Heat load Calc's

[JimD1]

In an electrical closet I have a 45, 75, 112.5(2) and a 150 kva transformers, 5 total. What figures do I use to calculate the heat gain for airconditioning? The room is 12 x 15.5 ft.

 

[Goorah]

Jim:

I'm a mechanical so please bear with me!

Let's see 150kVA =~ 150,000 whatchamacallits = (about) 150kW.

1 kW = 3,412 BTUH (the Brits don't even use BTUs!!)

So 150 kW = 150 x 3,412 = 511,800 BTUH. Divide taht by 12,000BTUH/ton and youhave a heat gain of a whopping 42.6 tons! This is a whole lot of heat to pump outside if you consider that mechanical cooling in this size range can cost about $800/ton. Better to just ventilate the closet with outside air ... unless you're in the Saharah; but check the max allowable op temps of your trannys.

 

[fredb]

Hello

Transformer losses may average 7% for an older transformer, newer units may lose as little as 1-2%. For example, a 1500KVA unit running at a load factor of 65% and having an efficiency of 98% will experience a heat loss of about 13KW. If the load factor went to 85% the heat loss would be about 20KW. Typically today, a 25KVA unit should not lose more than 200W. I would estimate your losses to be in the range of 4 to 7 KW.

The NEC requires 100cfm of ventilation air for each KW of transformer loss. This assumes of course that the entering air temperature is low enough to "remove" your load.

I hope this helps you out.

 

[Goorah]

Thanks, Fred .... I forgot: ALL that power IS going to heat; but NOT all in the closet. The wire "ducts" are taking it to the loads. So it's just a 2 ton load at 7kW of losses. Ah well, it was late last night. :-(

 

[JimD1]

Thank you both for your help. This will get me "in the ball park"

Jim