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PG&E’s Emerging Technologies Program ET13PGE1031
Sweetwater Spectrum Community
Zero Net Energy Monitoring Performance
Evaluation Report
ET Project Number: ET13PGE1031
Project Managers: Peter Turnbull & Mananya Chansanchai Pacific Gas and Electric Company Prepared By: Davis Energy Group 123 C St Davis, CA, 95616
Issued: December 19, 2014
Copyright, 2014, Pacific Gas and Electric Company. All rights reserved.
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PG&E’s Emerging Technologies Program ET13PGE1031
ACKNOWLEDGEMENTS
Pacific Gas and Electric Company’s (PG&E) Emerging Technologies Program is responsible for this project. It was developed as part of Pacific Gas and Electric Company’s Emerging Technologies – Technology Assessments program under internal project number ET13PGE1031. Davis Energy Group conducted this technology evaluation for Pacific Gas and Electric Company with overall guidance and management from Anna LaRue at Resource Refocus LLC and Loralyn Perry at Energy Matters. For more information on this project, contact Peter Turnbull at [email protected].
LEGAL NOTICE
This report was prepared for Pacific Gas and Electric Company (PG&E) for use by its employees and agents. Neither Pacific Gas and Electric Company nor any of its employees and agents:
(1) makes any written or oral warranty, expressed or implied, including, but not limited to those concerning merchantability or fitness for a particular purpose;
(2) assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, process, method, or policy contained herein; or
(3) represents that its use would not infringe any privately owned rights, including, but not limited to, patents, trademarks, or copyrights.
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PG&E’s Emerging Technologies Program ET13PGE1031
ABBREVIATIONS AND ACRONYMS
AHRI Air-Conditioning, Heating, & Refrigeration Institute
CEC California Energy Commission
DC Direct current
DDC Direct digital control
DEG Davis Energy Group
DOE Department of Energy
EER Energy efficiency ratio
HERS Home Energy Rating System
HSPF Heating seasonal performance factor
HVAC Heating, ventilation, and air conditioning
kW Kilowatt
kWh Kilowatt-hour
LEED Leadership in Energy and Environmental Design
PV Photovoltaic
RTD Resistance temperature device
SEER Seasonal energy efficiency ratio
SHGC Solar heat gain coefficient
TDV Time dependent valuation
ZNE Zero net energy
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PG&E’s Emerging Technologies Program ET13PGE1031
FIGURES Figure 1: Monthly electricity consumption and PV generation –
Residential Building ........................................................ 16
Figure 2: Monthly electricity consumption and PV electricity
generation – Community Building .................................... 17
Figure 3: Distribution of annual electricity consumption by end use
– Residential Building ..................................................... 17
Figure 4: Distribution of annual electricity consumption by end use
– Community Building .................................................... 18
Figure 5: Daily total energy usage and PV generation – Residential
Building ........................................................................ 19
Figure 6: Daily total energy usage and PV generation –
Community Building ....................................................... 20
Figure 7: Annual electricity use by end use compared to Title-24
software estimates – Residential Building ......................... 21
Figure 8: Measured vs. simulated monthly electricy use by end use
– Residential Building ..................................................... 22
Figure 9: Annual electricity use by end use compared to Title-24
software estimates – Community Building ........................ 23
Figure 10: Measured vs. Simulated monthly electricity use by end
use – Community Building .............................................. 23
Figure 11: EER* vs. Outdoor Temperature – Residential Building .... 25
TABLES Table 1: Building Efficiency Specifications ................................. 6
Table 2: Sweetwater Project Monitoring System History ......... 10
Table 3: Measurement Points – Residence Building #3 ........... 11
Table 4: Measurement Points – Community Building ............... 12
Table 5: Sensor Specifications ................................................. 13
Table 6: Percentage of Space Conditioning Load Supplied by
Radiant Delivery ......................................................... 16
Table 7: Measured Heat Pump Efficiency – Residence
Building 3 ................................................................... 25
Table 8: Measured Heat Pump Efficiency – Community
Building ...................................................................... 26
Table 9: Annual Electric Loads vs. PV Generation .................... 26
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CONTENTS
ABBREVIATIONS AND ACRONYMS _____________________________________________ II
FIGURES _______________________________________________________________ III
TABLES ________________________________________________________________ III
CONTENTS _____________________________________________________________ IV
EXECUTIVE SUMMARY _____________________________________________________ 1
INTRODUCTION __________________________________________________________ 4
BACKGROUND __________________________________________________________ 4
EMERGING TECHNOLOGY __________________________________________________ 5
Thermal Envelope .............................................................. 5 Mechanical Systems ........................................................... 5 Lighting and Appliances ...................................................... 8 Photovoltaic System ........................................................... 9
ASSESSMENT OBJECTIVES __________________________________________________ 9
TECHNOLOGY EVALUATION ________________________________________________ 9
TECHNICAL APPROACH/TEST METHODOLOGY _________________________________ 10
Field Testing of Technology .................................................... 10
Test Plan .............................................................................. 11
Measurements and Monitoring System Commissioning .......... 11
Instrumentation Plan ............................................................. 13
Data logger Specifications ................................................. 13 Sensor Types and Specifications......................................... 13
RESULTS_______________________________________________________________ 15
Data Analysis ........................................................................ 15
Occupant Feedback .......................................................... 15 Overall Building Performance ............................................. 15
EVALUATIONS __________________________________________________________ 21
Comparison of Predicted to Measured Site Energy ..................... 21
Residential Building 3 ....................................................... 21 Community Building ......................................................... 22 Projected TDV Savings ...................................................... 24
Heat Pump Performance Analysis ............................................ 24
Approach to Zero Net Site Energy Use ..................................... 26
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PG&E’s Emerging Technologies Program ET13PGE1031
CONCLUSIONS & RECOMMENDATIONS _______________________________________ 27
APPENDIX _____________________________________________________________ 29
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PG&E’s Emerging Technologies Program ET13PGE1031
EXECUTIVE SUMMARY
PROJECT GOAL
The primary objective of this project was to evaluate how closely the Sweetwater
Spectrum buildings achieved the design goals of attaining zero net energy
performance over the course of 12 months, and to compare original modeling
estimates to actual monitored data for the occupied buildings.
PROJECT DESCRIPTION
Sweetwater Spectrum is a planned community of four single-story 3,250 ft²
residences and a 2,990 ft² community center located in Sonoma, CA (CA Climate
Zone 2). The facility is designed to serve adults with autism spectrum disorders.
Each residence has four occupants in individual suites, with a shared kitchen, dining
and living-space. The buildings were completed in December, 2012, with full-time
occupancy starting January, 2013. A large portion of the architectural design was
structured with sensitivity to the occupants in mind, as was the location and
acoustical requirements of the mechanical equipment.
The community center includes a large community room, exercise room, kitchen,
office, and art supply room. In addition to supplying community building loads, the
meter for this building serves external loads including spas, swimming pool, well
pumps, a greenhouse facility and exterior site lighting.
The buildings were initially intended to exceed Title 24 by at least 25% and to
achieve LEED™ Gold certification. The owners elected not to pursue LEED
certification at the conclusion of the project. As a cost-saving measure, the size of
the solar photovoltaic (PV) arrays described in the construction documents was
reduced by 50%.
High performance building features include 2x6 walls with R-21 wall insulation, R-48
ceiling insulation, high performance windows, and slab-on-grade construction with
in-floor radiant heating and cooling delivery and supplemental forced air delivery.
