- The base envelope performance factor, using only the input for the proposed envelope performance factor. The calculation procedure shall not allow the user to directly modify the building component characteristics of the base design.
- 8760 hours per year.
- 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.
- Thermal mass effects.
- The number of thermal zones in the proposed design or nine thermal zones, whichever is greater.
- Air economizers with integrated control.
- Continuous daylight dimming controls and photosensors.
- Determine the ratio (Rc) of the floor area to the gross wall area for each unique combination of space-conditioning category and building area type. The index "c" refers to a combination of space-conditioning category and building area type as defined for each surface.
- Create a perimeter zone for each unique combination of building area type, above-grade-wall orientation, and space-conditioning category. If there is more than one above-grade-wall assembly for a building area type and orientation, each above-grade-wall assembly shall be placed end-to-end in the order it is defined. The area of each perimeter zone shall be the gross wall area of the zone times Rc or 1.25, whichever is smaller.
- For each unique combination of space-conditioning category and building area type with Rc greater than 1.25, interior zones shall be created and used in the trade-off procedure. The area of the interior zone shall be the total area for the unique combination of space-conditioning category and building area type less the area of the perimeter zones for that combination of space-conditioning category and building area type.
- Create a below-grade zone for each unique combination of space-conditioning category and building area type associated with below-grade walls. If there is more than one below-grade-wall assembly for a building area type, each below- grade-wall assembly shall be placed end-to-end in the order it is defined. The area of each below-grade zone shall be the gross wall area of the zone times Rc or 1.25, whichever is smaller.
- The wall height and the height of each thermal zone shall be 15 ft.
- Roof area and floor area associated with each building area type shall be prorated among all zones of the corresponding building area type in proportion to the zone area of each zone. Roof area and floor area in each zone shall be centered in the horizontal plane of the zone with the same aspect ratio as the horizontal plane of the zone.
- Slab-on-grade floor perimeter associated with each building area type shall be prorated among perimeter zones of the corresponding building area type in proportion to the area of each zone.
- Vertical fenestration area shall be assigned to the associated surface as described in Section C1.4. Vertical fenestration shall be centered on the associated surface with the same aspect ratio as the associated surface. Windows with equivalent U- factor, SHGC, and VT that do not include fins may be combined into a single window on the associated surface.
- Skylight area shall be assigned to the associated surface as described in Section C1.4. prorated among interior zones containing the roof area with which the skylight area is associated, in proportion to the associated roof area. If the total skylight area exceeds the associated roof area in interior zones, the remaining skylight area shall be prorated among perimeter zones containing the roof area with which the skylight area is associated, in proportion to the associated roof area.
- Each zone shall be modeled as being fully enclosed. Zone boundaries not created as described above shall be modeled as adiabatic interior surfaces.
- For each nonresidential zone associated with vertical fenestration, the daylight area shall be modeled as directly adjacent to the vertical fenestration with a width equal to the width of the vertical fenestration and a depth equal to the head height of the vertical fenestration.
- In each nonresidential zone associated with skylights, the daylight area under skylights shall be modeled as bounded, in each direction, by the edge of the skylight area plus 10 ft or the distance to the edge of the zone, whichever is less.
- For each daylight area associated with vertical fenestration, a photosensor shall be modeled as located at the center of the width of the daylight area, at the depth of the daylight area and at a height of 3 ft.
- For each daylight area associated with a skylight, a photosensor shall be modeled as located at the center of the horizontal plane of the skylight and at a height of 5 ft.
|I75Pa||=||air leakage rate of the building envelope (cfm/ft2) at a fixed building pressure differential of 0.3 in. of water, or 1.57 psf|
|S||=||total area of the building envelope (ft2) including the lowest floor, any below- grade walls or above-grade walls, and roof (including vertical fenestration and skylights)|
|IAGW||=||adjusted air leakage rate of the building envelope (cfm/ft2) at a reference wind speed of 10 mph and relative to the area of the above-grade walls|
|AAGW||=||the total area of above-grade walls that comprise the building envelope, ft2|
- Constant-volume fan control.
- Electrically-provided cooling with constant COP, excluding the indoor fan power equal to 4.4.
- Gas furnace with constant thermal efficiency equal to the minimum AFUE allowed for gas-fired warm-air furnaces with maximum capacity <225,000 Btu/h, in accordance with Table 6.8.1-5.
- The ventilation rate for each building area type shall be consistent with the ventilation rate in the building envelope trade-off schedules and loads for the applicable building area type.
- Air economizers, except in Climate Zones 0 and 1. The high-limit shutoff shall be "Fixed Dry Bulb" type as described in Table 220.127.116.11.3.
- System design supply air rates shall be based on a supply-air-to-room-air temperature difference of 20°F in cooling.
- System capacities used in the annual simulation shall be 1.5 times the capacities determined by the sizing simulations.
- Fans shall cycle ON whenever the space calls for heating or cooling. The fan power shall be 0.3 W/cfm, and the fan energy shall be modeled explicitly.
- All opaque assemblies shall be modeled with the maximum U-factor required in Section 5.5.3 for the appropriate class of construction, space-conditioning category, and climate zone. Mass walls and mass floors shall be modeled with HC equal to 7.2 Btu/ft2•°F. All other opaque assemblies shall be modeled with the same HC as the proposed design. Mass walls shall be modeled with equal mass on each side of the insulation. All other opaque assemblies shall be modeled with insulation on the exterior.
- The exterior roof surfaces shall be modeled with a solar reflectance and thermal emittance as required in Section 18.104.22.168.1(1a). All other roofs, including roofs exempted from the requirements in Section 22.214.171.124.1. shall be modeled the same as in the proposed design.
- 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 126.96.36.199. the area shall be reduced proportionally along each exposure until the limit set in Section 188.8.131.52 is met. If the fenestration area facing west or east of the proposed design exceeds the area limit set in Section 184.108.40.206. the baseline building performance shall be generated by simulating the building with its actual orientation and again after rotating the entire building 90, 180, and 270 degrees, then averaging the results of the four simulations. Fenestration U-factor and SHGC shall be the maximum allowed for the appropriate class of construction, space-conditioning category, and climate zone in accordance with Section 5.5.4. Where there is no SHGC requirement, the SHGC shall be equal to 0.40 for all vertical fenestration and 0.55 for skylights. The VT for fenestration in the base envelope design shall be equal to 1.10 times the SHGC.
- Manually operated interior shades shall be modeled on all vertical fenestration as described in Section C220.127.116.11. Permanent shading devices, such as fins and overhangs, shall not be modeled.
- Daylight areas and photosensor locations shall be modeled as described in Section C3.5.3 after reducing the fenestration area as described in Section C3.6(c).