Minimum Airflow, cfm 1700 Nominal 1180-1895

Baseline Energy Analysis

This RTU did not have an economizer, and used a fixed 8x8 inch OA damper (1/4 open), installed in the return ductwork, to provide a constant OA ventilation. Baseline percent OA was calculated as 11% OA based on measurements of return air (RA), supply air (SA) and OA temperature measurement during no heating/cooling operation. This represents the lower range of RTU ventilation with corresponding lower heating load.

Baseline data indicated low runtimes for the baseline 5-ton unit, most likely due to operation of the adjacent RTUs serving the same conditioned space in the restaurant (Figure 22). Past research [Kosar 2014] has shown that conventional RTUs processing 30% OA or less can see a very wide range of EFLHs in practice. This GTI study monitored over 100 RTUs on office, restaurant, and retail buildings and reported very diverse runtimes for groups of RTUs, with some RTUs on each building having little or no gas use. Several factors can affect RTU runtimes, including building envelope geometry and construction, internal loads, RTU location and capacity, as well as thermostat location and setpoints. This presents a challenge for a generalized marketing approach for applying condensing heating to any given building, since the payback of the high efficiency equipment premium is dependent on adequate RTU runtimes to generate sufficient gas savings.


Figure 22. Multiple RTUs installed at the Restaurant Field Site

For this site, GTI monitored runtime data for the remaining 10-ton and 5-ton RTUs installed adjacent to the baseline unit. The alternate 5-ton RTU had very little runtime. The adjacent 10-ton RTU had significantly higher runtimes than the baseline 5-ton RTU, as shown in Figure 23, indicating that the building load was not evenly distributed across the multiple RTUs. Thermostats for both RTUs had identical setpoints but were located in different sections of the restaurant, and the site was not willing to modify the setpoints. The combined gas consumption from all RTUs, shown in Figure 24, estimated from measured runtime, had the expected linear correlation with HDD, validating the measurement data. However, the 5-ton R8HE was the only condensing RTU product available in this capacity range to replace the RTUs at this site.


Figure 23. Comparison of RTU Heating Runtimes at Restaurant Site

y = 7.601x - 36.544R² = 0.543

y = 10.827x - 36.532R² = 0.745

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Figure 24. Combined RTU Gas Usage with respect to Heating Degree Days

y = 0.090x - 0.342R² = 0.776

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As presented in Figure 25, baseline results show gas consumption increasing with HDD base temperature 55F, as expected; however, scatter in the baseline RTU data results in a poor correlation between gas consumption and daily HDD. Energy use for heating is expected to be highly correlated to HDD, and this linear correlation forms the basis for accurately extrapolating gas consumption to estimate average annual energy use, and establishing the baseline for energy savings. Scatter in this data reflects the lower runtime for the baseline RTU as the building heating load is shared by adjacent RTUs.

Figure 25. Baseline RTU Gas Usage with respect to Heating Degree Days

y = 0.0084x - 0.0946R² = 0.4709

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Baseline RTU Heating Regression Total Gas Use vs. Heating Degree Days

Condensing RTU Equipment

Specifications

The Reznor R8HE condensing RTU was installed at the restaurant site in October 2016. Although marketed under several brand names as part of the Nortek Global HVAC family of companies, the R8HE was originally introduced as a slab mounted unit for large residential applications. The R8HE has been adapted for small commercial applications with rooftop curb mounting available and combustion condensate drainage options for discharge horizontally (out the side of the unit) or vertically (inside the roof curb and down through the base of the unit).

The Reznor R8HE is a “factory stocked, off-the-shelf” product that represents a significantly lower price point for condensing RTU equipment first cost, especially when compared to the other “factory built to


order” condensing RTU products targeted for early market applications for DOAS or MAUs. Hence the R8HE is an attractive product offering for this demonstration to explore potential cost-effective markets for condensing RTUs below 100% OA applications and into more mainstream (30% OA or less) applications. However, this product offering from Reznor has specific standard features that present complexities in drawing valid direct comparisons between the condensing and baseline RTU operations. R8HE specifications are listed in Table 14

Table 14. Condensing RTU Specifications

RTU Manufacturer/Model Number Reznor R8HE-060-096

Gas Input High fire/Low fire, Btu/hour 96,000 / 62,400

Heat Output High-fire/Low-fire, Btu/hour 91,200 / 59,300

Temp rise 49.7F / 32.3F

Air Flow, High-fire/Low-fire, cfm 1,895 cfm / 1,421 cfm

Air Flow, No-fire with fan on, cfm 947.5 cfm (50% of High-fire)

Nameplate Efficiency 95% AFUE

Cooling Output 4.8 tons (57.3K btuh)

Cooling Efficiency 14.0 SEER / 11 EER

At this site, both the baseline and condensing RTU thermostat fan controls operated continuously (“on” mode). The baseline non-condensing RTU had a single-stage burner and single-speed blower. The replacement R8HE comes standard with a two-stage burner and a multi-speed supply fan. Fan operation varies with respect to firing rate:

• High-fire at 100% airflow; • Low-fire at 75% airflow; and • No-fire at 50% airflow, when thermostat fan control in “on” versus “auto” mode.

Installation

The baseline RTU was installed on “sleeper” supports with ductwork run horizontally across the rooftop and a fixed 8x8 inch fixed OA damper. For a direct comparison with the baseline RTU, the R8HE was installed without the economizer and the fixed damper was kept in place in the return ductwork to maintain the same percent OA condition as the baseline Figure 26. Percent OA was calculated based on


measurements of return air, supply air, and OA temperature measurement with no heating/cooling operation, and averaged 11% OA for both the baseline and condensing RTUs.

Figure 26. Installation of Condensing RTU and Fixed OA Damper

Condensate best practices allow an option for horizontal discharge of the combustion condensate (out the side of the unit) if the condensate line is heat-taped and insulated. The installing contractor felt this was an inadequate option, and added a new RTU curb to this installation in order to comply with manufacturer instructions for a vertical drain into the conditioned space. This installation reported no freezing or other issues; however, the addition of a new curb with roofing modifications added significant installation costs in this particular situation.


Existing codes provide for wide discretion by the installing contractor, subject to AHJ approval, as to whether a sanitary sewer or storm drain connection is required for disposal, and whether or not a neutralizer is required. The installing contractor at this site chose not to install a neutralizer because multiple other water sources were emptying into the drain and diluting the condensate. The site passed local code inspection with no issues per the contractor. Best practices for condensate management are discussed in more detail in Appendix B.

Cooling Analysis

The graph in Figure 27 displays correlation between total electricity use and cooling degree days (base temperature 55F) for both the baseline RTU and the replacement RTU (R8HE). This analysis includes data with only cooling or fan operation; days with any heating runtime were excluded. The R8HE had a higher cooling efficiency of 14 SEER as compared to 9.7 SEER for the baseline RTU. The R8HE used less electricity during cooling than the baseline for a given CDD, despite the additional supply fan energy penalty for the R8HE.

Figure 27. Electricity Usage with respect to Cooling Degree Days

y = 8.221x + 51.968R² = 0.757

y = 4.298x + 66.075R² = 0.543

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Baseline RTU 9.7 SEER Replacement RTU 14 SEER


Cooling Energy Savings - Direct Comparison

For this site, the RTU cooling operation had longer runtimes and a stronger correlation between electricity use and CDD55, so the direct comparison method was used to determine electricity savings during cooling. Annual electric use for the baseline and condensing RTUs was estimated based on the linear relationship between measured total electric use and CDD55, normalized to the annual CDD55 for three Minnesota regions. Annual CDD55 are based on NOAA climate normals computed for the 30 year period from 1981 to 2010. Table 15 presents the estimated savings in electric use and electric costs during cooling due to the higher cooling efficiency of the replacement RTU (R8HE) relative to the baseline RTU. Electric savings of 44% to 46% exceed the estimated savings based on the relative cooling efficiencies (31%).

In Minnesota, the cooling loads vary by climate region. Despite increased cooling efficiencies generating up to 46% savings in electricity use, annual total cost savings ($75) were marginal in colder climates with fewer CDDs, such as Duluth, MN. On the other hand, for this demonstration site in Minneapolis-St. Paul, annual energy cost savings resulting from higher cooling efficiencies ($277) exceed annual net energy cost savings from higher heating efficiencies ($13). This is a function of the particularly low heating loads at this site as compared to 100%OA applications, as well as current energy prices. As with many energy efficiency technologies, energy savings benefits do not always translate into the expected cost savings due to current low energy prices. This case also highlights the key issues for identifying cost effective applications that can provide long runtimes and high heating loads to generate the energy cost savings adequate to offset the fan penalty and the first cost premium for condensing rooftop equipment.

Table 15. Cooling Energy and Cost Savings for Replacement vs Baseline RTU7


Normal Annual

CDD(55)*

Estimated Electric Savings

kWh/yr

Estimated Electric Percent Savings

Annual Energy Costs

Savings

Duluth MN ZONE1 205 790 45% $75

St. Cloud MN ZONE2 467 1818 47% $172

Minneapolis-St. Paul MN ZONE3 752 2936 47% $277

Heating Analysis

The condensing RTU was monitored for a full year from November 2016 to October 2017. Table 16 summarizes the monitored results for the baseline and condensing RTUs at the restaurant site. The annual total therms for both units reflect the low runtimes for this RTU. Based on measured data, the

7 CDD55 NOAA climate normals computed for the 30 year period from 1981 to 2010


R8HE initially starts in high-fire briefly, before switching to low-fire. Due to the low heating loads at this site, high-fire operation only occurs at startup, less than one minute continuously.

Table 16. Total Measured Energy Use for Condensing and Baseline RTUs

Monitored Results 2015 / 2016 Baseline RTU

2016 / 2017 Condensing RTU

Gas input (therms) 145 163

Heating electric input (kWh) 357 339

Remaining electric input (kWh) 36,569 24,948

HDD55 4,174 3,148

EFLH (hrs) 126 167

Figure 28 compares the daily gas consumption for the condensing RTUs and baseline RTU with respect to runtime HDD55. Gas use increases with increasing HDD55, but both RTUs have a poor correlation (R2<0.6), indicating that the change in HDD accounts for less than half the change in gas use due to low runtimes for both RTUs at this site. Figure 29 shows the daily EFLH for the condensing RTU and baseline RTU relative to HDD55. Daily EFLH was calculated based on measured daily gas use for each RTU divided by the specified total gas input capacity for that unit. The lower EFLH values, less than 10 hours per day, for both RTUs reflect the low runtimes and low heating loads for this particular installation. The condensing RTU had higher EFLH for a given HDD55 due to its lower capacity (96 MBH input) compared to the baseline (115 MBH).

Use of a multi-speed fan as a standard feature in the R8HE offers potential benefits in reducing fan energy use and the fan energy penalty due to the secondary heat exchanger in condensing RTUs. The use of a multi-speed blower motor reduces the electricity use of the supply fan, proportional to the change in the airflow ratio cubed. For example, a 25% reduction in airflow from high-fire to low-fire operation results in a 57.8% reduction in fan energy based on these fan laws. Since RTU operated in low-fire versus high-fire for the majority of the time, as is typical for two-stage heating RTUs, this feature can reduce electricity use for any RTU. For condensing RTUs, multi-speed fans are another approach to reduce the fan energy penalty.


Figure 28. Gas Usage with respect to Heating Degree Days

y = 0.0107x - 0.1699R² = 0.5446

y = 0.0084x - 0.0946R² = 0.4709

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Condensing and Baseline RTU Heating Regression Total Gas Use vs. Heating Degree Days

Condensing RTU 95%TE Baseline RTU 80%TE

y = 0.0122x - 0.0446R² = 0.5703

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Condensing and Baseline RTU Heating Regression Total Gas Use vs. Heating Degree Days

Condensing RTU 95%TE Baseline RTU 80%TE


Figure 29. Daily Equivalent Full Load Hours vs Heating Degree Days

y = 0.076x - 0.930R² = 0.471

y = 0.115x - 1.892R² = 0.546

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Condensing and Baseline RTU Heating Regression EFLH vs. Heating Degree Days

Baseline RTU Condensing RTU

Heating Energy Savings – Analytical Comparison – Low Runtimes

The multi-speed supply fan operation of the Reznor R8HE precludes direct comparisons between the R8HE and baseline operation. The analytical comparison methodology was used to estimate energy savings and the payback analysis. Fan energy use was based on an analytical projection for identical fan technologies with a representative additional pressure drop (0.20 inch W.G.) for the condensing RTU incurred over a full 8760 hours of annual fan runtime.

