ASHRAE+62.1-2022+(1) - Page 067
Extracted Content
Table K-1 Ventilation Intensity Brackets
Bracket (L/s)·m [2] cfm/ft [2] Commonly Encountered Space Typologies Bracket
1 0.0 to 1.0 0.0 to 0.2 Office, living room, main entry lobby
2 1.0 to 2.0 0.2 to 0.4 Reception area, general manufacturing, kitchen, lobby
3 2.0 to 3.0 0.4 to 0.6 Classroom, daycare
4 3.0 to 4.0 0.6 to 0.8 Restaurant dining room, places of religious worship
5 4.0 to 5.5 0.6 to 1.1 Auditorium, health club/aerobics room, bar, gambling
Not addressed: Lecture Hall and spectator areas (6 [L/s])/m [2] ) and disco/dance floors (10.3 [L/s]/m [2] )
K3. PRESCRIPTIVE PATH A CALCULATIONS
K3.1 Ventilation Intensity. Spaces have been defined by a ventilation intensity, which represents the amount of flow rate needed per Equation 6-1, divided by the floor area of the space. Its units are (L/s)/m [2] of floor area or cfm/ft [2] of floor area.
(K-1)
Ventilation Intensity
= ------- = ---------------------------------------- -
Az Az
------- Vbz = ---------------------------------------- Rp Pz + Ra A - z Az Az
Vbz
The ventilation intensity brackets in Table K-1 are used.
K3.2 Single Openings. The flow through a single sharp opening due to bidirectional buoyancy-driven flow ( Vbd_sharp ) (see Etheridge and Sandberg [1996] in Informative Appendix P) is expressed as follows:
(K-2)
where
Aw = free unobstructed area of the window, or openable area
T = temperature difference between indoors and outdoors. Given the conservative nature of a prescriptive path, a temperature difference of 1°C (1.8°F) is assumed for these calculations. In reality, this temperature will depend on the internal gains in the space and will likely be higher than 1°C (1.8°F), leading to higher airflows (and a smaller window area requirement).
Hs = vertical dimension of the opening
g = gravity constant
Tref = reference temperature in Kelvin (or Rankine), typically equal to Tin, Tout or an expected average. A reference temperature of 21°C (70°F, 294K) was assumed for these calculations.
A safety factor is incorporated assuming that an awning window is used. Awning (or top-hinged) windows are among the most common windows used for natural ventilation and, because of their uneven vertical area distribution, are more inefficient than a sliding window (sharp opening) at driving flow. An efficiency ( v ) of around 83% (value used in these calculations) when compared to sliding windows is inferred from
Vso = Vso _ sharp w
(K-3)
Assuming a height-to-width ratio for the window of RH/W ( R = H/W ), the window area can be rewritten as
2
(K-4)
Aw
= ---------- - RH / W
HS 2
The required openable area as a fraction of the zone’s floor area is therefore calculated by equating the bidirectional buoyancy-driven flow through a single awning opening ( Vso ) to the goal flow rate ( Vbz ) obtained from Table 6-1.
Vso = Vbz
(K-5)
ANSI/ASHRAE Standard 62.1-2022 65