directly to the outdoors without mixing with exhaust air from any other non-Airborne Infection Isolation room or exhaust system. d) Exhaust air grilles or registers in the patient room shall be located directly above the patient bed on the ceiling or on the wall near the head of the bed. e) The room envelope shall be sealed to limit leakage air flow at 0.01 in. w.c. (2.5 Pa) differential pressure across the envelope. f) Differential pressure between AII rooms and adjacent spaces that have a different function shall be a minimum of –0.01 in. w.c. (–2.5 Pa). The standard does not require any particular air volume flow rate differential to an AII room. To do so would then establish a mandatory effective leakage area in the room envelope. This is manifest from the following equation (Equation 28) found in the 2005 ASHRAE Handbook— Fundamentals in Chapter 27, Ventilation and Infiltration. (1) where Q = Airflow rate, cfm CD = Discharge coefficient for opening, dimensionless A = Cross-sectional area of opening, ft2 ρ = Air density, lbm/ft3 D p = Pressure difference across opening, in. of w.c. C3 = Unit of conversion factor = 776 Air Distribution Devices www.info.hotims.com/16018-60 Table 6.2 “Supply Air Outlets” (Table 2) prescribes supply air diffusers in accordance with the classification systems in Chapter 33, Space Air Diffusion, of the 2005 ASHRAE Handbook—Fundamentals. This provides implicit guidance regarding acceptable air distribution patterns. (This is an example where the standard acknowledges that the ventilaOctober 2008 56 ASHRAE Journal
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