Cooling an Electrical Room via Ventilation

[MichaelFehrenbach]

I have a question concerning utilizing ventilation to cool an electrical room.

The electrical room has 2 transformers that are generating 100,000 btu/hr of heat. I would like to provide ventilation to the space to handle this load. The summer design day temp is 94 degrees.

If I were to calculate the room temperature to be 100 degrees, then I would need 15,432 CFM to maintain that temp. That is a tremendous amount of air for a space that is 2000 ft3.

My question is what is the maximum ACH limit for an electric room where the air is being removed so quickly that the temperature rise from the transformers is not actually increasing the temp of the room and the room temp is ambient temp. At 15,432 CFM, the ACH rate is 463 and it will feel like a jet engine going off in that room.

Michael

 

[RandomUserName]

Hmmm. I think you are playing with fire here.

Your numbers are sound: 15,500 CFM will keep your room at 100°F on a 94°F day.

But this is an electrical room; not a comfort cooling application.

What happens when you get a heat wave in July with temps at 98°F or 99°F? In comfort cooling, units might be on 24/7 and only keep room air at 76°F or 77°F instead of the setpoint of 75°F. In your application the electrical room hits 101° ... 102°F ... 103°F .... climbing closer and closer to the 104°F that I believe most electrical items require the ambient temp not to exceed.

After your extreme heat wave, a massive cold front comes in; violent too. This front is packing a mean squall line and thunderstorms behind it. Temp quickly drops down to 80°F and it starts raining hard; our air is now 100% RH. Are you sure you want to introduce saturated air around an electrical room?

Are you prepared to install a redundant fan system and automatic controls for when system 1 unexpectedly goes down? If both system 1 and 2 go down can the electrical equipment been safely shut off without affecting workers / production / cost $$ to the owner?

I think you need to look at these options, the safeties, and cost of two 15,500 CFM air systems and compare them against a (estimating at this time) 10 TR CRAC unit moving about 4700 CFM.

 

[ProcessHVAC]

It's your call, but I would try to refrigerate the space and put some sort of emergency cooling ventilation with those loads and design temperatures.

 

[RossABQ]

Is this a Federal gov't (or federally funded) facility, and mechanical cooling of "utility spaces" is not allowed? Been there, done that...

 

[ssdd09]

Hi Michael,

You want to consider spot ventilation.

Regards,

 

[Ziggypump]

Why not indirectly cool/ventilate the space? An exhaust fan to pull room temp from an adjacent room has been used before. Your starting temp would be much lower, requiring much less air to maintain the 100F room temp.

I would agree with Random, as using a design degree day for this type of situation may not be the best idea. Design temp is not worst case temp.

 

[capliard]

In mining, we bring the RH up to bring temperature down, check your air psychrometric charts.
Link

Air at 94F an 0% RH can be brought down down about 55F just by vaporizing water. If your air is saturated in water, you'll have to climatize to bring temperature down. Vaporizing water is the cheapest way to cool a dry air flow.

About saturated air around electrical room, i believe it's not a problem unless there is no flow. Anyway, the heat rejected by electrical systems means the air will not be saturated the instant is takes that heat. Make sure there are no droplets carried by airflow and you'll be fine.

I don't know in which environment you work, but 15kcfm is not a lot of air. If you room is square and not tunnel-like, the air velocity will be fine. Check air velocity in room. If too high, you could rearrange the geometry in a rectangle and ventilate perpendicular to long side, therefore reducing air velocity.

You can install climatisation, if not sure, but it sure doesn't need to run all the time.

I hope you're in Nevada, not in Columbia!

Hope it helps.

Charles, mining engineer.

Ingenieur Minier. QuTbec, Canada.

 

[lukaiENG]

I have got around situations like this before by installing an exhaust/re-circulation fan sized for a larger delta (say 25F). when OAT is low, you exhaust air out of the room, when OAT is above say 75F you recirculate air through the space, passing it across a duct mounted cooling coil. This effectively makes the system a equivalent of an economizing CRAC unit.

 

[mirza057]

SSDD09,

The spot ventilation is a good Idea, are there any instances as such used in the electrical rooms? Do they work?

 

[cry22]

We always air-condition switch gear rooms, whether housing transformers or not.
You need to use two AC units ideally floor mounted with ductwork so you don't have to deal with condensate over electrical equipment.
two 4-ton units will do you just fine. Install an exhaust fan to operate in winter and as a stand-by.
Keep in mind that your equipment warranty has a disclaimer of max room temperature. you don't want to lose your warranty on a 1 million dollars plus equipment just because you do not want to spend 10K, do you?

 

[ssdd09]

Hi mirza057,

I've used spot ventilation on manufacturing plant with equipment that has high heat load. It does not make sense to cool the entire area if you could isolate the heat source. I also do not see any problem in applying it to transformer rooms.

Regards,