Under Project Type Variations, District Energy Systems, add the following text:
"Projects that are served by district energy systems (DES) may demonstrate compliance with EA Prerequisite Minimum Energy Performance and EA Credit Optimize Energy Performance by following one of the following methods.
• Path 1 ASHRAE 90.1-2016 Appendix G. No credit is documented for the purchased energy systems.
o Path 1A. ASHRAE 90.1-2016 Appendix G.
o Path 1B. ASHRAE 90.1-2016 Appendix G with ASHRAE 90.1-2022 Addendum a. (Revise the Appendix G methodology to remove the inherent penalty for DES)
• Path 2 Full DES performance accounting. Credit is documented for the purchased energy systems. The proposed design is modeled using a virtual plant consistent with the district energy system performance, and the baseline design is modeled with on-site systems from ASHRAE 90.1-2016 Appendix G for site generated thermal energy.
• Path 3 Large-scale District Energy Systems. GHG emissions savings associated with the upstream system are documented using the Large-Scale DES Calculator. No energy efficiency savings (using the cost or source energy metric) are documented for the upstream system.
The modeling path chosen by the project team may depend on the relative efficiency of the DES to which the project is connected, how much DES information is available, or whether an energy model already exists for the system. Whenever possible, incorporate system and equipment performance parameters directly into the energy simulation. Potential methods include developing efficiency curves and scheduling equipment operation and curves. Postprocessing of DES performance is acceptable if reasonable simulation methods are not available or are too onerous. All postprocessing methodologies must be fully documented.
All Paths: Scope of DES equipment inclusion
All downstream equipment must be included in the scope of EA Prerequisite Minimum Energy Performance and EA Credit Optimize Energy Performance. Downstream equipment includes heat exchangers, steam pressure reduction stations, pumps, valves, pipes, building electrical services, and controls.
Upstream equipment is included or excluded depending on the chosen path.
Path 1A. ASHRAE 90.1–2016, Appendix G
Model the proposed and baseline designs using purchased energy according to ASHRAE 90.1–2010, Appendix G.
Published purchased energy rates or conversion factors:
Energy Cost: Per ASHRAE 90.1, model the purchased energy rates for each district energy source (purchased hot water, purchased steam, or purchased chilled water) identically in the baseline and proposed design based on actual utility rates, if actual utility rates are available.
GHG Emissions: For the GHG emissions metric, if the published reference for electricity and fossil fuel GHG emission factors also reports emission factors for district energy (purchased hot water, purchased steam, or purchased chilled water), model these published emission factors for each district energy source identically in the baseline and proposed design.
Derivation of DES purchased energy rates or GHG emission factors when unpublished:
If purchased energy rates and/or GHG emission factors are not published for the district energy sources serving the project, derive these purchased energy rates and/or emission factors leveraging the electricity or fossil fuel data. For fossil fuel, use natural gas if the building does not receive fossil fuel and the district energy fuel source is unknown.
• District Chilled Water (CHW):
CHWFactor = ElectricityFactor x 0.325
• District Hot Water (HHW):
HHWFactor = FossilFuelFactor x 1.65
• District Steam Water (Steam):
SteamFactor = FossilFuelFactor x 1.85
Where:
• For the Cost Metric (See further guidance below for purchased energy rates)
o CHWFactor = Chilled water purchased energy rate ($ / unit energy)
o HHWFactor = Hot water purchased energy rate ($ / unit energy)
o SteamFactor = Steam purchased energy rate ($ / unit energy)
o ElectricityFactor = Electricity purchased energy rate ($ / unit energy)
o FossilFuelFactor = Fossil Fuel purchased energy rate ($ / unit energy)
Units of energy must be consistent throughout each equation (i.e. consistently $/kWh or $/kBtu)
• For the GHG Emissions Metric:
o CHWFactor = Chilled water GHG emissions factor
o HHWFactor = Hot water GHG emissions factor
o SteamFactor = Steam GHG emissions factor
o ElectricityFactor = Electricity GHG emissions factor
o FossilFuelFactor = Fossil Fuel GHG emissions factor
Units of each GHG emissions factor must be consistent (in weight of CO2eq emissions per unit of energy)
Additional guidance: Cost Metric ElectricityFactor and FossilFuelFactor.
For the cost metric, in a flat rate structure, in which the building cost per unit of electricity or building cost per unit of natural gas is the same throughout the year and there are no demand charges, then those flat rates become the ElectricityFactor and FossilFuelFactor for the project cost metric. If all energy rate structures are not flat, a preliminary run of the Option 1 baseline case energy model must first be completed to identify the virtual electric rate (ElectricityFactor) and fossil fuel rate (FossilFuelFactor) for the project.
To obtain the virtual fuel rate (FossilFuelFactor) when the connected building does not use fossil fuel but the DES central plant does, use a flat rate consistent with the central plant rates or the historic average local market rates.
Path 1B. ASHRAE 90.1-2016 Appendix G with ASHRAE 90.1-2022 Addendum a.
The project may apply ASHRAE 90.1-2022 Addendum a to the ASHRAE 90.1-2016 Appendix G criteria. This eliminates the inherent penalty in the ASHRAE 90.1-2016 Appendix G Performance Index Targets when modeling “purchased heat” and “purchased chilled water”. Replace all ASHRAE 90.1-2022 Addendum a references to Section 6 prescriptive criteria for the proposed building design with ASHRAE 90.1-2016 Section 6. For the baseline building design HVAC systems, the project team must exclusively reference ASHRAE 90.1-2022 with Addendum a. Free read-only versions of ASHRAE 90.1-2022 are available at https://www.ashrae.org/technical-resources/standards-and-guidelines/read....
90.1-2022 Addendum a criteria as applied to ASHRAE 90.1-2016 Appendix G:
• Model HVAC systems for the baseline building design per ASHRAE 90.1-2022 Appendix G criteria as if all heating and cooling generation equipment is on-site;
• Projects with purchased heat: Model the proposed building design using natural gas forced draft boilers that prescriptively comply with ASHRAE 90.1-2016 Section 6 in lieu of purchased heat. The number of boilers and boiler controls shall meet the requirements of ASHRAE 90.1-2022 Section G3.2.3.2 through G3.2.3.6, without exceptions. Forced draft boiler efficiencies shall be modeled per the mandatory and prescriptive requirements of ASHRAE 90.1-2016 Section 6. Boiler systems with design input exceeding 1,000,000 Btu/h may document credit for minimum turndown ratios per Table 6.5.4.1.
• Projects with purchased chilled water: Model the proposed building design using water-cooled chillers that prescriptively comply with ASHRAE 90.1-2016 Section 6 in lieu of purchased chilled water.
o Model the type and number of water-cooled electric chillers per ASHRAE 90.1-2022 Table G3.2.3.7 based on the peak coincident cooling load of baseline HVAC systems using chilled water (See 90.1-2022 Section G3.2.3.7).
o Model the chilled water (CHW) with a design supply temperature of 44 °F (7 °C) and return temperature of 56 °F (13.3 °C) (See 90.1-2022 Section G3.2.3.8)
o Model each chiller with separate condenser-water and primary chilled-water pumps interlocked to operate with the associated chiller per ASHRAE 90.1-2022 G3.2.3.11. Model the CHW loop as constant-flow primary and variable-flow secondary with the pump power of each loop modeled per 90.1-2022 Section G3.2.3.10, without exceptions. Model secondary loops with a pump motor demand of 30% of design wattage at 50% of design flow per the prescriptive criteria of ASHRAE 90.1-2016 Section 6.5.4.2. For systems with total modeled chilled water capacity exceeding 300,000 Btu/h (25 kW) utilizing DDC CHW control valves, model chilled water supply temperature reset based on valve positions until one valve is wide open or setpoint limits have been reached per ASHRAE 90.1-2016 Section 6.5.4.4.
o Model heat rejection as an axial fan cooling tower with design fan power = 40.2 gpm/hp per ASHRAE 90.1-2016 Table 6.8.1-7, and with design supply temperature and leaving water temperature determined per ASHRAE 90.1-2022 G3.2.3.11. If the total fan power for the heat rejection equipment exceeds 5 hp, model the cooling tower fans with variable-speed fan controls that reduce fan motor demand to no more than 30% of design wattage at 50% of design air volume per ASHRAE 90.1-2016 Section 6.5.11.
Path 2. Full DES performance accounting
For path 2, the energy model scope accounts for both downstream equipment and upstream equipment and requires calculation of the district energy average efficiencies using engineering analysis or monitored data or a combination of both.
Energy rates (Cost Metric)
All DES electricity and fuel rates must be identical in both the baseline and the proposed cases. Use local electricity and fuel rates as they would normally apply to the building for the energy sources under consideration. If this information is not available, use representative market rates.
Exception: For District cooling or district heating plants without cogeneration or fuel cells that operate under specific and atypical electric rate structures and actively take advantage of those rates through strategies such as load management or energy storage, use the rate structures as they apply to the DES.
Greenhouse Gas Emissions Factors
See the guidance in Further Explanation, Greenhouse Gas Emissions.
Baseline building systems
For systems with thermal energy delivered from the district energy system, model the baseline case with on-site systems per ASHRAE 90.1-2022 Addendum a criteria described above.
Proposed building plant
Model the proposed case with a virtual DES-equivalent plant. Use the same efficiencies as the entire upstream DES heating, and cooling, and combined heat and power (CHP) systems, including all distribution losses and energy use.
