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Princeton University Energy Design Guidelines – ASHRAE 90.1-2004 Guidance Notes

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ASHRAE 90.1-2004 Appendix G Guidance Notes

This document provides guidance on the use of ASHRAE 90.1-2004. It is meant

improve consistency in application of 90.1 between different design teams and

energy modelers.

Guidance specific to Princeton University will be denoted with the following symbol:

The guidance provided has been developed to allow energy model results to be

submitted to USGBC for LEED-NC Energy and Atmosphere credits. Guidance

which may conflict with previous USGBC rulings or ASHRAE interpretations will be

noted with a .

It is ultimately the responsibility of the design team to ensure compliance with New

Jersey energy code.

Definitions

Baseline Model/Design: this model reflects the minimum requirements of ASHRAE

90.1-2004.

Proposed Model/Design: this model reflects the building as designed.

HVAC System: refers to airside equipment, not plant equipment.

Thermal Block: a collection of one or more HVAC zones grouped together for

simulation purposes. Spaces need not be continuous to be combined within a

single thermal block.

Zone: a space or group of spaces within a building with heating and cooling

requirements that are sufficiently similar so that desired conditions can be

maintained throughout using a single sensor. The terms room and space are used

interchangeably.

G1. General

G1.1 Performance Rating Method Scope

For the purposes of demonstrating compliance with Princeton University’s

Design Standards, the Appendix G Performance Rating Method shall be used

exclusively. The Energy Cost Budget method (Chapter 11) does not meet this

requirement.

G1.2 Performance Rating

The proposed building must meet all mandatory requirements of ASHRAE 90.1

from sections 5.4, 6.4, 7.4, 8.4, 9.4 and 10.4.

Savings are to be calculated on an annual energy cost basis using the

methodology in the input/output spreadsheet (Appendix 3.3-14).

The annual energy cost for both models must include the impact of all process

loads that use natural gas, electricity, chilled water, hot water, or steam. Process

loads and associated schedules must be kept the same between the Baseline

and Proposed models.



G1.3 Trade-Off Limits

When existing and new construction elements are combined in one project, only

elements being changed are allowed to differ between the Baseline and

Proposed models.

For fit-out (core and shell) spaces, assumptions made for internal loads and

schedules must remain the same between the Baseline and Proposed models.

G1.4 Documentation Requirements

Documentation must be submitted to Princeton University according to the Energy Model

Documentation Schedule. The following supplements are provided:

Utility and Carbon Rate Structure (Appendix 3.3-13)

Input/Output Spreadsheet (Appendix 3.3-14)

Fan Power Calculator (Appendix 3.3-15)

Standard Utilization Schedules (Appendix 3.3-16)

Glazing Factor Calculation Spreadsheet (Appendix 3.3-17)

G2. Simulation General Requirements

G2.1 Performance Calculations

Both models should use the same modeling program, climate file, and utility rate

structure.

G2.2 Simulation Program

All simulation programs permitted by ASHRAE 90.1-2004 are permitted for

demonstrating compliance with Princeton University energy performance targets.

These include, but are not limited to:

o Trane Trace 700 or Carrier HAP

o DOE-2 based programs (eQuest, VisualDOE, PowerDOE)

o EnergyPlus

o Energy-10 (buildings less than 20,000 sf only)

G2.3 Climatic Data

Both models should use the Trenton-Mercer County TMY3 climate data file

available for download from:

http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm

G2.4 Energy Rates

Both models should use the utility rate and carbon rate structures provided in

Appendix 3.3-13.

G2.5 Exceptional Calculation Methods

Proposed Only

Systems that cannot be directly modeled in the simulation program being used

should be documented as exceptional calculation methods and highlighted in the

Input/Output spreadsheet.

These systems include, but are not limited to:

o Natural or Mixed Mode Ventilation

http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm



o Underfloor Air Distribution

o Displacement Ventilation

o Active or Passive Chilled Beams

o Radiant Panel or Floor Cooling and Heating

G3. Calculation of the Proposed and Baseline Building Performance

G3.1 Building Performance Calculations

G3.1.1 Baseline HVAC System Type and Description

Baseline Only

The Baseline system type should be selected according to section G3.1.1 in this

document.