Table 17 presents the estimated average annual gas use for each RTU. EFLH was based on the field site measurements normalized to the annual HDD55 for each region. Gas use was calculated using nameplate efficiencies for three regions in Minnesota: Minneapolis- St. Paul, the location of the demonstration site; and two colder regions, St. Cloud and Duluth to represent the range of potential energy savings for the state of Minnesota. Annual HDD55 for each region was based on NOAA climate normals computed for the 30-year period from 1981 to 2010.

Annual gas use calculated in the previous table form the basis for predicted energy savings and operating cost savings in Table 18 The increase in fan electricity use was based on an analytical projection for identical fan technologies (60% efficiency) with a representative additional pressure drop (0.20 inch W.G.) for the condensing RTU. For this application, the RTU fan operates continuously during occupied hours to provide ventilation. As a conservative estimate, the increased electric use (fan energy penalty) was calculated based on 8760 hours/year fan runtime and assumes a constant speed fan. The R8HE multi-speed supply fan has potential to lower electric use at the lower fan speed used for low-fire


burner operation, and as a result, actual electric use for the R8HE is expected to be lower than these estimates.

Table 17. Annual Gas Use for Condensing and Baseline RTUs8

Weather Data City Climate Zone Normal Annual HDD(55)*

Estimate EFLH

Baseline 80% AFUE Therms

Condensing 95% AFUE Therms

Duluth MN ZONE1 6584 754 860 724

St. Cloud MN ZONE2 5955 682 777 654

Minneapolis-St. Paul MN ZONE3 5192 594 677 570

Table 18. Estimated Annual Energy Savings for Heating9

Weather Data City Climate Zone Estimated Gas Savings Therms/yr

Percent Gas Savings

Increased Peak Electric

kW**

Increased Annual Electric

kWh/yr

Duluth MN ZONE1 136 16% 0.074 649

St. Cloud MN ZONE2 123 16% 0.074 649

Minneapolis-St. Paul MN ZONE3 107 16% 0.074 649

Annual energy costs for this demonstration site, shown in Table 19, are based on 2015 EIA Annual Average Commercial Prices: natural gas: $0.696 per therm based on 1050 Btu/c.f.; electricity: $0.0944 per kWh. Due to historically low natural gas rates and lower EFLH at this demonstration site, net energy cost savings ranged from $13 to $33 per year. Electricity savings from higher efficiency cooling were not included. Neutralizer maintenance costs were not included since it is not required by local codes.

Table 19. Net Energy Cost Savings for Condensing Heating10

Weather Data City Climate Zone Natural Gas Cost Savings

Electricity Cost Savings

Annual Maintenance

Net Cost Savings

Duluth MN ZONE1 $94 -$61 N/A $33

St. Cloud MN ZONE2 $85 -$61 N/A $24

Minneapolis-St. Paul MN ZONE3 $74 -$61 N/A $13

8 NOAA climate normals computed for the 30 year period from 1981 to 2010 9 Estimate based on 8760 hrs/yr, 0.20 in.W.G incremental pressure drop, 60% fan & motor efficiency 10 Assumes no condensate neutralizer and no incremental maintenance required for condensing RTU


Economics – Analytical Comparison – Low Runtimes

First Cost Premiums

Equipment costs premium for the condensing RTU, as reported by the distributor, were approx. $1,216 or $13.3 per 1000 Btu/hr of output heating capacity (91.2 MBH), with respect to an equivalent standard efficiency RTU by the same manufacturer. As the market expands for condensing equipment, equipment costs are expected to decrease due to larger production volumes and mass market pricing. As previously mentioned, DOE projects the equipment cost premium for condensing RTUs (not including the condensate management system and its installation) in a mature market to be $4.40 per 1000 Btu/hr of output heating capacity. Costs for the condensate management system will vary depending on the building size and the accessibility of the drain. In previous demonstrations by GTI, incremental costs for condensate management ranged from $1.45 per 1000 Btu/hr output heating capacity (sanitary drain with no neutralizer) to $6.08 per 1000 Btu/hr (storm drain with neutralizer). Installation costs are expected to decrease as installation contractors become more familiar with condensing rooftop equipment. If neutralizers are used, annual maintenance is estimated to run from $65 to $130 annually, a costly added deduction from the net energy cost savings every year.

The following economic analysis presents paybacks based on the actual demonstration costs for this site, as well as the following projections for mature market pricing:

• $4.40 per 1000 Btu/hr output heating capacity RTU equipment premium • $2.00 per 1000 Btu/hr output heating capacity installed condensate system premium • $100 annual maintenance, based on materials ($50) and labor ($50) for replacing neutralizer


Table 20 presents an analytical comparison of the condensing RTU, based on measured runtime, with an equivalent non-condensing RTU. EFLH determined from the demonstration was normalized based on the Normal Annual HDD Base55 for three Minnesota zones: Duluth (MN ZONE 1), St. Cloud (MN ZONE 2), and Minneapolis-St. Paul (MN ZONE 3). Annual energy savings for a condensing RTU were calculated based on nameplate heating efficiency (95% AFUE) with respect to a standard efficiency RTU (80% AFUE). Electricity savings from increased cooling efficiency were not included. Utility rates were based on EIA 2015 state averages for commercial customers. As shown in Table 20, the resulting net energy cost savings for the condensing RTU compared to the standard efficiency unit ranged from $13 to $33, due to the low runtimes for this field site.


Table 20. Low Runtime Annual Net Energy Costs for Condensing RTU



Capacity Btu/hr Out 91,200 91,200 91,200

Base AFUE/TE 80% 80% 80%

Base Btu/hr In 114,000 114,000 114,000

High Efficiency AFUE/TE 95% 95% 95%

High Efficiency Btu/hr In 96,000 96,000 96,000

Heat Equivalent Full Load Hours (EFLH)/Yr 754 682 594

Base therms/yr 860 777 677

High Efficiency therms/yr 724 654 570

Site Gas Savings therms/yr 136 123 107

Gas Cost Savings ($0.696/therm) $94 $85 $74


Fan CFM 1,895 1,895 1,895

Added Fan DP, inch WG 0.2 0.2 0.2

Fan & Motor Efficiency 60% 60% 60%

Added kW 0.074 0.074 0.074

Fan Operating Hours/Yr 8,760 8,760 8,760

Site Added Fan kWh/yr 649 649 649

Electric Savings ($0.0944/kWh) -$61 -$61 -$61

Net Energy Cost Savings $33.15 $24.10 $13.13


Simple Paybacks

Based on the net energy cost savings for each region, Table 21 presents a progressive series of condensing RTU paybacks for each region.

Table 21. Low Runtime Condensing RTU Paybacks

INSTALLED COSTS & PAYBACKS




Mature Market

Projection

Mature Market

Projection

Mature Market

Projection

ZONE1 ZONE2 ZONE3 ZONE1 ZONE2 ZONE3

with equipment cost premium only11 $1,216 $1,216 $1,216 $401 $401 $401

annual therm savings 136 123 107 136 123 107

annual gas cost savings $94 $85 $74 $94 $85 $74



annual net energy cost savings $33 $24 $13 $33 $24 $13

simple payback (years) >20 >20 >20 12.1 16.7 >20

with added condensate system cost11

$2,340 $2,340 $2,340 $182 $182 $182

total incremental installed cost

$3,556 $3,556 $3,556 $584 $584 $584

simple payback (years) >20 >20 >20 17.6 >20 >20


annual cost $100 $100 $100 $100 $100 $100

annual net O&M cost savings -$67 -$76 -$87 -$67 -$76 -$87

simple payback (years) #N/A #N/A #N/A #N/A #N/A #N/A



The low heating loads and low runtime for this site limit the net energy savings generated. Even with mature market pricing, the projected paybacks for the condensing RTU with low runtimes exceeds the life of the equipment, assumed to be 15 years Condensing RTUs were not cost effective in low capacity applications with low runtimes at current energy prices.

Table 22 illustrates the effect of natural gas and electricity rates on the net energy cost savings for this application. Current low rates for natural gas and/or higher electric rates significantly impact net energy cost savings, and in turn, the corresponding projected paybacks.

Table 22. Low Runtime Net Energy Cost Savings

Net Annual Energy Cost Savings: MN ZONE2

Electricity positive negative($/kWh)

0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16Gas Cost 0.50 29 22 16 9 3 -4 -10 -17 -23 -30 -36 -43($/therm) 0.55 35 29 22 16 9 3 -4 -10 -17 -23 -30 -36

0.60 41 35 28 22 15 9 2 -4 -11 -17 -24 -300.65 47 41 34 28 21 15 8 2 -5 -11 -18 -240.70 53 47 40 34 27 21 14 8 1 -5 -12 -180.75 60 53 47 40 34 27 21 14 8 1 -5 -120.80 66 59 53 46 40 33 27 20 14 7 1 -60.85 72 65 59 52 46 39 33 26 20 13 7 00.90 78 71 65 58 52 45 39 33 26 20 13 70.95 84 78 71 65 58 52 45 39 32 26 19 131.00 90 84 77 71 64 58 51 45 38 32 25 191.05 96 90 83 77 70 64 57 51 44 38 31 251.10 103 96 90 83 77 70 64 57 51 44 38 311.15 109 102 96 89 83 76 70 63 57 50 44 371.20 115 108 102 95 89 82 76 69 63 56 50 431.25 121 114 108 101 95 88 82 75 69 62 56 49

Economics – Analytical Comparison – High Runtimes


Using the same current cost premiums and project mature market prices as the previous example, an analytical comparison of the condensing and baseline RTUs with longer runtimes is presented in Table 23. This example shows the potential energy savings and economics for an RTU application with 1800 EFLH12. Annual energy savings for a condensing RTU were calculated based on nameplate efficiency (95% AFUE) with respect to a standard efficiency RTU (80% AFUE). Electricity savings from increased cooling efficiency were not included. Utility rates were based on EIA 2015 state averages for commercial customers. The resulting net energy cost savings for the condensing RTU compared to the standard efficiency unit was $164/yr.

12 Based on GTI’s ASHRAE study in which measured RTU runtimes ranged from 600 to 1800 EFLH [Kosar 2014].


Table 23. High Runtime Net Energy Costs for Condensing Heating

Net Energy Cost Assumptions


Capacity Btu/hr Out 91,200

Base AFUE/TE 80%

Base Btu/hr In 114,000

High Efficiency AFUE/TE 95%

High Efficiency Btu/hr In 96,000

Heat Equivalent Full Load Hours (EFLH)/Yr 1,800

Base therms/yr 2,052

High Efficiency therms/yr 1,728

Site Gas Savings therms/yr 324

Gas Cost Savings ($0.696/therm) $226


Fan CFM 1,895

Added Fan DP, inch WG 0.2

Fan & Motor Efficiency 60%

Added kW 0.074

Fan Operating Hours/Yr 8,760

Site Added Fan kWh/yr 649

Electric Savings ($0.0944/kWh) -$61

Net Energy Cost Savings $164.19


Simple Paybacks

Based on this net energy cost savings for RTUs with longer runtimes, a progressive series of condensing RTU paybacks is presented in Table 24.

Table 24. High Runtime Condensing RTU Paybacks

INSTALLED COSTS & PAYBACKS Current Market Prices Mature Market Projection

with equipment cost premium only13 $1,216 $401

annual therm savings 123 123

annual gas cost savings $226 $226

simple payback (years) 5.4 1.8


annual net energy cost savings $164 $164

simple payback (years) 7.4 2.4

with added condensate system cost13 $2,340 $182

Total Incremental Installed Cost $3,556 $584

simple payback (years) >20 3.6


annual cost $100 $100

annual net O&M cost savings $64 $64

simple payback (years) >20 9.1

The projected simple payback for the condensing RTU was 7.4 years based on current cost premiums, including the fan energy penalty. However, as you progress through the added cost of the condensate system installation, the simple payback increases to over 20 years, exceeding the life of the equipment.

