This section establishes criteria for compliance using total building performance. The following systems and loads shall be included in determining the total building performance: heating systems, cooling systems, service water heating, fan systems, lighting power, receptacle loads and process loads.
Compliance based on total building performance requires that a proposed building (proposed design) be shown to have an annual energy cost that is less than or equal to the annual energy cost of the standard reference design. Energy prices shall be taken from a source approved by the code official, such as the Department of Energy, Energy Information Administration’s State Energy Price and Expenditure Report. Code officials shall be permitted to require time-of-use pricing in energy cost calculations. Nondepletable energy collected off site shall be treated and priced the same as purchased energy. Energy from nondepletable energy sources collected on site shall be omitted from the annual energy cost of the proposed design.
Exception: Jurisdictions that require site energy (1 kWh = 3413 Btu) rather than energy cost as the metric of comparison.
Documentation verifying that the methods and accuracy of compliance software tools conform to the provisions of this section shall be provided to thecode official.
Permit submittals shall include a report documenting that the proposed design has annual energy costs less than or equal to the annual energy costs of the standard reference design. The compliance documentation shall include the following information:
- Address of the building.
- An inspection checklist documenting the building component characteristics of the proposed design as specified in Table C407.5.1(1). The inspection checklist shall show the estimated annual energy cost for both the standard reference design and the proposed design.
- Name of individual completing the compliance report.
- Name and version of the compliance software tool.
The code official shall be permitted to require the following documents:
- Documentation of the building component characteristics of the standard reference design.
- Thermal zoning diagrams consisting of floor plans showing the thermal zoning scheme for standard reference design and proposed design.
- Input and output reports from the energy analysis simulation program containing the complete input and output files, as applicable. The output file shall include energy use totals and energy use by energy source and end-use served, total hours that space conditioning loads are not met and any errors or warning messages generated by the simulation tool as applicable.
- An explanation of any error or warning messages appearing in the simulation tool output.
- A certification signed by the builder providing the building component characteristics of the proposed design as given in Table C407.5.1(1).
Except as specified by this section, thestandard reference design and proposed design shall be configured and analyzed using identical methods and techniques.
The standard reference design and proposed design shall be configured and analyzed as specified by Table C407.5.1(1). Table C407.5.1(1) shall include by reference all notes contained in Table C402.1.4.
SPECIFICATIONS FOR THE STANDARD REFERENCE AND PROPOSED DESIGNS
| BUILDING COMPONENT CHARACTERISTICS | STANDARD REFERENCE DESIGN | PROPOSED DESIGN |
| Space use classification | Same as proposed | The space use classification shall be chosen in accordance with Table C405.5.2 for all areas of the building covered by this permit. Where the space use classification for a building is not known, the building shall be categorized as an office building. |
| Roofs | Type: Insulation entirely above deck | As proposed |
| Gross area: same as proposed | As proposed | |
| U-factor: as specified in Table C402.1.4 | As proposed | |
| Solar absorptance: 0.75 | As proposed | |
| Emittance: 0.90 | As proposed | |
| Walls, above-grade | Type: Mass wall where proposed wall is mass; otherwise steel-framed wall | As proposed |
| Gross area: same as proposed | As proposed | |
| U-factor: as specified in Table C402.1.4 | As proposed | |
| Solar absorptance: 0.75 | As proposed | |
| Emittance: 0.90 | As proposed | |
| Walls, below-grade | Type: Mass wall | As proposed |
| Gross area: same as proposed | As proposed | |
| U-Factor: as specified in Table C402.1.4 with insulation layer on interior side of walls | As proposed | |
| Floors, above-grade | Type: joist/framed floor | As proposed |
| Gross area: same as proposed | As proposed | |
| U-factor: as specified in Table C402.1.4 | As proposed | |
| Floors, slab-on-grade | Type: Unheated | As proposed |
| F-factor: as specified in Table C402.1.4 | As proposed | |
| Opaque doors | Type: Swinging | As proposed |
| Area: Same as proposed | As proposed | |
| U-factor: as specified in Table C402.1.4 | As proposed | |
| Vertical fenestration other than opaque doors | Area
| As proposed |
| U-factor: as specified in Table C402.4 | As proposed | |
| SHGC: as specified in Table C402.4 except that for climates with no requirement (NR) SHGC = 0.40 shall be used | As proposed | |
| External shading and PF: None | As proposed | |
| Skylights | Area
| As proposed |
| U-factor: as specified in Table C402.4 | As proposed | |
| SHGC: as specified in Table C402.4 except that for climates with no requirement (NR) SHGC = 0.40 shall be used. | As proposed | |
| Lighting, interior | The interior lighting power shall be determined in accordance with Section C405.4.2. Where the occupancy of the building is not known, the lighting power density shall be 1.0 Watt per square foot (10.7 W/ m2) based on the categorization of buildings with unknown space classification as offices. | As proposed |