The Baseline model should have the same number of systems and the same

zone assignments to systems as the Proposed model to allow for direct

comparison between models.

G3.1.1.1 Purchased Heat

When the Proposed design makes use of the Princeton University steam system,

purchased steam should be modeled in both the Baseline and Proposed models

using the standard utility rate structure.

Table G3.1 Modeling Requirements for Calculating Proposed and Baseline Building Performance

1. Design Model

Baseline Only

The Baseline model must have the same basic geometry, thermal blocks,

zoning, process loads, and schedules as the Proposed model. The conditioned

floor should be identical between the Baseline and Proposed models.

Proposed Only

The Proposed model is meant to approximate, as closely as possible, the

proposed design of the project.

Even if no heating and/or cooling system is designed for a zone, the zone must

be included in the energy model to properly account for the energy consumption

of zone lighting and/or equipment.

Only elements of the project that are included in the current project scope are

allowed to differ between the Baseline and Proposed models. For example, any

future lab fit-out space must be assumed to be the same between both models

with respect to lighting, internal loads, airside systems, etc.

2. Additions and Alterations

Baseline and Proposed

The boundaries of the energy study should be agreed upon with the Princeton

University Project Manager at the beginning of Schematic Design.

3. Space Use Classification


Space classifications for each zone should be documented in the Input/Output



spreadsheet.

4. Schedules


Separate schedules should be used for occupancy, ventilation, lighting and

equipment.

Schedules should be the same for both models, except as noted in this

document. Use schedules provided as Appendix 3.13-16.

5. Building Envelope

Baseline Only

The Baseline model should be run in four orientations (0 degree rotation, 90

degree rotation, 180 degree rotation, and 270 degree rotation). If the averaged

result is greater than the result for as designed building orientation (0 degrees),

there is room for improvement to the building’s massing and fenestration

placement.

Baseline model envelope thermal properties should be based on 90.1, Chapter

5, Climate Zone 5A.

No external or internal shading devices should be included in the Baseline

model.

The Baseline model building envelope component areas should be identical to

the Proposed model with the following exceptions:

o The maximum allowed above-grade fenestration to wall ratio in the

Baseline model is 40%.

o The maximum skylight to roof ratio in the Baseline model is 5%. Skylight

is defined as fenestration with a slope of 60 degrees or less from

horizontal.

o Fenestration should be proportionally scaled in the Baseline model to

meet the above ratio limits. This applies only if the ratios are exceeded in

the Proposed model.

Proposed Only

As designed building envelope areas should be modeled.

Permanent external shading devices should be included in the Proposed model.

Internal shading that is not automated may not be included.

Fenestration

o All U-values should be assembly U-values. These values include the

effect of framing, edge spacers, and local thermal bridging. Use of

center-of-glass properties is not acceptable.

o All SHGC values should be assembly SHGC values. These values

include the effect of framing, edge spacers, and local thermal bridging.

Use of center-of-glass properties is not acceptable.

Envelope thermal performance values in 90.1, Normative Appendix A should be

used, in the absence of actual thermal calculations.

Green roofs and high reflectance roofs (EnergyStar) may be modeled with a

reflectance of 0.45.



Further guidance is provided in the Energy Guidelines Section 8: Envelope

Design Guidelines.

6. Lighting

Baseline Only

Lighting power densities may be specified either by the use of the space-by-

space method (90.1, Table 9.6.1) or the building area method (90.1, Table 9.5.1).

The two methods should not be combined in the same model. Lighting power

allowances should be tracked using the Input/Output spreadsheet.

Daylight control should be not be modeled in the Baseline model.

External lighting should be included, as per the limits described in 90.1, Table

9.4.5.

Proposed Only

Use estimated or as-designed lighting power densities.

Daylight control should be calculated by the energy modeling software when

possible. The use of ray-tracing daylight calculation software to create a lighting

use schedule is preferable.

For automatic lighting systems in addition to those required for minimum code

compliance, power adjustments should be made using Table G3.2. Alternatively,

lighting schedule adjustments can be made to the proposed model with credible

technical documentation.

