Two Speed Motors

[DanielRCI]

Hello,

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.
Please advise.
Thank you for reading.

[atmosphere]

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.