lowest possible pump speed for VFD
lowest possible pump speed for VFD
(OP)
till how low can i reduce the speeds of my condenser water pumps? is there a limit that the pump cannot be set as low as 30hz. we are 60 hz here in our country.
the application of the pump is because i really have a low delta T with my heat exchanger, the pump flow is 2000gpm and i am planning to reduce it to around 1000gpm by installing a VFD is is possible? or there will be problem with the pump (cavitation or whatsoever.)
please share some insights
the application of the pump is because i really have a low delta T with my heat exchanger, the pump flow is 2000gpm and i am planning to reduce it to around 1000gpm by installing a VFD is is possible? or there will be problem with the pump (cavitation or whatsoever.)
please share some insights





RE: lowest possible pump speed for VFD
RE: lowest possible pump speed for VFD
1. The electronics in a VFD can typically give you a 10:1 turndown (i.e. 60 Hz down to 6 Hz) but the turndown on a motor is an entirely different thing
2. For VFD service the pump motor has to rated for inverter duty service.
3. I typically do not run a pump at less than 30 Hz because the motor will overheat. When a motor is rated for VFD service the motor casing size is typically increased so that you have more surface area to dissipate the heat
4. I suppose you could ask a motor manufacturer what the allowable turndown is. If you want very low speeds you may have to go to things such as water cooled motors
RE: lowest possible pump speed for VFD
RE: lowest possible pump speed for VFD
what you guys think?
RE: lowest possible pump speed for VFD
RE: lowest possible pump speed for VFD
Think about swapping out the pump motor with a premium efficient motor. These are almost always called for when adding a VFD to water loops.
RE: lowest possible pump speed for VFD
I would recommend first get pump curve for different speeds (4 or 5 curves). If you know your pump supplier, he/she should be able to get this for you (I did same way!!!). This is very crucial since either you trim impeller or use VFD, along with the flow rate pump is bound to loose it's head capacity. Make sure @ 1000 gpm your pump is able to generate pressure more than your system pressure otherwise after reducing speed/trimming impeller you may find your pump is running at dead head!
To my knowledge, you should run VFD at least ~ 10% (6 Hz), this will ensure motor (if it is air-cooled) doesn't overheat. I am not sure about existance of such limit on pump side (as long as you don't run it on extreme side of curve).
RE: lowest possible pump speed for VFD