External lighting should be included, as designed.

7. Thermal Blocks – HVAC Zones Designed


Thermal blocks should be modeled as designed.

Floor areas used in the simulation tool should be measured from the inner face

of interior walls and outer face of perimeter walls. Areas must remain the same

between the Baseline and Proposed models.

8. Thermal Blocks – HVAC Zones Not Designed


Separate thermal blocks should be assumed for internal and perimeter spaces.

Spaces with exposed roof, below-grade wall, or slab-on-grade conditions should

be modeled separately from other spaces without one of these conditions.

9. Thermal Blocks – Multifamily Residential Buildings


Residence halls should be modeled using one zone for all adjacent units having

the similar perimeter exposure. Units with multiple perimeter exposures should

be modeled separately.

10. HVAC Systems

Baseline Only

The Baseline HVAC system should be modeled following the guidance in Table

G3.1.1A and G3.1.1B.



Proposed Only

The Proposed systems should be modeled as designed.

11. Service Hot Water Systems

Baseline Only

The Baseline model should use the same service hot water demand and fuel

source as the Proposed model. Efficiencies should be as per 90.1, Chapter 7.

Proposed Only

If a service hot water system has not yet been designed, a system should be

included with an estimated capacity based on tables in the 90.1 User’s Manual.

The fuel source should be purchased steam.

If a service hot water system has been designed, actual capacities should be

used in both models.

Credit may be taken for hot water use reductions in this calculation provided

that the reduction is demonstrated using the Input/Output spreadsheet.

12. Receptacle and Other Loads


Receptacle loads should include all process energy uses within the project

including, but not limited to:

o Elevators and escalators

o Laboratory equipment

o Computers and other office equipment

o Appliances

o Vending machines

Receptacle loads should be determined based on guidance in the ASHRAE

Fundamentals Handbook, measured data, or calculated equipment loads.

Receptacle loads must be kept the same between the Proposed and Baseline

models.

o Exception: credit may be taken for use of equipment that is more

efficient than industry norms. Any credit taken must receive prior

approval from PU and be stated in the Input/Output spreadsheet.

13. Modeling Limitations to the Simulation Program

Current energy simulation tools have inherent modeling limitations. Where

limitations occur, include a description in the Input/Output spreadsheet.

G3.1.2 General Baseline HVAC System Requirements

Table G3.1.1A Baseline HVAC System Types

Baseline Only

This table gives guidance on the baseline HVAC system type based on building type, size, fuel source, and number of floors.

When determining the number of floors, include below-grade levels in the count. Do not include non-occupied mechanical levels in the count.



When there is no heating system, use the “electric and other” column.

When there is a mix of non-residential and residential spaces within a building, use the majority (>50%) space type, measured by gross square footage.

Labs: for an individual air-handling unit system serving spaces with a minimum of 5,000 cfm exhaust, use System Type 5 or System Type 7. Reduce the exhaust and makeup air volume to 50% of peak design during unoccupied

periods ( 5% occupancy). This applies to airflow driven (e.g. fume-hood) labs ONLY.

All-electric buildings: heating to be electric resistance.

Geothermal heat pump systems: assume baseline systems 1, 3, 5, or 7.

Table G3.1.1B Baseline System Descriptions

Baseline Only

This table describes the baseline system types.

The type is determined from Table G3.1.1A.

For the majority of projects at Princeton University, system types using “fossil

fuel, fossil/electric hybrid, and purchased heat” will apply.

G3.1.2.1 Equipment Efficiencies

Baseline Only

HVAC equipment should be modeled as having the minimum efficiency levels

described in Section 6.4.

Note that EER and COP ratings sometimes include fan energy.

Use the following correlation chart to determine which 90.1, Chapter 6 efficiency

ratings to use:

System Type Efficiency Guidance

1. Packaged terminal air

conditioner

(Will not apply to most PU

buildings)

Use “PTAC (cooling mode) new construction” efficiency formula in

Table 6.8.1D for cooling.

Use peak system cooling load (Btu/h) to determine

efficiency level.

