An Act Relative to Green Communities
As part of Chapter 169 of the Acts of 2008, Massachusetts approved a stretch energy code concerning renewable and alternative energy efficiency in the commomvealth that may be adopted locally, The stretch energy code established energy provisions above those required by the base building code. The stretch energy code must be formally adopted by a municipality in accordance with methodologies by law. The stretch energy code as part of the 9th edition was amended effective on February 7, 2020, with a concurrency period to end August 7, 2020.
Municipalities that have adopted the stretch energy code shall use the energy efficiency requirements of this appendix as provided below. These requirements replace all previous stretch energy code requirements.
In all R-use buildings, of four stories or less above grade plane with one or more dwelling units, each dwelling unit shall comply with IECC 2018 Section R406 of 780 CMR 51.00: Massachusetts Residential Code as amended and all mandatory requirements of Chapters 13 and 51, as applicable.
All buildings over 100,000 square feet (9290 m2), and new supermarkets, laboratories and conditioned warehouses over 40,000 square feet (3716 m2) shall comply with 780 CMR 13 as amended, and shall demonstrate energy use per square foot at least 10 percent below the energy requirements of ANSI/ASHRAE/IESNA 90.1—2013 APPENDIX G (as amended by Sections C401.2, C402.1.5, C402.3, C405.3, C405.4, C405.10 and C406) Performance Rating Method on either a site or source energy basis. The additional Efficiency Package Options selected in accordance with Section C406.1 shall be included in calculating the baseline building performance value.
Exception: Exclusively R-use buildings complying with Section AA103.1 dwelling unit requirements.
New buildings not covered in Sections AA103.1 and AA103.2 shall comply with 780 CMR 13, as amended, or 780 CMR 51, as amended, based on the use and occupancy of the building.
For alterations, renovations, additions or repairs of existing buildings in these municipalities, the energy efficiency requirements of 780 CMR 13, as amended, or 780 CMR 51, as amended, shall be used as applicable based on the use and occupancy of the building.
(This appendix has been amended to conform to Massachusetts Commercial Stretch Energy Code Section AA102)
AA102 All buildings over 100,000 square feet, and new supermarkets, laboratories, and conditioned warehouses over 40,000 square feet shall comply with 780 CMR: 13.00: Energy Efficiency and shall demonstrate energy use per square foot at least 10% below the energy requirements of Appendix G on a site or source energy basis.
This building performance rating method is a modification of the Energy Cost Budget (ECB) Method in Section 11 and is intended for use in rating the energy efficiency of building designs that exceed the requirements of this standard. This appendix is provided for those wishing to use the methodology developed for this standard to quantify performance that substantially exceeds the requirements of Standard 90.1. It shall be used for evaluating the performance of all such proposed designs, including alterations and additions to existing buildings, except designs with no mechanical systems.
For the purpose of quantifying the projected Source Energy consumption of a building the Site to Source Fuel Conversion factors in Table C401.2.2 shall apply.
SITE TO SOURCE FUEL CONVERSION FACTORS
|Electricity (Grid Purchase)||2.80|
|Electricity (On-Site Solar or Wind)||1.00|
|Propane & Liquid Propane||1.01|
|Purchased District Heating |
| 1.20 |
|Purchased District Cooling||0.91|
|Fossil fuels not listed||1.1|
|Purchased Combined Heat and |
Power District Heat
- Determination of the source energy consumption and usage intensity when using purchased combined heat and power district heat shall be performed as an exceptional calculation using the Department of Energy Resources (DOER) approved Excel worksheet.
- Determination of the source energy consumption and usage intensity for heat generated by a combined heat and power system located onsite shall be performed using software meeting the requirements of ASHRAE 90.1 Section G 2.2 Simulation Program, and has an explicitly stated capability to determine both the site and source energy use intensity for combined heat and power systems without the requirement for exceptional calculations as defined in ASHRAE 90.1 Section G2.5.
This performance rating method requires conformance with the following provisions:
All requirements of Sections 5.4, 6.4, 7.4, 8.4, 9.4, and 10.4 are met, and all the requirements of the 2018 International Energy Conservation Code® (IECC®) Sections C401.2.3, C401.2.4, C402.1.5, C402.3, C405.3, C405.4, C405.10, and C406, as amended, are met. These sections contain the mandatory provisions of the standard and are prerequisites for this rating method. The improved performance of the proposed building design is calculated in accordance with provisions of this appendix using the following formula:
Percentage improvement = 100 × (Baseline building performance — Proposed building performance) / Baseline building performance
- Both the proposed building performance and the baseline building performance shall include all enduse load components, such as receptacle and process loads.
- Neither the proposed building performance nor the baseline building performance are predictions of actual energy consumption or costs for the proposed design after construction. Actual experience will differ from these calculations due to variations such as occupancy, building operation and maintenance, weather, energy use not covered by this procedure, changes in energy rates between design of the building and occupancy, and the precision of the calculation tool.
When the proposed modifications apply to less than the whole building, only parameters related to the systems to be modified shall be allowed to vary. Parameters relating to unmodified existing conditions or to future building components shall be identical for determining both the baseline building performance and the proposed building performance. Future building components shall meet the prescriptive requirements of Sections 5.5, 6.5, 7.5, 9.5, and 9.6. The proposed building envelope shall meet the requirements of the 2018 IECC Section C402.1.5.
Simulated performance shall be documented, and documentation shall be submitted to the rating authority. The information shall be submitted in a report and shall include the following:
- A brief description of the project, the key energy efficiency improvements, the simulation program used, the version of the simulation program, and the results of the energy analysis. This summary shall contain the calculated values for the baseline building performance, the proposed building performance, and the percentage improvement.