Each building is provided with two Daikin “Altherma” water-to-air heat pumps (13
SEER/ 11 HSPF) which supply hot and chilled water to the radiant and forced-air
distribution systems. Though it is likely that single heat pumps would have met the
heating and cooling loads, the redundancy serves as a hedge against equipment
failure. A demand-controlled ventilation system is also described in the construction
documents. The buildings are “all electric”, that is no natural gas was used for space
conditioning or water heating.
The Sweetwater Spectrum project was initiated as one of several zero net energy
demonstrations and provided the opportunity to evaluate the use of innovative HVAC
system solutions in a managed residential care facility. One of the problems in such
facilities is efficiently delivering comfort to multiple spaces, which this design has
overcome by providing zoned radiant floor heating and cooling and also forced air
distribution.
Two buildings were monitored between August 1, 2013 and July 31, 2014: one of the
four residential buildings (Building 3) and the community building. A total of 31 data
points were collected for the residential building and 23 for the community building.
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PROJECT FINDINGS/RESULTS
As originally designed, the residence and community buildings were intended to
meet the zero net energy goal of generating as much energy as required by the
buildings on an annual basis. Cost-cutting measures reduced the area of the PV array
by 50%. For the year that the project was monitored, the community building PV
system generated slightly more electricity than the building required, but only 35%
of the electricity consumed when the outbuilding loads were included. These loads
include spas, swimming pool, well pumps, greenhouse and exterior site lighting. The
PV system for Residence Building 3 generated 53% of the total energy consumed by
that building. Had the size of the array for the residential building not been reduced
it is likely it would have achieved the ZNE goal.
An EnergyPro evaluation using inputs updated to as-built conditions indicates
approximately 25% Time Dependent Valuation (TDV) savings relative to the 2008
standards. TDV estimates of energy savings using measured data were not
completed for this all-electric project.
Site energy use for the residential building was 70% higher than predicted by the as-
built EnergyPro evaluation. The higher than predicted energy use for the residential
buildings is mostly attributed to lighting and plug loads, which are much higher than
assumed by the initial model for typical residential occupancies. The type of
occupancy of the residential buildings is not well reflected by the assumptions used
in the Title 24 ACM Manual for residential occupancies. The four different buildings
each serve a different spectrum of autism and require different levels of care. The
occupants of Building 3 require significant care, and the building is staffed 24 hours
per day. High internal gains from lighting and plug loads in the residential building
contributed to its high cooling energy use. Issues related to the commissioning of
HVAC systems also may have been responsible for increased energy use.
The community building (excluding outbuilding loads) site energy use was 83% lower
than predicted. This building is used for daytime activities and houses Sweetwater
staff offices. The lower than predicted energy use for the community building may
also have been a consequence of Title 24 assumptions that are inconsistent with the
types of use in practice, as well as its good design.
PROJECT RECOMMENDATIONS
The high plug and lighting loads seen in the residential building should be
investigated and could be reduced by better use of controls and operation
management. Outbuilding loads should also be evaluated. Replacement of the
swimming pool pump with a variable speed pump should be strongly considered.
Control of the HVAC fans in both the residential and the community buildings was
seen to be inconsistent, varying between no use and continuous operation over the
monitoring period. Control improvements have been addressed during the post
occupancy commissioning period, which spanned from July – November 2014. Fans
should be controlled to provide the proper amounts of ventilation in accordance with
ASHRAE Standards 62.2 (residential) and 62.1 (community building). Demand
controlled ventilation using CO2 sensors is not an option under Standard 62.2, but
may be appropriate the residential buildings given the high occupancy density and
full time staffing. There are also opportunities to use the existing equipment (fans
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PG&E’s Emerging Technologies Program ET13PGE1031
and dampers) to reduce cooling energy use by providing nighttime cooling with
outside air and to provide humidity control.
Controlling humidity would allow more cooling to be delivered from the radiant
system, which would improve heat pump performance.
Reasons for the excessive fan operation were identified through the commissioning
process. Maintenance staff has made corrections to control functions for the fans and
replaced faulty sensors. Since then, temperature and humidity control has been
improved.
Performance of the Daikin Altherma heat pumps was reasonably consistent with
performance ratings, and in some cases better. Though only one of the two heat
pumps provided per building would likely meet the load requirements, having
redundant equipment may prove valuable in the future. The building owners could
experiment with shutting one of the units off, or alternating their use, to extend the
lifetime of both units. (Building managers indicated that they do alternate operation
of the pairs of heat pumps.)
This project provides a good template for the design of similar facilities that strive to
achieve zero net energy use. Development of cost studies and occupant feedback on
comfort would better inform future applications of this design strategy.
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PG&E’s Emerging Technologies Program ET13PGE1031
INTRODUCTION This report describes the results of a year-long evaluation of two occupied buildings
located in the Sweetwater Spectrum community, a home for adults with autism. This
project monitored one residential building that is representative of the four identical
residential buildings, as well as a community center building. The all-electric
buildings were designed with numerous energy efficiency measures to reduce
heating, cooling, and water heating loads, improve the efficiency of the HVAC
systems, and to offset usage by utilizing on-site renewables (PV and solar water
heating).
BACKGROUND Sweetwater Spectrum is a planned community of four single-story 3,250 ft²
residences and a 2,990 ft² community center located in Sonoma, CA (CA Climate
Zone 2). The facility is designed to serve adults with autism spectrum disorders.
Each residence has four occupants in individual suites, with a shared kitchen, dining
and living-space. The buildings were completed in December, 2012, with full-time
occupancy starting January, 2013. A large portion of the architectural design was
structured with sensitivity to the occupants in mind, as was the location and
acoustical requirements of the mechanical equipment.
The community center includes a large community room, exercise room, kitchen,
office, and art supply room. In addition to supplying community building loads, the
meter for this building serves external loads including spas, swimming pool, well
pumps, a greenhouse facility and exterior site lighting.
The Sweetwater Spectrum project was initiated as one of several zero net energy
demonstrations and provided the opportunity to evaluate the use of innovative HVAC
system solutions in a managed residential care facility. One of the problems in such
facilities is efficiently delivering comfort to the multiple residential zones, which this
design addressed by providing zoned hydronic radiant heating as well as forced air
distribution.
The buildings in this all-electric community were initially intended to exceed Title 24
by at least 25% and to achieve LEED™ Gold certification. The owners elected not to
pursue LEED certification at the conclusion of the project. As a cost-saving measure,
the size of the solar photovoltaic (PV) arrays described in the construction
documents was reduced by 50%.
Prior work supported by PG&E related to this project included three tasks, (1)
completion of a design review, (2) development of a commissioning plan, and (3)
preparation of a monitoring plan. The design review and monitoring plan were
completed1. As a result of construction delays and other issues, the commissioning
task was cancelled. The monitoring plan developed in the first phase of work was
implemented as this separate project beginning in May 2013.
1 Interim Report: Sweetwater Spectrum Community. Submitted to the Benningfield Group and PG&E, December 31, 2012.
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PG&E’s Emerging Technologies Program ET13PGE1031
EMERGING TECHNOLOGY The design applied several high performance building features, including 2x6 walls
with R-21 wall insulation, R-48 ceiling insulation, high performance windows, and
slab-on-grade construction with in-floor radiant heating and cooling delivery and
supplemental forced air delivery. Each building is provided with two Daikin
“Altherma” water-to-air heat pumps (13 SEER/ 11 HSPF) which supply hot and
chilled water to the radiant and forced-air distribution systems. Though it is likely
that single heat pumps would have met the heating and cooling loads, the
redundancy serves as a hedge against equipment failure. A demand-controlled
ventilation system is also described in the construction documents. The buildings are
“all electric”, that is no natural gas was used for space conditioning or water heating.