Use “Boilers, hot water” efficiency values in Table 6.8.1F for

heating.

Use peak building heating load (Btu/h) to determine

efficiency level.

Note that this will not apply for buildings that use PU

campus steam.

2. Packaged terminal heat

pump

(Will not apply to most PU

buildings)

Use “PTHP (cooling mode) new construction” efficiency formula in

Table 6.8.1D for cooling.

Use “PTHP (heating mode) new construction” efficiency formula in

Table 6.8.1D for heating.


efficiency level.



3. Packaged rooftop air

conditioner

Use “air-conditioners, air cooled, all other, single package”

efficiency values in Table 6.8.1A


efficiency level.

Use “Warm air furnace, gas fired” efficiency values in Table 6.8.1E

for heating.


efficiency level.

Note that this will not apply for buildings that use PU campus

steam.

4. Packaged rooftop heat

pump

Use “air-cooled (cooling mode), all other, single package”

efficiency values in Table 6.8.1B for cooling.

Use “air-cooled (heating mode), single package” efficiency values

in Table 6.8.1B for heating.


efficiency level.

5. Packaged rooftop VAV with

reheat (DX)

Use “air-conditioners, air cooled, all other, single package”

efficiency values in Table 6.8.1A


efficiency level.


heating.


efficiency level.


steam.


reheat (DX)

Not permitted at PU.


reheat (CHW)

See section 6.19 of this document for cooling plant efficiency

guidance.


heating.


efficiency level.


steam.

8. VAV with reheat (CHW) Not permitted at PU.

Systems 1, 3, 5, and 7 apply to all systems that use fossil fuel, fossil/electric hybrid, purchased heat, or geothermal, as the heat source. Systems 2, 4, 6, and 8 apply to all other heating sources.

G3.1.2.2 Equipment Capacities

Baseline Only

Equipment should be oversized by 15% for cooling and 25% for heating.



Sizing should follow the same process taken when determining peak cooling and

heating loads with additional guidance from 6.3 of this document.

Capacity adjustments should be made at plant and coil level.


Unmet load hours for both cases must be less than 300 hours (out of 8,760).

Note that most simulation tools report separate heating load hours not met from

cooling load hours not met. The sum of these two apply to these requirements.

Unmet load hours cannot differ between cases by more than 50 hours.

Unmet load hours are problematic in energy simulation tools, given the use of a

one-hour simulation time step coupled with spaces with large warm-up loads

and/or low airflow rates. Do not adjust schedules as a primary solution. Rather,

take the following steps:

Both models < 300 unmet load hours and proposed exceeds baseline by

> 50 unmet load hours: decrease baseline system capacities

incrementally.

Both models < 300 unmet load hours and baseline exceeds proposed by

> 50 unmet load hours: increase baseline system capacities

incrementally.

Either model > 300 unmet load hours: increase baseline and/or proposed

system capacities incrementally. Note that having a significant number of

load hours not met can be an indication of an inadequate HVAC system

design.

Capacity adjustments to resolve unmet load hours issues should be

made at coil level.

G3.1.2.2.1 Sizing Runs

Baseline Only

Baseline model sizing runs (peak cooling and heating load determination)

should be developed using 99.6% ASHRAE heating design temperatures and

1% ASHRAE dry-bulb and 1% wet-bulb cooling design temperatures. This

applies to energy modeling only. PU design standard conditions should be used

for actual equipment sizing. Reference: ASHRAE Fundamentals.

G3.1.2.3 Preheat Coils

Baseline Only

If there is a pre-heat coil in the proposed design system, a pre-heat coil should

be modeled in the baseline design system also.

G3.2.1.4 Fan System Operation


Fans should be modeled in both cases to operate continuously anytime

occupancy is greater than 5% of design. Fans should cycle to meet heating and

cooling loads during unoccupied hours.

Exception: for spaces with health and safety minimum airflow requirements

(labs or medical facility), fans should operate continuously.

G3.2.1.5 Ventilation




Ventilation rates should remain the same in both cases. This applies even if

ventilation rates provided are higher than minimums prescribed by NJ

Mechanical Code and/or ASHRAE 62.1. Fume hood ventilation in the baseline

and proposed models shall use the standard utilization schedules.

