return air fan

return air fan

A fan which withdraws air from an air-conditioned space and returns it (or part of it) to the central air-conditioning system.
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To simplify the simulation, it is assumed that the simulated building has a lumped interior zone and a lumped exterior zone, each served by one TB, and the return air fan power is ignored because it is relatively small compared to the supply fan.
The unit was equipped with both a supply and a return air fan, at fixed speeds, which combined could deliver 3817 cfm (1,801 l/s) at 2" (50 mm) wc external static pressure - this arrangement was changed part way through the monitoring period to reduce total airflow and overall electrical energy consumption.
The test AHU has both a supply air fan and return air fan, and both fans are equipped with variable-frequency drives (VFDs).
[H.sub.2]O) Q = airflow through each path, [m.sup.3]/s (cfm) R = relief air damper control signal for BPP and BPA damper controls S = path resistance factor [omega] = relative fan speed based on design speed [theta] = damper blade position (1 for fully open and 0 for fully closed) Subscripts d = design EF = exhaust air fan ex = exhaust air (path) inf = envelope infiltration (path) MA = mixed air plenum (node) oa = outdoor air (path) OAD = outdoor air damper ra = return air (path) RCD = recirculating air damper RE = relief or return air plenum (node) rec = recirculating air (path) rel = relief air (path) RF = return air fan RLD = relief air damper RM = room air or space (node) sa = supply air (path) SF = supply air fan TB = terminal box REFERENCES
generally described as complete removal of the existing air handling unit (AH-1) and return air fan (F-9) and replacement with new similar units.
The unit was equipped with both a supply and a return air fan, at fixed speeds, which combined could deliver 3817 cfm (1,801 l/s) at 2" (50 mm) wc external static pressure--this arrangement was changed part way through the monitoring period to reduce total airflow and overall electrical energy consumption.
Space was found in the return air section for a new return air fan, and new return duct installation was found to be feasible.
The return air fan is assumed to be reduced by the ratio of the System Four 350,694 cfm (165 492 L/s) to the base system 400,000 cfm (188 760 L/s).
(1.2 kPa) head Motor 50 hp (37.3 kW) size Return Air Fan Airflow 45,000 cfm (21.2 [m.sup.3]/s) Fan 1.5 in.
3 pieces of process return air fans made of plastic, each 26 250 m 3 / h.
Return air fans are controlled to maintain required airflow through all zone return dampers with minimized pressure drop.
If your AHUs have return air fans, ensure that they don't pull too much air during low demand.