Switchgear Heat Loss

[drktmplr12]

I'm tasked with developing the anticipated heat losses in an electrical room as an input to HVAC design.

The Eaton CAG Power Equipment Losses tables seem excessive for low voltage switchgear. I've included heat loss for each breaker and additional loss for each switchgear section. With that I have 17 tons. I still need to include 2700 HP worth of VFD's. The switchgear is rated 5000 A and has 6 sections in use at any given time.

Something doesn't feel right..I understand these are worst case assumptions, bit it seems odd that a switchgear section would give off that much heat even under full load.

Any opinions would be appreciated.

 

[Jraef]

An old old engineering book I had at one time gave me a "shotgun" rule for calculating heat loss on things like breakers and motor starters that used thermal heater elements for current sensing. It said to use .3W per running load amp per phase as the heat rejection. So if we apply that rule to Eaton's chart, an 800A 3 phase thermal-mag circuit breaker, carrying 640A continuous (80%) would be estimated at 576W of heat rejection. Eaton's chart says 400W, so I'd say that's actually a BETTER number than my old book said to use. Theirs is probably based on more empirical evidence rather than shotgun rules.

 

[drktmplr12]

It helps to have additional perspective. I'm going to discuss my results with some co workers as well.

Thanks for the feedback. :thumbsup: