Heads up: There are no amended sections in this chapter.

(This is a normative appendix and is part of this standard).

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 does NOT offer an alternative compliance path for minimum standard compliance; that is the intent of Section 11, Energy Cost Budget Method. Rather, 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.
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. 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

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.
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:
  1. 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.
  2. 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.
  3. 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.
  4. 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).
  5. 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).
  6. A table with a summary by end use of the energy cost savings in the proposed building performance.
  7. A site plan showing all adjacent buildings and topography which may shade the proposed building (with estimated height or number of stories).
  8. Building elevations and floor plans (schematic is acceptable).
  9. A diagram showing the thermal blocks used in the computer simulation.
  10. An explanation of any significant modeling assumptions.
  11. 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).
  12. 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.
  13. Purchased energy rates used in the simulations.
  14. An explanation of any error messages noted in the simulation program output.
  15. 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.
  16. 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:
  1. the same simulation program
  2. the same weather data
  3. 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:
  1. 8760 hours per year
  2. 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
  3. thermal mass effects
  4. ten or more thermal zones
  5. part-load performance curves for mechanical equipment
  6. capacity and efficiency correction curves for mechanical heating and cooling equipment
  7. air-side economizers with integrated control
  8. 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.
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:
  1. Step-by-step documentation of the Exceptional Calculation Method performed detailed enough to reproduce the results;
  2. Copies of all spreadsheets used to perform the calculations;
  3. A sensitivity analysis of energy consumption when each of the input parameters is varied from half to double the value assumed;
  4. The calculations shall be performed on a time step basis consistent with the simulation program used;
  5. 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.

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

No. Proposed Building Performance Baseline Building Performance
1. Design Model  
  1. The simulation model of the proposed design shall be consistent with the design documents, including proper accounting of fenestration and opaque envelope types and areas; interior lighting power and controls; HVAC system types, sizes, and controls; and service water heating systems and controls. All end-use load components within and associated with the building shall be modeled, including, but not limited to, exhaust fans, parking garage ventilation fans, snow-melt and freeze-protection equipment, facade lighting, swimming pool heaters and pumps, elevators and escalators, refrigeration, and cooking. Where the simulation program does not specifically model the functionality of the installed system, spreadsheets or other documentation of the assumptions shall be used to generate the power demand and operating schedule of the systems.
  2. All conditioned spaces in the proposed design shall be simulated as being both heated and cooled even if no heating or cooling system is to be installed.

    Exception: Spaces using Baseline System types 9 and 10 shall not be simulated with mechanical cooling.

  3. When the performance rating method is applied to buildings in which energy-related features have not yet been designed (e.g., a lighting system), those yet-to-be-designed features shall be described in the proposed design exactly as they are defined in the baseline building design. Where the space classification for a space is not known, the space shall be categorized as an office space.
The baseline building design shall be modeled with the same number of floors and identical conditioned floor area as 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:
  1. Work to be performed in excluded parts of the building shall meet the requirements of Sections 5 through 10.
  2. Excluded parts of the building are served by HVAC systems that are entirely separate from those serving parts of the building that are included in the building model.
  3. Design space temperature and HVAC system operating setpoints and schedules on either side of the boundary between included and excluded parts of the building are essentially the same.
  4. If a declining block or similar utility rate is being used in the analysis, and the excluded and included parts of the building are on the same utility meter, the rate shall reflect the utility block or rate for the building plus the addition.
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
4. Schedules  
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 and humidity 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 provide outdoor 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.
Exceptions:
  1. Where no heating and/or cooling system is to be installed, and a heating or cooling system is being simulated only to meet the requirements described in this table, heating and/or cooling system fans shall not be simulated as running continuously during occupied hours but shall be cycled on and off to meet heating and cooling loads during all hours.
  2. HVAC fans shall remain on during occupied and unoccupied hours in spaces that have health- and safety-mandated minimum ventilation requirements during unoccupied hours.
  3. HVAC fans shall remain on during occupied and unoccupied hours in systems primarily serving computer rooms.
Same as proposed building design
Exceptions:
  1. Setpoints and schedules for HVAC systems that automatically provide occupant thermal comfort via means other than directly controlling the air dry-bulb and wet-bulb temperature may be allowed to differ, provided that equivalent levels of occupant thermal comfort are demonstrated via the methodology in Section 5.2.3 of ASHRAE Standard 55, "Elevated Air Speed," or Appendix D of Standard 55, "Computer Program for Calculation of PMV-PPD."
  2. Schedules may be allowed to differ between proposed design and baseline building design when necessary to model nonstandard efficiency measures, provided that the revised schedules have the approval of the rating authority. Measures that may warrant use of different schedules include, but are not limited to, automatic lighting controls, automatic natural ventilation controls, automatic demand control ventilation controls, and automatic controls that reduce service water heating loads. In no case shall schedules differ where the controls are manual (e.g., manual operation of light switches or manual operation of windows).
5. Building Envelope  
  1. All components of the building envelope in the proposed design shall be modeled as shown on architectural drawings or as built for existing building envelopes.