Details of the efficiency measures included in the completed buildings are listed in
Table 1, along with a comparison to a baseline building built to minimum 2008 Title-
24 standards. No information on incremental costs is available for this project.
Following is detailed information on individual measures that were selected.
THERMAL ENVELOPE
Walls and Roof: The exterior wall construction is 2x6 framing, 24 inches on center.
The stud cavities were filled with fiberglass batt insulation. The cavity between the
roof joist members was sprayed with foam and then insulated with fiberglass to
provide a tight seal. Ceiling finishes were installed directly to the underside of the
joists, and the use of spray foam avoided the need to vent the ceiling cavity as
would otherwise be required by code. Most of the roof is covered with standing seam
metal roofing (AEP Span Cool Weathered Copper), which has a solar reflectance of
0.34 and an emittance of 0.87
Slab: It is a mandatory measure to insulate the perimeter of slab foundations that
incorporate radiant heating to an R-value of 5. These buildings were insulated at the
perimeter to R-7.5, and also at the underside to R-10. As a result the distribution
efficiency of the radiant system should be greater than 90%, with few losses going to
the ground.
Windows: The Pella windows installed at the residence buildings have a U-value of
0.29 and a solar heat gain coefficient (SHGC) of 0.28.
Air Tightness: Given the slab foundation and use of spray foam insulation at the roof,
the structure probably exceeds the current Title 24 assumption of 5 ACH50, however
no testing was performed. Since ducts were installed within the joist bays and below
the foam sprayed roof deck, most duct leakage is likely to the inside of the building
enclosure. However, no duct test data are available; duct testing was not a
mandatory measure under the 2008 standards.
MECHANICAL SYSTEMS
Heating and Cooling:
Because radiant floor distribution systems can utilize relatively cool water (~110°F)
for heating and relatively warm water (~60°F) for cooling (compared to forced air
distribution), the heat pumps do not need to work as hard as conventional heat
pumps due to the reduced “thermal lift” between the evaporator and the condenser.
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PG&E’s Emerging Technologies Program ET13PGE1031
Unfortunately, the primary-secondary loop configuration used in the Sweetwater
design does not take full advantage of this characteristic. Primary-secondary piping
is common in high temperature gas heat systems where boiler efficiency is not highly
dependent on water temperature, but can be detrimental to heat pump systems for
which efficiency is reduced by high condensing temperatures. In this case, the
variable speed capability of the heat pumps can adjust to varying loads and they are
capable of supplying hot and chilled water directly to the slabs, eliminating the need
for additional primary-secondary loop pump and improving efficiency.
Table 1: Building Efficiency Specifications
BUILDING COMPONENT
EFFICIENCY FEATURE BASE CASE
ZNE DESIGN - "AS-BUILT"
NOTES
ENVELOPE
Roofing Asphalt Shingle, standard
Standing seam metal (Reflectance 0.36
emmitance 0.87) & built-up
Prem comp shingle
Roof (attic) Vented attic, R-30 blown
No attic, joist bays insulated to R-47.8
Combination of
spray foam and fiberglass batt
Radiant Barrier Yes No
Wall (Exterior) 2x4 16"o.c., R-13 batt
2x6 24"o.c., cavities
filled with R-21 fiberglass batt insulation
Quality Insulation
Installation Verified (HERS)
No No
Foundation Type Slab-on-grade, no insulation
Slab-on-grade, R-7.5
foam at edge, R-10 foam underneath
5” slab with ½”
tubing installed 6” on-center
Exposed Thermal Mass N/A Slab floor Marmoleum
and carpet tile floor coverings
Envelope Leakage Verified (ACH50) (HERS)
No (5.0 assumed) Not tested
Windows (U-factor / SHGC)
U-value = 0.40
SHGC = 0.40
U-value = 0.29 SHGC = 0.28
HERS Measures Tight ducts
Radiant heating and cooling distribution with some forced air
deliver through ducts in semi-conditioned space
Duct leakage not tested but ducts are
mostly within the thermal envelope
HVAC SYSTEM
System Type Single speed heat pump
Two 4.5 ton air-to-water variable speed heat pumps per building
Daikin Altherma EBLQ054BA6VJU
Cooling 13 SEER / 10 EER 13 SEER 13 is nominal
value for Title
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BUILDING COMPONENT
EFFICIENCY FEATURE BASE CASE
ZNE DESIGN - "AS-BUILT"
NOTES
24 compliance
Furnace (AFUE) / Heat Pump (HSPF)
7.7 14.0 HSPF (from CF-1R)
11 is nominal
value for Title 24 compliance
Duct Location Attic
In joist bays and
below foam insulation applied to underside of roof deck
DUCT LEAKAGE - TESTED <
6% LEAKAGE (HERS) YES Not tested
Duct Insulation (R-value) R-6 R-4.5 (in conditioned space)
From specs
Verified Refrigerant Charge (HERS)
No No Factory charged
Verified Adequate Airflow (HERS)
No No
Verified Fan Watt/cfm < 0.58W/cfm (HERS)
No No
Nighttime Ventilation Cooling
None None Possible but
not implemented
Mechanical Ventilation Exhaust fan, continuous
Demand-controlled
using air handlers & dampers
WATER HEATING
Water Heating System Standard 50gal Gas, 0.62 EF
Solar thermal with
electric resistance backup, 0.9 EF
Solar DHW: Solar Fraction
N/A 68% (from Title 24 CF-1R)
Solar used on
residence buildings only
Distribution Type Kitchen Pipes Insulated
Recirculation, all hot water pipes insulated
Pump runs continuously
LIGHTING
LED% / CFL% / Incandescent
0% / 35% / 65% Linear fluorescent + LED
Controls None Vacancy sensors
OTHER ENERGY
EFFICIENCY FEATURES
EnergyStar Appliances None
Energy Star
dishwasher, refrigerator, and clothes washer
Cooking Gas Induction Electric
Clothes Dryer Electric Electric
Fireplace, yes/no & fuel No No
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BUILDING COMPONENT
EFFICIENCY FEATURE BASE CASE
ZNE DESIGN - "AS-BUILT"
NOTES
type
Home Energy Management System
N/A Siemens
% Better than 2008 Base Case
N/A 66.4%
ON-SITE GENERATION
Solar Photovoltaic System
None
Residences: 8.6 kW DC
Community Bldg: 14.4 kW DC
PV size reduced
by 50% from original specifications
The variable speed capability of the Altherma heat pump and coupling to massive
radiant heating/cooling panels makes it possible to eliminate a storage tank to
prevent short-cycling, which simplifies the system and saves cost. Also, efficiency
increases as the speed is reduced. It is difficult to develop standardized performance
ratings for variable speed air-to-water heat pumps with hydronic distribution because
the performance varies with speed, and the water temperatures supplied can vary
significantly depending on the application and load conditions. In 2012 Daikin came
to agreement with the California Energy Commission (CEC) on performance values
appropriate for the Altherma, settling on a SEER of 13 and an HSPF of 112. The Title
24 compliance calculations submitted for the project list an SEER of 13 and an HSPF
of 14.
Fresh Air Ventilation: Each building is provided with a central ventilation system that
consists of a constant volume fan coil that is ducted to all of the major rooms. The
residential fan coil is specified as 1825 CFM and the community building unit is
specified as 3500 CFM. Each coil is connected to the hydronic system so that
ventilation air can be tempered to avoid comfort problems, and each is “demand
controlled” by a CO2 sensor. Dampers were provided to allow mixing of recirculated
and outside air.