With projected mature market costs, paybacks are reduced to less than 3 years when considering just condensing RTU equipment premiums and the net energy cost savings alone. The addition of the



condensate system installation, at mature market costs, extends paybacks to less than 4 years. Annual maintenance costs for the neutralizer, for these cases, lengthen paybacks to 9.1 years. Table 25 shows the effect of natural gas and electricity rates on the net energy cost savings, which in turn, impact corresponding paybacks.

This field site demonstrated potential energy savings and payback for conventional RTUs with lower ventilation rates (0 to 30% OA). The RTU demonstrated at this field site had minimum ventilation (11%OA) and shorter runtime (594 to 754 EFLH) than typical RTU installations. At current energy prices, the analytical comparison for this case showed no economic benefit, even with mature market pricing, despite 16% savings in natural gas use. With longer runtimes (1800 EFLH) and projected mature market costs, this application could achieve paybacks of less than 4 years; however, annual maintenance costs for the neutralizer lengthen paybacks to 9.1 years.

Table 25. High Runtime Net Energy Cost Savings

Net Annual Energy Cost Savings:

Electricity positive negative($/kWh)

0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16Gas Cost 0.50 130 123 117 110 104 97 91 84 78 71 65 58($/therm) 0.55 146 139 133 126 120 113 107 100 94 87 81 74

0.60 162 155 149 142 136 129 123 116 110 103 97 900.65 178 172 165 159 152 146 139 133 126 120 113 1070.70 194 188 181 175 168 162 155 149 142 136 129 1230.75 211 204 198 191 185 178 172 165 159 152 146 1390.80 227 220 214 207 201 194 188 181 175 168 162 1550.85 243 236 230 223 217 210 204 197 191 184 178 1710.90 259 253 246 240 233 227 220 214 207 201 194 1880.95 275 269 262 256 249 243 236 230 223 217 210 2041.00 292 285 279 272 266 259 253 246 240 233 227 2201.05 308 301 295 288 282 275 269 262 256 249 243 2361.10 324 317 311 304 298 291 285 278 272 265 259 2521.15 340 334 327 321 314 308 301 295 288 282 275 2691.20 356 350 343 337 330 324 317 311 304 298 291 2851.25 373 366 360 353 347 340 334 327 321 314 308 301


Discussion of Results

This field study demonstrates how condensing heating in rooftop applications (90% to 95% TE) can generate significant gas savings across the range of capacities and applications compared to standard efficiency (80% TE) systems. In both applications, 100%OA MAUs and conventional RTUs, natural gas cost savings more than offset the expected increase in electricity costs due to the fan energy penalty, resulting in a positive net energy cost savings.

Despite significant gas savings and annual cost savings, current installation and maintenance costs for condensate management present an economic barrier for condensing MAUs. Annual costs savings from condensing MAUs were sufficient to offset current equipment premiums, but with the additional cost of the condensate management system, simple paybacks exceeded the life of the equipment, assumed 15 years. Current historically low natural gas prices contribute to the challenging economics for any energy efficiency technologies, including condensing RTUs.

As with most emerging technologies, condensing RTUs are manufactured in smaller production volumes and have higher first costs in comparison to the mature market pricing for competing established technologies. For condensing RTUs (excluding the condensate management system and its installation), DOE projects the equipment cost premium in a mature market to be $4.40 per 1000 Btu/hr of output heating capacity [DOE 2015]. The installed cost of the condensate management systems can vary widely due to specific site configurations and local code. Assuming projected mature market prices for both equipment and condensate systems, condensing MAUs have potential to achieve simple paybacks of 4.0 years. Although local Minnesota codes do not require it, some sites include a neutralizer in the condensate drain. Additional maintenance costs for annual neutralizer replacement, if required, extends the paybacks to 6-11 years.

As expected, the economics were more challenging for the demonstration of condensing heating in a smaller capacity conventional RTUs with lower ventilation rates (11%OA). In this field study, the target 5-ton RTU had unexpected low runtime (<600 EFLH) and low heating loads in part due to the operation of adjacent oversized RTUs. Due to low runtimes, the condensing RTU did not generate adequate cost savings to offset the installed cost premiums, even with projected mature market prices. An analytical assessment, based on nameplate efficiencies and field data, was used to estimate annual cost savings with longer runtimes (1800 EFLH). This analysis indicates that condensing heating in low-capacity conventional RTU applications has potential to achieve 6-year paybacks assuming mature market prices for both condensing equipment and condensate systems. Annual maintenance costs for the neutralizer replacement, if required, will lengthen paybacks to 9 years.


Situational Analysis

Market Development and Economic Trends Condensing RTUs have demonstrated potential energy savings in multiple field studies conducted by GTI. At current low energy prices and higher installed costs, applications with high heating loads are needed to generate adequate energy cost savings for favorable paybacks. In some high ventilation applications, such as DOAS, condensing heating has generated net energy cost savings and favorable paybacks at current costs. In this field study, condensing MAUs (100% OA) generated gas savings up to 17%; however, at current prices, installation and maintenance costs for condensate management presents an economic barrier. Cost effective application of condensing heating in low capacity conventional RTUs will require mature market pricing and/or equipment rebates to offset higher equipment costs and the installation costs of the condensate management.

A pending CEE assessment also identified 100% OA applications, such as DOAS and MAUs, as the most promising initial market entry for utilizing condensing heating in commercial rooftop products due to their higher heating loads and longer runtimes:

CEE members and program administrators have identified condensing gas PACs in the commercial market as an opportunity for potential energy savings and are evaluating the role of this technology in program portfolios. Condensing gas PACS serving as 100 percent outdoor air systems represent a significant market entry point due to their predicable runtimes and high heating loads that can yield considerable energy savings in reasonable timeframes. By targeting the most cost effective application for commercial condensing gas PACs, barriers can be addressed and best practices can be identified from the start, which can impact the success of future applications of condensing gas PACs in the commercial space.

DOAS are used in an increasing number of building applications as an effective and efficient approach to comply with ventilation standards. The state of Washington recently included a requirement for DOAS in its local building codes. To support this growing technology application, ASHRAE published a Dedicated Outdoor Air System Design Guide to provide guidance in designing a DOAS to balance installed cost, building energy use and indoor environmental quality. In addition, ASHRAE developed a pending Chapter on Dedicated Outdoor Air Systems for the ASHRAE Handbook

Minnesota RTU Market A recent study by Seventhwave for MN CARD characterized the Minnesota market for RTUs, including existing RTUs and the new/replacement market [Schuetter 2017]. However, markets for 100% OA RTUs, such as DOAS and MUAs were not included in this study.

The total estimated heating capacity of RTUs in Minnesota is approximately 23.8 million MBH with an average heating capacity of 205 MBH per RTU. Nearly three-fourths (72%) of individual RTUs have a heating capacity less than 225 MBH. However, RTUs with heating capacities over 225 MBH comprise


58% of the heating capacity of all RTUs. Natural gas heating dominates (97%) the Minnesota RTUs market, while the remainder use electric resistance heating.

Average heating efficiency of natural gas fired RTUs in Minnesota is the code-minimum 80% TE. Very few high efficiency condensing RTUs are currently installed, as they are a relatively new but growing technology option. According to the local sales agent for Reznor, Minnesota sales to date included “a few dozen” condensing RTUs and MAUs, each; and several dozen condensing DOAS.14

Condensing RTU Market

Manufacturers

The introduction of high efficiency, condensing gas heating components in RTUs has been led by smaller second-tier HVAC manufacturers, primarily with product lines directed at DOAS or MAU applications. Large HVAC manufacturers such as Trane and York recently began to offer condensing heating in limited quantities, only through their custom product services. These second-tier manufacturers generally serve smaller volume HVAC equipment niches not directly addressed by the major HVAC companies. Condensing RTUs have higher equipment costs related to the additional stainless steel condensing heat exchanger, a larger combustion inducer fan, and the combustion condensate system. The higher equipment cost for condensing RTUs reflects not only additional material costs, but also the initial lower volume, higher cost production of the non-major, second-tier HVAC manufacturers.

In addition to the Reznor-Nortek Global HVAC condensing product line demonstrated in this study, other manufacturers currently offer condensing products include:

• Reznor (Makeup Air and Dedicated Outdoor Air Systems; R8HE RTU ) • Engineered Air (DJX Series Indirect Condensing Appliance ) • Modine (Altherion DOAS ) • Munters (Munters Products – note product literature does not currently show condensing

option) • Ice-Western (HTDM 91+ Omega Series)

Current condensing RTU product lines offered from these manufacturers specify thermal efficiencies (TE) of 90% to 94% with heating input capacities up to 1,400 MBH and staged/modulated turndown ratios as high as 15:1. Product line airflows range from 1,000 to 44,000 cfm with cooling capacities from 5 to 35 tons.

Regional Energy Efficiency Programs

Condensing RTUs have demonstrated potential energy savings in recent pilot studies and are increasingly considered for inclusion in energy efficiency programs. As the implementer of the Nicor Gas

14 Email from Tom Morgan, John J Morgan Company, dated 10/4/2017.

http://www.reznorhvac.com/en/na/high-outside-air-systems

http://www.reznorhvac.com/en/na/products/product-high-efficiency-packaged-air-conditioning-r8he

http://www.engineeredair.com/index.php/our_products/category/indirect-fired#djx-series

http://modinehvac.com/web/products/commercial-ventilation-systems/atherion-packaged-ventilation-system.htm

https://www.munters.com/en/munters/products/

http://www.icewestern.com/wp-content/uploads/updated-HTDM-91-FINAL-PRINTERS-VERSION-WITH-ICEW.pdf


Emerging Technology Program (ETP) in Illinois and of GTI’s own ETP National Collaborative, GTI has conducted multiple field studies of this emerging technology to develop the performance datasets needed to derive new measures for utility energy efficiency programs. Pilot studies of condensing RTUs conducted for the Nicor Gas ETP and Northwest Energy Efficiency Alliances (NEEA) demonstrated net energy savings and confirmed applications with high EFLH and 100% OA operation, such as DOAS or MAU, as the most promising application for this emerging technology.

The Nicor Gas ETP field study reported 11% gas saving with a potential payback of 3.7 years for a condensing DOAS used in a “big-box” retail store. DOAS systems were identified as a potential early market application due to typically high heating loads with long runtimes, often operating 24/7 to meet ventilation requirements. In their 2015-2019 Natural Gas Business Plan, NEEA identified natural gas commercial condensing RTUs as one of five technologies with market transformation potential. The recent four-unit condensing RTU field trial conducted for NEEA included both 100% OA and 30% OA applications and confirmed condensing kitchen MAUs as a potential cost-effective application.

The Illinois Statewide Technical Reference Manual for Energy Efficiency (IL TRM), incorporated GTI’s work paper developed for Nicor Gas as a new measure for condensing DOAS (100% OA RTU) in Version 5.0, effective June 1, 2016.15 The more recent version of the IL TRM, Version 6, effective January 1, 2018, includes a custom rebate for gas-fired unitary HVAC systems heating 100% OA to provide ventilation or make-up air to C&I buildings, targeting applications such as DOAS or MAUs.

Condensing RTUs are include in other utility rebate programs as general prescriptive rebates or custom rebates. General prescriptive rebates range in thermal efficiency requirements and rebate amounts, some starting at 90% TE with a $250 rebate/unit while other start at 95% TE with a $600 rebate/unit. Custom rebate programs targeting specific applications, like DOAS or MAUs, determine savings based on annual fan runtime, airflow, incremental pressure drop, and combined fan and motor efficiency [CEE 2017]. Washington State approved building code language for prescriptive requirements for DOAS to become effective on July 1 2017.16 Leveraging these datasets and experience, GTI recently drafted a work paper for a Minnesota utility to develop a new measure for the State of Minnesota’s Energy Conservation Improvement Program. The complete draft is included in Appendix E.

