Cleaning Filters increase Amp Draw in Fans
Cleaning Filters increase Amp Draw in Fans
(OP)
Can someone explain the operation of a constant speed fan that would make a constant speed fan increase in Amp Draw after the filters have been cleaned? Is it because there is more air to blow? I would think that the lower static pressure on the system would cause the opposite, but that is not the case.





RE: Cleaning Filters increase Amp Draw in Fans
rmw
RE: Cleaning Filters increase Amp Draw in Fans
RE: Cleaning Filters increase Amp Draw in Fans
Forward curved fan have a rising power characteristic so that when more air is passed, the more power is drawn. If you take a side panel off an air handling unit when it is running, the fan motor may overload. However, if you use a backward curved fan, (depending on the manufacturer), you may find a slight rise and then a fall as the airflow rises.
We in the UK use both types in AHU's. FC fans are cheap, but I prefer BC curved fans because they are more tolerant to airflow etc.
Friartuck of sherwood
RE: Cleaning Filters increase Amp Draw in Fans
Units of Power are based on effort to move weight at a given pressure and volume. While air is relativly light in comparison to say water (8.33 lbs/gal)electrical energy will still increase to accomplish this additional level of loading on the fan motor.
The fan laws are based on Forward Curved fans that state the the volume of increase has a expondential impact on motor BHP [Cube Root of the (New CFM divided by the Old CFM)times the old BHP equals the New BHP ]
The type of fan wheel that you use gives some better qualities as stated in other responses.
RE: Cleaning Filters increase Amp Draw in Fans
Fans also exhibit odd behaviour. Try measuring the fan speed of a direct drive FC fan and then closing the duct damper to throttle it. The fan impellor speed up dramatically. This characteristic varies between fan types.
When you take a side panel off an air handling unit when it is running, the reduced system resistance allows the fan to push more air and absorb much more power (FC Fans). The net result is that unless the motor is suitably sized, or protected, it will overload. BC fans don't do that. Try using a current transformer to measure the variations, and you will get a few surprises.
Friar Tuck of Sherwood