Ventilation for generator compartment

[Ray D]

I built a metal box for the generator. I have a 500 CFM fan (a 10" in-line squirrel cage type) to ventilate the box while the unit is running.  Does anyone know if I would get better air movement by blowing into the box or turn the fan around and pull the air out??

Thanks,
Ray D

[Dreamscape]

First, I am not a scientist. 

I can only provide facts associated with the industry I work in.

When wanting to move air faster in a given space, exhaust the moving air to the outside, provide a smaller inlet for fresh air coming in. The air will be changed much faster then going the other way.

HTH, FWIW,

Paul

[gus]

If you seal the air flow equally either way it will make no difference.

I would put the fan at the air intake simply because cool air is better for the fan and motor than hot air.

Normally you don't want any fluid (air) to move too fast past anything to be cooled so the air has more time to absorb the heat.

A good example of this is when ill advised people remove engine thermostats in hopes the engine will run cooler. The exact opposite happens, the coolant moves so fast it doesn't absorb the heat and the engine actually runs hotter.

[Ray D]

Thanks Guys,

That is the exact info I was seeking.

Ray D

[TomC]

Gus- there is a big difference between air cooling and water cooling.  Air cooling- air has relatively little heat absorption capabilities so you want to have the air moving past an object as fast as possible to get the maximum cooling effect.  Point- wind chill factor.
But with water cooling, water can absorb alot of heat and it does it at a much slower rate, so your comment on thermostates is very correct.  Yes the thermostat prevents the engine from running cold, but also slows down the flow so the coolant can absorb the heat.

Personally- pushing the air through the gen box would seem better.  Then it will have a slightly positive pressure which helps any engine run better.  200 cfm would be enough (not including combustion air) for keeping the gen cooled.  Good Luck, TomC

[gus]

Tom,

You've convinced me. Logically it would seem that air as a poor heat absorber should move even slower to give it more time to absorb but obviously it absorbs so little heat it needs much greater volume to work at all. Your wind chill point says it well.

It just occured to me that we don't know if his gen is air or liquid cooled? Of course even liquid cooled ones are air cooled too!

[Ray D]

The generator is an 8Kw water cooled deisel.  The air would be for generator cooling and fresh air for the engine.

Ray D

[gus]

Ray,

In that case you may not even need a fan. Since the gen is enclosed the radiator fan can
move air through the radiator and out of the box if it is shrouded properly. This same exhausted air will pull fresh air into the box for combustion and gen cooling if constructed properly.

If the radiator fan just pushes or pulls air through the radiator with no shrouds then you need some ducts to direct the hot air out.

I'm assuming your gen is shrouded with a built in fan that blows air over the gen and probably the exhaust, most generators have this. This air also needs to be directed out of the box by ducting and it will also pull fresh air into the box.

In other words if you have ducts exhausting the hot air out of the box and an adequate opening for cool fresh to enter the box your gen will stay cool.

With no radiator shroud or ducting your extra fan may just stir up the air and not really remove the hot air. There is a lot to this and you need to plan it out carefully.

If it has a remote radiator all this does not apply.

You don't need a fan to blow air into the engine for combustion air, the engine will take care of that.

It is really kind of diffucult to try to help with this not knowing the layout.

To answer your original question, it makes no difference to the fan whether it pushes or pulls, it is all the same. However, as I said before, having the fan push the air into the box will keep the fan motor out of the hot exhaust air.