Equipment efficiencies, distribution losses, and distribution pumping energy may be determined using any of the following methods:
• Monitored data
• Engineering analysis
Efficiencies and losses may be determined and modeled at any level of time resolution, from hourly to annual. However, the time resolution must be sufficiently granular to capture and reasonably represent any significant time- or load-dependent interactions between systems, such as thermal storage or CHP. Monitoring and analytical methods may be combined as necessary and appropriate. Monitoring data for heating, cooling, pumping, and cogeneration may be used only if the thermal loads that are monitored represent at least 90% of the load on the campus or district plant predicted after building occupancy. Whether using monitoring or an analytical method, the methodologies must be fully documented. The following specific requirements apply.
Heating and cooling plants
Efficiencies, whether determined through monitoring or analytically, must include all operational effects, such as standby, equipment cycling, partial-load operation, internal pumping, and thermal losses.
Thermal distribution losses
Use monitored data or an engineering analysis.
• Monitored data determine the distribution losses for the DES by measuring the total thermal energy leaving the plant and comparing it with the total thermal energy used by the buildings connected to the DES. Rate the plant efficiency accordingly in the energy model:
Plant efficiency (%) x [100% – distribution loss (%)]
• An engineering analysis takes into consideration all distribution losses between the DES and the building. For distribution main losses, use a prorated amount based on load. For dedicated branch losses, use the total losses of the branch that feeds the building, including heat losses and steam trap losses. Compare the total losses with the total load of the building to get a percentage distribution loss relative to load and downgrade the plant’s efficiency accordingly in the energy model.
If thermal distribution losses are not measured or modeled, use the following default losses:
o Chilled water district cooling, 5%
o Hot water district heating, 10%
o Closed-loop steam systems, 15%
o Open-loop steam systems, 25%
For steam systems that are partially open and partially closed, prorate between the above 15% and 25% losses in accordance with the fraction of expected or actual condensate loss.
Pumping energy
Whether through monitored data or engineering analysis, determine pumping energy for the project by prorating the total pump energy of the DES by the ratio of the annual thermal load of the building to the total annual DES thermal load. Model the pump energy as auxiliary electrical load. Pumping energy must be determined or estimated where it applies.
District Energy Combined Heat and Power (CHP)
To model the proposed design virtual plant, first monitor or model the total electricity generation, fuel input, and heat recovery associated with the District Energy Combined Heat and Power (CHP):
• Determine annual electricity generation using one of the following methods:
o Monitor the total annual gross electricity generation. Also monitor the total annual parasitic loads, such as the annual electricity used for cooling the intake air for a turbine. Calculate the net annual electricity generation by subtracting all parasitic loads from the annual gross electricity generated.
o Model the generators in energy simulation software per Appendix G. Use peak electricity efficiencies and generator curves that match the installed generators. Apply measured or estimated load profiles as process loads to reflect the estimated total electric and thermal loads on the district energy CHP system. Use the total energy generated and total fuel input from this analysis. Any parasitic loads must be included in the analysis and subtracted from the annual electricity generation.
• Calculate annual fuel input using one of the following methods:
o Monitor the total annual fuel input to the generators.
o Model the generators in energy simulation software per Appendix G. Use peak electricity efficiencies and generator curves that match the installed generators.
• Calculate waste heat recovery using one of the following methods:
o Monitor the total waste heat recovered.
o Model the generators in energy simulation software per Appendix G. Use peak electricity efficiencies and generator curves that match the installed generators. Model the thermal equipment served by the CHP waste heat, such as boilers and absorption chillers, using the installed equipment capacities, efficiencies, and efficiency curves, and reflecting the total heating and cooling loads on the plant as a process load. Use the energy modeling outputs to identify the total heat recovered.
For baseline CHP electricity output, follow the general procedures described in this section for the proposed case, and adjust the results as follows depending on the results of the DES electricity allocation and the total modeled electricity use of the building in the Path 2 proposed case, including the electricity consumption of district plant equipment serving the building:
• Scenario A. If the building’s allocation of CHP-generated electricity is less than or equal to its modeled electricity consumption, no adjustment is necessary. The baseline building is charged with the energy used by its (non-CHP) systems at market rates using standard procedures.
• Scenario B. If the building’s allocation of CHP-generated electricity exceeds its modeled electricity consumption, include the amount of excess CHP electricity case as described in CHP fuel input formulas.
For the proposed design’s CHP electricity output, allocate the electricity generation to the building based on the fraction of thermal loads to the building for the DES sources that use recovered waste heat. For each DES source supplied to the building, determine the fraction of the recovered waste heat applied to that source as well as the amount serving the project building. For relatively simple DES systems, in which the recovered waste heat is used directly in the DES, and for which waste heat serves only heating loads in the connected buildings, use the formula for simple systems:
For CHP plants in which a portion of the recovered heat is used to drive absorption chillers that provide cooling through a DES chilled-water loop, or a portion of the recovered heat is used for a third, separate district energy source (e.g., if the building connects to both a steam loop and a hot-water loop), calculate the electricity generation assigned to each building using the formula for heat recovery-driven chillers.
