Heads up: There are no amended sections in this chapter.
The building Energy Cost Budget Method is an alternative to the prescriptive provisions of this standard. It may be employed for evaluating the compliance of all proposed designs except designs with no mechanical system.
When the building permit being sought applies to less than the whole building, only the calculation parameters related to the systems to which the permit applies shall be allowed to vary. Parameters relating to unmodified existing conditions or to future building components shall be identical for both the energy cost budget and the design energy cost calculations. Future building components shall meet the prescriptive requirements of Sections 5.5, 6.5, 7.5, and either 9.5 or 9.6.
For new buildings or additions, the building Energy Cost Budget Method results shall not be submitted for building permit approval to the authority having jurisdiction prior to submittal for approval of the building envelope design.

Compliance with Section 11 will be achieved if

  1. all requirements of Sections 5.4, 6.4, 7.4, 8.4, 9.4, 10.4, and Section 6.7 are met;
  2. the design energy cost, as calculated in Section 11.5, does not exceed the energy cost budget as calculated by the simulation program described in Section 11.4;
  3. the energy efficiency level of components specified in the building design meet or exceed the efficiency levels used to calculate the design energy cost; and
  4. In new buildings 25,000 square feet and greater, the building envelope shall comply with either:

    1. Section 5.5, "Prescriptive Building Envelope Option," or
    2. An envelope performance factor shall be calculated in accordance with Appendix C of this standard, and buildings shall comply with one of the following:

      1. For multifamily, hotel/motel and dormitory building area types, the margin by which the proposed envelope performance factor exceeds the base envelope performance factor shall not be greater than 15%. For compliance with this requirement, the base envelope performance factor shall be calculated using metal framing operable windows. In buildings with window area accounting for 40% or more of the gross wall area, the SHGC of the vertical fenestration on east and west oriented façade may be reduced by the following multiplier to account for the permanent site shading from existing buildings or infrastructure.

        MWest = 0.l8 + 0.33/WWR

        MEast = 0.35 + 0.26/WWR

        Where:

        MWest = SHGC multiplier for the West façade

        MEast = SHGC multiplier for the East façade

        WWR = the ratio of proposed vertical fenestration area to the gross wall area in consistent units

        The multiplier may be applied to the rated SHGC of the vertical fenestration which has at least 50% of the area located directly opposite of the shading surfaces and no higher from the street level than the difference between the shading surface height and the shading surface distance from the façade. Orientation must be determined following Section 5.5.4.5, Fenestration Orientation.

      2. For all other building area types, the margin by which the proposed envelope performance factor exceeds the base envelope performance factor shall be not greater than 7%. For compliance with this requirement, the base envelope performance factor shall be calculated using metal framing fixed windows.
      3. For mixed-use buildings, the margin shall be calculated as the gross wall areaweighted average of items (i) and (ii) above

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 or BLAST). For components that cannot be modeled by the simulation program, the exceptional calculation methods requirements in Section 11.4.5 shall be used.

The simulation program shall be approved by the adopting authority and shall, at a minimum, have the ability to explicitly model all of the following:

  1. A minimum of 8760 hours per year.
  2. Hourly variations in occupancy, lighting power, miscellaneous equipment power, thermostat set points, 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 mechanical cooling equipment.
  7. Air-side economizer and fluid economizer with integrated control.
  8. The budget building design characteristics specified in Section 11.4.5.

The simulation program shall have the ability to either

  1. directly determine the design energy cost and energy cost budget or
  2. produce hourly reports of energy use by energy source suitable for determining the design energy cost and energy cost budget 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 Section 6.4.2 for both the proposed design and the budget building design.
The simulation program shall be tested according to ASHRAE Standard 140, except for 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 city 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. Such selected weather data shall be approved by the authority having jurisdiction.
Site-recovered energy shall not be considered purchased energy and shall be subtracted from the proposed design energy consumption prior to calculating the design energy cost. On-site renewable energy, generated by systems included on the building permit, and used directly by the building shall be subtracted from the proposed design energy consumption prior to calculating the design energy cost. The reduction in design energy cost associated with on-site renewable energy shall be no more than 5% of the calculated energy cost budget.
The design energy cost and energy cost budget shall be determined using rates for purchased energy (such as electricity, gas, oil, propane, steam, and chilled water) that are approved by the adopting authority. Where on-site renewable energy or site-recovered energy is used, the budget building design shall be based on the energy source used as the backup energy source, or electricity if no backup energy source has been specified. Where the proposed design includes electricity generated from sources other than on-site renewable energy, the baseline design shall include the same generation system, excluding its site-recovered energy.