    Exceptions: The following building elements are permitted to differ from architectural drawings.

    1. All uninsulated assemblies (e.g., projecting balconies, perimeter edges of intermediate floor stabs, concrete floor beams over parking garages, roof parapet) shall be separately modeled using either of the following techniques:
      1. Separate model of each of these assemblies within the energy simulation model.
      2. Separate calculation of the U-factor for each of these assemblies. The U-factors of these assemblies are then averaged with larger adjacent surfaces using an area-weighted average method. This average U-factor is modeled within the energy simulation model.

        Any other envelope assembly that covers less than 5% of the total area of that assembly type (e.g., exterior walls) need not be separately described, provided that it is similar to an assembly being modeled. If not separately described, the area of an envelope assembly shall be added to the area of an assembly of that same type with the same orientation and thermal properties.

    2. Exterior surfaces whose azimuth orientation and tilt differ by less than 45 degrees and are otherwise the same may be described as either a single surface or by using multipliers.
    3. The exterior roof surface shall be modeled using the aged solar reflectance and thermal emittance determined in accordance with Section 5.5.3.1.1(a). Where aged test data are unavailable, the roof surface may be modeled with a reflectance of 0.30 and a thermal emittance of 0.90.
    4. Manual fenestration shading devices, such as blinds or shades, shall be modeled or not modeled, the same as in the baseline. Automatically controlled fenestration shades or blinds shall be modeled. Permanent shading devices, such as fins, overhangs, and light shelves, shall be modeled.
    5. Automatically controlled dynamic glazing may be modeled. Manually controlled dynamic glazing shall use the average of the minimum and maximum SHGC and VT.
  2. Infiltration shall be modeled using the same methodology, air leakage rate, and adjustments for weather and building operation in both the proposed design and the baseline design. These adjustments shall be made for each simulation time step and must account for but not be limited to weather conditions and HVAC system operation, including strategies that are intended to positively pressurize the building. The air leakage rate of the building envelope (I75Pa) at a fixed building pressure differential of 0.3 in. H2O shall be 0.4 cfm/ft2. The air leakage rate of the building envelope shall be converted to appropriate units for the simulation program using one of the methods in Section G3.1.1.4.

    Exception: When whole-building air leakage testing, in accordance with ASTM E779, 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:
  1. Orientation. The baseline building performance shall be generated by simulating the building with its actual orientation and again after rotating the entire building 90, 180, and 270 degrees, then averaging the results. The building shall be modeled so that it does not shade itself.

    Exceptions:

    1. If it can be demonstrated to the satisfaction of the program evaluator that the building orientation is dictated by site considerations.
    2. Buildings where the vertical fenestration area on each orientation varies by less than 5%.
  2. Opaque Assemblies. Opaque assemblies used for new buildings, existing buildings, or additions shall conform with the following common, lightweight assembly types and shall match the appropriate assembly maximum U-factors in Tables 5.5-1 through 5.5-8:
  3. Vertical Fenestration Areas. For building area types included in Table G3.1.1-1, vertical fenestration areas for new buildings and additions shall equal that in Table G3.1.1-1 based on gross above-grade exterior wall area. Where a building has multiple building area types, each type shall use the values in the table. The vertical fenestration shall be distributed on each face of the building in the same proportion as in the proposed design. For building areas not shown in Table G3.1.1-1, vertical fenestration areas for new buildings and additions shall equal that in the proposed design or the maximum allowed in Tables 5.5-1 through 5.5-8, whichever is smaller, and shall be distributed on each face of the building in the same proportions in the proposed design. The fenestration area for an existing building shall equal the existing fenestration area prior to the proposed work and shall be distributed on each face of the building in the same proportions as the existing building. For portions of those tables where there are no SHGC requirements, the SHGC shall be equal to that determined in accordance with Section C3.6(c). The VT shall be equal to that determined in accordance with Section C3.6(c).
  4. Vertical Fenestration Assemblies. Fenestration for new buildings, existing buildings, and additions shall comply with the following:
  5. Skylights and Glazed Smoke Vents. Skylight area shall be equal to that in the proposed building design or the maximum allowed in Tables 5.5-1 through 5.5-8, whichever is smaller. If the skylight area of the proposed building design is greater than the maximum area allowed in Tables 5.5-1 through 5.5-8, baseline skylight area shall be decreased by an identical percentage in all roof components in which skylights are located to reach the maximum allowed in Tables 5.5-1 through 5.5-8. Skylight orientation and tilt shall be the same as in the proposed building design. Skylight U-factor and SHGC properties shall match the appropriate requirements in s 5.5-1 through 5.5-8.
  6. Roof Solar Reflectance and Thermal Emittance. The exterior roof surfaces shall be modeled with a solar reflectance and thermal emittance as required in Section 5.5.3.1.1(a). All other roofs, including roofs exempted from the requirements in Section 5.5.3.1.1, shall be modeled using a solar reflectance of 0.30 and a thermal emittance of 0.90.
  7. Roof Albedo. All roof surfaces shall be modeled with a reflectivity of 0.30.
6. Lighting  
Lighting power in the proposed design shall be determined as follows:
  1. Where a complete lighting system exists, the actual lighting power for each thermal block shall be used in the model.
  2. Where a lighting system has been designed, lighting power shall be determined in accordance with Sections 9.1.3 and 9.1.4.
  3. Where lighting neither exists nor is specified, lighting power shall be determined in accordance with the Building Area Method for the appropriate building type.
  4. Lighting system power shall include all lighting system components shown or provided for on the plans (including lamps and ballasts and task and furniture-mounted fixtures).

    Exception: For multifamily dwelling units, hotel/motel guest rooms, and other spaces in which lighting systems are connected via receptacles and are not shown or provided for on building plans, assume identical lighting power for the proposed and baseline building designs in the simulations.

  5. Lighting power for parking garages and building facades shall be modeled.
  6. The lighting schedules in the proposed building design shall reflect the mandatory automatic lighting control requirements in Section 9.4.1 (e.g., programmable controls or occupancy sensors).

    Exception: Automatic daylighting controls required by Section 9.4.1 shall be modeled directly in the proposed building design or through schedule adjustments determined by a separate daylighting analysis approved by the rating authority.

  7. Automatic lighting controls included in the proposed building design but not required by Section 9.4.1 may be modeled directly in the building simulation or be modeled in the building simulation through schedule adjustments determined by a separate analysis approved by the authority having jurisdiction. As an alternative to modeling such lighting controls, the proposed building design lighting power may be reduced by the sum of all additional allowances per Section 9.6.3 and Table 9.6.3, which are calculated individually as the lighting power under control multiplied by cf, where cf is the appropriate control factor given in Table 9.6.3 corresponding to the space type and the lighting controls designed to be used.
  1. Lighting power in the baseline building design shall be determined using the same categorization procedure (Building Area Method or Space-by-Space Method) and categories as the proposed design with lighting power set equal to the maximum allowed for the corresponding method and category in Section 9.2. Additional interior lighting power for nonmandatory controls allowed under Section 9.6.3 shall not be included in the baseline building design.
  2. Mandatory automatic lighting controls required by Section 9.4.1 shall be modeled the same as the proposed building design.
7. Thermal BlocksHVAC 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:

  1. The space use classification is the same throughout the thermal block.
  2. All HVAC zones in the thermal block that are adjacent to glazed exterior walls face the same orientation or their orientations vary by less than 45 degrees.
  3. All of the zones are served by the same HVAC system or by the same kind of HVAC system.
Same as proposed building design
8. Thermal BlocksHVAC 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:
  1. Separate thermal blocks shall be assumed for interior and perimeter spaces. Interior spaces shall be those located greater than 15 ft from an exterior wall. Perimeter spaces shall be those located within 15 ft of an exterior wall.
  2. Separate thermal blocks shall be assumed for spaces adjacent to glazed exterior walls; a separate zone shall be provided for each orientation, except that orientations that differ by less than 45 degrees may be considered to be the same orientation. Each zone shall include all floor area that is 15 ft or less from a glazed perimeter wall, except that floor area within 15 ft of glazed perimeter walls having more than one orientation shall be divided proportionately between zones.
  3. Separate thermal blocks shall be assumed for spaces having floors that are in contact with the ground or exposed to ambient conditions from zones that do not share these features.
  4. Separate thermal blocks shall be assumed for spaces having exterior ceiling or roof assemblies from zones that do not share these features.
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:
  1. Where a complete HVAC system exists, the model shall reflect the actual system type using actual component capacities and efficiencies.
  2. Where an HVAC system has been designed, the HVAC model shall be consistent with design documents. Mechanical equipment efficiencies shall be adjusted from actual design conditions to the standard rating conditions specified in Section 6.4.1 if required by the simulation model. Where efficiency ratings include supply fan energy, the efficiency rating shall be adjusted to remove the supply fan energy from the efficiency rating in the baseline building design. The equations in Section G3.1.2.1 shall not be used in the proposed building. The proposed building HVAC system shall be modeled using manufacturers' full- and part-load data for the HVAC system without fan power.
  3. Where no heating system exists or no heating system has been specified, the system characteristics shall be identical to the system modeled in the baseline building design.
  4. Where no cooling system exists or no cooling system has been specified, the cooling system shall be identical to the system modeled in the baseline building design.

    Exception to (d): Spaces using baseline HVAC system types 9 and 10.

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:
  1. Where a complete service hot-water system exists, the proposed design shall reflect the actual system type using actual component capacities and efficiencies.
  2. Where a service hot-water system has been specified, the service hot-water model shall be consistent with design documents.
  3. Where no service hot-water system exists or has been specified but the building will have service hot-water loads, a service hot-water system shall be modeled that matches the system in the baseline building design and serves the same hot-water loads.
  4. For buildings that will have no service hot-water loads, no service hot-water system shall be modeled.
  5. Where a combined system has been specified to meet both space heating and service water heating loads, the proposed design shall reflect the actual system type using actual component capacities and efficiencies.
The service hot-water system in the baseline building design shall conform with the following conditions:
  1. Where the complete service hot-water system exists, the baseline building design shall be as specified in Table G3.1.1-2 using the actual component capacities.
  2. Where a new service hot-water system has been specified, the heating method shall be as specified in Table G3.1.1-2. The system shall be sized according to the provisions of Section 7.4.1 and the equipment shall match the minimum efficiency requirements in Section 7.4.2.
  3. Where no service hot-water system exists or has been specified but the building will have service hot-water loads, a service water system(s) using the heating method as specified in Table G3.1.1-2 and matching minimum efficiency requirements of Section 7.4.2 shall be assumed and modeled identically in the proposed and baseline building designs.
  4. For buildings that will have no service hot-water loads, no service hot-water heating shall be modeled.
  5. Where a combined system has been specified to meet both space heating and service water heating loads, the baseline building system shall use separate systems meeting the minimum efficiency requirements applicable to each system individually.
  6. For large, 24-hour-per-day facilities that meet the prescriptive criteria for use of condenser heat recovery systems described in Section 6.5.6.2, a system meeting the requirements of that section shall be included in the baseline building design regardless of the exceptions to Section 6.5.6.2.

    Exception: If a condenser heat recovery system meeting the requirements described in Section 6.5.6.2 cannot be modeled, the requirement for including such a system in the actual building shall be met as a prescriptive requirement in accordance with Section 6.5.6.2, and no heat-recovery system shall be included in the proposed or baseline building designs.

  7. Service hot-water energy consumption shall be calculated explicitly based upon the volume of service hot water required and the entering makeup water and the leaving service hot-water temperatures. Entering water temperatures shall be estimated based upon the location. Leaving temperatures shall be based upon the end-use requirements.
  8. Where recirculation pumps are used to ensure prompt availability of service hot water at the end use, the energy consumption of such pumps shall be calculated explicitly.
  9. Service water loads and usage shall be the same for both the baseline building design and the proposed design and shall be documented by the calculation procedures described in Section 7.2.1.

