Minimum fan speed for vfd
Minimum fan speed for vfd
(OP)
I am evaluating the energy savings for installing a vfd on a 30 hp cooling tower fan. Can someone tell me what is the minimum speed I can expect the VFD to run reliably?
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
Minimum fan speed for vfd
|
RE: Minimum fan speed for vfd
The limiting factor will most likely be motor cooling.
Ask the motor manufacturer.
RE: Minimum fan speed for vfd
Another consideration for the large fans is "cogging", also related to the gearbox.
Stay above 30% if you want to be assured of long life.
RE: Minimum fan speed for vfd
This can be a minor detail and self managing if the moisture laden air simply turns around and goes back through the tower. But it can lead to some real damages if the CT is winter time operational or if you have confines that can lead to mold growth or similar.
If the cooling tower is in the middle of a field and well above ground, you could experiment to establish the limit; or you can undertake the psychrometrics based on your "season" of operation and limit or potentially instrument accordingly.
Those who operate VFD's 24/7/365 have found that pumped volume becomes an accompanying topic at O/D temperatures below 45-deg. F.
RE: Minimum fan speed for vfd
RE: Minimum fan speed for vfd
There are VFD's on the market that also include a function called Sleep/Hibernation mode. This, in combination with a minimum speed will automatically shut the VFD down if the speed is idling at minimum for any length of time. If it switches off automatically, then this is where the big savings in energy, low acoustic noise and wear/tear will be minimised even more. Very common on cooling tower applications to use something like this.
RE: Minimum fan speed for vfd