When modeling CHP fuel input, allocate the CHP input fuel to the project building based on a proration and assignment of the total input fuel according to the results of the CHP electricity allocation described above for CHP electricity output. Use the energy cost and greenhouse gas emissions factors associated with the fuels input to the CHP. For the proposed case (all projects), calculate the CHP input fuel allocated to the building as follows:
For the baseline (scenario B in CHP electricity output only): calculate the CHP input fuel allocated to the building as follows:
The model must include CHP generator efficiencies, based on either ongoing operations (existing CHP) or design specifications (new CHP).
Path 3 Large-scale District Energy System
Path 3 provides a streamlined method for documenting improved greenhouse gas (GHG) emissions performance associated with large scale district energy systems.
Complete the baseline and proposed energy modeling consistent with the guidance for Path 1A. ASHRAE 90.1–2016, Appendix G.
Follow the additional instructions in the Large-Scale DES Calculator (uploaded in the Credit Resources section of the credit library) to demonstrate GHG emissions improvement associated with the district energy plant.
Optional: Projects may generate two sets of baseline and proposed models to separately document the greenhouse gas emissions metric using Path 1A. ASHRAE 90.1-2016 Appendix G with the large-scale district energy calculator, and the cost metric using Path 1B. ASHRAE 90.1-2016 Appendix G with ASHRAE 90.1-2022 Addendum a.
Special Situations for DES Energy Models
Service water heating
If service water is heated in full or in part by DES-supplied heat: For projects applying Path 1A or Path 3, model the energy source as purchased energy.
Projects applying Path 1B shall model the DES supplied service water heating in the Proposed building per 90.1-2022 addendum a replacing all ASHRAE 90.1-2022 Addendum a references to Section 7 mandatory and prescriptive criteria for the proposed building design with ASHRAE 90.1-2016 Section 7. The Baseline shall be modeled per 90.1-2016 Appendix G requirements.
For projects applying Path 2, model the baseline service water heating matching ASHRAE 90.1-2016 Appendix G modeling guidance for a stand-alone on-site service water heating system, and use the Path 2 guidance to model the average efficiency for the proposed design.
Heating converted to cooling
Sometimes the district or campus system heating energy supply is converted to chilled water using absorption chillers or other similar technologies to serve cooling loads. In this circumstance, the equipment that converts heating to cooling may reside within the DES itself, (i.e., DES provides cooling to the building) or within the connected buildings (i.e., DES provides heating to the building; building converts heating to cooling). When the equipment that converts DES-supplied heat into cooling is part of the LEED project’s scope of work, the project must apply either Path 1B, Path 2, or Path 3.
Other DES systems
DES also often incorporate special features, such as thermal storage, ground or surface water cooling, and waste heat recovery. These features should be incorporated into the proposed virtual plant to the greatest extent practical using the general principles presented in this guidance.
Combined Heat and Power (CHP) or other Non-Renewable Electricity Generation Systems
For projects with combined heat and power or other non-renewable electricity generation systems, amend ASHRAE 90.1-2016 G2.4.2 Annual Energy Costs as follows:
Where the proposed design includes on-site electricity generation systems other than on-site renewable energy systems, adjust the baseline and proposed model using one of the following methods:
1. No credit for on-site electricity generation:
o Model on-site electricity generation systems including all fuel inputs and associated site-recovered energy identically in the baseline design and the proposed design, OR
o Model purchased electricity instead of the on-site electricity generation. Model any site-recovered energy from the on-site electricity generation system identically in the baseline and proposed design (either crediting it towards the thermal loads for both the baseline and proposed design or ignoring the site-recovered energy contribution in both the baseline and proposed design).
2. Credit for on-site electricity generation:
Model the baseline design using purchased electricity for all regulated energy sources except HVAC heating and/or service water heating modeled in accordance with Appendix G criteria. Model the proposed design to include the proposed on-site generation system including site-recovered energy. For the cost metric, natural gas or fuel rates for both the baseline and proposed design must be modeled using the current published rates for natural gas associated with the baseline design fuel usage excluding monthly meter charges and shall not be discounted for high fuel usage associated with on-site generation equipment."
Delete:
"If claiming no credit for an upstream district energy system, apply ASHRAE 90.1-2016 requirements, which stipulate that each thermal energy source serving the building shall be modeled as purchased energy, with identical utility rates modeled in the baseline and proposed case. For the GHG emissions metric, use the GHG emissions factors for the relevant energy source.
If claiming credit for an upstream district energy system, contact USGBC to discuss the applicable modeling approach."
"Projects that are served by district energy systems (DES) may demonstrate compliance with EA Prerequisite Minimum Energy Performance and EA Credit Optimize Energy Performance by following one of the following methods.
• Path 1 ASHRAE 90.1-2016 Appendix G. No credit is documented for the purchased energy systems.
o Path 1A. ASHRAE 90.1-2016 Appendix G.
o Path 1B. ASHRAE 90.1-2016 Appendix G with ASHRAE 90.1-2022 Addendum a. (Revise the Appendix G methodology to remove the inherent penalty for DES)
• Path 2 Full DES performance accounting. Credit is documented for the purchased energy systems. The proposed design is modeled using a virtual plant consistent with the district energy system performance, and the baseline design is modeled with on-site systems from ASHRAE 90.1-2016 Appendix G for site generated thermal energy.
• Path 3 Large-scale District Energy Systems. GHG emissions savings associated with the upstream system are documented using the Large-Scale DES Calculator. No energy efficiency savings (using the cost or source energy metric) are documented for the upstream system.
The modeling path chosen by the project team may depend on the relative efficiency of the DES to which the project is connected, how much DES information is available, or whether an energy model already exists for the system. Whenever possible, incorporate system and equipment performance parameters directly into the energy simulation. Potential methods include developing efficiency curves and scheduling equipment operation and curves. Postprocessing of DES performance is acceptable if reasonable simulation methods are not available or are too onerous. All postprocessing methodologies must be fully documented.
All Paths: Scope of DES equipment inclusion
All downstream equipment must be included in the scope of EA Prerequisite Minimum Energy Performance and EA Credit Optimize Energy Performance. Downstream equipment includes heat exchangers, steam pressure reduction stations, pumps, valves, pipes, building electrical services, and controls.
Upstream equipment is included or excluded depending on the chosen path.
Path 1A. ASHRAE 90.1–2016, Appendix G
Model the proposed and baseline designs using purchased energy according to ASHRAE 90.1–2010, Appendix G.
Published purchased energy rates or conversion factors:
Energy Cost: Per ASHRAE 90.1, model the purchased energy rates for each district energy source (purchased hot water, purchased steam, or purchased chilled water) identically in the baseline and proposed design based on actual utility rates, if actual utility rates are available.
GHG Emissions: For the GHG emissions metric, if the published reference for electricity and fossil fuel GHG emission factors also reports emission factors for district energy (purchased hot water, purchased steam, or purchased chilled water), model these published emission factors for each district energy source identically in the baseline and proposed design.
Derivation of DES purchased energy rates or GHG emission factors when unpublished:
If purchased energy rates and/or GHG emission factors are not published for the district energy sources serving the project, derive these purchased energy rates and/or emission factors leveraging the electricity or fossil fuel data. For fossil fuel, use natural gas if the building does not receive fossil fuel and the district energy fuel source is unknown.
• District Chilled Water (CHW):
CHWFactor = ElectricityFactor x 0.325
• District Hot Water (HHW):
HHWFactor = FossilFuelFactor x 1.65
• District Steam Water (Steam):
SteamFactor = FossilFuelFactor x 1.85
Where:
• For the Cost Metric (See further guidance below for purchased energy rates)
o CHWFactor = Chilled water purchased energy rate ($ / unit energy)
o HHWFactor = Hot water purchased energy rate ($ / unit energy)
o SteamFactor = Steam purchased energy rate ($ / unit energy)
o ElectricityFactor = Electricity purchased energy rate ($ / unit energy)
o FossilFuelFactor = Fossil Fuel purchased energy rate ($ / unit energy)
Units of energy must be consistent throughout each equation (i.e. consistently $/kWh or $/kBtu)
• For the GHG Emissions Metric:
o CHWFactor = Chilled water GHG emissions factor
o HHWFactor = Hot water GHG emissions factor
o SteamFactor = Steam GHG emissions factor
o ElectricityFactor = Electricity GHG emissions factor
o FossilFuelFactor = Fossil Fuel GHG emissions factor
Units of each GHG emissions factor must be consistent (in weight of CO2eq emissions per unit of energy)
Additional guidance: Cost Metric ElectricityFactor and FossilFuelFactor.
For the cost metric, in a flat rate structure, in which the building cost per unit of electricity or building cost per unit of natural gas is the same throughout the year and there are no demand charges, then those flat rates become the ElectricityFactor and FossilFuelFactor for the project cost metric. If all energy rate structures are not flat, a preliminary run of the Option 1 baseline case energy model must first be completed to identify the virtual electric rate (ElectricityFactor) and fossil fuel rate (FossilFuelFactor) for the project.
To obtain the virtual fuel rate (FossilFuelFactor) when the connected building does not use fossil fuel but the DES central plant does, use a flat rate consistent with the central plant rates or the historic average local market rates.
Path 1B. ASHRAE 90.1-2016 Appendix G with ASHRAE 90.1-2022 Addendum a.
The project may apply ASHRAE 90.1-2022 Addendum a to the ASHRAE 90.1-2016 Appendix G criteria. This eliminates the inherent penalty in the ASHRAE 90.1-2016 Appendix G Performance Index Targets when modeling “purchased heat” and “purchased chilled water”. Replace all ASHRAE 90.1-2022 Addendum a references to Section 6 prescriptive criteria for the proposed building design with ASHRAE 90.1-2016 Section 6. For the baseline building design HVAC systems, the project team must exclusively reference ASHRAE 90.1-2022 with Addendum a. Free read-only versions of ASHRAE 90.1-2022 are available at https://www.ashrae.org/technical-resources/standards-and-guidelines/read....
90.1-2022 Addendum a criteria as applied to ASHRAE 90.1-2016 Appendix G:
• Model HVAC systems for the baseline building design per ASHRAE 90.1-2022 Appendix G criteria as if all heating and cooling generation equipment is on-site;
• Projects with purchased heat: Model the proposed building design using natural gas forced draft boilers that prescriptively comply with ASHRAE 90.1-2016 Section 6 in lieu of purchased heat. The number of boilers and boiler controls shall meet the requirements of ASHRAE 90.1-2022 Section G3.2.3.2 through G3.2.3.6, without exceptions. Forced draft boiler efficiencies shall be modeled per the mandatory and prescriptive requirements of ASHRAE 90.1-2016 Section 6. Boiler systems with design input exceeding 1,000,000 Btu/h may document credit for minimum turndown ratios per Table 6.5.4.1.
• Projects with purchased chilled water: Model the proposed building design using water-cooled chillers that prescriptively comply with ASHRAE 90.1-2016 Section 6 in lieu of purchased chilled water.
o Model the type and number of water-cooled electric chillers per ASHRAE 90.1-2022 Table G3.2.3.7 based on the peak coincident cooling load of baseline HVAC systems using chilled water (See 90.1-2022 Section G3.2.3.7).
o Model the chilled water (CHW) with a design supply temperature of 44 °F (7 °C) and return temperature of 56 °F (13.3 °C) (See 90.1-2022 Section G3.2.3.8)
o Model each chiller with separate condenser-water and primary chilled-water pumps interlocked to operate with the associated chiller per ASHRAE 90.1-2022 G3.2.3.11. Model the CHW loop as constant-flow primary and variable-flow secondary with the pump power of each loop modeled per 90.1-2022 Section G3.2.3.10, without exceptions. Model secondary loops with a pump motor demand of 30% of design wattage at 50% of design flow per the prescriptive criteria of ASHRAE 90.1-2016 Section 6.5.4.2. For systems with total modeled chilled water capacity exceeding 300,000 Btu/h (25 kW) utilizing DDC CHW control valves, model chilled water supply temperature reset based on valve positions until one valve is wide open or setpoint limits have been reached per ASHRAE 90.1-2016 Section 6.5.4.4.
o Model heat rejection as an axial fan cooling tower with design fan power = 40.2 gpm/hp per ASHRAE 90.1-2016 Table 6.8.1-7, and with design supply temperature and leaving water temperature determined per ASHRAE 90.1-2022 G3.2.3.11. If the total fan power for the heat rejection equipment exceeds 5 hp, model the cooling tower fans with variable-speed fan controls that reduce fan motor demand to no more than 30% of design wattage at 50% of design air volume per ASHRAE 90.1-2016 Section 6.5.11.
Path 2. Full DES performance accounting
For path 2, the energy model scope accounts for both downstream equipment and upstream equipment and requires calculation of the district energy average efficiencies using engineering analysis or monitored data or a combination of both.
Energy rates (Cost Metric)
All DES electricity and fuel rates must be identical in both the baseline and the proposed cases. Use local electricity and fuel rates as they would normally apply to the building for the energy sources under consideration. If this information is not available, use representative market rates.
Exception: For District cooling or district heating plants without cogeneration or fuel cells that operate under specific and atypical electric rate structures and actively take advantage of those rates through strategies such as load management or energy storage, use the rate structures as they apply to the DES.
Greenhouse Gas Emissions Factors
See the guidance in Further Explanation, Greenhouse Gas Emissions.
Baseline building systems
For systems with thermal energy delivered from the district energy system, model the baseline case with on-site systems per ASHRAE 90.1-2022 Addendum a criteria described above.
Proposed building plant
Model the proposed case with a virtual DES-equivalent plant. Use the same efficiencies as the entire upstream DES heating, and cooling, and combined heat and power (CHP) systems, including all distribution losses and energy use.
