Return Air Fan Speed Serving multiple air handling units
Return Air Fan Speed Serving multiple air handling units
(OP)
Im commissioning a central plant air handling system for a commercial building at present. One return air fan serves 3 air handling units. The fan is rated at 45 m3/s and each air handling unit is rated at 15m3/s approx. Its a VAV system so the AHU fans ramp up and down on a VSD to maintain a constant supply air pressure. How can I control the speed of the return air fan?. We have no air flow stations on the return air system. I was thinking of using the return air attenuator for which we can plot a system curve and depending of pressure drop equate the air flow rate. This would be done via the BMS of course. Some people say put a pressure sensor in the return air shaft, and maintain a constant pressure here. I have my reservations about this one. Any ideas?





RE: Return Air Fan Speed Serving multiple air handling units
RE: Return Air Fan Speed Serving multiple air handling units
RE: Return Air Fan Speed Serving multiple air handling units
RE: Return Air Fan Speed Serving multiple air handling units
You can use air measuring stations that install at the inlet of centrifugal fans. You will need two sets for DWDI (double width double inlet fans) and must sum them to get the airflow. You can track track the supply air CFM with an offsdet equal to the design minimum outdoor air but because of the high rise & plenum shaft return riser, expect to have stratification which may be a problem if you don't have proper zoning & supplemental heaters particulary at the buiding entries.
RE: Return Air Fan Speed Serving multiple air handling units