The design energy cost and energy cost budget shall be calculated using

  1. the same simulation program,
  2. the same weather data, and
  3. the same purchased energy rates.

When the simulation program does not model a design, material, or device, the authority having jurisdiction may approve an exceptional calculation method to be used to demonstrate compliance with Section 11. Applications for approval of an exceptional method to include theoretical and empirical information verifying the method's accuracy shall include documentation to demonstrate that the exceptional calculation method and results

  1. make no change in any input parameter values specified by this standard and the adopting authority,
  2. provide input and output documentation that facilitates the enforcement agency's review and meets the formatting and content required by the adopting authority, and
  3. are supported with instructions for using the method to demonstrate that the energy cost budget and design energy cost required by Section 11 are met.

The simulation model for calculating the design energy cost and the energy cost budget shall be developed in accordance with the requirements in Table 11.5.1.

Table 11.5.1 Modeling Requirements for Calculating Design Energy Cost and Energy Cost Budget
Proposed Design (Column A) Budget Building Design (Column B)
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 area; interior lighting power and controls; HVAC system types, sizes, and controls; and service water-heating systems and controls.
  2. All conditioned spaces in the proposed design shall be simulated as being both heated and cooled, even if no cooling or heating system is being installed. Temperature and humidity control set points and schedules, as well as temperature control throttling range, shall be the same for proposed design and baseline building design.
  3. When the Energy Cost Budget 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 so that they minimally comply with applicable mandatory and prescriptive requirements from Sections 5 through 10. Where the space classification for a building is not known, the building shall be categorized as an office building.
The budget building design shall be developed by modifying the proposed design as described in this table. Except as specifically instructed in this table, all building systems and equipment shall be modeled identically in the budget building design and proposed design.
2. Additions and Alterations
It is acceptable to demonstrate compliance using building models that exclude parts of the existing building, provided all of the following conditions are met:
  1. Work to be performed under the current permit application 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 set points and schedules on either side of the boundary between included and excluded parts of the building are identical.
  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 design.
3. Space Use Classification
The building area type or space type classifications shall be chosen in accordance with Section 9.5.1 or 9.6.1. The user or designer shall specify the space use classifications using either the building area type or space type categories but shall not combine the two types of categories within a single permit application. More than one building area type category may be used for a building if it is a mixed-use facility. Same as proposed design.
4. Schedules
The schedule types listed in Section 11.4.1.1(b) shall be required input. Temperature control set points and schedules shall be in accordance with the rules of the department for the applicable space types, unless as determined by the designer and approved by the authority having jurisdiction. Required schedules shall be identical for the proposed design and budget building design. Same as proposed design.
Temperature and Humidity Schedules. Temperature and humidity control set points and schedules as well as temperature control throttling range shall be the same for the proposed design and baseline design.
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.
5. Building Envelope
All components of the building envelope in the proposed design shall be modeled as shown on architectural drawings or as installed for existing building envelopes. Opaque portions of the curtain wall shall use the default U-factors in Table 5.5.3, unless an alternative method is approved by the department.
Exceptions: The following building elements are permitted to differ from architectural drawings.
  1. Any building 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 its U-factor is similar to an assembly being modeled. If not separately described, the area of a building envelope assembly must be added to the area of the adjacent assembly of that same type. The U-factors of these assemblies shall be averaged with larger adjacent surfaces using an area-weighted average method. When the total area of penetrations from through-the-wall mechanical equipment or equipment listed in Table 6.8.1-4 exceeds 1% of the opaque above-grade wall area, the mechanical equipment penetration area shall be calculated as a separate wall assembly with a default U-factor of 0.5. Where mechanical equipment has been tested in accordance with testing standards approved by the authority having jurisdiction, the mechanical equipment penetration area may be calculated as a separate wall assembly with the U-factor as determined by such test.
  2. Exterior surfaces whose azimuth orientation and tilt differ by no more 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 shall be modeled with a solar reflectance of 0.30 and a thermal emittance of 0.90.
  4. Manually operated fenestration shading devices, such as blinds or shades, shall not be modeled. Permanent shading devices, such as fins, overhangs, and lightshelves, shall be modeled.
The budget building design shall have identical conditioned floor area and identical exterior dimensions and orientations as the proposed design, except as follows:
  1. Opaque assemblies, such as roof, floors, doors, and walls, shall be modeled as having the same heat capacity as the proposed design but with the minimum U-factor required in Section 5.5 for new buildings or additions and Section 5.1.3 for alterations.
  2. 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 the same as the proposed design.
  3. No shading projections are to be modeled; fenestration shall be assumed to be flush with the wall or roof. If the fenestration area for new buildings or additions exceeds the maximum allowed by Section 5.5.4.2, the area shall be reduced proportionally along each exposure until the limit set in Section 5.5.4.2 is met. If the vertical fenestration area facing west or east of the proposed design exceeds the area limit set in Section 5.5.4.5 then the energy cost budget shall be generated by simulating the budget building design with its actual orientation and again after rotating the entire budget building design 90, 180, and 270 degrees and then averaging the results. Fenestration U-factor shall be equal to the criteria from Tables 5.5-4‡ through 5.5-6‡ for the appropriate climate, and the SHGC shall be equal to the criteria from Tables 5.5-4‡ through 5.5-6‡ for the appropriate climate. 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). The fenestration model for building envelope alterations shall reflect the limitations on area, U-factor, and SHGC as described in Section 5.1.3.
Exceptions: When trade-offs are made between an addition and an existing building, as described in the exception to Section 4.2.1.2, the building envelope assumptions for the existing building in the budget building design shall reflect existing conditions prior to any revisions that are part of this permit.
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 no lighting exists or is specified, lighting power shall be determined in accordance with the Building Area Method for the appropriate building area type.
  4. Lighting system power shall include all lighting system components shown or provided for on plans (including lamps, ballasts, task fixtures, and furniture-mounted fixtures). For dwelling units, hotel/motel guest rooms, and dormitory-living quarters in which lighting systems include plug-in light fixtures that are not shown or provided for on design documents, assume identical lighting power for the proposed design and baseline building design in the simulations.
  5. The lighting schedules in the proposed 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 design or through schedule adjustments determined by a daylighting analysis approved by the building official.
  6. Automatic lighting controls included in the proposed design but not required by Section 9.4.1 may be modeled using the following methods for each luminaire control:
    1. Daylight controls shall 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. Modeling and schedule adjustments shall separately account for primary sidelighted areas, secondary side-lighted areas, and toplighted areas.
    2. For automatic controls other than daylighting, the proposed design lighting power may be reduced for each luminaire under control by dividing the rated lighting power of the luminaire by the factor (1 +Σ CF), where Σ CF indicates the sum of all applicable control factors (CF) per Section 9.6.3 and Table 9.6.3.
  1. Lighting power in the budget 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 budget building design.
  2. Power for fixtures not included in the lighting power calculation shall be modeled identically in the proposed design and budget building design.
  3. Mandatory automatic lighting controls required by Section 9.4.1 shall be modeled the same as the proposed 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.
Exceptions: Different HVAC zones may be combined to create a single thermal block or identical thermal blocks to which multipliers are applied, provided 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 and glazed semiexterior walls face the same orientation or their orientations are within 45 degrees of each other.
  3. All of the zones are served by the same HVAC system or by the same kind of HVAC system.
Same as proposed 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:
  1. Separate thermal blocks shall be assumed for interior and perimeter spaces. Interior spaces shall be those located more than 15 ft from an exterior wall or semiexterior wall. Perimeter spaces shall be those located closer than 15 ft from an exterior wall or semiexterior wall. A separate thermal zone does not need to be modeled for areas adjacent to semiexterior walls that separate semiheated space from conditioned space.
  2. Separate thermal blocks shall be assumed for spaces adjacent to glazed exterior walls or glazed semiexterior walls; a separate zone shall be provided for each orientation, except that orientations that differ by no more 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 roof assemblies from zones that do not share these features.
Same as proposed design.
9. Thermal Blocks—Multifamily Residential Buildings
Residential spaces shall be modeled using one thermal block per space except that those 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 design.
10. HVAC Systems
The HVAC 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 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 budget building design. The equations in Section 11.5.2 shall not be used in the proposed design. The proposed design HVAC system shall be modeled using manufacturers' full- and partload data for the HVAC system without fan power.
  3. Where no heating system exists or no heating system has been specified, the heating system shall be modeled as fossil fuel. The system characteristics shall be identical to the system modeled in the budget building design.
  4. Where no cooling system exists or no cooling system has been specified, the cooling system shall be modeled as an air-cooled single-zone system, one unit per thermal block. The system characteristics shall be identical to the system modeled in the budget building design.
The HVAC system type and related performance parameters for the budget building design shall be determined from Figure 11.5.2, the system descriptions in Table 11.5.2-1 and accompanying notes, and in accord with rules specified in Section 11.5.2(a) through 11.5.2(k).
11. Service Water-Heating Systems
The service water-heating 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 water-heating system exists, the model shall reflect the actual system type using actual component capacities and efficiencies.
  2. Where a service water-heating system has been designed, the service water-heating model shall be consistent with design documents.
  3. Where no service water-heating system exists or is specified, no service water heating shall be modeled.
The service water-heating system type in the budget building design shall be identical to the proposed design. The service water-heating system performance of the budget building design shall meet the requirements of Sections 7.4 and 7.5.
Exceptions:
  1. If the service water-heating system type is not listed in Table 7.8, it shall be identical to the proposed design.
  2. Where Section 7.5 applies, the boiler shall be split into a separate space-heating boiler and hot-water heater with efficiency requirements set to the least efficient allowed.
  3. For 24-hour 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. 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 design or budget building design.
Service water loads and use shall be the same for both the proposed design and baseline building design and typical of the proposed building type.
12. Miscellaneous Loads
Receptacle, motor, and process loads shall be modeled and estimated based on the building area type or space type category and shall be assumed to be identical in the proposed and budget building designs. These loads shall be included in simulations of the building and shall be included when calculating the energy cost budget and design energy cost. All end-use load components within and associated with the building shall be modeled, unless specifically excluded by Sections 13 and 14 of Table 11.5.1, including but not limited to exhaust fans, parking garage ventilation fans, exterior building lighting, swimming pool heaters and pumps, elevators and escalators, refrigeration equipment, and cooking equipment. Receptacle, motor, and process loads shall be modeled and estimated based on the building area type or space type category and shall be assumed to be identical in the proposed design and budget building design. These loads shall be included in simulations of the building and shall be included when calculating the energy cost budget and design energy cost. All end-use load components within and associated with the building shall be modeled, unless specifically excluded by Sections 13 and 14 of Table 11.5.1, including, but not limited to, exhaust fans, parking garage ventilation fans, exterior building lighting, swimming pool heaters and pumps, elevators and escalators, refrigeration equipment, and cooking equipment.
13. Modeling Exceptions
All elements of the proposed design building envelope, HVAC, service water heating, lighting, and electrical systems shall be modeled in the proposed design in accordance with the requirements of Sections 1 through 12 of Table 11.5.1.
Exceptions: Components and systems in the proposed design may be excluded from the simulation model provided that
  1. component energy use does not affect the energy use of systems and components that are being considered for trade-off and
  2. the applicable prescriptive requirements of Sections 5.5, 6.5, 7.5, and either 9.5 or 9.6 applying to the excluded components are met.
None.
14. Modeling Limitations to the Simulation Program
If the simulation program cannot model a component or system included in the proposed design, one of the following methods shall be used with the approval of the authority having jurisdiction:
  1. Ignore the component if the energy impact on the trade-offs being considered is not significant.
  2. Model the component substituting a thermodynamically similar component model.
  3. Model the HVAC system components or systems using the budget building design's HVAC system in accordance with Section 10 of Table 11.5.1. Whichever method is selected, the component shall be modeled identically for both the proposed design and budget building design.
Same as proposed design.