- An overview of the project that includes: the number of stories (above and below grade), the typical floor size, the uses in the building (e.g., office, cafeteria, retail, parking, etc.), the gross area of each use, and whether each use is conditioned space.
- A list of the energy-related features that are included in the design and on which the performance rating is based. This list shall document all energy features that differ between the models used in the baseline building performance and proposed building performance calculations.
- A list showing compliance for the proposed design with all the requirements of 5.4, 6.4, 7.4, 8.4, 9.4, and 10.4 (mandatory provisions) and all the requirements of the 2018 IECC Sections C401.2.3, C401.2.4, C402.1.5, C402.3, C405.3, C405.4, C405.10, and C406, as amended.
- A list identifying those aspects of the proposed design that are less stringent than the requirements of 5.5, 6.5, 7.5, 9.5, and 9.6 (prescriptive provisions).
- A table with a summary by end use of the energy cost savings in the proposed building performance.
- A site plan showing all adjacent buildings and topography which may shade the proposed building (with estimated height or number of stories).
- Building elevations and floor plans (schematic is acceptable).
- A diagram showing the thermal blocks used in the computer simulation.
- An explanation of any significant modeling assumptions.
- Backup calculations and material to support data inputs (e.g., U-factors for envelope assemblies, NFRC ratings for fenestration, end-uses identified in 1. Design Model, paragraph [a], in Table G3.1).
- Input and output report(s) from the simulation program or compliance software including a breakdown of energy usage by at least the following components: lights, internal equipment loads, service water heating equipment, space heating equipment, space cooling and heat rejection equipment, fans, and other HVAC equipment (such as pumps). The output reports shall also show the amount of unmet load hours for both the proposed design and baseline building design.
- Purchased energy rates used in the simulations.
- An explanation of any error messages noted in the simulation program output.
- For any exceptional calculation method(s) employed, document the predicted energy savings by energy type, the energy cost savings, a narrative explaining the exceptional calculation method performed, and theoretical or empirical information supporting the accuracy of the method.
- The reduction in proposed building performance associated with on-site renewable energy.
The proposed building performance and baseline building performance shall be calculated using the following:
- the same simulation program
- the same weather data
- the same energy rates
The simulation program shall be a computer-based program for the analysis of energy consumption in buildings (a program such as, but not limited to, DOE-2, BLAST, or EnergyPlus). The simulation program shall include calculation methodologies for the building components being modeled. For components that cannot be modeled by the simulation program, the exceptional calculation methods requirements in Section G2.5 shall be used.
The simulation program shall be approved by the rating authority and shall, at a minimum, have the ability to explicitly model all of the following:
- 8760 hours per year
- hourly variations in occupancy, lighting power, miscellaneous equipment power, thermostat setpoints, and HVAC system operation, defined separately for each day of the week and holidays
- thermal mass effects
- ten or more thermal zones
- part-load performance curves for mechanical equipment
- capacity and efficiency correction curves for mechanical heating and cooling equipment
- air-side economizers with integrated control
- baseline building design characteristics specified in Section G3
The simulation program shall have the ability to either (1) directly determine the proposed building performance and baseline building performance or (2) produce hourly reports of energy use by an energy source suitable for determining the proposed building performance and baseline building performance using a separate calculation engine.
The simulation program shall be capable of performing design load calculations to determine required HVAC equipment capacities and air and water flow rates in accordance with generally accepted engineering standards and handbooks (for example, ASHRAE Handbook—Fundamentals) for both the proposed design and baseline building design.
The simulation program shall be tested according to ASHRAE Standard 140, except Sections 7 and 8, and the results shall be furnished by the software provider.
The simulation program shall perform the simulation using hourly values of climatic data, such as temperature and humidity from representative climatic data, for the site in which the proposed design is to be located. For cities or urban regions with several climatic data entries, and for locations where weather data are not available, the designer shall select available weather data that best represent the climate at the construction site. The selected weather data shall be approved by the rating authority.
Site-recovered energy shall not be considered purchased energy and shall be subtracted from the proposed design energy consumption prior to calculating the proposed building performance. On-site renewable energy generated by systems included on the building permit that is used by the building shall be subtracted from the proposed design energy consumption prior to calculating the proposed building performance.
The design energy cost and baseline energy cost shall be determined using either actual rates for purchased energy or state average energy prices published by DOE's Energy Information Administration (EIA) for commercial building customers, but rates from different sources may not be mixed in the same project. Where on-site renewable energy or site-recovered energy is used, the baseline building design shall be based on the energy source used as the backup energy source or the baseline system energy source in that category if no backup energy source has been specified.
Informative Note: The above provision allows users to gain credit for features that yield load management benefits. Where such features are not present, users can simply use state average unit prices from EIA, which are updated annually and readily available on EIA's web site (http://www.eia.doe.gov/).
When the simulation program does not model a design, material, or device of the proposed design, an Exceptional Calculation Method shall be used if approved by the Rating Authority. If there are multiple designs, materials, or devices that the simulation program does not model, each shall be calculated separately and Exceptional Savings determined for each. At no time shall the total Exceptional Savings constitute more than half of the difference between the baseline building performance and the proposed building performance. All applications for approval of an exceptional method shall include:
- Step-by-step documentation of the Exceptional Calculation Method performed detailed enough to reproduce the results;
- Copies of all spreadsheets used to perform the calculations;
- A sensitivity analysis of energy consumption when each of the input parameters is varied from half to double the value assumed;
- The calculations shall be performed on a time step basis consistent with the simulation program used;
- The Performance Rating calculated with and without the Exceptional Calculation Method.
The simulation model for calculating the proposed and baseline building performance shall be developed in accordance with the requirements in Table G3.1.
Modeling Requirements for Calculating Proposed and Baseline Building Performance
|No.||Proposed Building Performance||Baseline Building Performance|
|1. Design Model|
| ||The baseline building design shall be modeled with the |
same number of floors and identical conditioned floor areaas the proposed design.
|2. Additions and Alterations|
|It is acceptable to predict performance using building models that exclude parts of the existing building provided that all of the following conditions are met: ||Same as proposed building design|
|3. Space Use Classification|
|Usage shall be specified using the building type or space type lighting classifications in accordance with Section 9.5.1 or 9.6.1. The user shall specify the space use classifications using either the building type or space type categories but shall not combine the two types of categories. More than one building type category may be used in a building if it is a mixed-use facility. If space type categories are used, the user may simplify the placement of the various space types within the building model, provided that building-total areas for each space type are accurate.||Same as proposed building design|
|Schedules capable of modeling hourly variations in occupancy, lighting power, miscellaneous equipment power, thermostat setpoints, and HVAC system operation shall be used. The schedules shall be typical of the proposed building type as determined by the designer and approved by the rating authority. |
Temperature and Humidity Schedules. Temperature andhumidity control setpoints and schedules as well as temperature control throttling range shall be the same for proposed and baseline building designs.
HVAC Fan Schedules. Schedules for HVAC fans that provideoutdoor air for ventilation shall run continuously whenever spaces are occupied and shall be cycled on and off to meet heating and cooling loads during unoccupied hours.
|Same as proposed building design |
|5. Building Envelope|
Exceptions: When whole-building air leakage testing, in accordance with ASTM 779, is specified during design and completed after construction, the proposed design air leakage rate of the building envelope shall be as measured.
|Equivalent dimensions shall be assumed for each exterior envelope component type as in the proposed design; i.e., the total gross area of exterior walls shall be the same in the proposed and baseline building designs. The same shall be true for the areas of roofs, floors, and doors, and the exposed perimeters of concrete slabs on grade shall also be the same in the proposed and baseline building designs. The following additional requirements shall apply to the modeling of the baseline building design: |
|Proposed building interior lighting shall conform to the requirements of the 2018 IECC Section C405.3, as amended. Proposed building exterior lighting shall conform to the requirements of the 2018 IECC Section C405.4, as amended. Lighting power in the proposed design shall be determined as follows: || |
|7. Thermal Blocks—HVAC Zones Designed|
|Where HVAC zones are defined on HVAC design drawings, each HVAC zone shall be modeled as a separate thermal block. |
Exception: Different HVAC zones may be combined to create a single thermal block or identical thermal blocks to which multipliers are applied, provided that all of the following conditions are met:
|Same as proposed building design|
|8. Thermal Blocks—HVAC Zones Not Designed|
|Where the HVAC zones and systems have not yet been designed, thermal blocks shall be defined based on similar internal load densities, occupancy, lighting, thermal and space temperature schedules, and in combination with the following guidelines: ||Same as proposed building design|
|9. Thermal Blocks—Multifamily Residential Buildings|
|Residential spaces shall be modeled using at least one thermal block per dwelling unit, except that those units facing the same orientations may be combined into one thermal block. Corner units and units with roof or floor loads shall only be combined with units sharing these features.||Same as proposed building design|
|10. HVAC Systems|
|The HVAC system type and all related performance parameters in the proposed design, such as equipment capacities and efficiencies, shall be determined as follows: ||The HVAC system(s) in the baseline building design shall be of the type and description specified in Section G3.1.1, shall meet the general HVAC system requirements specified in Section G3.1.2, and shall meet any system-specific requirements in Section G3.1.3 that are applicable to the baseline HVAC system type(s). |
If the proposed design includes computer room humidification then the computer room humidification system, schedules, and setpoints in the baseline building design shall be the same as in the proposed design.
For systems serving computer rooms, the baseline shall not have reheat for the purpose of dehumidification.
Fossil fuel systems shall be modeled using natural gas as their fuel source.
Exception: For fossil fuel systems where natural gas is not available for the proposed building site as determined by the rating authority, the baseline HVAC system(s) shall be modeled using propane as their fuel source.
|11. Service Hot-Water Systems|
|The service hot-water system type and all related performance parameters, such as equipment capacities and efficiencies, in the proposed design shall be determined as follows: ||The service hot-water system in the baseline building design shall conform with the following conditions: |
|12. Receptacle and Other Loads|
|Receptacle and process loads, such as those for office and other equipment, shall be estimated based on the building type or space type category and shall be assumed to be identical in the proposed and baseline building designs, except as specifically authorized by the rating authority. These loads shall be included in simulations of the building and shall be included when calculating the baseline building performance and proposed building performance.||Other systems, such as motors covered by Section 10, and miscellaneous loads shall be modeled as identical to those in the proposed design including schedules of operation and control of the equipment. Where there are specific efficiency requirements listed in Sections 5 through 10, these systems or components shall be modeled as having the lowest efficiency allowed by those requirements. Where no efficiency requirements exist, power and energy rating or capacity of the equipment shall be identical between the baseline building and the proposed design with the following exception: variations of the power requirements, schedules, or control sequences of the equipment modeled in the baseline building from those in the proposed design shall be allowed by the rating authority based upon documentation that the equipment installed in the proposed design represents a significant verifiable departure from documented conventional practice. The burden of this documentation is to demonstrate that accepted conventional practice would result in baseline building equipment different from that installed in the proposed design. Occupancy and occupancy schedules shall not be changed.|
|13. Modeling Limitations to the Simulation Program|
|If the simulation program cannot model a component or system included in the proposed design explicitly, substitute a thermodynamically similar component model that can approximate the expected performance of the component that cannot be modeled explicitly.||Same as proposed building design|
|14. Exterior Conditions|
| ||Same as proposed building design|
|15. Distribution Transformers|
|Low-voltage dry-type distribution transformers shall be modeled if the transformers in the proposed design exceed the efficiency required in Table 8.4.4.||Low-voltage dry-type distribution transformers shall be modeled only if the proposed building transformers exceed the efficiency requirements of Table 8.4.4. If modeled, the efficiency requirements from Table 8.4.4 shall be used. The ratio of the capacity to peak electrical load of the transformer shall be the same as the ratio in the proposed design.|
|16. Solar PV and EV Ready Requirements|
|17. Mandatory C406 Requirements in Massachusetts|
|Same as baseline building.||The baseline building shall conform to the 2018 IECC Section C406 "Additional Efficiency Measures," as amended.|
HVAC systems in the baseline building design shall be based on usage, number of floors, conditioned floor area, and climate zone as specified in Table G3.1.1-3 and shall conform with the system descriptions in Table G3.1.1-4. For systems 1, 2, 3, 4, 9, 10, 11, 12, and 13 each thermal block shall be modeled with its own HVAC system. For systems 5, 6, 7, and 8 each floor shall be modeled with a separate HVAC system. Floors with identical thermal blocks can be grouped for modeling purposes.
- Use additional system type(s) for nonpredominant conditions (i.e., residential/nonresidential or heating source) if those conditions apply to more than 20,000 ft2 of conditioned floor area.
- If the baseline HVAC system type is 5, 6, 7, 8, 9, 10, 11, 12, or 13 use separate single-zone systems conforming with the requirements of System 3 or System 4 (depending on building heating source) for any spaces that have occupancy or process loads or schedules that differ significantly from the rest of the building. Peak thermal loads that differ by 10 Btu/h•ft2 or more from the average of other spaces served by the system or schedules that differ by more than 40 equivalent full-load hours per week from other spaces served by the system are considered to differ significantly. Examples where this exception may be applicable include, but are not limited to, natatoriums and continually occupied security areas. This exception does not apply to computer rooms.
- For laboratory spaces in a building having a total laboratory exhaust rate greater than 5000 cfm, use a single system of type 5 or 7 serving only those spaces. The lab exhaust fan shall be modeled as constant horsepower reflecting constant-volume stack discharge with outdoor air bypass.
- For kitchens with a total exhaust hood airflow rate greater than 5,000 cfm, use system type 5 or 7 with a demand ventilation system on 75% of the exhaust air. The system shall reduce exhaust and replacement air system airflow rates by 50% for one half of the kitchen occupied hours in the baseline design. If the proposed design uses demand ventilation the same airflow rate schedule shall be used. The maximum exhaust flow rate allowed for the hood or hood section shall meet the requirements of Section 18.104.22.168.3 for the numbers and types of hoods and appliances provided for the in the proposed design.
- Thermal zones designed with heating only systems in the proposed design, serving storage rooms, stairwells, vestibules, electrical/mechanical rooms, and restrooms not exhausting or transferring air from mechanically cooled thermal zones in the proposed design shall use System type 9 or 10 in the baseline building design.
- If the baseline HVAC system type is 9 or 10, all spaces that are mechanically cooled in the proposed building design shall be assigned to a separate baseline system determined by using the area and heating source of the mechanically cooled spaces.
- Computer rooms in buildings with a total computer room peak cooling load >3,000,000 Btu/h kW or a total computer room peak cooling load >600,000 Btu/h where the baseline HVAC system type is 7 or 8 shall use System 11. All other computer rooms shall use System 3 or 4.
- For hospitals, depending on building type, use System 5 or 7 in all climate zones.
Baseline Building Vertical Fenestration Percentage of Gross Above-Grade-Wall Area
|Building Area Typesa||Baseline Building Gross Above-Grade-Wall Area|
|Hotel/motel (≤75 rooms)||24%|
|Hotel/motel (>75 rooms)||34%|
|Office (≤5000 ft2)||19%|
|Office (5000 to 50,000 ft2)||31%|
|Office (>50,000 ft2)||40%|
|Restaurant (quick service)||34%|
|Restaurant (full service)||24%|
|Retail (stand alone)||11%|
|Retail (strip mall)||20%|
|School (secondary and university)||22%|
- In cases where both a general building area type and a specific building area type are listed, the specific building area type shall apply.
|Building Area Type||Baseline Heating Method|
|Automotive facility||Gas storage water heater|
|Convention center||Electric resistance storage water heater|
|Courthouse||Electric resistance storage water heater|
|Dining: Bar lounge/leisure||Gas storage water heater|
|Dining: Cafeteria/fast food||Gas storage water heater|
|Dining: Family||Gas storage water heater|
|Dormitory||Gas storage water heater|
|Exercise center||Gas storage water heater|
|Fire station||Gas storage water heater|
|Gymnasium||Gas storage water heater|
|Health-care clinic||Gas storage water heater|
|Hospital||Gas storage water heater|
|Hotel||Gas storage water heater|
|Library||Electric resistance storage water heater|
|Manufacturing facility||Gas storage water heater|
|Motel||Gas storage water heater|
|Motion picture theater||Electric resistance storage water heater|
|Multifamily||Gas storage water heater|
|Museum||Electric resistance storage water heater|
|Office||Electric resistance storage water heater|
|Parking garage||Electric resistance storage water heater|
|Penitentiary||Gas storage water heater|
|Performing arts theater||Gas storage water heater|
|Police station||Electric resistance storage water heater|
|Post office||Electric resistance storage water heater|
|Religious building||Electric resistance storage water heater|
|Retail||Electric resistance storage water heater|
|School/university||Gas storage water heater|
|Sports arena||Gas storage water heater|
|Town hall||Electric resistance storage water heater|
|Transportation||Electric resistance storage water heater|
|Warehouse||Electric resistance storage water heater|
|Workshop||Gas storage water heater|
|All Others||Gas storage water heater|
Baseline HVAC System Types
|Building Type||Climate Zones 3b, 3c, and 4—8||Climate Zones 1—3a|
|Residential||System 1—PTAC||System 2—PTHP|
|Public assembly <120,000 ft2||System 3—PSZ-AC||System 4—PSZ-HP|
|Public assembly ≥120,000 ft2||System 12—SZ-CV-HW||System 13—SZ-CV-ER|
|Nonresidential and 3 floors or fewer and <25,000 ft2||System 3—PSZ-AC||System 4—PSZ-HP|
|Nonresidential and 4 or 5 Floors and <25,000 ft2 or 5 floors or fewer and 25,000 ft2 to 150,000 ft2||System 5—Packaged VAV with reheat||System 6—Packaged VAV with PFP boxes|
|Nonresidential and more than 5 floors or >150,000 ft2||System 7—VAV with reheat||System 8—VAV with PFP boxes|
|Heated-only storage||System 9—Heating and ventilation||System 10—Heating and ventilation|
|Retail and 2 floors or fewer||System 3—PSZ-AC||System 4—PSZ-HP|
- Residential building types include dormitory, hotel, motel, and multifamily. Residential space types include guest rooms, living quarters, private living space, and sleeping quarters. Other building and space types are considered nonresidential.
- Where attributes make a building eligible for more than one baseline system type, use the predominant condition to determine the system type for the entire building except as noted in Exception (1) to Section G3.1.1.
- For laboratory spaces in a building having a total laboratory exhaust rate greater than 5000 cfm, use a single system of type 5 or 7 serving only those spaces.
- For hospitals, depending on building type, use System 5 or 7 in all climate zones.
- Public assembly building types include houses of worship, auditoriums, movie theaters, performance theaters, concert halls, arenas, enclosed stadiums, ice rinks, gymnasiums, convention centers, exhibition centers, and natatoriums.
Baseline System Descriptions
|System No.||System Type||Fan Control||Cooling Type||Heating Type|
|1. PTAC||Packaged terminal air conditioner||Constant volume||Direct expansion||Hot-water fossil fuel boiler|
|2. PTHP||Packaged terminal heat pump||Constant volume||Direct expansion||Electric heat pump|
|3. PSZ-AC||Packaged rooftop air conditioner||Constant volume||Direct expansion||Fossil fuel furnace|
|4. PSZ-HP||Packaged rooftop heat pump||Constant volume||Direct expansion||Electric heat pump|
|5. Packaged VAV with Reheat||Packaged rooftop VAV with reheat||VAV||Direct expansion||Hot-water fossil fuel boiler|
|6. Packaged VAV with PFP Boxes||Packaged rooftop VAV with parallel fan power boxes and reheat||VAV||Direct expansion||Electric resistance|
|7. VAV with Reheat||VAV with reheat||VAV||Chilled water||Hot-water fossil fuel boiler|
|8. VAV with PFP Boxes||VAV with parallel fan-powered boxes and reheat||VAV||Chilled water||Electric resistance|
|9. Heating and Ventilation||Warm air furnace, gas fired||Constant volume||None||Fossil fuel furnace|
|10. Heating and Ventilation||Warm air furnace, electric||Constant volume||None||Electric resistance|
|11. SZ—VAV||Single-zone VAV||VAV||Chilled water||See note.|
|12. SZ-CV-HW||Single zone||Constant volume||Chilled water||Hot-water fossil fuel boiler|
|13. SZ-CV-ER||Single zone||Constant volume||Chilled water||Electric resistance|
- For purchased chilled water and purchased heat, see G22.214.171.124.
- Where the proposed design heating source is electric or other, the heating type shall be electric resistance. Where the proposed design heating source is fossil fuel, fossil/electric hybrid, or purchased heat, the heating type shall be hot-water fossil fuel boiler.
For systems using purchased hot water or steam, the heating source shall be modeled as purchased hot water or steam in both the proposed and baseline building designs. Hot water or steam costs shall be based on actual utility rates, and on-site boilers, electric heat, and furnaces shall not be modeled in the baseline building design.
For systems using purchased chilled water, the cooling source shall be modeled as purchased chilled water in both the proposed and baseline building designs. Purchased chilled water costs shall be based on actual utility rates, and on-site chillers and direct expansion equipment shall not be modeled in the baseline building design.
G126.96.36.199 Baseline HVAC System Requirements for Systems Utilizing Purchased Chilled Water and/or Purchased Heat
If the proposed building design uses purchased chilled water and/or purchased heat, the following modifications to the Baseline HVAC System Types in Table G3.1.1-4 shall be used:
If the proposed building design uses purchased heat, but does not use purchased chilled water, then Tables G3.1.1-3 and G3.1.1-4 shall be used to select the Baseline HVAC System Type and purchased heat shall be substituted for the Heating Type in Table G3.1.1-4. The same heating source shall be used in the proposed and baseline building design.
If the proposed building design uses purchased chilled water, but does not use purchased heat, then Tables G3.1.1-3 and G3.1.1-4 shall be used to select the Baseline HVAC System Type, with the modifications listed below:
- Purchased chilled water shall be substituted for the Cooling Types in Table G3.1.1-4.
- System 1 and 2 shall be constant-volume fan-coil units with fossil fuel boiler(s).
- System 3 and 4 shall be constant-volume single-zone air handlers with fossil fuel furnace(s).
- System 7 shall be used in place of System 5.
- System 8 shall be used in place of System 6.
If the proposed building design uses purchased chilled water and purchased heat, then Tables G3.1.1-3 and G3.1.1-4 shall be used to select the Baseline HVAC System Type, with the following modifications:
All on-site distribution pumps shall be modeled in both the baseline and proposed designs.
The air leakage rate of the building envelope (I75Pa) at a pressure differential of 0.3 in. H2O shall be converted to appropriate units for the simulation program using one of the following formulas:
For methods describing infiltration as a function of floor area,
For methods describing infiltration as a function of exterior wall area,
When using the measured air leakage rate of the building envelope at a pressure differential of 0.3 in. H2O for the proposed design, the air leakage rate shall be calculated as follows:
I75Pa = air leakage rate of the building envelope expressed in cfm/ft2 at a fixed building pressure differential of 0.3 in. H2O, or 1.57 psf
Q = volume of air in cfm flowing through the whole-building envelope when subjected to an indoor/ outdoor pressure differential of 0.3 in. H2O, or 1.57 psf, in accordance with ASTM E779
S = total area of the envelope air pressure boundary (expressed in ft2), including the lowest floor, any below- or above-grade walls, and roof (or ceiling) (including windows and skylights), separating the interior conditioned space from the unconditioned environment measured
IFLR = adjusted air leakage rate (expressed in cfm/ft2) of the building envelope at a reference wind speed of 10 mph and the total gross floor area
AFLR = total gross floor area, ft2
IEW = adjusted air leakage rate (expressed in cfm/ft2) of the building envelope at a reference wind speed of 10 mph and the above ground exterior wall area
AEW = total above-grade exterior wall area, ft2
Exception: A multizone airflow model alternate method to model building envelope infiltration may be used provided the following criteria are met:
- If the calculations are made independently of the energy simulation program, the proposed method must comply with Section G2.5.
- The method for converting the air infiltration rate of the building envelope at 0.3 in. H2O, or 1.57 psf, to the appropriate units for the simulation program is fully documented and submitted to the rating authority for approval.
HVAC systems in the baseline building design shall conform with the general provisions in this section.
All HVAC equipment in the baseline building design shall be modeled at the minimum efficiency levels, both part load and full load, in accordance with Section 6.4. Chillers shall use Path A efficiencies as shown in Table 6.8.1-3. Where efficiency ratings include supply fan energy, the efficiency rating shall be adjusted to remove the supply fan energy. For Baseline HVAC Systems 1, 2, 3, 4, 5, and 6, calculate the minimum COPnfcooling and COPnfheating using the equation for the applicable performance rating as indicated in Tables 6.8.1-1 through 6.8.1-4. Where a full- and part-load efficiency rating is provided in Tables 6.8.1-1 through 6.8.1-4, the full-load equation below shall be used:
where COPnfcooling and COPnfheating are the packaged HVAC equipment cooling and heating energy efficiency, respectively, to be used in the baseline building, which excludes supply fan power, and Q is the AHRI-rated cooling capacity in Btu/h.
The equipment capacities (i.e. system coil capacities) for the baseline building design shall be based on sizing runs for each orientation (per Table G3.1, No. 5a) and shall be oversized by 15% for cooling and 25% for heating, i.e., the ratio between the capacities used in the annual simulations and the capacities determined by the sizing runs shall be 1.15 for cooling and 1.25 for heating.
Weather conditions used in sizing runs to determine baseline equipment capacities shall be based either on hourly historical weather files containing typical peak conditions or on design days developed using 99.6% heating design temperatures and 1% dry-bulb and 1% wet-bulb cooling design temperatures.
Unmet load hours for the proposed design or baseline building designs shall not exceed 300 (of the 8760 hours simulated). Alternatively, unmet load hours exceeding these limits may be accepted at the discretion of the rating authority provided that sufficient justification is given indicating that the accuracy of the simulation is not significantly compromised by these unmet loads.
If the HVAC system in the proposed design has a preheat coil and a preheat coil can be modeled in the baseline system, the baseline system shall be modeled with a preheat coil controlled in the same manner as the proposed design.
Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours. If the supply fan is modeled as cycling and fan energy is included in the energy-efficiency rating of the equipment, fan energy shall not be modeled explicitly. Supply, return, and/or exhaust fans will remain on during occupied and unoccupied hours in spaces that have health and safety mandated minimum ventilation requirements during unoccupied hours.
Minimum ventilation system outdoor air intake flow shall be the same for the proposed and baseline building designs.
- When modeling demand-control ventilation in the proposed design when its use is not required by Section 6.3.2(q) or Section 188.8.131.52.
- When designing systems in accordance with Standard 62.1, Section 6.2, "Ventilation Rate Procedure," reduced ventilation airflow rates may be calculated for each HVAC zone in the proposed design with a zone air distribution effectiveness (Ez) > 1.0 as defined by Table 6-2 in Standard 62.1. Baseline ventilation airflow rates in those zones shall be calculated using the proposed design Ventilation Rate Procedure calculation with the following change only. Zone air distribution effectiveness shall be changed to (Ez) = 1.0 in each zone having a zone air distribution effectiveness (Ez) > 1.0. Proposed design and baseline design Ventilation Rate Procedure calculations, as described in Standard 62.1, shall be submitted to the rating authority to claim credit for this exception.