National Accounts

Although the selection of most RTU equipment is based on lowest first costs, owner-occupied buildings such as national accounts have greater economic incentive to select higher efficiency equipment to reduce lifecycle costs. Implementation of a new emerging technology by key national accounts has potential to lead to increased market growth. National accounts can introduce new technology at multiple sites with similar building layouts and HVAC strategies, and as a result, achieve more consistent

15 Illinois Statewide Technical Reference Manual for Energy Efficiency, Version 5 Illinois Statewide Technical Reference Manual, 4.4.37 Unitary HVAC Condensing Furnace 16 NEEA DOAS Feature Story

http://www.ilsag.info/il_trm_version_5.html

http://ilsagfiles.org/SAG_files/Technical_Reference_Manual/Version_5/Final/IL-TRM_Effective_060116_v5.0_Vol_2_C_and_I_021116_Final.pdf

http://neea.org/neea-newsroom/dedicated-outdoor-air-systems-(doas)-feature-story


energy savings. In addition, national accounts can leverage direct manufacturing relationships and the ability to purchase large quantities, which can reduce initial low volume pricing.

Several national accounts already have existing relationships with these condensing RTU manufacturers. These second-tier manufacturers traditionally fill the market niche for smaller volume HVAC equipment, while major HVAC companies focus on large volume markets with economies of scale needed for mass market product lines. That has often left end users, including major national accounts like Walmart, to work with smaller HVAC manufacturers like Munters to meet their more specialized equipment needs for products such as DOAS. Walmart has indicated, through its equipment supplier Munters, its intention to start incorporating condensing DOAS equipment into new stores during 2018.

Energy Conservation Potential for Minnesota The utilization of condensing RTUs has significant natural gas conservation potential and non-energy benefits, including energy cost savings and greenhouse gas emissions reductions. Applications with 100% OA, such as DOAS and MAUs, are the most promising initial market entry for utilizing condensing heating in commercial rooftop products due to the higher heating loads and longer runtimes.

Higher occupancy C&I buildings such as daycare centers, theaters, restaurants, auditoriums, health clubs, etc., must meet ventilation requirements as specified in ASHRAE 62.1. DOAS are used to condition the ventilation load, and are paired with conventional RTUs or other HVAC technologies in many of these applications. MAUs also condition 100% OA but are operated to maintain building pressurization and offset exhaust loads, such as commercial kitchen exhaust or hotel corridors. Improved heating efficiency in these applications, especially in Minnesota’s cold climate, can provide significant energy and operating cost savings.

Since ventilation requirements range considerably for different building activities, GTI developed a “top-down” analysis to provide a statewide picture of the savings potential as shown in Table 26. Details for this approach are presented in the Appendix C. Since the more recent market studies do not provide details for 100% OA RTUs, GTI used the EIA Commercial Building Energy Consumption Survey (CBECS) database for detailed data on regional building types as the basis for this analysis. ASHRAE Standard 62.1-2010 ventilation air requirements (cfm/ft2) were determined for a variety of building end uses. These activities were paired to corresponding categories in the CBECS. Five target building types were identified that would be compatible with DOAS or MAU applications: Education, Public Assembly, Food Service, Retail, and Inpatient Healthcare. Based on CBECS, total square footage by building types was determined for Minnesota using population-based ratios.

Minneapolis/St. Paul weather data was used to calculate the HDD to estimate the heating load and three different percent multipliers were used for each building category to represent ranges in operating hours. Credit for gas savings was based on heating only the ventilation air in these calculations to represent 100% OA RTUs, namely DOAS and MAUs. Actual gas savings per operating hour may be higher for mixed-air (30 to 60% OA) or conventional RTUs (0 to 30 % OA) due to additional non-ventilation heating loads.


Table 26. Condensing RTU Energy Conservation Potential for Natural Gas Only

SAVINGS ESTIMATE GRID Range for Total Amount

of Market Penetration

Low Savings Estimate in Minnesota

Market

Most Likely Savings in Minnesota

Market

High Savings Estimate in Minnesota

Market

▼ (Therms) (Therms) (Therms)

Range of Savings Estimate for Minnesota Market ►

21,947,620 28,773,034 35,598,448

Low Estimate of Total Market Penetration

1% 219,476 287,730 355,984

Most Likely Estimate of Total Market Penetration

2.5% 548,691 719,326 889,961

High Estimate of Total Market Penetration

5% 1,097,381 1,438,652 1,779,922

Condensing RTUs have a slight increase in fan energy due to the added pressure drop of the condensing heat exchanger, estimated at 0.20 inch WC. This increase in fan energy was not included in these calculations. For the most likely savings and market penetration case, the fan energy penalty would reduce energy saving by approximate 4%. Typically, this penalty is more than offset by the natural gas savings, particularly in 100% OA systems with large EFLHs. In addition, many high efficiency RTUs incorporate advanced ventilation controls, such as variable frequency drives (VFD) and demand-control ventilation (DCV), which can minimize the increased fan energy due to the added pressure drop. Note that some early demonstrations have indicated significantly higher pressure drops for particular makes/models of condensing RTUs than expected, exceeding laboratory and field measurements of other product lines. This issue will continue to be investigated.

To estimate preliminary statewide savings, three conservative market penetration levels were used (1%, 2.5%, and 5%). If only 2.5% of the target buildings types in Minnesota (Education, Public Assembly, Food Service, Retail, and Inpatient Healthcare) adopted RTUs with condensing heating, annual natural gas savings is estimated to range from 548,691 to 889,961 therms annually.

Transferability Condensing RTUs are emerging in the marketplace through “second tier” HVAC manufacturers, such as Reznor, and are currently being incorporated into several state utility EEPs. Targeting C&I buildings with high ventilation requirements, this technology has the potential as a new EEP measure for both natural gas and combined utilities in Minnesota. As a complementary addition to existing custom and/or prescriptive commercial EEPs, condensing heating technology is a promising “next step” option as EEPs look for new savings opportunities.


Non-Energy Impacts High efficiency condensing RTUs provide a more cost-effective means for achieving acceptable indoor air quality to meet current ASHRAE standard ventilation air requirements. In addition to reducing natural gas use, high efficiency RTUs with high efficiency cooling will reduce electric use and peak electric demand. More efficient use of energy also reduces greenhouse gas emissions and source energy use. Preliminary calculations based on the most likely energy savings case and a 2.5% market penetration would result in an emissions reduction of 7,223,000 lbs. carbon dioxide equivalent (CO2e) per year, including the effect of increased electricity due to the fan penalty. Preliminary calculations of the full-fuel-cycle energy use, including the fan penalty, indicate a net source energy reduction of 64,070 MMBtu/yr. Further details are shown in Appendix D


Conclusions and Recommendations

Summary

This field study demonstrates condensing heating can generate potential gas savings up to 17% across the range of capacities and applications compared to standard efficiency (80% TE) systems. In both applications, 100%OA MAUs and conventional RTUs, natural gas cost savings more than offset the expected increase in electricity costs due to the fan energy penalty, resulting in a positive net energy cost savings. At current equipment prices, the cost effectiveness of condensing MAUs is dependent on the site-specific costs of the condensate management system. With mature market pricing, condensing MAUs have potential to achieve simple paybacks of 4 years. Cost effective application of condensing heating in low capacity conventional RTUs is more challenging, and will require mature market pricing and/or equipment rebates to offset the higher cost premium.

In addition to energy and cost savings, this field study successfully demonstrated best practices for combustion condensate management to provide adequate freeze protection in colder climate rooftop environments. Especially for installation contractors unfamiliar with this technology, the manufacturer must provide clear and detailed installation instructions to ensure proper condensate management to prevent condensate freezing. In this study, installation issues regarding condensate management occurred at both field sites. Existing codes for disposal of combustion condensate provide for wide discretion by the installing contractor, subject to AHJ approval, as to whether a sanitary sewer or storm drain connection is utilized for disposal, and whether or not a neutralizer is installed. For the two field sites in this study, both installing contractors piped condensate to a sanitary sewer connection while only one installed a neutralizer.

This field study confirms 100% OA applications as the most promising initial market entry for utilizing condensing heating in commercial rooftop products. These applications, such as DOAS and MAU, provide the long, predictable runtimes and larger heating loads required to generate net energy savings large enough to payback the installed cost premium in the most attractive timeframes. Following multiple pilot studies demonstrating the potential energy savings for condensing heating in commercial application, condensing RTUs are increasingly included in some utility rebate programs, either as general prescriptive rebates or custom rebates for specific applications, such as DOAS/MAU. Leveraging these datasets and experience, GTI recently drafted a work paper for a Minnesota utility to develop a new measure for 100% OA condensing RTUs for the State of Minnesota’s Energy Conservation Improvement Program (Appendix E).

Recommendations

This field study highlights a number of key factors in identifying cost-effective market entry applications for condensing RTUs. As demonstrated in this field study, the cost-effective application of condensing RTUs is dependent on several factors including OA loads, equipment sizing, and runtimes for installed


equipment. 100%OA applications, such as DOAS and MAU, can provide the long, predictable runtimes and larger heating loads needed to generate sufficient gas savings. In addition, sizing equipment to match the load rather than oversizing, as is common practice, can improve runtimes for specific equipment. Site-specific heating load and supply airflow calculations must be done for proper sizing instead of implementing like-for-like replacements. Thirdly, conventional RTUs on any given building have been shown in practice to have very diverse runtimes. This presents a challenge in selecting such applications for condensing heating, since the economics are very dependent on adequate RTU runtimes.

Reductions in equipment cost premiums and installed costs for condensate systems are needed to consistently achieve favorable paybacks in the broader RTU market, beyond 100%OA applications. As shown in this field study, condensing heating equipment can achieve favorable paybacks in 100%OA and conventional RTUs applications with high runtimes assuming projected mature market pricing.

Incremental costs of the condensate management system is more difficult to generalize given specific site and local code requirements. Based on this field study, installation costs for the condensate management system are a key element in the total cost premium. Installation and material costs for condensate systems are very site-specific depending on the building size and configuration, and access to the appropriate drain connection. In addition, existing codes provide for wide discretion by the installing contractor, subject to AHJ approval, as to whether a sanitary sewer or storm drain is utilized for disposal, and whether or not a neutralizer is installed. Although the cost of a neutralizer is based on the furnace capacity, the remaining costs of the condensate management system are fixed for a given site. Therefore, higher capacity equipment with corresponding higher therm savings will achieve payback sooner than lower capacity equipment.

Next Steps

Based on these results of this field study, GTI recommends the following next steps:

• Expand the recent RTU market study for Minnesota to characterize DOAS and MAU markets. Codes and standards are evolving to utilize DOAS in an increasing number of building applications as an effective approach to comply with ventilation standards. These high ventilation applications have unique operating requirements that differ from conventional RTUs.

• A summary of best practices for condensate management, including codes and manufacturer instructions, are included in the report appendices. Although current codes provide much latitude regarding condensate disposal, clear and specific instructions will reduce confusion around installation requirements to prevent freezing or other operational issues, while still minimizing costs. Increasing the familiarity and uniformity of installation will be the first step in reducing installed costs. Best practices in condensate management need to be disseminated throughout the industry, in addition to detailed manufacturer installation instructions and contractor training.


• Consider the draft work paper to develop a new measure for the State of Minnesota’s Energy Conservation Improvement Program for condensing RTUs, specifically in 100%OA applications such as DOAS or MAUs.

• Continued product development and design improvement for condensing RTUs are needed to minimize the fan energy penalty in order to increase net energy savings and improve economics. These developments may include multi-speed fans, VFD, controls strategies, and heat exchanger designs.


References

ASHRAE Design Guide for Dedicated Outdoor Air Systems (DOAS), 2017.

Illinois Statewide Technical Reference Manual for Energy Efficiency, Version 6.0, Final February 8th, 2017, Effective: January 1st, 2018. Illinois Statewide Technical Reference Manual for Energy Efficiency, Version 6

Bingham, Luke, 2015. Condensate Management. Utilization Technology Development, NFP. UTD Project No. 1.13.D (GTI Project No. 21809). Des Plaines IL: UTD/GTI.