The HVAC system type and related performance parameters for the budget building design shall be determined from Figure 11.5.2, the system descriptions in Table 11.5.2-1 and accompanying notes, and the following rules:

  1. Budget Building Systems Not Listed. Components and parameters not listed in Figure 11.5.2 and Table 11.5.2-1 or otherwise specifically addressed in this subsection shall be identical to those in the proposed design.

    Exception to 11.5.2(a)

    Where there are specific requirements in Sections 6.4 and 6.5, the component efficiency in the budget building design shall be adjusted to the lowest efficiency level allowed by the requirement for that component type.

  2. Minimum Equipment Efficiency. All HVAC and service water-heating equipment in the budget building design shall be modeled at the minimum efficiency levels, both part load and full load, in accordance with Sections 6.4 and 7.4. Chillers shall use Path A efficiencies as shown in Table 6.8.1-3.
  3. Supply Fan Energy in Certain Package Equipment. Where efficiency ratings include supply fan energy, the efficiency rating shall be adjusted to remove the supply fan energy. For Budget System Types 3, 4, 6, 9, and 11, 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 multiple HVAC zones are combined into a single thermal block in accordance with Table 11.5.1, the efficiencies for the budget System Types 6, 8, and 10 taken from Tables 6.8.1-1 through 6.8.1-4, shall be based on 9,000 Btu/hr equipment capacity for residential spaces; otherwise, it shall be based on the capacity of the thermal block divided by the number of HVAC zones. Budget System Types 3, 6, 9 and 11 efficiencies taken from Table 6.8.1-1 through 6.8.1-4 shall be based on the cooling equipment capacity of a single floor when grouping identical floors in accordance with Table 11.5.1. Where a full- and part-load efficiency rating is provided in Tables 6.8.1-1 through 6.8.1-4, the fullload 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 budget building design, which excludes supply fan power, and Q is the AHRI-rated cooling capacity in Btu/h. If Q is greater than 760,000 Btu/h, use 760,000 Btu/h in the calculation.

    EER, SEER, COP, and HSPF shall be at AHRI test conditions. Fan energy shall be modeled separately according to Section 11.5.2(h). Supply and return/relief system fans shall be modeled as operating at least whenever the spaces served are occupied, except as specifically noted in Table 11.5.2-1.

  4. Minimum Outdoor Air Ventilation Rate. Minimum outdoor air ventilation rates shall be the same for both the budget building design and proposed design. Exhaust air heat recovery shall be modeled for the budget building design in accordance with Section 6.5.6.1.

    Exception to (d):

    Where the minimum outdoor air intake flow in the proposed design is provided in excess of the amount allowed by Section 6.5.3.7, the baseline building design shall be modeled to reflect the minimum amount allowed by Section 6.5.3.7 and will be less than or equal to the proposed design.

