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Thread: Two Speed Motors
11-24-2011, 04:40 PM #1New Guest
- Join Date
- Nov 2011
Two Speed Motors
I looking for information regarding two-speed motors. I am trying to do a comparison between the existing (two-speed motor) and a VSD for a cooling tower, 30 HP motor.
My layout for the VSD is as follows
50% Load = 2 hours/day
60% = 3
70% = 6
80% = 6
90% = 4
100% = 3
Using this (very basic) layout I can estimate consumption for the VSD. However, I am uncertain how to approach two speed motors. The assumption is 50% & 100% load, but I do not think this is correct.
Thank you for reading.
11-26-2011, 10:07 AM #2Professional Member
- Join Date
- Dec 2003
- Northern VA
It seems you are asking if on a present two speed motor (can I guess an Evapco tower?) whether the low speed operation delivers 50% capacity all the way around.
For instance, at low spd. does it turn 850 rpm (50 % of 1725 rpm),does the blower wheel or prop fan thus deliver 50% of its' full speed CFM. and does the heat rejected therefore equal 50% of the tower's rated capacity?
If this is the question, in light of the law of diminishing returns, I don't think this will bear out.
In my opinion, to get a more accurate idea of what the low speed perfomance is in reality, I would base my percentages primarily from the motor amp draw at low speed compared with the high speed, and secondly the difference between the temp. split between fluid in / out.
I would make sure the belts and pulleys are in good condition before I get the amp draw.
Is this a wet/dry tower with a 1st stage jet pump? You may want to get the same readings in both dry and wet mode and compare.
Hope this helps.
And Good Luck."Iron sharpeneth iron..."