ASHRAE-90.1-2022- - Page 009

Extracted Content

cooldown: reduction of space temperature down to occupied set point after a period of shutdown or setup.

cooled space: see space, conditioned space .

cooling degree-day, base (CDD): see degree-day.

cooling design temperature: the outdoor dry-bulb temperature equal to the temperature that is exceeded by 1% of the number of hours during a typical weather year.

critical circuit: the hydronic circuit that determines the minimum differential pressure that the pump must produce to satisfy the zone loads (e.g., the circuit with the most-open valve). The critical circuit is the one with the highest pressure drop required to satisfy its load. At part-load conditions, the critical circuit can change based on zone loads.

daylight area: the floor area substantially illuminated by daylight.

daylight area under roof monitors: the daylight area under roof monitors is the combined daylight area under each roof monitor within each space . The daylight area under each roof monitor is the product of

a. the width of the vertical fenestration above the ceiling level plus, on each side, the smallest of

1. 2 ft,
2. the distance to any 5 ft or higher vertical obstruction, or
3. the distance to the edge of any primary sidelighted area and b. the smaller of the following horizontal distances inward from the bottom edge of the vertical fenes-

tration (see Figure 3.2-1):

1. The monitor sill height (MSH) (the vertical distance from the floor to the bottom edge of the monitor glazing)
2. The distance to the nearest face of any opaque vertical obstruction, where any part of the obstruction is farther away than the difference between the height of the obstruction and the monitor sill height (MSH – OH) daylight area under skylights: the daylight area under skylights is the combined daylight area under each skylight within a space . The daylight area under each skylight is bounded by the opening beneath the skylight and horizontally in each direction (see Figure 3.2-2), the smaller of

a. 70% of the ceiling height (0.7 × CH) or b. the distance to the nearest face of any opaque vertical obstruction, where any part of the obstruction

is farther away than 70% of the distance between the top of the obstruction and the ceiling (0.7 ×

[CH – OH], where CH = the height of the ceiling at the lowest edge of the skylight, and OH = the height to the top of the obstruction). daylight area under skylights in multistory spaces: the daylight area under skylights in multistory spaces shall include floor areas directly beneath the skylight and portions of the uppermost floor adjacent to the multistory space that meet the criteria for a daylight area under skylights, where CH is the ceiling height of the uppermost floor (see Figure 3.2-3). primary sidelighted area: the total primary sidelighted area is the combined primary sidelighted area within each space . Each primary sidelighted area is directly adjacent to vertical fenestration in an exterior wall below the ceiling (see Figure 3.2-4).

a. The primary sidelighted area width is the width of the vertical fenestration plus, on each side, the

smaller of

1. one half of the vertical fenestration head height (where head height is the distance from the floor to the top of the glazing) or
2. the distance to any 5 ft or higher opaque vertical obstruction. b. The primary sidelighted area depth is the horizontal distance perpendicular to the vertical fenes-

tration, which is the smaller of

1. one vertical fenestration head height or
2. the distance to any 5 ft or higher opaque vertical obstruction. secondary sidelighted area: the total secondary sidelighted area is the combined secondary sidelighted area within a space . Each secondary sidelighted area is directly adjacent to a primary sidelighted area (see Figure 3.2-5):

a. The secondary sidelighted area width is the width of the vertical fenestration plus, on each side,

the smaller of

1. one half of the vertical fenestration head height or
2. the distance to any 5 ft or higher opaque vertical obstruction.

ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 7