Exception 1: when demand controlled ventilation is used, the proposed model

ventilation rates may be adjusted through use of the appropriate occupancy

schedule contained in Appendix 3.3-16.

Exception 2: proposed model ventilation rates may be adjusted to account for

use of fume hood auto-sash closure mechanisms by using the

“Weekend/Holiday” schedule at all times.

The use of low-flow fume hoods is encouraged. As a process credit, the

baseline model should assume a face velocity of 100 fpm. The proposed model

should include actual fume hood face velocity.

Ventilation schedules may not deviate from those in Appendix 3.3-16 without

prior approval from Princeton University.

G3.2.1.6 Economizers

G3.2.1.7 Economizer High-Limit Shutoff

Baseline Only

Princeton University is at the eastern edge of Mercer County, which falls under

ASHRAE 90.1 Climate Zone 5A.

Outdoor air economizers should be provided as per the following:

System Type Economizer Requirement

1. Packaged terminal air conditioner

2. Packaged terminal heat pump

Not required

3. Packaged rooftop air conditioner

4. Packaged rooftop heat pump

5. Packaged rooftop VAV with reheat (DX)

6. Packaged rooftop VAV with reheat (DX)

7. Packaged rooftop VAV with reheat (CHW)

8. VAV with reheat (CHW)

Economizer Included - 70F High-Limit Shutoff

Exception: systems that make use of gas-phase filtration to meet requirements

of ASHRAE 62.1 (Section 6.1.2).

Proposed Only

Model airside economizers as designed. Ensure that the control algorithm

matches what is specified (e.g. enthalpy, dry-bulb, fixed differential, etc.).

G3.1.2.8 Design Airflow Rates

Baseline Only

System baseline design supply airflow rates should be based on a supply-air to

room-air temperature difference of 20F. For example, if the target space

temperature is 77F, the design supply temperature should be set at 57F. This

requirement ties directly into calculation of baseline system fan power.



If there are return fans in the proposed design, return fans should also be

modeled in the baseline model with a design airflow rate equal to 90% of the

supply.

G3.1.2.9 System Fan Power

Baseline Only

Due to the complexity of fan power calculations, power should be calculated

using the Fan Power Calculation Spreadsheet (Appendix 3.3-15). Requirements

are based on ASHRAE 90.1-2007.

The following is a summary of requirements:

System Type Fan Power

1. Packaged terminal air conditioner

2. Packaged terminal heat pump

Pfan = CFMs x 0.3

3. Packaged rooftop air conditioner

4. Packaged rooftop heat pump

Pfan = bhp x 746 / Fan Motor Efficiency

bhp = CFMs x 0.00094 + A


reheat (DX)


reheat (DX)


reheat (CHW)

8. VAV with reheat (CHW)

Pfan = bhp x 746 / Fan Motor Efficiency

bhp = CFMs x 0.0013 + A

Pfan = electric power to fan motor (watts).

bhp = brake horsepower calculated from Table G3.1.2.9.

Fan Motor Efficiency = efficiency from Table 10.8 for next motor size greater than

the bhp using the enclosed motor at 1,800.

CFMs = baseline system maximum design supply fan airflow rate in cfm.

A = value calculated from Section 6.5.3.1.1.

Proposed Only

Use the Fan Power Calculation Spreadsheet.

G3.1.2.10 Exhaust Air Energy Recovery

Baseline Only

Heat recovery should be modeled when CFMs > 5,000 cfm AND the outdoor air

fraction > 70%.

When heat recovery applies, use 50% for the baseline effectiveness. This

effectiveness is based on enthalpy. Heat pipes, run-around loops, fixed-plate

heat exchangers, and other sensible only devices will likely NOT meet this

requirement for the Princeton climate.

