[rescue] Deciding how to place machines in a rack.

Sridhar Ayengar ploopster at gmail.com
Fri Mar 7 11:40:39 CST 2008

Earl Baugh wrote:
> But I'm curious about two things.  First, I'm trying to understand the
> purpose of the fans at the top of the rack.
> If this approach is to move the hot air out the back, I'm thinking I'll just
> have a hot spot behind the rack and that the top fans will
> just be pulling air from the front and back near the top.   Is this really
> assisting the cooling?  I can believe with the doors off
> that it's going to move that much air from the bottom of the rack.  Or is it
> to pull heat from the "stack" of machines?
> I'm just trying to understand this....  In my head I was thinking having the
> doors would help the top fans pull air from the
> bottom.  But I hadn't thought about the way they'd also hold in heat from
> all the machines, and that you'd get that hot air
> exhaust coming around and re-circulating thru the machines.  Very very
> helpful to know that that happens....

The purpose of the fan tray in a rack is to pull the hot air, which is 
collecting in the top of the rack, up and out.  It will also pull cool 
air from under the rack up and in.  This air will also flow past the 
intakes on the front of the equipment, providing cooler air than would 
be collected otherwise.

Peace...  Sridhar

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