- If the minimum outdoor air intake flow in the proposed design is provided in excess of the amount required by the rating authority or building official then the baseline building design shall be modeled to reflect the greater of that required by the rating authority or building official and will be less than the proposed design.
- For baseline systems serving only laboratory spaces that are prohibited from recirculating return air by code or accreditation standards, the baseline system shall be modeled as 100% outdoor air.
Outdoor air economizers shall not be included in baseline HVAC Systems 1, 2, 9, and 10. Outdoor air economizers shall be included in baseline HVAC Systems 3 through 8, and 11, 12, and 13 based on climate as specified in Table G184.108.40.206.
Exceptions: Economizers shall not be included for systems meeting one or more of the exceptions listed below.
- Systems that include gas-phase air cleaning to meet the requirements of Section 6.1.2 in Standard 62.1. This exception shall be used only if the system in the proposed design does not match the building design.
- Where the use of outdoor air for cooling will affect supermarket open refrigerated casework systems. This exception shall only be used if the system in the proposed design does not use an economizer. If the exception is used, an economizer shall not be included in the baseline building design.
- Systems that serve computer rooms complying with Section G220.127.116.11.1.
Climate Conditions under which Economizers are Included for Comfort Cooling for Baseline Systems 3 through 8 and 11, 12, and 13
|1a, 1b, 2a, 3a, 4a||NR|
Systems that serve computer rooms that are HVAC System 3 or 4 shall not have an economizer. Systems that serve computer rooms that are HVAC System 11 shall include an integrated water-side economizer meeting the requirements of Section 18.104.22.168 in the baseline building design. If the simulation software cannot model an integrated water-side economizer, then an air-side economizer shall be modeled.
The high-limit shutoff shall be a dry-bulb fixed switch with setpoint temperatures in accordance with the values in Table G22.214.171.124.
Economizer High-Limit Shutoff
|Climate Zone||High-Limit Shutoff|
|1b, 2b, 3b, 3c, 4b,||75°F|
|4c, 5b, 5c, 6b, 7, 8|
|2a, 3a, 4a||28 Btu/lb|
|5a, 6a, 7a||70°F|
System design supply airflow rates for the baseline building design shall be based on a supply-air-to-room-air temperature difference of 20°F or the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is greater. If return or relief fans are specified in the proposed design, the baseline building design shall also be modeled with fans serving the same functions and sized for the baseline system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger.
- For systems serving laboratory spaces, use a supply-air-to-room-air temperature difference of 17°F or the required ventilation air or makeup air, whichever is greater.
- If the proposed design HVAC design airflow rate based on latent loads is greater than the design airflow rate based on sensible loads, then the same supply-air-to-room-air humidity ratio difference (gr/lb) used to calculate the proposed design airflow shall be used to calculate design airflow rates for the baseline building design.
System design supply airflow rates for the baseline building design shall be based on the temperature difference between a supply air temperature setpoint of 105°F and the design space heating temperature setpoint, the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is greater. If the Proposed Building Design includes a fan(s) sized and controlled to provide non-mechanical cooling, the baseline building design shall include a separate fan to provide non-mechanical cooling, sized and controlled the same as the proposed building design.
System fan electrical power for supply, return, exhaust, and relief (excluding power to fan-powered VAV boxes) shall be calculated using the following formulas:
For Systems 1 and 2,
For Systems 3 through 8, and 11, 12, and 13,
For Systems 9 and 10 (supply fan),
For Systems 9 and 10 (nonmechanical cooling fan if required by Section G126.96.36.199.2)
Pfan = electric power to fan motor (watts)
bhp = brake horsepower of baseline fan motor from Table G188.8.131.52
fan motor efficiency = the efficiency from Table 10.8-2 for the next motor size greater than the bhp using a totally enclosed fan cooled motor at 1800 rpm.
CFMs = the baseline system maximum design supply fan airflow rate in cfm
CFMnmc = the baseline nonmechanical cooling fan airflow in cfm
Baseline Fan Brake Horsepower
|Baseline Fan Motor Brake Horsepower|
|Constant Volume |
|Variable Volume |
|Variable Volume |
|CFMs • 0.00094 + A||CFMs • 0.0013 + A||CFMs × 0.00062 + A|
- Where A is calculated according to Section 184.108.40.206.1 using the pressure drop adjustment from the proposed building design and the design flow rate of the baseline building system.
- Do not include pressure drop adjustments for evaporative coolers or heat recovery devices that are not required in the baseline building system by Section G220.127.116.11.
The calculated system fan power shall be distributed to supply, return, exhaust, and relief fans in the same proportion as the proposed design.
Exhaust air energy recovery shall be modeled for the baseline building design in accordance with Section 18.104.22.168.
Baseline HVAC systems shall conform with provisions in this section, where applicable, to the specified baseline system types as indicated in section headings.
Electric air-source heat pumps shall be modeled with electric auxiliary heat. The systems shall be controlled with multistage space thermostats and an outdoor air thermostat wired to energize auxiliary heat only on the last thermostat stage and when outdoor air temperature is less than 40°F.
The boiler plant shall use the same fuel as the proposed design and shall be natural draft, except as noted in Section G22.214.171.124. The baseline building design boiler plant shall be modeled as having a single boiler if the baseline building design plant serves a conditioned floor area of 15,000 ft2 or less and as having two equally sized boilers for plants serving more than 15,000 ft2. Boilers shall be staged as required by the load.
Hot-water design supply temperature shall be modeled as 180°F and design return temperature as 130°F.
Hot-water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 180°F at 20°F and below, 150°F at 50°F and above, and ramped linearly between 180°F and 150°F at temperatures between 20°F and 50°F.
