ASHRAE-90.1-2022- - Page 288
Extracted Content
C3.5.2 Model Geometry and Thermal Zones. The building model shall be divided into thermal zones described as follows:
a. 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 condition- ing category and building area type as defined for each surface. b. Create a perimeter zone for each unique combination of building area type, above - grade - wall orienta-
tion, and space conditioning category . If there is more than one above - grade - wall assembly for a build- ing 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. c. 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. d. 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. e. The wall height and the height of each thermal zone shall be 15 ft. f. 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. g. 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. h. Vertical fenestration area shall be assigned to the associated surface as described in Section C1.4. Verti-
cal 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. i. Skylight area shall be assigned to the associated surface as described in Section C1.4 and Figure 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. j. Each zone shall be modeled as being fully enclosed. Zone boundaries not created as described above shall be modeled as adiabatic interior surfaces.
C3.5.3 Daylight Area and Photosensor Location. Daylight areas and photosensors shall not be modeled in residential zones. In each nonresidential zone, daylight areas and photosensor locations shall be modeled in accordance with the following:
a. 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 . b. 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. c. 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. d. 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.
C3.5.4 Schedules. The schedule types listed in Section C3.1.1(c) shall be required input. The schedules shall be consistent with those in the building envelope trade-off schedules and loads [1] for the applicable building area type.
1 Schedules and internal loads by building area type are found at http://sspc901.ashraepcs.org/documents.php.
286 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)