Each room has its own booster fan and receives air which has been cooled and filtered by the primary rooftop air handler. Each individual booster fan has its own HEPA filter and a variable frequency drive to maintain supply air volume as the filter loads. Final supply air to the patient room is delivered through a constant volume box. Final supply air to the anteroom is delivered through a variable volume box. The return air system is not used.
Exhaust air is drawn from each patient room through a variable volume box and from the ante-room through a constant volume box. Under normal conditions, the control system measures the pressure relationships between the rooms and maintains proper patient room pressurization by varying the volume of both the exhaust air from the patient room and the supply air to the anteroom.
If the primary rooftop supply fan fails the individual room booster fan has adequate residual fan capacity to draw needed supply air through the inoperative rooftop unit. If the isolation exhaust fan fails, a bypass damper to the primary return duct opens. If both fail, supply boxes provide at least 50% design air quantity to maintain positive pressurization.