Exceptions:

o Systems serving spaces that are not cooled and that are heated to less

than 60F.



o Systems exhausting toxic, flammable, or corrosive fumes or paint or

dust. This exception only applies if heat recovery is not used in the

proposed design. Labs are addressed separately from this exception.

o Commercial kitchen hoods classified as Type I by NFPA 96. This

exception only applies if heat recovery is not used in the proposed

design.

o When the exhaust rate that would return to the heat recovery device is

less than 75% of the design outdoor flow. This exception only applies if

heat recovery is not used in the proposed design.

o For lab systems with exhaust rates of 5,000 cfm or less. For lab systems

with exhaust rates less than 5,000 cfm, heat recovery does not need to

be modeled in the baseline, even if it is used.

Proposed Only

Model heat recovery as designed. Ensure that sensible and latent heat recovery

effectiveness are matched to actual equipment sections. Ensure that control

algorithms and airside pressure is properly modeled. Bypass of the heat recovery

device is required to allow air economizer operation, when included.

G3.1.3 System-Specific Baseline HVAC System Requirements

The following items apply to only certain baseline types.

G3.1.3.1 Heat Pumps (Systems 2 and 4)

Baseline Only

Model with auxiliary electric heat. Energize only when outdoor air temperature is

< 40F.

G3.1.3.2 Type and Number of Boilers (Systems 1, 5, and 7)

Baseline Only

For the Appendix G compliant model (Baseline 1 of the PU Energy

Guidelines), and buildings that use Princeton University steam, this section does

not apply. For Baseline 3 required by the PU Energy Guidelines, this section

shall apply.

For buildings with stand-alone heating, the baseline boiler should use the same

fuel source as the proposed design. This will typically be natural gas.

Model a single boiler if the heating plant serves 15,000 gsf.

Model two equally sized boilers if the heating plant serves > 15,000 gsf.

G3.1.3.3 Hot-Water Supply Temperature (Systems 1, 5, and 7)

Baseline Only

Model the hot-water design supply water temperature at 180F. The return water

temperature should be modeled as 130F. Pumps should be sized accordingly.

G3.1.3.4 Hot-Water Supply Temperature Reset (Systems 1, 5, and 7)

Baseline Only

Hot water supply temperatures should be reset as follows:

Outdoor Temperature Hot Water Supply Temperature



20F 180F

Between 20F and 50F Vary linearly between 150F and 180F

50F 150F

G3.1.3.5 Hot-Water Pumps (Systems 1, 5, and 7)

Baseline Only

Baseline power should be modeled at 19 W/gpm. The flow rate used should be

calculated at the baseline peak hot water demand with a 50F delta. For

example, if 500 gpm is the peak flow rate, the baseline pump power is 9,500 W

(12.73 HP).

Model hot water pump system as primary only.

Model pump control using variable-speed drives for system serving < 120,000 sf.

Model pump control by riding the pump curve (constant-volume) for system

serving 120,000 sf.

Proposed Only

Model pump system as designed. Do not use nameplate horsepower in the

model. Use actual operating horsepower.

G3.1.3.6 Piping Losses (Systems 1, 5, 7, and 8)


Do not model piping heat gains or losses for any system.

G3.1.3.7 Type and Number of Chillers (Systems 7 and 8)

Baseline Only

Although most buildings at Princeton University make use of the campus

chilled water system, electric chillers must be modeled in the baseline. The

impact of the campus plant is addressed through use of the utility rate structure

described in Appendix 3.3-13.

The baseline chillers should be modeled based on the peak building cooling load

:

Building Peak

Cooling Load

Number and Type of Chillers COP / IPLV

< 150 tons 1 water-cooled screw chiller 4.45 / 5.2 (From Table 6.8.1C)

150 tons,

300 tons

1 water-cooled screw chiller 4.90 / 5.6 (From Table 6.8.1C)

> 300 tons,

< 600 tons

2 water-cooled screw chillers

sized equally

4.90 / 5.6 (From Table 6.8.1C)

600 tons 2 water-cooled centrifugal chillers

minimum with chillers added that

no chiller is larger than 800 tons,

all sized equally.

6.1 / 6.4 (From Table 6.8.1J)

The above chart is from ASHRAE 90.1-2007 and represents a substantial change

from 90.1-2004, but one that is more appropriate. The equivalent chart in 90.1-2004



based the baseline chiller selection on building square footage.

