Isolation Room

[Norm01]

I have an existing hospital that is going to be adding two isolation rooms with a common ante room. The existing HVAC system is a constant volume dual duct system. I was thinking of using two separate exhaust fans (one for each room). Each room would be supplied with its own dual duct box. It was mentioned on a previous thread that with a dual duct system the exhaust could be varied to maintain pressure differentials.
Is this done with a two speed exhaust fan or a VAV box on the exhaust ductwork?
Also, given the common ante room I was thinking of supplying and exhausting this area from a system serving one of the rooms. Any thoughts on this? Would this lead to balancing issues?
Thanks.

 

[mauricestoker]

One thing I would recommend is including a bubble-tight damper on the supply discharge from the mixing box. An interlock would be needed between exhaust fan (perhaps a CT on motor and dP in duct) to make sure that if the exhuast goes off or you go positive, the buuble tight damper would close. End switch on buuble tight would not open until CT amp's and/or CT ampereage is satisfied.

A VFD on the exhaust would compensate for filter loading. Not sure if the vestibule would need an exhaust, that would depend on how much air you are sending through the doors. If your balance if for 100 CFM to each isolation room, plus maybe 40 CFM out vestibule entry door, you would need need supply until 240 CFM. Keep in mind that if one isolation room goes down, the other needs to stay in operation.