The baseline building design hot-water pump power shall be 19 W/gpm. The pumping system shall be modeled as primary-only with continuous variable flow. Hot-water systems serving 120,000 ft2 or more shall be modeled with variable-speed drives, and systems serving less than 120,000 ft2 shall be modeled as riding the pump curve.
Exception: The pump power for systems using purchased heat shall be 14 W/gpm.
Piping losses shall not be modeled in either the proposed or baseline building designs for hot-water, chilled-water, or steam piping.
Electric chillers shall be used in the baseline building design regardless of the cooling energy source, e.g. direct fired absorption or absorption from purchased steam. The baseline building design's chiller plant shall be modeled with chillers having the number and type as indicated in Table G126.96.36.199 as a function of building peak cooling load.
Exception: Systems using purchased chilled water shall be modeled in accordance with Section G188.8.131.52.
Type and Number of Chillers
|Building Peak |
|Number and Type of Chiller(s)|
|≤300 tons||1 water-cooled screw chiller|
|>300 tons,||2 water-cooled screw chillers sized equally|
|≥600 tons||2 water-cooled centrifugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally|
Chilled-water design supply temperature shall be modeled at 44°F and return water temperature at 56°F.
Chilled-water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 44°F at 80°F and above, 54°F at 60°F and below, and ramped linearly between 44°F and 54°F at temperatures between 80°F and 60°F.
Exception: If the baseline chilled-water system serves a computer room HVAC system, the supply chilled-water temperature shall be reset higher based on the HVAC system requiring the most cooling; i.e., the chilled-water setpoint is reset higher until one cooling-coil valve is nearly wide open. The maximum reset chilled-water supply temperature shall be 54°F.
The baseline building design pump power shall be 22 W/gpm. Chilled-water systems with a cooling capacity of 300 tons or more shall be modeled as primary/secondary systems with variable-speed drives on the secondary pumping loop. Chilled-water pumps in systems serving less than 300 tons cooling capacity shall be modeled as a primary/secondary systems with secondary pump riding the pump curve. For computer room systems using System 11 with an integrated water-side economizer, the baseline building design primary chilled-water pump power shall be increased 5 W/gpm for flow associated with the water-side economizer.
Exception: The pump power for systems using purchased chilled water shall be 16 W/gpm.
The heat rejection device shall be an axial fan open circuit cooling tower with variable-speed fan control and shall meet the performance requirements of Table 6.8.1-7. Condenser water design supply temperature shall be calculated using the cooling tower approach to the 0.4% evaporation design wetbulb temperature as generated by the formula below, with a design temperature rise of 10°F.
where WB is the 0.4% evaporation design wet-bulb temperature in °F; valid for wet bulbs from 55°F to 90°F.
The tower shall be controlled to maintain a 70°F leaving water temperature where weather permits, floating up to leaving water temperature at design conditions. The baseline building design condenser-water pump power shall be 19 W/gpm. For computer room systems using System 11 with an integrated water-side economizer, the baseline building design condenser water-pump power shall be increased 5 W/gpm for flow associated with the water-side economizer. Each chiller shall be modeled with separate condenser water and chilled-water pumps interlocked to operate with the associated chiller.
The air temperature for cooling shall be reset higher by 5°F under the minimum cooling load conditions.
Minimum volume setpoints for VAV reheat boxes shall be 30%of zone peak airflow, the minimum outdoor airflow rate or the airflow rate required to comply with applicable codes or accreditation standards, whichever is larger.
Exception: Systems serving laboratory spaces shall reduce the exhaust and makeup air volume during unoccupied periods to the largest of 50% of zone peak airflow, the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards.
Fans in parallel VAV fan-powered boxes shall be sized for 50% of the peak design primary air (from the VAV air-handling unit) flow rate and shall be modeled with 0.35 W/cfm fan power. Minimum volume setpoints for fan-powered boxes shall be equal to 30% of peak design primary airflow rate or the rate required to meet the minimum outdoor air ventilation requirement, whichever is larger. The supply air temperature setpoint shall be constant at the design condition.
VAV system supply fans shall have variable-speed drives, and their part-load performance characteristics shall be modeled using either Method 1 or Method 2 specified in Table G184.108.40.206.
|Method 1—Part-Load Fan Power Data|
|Fan Part-Load Ratio||Fraction of Full-Load Power|
|Method 2—Part-Load Fan Power Equation|
Pfan = 0.0013 + 0.1470 × PLRfan + 0.9506 × (PLRfan)2 — 0.0998 × (PLRfan)3
Pfan = fraction of full-load fan power and
PLRfan = fan part-load ratio (current L/s/design L/s).
Computer room equipment schedules shall be modeled as a constant fraction of the peak design load per the following monthly schedule:
Month 1, 5, 9—25%
Month 2, 6, 10—50%
Month 3, 7, 11—75%
Month 4, 8, 12—100%
Minimum volume setpoint shall be 50% of the maximum design airflow rate, the minimum ventilation outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is larger.
Fan volume shall be reset from 100% airflow at 100% cooling load to minimum airflow at 50% cooling load. Supply air temperature setpoint shall be reset from minimum supply air temperature at 50% cooling load and above to space temperature at 0% cooling load. In heating mode supply air temperature shall be modulated to maintain space temperature, and fan volume shall be fixed at the minimum airflow.
If the proposed design HVAC system(s) have humidistatic controls, then the baseline building design shall use mechanical cooling for dehumidification and shall have reheat available to avoid overcooling. When the baseline building design HVAC system does not comply with any of the exceptions in Section 220.127.116.11, then only 25% of the system reheat energy shall be included in the baseline building performance. The reheat type shall be the same as the system heating type.