| Lighting, exterior | The lighting power shall be determined in accordance with Table C405.5.2(2). Areas and dimensions of tradable and nontradable surfaces shall be the same as proposed. | As proposed |
| Internal gains | Same as proposed | Receptacle, motor and process loads shall be modeled and estimated based on the space use classification. All end-use load components within and associated with the building shall be modeled to include, but not be limited to, the following: exhaust fans, parking garage ventilation fans, exterior building lighting, swimming pool heaters and pumps, elevators, escalators, refrigeration equipment and cooking equipment. |
| Schedules | Same as proposed | Operating schedules shall include hourly profiles for daily operation and shall account for variations between weekdays, weekends, holidays and any seasonal operation. Schedules shall model the time- dependent variations in occupancy, illumination, receptacle loads, thermostat settings, mechanical ventilation, HVAC equipment availability, service hot water usage and any process loads. The schedules shall be typical of the proposed building type as determined by the designer and approved by the jurisdiction. |
| Mechanical ventilation | Same as proposed | As proposed, in accordance with Section C403.2.6. |
| Heating systems | Fuel type: same as proposed design | As proposed |
| Equipment typea: as specified in Tables C407.5.1(2) and C407.5.1(3) | As proposed | |
| Efficiency: as specified in Tables C403.2.3(4) and C403.2.3(5) | As proposed | |
| Capacityb: sized proportionally to the capacities in the proposed design based on sizing runs, and shall be established such that no smaller number of unmet heating load hours and no larger heating capacity safety factors are provided than in the proposed design. | As proposed | |
| Cooling systems | Fuel type: same as proposed design | As proposed |
| Equipment typec: as specified in Tables C407.5.1(2) and C407.5.1(3) | As proposed | |
| Efficiency: as specified in Tables C403.2.3(1), C403.2.3(2) and C403.2.3(3) | As proposed | |
| Capacityb: sized proportionally to the capacities in the proposed design based on sizing runs, and shall be established such that no smaller number of unmet cooling load hours and no larger cooling capacity safety factors are provided than in the proposed design. | As proposed | |
| Economizerd: same as proposed, in accordance with Section C403.3. | As proposed | |
| Service water heatinge | Fuel type: same as proposed | As proposed |
| Efficiency: as specified in Table C404.2 | For Group R, as proposed multiplied by SWHF. For other than Group R, as proposed multiplied by efficiency as provided by the manufacturer of the DWHR unit. | |
| Capacity: same as proposed | As proposed | |
| Where no service water hot water system exists or is specified in the proposed design, no service hot water heating shall be modeled. |
SWHF = Service water heat recovery factor, DWHR = Drain water heat recovery.
- Where no heating system exists or has been specified, the heating system shall be modeled as fossil fuel. The system characteristics shall be identical in both the standard reference design and proposed design.
- The ratio between the capacities used in the annual simulations and the capacities determined by sizing runs shall be the same for both the standard reference design and proposed design.
- 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 zone. The system characteristics shall be identical in both the standard reference design and proposed design.
- If an economizer is required in accordance with Table C403.3 and where no economizer exists or is specified in the proposed design, then a supply-air economizer shall be provided in the standard reference design in accordance with Section C403.3.
The SWHF shall be applied as follows:
- Where potable water from the DWHR unit supplies not less than one shower and not greater than two showers, of which the drain water from the same showers flows through the DWHR unit then SWHF = [1 – (DWHR unit efficiency • 0.36)].
- Where potable water from the DWHR unit supplies not less than three showers and not greater than four showers, of which the drain water from the same showers flows through the DWHR unit then SWHF = [1 – (DWHR unit efficiency • 0.33)].
- Where potable water from the DWHR unit supplies not less than five showers and not greater than six showers, of which the drain water from the same showers flows through the DWHR unit, then SWHF = [1 – (DWHR unit efficiency • 0.26)].
- Where Items 1 through 3 are not met, SWHF = 1.0.
HVAC SYSTEMS MAP
| CONDENSER COOLING SOURCEa | HEATING SYSTEM CLASSIFICATIONb | STANDARD REFERENCE DESIGN HVC SYSTEM TYPEc | ||
| Single-zone Residential System | Single-zone Nonresidential System | All Other | ||
| Water/ground | Electric resistance | System 5 | System 5 | System 1 |
| Heat pump | System 6 | System 6 | System 6 | |
| Fossil fuel | System 7 | System 7 | System 2 | |
| Air/none | Electric resistance | System 8 | System 9 | System 3 |
| Heat pump | System 8 | System 9 | System 3 | |
| Fossil fuel | System 10 | System 11 | System 4 | |
- Select “water/ground” where the proposed design system condenser is water or evaporatively cooled; select “air/none” where 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.” Where 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 groundwater-source heat pumps, the standard reference design HVAC system shall be water-source heat pump (System 6).
