Exhaust Fan when Heat Pump is in Econo
Exhaust Fan when Heat Pump is in Econo
(OP)
I have noticed that all manufactures of equipment (Trane, Carrier, York) have no power exhaust on side discharge units. I have a 3 unit heat pump system with 15 tons each (2 units will be running at a time, 1 backup). The system max cfm is 12000 cfm (6000cfm/unit), existing exhaust fan for bathrooms, closets, etc is 2000 cfm. If one Heat pump is running i sized one fan for 4000 cfm (6000cfm -2000cfm), and another at 10,000 cfm (12,000cfm-2000). Should I size exhaust fans smaller and let a slight build up in pressure? Is there a rule of thumb for power exhaust units? I noticed that many manufactures use about 1/3 to 1/2 inlet amount to size power exhausts. i.e. 8000 cfm inlet, 4000 cfm power exhaust. Are there any exhaust fans that have 2 speed, that can be controlled by control unit without VAV drive?





RE: Exhaust Fan when Heat Pump is in Econo
RE: Exhaust Fan when Heat Pump is in Econo
DrRTU is correct. Power exhaust units can be installed in the return air ductwork. Usually they are multiple fans and are sequentially turned on as the OA damper open to attain the design economizer mixed air temperature (which should be reset up as it gets cooler outdoors). Ideally there should be about 0.05 CFM/SF floor area not returned for pressurization (to avoid infiltration).
RE: Exhaust Fan when Heat Pump is in Econo