Water Heating: Closed loop solar water heaters serve each of the residential
buildings. Primary water heating for each building is provided by electric resistance
storage type water heaters. Hot water recirculation pumps are controlled to operate
continuously.
LIGHTING AND APPLIANCES
The 2008 California Title 24 standards for residential lighting require a certain
percentage of high efficacy fluorescent fixtures in kitchens, but allow either
fluorescent fixtures or incandescent fixtures with vacancy sensors (or dimmers in
some rooms) in other locations. The specifications for the Sweetwater buildings call
for a combination of T8 linear fluorescent fixtures for general illumination and LED
fixtures for spotlights and exterior lighting. Some of the lights are controlled on
2 Final Evaluation Report - Proposed Compliance Option for: Altherma Air-to-Water Source Heat Pump for the Residential Energy Efficiency Standards. California Energy Commission staff report # CEC‐400‐2011‐010‐SF, March 2012.
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automatic dimmers. Except for the swimming pool heater, no natural gas is used on
site.
PHOTOVOLTAIC SYSTEM
The shed-type standing seam metal roofs are designed to face nearly due south,
presenting a near ideal orientation and surface for mounting the PV modules. Initial
plans show the residence buildings equipped with 72 240 W modules each, and 120
240 W modules mounted on the community building. The sizes of the PV arrays
ultimately mounted on the buildings were reduced by 50%, resulting in an 8.6 kW
array installed on each of the resident buildings and a 14.4 kW array installed on the
community building.
ASSESSMENT OBJECTIVES The main objective of this project is to evaluate how closely the Sweetwater project
achieved the zero net energy design goal, and to compare modeled energy use to
the measured energy use. While the project has aggressive energy efficiency goals,
the 50% reduction from the original PV surface area significantly reduced the
likelihood of achieving zero net energy. However, the project also offers the unique
opportunity to assess the performance of air-to-water heat pumps with zoned radiant
heat distribution applied to communal living establishments such as retirement
homes and limited care facilities. The combination of high performance building
enclosure, high efficiency HVAC system (as used in these buildings), and
appropriately sized PV systems could represent a best practices pathway to zero net
energy in these building types.
TECHNOLOGY EVALUATION This project provided monitoring and evaluation to determine whole building
performance for the residential building and the community building. Specific end
uses including HVAC systems (heat pump units, circulating pumps, and fan coils),
water heating energy, and PV energy delivered to the buildings and the grid were
also monitored. Miscellaneous end uses such as lighting, appliances, and plug loads
were measured by subtracting HVAC end uses from whole house power, which was
measured at the main panel. When it was discovered that the panel for the
community building included extraneous power for the spa and swimming pool
equipment and greenhouse, monitoring of these circuits was added.
In order to qualify the results, outdoor temperature and indoor temperatures at
multiple locations were also measured. Monitoring of water flows and temperatures
also enabled the calculation of energy delivered by the heat pumps, as well as heat
pump efficiency. A detailed list of monitoring points is included in the Test Plan
section which follows.
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PG&E’s Emerging Technologies Program ET13PGE1031
California uses a Time Dependent Valuation (TDV) based definition of zero net
energy. The TDV approach assigns higher values to energy used during high
demand periods. To evaluate energy use using this definition, a prior project report3
used a somewhat complex process to estimate the time dependent value of
measured energy consumption and to compare it to the TDV energy predicted by the
compliance model. Compliance models calculate TDV energy by applying a
conversion factor to site electric (and gas) energy use that considers the societal
value at each hour of the day. This prior method related TDV values for the climate
zone to particular temperature conditions in the weather file, created bins of site
energy use corresponding to those weather conditions, and applied TDV multipliers
to the binned data. Results were then compared to the TDV quantities reported by
the energy compliance model (EnergyPro). As the Sweetwater project did not
approach the ZNE goal, due to the reduction in size of the PV systems and the large
outbuilding loads, this exercise was deemed to be unnecessary. Instead, measured
site energy use was directly compared to predicted site energy use obtained from the
Title 24 compliance software (EnergyPro).
TECHNICAL APPROACH/TEST METHODOLOGY
FIELD TESTING OF TECHNOLOGY Long-term monitoring followed by data analysis was employed to identify building
and system performance over the 12 month evaluation period. Power monitors were
used to measure true RMS power for the end uses listed in Tables 2 and 3. HVAC
energy delivery was measured using water side measurements (from flow and
temperature differences), which were then used to calculate seasonal efficiency of
the heat pumps. Water heating system performance was also measured using flows
and temperature differences for the residential building only, including contributions
from the solar water heater. Electricity use by the community building electric water
heater is included in building miscellaneous loads. Gas energy use by the swimming
pool heater was not monitored.
Monitoring data was carefully reviewed and analyzed in an effort to respond to the
research goals of this project. Table 2 chronicles the problems encountered with the
monitoring equipment, the site visits, and any changes that may have affected the
monitoring data.
Table 2: Sweetwater Project Monitoring System History
DATE DESCRIPTION
6/28/13 The data logger for the community building was non-responsive.
7/2/13 – 7/12/13 Inspected the community center logger and
found that channels were blown, possibly a result of an accidental short caused by the project electrician. Replaced the logger with a
3 ”Cottle House Zero Net Energy Home Monitoring” (2014) - http://www.etcc-ca.com/reports/cottle-house-zero-net-energy-home-monitoring
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PG&E’s Emerging Technologies Program ET13PGE1031
DATE DESCRIPTION
borrowed unit and resumed monitoring.
7/15/13 Discovered that the Dent PowerScout 18 power
monitors were reporting instantaneous, not averaged power. Also discovered that the Dent was not correctly communicating via the Modbus link to the data logger, resulting in out of sync time stamps. Remedial actions were taken.
9/18/13 Replaced the borrowed logger with the repaired original logger.
Due to ongoing commissioning efforts by the controls contractor which produced
irregular system operation as verified by indoor temperature readings, as well as the
loss of data in July, the project team pushed back the official start of monitoring
reporting. Accordingly, the effective monitoring period was shifted to cover August 1,
2013 to August 1, 2014.
TEST PLAN Each of the two buildings, Residence Building #3 and the community center building,
were equipped with data loggers and modems for continuously collecting, storing,
and transferring data via cellular communications. Sensors were scanned every 15
seconds, and data was summed or averaged (as appropriate) and stored in data
logger memory every 15 minutes.
MEASUREMENTS AND MONITORING SYSTEM COMMISSIONING
Short term measurements were made on site to verify readings from the various
sensors, including temperature sensors and power monitors. More detailed
information on commissioning procedures is provided in the Interim Report. Table 3
and 4 list the measurement points that were monitored on a continuous basis for the
residence and community buildings, respectively.
