ASHRAE-90.1-2022- - Page 289
Extracted Content
C3.5.5 Building Envelope. The building envelope shall reflect the information specified in Section C1. Exception to C3.5.5: Where three-year-aged test data for the solar reflectance and three-year-aged ther mal emittance of the exterior roof surface are unavailable, the exterior roof surface shall be modeled with a solar reflectance of 0.30 and a thermal emittance of 0.90.
C3.5.5.1 Shading. Manually operated interior shades shall be modeled on all vertical fenestration . Shades shall be modeled to be in the lowered position when either the transmitted luminance is greater than 200 cd/ft [2] or the direct solar transmitted energy exceeds 30 Btu/h·ft [2] and then remain lowered for rest of the day. Shades shall be modeled with visible light transmittance of 0.10, visible light reflectance of 0.40, solar transmittance of 0.21, and solar reflectance of 0.23. Permanent shading devices such as fins and overhangs shall be modeled.
C3.5.5.2 Dynamic Glazing. Automatically controlled dynamic glazing is allowed to be modeled. Manually controlled dynamic glazing shall use the average of the minimum and maximum values for both SHGC and VT .
C3.5.5.3 Air Leakage. The air leakage rate of the building envelope ( I75Pa ) at a pressure differential of 75 Pa (0.30 in. of water) shall be 0.35 cfm/ft [2] of building envelope area when air leakage compliance is based on whole- building pressurization testing and shall be 0.45 cfm/ft [2] of building envelope area when air leakage compliance is based on verification. The air leakage of the building envelope shall be converted to the appropriate units to describe the air leakage as a function of the area of walls that separate conditioned spaces and semiheated spaces from the exterior as follows:
IAGW = 0.112 × I75Pa × S / AAGW where
I75Pa = air leakage rate of the building envelope (cfm/ft [2] ) at a fixed building pressure differential of 75 Pa (0.30 in. of water)
S = total area of the building envelope (ft [2] ) 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/ft [2] ) 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, ft [2]
Exception to C3.5.5.3: If the simulation program cannot simulate air leakage as a function of the area
of walls that separate conditioned spaces and semiheated spaces from the exterior, the air leakage of the building envelope shall be converted to the appropriate units to describe the air leakage as a function of gross floor area as follows:
IFLR = 0.112 × I75Pa × S / AFLR where
IFLR = adjusted air leakage rate of the building envelope (cfm/ft [2] ) at a reference wind speed of 10 mph
and relative to the gross floor area
AFLR = gross floor area, ft [2]
C3.5.5.3.1 Air Leakage Schedule. To simulate air leakage as described in Section 5.4.3, infiltration shall be adjusted in accordance with the infiltration schedule in the building envelope trade-off schedules and loads for the applicable building area type.
C3.5.5.4 Thermal Bridges. Linear and point thermal bridges in the proposed design shall be either of the following:
a. Not modeled where option (a) or (c) is selected in Section C1.2.7. b. Entered as individual thermal bridge inputs of length or count where option (b) is selected in Section
C1.2.7 and addressed as follows:
- Individual thermal bridges in the proposed design that are indicated to comply with the requirements of Sections 5.5.5.1 through 5.5.5.5 need not be modeled.
- Individual thermal bridges in the proposed design that are indicated to not comply with the requirements of Sections 5.5.5.1 through 5.5.5.5 shall be modeled.
- Individual thermal bridges in the proposed design that are indicated to be not applicable with the requirements of Sections 5.5.5.1 through 5.5.5.5 need not be modeled. C3.5.6 Interior Surfaces. Interior surfaces shall be modeled with visible light reflectances of 0.80 for ceilings, 0.50 for walls, and 0.20 for floors. Interior surfaces shall be modeled with a thermal emittance of 0.90.
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 287