Equipment efficiencies, distribution losses, and distribution pumping energy may be determined using any of the following methods:
• Monitored data
• Engineering analysis
Efficiencies and losses may be determined and modeled at any level of time resolution, from hourly to annual. However, the time resolution must be sufficiently granular to capture and reasonably represent any significant time- or load-dependent interactions between systems, such as thermal storage or CHP. Monitoring and analytical methods may be combined as necessary and appropriate. Monitoring data for heating, cooling, pumping, and cogeneration may be used only if the thermal loads that are monitored represent at least 90% of the load on the campus or district plant predicted after building occupancy. Whether using monitoring or an analytical method, the methodologies must be fully documented. The following specific requirements apply.
Heating and cooling plants
Efficiencies, whether determined through monitoring or analytically, must include all operational effects, such as standby, equipment cycling, partial-load operation, internal pumping, and thermal losses.
Thermal distribution losses
Use monitored data or an engineering analysis.
• Monitored data determine the distribution losses for the DES by measuring the total thermal energy leaving the plant and comparing it with the total thermal energy used by the buildings connected to the DES. Rate the plant efficiency accordingly in the energy model:
Plant efficiency (%) x [100% – distribution loss (%)]
• An engineering analysis takes into consideration all distribution losses between the DES and the building. For distribution main losses, use a prorated amount based on load. For dedicated branch losses, use the total losses of the branch that feeds the building, including heat losses and steam trap losses. Compare the total losses with the total load of the building to get a percentage distribution loss relative to load and downgrade the plant’s efficiency accordingly in the energy model.
If thermal distribution losses are not measured or modeled, use the following default losses:
o Chilled water district cooling, 5%
o Hot water district heating, 10%
o Closed-loop steam systems, 15%
o Open-loop steam systems, 25%
For steam systems that are partially open and partially closed, prorate between the above 15% and 25% losses in accordance with the fraction of expected or actual condensate loss.
Pumping energy
Whether through monitored data or engineering analysis, determine pumping energy for the project by prorating the total pump energy of the DES by the ratio of the annual thermal load of the building to the total annual DES thermal load. Model the pump energy as auxiliary electrical load. Pumping energy must be determined or estimated where it applies.
District Energy Combined Heat and Power (CHP)
To model the proposed design virtual plant, first monitor or model the total electricity generation, fuel input, and heat recovery associated with the District Energy Combined Heat and Power (CHP):
• Determine annual electricity generation using one of the following methods:
o Monitor the total annual gross electricity generation. Also monitor the total annual parasitic loads, such as the annual electricity used for cooling the intake air for a turbine. Calculate the net annual electricity generation by subtracting all parasitic loads from the annual gross electricity generated.
o Model the generators in energy simulation software per Appendix G. Use peak electricity efficiencies and generator curves that match the installed generators. Apply measured or estimated load profiles as process loads to reflect the estimated total electric and thermal loads on the district energy CHP system. Use the total energy generated and total fuel input from this analysis. Any parasitic loads must be included in the analysis and subtracted from the annual electricity generation.
• Calculate annual fuel input using one of the following methods:
o Monitor the total annual fuel input to the generators.
o Model the generators in energy simulation software per Appendix G. Use peak electricity efficiencies and generator curves that match the installed generators.
• Calculate waste heat recovery using one of the following methods:
o Monitor the total waste heat recovered.
o Model the generators in energy simulation software per Appendix G. Use peak electricity efficiencies and generator curves that match the installed generators. Model the thermal equipment served by the CHP waste heat, such as boilers and absorption chillers, using the installed equipment capacities, efficiencies, and efficiency curves, and reflecting the total heating and cooling loads on the plant as a process load. Use the energy modeling outputs to identify the total heat recovered.
For baseline CHP electricity output, follow the general procedures described in this section for the proposed case, and adjust the results as follows depending on the results of the DES electricity allocation and the total modeled electricity use of the building in the Path 2 proposed case, including the electricity consumption of district plant equipment serving the building:
• Scenario A. If the building’s allocation of CHP-generated electricity is less than or equal to its modeled electricity consumption, no adjustment is necessary. The baseline building is charged with the energy used by its (non-CHP) systems at market rates using standard procedures.
• Scenario B. If the building’s allocation of CHP-generated electricity exceeds its modeled electricity consumption, include the amount of excess CHP electricity case as described in CHP fuel input formulas.
For the proposed design’s CHP electricity output, allocate the electricity generation to the building based on the fraction of thermal loads to the building for the DES sources that use recovered waste heat. For each DES source supplied to the building, determine the fraction of the recovered waste heat applied to that source as well as the amount serving the project building. For relatively simple DES systems, in which the recovered waste heat is used directly in the DES, and for which waste heat serves only heating loads in the connected buildings, use the formula for simple systems:
For CHP plants in which a portion of the recovered heat is used to drive absorption chillers that provide cooling through a DES chilled-water loop, or a portion of the recovered heat is used for a third, separate district energy source (e.g., if the building connects to both a steam loop and a hot-water loop), calculate the electricity generation assigned to each building using the formula for heat recovery-driven chillers.