    Exceptions:

    1. Service hot-water usage can be demonstrated to be reduced by documented water conservation measures that reduce the physical volume of service water required. Examples include low-flow shower heads. Such reduction shall be demonstrated by calculations.
    2. Service hot-water energy consumption can be demonstrated to be reduced by reducing the required temperature of service mixed water, by increasing the temperature, or by increasing the temperature of the entering makeup water. Examples include alternative sanitizing technologies for dishwashing and heat recovery to entering makeup water. Such reduction shall be demonstrated by calculations.
    3. Service hot-water usage can be demonstrated to be reduced by reducing the hot fraction of mixed water to achieve required operational temperature. Examples include shower or laundry heat recovery to incoming cold-water supply, reducing the hot-water fraction required to meet required mixed-water temperature. Such reduction shall be demonstrated by calculations.
  10. Gas storage water heaters shall be modeled using natural gas as their fuel source.

    Exception: Where natural gas is not available for the proposed building site, as determined by the rating authority, gas storage water heaters shall be modeled using propane as their fuel source.

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  
  1. Shading by Adjacent Structures and Terrain. The effect that structures and significant vegetation or topographical features have on the amount of solar radiation being received by a structure shall be adequately reflected in the computer analysis. All elements whose effective height is greater than their distance from a proposed building and whose width facing the proposed building is greater than one-third that of the proposed building shall be accounted for in the analysis.
  2. Ground Temperatures for Below-Grade Wall and Basement Floor Heat-Loss Calculations. It is acceptable to use either an annual average ground temperature or monthly average ground temperatures for calculation of heat loss through below-grade walls and basement floors.
  3. Water Main Temperatures for Service Water Heating Calculations. It is acceptable to use either an annual water main supply temperature or monthly average water main supply temperatures for calculating service water heating. If annual or monthly water main supply temperatures are not available from the local water utility, annual average ground temperatures may be used.
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.
HVAC systems in the baseline building design shall be based on usage, number of floors, and 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.

Exceptions:

  1. 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.
  2. 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.
  3. 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.
  4. 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 6.5.7.1.3 for the numbers and types of hoods and appliances provided for the in the proposed design.
  5. 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.
  6. 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.
  7. 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.
  8. For hospitals, depending on building type, use System 5 or 7 in all climate zones.

TABLE G3.1.1-1 Baseline Building Vertical Fenestration Percentage of Gross Above-Grade-Wall Area

Building Area Typesa Baseline Building Gross Above-Grade-Wall Area
Grocery Store 7%
Healthcare (outpatient) 21%
Hospital 27%
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 (primary) 22%
School (secondary and university) 22%
Warehouse (nonrefrigerated) 6%

a. In cases where both a general building area type and a specific building area type are listed, the specific building area type shall apply.

TABLE G3.1.1-2 Baseline Service Hot-Water System

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

TABLE G3.1.1-3 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

Notes:

1. 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.

2. 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.

3. 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.

4. For hospitals, depending on building type, use System 5 or 7 in all climate zones.

5. 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.

G3.1.1-4 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

Notes:

1. For purchased chilled water and purchased heat, see G3.1.1.3.

2. 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.
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:
  1. Purchased chilled water shall be substituted for the Cooling Types in Table G3.1.1-4.
  2. System 1 and 2 shall be constant-volume fan-coil units with fossil fuel boiler(s).
  3. System 3 and 4 shall be constant-volume single-zone air handlers with fossil fuel furnace(s).
  4. System 7 shall be used in place of System 5.
  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:
  1. Purchased heat and purchased chilled water shall be substituted for the Heating Types and Cooling Types in Table G3.1.1-4.
  2. System 1 shall be constant-volume fan-coil units.
  3. System 3 shall be constant-volume single-zone air handlers.
  4. System 7 shall be used in place of System 5.
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,

IFLR = 0.112 × I75Pa × S/AFLR

For methods describing infiltration as a function of exterior wall area,

IEW = 0.112 × I75Pa × S/AEW

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 = Q/S

where

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 E 779
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:

  1. If the calculations are made independently of the energy simulation program, the proposed method must comply with Section G2.5.
  2. 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:

COPnfcooling = 7.84E-8 × EER × Q + 0.338 × EER

COPnfcooling = —0.0076 × SEER2 + 0.3796 × SEER

COPnfheating = 1.48E-7 × COP47 × Q + 1.062 × COP47
(applies to heat-pump heating efficiency only)

COPnfheating = —0.0296 × HSPF2 + 0.7134 × HSPF

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.