CEE, 2017. Gas PAC Market Characterization and Technology Assessment, Draft Report, Consortium for Energy Efficiency, June 28, 2017. CEE Gas PAC Market Characterization and Technology Assessment

Department of Energy – Energy Information Administration (DOE-EIA), 2016. Average Annual Retail Prices by Area, Minnesota: Natural Gas – Commercial Price, Electricity – Commercial Price, DOE-EIA 2016 Average Annual Retail Prices, Minnesota: Natural Gas – Commercial Price, DOE-EIA 2016. Average Annual Retail Prices by Area, Minnesota: Electricity – Commercial Price, (accessed 10/2/2017).

Department of Energy (DOE), 2015. Rulemaking for Commercial Warm Air Furnace Standard, Technical Support Document. DOE Commercial Warm Air Furnace Website, 2015-01-16 Technical Support Document: Energy Efficiency Program for Consumer Products and Commercial and Industrial Equipment: Commercial Warm Air Furnaces

Evergreen Economics, 2017. Rooftop HVAC Market Characterization Study, Northwest Energy Efficiency Alliance, REPORT #E17-346. NEEA REPORT #E17-346 Rooftop HVAC Market Characterization Study

Gas Technology Institute and Washington State University, 2016. Condensing Gas Heating RTU Demonstration, Interim Report, Northwest Energy Efficiency Alliance.

International Association of Plumbing and Mechanical Officials (IAPMO) website, 2015 Minnesota Plumbing Code. IAPMO Minnesota Plumbing Code Website (Accessed 10/9/2017)

International Association of Plumbing and Mechanical Officials (IAPMO) website, Uniform Plumbing Code, 2015 Edition, IAPMO Uniform Plumbing Code Website (Accessed 10/9/2017)

International Code Council, 2012. 2012 International Fuel Gas Code.

Kosar, D., 2013. Nicor Gas Energy Efficiency Emerging Technology Program, 1001: High Efficiency Heating Rooftop Units (RTUs), Public Project Report – Executive Summary, Gas Technology Institute, Des Plaines, IL. Nicor Gas Energy Efficiency Emerging Technology Program, 1001: High Efficiency Heating Rooftop Units (RTUs) – Executive Summary

Kosar, Douglas, et al. 2014. Field Monitoring of Rooftop Unit (RTU) Heating Runtimes and Gas Usage for Selected Commercial Buildings (NY-14-C084). American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Papers CD: 2014 ASHRAE Winter Conference. Atlanta: ASHRAE.



https://library.cee1.org/system/files/library/13318/DRAFT_CEE__GasPACMarketTechAssessment_IndustryReviewVersion__6.28.17.pdf

https://www.eia.gov/opendata/qb.php?category=461513&sdid=NG.N3020MN3.A

https://www.eia.gov/opendata/qb.php?category=461513&sdid=NG.N3020MN3.A

https://www.eia.gov/opendata/qb.php?category=1013&sdid=ELEC.PRICE.MN-COM.A

https://www.eia.gov/opendata/qb.php?category=1013&sdid=ELEC.PRICE.MN-COM.A

https://www1.eere.energy.gov/buildings/appliance_standards/rulemaking.aspx/ruleid/70

http://www.regulations.gov/#!documentDetail;D=EERE-2013-BT-STD-0021-0012



https://neea.org/docs/default-source/reports/rooftop-hvac-market-characterization-report.pdf?sfvrsn=20

http://www.iapmo.org/Pages/MinnesotaPlumbingCode.aspx

http://codes.iapmo.org/home.aspx?code=UPC

https://www.nicorgasrebates.com/resources/Emerging-technology

https://www.nicorgasrebates.com/resources/Emerging-technology


Kosar, Douglas, et al. 2015. High Efficiency Gas Heating Rooftop Packaged Air Conditioner (Gas PAC). Utilization Technology Development, NFP. UTD Project No. 1.9.A (GTI Project No. 20864). Des Plaines IL: UTD/GTI.

Kosar, Douglas, 2015. Personal communication Dick Lord, Director of Product Engineering, Carrier Corporation.

Kosar, D., 2015. Positioning Markets to Transition from Non-Condensing to Condensing Heating in Rooftop Units (RTUs), CEE 2015 Industry Partners Meeting, Bloomingdale, IL, September 17, 2015.

Minnesota Administrative Rules, Minnesota Plumbing Board, Plumbing Code Chapter 4714. Minnesota Administrative Rules, CHAPTER 4714, PLUMBING CODE, Minnesota Administrative Rules CHAPTER 4714.0814 CONDENSATE WASTES AND CONTROL (accessed 10/7/2017).

Minnesota Technical Reference Manual (TRM), Version 2.1 Minnesota Technical Reference Manual (TRM)

National Climatic Data Center (NCDC), 2017. 1981-2010 Climate Normals, National Climatic Data Center (NCDC), 2017. 1981-2010 Climate Normals (accessed 10/02/2017).

Reznor, 2015. R8HE / PPG3HE SERIES INSTALLATION INSTRUCTIONS, Reznor R8HE / PPG3HE SERIES INSTALLATION INSTRUCTIONS (accessed 09/28/2017).

Reznor, 2016. Installation / Operation Applies to: PREEVA® Outdoor Air Handler Model RDH, Model REH, Model RHH, and Model RXH, PREEVA® Outdoor Air Handler Model RDH, Model REH, Model RHH, and Model RXH Installation / Operation Manual (accessed 10/02/2017)

Seventhwave and Center for Energy and Environment, 2017. Commercial Roof-top Units in Minnesota, Characteristics and Energy Performance, Final Report Conservation Applied Research & Development (CARD), Minnesota Department of Commerce Division of Energy Resources, COMM-20140512-86450. Commercial Roof-top Units in Minnesota, Characteristics and Energy Performance, Final Report

https://www.revisor.mn.gov/rules/?id=4714

https://www.revisor.mn.gov/rules/?id=4714

https://www.revisor.mn.gov/rules/?id=4714.0814

https://www.revisor.mn.gov/rules/?id=4714.0814

https://mn.gov/commerce/industries/energy/utilities/cip/technical-reference-manual/

https://mn.gov/commerce/industries/energy/utilities/cip/technical-reference-manual/

https://gis.ncdc.noaa.gov/maps/ncei/normals

https://gis.ncdc.noaa.gov/maps/ncei/normals

http://www.reznorhvac.com/files/709726A.pdf

http://www.reznorhvac.com/files/709726A.pdf

http://www.reznorhvac.com/files/I-RDH-REH-RHH-RXH.pdf

http://www.reznorhvac.com/files/I-RDH-REH-RHH-RXH.pdf

https://www.cards.commerce.state.mn.us/CARDS/security/search.do?method=showPoup&documentId=%7bAC3FB94A-9598-4A9C-BF02-967BFAC28FF3%7d&documentTitle=386204&documentType=6


Appendix A: Reznor RHH Select Installation Instructions


Appendix B: Condensate Management Best Practices

In addition to the economic challenges confronting cost effective applications of condensing RTUs, successful market development will also hinge on implementation of best practices for installation of the companion combustion condensate management systems. These best practices must provide for code acceptable disposal, including any requirements for neutralization of its acidic content, along with adequate freeze protection in cold climate rooftop environments.

Best practices for combustion condensate management systems for condensing RTUs are generally dictated by the governing building codes at the state level and the manufacturer provided installation instructions. This section will first address the governing national and state codes for Minnesota regarding combustion condensate. Second, this report section will address best practices for condensate management, representative manufacturer installation instructions, including the demonstration equipment manufacturer Reznor, and the actual contractor installation practices at the two demonstration sites.

Building Codes & Combustion Condensate Management

Within building codes, condensate management is covered by two specialty codes – the mechanical code and the plumbing code – as fluid condensate from mechanical systems are then transported by the building’s plumbing system. Condensate management up to the point of disposal (i.e. fixture or drain) is typically covered by mechanical codes. Mechanical code coverage includes provisions for having a proper slope and diameter for the condensate line coming from a condensing or high-efficiency appliance to ensure the proper operation of the appliance. It also has provisions for acceptable condensate disposal locations.

Condensate management at the point of disposal is typically governed by plumbing codes. Plumbing codes may regulate the disposal of condensate from fuel-burning appliances by including provisions for neutralizing or diluting the condensate as well as placing restrictions on the material used in the drainage system that the condensate will flow through.

State level codes typically adopt national model building codes in their entirety, or with amendments that alter, delete, or add sections to the model code language. Two nationally and internationally recognized model building code-making bodies are the International Code Council (ICC) and the International Association of Plumbing and Mechanical Officials (IAPMO). The ICC mechanical and plumbing codes are the International Mechanical Code (IMC) and the International Plumbing Code (IPC). The IAPMO mechanical and plumbing codes are the Uniform Plumbing Code (UPC) and the Uniform Mechanical Code (UMC). Provisions for condensate management may be in either a dedicated section with explicit mention of origin from fuel-burning appliances or in sections that regulate the disposal of corrosive or indirect wastes [Bingham 2015].



One other code is noteworthy in the context of condensate management – the American Gas Association’s (AGA) and National Fire Protection Association’s (NFPA) National Fuel Gas Code (NFGC). The ICC International Fuel Gas Code (IFGC) used the NFGC as a basis for technical development. The NFGC defers condensate management to manufacturer provided installation instructions and the IFGC language on condensate management is largely from the corresponding ICC IPC.

As is typical with state code officials, Minnesota has adopted national model building codes:

• The 2015 Minnesota State Mechanical and Fuel Gas Code became effective Jan. 24, 2015. Minnesota Rules Chapter 1346 rule adopted by reference Chapters 2 through 15 of the International Mechanical Code, Chapters 2 through 8 of the 2012 International Fuel Gas Code (including amendments to both).17

• Minnesota adopted the national 2012 Uniform Plumbing Code along with a list of amendments on January 23rd, 2016.18

Key highlights from relevant IMC and UPC codes sections for condensing RTUs are provided below to give context for the installations at the two demonstration sites and to support the best practices presented here for condensate management.

International Mechanical Code (IMC) The IMC explicitly references condensate from fuel-burning condensing appliances. Provisions indicate that the condensate should be disposed of in accordance with manufacturer provided installation instructions and into an approved fixture, with approval always subject to the authority having jurisdiction (AHJ). The AHJ is typically the local building inspector or code official. Furthermore, the IMC notes the condensate piping must be of approved corrosion-resistant material. While the slope is explicitly defined, the diameter of the piping is restricted to being as large, or larger, than that of the drain connection from the appliance. Below is text from the Minnesota Mechanical and Fuel Gas Code:19

17 2015 Minnesota State Mechanical and Fuel Gas Code (accessed 10/7/2017) 18 Minnesota Administrative Rules (accessed 10/9/2017) 19 2015 Minnesota State Mechanical and Fuel Gas Code (accessed 10/9/2017)

https://www.dli.mn.gov/ccld/PDF/FS%201346.pdf

https://www.revisor.mn.gov/rules/?id+4714

https://www.dli.mngov/CCLD/PDF/1346%2001-23-15.pdf



Uniform Plumbing Code (UPC) The 2015 UPC Section Condensate Waste and Control, Subsection 814.1 Condensate Disposal and Subsection 814.4 Appliance Condensate Drains reiterates many of the same IMC requirements for condensate management from condensing appliances including discharge to an approved plumbing fixture or disposal area, along with drain pipe size, slope and corrosion resistance. The following is text from the 2015 Minnesota Plumbing Code20 regarding combustion condensate management:

The UPC also contains sections addressing potential neutralization of acidic condensate or neutralizing devices, as well as material selection for drainage pipe. One set of code language addressing detrimental wastes appears under the 2015 MN Plumbing Code Section 306.0 Industrial Wastes, Subsections 306.1 Detrimental Wastes and 306.2 Safe Discharge (identical to the 2015 UPC), which requires treatment of discharged wastes that could be detrimental to the sewer system or sewage treatment plant operation, deleterious to surface or subsurface waters. The industrial designation seems to imply that treatment

20 The International Association of Plumbing and Mechanical Officials (IAPMO) website, 2015 Minnesota Plumbing Code, Code 12 Chapter 8 Indirect Wastes, The International Association of Plumbing and Mechanical Officials (IAPMO) website (Accessed 10/9/2017)





should occur with large volumes of waste originating from manufacturing processes, etc. The following is text from the 2015 Minnesota Plumbing Code:

The UPC and Minnesota Plumbing Code also contains explicit provisions for drainage system materials carrying undiluted condensate wastes from fuel-burning appliances in Section 807.2 Undiluted Condensate Waste (identical to 2015 UPC section). However, this section does not mention neutralization requirements but does list what type of materials the drainage system conveying the wastes should be made of, as the integrity of the plumbing system is of primary importance. The exact code text follows from the MN state code:

Minnesota State Code (IMC/UPC) Summary Based on the preceding review of the relevant Minnesota state mechanical and plumbing code, and the national model building codes from which they were adopted/adapted, code compliance for combustion condensate addresses these two key areas:

1. Disposal location

• broadly defined as “an approved plumbing fixture or disposal area” in both mechanical and pluming codes

• that location is further stipulated as “in accordance with the manufacturer’s installation instructions” in the mechanical code



• approval always subject to the Authority Having Jurisdiction (AHJ), typically the local building inspector or code official

2. Neutralization

• only industrial wastes are explicitly required to be treated or rendered safe before discharge in the plumbing code

• no explicit requirements for neutralization of combustion condensate from fuel burning appliances in the plumbing or mechanical code

This existing code language appears to provide for wide discretion by the installing contractor, subject to AHJ approval, as to whether a sanitary sewer or storm drain connection is utilized for disposal, and whether or not a neutralizer is installed.

