Many data centre operators have been increasing the operating temperature in their data centres to reduce the massive costs of cooling. But, warns Alan Beresford, Technical Director and MD with EcoCooling they run the risk of significantly more failures.
ASHRAE (the American Society of Heating and Refrigeration Engineers) is generally considered to set the standards globally for data centre cooling. A few years ago it relaxed its recommended operating range for data servers from 20-25℃ (Celsius) to 18-27℃.
For decades, said Beresford, data centres have operated at a 20-21℃ temperature. With the relaxation in the ASHRAE 2011 recommendation plus the pressure to cut costs - data centres have begun to significantly increase the cold aisle temperature to 24-25℃ and in some cases right up to 27℃.
But many of them have not taken into account the study of server reliabilities detailed in the ASHRAE 2001 Thermal Guidelines for Data Processing Environments - which predicts that if the cold aisle temperature is increased from 20℃ to 25℃, the level of failures increases by a very significant 24%. Upping the temperature to 27.5℃ increases the failure rates by a massive 34%.
Warns Beresford: And if the air temperature going into the front of the servers is 27℃ its going to be very hot (34-37℃) coming out of the rear. For blade servers it can be a blistering 42℃ at the rear!
Its not just the servers that can fail, states Beresford, at the rear of the servers are electric supply cables, power distribution units and communication cables. Most of these are simply not designed to work at such elevated temperatures and are liable to early mortality.
Interestingly, again according to ASHRAEs published figures, if the temperature is reduced to 17℃ the server reliability is improved by 13 per cent compared to conventional 20℃ operations.
To cool the air to 17℃ would be completely uneconomic with conventional refrigeration cooling, said Beresford, our modelling shows it would require over 500kW kilowatts of electricity for every megawatt of IT equipment.
However, with our evaporative direct air cooling CRECs (Computer Room Evaporative Coolers), this 17℃ operation would require less than 40kW kilowatts a saving of over 450kW compared to conventional refrigeration and a reduction of PUE (Power Usage Effectiveness) of 0.45.
When given the option of cooling a data centre with refrigeration at 27℃ compared with evaporative cooling at 17℃ at less than 10% of the energy use, 40% less temperature related server failures and a more stable environment for other components it is clear why over 150 UK data center operators have adopted this approach.
Alan Beresford has prepared an informative webinar explaining how evaporative cooling works and why it uses so little energy compared to conventional refrigeration.
Beresford adds a final point, when Engineers and technicians are working on servers, its usually at the rear where all the connections are. If they are going to have to work regularly in temperatures of 34℃ to 42℃ there might be health issues to consider too. Keeping their working environment under 30℃ is a far more acceptable solution.
View Evaporative space cooling: CREC Product Entry