Not an Electrical Engineer
Not an Electrical Engineer
(OP)
Since I am not an electrical engineer, I have a question about Motor Control Centers and how to calculate the cooling load. I have a client with a MCC that he wants me to upgrade the AC. Obviously, the MCC is full of starters, breakers, etc. Do I size the AC based on the Hp rating of the starters, the Amp rating of the MCC or the total power coming into the room (5,000 Amps)? How would I go about calculating the load from the MCC in the room? I have looked at the ASHRAE manuals and can't seem to find anything on MCCs.
thanks for your help - DOUGLAS
thanks for your help - DOUGLAS





RE: Not an Electrical Engineer
RE: Not an Electrical Engineer
RE: Not an Electrical Engineer
I agree that actual electrical equipment values from the manufacturer are (of course) the best, when available; but cooling load calculations are full of assumptions anyhow and it is nice to have some rules-of-thumb to quickly get an idea of how big of a system might be necessary. Plus some of the MCC's/electrical rooms I've looked at and have had to add some cooling to have some pretty ancient equipment of which I'm not sure the manufacturers are even around anymore.
At any rate, there's a rule of thumb in "HVAC Equations, Data, and Rules of Thumb" by Arthur A Bell which gives 500 watts per section (vertical 20"W x 20"D x 84"H). At this rate, a 7 vertical-sectioned MCC (decent sized MCC) only contributes 1-ton of heat gain. Not a substantial load. Obviously some other assumptions are necessary for transformers, switchgear, VFDs, etc. It's all in the book--a good reference for those doing HVAC design IMO.
It has some numbers for low voltage through medium voltage starters as well if you're inclined to tally up the actual "buckets" and/or have a single line diagram handy.
RE: Not an Electrical Engineer
RE: Not an Electrical Engineer