Condensate Management Best Practices

As was detailed in the codes review, the codes defer to the manufacturer and their installation instructions for certain aspects of the design and construction of the condensate disposal system. However, the manufacturer will defer to state and local codes for certain aspects of the design and construction of the condensate disposal system as well, setting up a circular ambiguity.

Both demonstration sites had condensing units installed from the same manufacturer Reznor. The Reznor R8HE product was installed at the restaurant site and the Reznor RHH was installed at the hotel site. Each Reznor product line comes with a set of installation instructions for the mechanical contractor laying out the condensate drain installation. Those installation instructions will be highlighted here along with the best practices and the actual contractor installation experiences.

According to best practices for combustion condensate disposal, as documented by GTI [Bingham 2016], the drain line drops vertically through the inside of the roof curb followed by a drain trap inside the conditioned space. Any non-vertical drain lines outside the conditioned space should be avoided. Key best practices for condensate drain installation include:

• Prepositioning the flexible condensate line, up through the roof deck or duct passage opening inside the roof curb, for connection to the RTU drain port.

• Then setting the RTU on the roof curb for completion of the condensate line connection in the RTU.

• Bringing the drain line immediately into a conditioned space below the RTU, if possible, to avoid the need for any heat tape and/or insulation on the drain line.

• Placing the drain trap in a serviceable area in the conditioned space below the RTU to avoid freezing conditions.



• Ensuring that all drain line connections downstream of the RTU drain are non-serviceable until accessible areas within the building interior are reached.

Additional best practices include:

• Planning the balance of the drain line route to a condensate disposal location that allows the code required plumbing slope and gravity to drain the condensate to the disposal location without requiring a condensate pump.

When installing multiple condensing RTUs on a building, the separate drain lines can be connected together into a common drain line, but only DOWNSTREAM of the individual RTU drain traps, per Reznor (and other manufacturers).

Reznor R8HE Condensate Installation Instructions Figure 30 from the Reznor R8HE installation manual [Reznor 2015] illustrates the configuration of the RTU condensate drain line in a typical rooftop installation. The Reznor R8HE instructions do not stipulate the condensate disposal location, so the plumbing fixture or other disposal area location is left to the selection of the installing contractor and approval of the local code authority.

Figure 30. Reznor R8HE Installation Schematic

At the restaurant site, the original RTU was installed on “sleeper” supports with ducting run horizontally across the rooftop, as shown on the left in. Condensate best practices allow an option for horizontal discharge of the combustion condensate (out the side of the unit) if the condensate line is heat-taped and insulated. It can be run be horizontally along the roof, with adequate slope for draining, and



brought into the heated space along the supply or return ducts, or any other convenient place. The installing contractor felt this was an inadequate option, and added a new RTU curb to this installation in order to comply with the manufacturer instructions for a vertical drain into the conditioned space (Photo on right, Figure 31). This installation reported no freezing or other issues; however, the addition of a new curb with roofing modifications added significant installation costs.

Figure 31. Existing RTU Installed on “sleepers” Instead of a Roof Curb

The installing contractor at this site chose not to install a neutralizer because multiple other water sources were draining into the drain (Figure 32) assuming the acidic condensate would be diluted. The site passed local code inspection with no issues per the contractors. As seen with the other demonstrations, code requirements, manufacturer installation instructions, and interpretations of both vary locally on the need for a neutralizer and the disposal location, either to a storm or sanitary drain connection. This can have a significant effect on the resulting cost effectiveness of condensing RTU applications as seen in the payback economics presented for this and the other sites.

Figure 32. Reznor R8HE Condensate Drain Installation



Reznor RHH Condensate Installation Instructions Figure 33 from the Reznor RHH installation manual [Reznor 2016] shows the underside of this RTU with its condensate drain line connections for a typical rooftop installation.

Figure 33. Reznor RHH Condensate Drain Installation Instructions

Reznor RHH Installation at Hotel Site At the hotel site, the RHH condensate line was not installed per manufacturer instructions due to lack of familiarity with the unique condensate management requirements for condensing RTU. This allowed condensate to collect in the line and freeze at very low ambient temperatures (below 5F). Following feedback from GTI and Reznor, the MAU had to be lifted from the curb and the condensate line was installed correctly. This site passed local code inspections per the contractors.

According to best practices for combustion condensate disposal, as documented by GTI [Bingham 2015], the drain line drops vertically through the inside of the roof curb followed by a drain trap inside the



conditioned space. Previous field studies by GTI, in cold climates such as Minnesota, demonstrated that insulation and heat tape are not necessary to prevent freezing as long as best practices are followed. If the installation must have horizontal drain lines outside the conditioned space due to site specific characteristics, the lines must be insulated and wrapped in heat tape.

At this site, once inside the conditioned space, the condensate line is connected to a drain trap in a serviceable area. The drain line was installed with the code required plumbing slope allowing gravity to drain without a condensate pump. The condensate drain line can be installed along the inside of the roof deck to achieve the required plumbing slope. Existing codes provide for wide discretion by the installing contractor, subject to AHJ approval, as to whether a sanitary sewer or storm drain connection is utilized for disposal, and whether or not a neutralizer is installed. As shown in Figure 34, the condensate line from the RHH (red) is run directly vertical into the conditioned space (shown left). The condensate is neutralized before draining into the sanitary sewer (shown left). A calcium carbonate neutralizer was added to the drain line, to counteract the acidic content of the combustion condensate. Condensate neutralizers are a well-established product developed for the condensing boiler market. The neutralizer calcium carbonate should be replenished when outlet pH drops below 5.5. The amount of calcium carbonate is typically sized for an annual maintenance interval. Union fittings on either side of the neutralizer that allow a service technician to remove the neutralizer and unscrew the cap at either end to add calcium carbonate.

Figure 34. MAU Condensate Drain at the Hotel Demonstration Site

GTI and the installing contractor provided suggestions to Reznor for clarifying this requirement in their installation manual (Appendix A). The contractor was following instructions for the RDH (standard efficiency unit) instead of the high efficiency RHH condensing unit. The instructions for condensing RTUs should be clearly set apart, identified by both part number and description (“condensing heating module”), describing the condensate management and other unique requirements. Another option would be for a separate installation manual for condensing units. Other recommendations included



labels on the outside of the cabinet, identifying this unit as a condensing MAU, and including or referencing the section in the manual for the condensate installation. This would alert contractors to review instructions before lowering the unit onto the curb. In addition, as there are multiple cutouts in the bottom of the cabinet, the opening for the condensate line could be marked, or the condensate line could be pre-installed to ensure it is directed vertically into the condition space.

Another suggestion was to color-code the condensing HX condensate line to differentiate it from condensate lines from the non-condensing HX or the cooling coil. This unit had three condensate drains: 1) condensate from HX box drain pan during heating; 2) condensate from inducer fan during heating; and 3) condensate in burner box during cooling (or economizing operation since this unit was heating only) when cool air may condense from the AC coil itself water form moist air inside the burner box – this is drained to outside, just like condensate from the AC coil.

Neutralizers Although a neutralizer was only applied in one of the two demonstration sites and is not currently required by MN state code, the trend in codes [Bingham 2015] is likely to result in more regulations to require their use in the future with condensing gas equipment. Neutralizers are a fairly mature technology having been developed a decade or more ago in conjunction with the widespread introduction of condensing boilers. Neutralizers are often directly available as an option from the condensing equipment manufacturer itself or readily available as an aftermarket component from several suppliers, for example JJM Boiler Works (JJM Boiler Works Website) and Axiom Industries (Axiom Industries Website). Installing contractors already experienced with condensing boilers, condensing unit heaters, etc. have ready access to neutralizers from their HVAC parts suppliers.

A common form that a neutralizer takes is a PVC pipe that is usually filled with calcium carbonate (although magnesium hydroxide is beginning to enter the market as a higher performance alternative) and installed in line with the condensate drain line before the point of disposal, i.e., sanitary sewer drain or storm sewer drain (). The neutralizer is sized for the connected condensate load which is based typically on the gallons of condensate produced annually. An industry rule of thumb has been 1 gallon of condensate produced each hour for every 100,000 Btu per hour of input capacity that is firing for that hour. The EFLHs that the input capacity is firing annually will establish the total gallons of condensate for the year. However, this will vary somewhat with condensing efficiency level, which is also affected by ambient temperature conditions especially when processing 100% OA loads with RTUs. It is good practice to be somewhat conservative then in neutralizer sizing for RTUs and build in a factor of safety. Neutralizers generally range in cost (uninstalled) from $50 to $250 for 2,000 gallons (100,000 Btu/hr input firing for 2,000 EFLHs) to 40,000 gallons (400,000 Btu/hr input firing for 10,000 EFLHs) of condensate neutralization capacity, respectively.

If maintenance intervals are planned to be greater than one year then the sizing calculation above must be adjusted accordingly. The calcium carbonate is consumed when it reduces the acidity of the condensate and must be replenished. As was done at site A, there are union fittings on either side of the neutralizer that allow a service technician to remove the neutralizer and unscrew the cap at either end

http://jjmboilerworks.com/

http://www.axiomind.com/

http://www.axiomind.com/



to add calcium carbonate. Depending on the size of the neutralizer, annual maintenance is presently estimated to run from $65 to $130 annually, a costly added deduction from the net energy cost savings every year.

Condensate Pumps No condensate pumps were required at either demonstration site and generally should not be required in rooftop applications of RTUs. Typical installations use building interior sanitary drain that can be reached by using the code prescribed plumbing slope and gravity to flow the condensate to the drain, without the need for a pump. However, pumps may be required in those instances where vertical obstructions block the horizontal path of the drain line, or the length of the drain line run and the available height are insufficient to reach the drain by gravity. In those instances the use of a pump would be required.

The placement of the pump will be dependent on the site specific situation, but it will be placed downstream of the condensate trap and at a serviceable, but limited access location where the condensate lift is required. That location could be at the point where the condensate line must go up and over a vertical obstruction or the preceding run of drain line is approaching the point where it can drain no further by gravity.

Condensate pumps are a mature technology and are often directly available as an option from the condensing equipment manufacturer itself or readily available as an aftermarket component from a large number of suppliers. Installing contractors have ready access to condensate pumps from their HVAC parts suppliers. Condensate pumps generally range in cost (uninstalled) from $30 to $90 for 1 gallon per hour to 200 gallons per hour of condensate, respectively, and will last the life of the RTU equipment without maintenance.