G3.1.3.8 Chilled Water Design Supply Temperature (Systems 7 and 8)

Baseline Only

The baseline chilled water design supply temperature should be modeled at 44F

and return water temperature at 56F.

Proposed Only

The actual chilled water design conditions should be used. Princeton

University default values are 45F with a 20F delta. No actual electric chiller(s)

should be modeled. Performance is addressed through use of the chilled water

utility rate structure described in Appendix 3.3-13.

G3.1.3.9 Chilled Water Supply Temperature Reset (Systems 7 and 8)

Baseline Only

Chilled water supply temperatures should be reset as follows:

Outdoor Temperature Chilled Water Supply Temperature

80F 44F

Between 60F and 80F Vary linearly between 44F and 54F

60F 54F

G3.1.3.10 Chilled Water Pumps (Systems 7 and 8)

Baseline Only

Baseline power should be modeled at 22 W/gpm. The flow rate used should be

calculated at the baseline peak chilled water demand with a 12F delta. For

example, if 500 gpm is the peak flow rate, the baseline pump power is 11,000 W

(14.75 HP).

Model primary/secondary chilled water pumping scheme with variable-speed

drive on the secondary pump for peak building cooling load ≥ 300 tons.

Model primary/secondary chilled water pumping scheme with secondary pump

riding the pump curve (constant volume) for peak building cooling load < 300

tons.

Proposed Only

Model pump system as designed. Do not use nameplate horsepower in the

model. Use actual operating horsepower.

G3.1.3.11 Heat Rejection (Systems 7 and 8)

Baseline Only

Although most buildings at Princeton University make use of the campus

chilled water system, heat rejection must be modeled in the baseline. The

impact of the campus plant is addressed through use of the utility rate structure

described in Appendix 3.3-13.

The heat rejection device should be an axial fan cooling tower with two-speed

fans with fan power totaling 38.2 gpm/hp (Table 6.8.1G). The gpm should be

calculated based on a condenser water delta of 10F with leaving condenser

water temperature of 85F at design wet bulb conditions. For example, if the

condenser water flow rate is 500 gpm, the baseline fan power would be 13.09



HP.

The leaving condenser water temperature should be allowed to float between

70F and 85F, weather permitting.

Baseline condenser water pump power should be modeled at 19 W/gpm. The

flow rate used should be calculated at the baseline peak condenser water

demand with a 10F delta. For example, if 500 gpm is the peak flow rate, the

baseline pump power is 9,500 W (12.73 HP).

G3.1.3.12 Supply Air Temperature Reset (Systems 5 through 8)

Baseline Only

The air temperature for cooling should be reset upwards by 5F under minimum

cooling load conditions.

G3.1.3.13 VAV Minimum Flow Setpoints (Systems 5 and 7)

Baseline Only

Minimum volume setpoints for VAV reheat boxes should be 0.4 cfm/sf or the

minimum ventilation rate, whichever is larger.

For labs, the minimum VAV box setpoint should be set to what is required for

health and safety.

G3.1.3.14 Fan Power (Systems 6 and 8)

Not applicable to Princeton University buildings.

G3.1.3.15 VAV Fan Part-Load Performance (Systems 5 through 8)

Baseline Only

VAV system supply fans should have variable-speed drives with the following

power curve (Table G3.1.3.15):

00.03

0.07

0.13

0.21

0.3

0.41

0.54

0.68

0.83

1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Fan Part-Load Ratio

Fra

cti

on

of

Fu

ll-L

oad

Po

wer

Table G3.2 Power Adjustment Percentages for Automatic Lighting Controls

Proposed Only



The following power adjustments should be made to account for automatic

lighting controls:

Automatic Control

Device

Non-24-h and 5,000 sf total

conditioned building area

All Other

1. Programmable

timing control

10% 0%

2. Occupancy

sensor

15% 10%

3. Occupancy

sensor and

programmable

timing control

15% 10%

ashrae 90.1-2004 appendix g guidance notes · ashrae 90.1-2004 appendix g guidance notes ... hvac...

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