- 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) and 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 standard reference design and the primary heating source type shall be used to determine standard reference design HVAC system type.
- Select the standard reference design HVAC system category: The system under “single-zone residential system” shall be selected where 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 where 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.
SPECIFICATIONS FOR THE STANDARD REFERENCE DESIGN HVAC SYSTEM DESCRIPTIONS
| SYSTEM NO. | SYSTEM TYPE | FAN CONTROL | COOLING TYPE | HEATING TYPE |
| 1 | Variable air volume with parallel fan-powered boxesa | VAVd | Chilled watere | Electric resistance |
| 2 | Variable air volume with reheatb | VAVd | Chilled watere | Hot water fossil fuel boilerf |
| 3 | Packaged variable air volume with parallel fan- powered boxesa | VAVd | Direct expansionc | Electric resistance |
| 4 | Packaged variable air volume with reheatb | VAVd | Direct expansionc | Hot water fossil fuel boilerf |
| 5 | Two-pipe fan coil | Constant volumei | Chilled watere | Electric resistance |
| 6 | Water-source heat pump | Constant volumei | Direct expansionc | Electric heat pump and boilerg |
| 7 | Four-pipe fan coil | Constant volumei | Chilled watere | Hot water fossil fuel boilerf |
| 8 | Packaged terminal heat pump | Constant volumei | Direct expansionc | Electric heat pumph |
| 9 | Packaged rooftop heat pump | Constant volumei | Direct expansionc | Electric heat pumph |
| 10 | Packaged terminal air conditioner | Constant volumei | Direct expansion | Hot water fossil fuel boilerf |
| 11 | Packaged rooftop air conditioner | Constant volumei | Direct expansion | Fossil fuel furnace |
For SI: 1 foot = 304.8 mm, 1 cfm/ft2 = 0.4719 L/s, 1 Btu/h = 0.293/W, °C = [(°F) -32/1.8].
- VAV with parallel boxes: Fans in parallel VAV fan-powered boxes shall be sized for 50 percent 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 Section C403.4.4, Exception 4. Supply air temperature setpoint shall be constant at the design condition.
- VAV with reheat: Minimum volume setpoints for VAV reheat boxes shall be 0.4 cfm/ft2 of floor area. Supply air temperature shall be reset based on zone demand from the design temperature difference to a 10°F temperature difference under minimum load conditions. Design airflow rates shall be sized for the reset supply air temperature, i.e., a 10°F temperature difference.
- Direct expansion: The fuel type for the cooling system shall match that of the cooling system in the proposed design.
- VAV: Where the proposed design system has a supply, return or relief fan motor 25 hp or larger, the corresponding fan in the VAV system of the standard reference design shall be modeled assuming a variable-speed drive. For smaller fans, a forward-curved centrifugal fan with inlet vanes shall be modeled. Where the proposed design’s system has a direct digital control system at the zone level, static pressure setpoint reset based on zone requirements in accordance with Section C403.4.1 shall be modeled.
- Chilled water: For systems using purchased chilled water, the chillers are not explicitly modeled and chilled water costs shall be based as determined in Sections C407.3 and C407.5.2. Otherwise, the standard reference design’s chiller plant shall be modeled with chillers having the number as indicated in Table C407.5.1(4) as a function of standard reference building chiller plant load and type as indicated in Table C407.5.1(5) as a function of individual chiller load. Where chiller fuel source is mixed, the system in the standard reference 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 C403.4.3.3. Pump system power for each pumping system shall be the same as the proposed design; where the proposed design has no chilled water pumps, the standard reference design pump power shall be 22 W/gpm (equal to a pump operating against a 75-foot head, 65-percent 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 C403.4.3.3. The heat rejection device shall be an axial fan cooling tower with two-speed fans where required in Section C403.4.3. Condenser water design supply temperature shall be 85°F or 10°F approach to design wet-bulb temperature, whichever is lower, with a design temperature rise of 10°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; where the proposed design has no condenser water pumps, the standard reference design pump power shall be 19 W/gpm (equal to a pump operating against a 60-foot head, 60-percent 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.
- 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 standard reference design boiler plant shall be modeled with a single boiler where the standard reference design plant load is 600,000 Btu/h and 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 C403.4.3.3. Pump system power for each pumping system shall be the same as the proposed design; where the proposed design has no hot water pumps, the standard reference design pump power shall be 19 W/gpm (equal to a pump operating against a 60-foot head, 60-percent 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 C403.4.3.3.