Table 3: Measurement Points – Residence Building #3
Name Description Location Sensor Type
TAI1 Temp, air, indoor, Zone 1 Near Z1 T-stat RTD, 4-20ma
RHI1 RH, air, indoor, Zone 1 "" RH, 4-20ma
TAI3 Temp, air, indoor, Zone 3 Near Z3 T-stat RTD, 4-20ma
RHI3 RH, air, indoor, Zone 3 "" RH, 4-20ma
TAI2 Temp, air, indoor, Zone 2 Near Z2 T-stat RTD, 4-20ma
TAI4 Temp, air, indoor, Zone 4 Near Z4 T-stat RTD, 4-20ma
TAI5 Temp, air, indoor, Zone 5 Near Z5 T-stat RTD, 4-20ma
TAI6 Temp, air, indoor, Zone 6 Near Z6 T-stat RTD, 4-20ma
TAI7 Temp, air, indoor, Zone 7 Near Z7 T-stat RTD, 4-20ma
TWFS Temp, Water, Entering Fan Coil Mechanical Room Immersion TT
TWFR Temp, Water, Leaving Fan Coil Mechanical Room Immersion TT
TWZS Temp, Water, Entering Zones Mechanical Room Immersion TT
TWZR Temp, Water, Leaving Zones Mechanical Room Immersion TT
TWH Temp, Water, DHW Supply Mechanical Room Immersion TT
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PG&E’s Emerging Technologies Program ET13PGE1031
TWCS Temp, Water, Cold Water Supply Mechanical Room Immersion TT
TWSE Temp, Water, Entering Solar Mechanical Room Immersion TT
TWSL Temp, Water, Leaving Solar Mechanical Room Immersion TT
FWZ Flow, Floor Zones Mechanical Room Flow meter
FFC Flow, Fan Coil Mechanical Room Flow meter
FWS Flow, Solar System Mechanical Room Flow meter
FWD Flow, Domestic Hot Water Mechanical Room Flow meter
EHSE Energy, Total House Main Service Panel Power Meter
EPV Energy, PV Main Service Panel Power Meter
EGEN Energy, Generated to Grid Main Service Panel Power Meter
SRP Status, Recirc Pump Mechanical Room Relay
EHP1 Energy, Heat Pump Mechanical Room Power Meter
EFC Energy, Fan Mechanical Room Power Meter
EP7 Energy, Pump Mechanical Room Power Meter
EP1 Energy, Pump (Zone) Mechanical Room Power Meter
EWH Energy Water Heater Mechanical Room Power Meter
ESP Energy Solar Loop Pump Mechanical Room Power Meter
Table 4: Measurement Points – Community Building
Name Description Location Sensor Type
TAO Temp, air, outdoor NorthFace RTD, 4-20ma
RHO RH, air, outdoor "" RH, 4-20ma
TAI1 Temp, air, indoor, Zone 1 Near Z1 T-stat RTD, 4-20ma
RHI1 RH, air, indoor, Zone 1 "" RH, 4-20ma
TAI2 Temp, air, indoor, Zone 2 Near Z2 T-stat RTD, 4-20ma
TAI4 Temp, air, indoor, Zone 4 Near Z4 T-stat RTD, 4-20ma
TAI5 Temp, air, indoor, Zone 5 Near Z5 T-stat RTD, 4-20ma
TAI6 Temp, air, indoor, Zone 6 Near Z6 T-stat RTD, 4-20ma
TAI7 Temp, air, indoor, Zone 7 Near Z7 T-stat RTD, 4-20ma
TWFS Temp, Water, Entering Fan Coil Mechanical Room Immersion TT
TWFR Temp, Water, Leaving Fan Coil Mechanical Room Immersion TT
TWZS Temp, Water, Entering Zones Mechanical Room Immersion TT
TWZR Temp, Water, Leaving Zones Mechanical Room Immersion TT
FWZ Flow, Floor Zones Mechanical Room Flow meter
FFC Flow, Fan Coil Mechanical Room Flow meter
EHSE Energy, Total House Main Service Panel Power Meter
EPV Energy, PV Main Service Panel Power Meter
EGEN Energy, Generated to Grid Main Service Panel Power Meter
EHP4 Energy, Heat Pump Mechanical Room Power Meter
EFC Energy, Fan Mechanical Room Power Meter
EP9 Energy, Pump Mechanical Room Power Meter
EP3 Energy, Pump (Zone) Mechanical Room Power Meter
EOB Energy, Outbuildings Main Service Panel Power Meter
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INSTRUMENTATION PLAN
DATA LOGGER SPECIFICATIONS
Data Electronics Model DT-800 data loggers were used to collect and store
monitoring data. Analog inputs were single-ended type (all referenced to ground).
Digital inputs were used for power monitors and status signals; high speed counter
inputs were used with water flow meters. The data loggers were provided with an
RS232 communications interface and battery backup. They also included integral
cold junction circuitry for direct measurement of Type T thermocouples. The table
below provides detailed specifications for the data logger.
Manufacturer: dataTaker, Inc.
Model: DT-85
Analog Inputs: Up to 32 single-ended
Digital Inputs: 8 bidirectional + 4 high speed counters (100 kHz)
Analog Accuracy: 0.1%
Memory: 128 MB flash, approx. 10,000,000 data points
Communications: Ethernet, USB, RS232/485, Modbus
SENSOR TYPES AND SPECIFICATIONS
Standard specifications for the sensor types used are listed in Table 5: 5. Sensor
selection was based on functionality, accuracy, cost, reliability, and durability. Signal
ranges for temperature sensors correspond approximately to listed spans.
Table 5: Sensor Specifications
TYPE APPLICATION MFG/MODEL SIGNAL SPAN ACCURACY
RTD Outdoor temp and RH
RM Young 41372VF 0-10V -50 – 150°F ±1F
0 – 100% +1%RH
RTD Indoor temperature / RH
General Eastern
MRHT 3-2-1 4-20 mA
50 - 90ºF ±1.5F
0 – 100% +2%RH
RTD Duct temperature / RH – HRV
Vaisala HMD60Y 4-20 mA -4 - 176ºF ±1.5F
0 – 100% ±2%RH
RTD Duct temperature / RH – Air Handler
General Eastern
MRHT 3-2-1 4-20 mA
32 - 132ºF ±1.5F
0 – 100% ±2%RH
RTD Indoor temperature – Attic, Crawlspace
LM34 10 mV /°F
50 - 90ºF ±1F
Type T Thermocouple
Surface / Air temperatures
Omega -99 to 500ºF 0.4%
24VAC Relay Fresh air Damper
Status, zone damper status
Omron Dry contact
n/a n/a
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PG&E’s Emerging Technologies Program ET13PGE1031
Power monitor
All circuits except those listed below
Dent Instruments PowerScout 18
Modbus Varies by circuit
±0.5%
Power monitor
PV power to grid and outbuildings (pool, etc.)
Watt Node WNB-3-D-240-PV
Pulse CTA/40 ±0.5%
Pressure Transducer
Air Pressure SETRA 4-20mA 0-0.5inWC ±1%FS
Gas Pulse Meter
Water Heater IMAC Pulse 10 pulses/cuft
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PG&E’s Emerging Technologies Program ET13PGE1031
RESULTS The following data summaries are presented for the 12 month period between
August 1, 2013 and July 31, 2014.
DATA ANALYSIS
OCCUPANT FEEDBACK
No direct feedback was provided by occupants. Building managers initially expressed
concerns about indoor temperatures that were outside comfort expectations in some
zones. This was corrected over a period of time by Siemens, the contactor for the
direct digital controls (DDC) system.
OVERALL BUILDING PERFORMANCE
MONTHLY AND ANNUAL ENERGY USE
The energy performance of the two Sweetwater buildings was evaluated to
determine site energy use and energy supplied to the grid. In addition, measured
site energy use for HVAC and water heating was compared to site energy use
predicted by EnergyPro. Modifications were made to the EnergyPro input files that
were used for compliance (obtained from the mechanical engineer) to update wall
and roof U-values and window U-value and SHGC. An HSPF of 14 was used in the
compliance assumptions; in the updated as-built model, this was corrected to the
HSPF 11 value that the Energy Commission stipulated should be used for Altherma
heat pumps.