Appendix C: Energy Conservation Potential – Calculation Details

GTI developed an analysis of energy conservation potential for high efficiency condensing RTU technology in Minnesota. Since energy savings from high efficiency RTUs will vary depending on the fraction of outside air being provided for ventilation, GTI utilized a “top-down” approach to estimate potential energy savings for this emerging technology over a range of outside air requirements and provide a state-wide picture of the savings potential. This analysis focuses on energy saving opportunities in applications with 100% OA, the recognized initial market entry for this condensing

Step 1 – Determine Ventilation Air

Based on ASHRAE Standard 62.1 (2010), the ventilation air requirements were calculated for a large range of occupancy categories. The occupant density (#/1000 ft2) was multiplied by the combined outdoor air rate (cfm/person) and divided by 1,000, and added to any additional, prescriptive cfm/ft2 end use requirement, to determine the total cfm/ft2. GTI then generally grouped each of the occupancy categories into five key building categories in the EIA’s Commercial Building Energy Consumption Survey (CBECS) database:

1. Education – 0.425 cfm/ft2 2. Public Assembly – 0.750 cfm/ft2 3. Food Service – 0.900 cfm/ft2 4. Retail (Other than Mall) – 0.240 cfm/ft2 5. Health Care (Inpatient) – 0.333 cfm/ft2

It is important to note that supply air, combining return air, and ventilation air, can vary depending on other non-ventilation building loads, but typically ranges from 0.5 to 1.5 cfm/ft2 for most spaces. Given this diversity in non-ventilation building loads across these building categories, GTI only took credit for the gas savings in heating only the ventilation air in these calculations representing 100% OA RTUs, namely DOAS and MAUs. Actual gas savings for mixed air (30 to 60% OA) or conventional RTUs (0 to 30 %OA) may be higher for given operating hours due to additional non-ventilation heating loads. These calculations also did not include the slight increase in electricity consumption for the RTU supply fan to overcome the additional in-line pressure drop of the secondary condensing heat exchanger of 0.20 inch WC.

Step 2 – Minnesota Building Square Footage

In order to determine the total square footage for each of these five building types in Minnesota, GTI relied upon the CBECS database. Square footage is reported in CBECS by census region and division, with Minnesota falling into the West North Central category. The West North Central category also includes



Iowa, Kansas, Missouri, Nebraska, North Dakota, and South Dakota. GTI applied a population-based ratio to the total West North Central square footage reported in CBECS to estimate the Minnesota fraction. Population data was sourced from the Census Bureau for the year 2003 to correspond with the CBECS 2003 data. Census data indicated that Minnesota accounted for about 26% of the population of the West North Central census region and division. This ratio was then applied to the total square footage for each of the five building categories, as shown in Table 27.

Table 27. CBECs Total Floor Space for Target Market Building Types

Location

Total Floor Space (million square feet) Principal Building Activity

Education Public Assembly

Food Service Retail (Other than Mall)

Healthcare (Inpatient)

West North Central 552 377 206 337 Q* Minnesota 143 97 53 87 N/A *Q = Data withheld by EIA because the Relative Standard Error was >50%, or <20 buildings sampled

Step 3 – Calculated Heat Load

Once GTI had developed estimates for the ventilation air requirements, determined the target building types, and calculated the total number of square foot in Minnesota for each of the targeted building types, the next step focused on calculating the heat load. Minneapolis/St. Paul area weather data was used to calculate that approximately 32 Btu/cfm-HDD65 of heating load was required for conditioning outside air to space neutral (72°F).

Step 4 – Building Operating Schedules

It is expected that there will be variation in the building operating hours even within the same building type. For example, an ice rink and night club will have different typical operating hours, while both still fall under the Public Assembly building type. Therefore, GTI developed three different percent multipliers that would be applied against the HDD65 value of 7,580. This HDD65 value was based on the 1981-2010 30-year average for NOAA/NCDC.21

1. Education – 30%, 40%, 50% 2. Public Assembly – 20%, 30%, 40% 3. Food Service – 50%, 60%, 70% 4. Retail (Other than Mall) – 40%, 50%, 60% 5. Health Care (Inpatient) – 60%, 75%, 90%

These percent multipliers were applied in an equation to determine the Low, Most Likely, and High ventilation heat loads (Btu) for each building type. The Btu of ventilation heat loads were divided by 0.80

21 National Climatic Data Center (NCDC), 2017. 1981-2010 Climate Normals

http://climate.umn.edu/pdf/normals_means_and_extremes/msp_normals_1981-2010.pdf



to determine the gas use for conventional efficiency, non-condensing heating (baseline) and divided by 0.90 to determine the gas use for condensing, high efficiency heating. The different between these two values represented the savings.

Step 5 – Market Penetration

GTI also wanted to account for the likely adoption of the technology into the marketplace in these potential energy savings calculations. Given the high current costs of this technology, GTI conservatively estimates a low market penetration of one percent, a most likely market penetration of 2.5%, and a high market penetration of 5%. These market penetrations were applied to the Low, Most Likely, and High gas savings to develop therm savings estimates for Minnesota as shown in the Savings Estimate Grid in the main portion of this proposal.

Table 28. Energy Conservation Potential Calculations (Excerpt)


Appendix D: Emissions Reduction Potential Supporting Information

Table 29. Energy Conservation Potential Calculations

Composite Emission Factors Natural Gas, lb/MMBtu

MROW eGrid Subregion Non-Baseload Electricity,

lb/MWh

CO2 131.1 2,354.20 SO2 0.027 6.57 NOx 0.17 4.19 Hg 0 0 CH4 0.38 6.89 N2O 0.003 0.04 CO2e 141.28 2,539.36 Source Energy Factor (Btu/Btu) 1.09 3.63

Table 30. Emissions and Source Energy Savings with 2.5% Market Penetration

Natural Gas Emission Decrease

Electricity Emission Increase

Net Emissions Reduction

CO2 (1000 lbs) 9,430 2,725 6,705 SO2 (lbs) 1,942 7,605 (5,663) NOx (lbs) 12,229 4,850 7,379 Hg (lbs) - 35 (35) CH4 (lbs) 27,334 7,975 19,359 N2O (lbs) 216 46 169 CO2e (1000 lbs) 10,163 2,939 7,223

Net Source Energy Reduction

Source Energy Factor (MMBtu) 78,407 14,336 64,070


Appendix E

State of Minnesota Technical Reference Manual

Energy Conservation Improvement Programs

DRAFT Work Paper: Condensing Furnace in Unitary HVAC System

New Measure Commercial/Industrial (C/I) HVAC – Condensing Furnace in Unitary HVAC System

Douglas Kosar, Gas Technology Institute

Appendix E: TRM DRAFT Work Paper: Condensing Furnace in Unitary HVAC System


Overview

This measure covers an indirect gas fired condensing furnace that is part of a unitary heating, ventilating, and air conditioning (HVAC) system, either single package or split system, that is used to condition 100% outside air (OA) for introduction into commercial and industrial (C&I) building spaces. The unitary equipment can provide either heating only or heating and air conditioning in an indoor (non-weatherized) or outdoor (weatherized) system package.

Condensing heating technology has already achieved significant penetration of the residential furnace market. However, the introduction of condensing furnaces in unitary packages for the commercial and industrial (C&I) market, especially weatherized systems like rooftop units (RTUs), has been slowed by certain economic and technical challenges. Economically, the most cost effective, initial C&I markets must be established that can pay back the condensing equipment cost premium along with the additional installation and any ongoing maintenance costs for the combustion condensate drainage and disposal system. Technically, that condensate system must meet code acceptable disposal requirements, including any requirements for neutralization of its acidic content, and for outdoor installations, it must provide adequate freeze protection as well.

The initial, most cost-effective markets for condensing furnaces in unitary HVAC systems will be in C&I building applications that have sufficiently large heating loads and long heating runtimes to drive resulting gas usage high enough to generate net energy cost savings that are adequate to pay back installed cost premiums in attractive timeframes. The conditioning of OA for ventilation to maintain indoor air quality presents a large heating load and some buildings, like “big box” retail stores, even utilize unitary packages that are dedicated outside air systems (DOAS) to condition 100% OA for building ventilation. Other buildings, such as hotel/apartment buildings or restaurants, will use unitary packages that are make-up air systems (MUAS) to condition 100% OA for corridors or kitchens, respectively, to compensate for exhaust and maintain neutral or slightly positive building pressurization. Over the heating season, a DOAS, MUAS, or any such unitary HVAC system that conditions 100% OA, will warm cold outside air to its required supply air temperature and will operate continuously during the building’s HVAC operating schedule. Utilizing condensing instead of non-condensing furnaces in 100% OA unitary systems can provide significant gas savings with promising payback economics as validated in a recent pilot of this emerging technology [1].

This new measure targets such 100% OA applications and provides a methodology for quantifying gas savings. Note that savings on gas use during the heating season will be accompanied by increased electric use to move supply air year round through the additional pressure drop of the secondary condensing heat exchanger of the furnace in the unitary HVAC system. Unlike a residential furnace application, the DOAS or MUAS supply air fan will typically run continuously during the HVAC operating schedule to meet ventilation or make-up air requirements in C&I buildings. The methodology accounts for that added electric use as well.



New Measure Characterizations

Description This measure applies to a constant volume (CV) DOAS, MUAS, or any unitary HVAC system that is utilizing an indirect gas fired process to heat 100% OA to provide ventilation or make-up air to C&I building spaces. The unitary package must contain an indirect gas-fired, warm air furnace section, but the unitary package can be with or without an electric air conditioning section. The unitary package can be either a single package or split system that is applied indoors (non-weatherized) or outdoors (weatherized).

This measure excludes demand control ventilation, condensing unit heaters, and high efficiency (condensing) furnaces with annual fuel utilization efficiency (AFUE) ratings (for furnaces with less than 225,000 Btu/hr input capacity), which are covered by other measures for the C&I sector in the Technical Reference Manual (TRM) [2].

Definition of Efficient Equipment To qualify for this measure, the efficient unitary equipment must contain a condensing, warm air furnace with a natural gas thermal efficiency (TE) rating of 90% or higher, or alternatively, the unitary package must have equipment nameplate information for natural gas that identifies a heating output and heating input rating that has an output over input ratio of 0.90 or higher. These ratings must be certified by a recognized testing laboratory in accordance with American National Standards Institute (ANSI) Standard Z21.47 for Gas-Fired Central Furnaces [3]. The furnace must be vented and condensate disposed of in accordance with the equipment manufacturer installation instructions and applicable codes.

Definition of Baseline Equipment The baseline equipment is expected to be unitary equipment that contains a non-condensing, warm air furnace with a natural gas TE rating of 80%, or alternatively, the unitary package will have equipment nameplate information for natural gas that identifies a heating output and heating input rating that has an output over input ratio of 0.80. These ratings must be certified by a recognized testing laboratory in accordance with American National Standards Institute (ANSI) Standard Z21.47 for Gas-Fired Central Furnaces.

Note the current Department of Energy (DOE) federal minimum efficiency standard is 80% TE for 225,000 Btu/hr and higher input capacity furnaces per the Energy Conservation Standard for Commercial Warm Air Furnaces [4]. In the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Standard 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings [5] that minimum TE requirement is extended below 225,000 Btu/hr input capacity



to require all commercial warm air furnaces and combination warm air furnace/air conditioning units to meet the minimum 80% TE.

Deemed Lifetime of Efficient Equipment The expected measure life is assumed to be 15 years, which is consistent with the established TRM measure life for single-package and split system unitary HVAC packages. In colder climates these unitary packages typically contain a gas-fired, warm air furnace section, with an electric air conditioning section.

Deemed Measure Cost The actual incremental equipment and installation costs should be used, if available. If not, the incremental cost of $5.42 per 1000 Btu/hr of output capacity should be used for the condensing furnace equipment (as part of a unitary package) and its installation (including the combustion condensate drainage and disposal system). This incremental cost is from the DOE Technical Support Document for the Notice of Proposed Rulemaking (NOPR) for the Commercial Warm Air Furnace Standard6. Per the DOE documentation, it is based on their representative 250,000 Btu/hr input capacity furnace at a 92%TE.