EER, SEER, COP, and HSPF shall be at AHRI test conditions. Fan energy shall be modeled separately according to Section G3.1.2.10.

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.

Exceptions:

  1. When modeling demand-control ventilation in the proposed design when its use is not required by Section 6.3.2(q) or Section 6.4.3.10.
  2. 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.
  3. 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.
  4. 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 G3.1.2.7.

Exceptions: Economizers shall not be included for systems meeting one or more of the exceptions listed below.

  1. 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.
  2. 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.
  3. Systems that serve computer rooms complying with Section G3.1.2.7.1.

TABLE G3.1.2.7 Climate Conditions under which Economizers are Included for Comfort Cooling for Baseline Systems 3 through 8 and 11, 12, and 13

Climate Zone Conditions
1a, 1b, 2a, 3a, 4a NR
Others Economizer Included

Note: NR means that there is no conditioned building floor area for which economizers are included for the type of zone and climate.

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 waterside economizer meeting the requirements of Section 6.5.1.2 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 G3.1.2.8.

TABLE G3.1.2.8 Economizer High-Limit Shutoff

Climate Zone High-Limit Shutoff
1b, 2b, 3b, 3c, 4b, 4c, 5b, 5c, 6b, 7, 8 75°F
2a, 3a, 4a 28 Btu/lb
5a, 6a, 7a 70°F
Others 65°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.

Exceptions:

  1. 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.
  2. 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,

Pfan = CFMs × 0.3

For Systems 3 through 8, and 11, 12, and 13,

Pfan = bhp × 746/fan motor efficiency

For Systems 9 and 10 (supply fan),

Pfan = CFMs × 0.3

For Systems 9 and 10 (nonmechanical cooling fan if required by Section G3.1.2.9.2)

Pfan = CFMnmc × 0.054

where

Pfan = electric power to fan motor (watts)
bhp = brake horsepower of baseline fan motor from Table G3.1.2.10
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

TABLE G3.1.2.10 Baseline Fan Brake Horsepower

Baseline Fan Motor Brake Horsepower
Constant Volume
Systems 3—4
Variable Volume
Systems 5—8
Variable Volume
System 11
CFMs • 0.00094 + A CFMs • 0.0013 + A CFMs • 0.00062 + A

Notes:

  1. Where A is calculated according to Section 6.5.3.1.1 using the pressure drop adjustment from the proposed building design and the design flow rate of the baseline building system.
  2. Do not include pressure drop adjustments for evaporative coolers or heat recovery devices that are not required in the baseline building system by Section G3.1.2.10.
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 6.5.6.1.
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 G3.1.1.1. 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 G3.1.3.7 as a function of building peak cooling load.

Exception: Systems using purchased chilled water shall be modeled in accordance with Section G3.1.1.3.

TABLE G3.1.3.7 Type and Number of Chillers

Building Peak Cooling Load Number and Type of Chiller(s)
≤300 tons 1 water-cooled screw chiller
>300 tons,
<600 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 wet-bulb temperature as generated by the formula below, with a design temperature rise of 10°F.

Approach10°F Range = 25.72 — (0.24 × WB)

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 G3.1.3.15.

TABLE G3.1.3.15 Part-Load Performance for VAV Fan Systems

Method 1—Part-Load Fan Power Data
Fan Part-Load Ratio Fraction of Full-Load Power
0.00 0.00
0.10 0.03
0.20 0.07
0.30 0.13
0.40 0.21
0.50 0.30
0.60 0.41
0.70 0.54
0.80 0.68
0.90 0.83
1.00 1.00
Method 2—Part-Load Fan Power Equation
Pfan = 0.0013 + 0.1470 × PLRfan + 0.9506 × (PLRfan)2 — 0.0998 × (PLRfan)3
where

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 6.5.2.3, 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.
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