Figure 1 and Figure 2 display monthly electricity consumption for the Residence
Building 3 and the Community Building, respectively, for each major end use. PV
production is shown as negative values below the x-axis. In Figures 2 and 3 monthly
net electricity is displayed by the solid line in the graph. Figures 3 and 4 show the
breakdown of annual electricity end use for the two buildings.
For the residential building, 53% of total site electricity usage was offset by the 8.6
kW DC rated PV system over the 12 month monitoring period. For the community
building the 14.4 kW DC PV system offset 35% of the total annual electricity use.
However, if outbuilding loads are excluded, the PV system generated about 200 kWh
more than the 19,723 kWh consumed by the community building.
Observations of monitoring data suggest that adjustments were being made to the
HVAC systems throughout the year. In particular, there was inconsistency in the
operation of fans and in temperature control settings that were likely occurring as
control systems were being commissioned and adjusted.
Cooling system operation was observed in both buildings from August through
October of 2013 and from April through July of 2014, with some overlapping of
heating and cooling, particularly in shoulder months. Heating and cooling were
supplied by both the radiant floors and the fan coils. The percentages that radiant
delivery contributed to heating and cooling demand are listed in Table 6.
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PG&E’s Emerging Technologies Program ET13PGE1031
Table 6: Percentage of Space Conditioning Load Supplied by Radiant
Delivery
Building Heating Cooling
Residential 85% 33%
Community 67% 58%
FIGURE 1: MONTHLY ELECTRICITY CONSUMPTION AND PV GENERATION – RESIDENTIAL BUILDING
-2,000
-1,500
-1,000
-500
0
500
1,000
1,500
2,000
2,500
Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14 Jul-14
Mo
nth
ly E
lect
rici
ty C
on
sum
pti
on
(kW
h)
PV Space Cooling Space Heating Plug Loads+Misc Water Heating Monthly Net
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FIGURE 2: MONTHLY ELECTRICITY CONSUMPTION AND PV ELECTRICITY GENERATION – COMMUNITY BUILDING
FIGURE 3: DISTRIBUTION OF ANNUAL ELECTRICITY CONSUMPTION BY END USE – RESIDENTIAL BUILDING
-3,000
-2,000
-1,000
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14 Jul-14Mo
nth
ly E
lect
rici
ty C
on
sum
pti
on
(kW
h)
PV Space Cooling Space Heating Plug Loads+Misc Outbuildings Monthly Net
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PG&E’s Emerging Technologies Program ET13PGE1031
FIGURE 4: DISTRIBUTION OF ANNUAL ELECTRICITY CONSUMPTION BY END USE – COMMUNITY BUILDING
DAILY ENERGY USE
Error! Reference source not found.5 and 6 display daily electricity consumption
or the residential and community buildings, respectively. Average daily electricity
consumption for the residential building was 64.2 kWh and for the community
building was 154.8 kWh.
These figures show very little seasonal variation, which reflects the fact that HVAC
energy use only represents 35% and 19% of total energy use for the residential and
community buildings, respectively. Also, fan energy for both fresh air ventilation and
heating/cooling constituted 20% of HVAC energy use in the residential building and
9% of HVAC energy use in the community building.
MECHANICAL SYSTEM OBSERVATIONS
Each building is served by two heat pumps. The pairs of heat pumps were monitored
using a single current transducer, so it was not possible to determine from the data
whether one or two were operating at any given time, but the control strategy
outlined in the drawings suggests they are staged. Monthly heat pump energy
consumption was apportioned by multiplying heat pump electrical use by the fraction
of measured heating or cooling delivered for each month. Monitored water
temperatures were used to determine whether the heat pumps were operating in
heating or cooling mode at any given time.
The fan coil in the residential building was cycled coincident with the heat pump part
of the year and was out of commission most of February 2014. The community
building fan coil did not operate at all August through November 2013 or in March of
2014, but ran continuously through part of the remainder of the year.
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PG&E’s Emerging Technologies Program ET13PGE1031
Construction documentation indicates that the fans would be “demand controlled”
using a CO2 sensor. This type of ventilation control is typically used in commercial
buildings, but is inconsistent with the residential ventilation standard, ASHRAE 62.2,
which prescribes continuous or intermittent ventilation at rates that are a function of
the building conditioned floor area and number of bedrooms. It was not clear from
the available documentation what specific control strategy would be adopted for the
fans and for control of the dampers which mix outdoor and return air, and the fan
control strategy appeared to vary through the year with some continuous operation
and some cycling with heat pump operation. For this analysis fan energy was
apportioned to heating or cooling, depending on the season.
Water heating was only monitored as a separate end use for the residential building.
The residential water heating system consists of two flat-plate collectors
(approximately 48 ft2 total) connected to an 80 gallon storage tank with an included
heating element for supplemental heat. A closed glycol loop transfers heat from the
collectors to the storage tank via a heat exchanger integrated with the tank. A pump
that recirculates hot water to the fixtures was apparently operated continuously.
Water heater electrical use in Building 3 averaged 9 kWh per day. Hot water use
ranged from a low of 41 gallons per day in July 2014 to a high of 140 gallons per day
in August 2013, and averaged 92 gallons per day.
If standby loss from the solar storage tank and recirculation piping losses are
considered as part of the hot water load, the calculated annual contribution of the
solar water heater to total water heating energy use was 25%. Including energy
used by the solar collector pump, the effective energy factor (hot water delivered
divided by electrical energy input in Btu’s) averaged 1.33 over the year, and ranged
from 0.86 to 2.55. Given the hot water load and collector area, this result is not
surprising.
FIGURE 5: DAILY TOTAL ENERGY USAGE AND PV GENERATION – RESIDENTIAL BUILDING
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FIGURE 6: DAILY TOTAL ENERGY USAGE AND PV GENERATION – COMMUNITY BUILDING
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EVALUATIONS
COMPARISON OF PREDICTED TO MEASURED SITE ENERGY
RESIDENTIAL BUILDING 3
EnergyPro files were obtained from the project mechanical engineer for Residence Building 3
and the community building. Upon review it was found that inputs for wall and roof R-
values, and window U-value and solar heat gain coefficients were inconsistent with as-built
conditions. In general, these adjustments would improve the modeled building performance.
However, the compliance documents listed an HSPF value of 14 for the Altherma heat
pump, whereas the CEC ruling established an HSPF of 114. Also, the input files included a
68% solar fraction, which given the size of the collectors relative to the hot water load
appeared excessive. Instead, a value of 25%, which is consistent with what was measured,
was substituted in the EnergyPro model. The modified EnergyPro input files were used to
generate monthly estimates of site energy use for space heating, cooling, water heating,
and miscellaneous use (lighting, appliances, and plug loads). It should be recognized that
model results were not normalized to actual year weather.
Figure 7 illustrates the significant difference between energy use predicted by EnergyPro
(simulated) vs. monitored energy use for the residential building. Cooling energy use was
160% higher, heating 57% higher, and lighting and miscellaneous uses 114% higher than
predicted. Only water heating was close, at 13% lower than predicted. Overall energy use
was 70% higher than predicted.
FIGURE 7: ANNUAL ELECTRICITY USE BY END USE COMPARED TO TITLE-24 SOFTWARE ESTIMATES – RESIDENTIAL
BUILDING
4 Final Evaluation Report – Proposed Compliance Option for Altherma Air-to-Water Source Heat Pump for the Residential Energy Efficiency Standards. CEC‐400‐2011‐010‐SF. March 2012.