When modeling CHP fuel input, allocate the CHP input fuel to the project building based on a proration and assignment of the total input fuel according to the results of the CHP electricity allocation described above for CHP electricity output. Use the energy cost and greenhouse gas emissions factors associated with the fuels input to the CHP. For the proposed case (all projects), calculate the CHP input fuel allocated to the building as follows:
For the baseline (scenario B in CHP electricity output only): calculate the CHP input fuel allocated to the building as follows:
The model must include CHP generator efficiencies, based on either ongoing operations (existing CHP) or design specifications (new CHP).
Path 3 Large-scale District Energy System
Path 3 provides a streamlined method for documenting improved greenhouse gas (GHG) emissions performance associated with large scale district energy systems.
Complete the baseline and proposed energy modeling consistent with the guidance for Path 1A. ASHRAE 90.1–2016, Appendix G.
Follow the additional instructions in the Large-Scale DES Calculator (uploaded in the Credit Resources section of the credit library) to demonstrate GHG emissions improvement associated with the district energy plant.
Optional: Projects may generate two sets of baseline and proposed models to separately document the greenhouse gas emissions metric using Path 1A. ASHRAE 90.1-2016 Appendix G with the large-scale district energy calculator, and the cost metric using Path 1B. ASHRAE 90.1-2016 Appendix G with ASHRAE 90.1-2022 Addendum a.
Special Situations for DES Energy Models
Service water heating
If service water is heated in full or in part by DES-supplied heat: For projects applying Path 1A or Path 3, model the energy source as purchased energy.
Projects applying Path 1B shall model the DES supplied service water heating in the Proposed building per 90.1-2022 addendum a replacing all ASHRAE 90.1-2022 Addendum a references to Section 7 mandatory and prescriptive criteria for the proposed building design with ASHRAE 90.1-2016 Section 7. The Baseline shall be modeled per 90.1-2016 Appendix G requirements.
For projects applying Path 2, model the baseline service water heating matching ASHRAE 90.1-2016 Appendix G modeling guidance for a stand-alone on-site service water heating system, and use the Path 2 guidance to model the average efficiency for the proposed design.
Heating converted to cooling
Sometimes the district or campus system heating energy supply is converted to chilled water using absorption chillers or other similar technologies to serve cooling loads. In this circumstance, the equipment that converts heating to cooling may reside within the DES itself, (i.e., DES provides cooling to the building) or within the connected buildings (i.e., DES provides heating to the building; building converts heating to cooling). When the equipment that converts DES-supplied heat into cooling is part of the LEED project’s scope of work, the project must apply either Path 1B, Path 2, or Path 3.
Other DES systems
DES also often incorporate special features, such as thermal storage, ground or surface water cooling, and waste heat recovery. These features should be incorporated into the proposed virtual plant to the greatest extent practical using the general principles presented in this guidance.
Combined Heat and Power (CHP) or other Non-Renewable Electricity Generation Systems
For projects with combined heat and power or other non-renewable electricity generation systems, amend ASHRAE 90.1-2016 G2.4.2 Annual Energy Costs as follows:
Where the proposed design includes on-site electricity generation systems other than on-site renewable energy systems, adjust the baseline and proposed model using one of the following methods:
1. No credit for on-site electricity generation:
o Model on-site electricity generation systems including all fuel inputs and associated site-recovered energy identically in the baseline design and the proposed design, OR
o Model purchased electricity instead of the on-site electricity generation. Model any site-recovered energy from the on-site electricity generation system identically in the baseline and proposed design (either crediting it towards the thermal loads for both the baseline and proposed design or ignoring the site-recovered energy contribution in both the baseline and proposed design).
2. Credit for on-site electricity generation:
Model the baseline design using purchased electricity for all regulated energy sources except HVAC heating and/or service water heating modeled in accordance with Appendix G criteria. Model the proposed design to include the proposed on-site generation system including site-recovered energy. For the cost metric, natural gas or fuel rates for both the baseline and proposed design must be modeled using the current published rates for natural gas associated with the baseline design fuel usage excluding monthly meter charges and shall not be discounted for high fuel usage associated with on-site generation equipment."
Delete:
"If claiming no credit for an upstream district energy system, apply ASHRAE 90.1-2016 requirements, which stipulate that each thermal energy source serving the building shall be modeled as purchased energy, with identical utility rates modeled in the baseline and proposed case. For the GHG emissions metric, use the GHG emissions factors for the relevant energy source.
If claiming credit for an upstream district energy system, contact USGBC to discuss the applicable modeling approach."
