Monday, 17 October 2011

Half of US data centres are using natural cooling

Green Grid Research published by the Green Grid, a non-profit consortium working to improve data centre efficiency, shows that 49% of data centres in the US are now using natural cooling to save energy and cost. Another 24% said they are considering doing the same in the near future. The average savings were 20% on energy costs and 7% on maintenance costs.

The results come from a survey on the use of economisers – cooling devices that take advantage of outdoor conditions to provide all or some of the data centre cooling, reducing the need for refrigeration. Economisers are either air-driven, with cool air blown straight into the facility or using heat exchangers to cool the outside air first, or they use the outside air to help chill the water used to create the cool air inside the data centre itself.

Despite the savings, it seems that the economisers are not being used as much as they could be. They were only used around 80% of the time they would be effective due to concerns about switching between the economiser and other mechanical cooling systems and the maintenance of the economiser itself.

The main barrier to using economisers was the difficulty in retrofitting existing facilities, reliability concerns and initial installation costs. But the level of satisfaction suggests the effort is worth it, with 80% saying they would recommend economiser use.

The survey was conducted in early 2011. A total of 115 people responded, all familiar with their data centres’ cooling system. Only those with data centres larger than 2,500 square feet were asked to participate because of the low likelihood of economisation being used in smaller facilities. Of those that responded, half had data centres smaller than 25,000 and the rest were larger. Most data centres (90%) were located in the US, with 6% in Europe.

It’s good news, although a bit of a surprise, that economisers are being used so much – a major contributor to green IT in the data centre. Of course the amount of time they can be effective depends on outside air temperature, so will vary considerably. Looking at the report itself, the data suggests that over 60% of data centres have the economisers on for less than half the year.

Even when they are on they will mostly only be partially contributing to cooling. Even so, I would have expected to see some impact on power usage effectiveness (PUE), the Green Grid data centre metric that compares total data centre power use with the power required to drive the IT equipment. The less cooling power used the lower (and better) the PUE. But while over 70% of respondents reported their PUE, the report found that there was no statistically significant difference between the PUE reported by those who use economisers and by those who don’t.

You would think the 20% savings in energy costs would show up in a reduced PUE. The study notes that ‘The lack of correlation does not seem to affect owners’ satisfaction with economisers or the perceived savings in an individual application of economisers’. It does rather suggest that either the economisers savings are over-estimated or the PUE calculations are out. Either way, it’s something that the Green Grid plans to investigate further.

© The Green IT Review

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