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PG&E’s Emerging Technologies Program ET13PGE1031
There are several circumstances that explain the high usage relative to the Title 24
residential compliance model results. The compliance model calculates internal heat gain
from people, lights, and appliances by assuming 20,000 Btu/day for each dwelling unit plus
15 Btu/day for each square foot of conditioned floor area. Building 3 houses residents who
require around-the-clock staff engagement. Therefore, each building is occupied by 32
people in each 24-hours period, far more than a typical residence of similar size. Lastly,
HVAC systems were not fully commissioned during the majority of time the building was
monitored.
Figure 8 compares measured and simulated end uses for the residential building on a
monthly basis. Cooling and heating energy use varies seasonally as expected in both cases,
but the magnitudes are significantly different. Overall, lighting, plugs, and other
miscellaneous uses are responsible for the greatest magnitude in the discrepancy between
measured and simulated use. As noted, the type of occupancy, operating schedule, and
number of occupants helps account for this difference.
FIGURE 8: MEASURED VS. SIMULATED MONTHLY ELECTRICITY USE BY END USE – RESIDENTIAL BUILDING
COMMUNITY BUILDING
The community building site energy use was also considerably different than what was
estimated by EnergyPro, but with significantly less energy used than was predicted by the
model. Figure 10 compares monitored and simulated energy use for all end uses except the
outbuildings. The outbuildings are included on the meter for the building, but since they are
not considered in the Title 24 calculations this energy use was not shown in the Figure 10
comparison. Excluding the outbuildings, the community building alone used 19,723 kWh
over the one year period, 83% less than predicted by the model. The outbuildings, which
include the swimming pool, spa, welcome center, and greenhouse, used 36,780 kWh.
The model predicted high fan energy use (13,402 kWh) for the commercial building which,
as for the residential building was allocated to heating and cooling in proportion to the
respective loads. Monitored fan energy use was only 707 kWh. If modeled fan energy were
substituted for the measured value, the discrepancy between measured and simulated
energy use would fall from 83% to just 18%. Since much of the heating and cooling is
Measured Simulated
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PG&E’s Emerging Technologies Program ET13PGE1031
Measured Simulated
delivered from the radiant floor, the Title 24 model would tend to over predict fan energy
use in this case.
FIGURE 9: ANNUAL ELECTRICITY USE BY END USE COMPARED TO TITLE-24 SOFTWARE ESTIMATES – COMMUNITY
BUILDING
Figure 10 compares the distribution of energy use for measured vs. simulated data by
month. For the reason described above, outbuilding energy use was not included in these
graphs. Again, the high fan energy assumption in the Title 24 model is largely responsible
for the relatively high heating and cooling energy in the simulated data.
FIGURE 10: MEASURED VS. SIMULATED MONTHLY ELECTRICITY USE BY END USE – COMMUNITY BUILDING
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PG&E’s Emerging Technologies Program ET13PGE1031
PROJECTED TDV SAVINGS
Using the corrected EnergyPro Version 5 input files, TDV energy savings of 26.2% and
23.5% were calculated for the residence and community buildings, respectively. Given these
margins, the buildings would likely comply under the 2013 standards, though this analysis
was not completed.
HEAT PUMP PERFORMANCE ANALYSIS The key emerging technologies utilized in the Sweetwater project are the air source heat
pumps coupled to radiant distribution systems that provide the majority of heating and a
significant amount of cooling (as seen in Table 6). There are some challenges to identifying
the performance of the heat pumps from the data collected and comparing measured data
to manufacturer’s rated conditions as well as to efficiencies of other equipment types.
In the absence of an AHRI test procedure for air source
heat pumps, the CEC issued an evaluation report (cited
above in Footnote 4) that established performance values
for use in completing compliance calculations for the
Altherma, prescribing a SEER of 13 and HSPF of 11.
European Standard EN14511 was used to determine a COP
under similar rating conditions as used for air-to-air heat
pumps, based on a leaving water temperature of 95°F and
an outdoor temperature of 44°F. As described by
Francisco5, the AHRI test method for HSPF applies three
different temperature conditions (17°F, 35°F, and 45°F),
and takes into account defrost cycle losses and electric
resistance heating needed to maintain comfort during
defrost cycles and under outdoor temperature conditions
that require supplemental heating. The CEC used the
range of COP’s provided by Daikin to choose a COP of 4.2, which when converted to HSPF
using the method from the standards6, yields the HSPF of 11. Because Standard EN14511
does not include an SEER test method, the current federal minimum SEER value of 13 was
somewhat arbitrarily assigned.
In theory, air-to-water heat pumps with radiant distribution should perform well because of
the relatively low temperatures required for heating and high temperatures required for
cooling when used with radiant distribution. The floor serves to provide a very large heat
transfer surface area compared to what is typically found in finned coils, allowing more
moderate temperatures to be used in meeting heating and cooling needs. The resulting
moderate evaporator (in cooling) and condenser (in heating) temperatures mean “thermal
lift” is reduced and compressors in these systems should not have to work as hard to raise
or lower the temperature of the heat transfer medium (air or water). Other factors include
lower power required by pumps vs. fans, the variable speed capability of the Altherma
which should result in improved efficiency at lower speeds, and the elimination of the need
for electric resistance heating for defrost cycles.
5 Francisco, P., L. Palmiter, D. Baylin (2004). Understanding Heating Seasonal Performance Factor for Heat Pumps. Proceedings, 2004 ACEEE Summer Study. 6 HSPF = 3.2 x COP – 2.4
Typical Daikin Altherma Heat Pump
(Source: Davis Energy Group photo)
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PG&E’s Emerging Technologies Program ET13PGE1031
In an effort to identify correlations between heat pump performance and outdoor
temperature, the “application EER” (EER*)for the residential building was calculated using
the equation below and plotted as shown in Figure 11.
EER* = Qdel / (Ehp + Epump)
Where: Qdel = rate of cooling energy delivered in kBtu/hr
Ehp = heat pump electricity demand in kW
Epump = pump electricity demand in kW
The data show no clear trends; in fact the EER appears to be rising instead of falling with
increasing outdoor temperature. The wide scatter is likely a result of operation at a variety
of speeds and part load conditions. Since a single circuit serving both heat pumps was
monitored it was not possible to distinguish whether one or both were operating at any
given time.
To calculate seasonal performance values, heating and cooling energy supplied were divided
by heat pump energy for both buildings, resulting in the values listed in Tables 7 and 8. To
account for all related energy uses, performance values are shown with and without pumps
and fans. HSPF’s were calculated using the Title 24 standards formula for ground source
heat pumps (see footnote 5).
FIGURE 11: EER* VS. OUTDOOR TEMPERATURE – RESIDENTIAL BUILDING
Table 7: Measured Heat Pump Efficiency – Residence Building 3
Components COP HSPF EER
HP only 6.9 19.6 16.6
HP + Pumps 5.8 16.1 14.5
HP+ Pumps & Fans 4.9 13.4 11.3
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PG&E’s Emerging Technologies Program ET13PGE1031
Table 8: Measured Heat Pump Efficiency – Community Building
Components COP HSPF EER
HP only 6.2 17.5 16.8
HP + Pumps 4.5 12.1 12.6
HP+ Pumps & Fan 4.3 11.3 11.1
When including pump energy, the averaged measured seasonal EERs are not far from the
13 SEER rated value but the averaged HSPFs are significantly higher than the CEC rating of
11. The lower heat pump performance seen for the community building may be a result of
greater part load operation, and possibly excessive pump power. Flow rates were seen to be
greater than the recommended 3 gpm per ton generally specified.
