Thursday, 26 August 2010


Some years ago, we undertook a small experiment with our server room. We had heard that other people were reducing the amount of A/C cooling they used and we wanted to see if it was appropriate for us.

Like a lot of other places, our small server room was kept cool to keep the servers cool; if we were to spend any length of time in there, we would need to put on a jumper or even a fleece to stay warm, as the room was around 10 degrees centigrade. The A/C units were running non stop, and we wanted to see if we could reduce the electric we used.

Essentially, we made a load of measurements to get a base line. These included the core temperature of the UPS, some measurements of the servers and various places within the server room. We were fortunate that our engineering manager had a device that we could borrow for this as he was conducting a number of tests to help the company work towards ISO14001.

He also had a device that allowed us to measure the amount of power drawn by various devices – we seemed to get a couple of slightly odd readings, but when we discounted those, the average values appeared to match what would be expected. We therefore assumed that the errors we had were down to incorrect use.

Having got our base line values, we then started to increase the ambient temperature of the room, and examine what affect this had. Each time, we would leave the changed settings for a couple of weeks to see what would happen; in each case, there was no sign of distress on the servers, so we were able to increase the temperature again.

After some time, we found that the “sweet spot” was between 20 and 24 degrees centigrade. Above 24 degrees, we would see the fans in the servers starting to work much harder and draw more power. Below 20 degrees, the A/C was still running almost all the time. However, in that range, we found that we had the A/C unit running at its least power draw whilst the servers ran at a comfortable level.

We found that in the racks, we had a few “hot spots”; places where the temperature was quite a bit higher than the ambient temperature of the room. We were told that this is normal and generally considered a good thing; these create a thermal current that allows the cooling to happen naturally. The interesting thing was that although the ambient temperature increased by 12 degrees, the hot spots only increased by 3-4 degrees.

Part of the work meant that we had to make sure that the racks were properly positioned in the room to allow for adequate air flow, and the direction of air from the A/C also had to be optimised to prevent “air curtains” forming at various places. We also had to make sure that things such as blanking plates were used to ensure a properly controlled air current within the racks.

Although this all sounds very grand, the room is quite small and most of the work was done in between our normal activities. We were able to make use of some additional advice from the A/C supplier, but that was relatively minor. The total amount of work required was actually quite small, but the results have been very good. We have seen a reduction in power consumption of just under 50% for the server room as a whole – which translates into significant cost savings.

I’ve added a link to a resource that I would recommend to anyone wanting to do work on their server room facilities. It is primarily aimed at North America, but there are some bits that are specifically for the European market. It will take some time to go through all of it, but I consider that it would be time well spent.

The really good thing - we now have a server room that we can work in, in reasonable comfort all the time!

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