VAV used as CAV in hospitals

[seanhkim]

I'm searching cases that VAV in hospitals are actually used as CAV because of several reasons. The biggest reason would be concerns of loosing pressure relationship between rooms in case of VAV. But is it the case happening in most hospitals? Is there any way to assure constant pressure relationship with VAV?

 

[lilliput1]

The 2006 AIA Deswign Guideline for Healthcare Facilities has a table showing the required minimum ACPH supply air, outdoor air and relative pressure of certain rooms. VAV is allowed but the minimum ACPH would have to be followed. If pressurization is critical and minimum ACPH is high (as isolation rooms with minimum 12 ACPH) you can use CV pressure independent air terminal boxes w/ HW reheat and with fxed differential (say minimum 200 CFM exhaust more than supply), The VAV AHU is typically controlled by having the VFD supply fan maintain a static pressure setpoint at the woprst duct run, measuring the curent supply fan CFM and controlling the VFD return fan speed to produce CFM equal to the supply CFM minum the design minimum OA CFM. The design minimum OA CFM being the maximum of either the OA ventilation air required or the sum of the exhaust air CFM plus pressurization air equal to 0.5 CFM/SF x SF floor area. Also note the AIA Standard requirement of having MERV 14 final filters downstream of the supply fan in addition to the MERV 8 initial filter upstream of the fan and coils. OA intatake must be minimum 3'-0" above the roof or 6'-0" above the ground and minimum 25'-0" away from exhaust air sources not HEPA filtered.