Electrical Room Ventilation

[Fattony11]

I am trying to ventilate a small room containing some electrical equipment (VFD's, Chokes, a small Transformer)with an exhaust fan and a mechanical damper but I don't really know how to estimate a heat output for the equipment in the room. I was hoping that someone may be able to tell me a rule of thumb for calculating air makeup rates so I can determine what size fan to use.

 

[RossABQ]

The best we've come up with (conservative) is that at most 10% (usually more like 5%) of the actual load going thru the electrical gear shows up as waste heat. Note that it is actual load, not the nameplate of the equipment. Their equipment comes in discrete sizes too, and is sized to hit a peak requirement with safety margin, so that using nameplate data will give you too high a number. Your best bet is to get them to give you a good idea of actual peak and average loads, like from Dapper or similar software (if it's being used).

 

[KenRad]

On most of my electrical rooms, I've used somewhere around 6 CFM per square foot. This is in the southeast US, in rooms containing transformers and substations.

For control, I put the fan on a VFD, controlled by a temperature sensor. I put the roof-mounted fan on the side of the room opposite the outside wall where the louvers are, so the outside air sweeps the entire room. And I put gravity dampers on the louvers, which open more as the fan speed increases.

The VFD keeps the fan from cycling excessively during colder months, and allows you to oversize the system to accommodate future growth.

---KenRad

 

[atlas06]

http://www.eng-tips.com/viewthread.cfm?qid=172106&page=1

See this thread, I aasked the question a while back, and I got some good answers.

 

[lilliput1]

KenRad,
You should use motor operated intake damper. Gravity damper in intake application would not keep out wind driven infiltration. The wind would blow it open similar to if you made the room negative to open them.

 

[marcoh]

Rough rule of thumb for transformers is 1L/s per transformer kVa.

Good VSD are generally around 97% efficient therefore 3% heat rejection.

Switchboards are alway tricky and I would say most switchrooms ventilation systems are very conservatively sized! I once had an electrical engineer calculate the heat loss to 2 decimal places once (something like 10567.83 watts heat rejection and he was willing to round, reluctantly, to 11kW. lol I normally use 600W per cubicle as a guess.

 

[STYMIEDPIPER]

You did not specify application
Also, consider your environment.
Is your electrical room in a commercial type atmosphere or in a heavy industrial facility where the adjacent exterior wall temp may be 100 deg F or higher due to the manufacturing process at the facility.
Look at the thread that ATLAS has referenced. I particularily agree with the response of oversizing the ventilation.
Nobody has ever complained that their electrical room is too cool. But you will always hear the complaints if the room is too warm.