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, and 10.4 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; and
  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.
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). The simulation program shall include calculation methodologies for the building components being modeled.

Note to Adopting Authority: ASHRAE Standing Standard Project Committee 90.1 recommends that a compliance shell implementing the rules of a compliance supplement that controls inputs to and reports outputs from the required computer analysis program be adopted for the purposes of easier use and simpler compliance.

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 1400 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 and water-side economizers 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 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 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, that is 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.
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.
Where no simulation program is available that adequately models 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

No. Proposed Building Design (Column A) Design Energy Cost (DEC) Budget Building Design (Column B) Energy Cost Budget (ECB)
1. Design Model
  1. The simulation model of the proposed building 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 building design shall be simulated as being both heated and cooled, even if no cooling or heating system is being installed. Temperature and humidity control setpoints and schedules, as well as temperature control throttling range, shall be the same for proposed and baseline building designs.
  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 building 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 building 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 setpoints 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 building design
3. Space Use Classification
The building 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-type or space-type categories but shall not combine the two types of categories within a single permit application. More than one building-type category may be used for a building if it is a mixed-use facility. Same as proposed building design
4. Schedules
The schedule types listed in Section 11.4.1.1(b) shall be required input. The schedules shall be typical of the proposed building type as determined by the designer and approved by the authority having jurisdiction. Required schedules shall be identical for the proposed building design and budget building design. Same as proposed building design
5. Building Envelope
All components of the building envelope in the proposed building design shall be modeled as shown on architectural drawings or as installed for existing building envelopes.

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

  1. Any envelope assembly that covers less than 5% of the total area of that assembly type (e.g., exterior walls) need not be separately described. If not separately described, the area of an envelope assembly must be added to the area of the adjacent assembly of that same type.
  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 is 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 building 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 building 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 exterior 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 building 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 5.5-1 through 5.5-8 for the appropriate climate, and the SHGC shall be equal to the criteria from Tables 5.5-1 through 5.5-8 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 envelope alterations shall reflect the limitations on area, U-factor, and SHGC as described in Section 5.1.3.

    Exception: When trade-offs are made between an addition and an existing building, as described in the exception to Section 4.2.1.2, the 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 building 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 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).
  5. 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.

  6. 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 density 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 budget building design shall be determined using the same categorization procedure (building area method or space-by-space method) and categories as the proposed building 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 LPD calculation shall be modeled identically in the proposed building design and budget building design.
  3. 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.

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 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 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:
  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. Perimeter spaces shall be those located closer than 15 ft from 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 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 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 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 building design
10. HVAC Systems
The HVAC system type and all related performance parameters, such as equipment capacities and efficiencies, in the proposed building 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 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 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 Hot-Water Systems
The service hot-water system type and all related performance parameters, such as equipment capacities and efficiencies, in the proposed building design shall be determined as follows:
  1. Where a complete service hot-water system exists, the model shall reflect the actual system type using actual component capacities and efficiencies.
  2. Where a service hot-water system has been designed, the service hot-water model shall be consistent with design documents.
  3. Where no service hot-water system exists or is specified, no service hot-water heating shall be modeled.
The service hot-water system type in the budget building design shall be identical to the proposed building design. The service hot-water system performance of the budget building design shall meet the requirements of Table 7.8.
Exceptions:
  1. If the service hot water system type is not listed in Table 7.8, it shall be identical to the proposed building 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 or budget building design.
12. Miscellaneous Loads
Receptacle, motor, and process loads shall be modeled and estimated based on the building 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 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.
13. Modeling Exceptions
All elements of the proposed building design envelope, HVAC, service water heating, lighting, and electrical systems shall be modeled in the proposed building design in accordance with the requirements of Sections 1 through 12 of Table 11.5.1.

Exceptions: Components and systems in the proposed building design may be excluded from the simulation model provided that

  1. component energy usage does not affect the energy usage 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 building 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 building design and budget building design models.
Same as proposed 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 the following rules:
  1. 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 building design.

    Exception: 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. All HVAC and service water heating equipment in the budget building 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. 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 a full- and part-load efficiency rating is provided in Tables 6.8.1-1 though 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 budget building design, 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 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 rates shall be the same for both the budget building design and proposed building design. Exhaust air heat recovery shall be modeled for the budget building design in accordance with Section 6.5.6.1.
  5. Budget building systems as listed in Table 11.5.2-1 shall have outdoor air economizers or water economizers, the same as in the proposed building, in accordance with Section 6.5.1. The high-limit shutoff shall be in accordance with Table 11.5.2-4.
  6. If the proposed building 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. 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 building 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 (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 building 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. The equipment capacities for the budget building design shall be sized proportionally to the capacities in the proposed building 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 building design and budget building design. Unmet load hours for the proposed design or baseline building designs shall not exceed 300. The unmet load hours for the proposed design shall not exceed the unmet load hours for the budget building. 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.
  10. Each HVAC system in a proposed building 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 building design system condenser is water or evaporatively cooled; enter at "Air" 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 building design does not require heat rejection, the system shall be treated as if the condenser water type were "Air." For proposed building designs with ground-source or groundwater-source heat pumps, the budget system shall be water-source heat pump (System 6).
    2. Select the path that corresponds to the proposed building 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. 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 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 in the proposed design.

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 setpoints 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 setpoint shall be constant at the design condition [see Section 11.5.2(g)].
  2. VAV with Reheat: Minimum volume setpoints 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 building 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 G.3.1.3.15. If the proposed building design's system has a DDC system at the zone level, static pressure setpoint 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 building 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 building design; if the proposed building 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:

    Approach10°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 building design; if the proposed building 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 building 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 building design; if the proposed building 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. Hot-water 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 axial fan closed-circuit 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 building design and shall be natural draft. If no boilers exist in the proposed building 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 building design; if the proposed building 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 building 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 building.

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
Water (integrated) When its operation will no longer reduce HVAC system energy

FIGURE 11.5.2 HVAC systems map.

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. 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.
  3. The input and output report(s) 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.
  4. An explanation of any error messages noted in the simulation program output.
  5. The reduction in design energy cost associated with onsite renewable energy.
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