What size intake holes in the wall do I need?

euser1984

Hi,
I'm going to be extracting air from a room at 2300 m3/h into my attic (the room is more or less sealed except around the sides on the entry door).

The dimensions of the room are 4.7 x 3.9 meters and 2.1 meters high.

I'm know I'm going to have to put some holes into the wall to the outside. The fan intake circumference is 12 inches and will be mounted on the ceiling - or rather will be installed in the attic and ducted from the room.

Will a 12 inch hole do the trick then or would a few smaller ones make any difference?

Thanks a mill.

antoinolachtnai

You are going to be changing the air 2300m3/37m3 = 62 times an hour at that rate. That's a lot of air.

This website gives a formula for how much of an opening you need.

http://www.tombling.com/cooling/factory-and-workshop-cooling.htm

I really don't know where they got the factor at the end (.3268) from but it sounds in the right ball park.

In your case, I think this works out at about 2 square meters of opening. That's basically leaving the door open. It's a massive amount of air movement.

You need to be sure that the air is forced through the heat source, and cannot easily bypass it.

ART6

There's another consideration here. If you pump that amount of air into the attic, how is it going to get out again? You would need to be sure that your soffits have vents capable of taking that amount of air, otherwise you will pressurise your attic. Your ceilings might not appreciate that!

Are you turning the room into a paint spray booth?:D

euser1984

I'm just attaching a pdf here of the plan I've made up. Can you let me know what you think?

euser1984

antoinolachtnai wrote: »

In your case, I think this works out at about 2 square meters of opening. That's basically leaving the door open. It's a massive amount of air movement.

Really?
I would have thought it would only need to be the same diameter as the fan circumference?

antoinolachtnai

Nope. It is like a lake that is feeding a 12-inch firehose (where the room is the lake and the outlet of the fan is the firehose).

I would get a speed controller unit for that fan, and just try it out. It will probably be fine.

antoinolachtnai

Nope. It is like a lake that is feeding a 12-inch firehose (where the room is the lake and the outlet of the fan is the firehose).

I would get a speed controller unit for that fan, and just try it out. It will probably be fine.

antoinolachtnai

I am just going by the calculation the guy has on the website. Plug in the numbers yourself and see what it gives. But it sounds right to me. It is like a lake that is feeding a 12-inch firehose (where the room is the lake and the outlet of the fan is the firehose).

I would get a speed controller unit for that fan, and just try it out. It will probably be fine.

In your diagram, you have down that you want 500 cubic meters/hour of air going through each computer and it is fan-assisted. Surely this is the air intake and surely you are trying to pull all the cold air through the computers? Why do you want additional intakes?

I do not think the idea of having an air intake directly from the outside for each computer is a very good one but that is a separate issue.

euser1984

antoinolachtnai wrote: »

I am just going by the calculation the guy has on the website. Plug in the numbers yourself and see what it gives. But it sounds right to me. It is like a lake that is feeding a 12-inch firehose (where the room is the lake and the outlet of the fan is the firehose).

I would get a speed controller unit for that fan, and just try it out. It will probably be fine.

In your diagram, you have down that you want 500 cubic meters/hour of air going through each computer and it is fan-assisted. Surely this is the air intake and surely you are trying to pull all the cold air through the computers? Why do you want additional intakes?

I do not think the idea of having an air intake directly from the outside for each computer is a very good one but that is a separate issue.

Sorry no all the intakes for the computers will not be fan assisted. The intention is that the air will be sucked through via pressure?

I figured if each machine needed 500m3/h then 2000m3/h exhaust would do the trick.

euser1984

Actually just to add; can't believe I forgot to add this when I posted the pdf.

The plan is to use a large piece of rectangular ducting like this http://www.ductstore.co.uk/acatalog/800mm_Long_Straight_Lengths.html.

On the external wall there will be just one hole to draw air from outside with something like this link. http://www.ductstore.co.uk/acatalog/Meshed_Outlets.html

Then use four of these on the rectangle (rectangle will be the size of all the four machines combined. http://www.ductstore.co.uk/acatalog/Spigots_on_Plates.html

And in between the main air intake and the rectangular frame a filter like this http://www.ductstore.co.uk/acatalog/info_FILB.html

One of my concerns is the air being too cold in winter and the fact that the air might not be pulled through the four holes evenly? As someone has mentioned I can use the speed controller to determine what pressure I need pulled in through the external vent.

antoinolachtnai

Where did you get that figure for air changes on the computers?

Personally, I would try it with one big fan right above and slightly behind the four machines. I would leave the door open if necessary to ventilate. Once things are working well like that you can do something more permanent.

You could put the computers corner to corner, in a circle right under the fan if you wanted to be a bit fancier (arrange with corners butten up together so that ear fans are blowing into the centre).

But really, I think it will be fine. The big issue is whether the cases are able to get the heat out of the case fast enough.

You are right to be concerned about drawing outside air directly in.

None of this would be the recommended way to set up or operate a small data centre.

ART6

euser1984 wrote: »

One of my concerns is the air being too cold in winter and the fact that the air might not be pulled through the four holes evenly? As someone has mentioned I can use the speed controller to determine what pressure I need pulled in through the external vent.

If you are going to run ducts from the air intake to each of the computers then it is extremely unlikely that an equal amount of air will go through each as ductwork lengths and any bends will have a significant effect. The only way of ensuring equal air flows would be to fit butterfly dampers in each duct leg immediately before each computer, and balance the system by opening or closing them until you get equal air flow.

Where the air temperature is concerned, cold air is more dense than hot air, so in winter you might need less air flow through the computers. I summer it would be the other way round. In that case it might be worth fitting a thermostatic speed controller -- that would make the fan run at the appropriate speed for the air temperature. See http://www.icmag.com/ic/showthread.php?t=42770 for a DIY one.