Cooling Plenum

by robbieD

 As you have already seen, Shoarthing (and me too, now) are big on keeping our burning machines cool.  Don't forget that we also want to keep these cool machines quiet.  The theory that he passed on to me was that if we have an intake plenum (like an air-intake box for an auto) with its fans having the same throughput of air [cfm] as the exhaust fans mounted at the back of the case, we can control the direction & reduce any turbulence & stagnant hot-spots of the air cooling the computer case.

I was disconnecting all my drives before I realized I should have a "Before" picture.

The reason we can better utilize this passing air by taking it thru a plenum first is the air has a chance to settle down & flow as one body; also, any fan[s] work far more efficiently with a open volume in front & behind them. 

With most all store-bought cases air is drawn in [& exhausted] through a rough circle of stamped holes. You only have to take a quick measure to realise the total area of the apertures is around 50-60% of the area swept by the fan. On top of this, the fan is mounted right by what is effectively a half-closed door.  Result: a turbulent, half-choked flow.  If the air is drawn in easily, brought through the plenum and settled down, it can be aimed coherently through the case - ideally to equal balanced exhausts drawing the heated air out. 

There is one more reason for the plenum (actually more): by attaching the fans to the back, sides, or top of the plenum, you move their noise right back inside the computer.  With the fans screwed direct to the computer case - & threshing in turbulent air - their noise is right up front too.

Here are some thumbnails of the progress

(click on thumbnail to enlarge)

When I first bought this case, I would get up in the middle of the night and wonder what the noise was down the hall.  This thing was so loud it bothered me.  That was with one intake and one exhaust fan.  (32 cfm. in and 32 cfm. out)  I now have two intake fans and two exhaust fans (64 cfm. in and 64 cfm. out) and it is much quieter than with the previous configuration.

We'll post some test figures from this & other similar installations in a couple of days - shoarthing's plenum installation brought case-temps down by 8C - that's 13F

If you have any comments/questions about this review please go here