Hot air extraction – more efficient server room cooling


In addition to the power for servers, a huge cost we have is cooling them. 6kW of servers is going to require some chilling. Our data room has air conditioning and it works very hard for a living particularly in summer where the heat differential on the aircon exchanger outside is lower. In a big data centre you’d pump chilled air into a ‘cold aisle’ in front of a load of racks, and then have a ‘hot aisle’ behind them where you suck the air back into the A/C. Unfortunately our building wasn’t designed with this in mind so we simply have a wall mounted unit that cools the whole room. The problem with cooling the room though, is there’s no way of making sure the servers see chilled air, they might get air that has come directly from the back of the rack and sucked back round again.

Whilst doing some tidying up I spotted one of our old extraction fans from years gone by. When we were a much smaller company, air was drawn into the room at one end and extracted at the other end. It kept things cool enough until we started to need more equipment and then A/C was the only option.

Anyway, below, you can see the unused fan and our main server rack to the left.


There are probably some very expensive hot air extraction systems on the market, but I figured there was no point in spending a lot of cash to trial it out. B&Q to the rescue for some gaffa tape and guttering pipe. Add in the old box from my Herman Miller ‘Mirra’ chair, and an hour of creativity and we have a working hot air extraction system…..


I simply made a baffle infront of the fan and added ducting that goes down behind the server. It’s not pretty, but it does work:


There… proof it works! We dropped the temp measured at the top of the rack by a degree. Air intake temps on the servers lowered even more. Our SQL server was drawing in 24 degree air previously, and is now a lot more chilled. (21 degrees!). The UPS unit on the floor beside the rack had a similar drop from 25deg to 22deg.

We’ve massively reduced the strain on our air con unit for the grand sum of about £50 and the overhead of a 100W fan. (which is more than offset by the potential savings in air con for that room)

The next thing to try is adding curtains from the side of the rack to the wall to force the hot air into the extracted area.

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