  5. Economizers. Budget building systems as listed in Table 11.5.2-1 shall have air economizers or fluid economizers, the same as in the proposed design, in accordance with Section 6.5.1. The high-limit shutoff shall be in accordance with Table 11.5.2-4.
  6. Preheat Coils. If the proposed design system has a preheat coil, the budget building design's system shall be modeled with a preheat coil controlled in the same manner.
  7. Supply Airflow Rates. System design supply air rates for the budget building design shall be based on a supply-air-to-room-air temperature difference of 20°F. If return or relief fans are specified in the proposed design, the budget building design shall also be modeled with the same fan type sized for the budget system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger.
  8. Fan System Efficiency. Fan system efficiency (bhp per cfm of supply air, including the effect of belt losses but excluding motor and motor drive losses) shall be the same as the proposed design or up to the limit prescribed in Section 6.5.3.1, whichever is smaller. If this limit is reached, each fan shall be proportionally reduced in brake horsepower until the limit is met. Fan electrical power shall then be determined by adjusting the calculated fan hp by the minimum motor efficiency prescribed by Section 10.4.1 for the appropriate motor size for each fan.
  9. Equipment Capacities. The equipment capacities for the budget building design shall be sized proportionally to the capacities in the proposed design based on sizing runs, i.e., the ratio between the capacities used in the annual simulations and the capacities determined by the sizing runs shall be the same for both the proposed design and budget building design. Unmet load hours for the proposed design or baseline building designs shall not exceed 300 hours. The unmet load hours for the proposed design shall not exceed the unmet load hours for the budget building design. Alternatively, unmet load hours exceeding these limits may be approved by the building official, provided that sufficient justification is given indicating that the accuracy of the simulation is not significantly compromised by these unmet loads.
  10. Determining the HVAC System. Each HVAC system in a proposed design is mapped on a one-to-one correspondence with one of eleven HVAC systems in the budget building design. To determine the budget building system, do the following:

    1. Enter Figure 11.5.2 at "Water" if the proposed design system condenser is water or evaporatively cooled; enter Figure 11.5.2 at "Air/None" if the condenser is air cooled. Closed-circuit dry coolers shall be considered air cooled. Systems utilizing district cooling shall be treated as if the condenser water type were "water." If no mechanical cooling is specified or the mechanical cooling system in the proposed design does not require heat rejection, the system shall be treated as if the condenser water type were "Air." For proposed designs with ground-source or groundwatersource heat pumps, the budget system shall be water-source heat pump (System 6).
    2. Select the path that corresponds to the proposed design heat source: electric resistance, heat pump (including air source and water source), or fuel-fired. Systems utilizing district heating (steam or hot water) shall be treated as if the heating system type were "Fossil Fuel." Systems with no heating capability shall be treated as if the heating system type were "Fossil Fuel." For systems with mixed fuel heating sources, the system or systems that use the secondary heating source type (the one with the smallest total installed output capacity for the spaces served by the system) shall be modeled identically in the budget building design, and the primary heating source type shall be used in Figure 11.5.2 to determine budget system type.
    3. Select the budget building design system category. The system under "Single-Zone Residential System" shall be selected if the HVAC system in the proposed design is a single-zone system and serves a residential space. The system under "Single-Zone Nonresidential System" shall be selected if the HVAC system in the proposed design is a single-zone system and serves other than residential spaces. The system under "All Other" shall be selected for all other cases.