Loadshape N/A

Coincidence Factor N/A



Algorithm

Calculation of Energy Savings

The following methodology provides formulas for estimating gas heating savings associated with condensing furnaces in unitary HVAC packages when applied as a constant volume DOAS, MUAS, or any RTU that is indirectly heating 100% OA. These types of HVAC systems typically run continuously during the HVAC operating schedule to provide building ventilation and maintain indoor air quality or to compensate for exhaust and maintain neutral or slightly positive building pressurization. The algorithm estimates the gas use reduction resulting from utilizing condensing heating of 90% or higher TE in place of the federal minimum TE of 80% (or other user defined baseline TE) for commercial warm air furnaces.

The methodology provides a representative group of operating schedules for the market sector applications highlighted earlier based on DOE commercial reference building models [7]. Heating loads during the operating schedule are determined based on hourly differences between a range of supply air (SA) heated to temperatures and the OA temperature using Typical Meteorological Year (TMY3) [8] weather data. These hourly heating loads are generated for all hours when the OA temperature is below the base temperature of 55°F for heating in C&I settings per the TRM. To accommodate the variability in heating base temperatures in C&I settings, these hourly heating loads are also generated for base temperatures of 45°F and 65°F for heating. The hourly heating loads are then summed for the entire year. The annual heating loads are calculated in this manner for the three TRM climate zones (and their associate TMY3 weather data cities): Climate Zone 1 (Duluth), Climate Zone 2 (St. Cloud), and Climate Zone 3 (Minneapolis-St. Paul). The annual heating load for each TMY3 weather data city is then normalized to its National Climatic Data Center (NCDC) [9] 30 year (1981-2010) weather average by multiplying by the heating degree day (HDD) ratio of the NCDC/TRM HDD55 over the TMY3 HDD55 (HDD at base temperature of 55°F), and likewise for the annual heating loads for HDD45 (HDD at base temperature of 45°F) and HDD65 (HDD at base temperature of 65°F), using the values in Table 31 and Table 32.

Table 31. NCDC HDD Values for All Climate Zones

Climate Zone - Weather Data City

NCDC 30 Year Average

HDD45 [9]


HDD55 [9]


HDD65 [9]

1 - Duluth 4327 6584 9444

2 - St. Cloud 3908 5955 8531

3 - Minneapolis-St. Paul 3291 5192 7581

The annual heating loads on a per unit airflow basis are then used in conjunction with the actual airflow of the 100% OA system and its condensing efficiency to calculate the gas heating savings versus the baseline (non-condensing) heating efficiency. This measure results in additional electric use by the



unitary HVAC package due to the additional pressure drop of the condensing heat exchanger of the warm air furnace section.

Table 32. TMY3 HDD Values for Climate Zone 2

Climate Zone - Weather Data City

TMY3 HDD45 [8]

TMY3 HDD55 [8]

TMY3 HDD65 [8]

1 - Duluth 4536 6821 9710

2 - St. Cloud 4431 6511 9106

3 - Minneapolis-St. Paul 3420 5413 7856

Electric Energy Savings

As noted previously, this measure results in additional SA fan electric use by the unitary HVAC system due to the additional pressure drop of the condensing heat exchanger of the warm air furnace section.

∆kWh = - (tFAN * cfm * ∆P) / (ηFAN/MOTOR * 8520)

Where:

tFAN = annual fan runtime (hr), refer to Tables 1 through 4

cfm = airflow (cfm), use actual or rated system airflow

∆P = incremental pressure drop (inch W.G.), assume 0.15 if actual value not known1

ηFAN/MOTOR = combined fan and motor efficiency, assume 0.60 if actual value not known1

8520 = conversion factor (fan horsepower – HP – calculation constant of 6356 for standard air conditions adjusted by 1 HP = 0.746 kW, or 6356/ 0.746 = 8520 for this kW calculation)

EXAMPLE:

For a “big box” retail store operating 24 hours a day and 7 days a week (8760 hours per year) with a 5000 cfm DOAS that has an incremental pressure drop of 0.15 inch W.G. and a combined fan and motor efficiency of 0.6 has annual kWh savings of:

∆kWh = - (tFAN * cfm * ∆P) / (ηFAN/MOTOR * 8520)

= - (8760 * 5000 * 0.15) / (0.6 * 8520)

= - 1285 kWh



Summer Coincident Peak Demand Savings

The additional SA fan electric use by the unitary HVAC system will typically result in a modest electric demand increase.

∆kW = ∆kWh / tFAN

EXAMPLE:

Continuing the previous example:

∆kW = ∆kWh / tFAN

= - 1285 / 8760

= - 0.15 kW

Natural Gas Savings

∆Therms = [QOA * cfm * (1/TENC - 1/TEC)]/ 100,000

Where:

QOA = annual outside air (OA) heating load per cfm of OA (Btu/cfm)

First, select the most representative operating schedule for the application from among the four (4) scenarios listed below and its set of three (3) applicable tables. Second, select the table in that set with the most representative HDD base temperature – the base temperature for OA below which heating is required. If that base temperature is not readily determined, select the TRM default base temperature of 55°F (HDD55) for heating in C&I settings. Third, select the climate zone within that table. Fourth, select an appropriate heated to supply air (SA) temperature within that table. Use the resulting QOA value, with linear interpolation allowed between SA temperatures.

The four (4) scenarios available are indicative of the following building applications and operating schedules:

1. 24 hour a day and 7 day a week (24/7) operation, with HVAC operating schedule of 8760 hours per year, typical of large retail stores with DOAS, hotel/multifamily buildings with corridor MUAS, and healthcare facilities with DOAS. Use Table 33 through Table 35.

2. 6:00 AM to 1:00 AM every day operation, with HVAC operating schedule of 7300 hours per year, typical of full service and quick service restaurants with kitchen MUAS. Use Table 36 through Table 38 .



3. 7:00 AM to 9:00 PM Monday-Friday, 7:00 AM to 10:00 PM Saturday, and 9:00 AM to 7:00 PM Sunday operations, with HVAC operating schedule of 5266 hours per year, typical of non-24/7 retail stores with DOAS. Use Table 39 through Table 41.

4. 7:00 AM to 9:00 PM Monday-Friday operation, with HVAC operating schedule of 3911 hours per year, typical of school buildings with DOAS. Use Table 42 through Table 44.

TENC = non-condensing thermal efficiency (TE), use federal minimum TE of 80% (0.80) or actual TE if known

TEC = condensing thermal efficiency (TE), use actual TE or if unknown assume 90% (0.90)

100,000 = conversion factor (1 therm = 100,000 Btu)

EXAMPLE:

Continuing the previous example for a 5000 cfm DOAS operating 8760 hours per year, in a climate zone 3 (Minneapolis-St. Paul) application with a heating base temperature of 55°F (HDD55) using a 90% TE condensing DOAS with a supply air temperature from the DOAS of 95°F:

∆Therms = [QOA * cfm * (1/TENC - 1/TEC)]/ 100,000

= 353,470 * 5,000 * (1/0.80 – 1/0.90)/100,000

= 2,455 therms



8760 Hour Annual Operation Scenario

Table 33. 8760 Hour Annual Operation Scenario for HDD45

Supply Air Fan Runtime = 8760 Hours Qoa (Annual Btu/cfm) At Supply Air Temperature Of

Climate Zone - Weather Data City 75°F 85°F 95°F 105°F

1 - Duluth 263,544 314,006 364,469 414,932

2 - St. Cloud 229,238 271,885 314,533 357,180

3 - Minneapolis-St. Paul 219,075 263,665 308,256 352,846




1 - Duluth 297,862 361,464 425,067 488,669

2 - St. Cloud 263,268 317,725 372,182 426,639





1 - Duluth 325,774 406,760 487,746 568,732

2 - St. Cloud 291,724 362,324 432,924 503,525








1 - Duluth 213,078 253,949 294,820 335,690

2 - St. Cloud 183,859 218,190 252,521 286,853





1 - Duluth 240,591 292,007 343,422 394,838

2 - St. Cloud 210,833 254,513 298,193 341,873





1 - Duluth 263,774 329,729 395,683 461,638

2 - St. Cloud 233,650 290,379 347,109 403,838








1 - Duluth 147,543 175,855 204,167 232,479

2 - St. Cloud 126,133 149,833 173,534 197,234





1 - Duluth 166,693 202,346 237,999 273,653

2 - St. Cloud 144,495 174,563 204,631 234,700





1 - Duluth 182,841 228,764 274,688 320,611

2 - St. Cloud 159,603 198,323 237,042 275,762








1 - Duluth 110,060 131,047 152,034 173,020

2 - St. Cloud 92,356 109,827 127,297 144,768





1 - Duluth 123,414 149,477 175,539 201,601

2 - St. Cloud 105,780 127,926 150,072 172,219





1 - Duluth 136,120 170,289 204,459 238,628

2 - St. Cloud 117,002 145,655 174,308 202,961




Water and Other Non-Energy Impact Descriptions and Calculations

N/A

Deemed O&M Cost Adjustment Calculation

The actual incremental annual maintenance costs should be used, if available. If not, the incremental cost of $0.05 per 1000 Btu/hr of output capacity should be used for maintaining the combustion condensate disposal system yearly. This incremental cost is from the DOE Technical Support Document for the Notice of Proposed Rulemaking (NOPR) for the Commercial Warm Air Furnace Standard [6]. Per the DOE documentation, it is based on their representative 250,000 Btu/hr input capacity furnace at a 92%TE.



Proposed Changes to Existing Measures

N/A



References

1. Nicor Gas energySmart Emerging Technology Program, High Efficiency Heating Rooftop Units (RTUs), 2013. http://www.nicorgasrebates.com/resources/Emerging-technology (Accessed December 11, 2015).

2. State of Minnesota Technical Reference Manual for Energy Conservation Improvement Programs, 2015. https://mn.gov/commerce/industries/energy/utilities/cip/technical-reference-manual/index.jsp (Accessed December 11, 2015 with Version 2.0, effective January 1, 2016 – December 31, 2017, provided via December 9 , 2015 email by CenterPoint Energy).

3. American National Standards Institute (ANSI), ANSI Z21.47 Standard for Central Gas-Fired Central Furnaces, 2012. http://www.techstreet.com/products/1837013#product (Accessed December 11, 2015).

4. Department of Energy (DOE), Commercial Warm Air Furnace Standard DOE 10 CFR, Part 431, Subpart D – Commercial Warm Air Furnaces, 2004. https://www.law.cornell.edu/cfr/text/10/part-431/subpart-D (Accessed December 11, 2015).

5. American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE), ASHRAE Standard 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings, 2013. https://www.ashrae.org/resources--publications/bookstore/standard-90-1 (Accessed December 11, 2015).

6. Department of Energy (DOE), Rulemaking for Commercial Warm Air Furnace Standard, Technical Support Document 2015. https://www1.eere.energy.gov/buildings/appliance_standards/rulemaking.aspx/ruleid/70 (Accessed December 11, 2015).

7. Department of Energy (DOE) National Renewable Energy Laboratory, Commercial Reference Building Models of the National Building Stock, 2011. http://www.nrel.gov/docs/fy11osti/46861.pdf (Accessed December 11, 2015).

8. Department of Energy (DOE) National Renewable Energy Laboratory, Users Manual for TMY3 Data Sets, 2008. http://www.nrel.gov/docs/fy08osti/43156.pdf (Accessed December 11, 2015).

9. National Climatic Data Center, 1981-2010 Climate Normals, 2015. https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data (Accessed December 11, 2015).

http://www.nicorgasrebates.com/resources/Emerging-technology

http://www.nicorgasrebates.com/resources/Emerging-technology

https://mn.gov/commerce/industries/energy/utilities/cip/technical-reference-manual/index.jsp

https://mn.gov/commerce/industries/energy/utilities/cip/technical-reference-manual/index.jsp

http://www.techstreet.com/products/1837013#product

http://www.techstreet.com/products/1837013#product

https://www.law.cornell.edu/cfr/text/10/part-431/subpart-D

https://www.law.cornell.edu/cfr/text/10/part-431/subpart-D

https://www.ashrae.org/resources--publications/bookstore/standard-90-1

https://www.ashrae.org/resources--publications/bookstore/standard-90-1



http://www.nrel.gov/docs/fy11osti/46861.pdf




https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data

field study of condensing heating in makeup-air and mixed ...field study of high efficiency heating...

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