A study of another Altherma air-to-water heat pump completed under a Building America
project7 found full load COPs averaging above 4 at an outdoor temperature of 45°F and a
leaving water temperature of 94°F, close to manufacturer’s rated performance at these
conditions. The average seasonal COP was 4.18.
APPROACH TO ZERO NET SITE ENERGY USE Table 9 lists total electrical energy use for each building and separately lists the energy use
of the community building with (total) and without the outbuilding loads included
(community building only). These results show that, excluding the outbuilding loads, the
community building is effectively achieving zero net performance on a site energy basis.
Had the PV system on the residence building not been decreased in size by 50%, it is likely
that it too would have achieved zero net energy.
Table 9: Annual Electric Loads vs. PV Generation
Building/Load
Energy
Use
PV
Generation
PV
Contribution
Residential Building 23,424 12,386 53%
Community Building (only) 19,724 19,942 101%
Community Building (total) 56,504 19,942 35%
7 See http://www.nrel.gov/docs/fy14osti/60135.pdf
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CONCLUSIONS & RECOMMENDATIONS The 50% reduction in the size of the PV system ruled out the possibility of achieving zero
net energy use for the residential building, but excluding the loads for the pool, spas,
greenhouse, and well pumps, the community building generated about 200 kWh more than
it used for the year. Doubling the output of the community building PV system would have
resulted in it providing about 70% of the annual electricity consumed by the building
including the outbuilding loads. The well pumps and greenhouse were not part of the design
process and not initially considered part of the facility loads.
With updated inputs to reflect as-built conditions, the TDV savings calculated using
EnergyPro Version 5 showed the buildings to perform approximately 25% better than 2008
Title 24 standards. Given the step up in the 2013 code, the buildings evaluated would
probably still comply.
A comparison of monitored performance to the predicted site energy use from the Title 24
compliance model simulations indicated much higher measured energy use for the
residential building and much lower measured use for the community building than
predicted by the simulations. The high use for the residential building stems from the type
of occupancy, the high number of occupants, and 24 hour staffing, all of which are not
characteristic of the assumptions used by the compliance model for single family homes. As
low-rise residential buildings the buildings would not qualify as “non-residential” under the
standards, as would a health care facility. The high plug and lighting loads indicate high
internal gains and hence higher cooling loads than for typical residences. Equipment that
had not been fully commissioned also accounted for the higher than modeled energy use.
Inconsistent operation of fans and other equipment that occurred with the ongoing
commissioning and efforts to adjust comfort conditions during the year may have also
contributed to measured performance that was at variance with predictions8.
Monitoring results suggest that one heat pump would be sufficient to carry the load of each
of the buildings. An analysis completed during the design review phase of this project
suggested that the pumps within the Altherma units may have sufficient capacity to deliver
water to the radiant floor piping. The variable capacity of the Altherma and the thermal
capacitance of the slab foundation would allow future designs to avoid the cost, increased
pumping energy, and probable reduced performance of the primary-secondary piping used
in the Sweetwater design.
The fan coils were intended to provide tempered fresh air supplied through slot diffusers
using demand control (CO2 sensors mounted in each of the rooms). The fans were originally
specified to be variable volume, though constant volume fans were installed. There is also a
reference to an economizer function in the design narrative.
For the residential building, fan energy could be reduced and indoor air quality improved by
installing a variable frequency drive (as originally specified) and setting the fan to deliver
constant airflow in accordance with ASHRAE Standard 62.2 (<200 cfm), with sensors used
to boost airflow when CO2 levels are elevated. The fan coil is intended to provide humidity
control. The fan coils and dampers could also be operated to provide supplemental cooling
as needed as well as provide free nighttime cooling. For the community building, the fan
should be operated to deliver fresh air in accordance with ASHRAE Standard 62.1 and
8 Performance model predictions rarely align well with measured performance.
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similar control strategies could be used as in the residential buildings to reduce energy use
and assure comfort.
The high electric load from the outbuildings (swimming pool, spas, greenhouse, and well
pumps) should be investigated; an audit may discover ways that this load can be
decreased. One observation made during the maintenance of the monitoring equipment was
that the swimming pool pump is fixed speed. Replacing it with a variable speed pump could
reduce pumping energy substantially, particularly if the filtration schedule is adjusted to just
meet the requirements of California health regulations, and the payback period could be
very short.
In conclusion, though the residential buildings used more energy than expected for typical
residential occupancies, they may have achieved zero net energy had the originally specified
PV area been installed. Monitoring showed that the community building did produce more
energy than it consumed over the period of monitoring if the external loads (spa, pool,
greenhouse, well pumps) are excluded, despite that its PV area was also reduced by half.
Operational improvements to better control fans and replacing the swimming pool pump
with a variable speed pump are two obvious recommendations that would reduce energy
use below monitored levels. The building owners may also wish to investigate use of fans
for ventilation cooling was well as fresh air ventilation and supplemental heating and
cooling.
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APPENDIX
Tabulated Monthly End Use Values and PV Production
Site Plan
Original System Schematic
As-Built Modifications to System Schematic
As-Built Solar Water Heating System Schematic
Altherma Performance Curves – Heating
Altherma Performance Curves – Cooling
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Monthly End Use Values and PV Production
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Site Plan
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Original System Schematic from Construction Documents
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As-Built Modifications to System Schematic
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As-Built Solar Water Heating System Schematic
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Altherma Heating Performance Curves – Engineering Data
0
1
2
3
4
5
6
0 50 100 150
Po
we
r (k
W)
Leaving Water Temperature (oF)
Altherma OADB=68
Altherma OADB=59
Altherma OADB=54
Altherma OADB=45
Altherma OADB=36
Altherma OADB=25
Altherma OADB=190
1
2
3
4
5
6
0 20 40 60 80
Po
we
r (k
W)
Outdoor Air Temperature (oF)
Altherma LWT=131
Altherma LWT=122
Altherma LWT=113
Altherma LWT=104
Altherma LWT=95
Altherma LWT=86
0
10
20
30
40
50
60
70
0 20 40 60 80
Cap
acit
y (k
Wb
u/h
)
Outdoor Air Temperature (oF)
Altherma LWT=131
Altherma LWT=122
Altherma LWT=113
Altherma LWT=104
Altherma LWT=95
Altherma LWT=86
0
1
2
3
4
5
6
7
0 20 40 60 80
CO
P
Outdoor Air Temperature (oF)
Altherma LWT=131
Altherma LWT=122
Altherma LWT=113
Altherma LWT=104
Altherma LWT=95
Altherma LWT=86
0
10
20
30
40
50
60
70
0 50 100 150
Cap
acit
y (k
Btu
/h)
Leaving Water Temperature (oF)
Altherma OADB=68
Altherma OADB=59
Altherma OADB=54
Altherma OADB=45
Altherma OADB=36
Altherma OADB=25
Altherma OADB=19
0
1
2
3
4
5
6
7
0 50 100 150
CO
P
Leaving Water Temperature (oF)
Altherma OADB=68
Altherma OADB=59
Altherma OADB=54
Altherma OADB=45
Altherma OADB=36
Altherma OADB=25
Altherma OADB=19
36
PG&E’s Emerging Technologies Program ET13PGE1031
Altherma Cooling Performance Curves – Engineering Data