During normal operation, this outdoor 34,000 CFM unit recovers energy by passing 7,400 CFM of outside air through a plate HX. Constant volume toilet exhaust air and relief air from the return plenum are sent through the exhaust side of the HX.
When switched to economizing operation, this toilet exhaust and relief air are bypassed around the HX, and the minimum OA damper is closed. All the economizing outside air is brought through (2) OA dampers on the sides of the unit.