  11. Kitchen Exhaust. For kitchens with a total exhaust hood airflow rate greater than 5000 cfm, use 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 building 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 6.5.7.2.2 for the numbers and types of hoods and appliances provided in the proposed design.
Figure 11.5.2 HVAC systems map.
Table 11.5.2-1 Budget System Descriptions
System No. System Type Fan Control Cooling Type Heating Type
1 VAV with parallel fan-powered boxesa VAVd Chilled watere Electric resistance
2 VAV with reheatb VAVd Chilled watere Hot-water fossil fuel boilerf
3 Packaged VAV with parallel fan-powered boxesa VAVd Direct expansionc Electric resistance
4 Packaged VAV with reheatb VAVd Direct expansionc Hot-water fossil fuel boilerf
5 Two-pipe fan coil Single- or two-speed fan i,j Chilled watere Electric resistance
6 Water-source heat pump Single- or two-speed fan i,j Direct expansionc Electric heat pump and boilerg
7 Four-pipe fan-coil Single- or two-speed fan i,j Chilled watere Hot-water fossil fuel boilerf
8 Packaged terminal heat pump Single-speed fani Direct expansionc Electric heat pumph
9 Packaged rooftop heat pump Single- or two-speed fan i,j Direct expansionc Electric heat pumph
10 Packaged terminal air conditioner Single-speed fani Direct expansion Hot-water fossil fuel boilerf
11 Packaged rooftop air conditioner Single- or two-speed fan i,j Direct expansion Fossil fuel furnace
  1. VAV with Parallel Fan-Powered Boxes: Fans in parallel VAV fan-powered boxes shall be sized for 50% of the peak design flow rate and shall be modeled with 0.35 W/cfm fan power. Minimum volume set points for fan-powered boxes shall be equal to the minimum rate for the space required for ventilation consistent with Exception 1(b) to Section 6.5.2.1. Supply air temperature set point shall be constant at the design condition (see Section 11.5.2[g]).
  2. VAV with Reheat: Minimum volume set points for VAV reheat boxes shall be 30% of zone peak airflow or the minimum ventilation rate, whichever is larger, consistent with Exception 1(a) to Section 6.5.2.1. The supply air temperature for cooling shall be reset higher by 5°F under the minimum cooling load conditions.
  3. Direct Expansion: The fuel type for the cooling system shall match that of the cooling system in the proposed design.
  4. VAV: Constant volume can be modeled if the system qualifies for Exception (2) to Section 6.5.2.1. Otherwise, the supply, return, or relief fan motor shall be modeled assuming a variable-speed drive and shall meet the VAV fan part-load performance requirements of Section G3.1.3.15. If the proposed design's system has a DDC system at the zone level, static pressure set-point reset based on zone requirements in accordance with Section 6.5.3.2.3 shall be modeled.
  5. Chilled Water: For systems using purchased chilled water, the chillers are not explicitly modeled, and chilled-water costs shall be based as determined in Section 11.4.3. Otherwise, the budget building design's chiller plant shall be modeled with chillers having the number as indicated in Table 11.5.2-2 as a function of budget building design chiller plant load and type as indicated in Table 11.5.2-3 as a function of individual chiller load. Where chiller fuel source is mixed, the system in the budget building design shall have chillers with the same fuel types and with capacities having the same proportional capacity as the proposed design's chillers for each fuel type. Chilled-water supply temperature shall be modeled at 44°F design supply temperature and 56°F return temperature. Piping losses shall not be modeled in either building model. Chilled-water supply water temperature shall be reset in accordance with Section 6.5.4.4. Pump system power for each pumping system shall be the same as for the proposed design; if the proposed design has no chilled-water pumps, the budget building design pump power shall be 22 W/gpm (equal to a pump operating against a 75 ft head, 65% combined impeller and motor efficiency). The chilled-water system shall be modeled as primary-only variable flow with flow maintained at the design rate through each chiller using a bypass. Chilled-water pumps shall be modeled as riding the pump curve or with variable-speed drives when required in Section 6.5.4.2. The heat-rejection device shall be an open-circuit axial-fan cooling tower with variable-speed fan control, if required in Section 6.5.5, 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:

    Approach 10°FRange= 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. Pump system power for each pumping system shall be the same as the proposed design; if the proposed design has no condenser water pumps, the budget building design pump power shall be 19 W/gpm (equal to a pump operating against a 60 ft head, 60% combined impeller and motor efficiency). Each chiller shall be modeled with separate condenser water and chilled-water pumps interlocked to operate with the associated chiller.

  6. Fossil Fuel Boiler: For systems using purchased hot water or steam, the boilers are not explicitly modeled and hot-water or steam costs shall be based on actual utility rates. Otherwise, the boiler plant shall use the same fuel as the proposed design and shall be natural draft. The budget building design boiler plant shall be modeled with a single boiler if the budget building design plant load is 600,000 Btu/h or less and with two equally sized boilers for plant capacities exceeding 600,000 Btu/h. Boilers shall be staged as required by the load. Hot-water supply temperature shall be modeled at 180°F design supply temperature and 130°F return temperature. Piping losses shall not be modeled in either building model. Hot-water supply water temperature shall be reset in accordance with Section 6.5.4.4. Pump system power for each pumping system shall be the same as for the proposed design; if the proposed design has no hot-water pumps, the budget building design pump power shall be 19 W/gpm (equal to a pump operating against a 60 ft head, 60% combined impeller and motor efficiency). The hot-water system shall be modeled as primary-only with continuous variable flow. Hotwater pumps shall be modeled as riding the pump curve or with variable-speed drives when required by Section 6.5.4.2.
  7. Electric Heat Pump and Boiler: Water-source heat pumps shall be connected to a common heat pump water loop controlled to maintain temperatures between 60°F and 90°F. Heat rejection from the loop shall be provided by an closed-circuit axial-fan evaporative fluid cooler with two-speed fans if required in Section 6.5.5.2. Heat addition to the loop shall be provided by a boiler that uses the same fuel as the proposed design and shall be natural draft. If no boilers exist in the proposed design, the budget building boilers shall be fossil fuel. The budget building design boiler plant shall be modeled with a single boiler if the budget building design plant load is 600,000 Btu/h or less and with two equally sized boilers for plant capacities exceeding 600,000 Btu/h. Boilers shall be staged as required by the load. Piping losses shall not be modeled in either building model. Pump system power shall be the same as for the proposed design; if the proposed design has no pumps, the budget building design pump power shall be 22 W/gpm, which is equal to a pump operating against a 75 ft head, with a 65% combined impeller and motor efficiency. Loop flow shall be variable with flow shutoff at each heat pump when its compressor cycles OFF as required by Section 6.5.4.5. Loop pumps shall be modeled as riding the pump curve or with variable-speed drives when required by Section 6.5.4.2.
  8. Electric Heat Pump: Electric air-source heat pumps shall be modeled with electric auxiliary heat. The system shall be controlled with a multistage space thermostat 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.
  9. Fan System Operation: Fans shall be controlled in the same manner as in the proposed design; i.e., fan operation whenever the space is occupied or fan operation cycled ON calls for heating and cooling.
  10. Fan Speed Control: Fans shall operate as one or two speed as required by Section 6.5.3.2, regardless of the fan speed control used in the proposed design.
Table 11.5.2-2 Number of Chillers
Total Chiller Plant Capacity Number of Chillers
≤300 tons One
>300 tons, <600 tons Two sized equally
≥600 tons Two minimum with chillers added so that no chiller is larger than 800 tons, all sized equally
Table 11.5.2-3 Water Chiller Types
Individual Chiller Plant Capacity Electric Chiller Type Fossil Fuel Chiller Type
≤100 tons Reciprocating Single-effect absorption, direct fired
>100 tons, <300 tons Screw Double-effect absorption, direct fired
≥300 tons Centrifugal Double-effect absorption, direct fired
Table 11.5.2-4 Economizer High-Limit Shutoff
Economizer Type High-Limit Shutoff
Air Table 6.5.1.1.3
Fluid (integrated) When its operation will no longer reduce HVAC system energy

Compliance shall be documented and submitted to the authority having jurisdiction. The information submitted shall include the following:

  1. The energy cost budget for the budget building design and the design energy cost for the proposed design.
  2. The simulation program used and the version of the simulation program.
  3. 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.
  4. A list of the energy-related features that are included in the design and on which compliance with the provisions of Section 11 is based. This list shall document all energy features that differ between the models used in the energy cost budget and the design energy cost calculations.
  5. A list showing compliance for the proposed design with all of the requirements of Sections 5.4, 6.4, 7.4, 8.4, 9.4 and 10.4 (mandatory provisions).
  6. Building elevations and floor plans.
  7. A diagram showing the thermal blocks used in the computer simulation.
  8. An explanation of any significant modeling assumptions.
  9. Backup calculations and material to support data inputs.
  10. The input and output reports from the simulation program, 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 time any loads are not met by the HVAC system for both the proposed design and budget building design.
  11. Purchased energy rates used in the simulations.
  12. An explanation of any error messages noted in the simulation program output.
  13. For any exceptional calculation methods employed, document the predicted energy savings by energy type, the energy cost savings, a narrative explaining the exceptional calculation method performed and documentation as required in Section 11.4.5.
  14. The reduction in design energy cost associated with on-site renewable energy.
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