- 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 where required in Section C403.4.1. 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. Where no boilers exist in the proposed design, the standard reference building boilers shall be fossil fuel. The standard reference design boiler plant shall be modeled with a single boiler where the standard reference 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 the proposed design; where the proposed design has no pumps, the standard reference design pump power shall be 22 W/gpm, which is equal to a pump operating against a 75-foot head, with a 65-percent 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 C403.4.3.3. Loop pumps shall be modeled as riding the pump curve or with variable speed drives when required by Section C403.4.3.3.
- 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.
- Constant volume: 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. Where the fan is modeled as cycling and the fan energy is included in the energy efficiency rating of the equipment, fan energy shall not be modeled explicitly.
NUMBER OF CHILLERS
| TOTAL CHILLER PLANT CAPACITY | NUMBER OF CHILLERS |
| ≤ 300 tons | 1 |
| > 300 tons, < 600 tons | 2, sized equally |
| ≥ 600 tons | 2 minimum, with chillers added so that no chiller is larger than 800 tons, all sized equally |
For SI: 1 ton = 3517 W.
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 |
For SI: 1 ton = 3517 W.
The standard reference design and proposed design shall be analyzed using identical thermal blocks as specified in Section C407.5.2.1, C407.5.2.2 or C407.5.2.3.
Where HVAC zones are defined on HVAC design drawings, each HVAC zone shall be modeled as a separate thermal block.
Exception: Different HVAC zones shall be allowed to be combined to create a single thermal block or identical thermal blocks to which multipliers are applied provided:
- The space use classification is the same throughout the thermal block.
- 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 (0.79 rad) of each other.
- All of the zones are served by the same HVAC system or by the same kind of HVAC system.
Where HVAC zones have not yet been designed, thermal blocks shall be defined based on similar internal load densities, occupancy, lighting, thermal and temperature schedules, and in combination with the following guidelines:
- Separate thermal blocks shall be assumed for interior and perimeter spaces. Interior spaces shall be those located more than 15 feet (4572 mm) from an exterior wall. Perimeter spaces shall be those located closer than 15 feet (4572 mm) from an exterior wall.
- Separate thermal blocks shall be assumed for spaces adjacent to glazed exterior walls: a separate zone shall be provided for each orientation, except orientations that differ by not more than 45 degrees (0.79 rad) shall be permitted to be considered to be the same orientation. Each zone shall include floor area that is 15 feet (4572 mm) or less from a glazed perimeter wall, except that floor area within 15 feet (4572 mm) of glazed perimeter walls having more than one orientation shall be divided proportionately between zones.
- 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.
- Separate thermal blocks shall be assumed for spaces having exterior ceiling or roof assemblies from zones that do not share these features.
Residential spaces shall be modeled using one thermal block per space except that those facing the same orientations are permitted to be combined into one thermal block. Corner units and units with roof or floor loads shall only be combined with units sharing these features.
Calculation procedures used to comply with this section shall be software tools capable of calculating the annual energy consumption of all building elements that differ between the standard reference design and the proposed design and shall include the following capabilities.
- Building operation for a full calendar year (8,760 hours).
- Climate data for a full calendar year (8,760 hours) and shall reflect approved coincident hourly data for temperature, solar radiation, humidity and wind speed for the building location.
- Ten or more thermal zones.
- Thermal mass effects.
- Hourly variations in occupancy, illumination, receptacle loads, thermostat settings, mechanical ventilation, HVAC equipment availability, service hot water usage and any process loads.
- Part-load performance curves for mechanical equipment.
- Capacity and efficiency correction curves for mechanical heating and cooling equipment.
- Printed code official inspection checklist listing each of the proposed design component characteristics from Table C407.5.1(1) determined by the analysis to provide compliance, along with their respective performance ratings including, but not limited to, R-value, U-factor, SHGC, HSPF, AFUE, SEER, EF.
Performance analysis tools complying with the applicable subsections of Section C407 and tested according to ASHRAE Standard 140 shall be permitted to beapproved. Tools are permitted to be approved based on meeting a specified threshold for a jurisdiction. The code official shall be permitted to approve tools for a specified application or limited scope.
Where the simulation program does not model a design, material or device of the proposed design, an exceptional calculation method shall be used where approved by the code official. Where 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. The total exceptional savings shall not constitute more than half of the difference between the baseline building performance and the proposed building performance. Applications for approval of an exceptional method shall include all of the following:
- Step-by-step documentation of the exceptional calculation method performed, detailed enough to reproduce the results.
- Copies of all spreadsheets used to perform the calculations.
- A sensitivity analysis of energy consumption where each of the input parameters is varied from half to double the value assumed.
- The calculations shall be performed on a time step basis consistent with the simulation program used.
- The performance rating calculated with and without the exceptional calculation method.