ASHRAE-90.1-2022- - Page 290
Extracted Content
C3.5.7 Lighting. The modeled lighting power shall be determined using the lighting power density allowances in Table 9.5.1 for the applicable building area type. The modeled lighting power shall be adjusted in accordance with the lighting schedule in the building envelope trade-off schedules and loads for the applicable building area type. Fifty percent (50%) of lighting in daylight areas shall be modeled with continuous daylight dimming controls such that when sufficient daylight is available at the corresponding photosensor, lighting power is reduced to maintain a minimum 50 fc for conditioned spaces and 30 fc for semiheated spaces . The minimum light output for the continuous daylight dimming shall be 6% of peak light output. Power input shall be modeled as 20% of lighting power at the minimum light output and scaled linearly to 100% of lighting power at peak light output. C3.5.8 HVAC Systems. One HVAC system shall be provided for each thermal zone and shall have the following characteristics:
a. Constant-volume fan control. b. Electrically provided cooling with EER from Table 6.8.1-1, based on requirements for split- system air
conditioners with heating section type “all other” between 65,000 Btu/h and 135,000 Btu/h. The EER shall be adjusted to remove the fan power in accordance with Section 12.5.2(c). c. 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. d. The ventilation rate for each building area type shall be consistent with the ventilation rate in the build-
ing envelope trade-off schedules and loads for the applicable building area type. e. Air economizers, except in Climate Zones 0 and 1. The high-limit shutoff shall be “Fixed Dry Bulb” type
as described in Table 6.5.1.1.3. f. System design supply air rates shall be based on a supply-air-to-room-air temperature difference of 20°F in cooling. g. System capacities used in the annual simulation shall be 1.5 times the capacities determined by the sizing
simulations. h. 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.
C3.5.9 Miscellaneous Loads. Miscellaneous loads shall be modeled as included in the building envelope trade-off schedules and loads for the applicable building area type.
C3.5.10 Occupant Density. The occupant density shall be modeled according to the peak occupant density and the occupancy rate schedule in the building envelope trade-off schedules and loads for the applicable building area type.
C3.5.11 Heat Gain from Occupants. The sensible and latent heat gain due to occupants shall be modeled as included in the building envelope trade-off schedules and loads for the applicable building area type.
C3.6 Calculation of Base Envelope Performance Factor. The simulation model for calculating the base envelope performance factor shall modify the simulation model for calculating the proposed envelope perfor- mance factor as follows:
a. All opaque assemblies shall be modeled with the U-factor not greater than that 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/ft [2] ·°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. b. Thermal bridges :
- Where option (a) is selected in Section C1.2.7, no modifications to the assembly U-factors are required.
- Where option (b) is selected in Section C1.2.7, the U-factor of the assembly interrupted shall be modified per Section A10.2 using the default values in Table A10.1 for the appropriate class of construc- tion . Each of the linear thermal bridges or point thermal bridges identified in Sections 5.5.5.1 through 5.5.5.5 shall be modeled in the simulation model for calculating the proposed envelope performance. Where the balcony length in the proposed design is greater than allowed by Section 5.5.5.2.2, the area shall be reduced proportionally along each exposure until the limit set in Section 5.5.5.2.2 is met.
- Where option (c) is selected in Section C1.2.7, no modifications to the assembly U-factors are required. c. The exterior roof surfaces shall be modeled with a solar reflectance and thermal emittance as required in
Section 5.5.3.1.4(a). All other roofs, including roofs exempted from the requirements in Section 5.5.3.1.4, shall be modeled the same as in the proposed design . The above-grade wall surfaces of buildings shall be
288 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)