In the talk I gave at the Efficient Data Center Summit, I note that the hottest place on earth over recorded history was Al Aziziyah Libya in 1922 where 136F (58C) was indicated (see Data Center Efficiency Summit (Posting #4)). What’s important about this observation from a data center perspective is that this most extreme temperature event ever, is still less than the specified maximum temperatures for processors, disks, and memory. What that means is that, with sufficient air flow, outside air without chillers could be used to cool all components in the system. Essentially, it’s a mechanical design problem. Admittedly this example is extreme but it forces us to realize that 100% free air cooling possible. Once we understand that it’s a mechanical design problem, then we can trade off the huge savings of higher temperatures against the increased power consumption (semiconductor leakage and higher fan rates) and potentially increased server mortality rates.
We’ve known for years that air side economization (use of free air cooling) is possible and can limit the percentage of time that chillers need to be used. If we raise the set point in the data center, chiller usage falls quickly. For most places on earth, a 95F (35C) set point combined with free air cooling and evaporative cooling are sufficient to eliminate the use of chillers entirely.
Mitigating the risk of increased server mortality rates, we now have manufacturers beginning to warrant there equipment to run in more adverse conditions. Rackable Systems recently announced that CloudRack C2 will support full warrantee at 104F (40C): 40C (104F) in the Data Center. Ty Schmitt of Dell confirms that all Dell servers are warranted at 95F (35C) inlet temperatures.
In this study Don Atwood and John Miner of Intel IT take the a datacenter module and divide it up into two rooms of 8 racks each. One room is run as a control with re-circulated air the their standard temperatures. The other room is run on pure outside air with the temperature allowed to range between 65F and 90F. If the outside temp falls below 65, server heat is re-circulated to maintain 65F. If over 90F, then the air conditioning system is used to reduced to 90F. The servers ran silicone design simulations at an average utilization rate of 90% for 10 months.
The short summary is that the server mortality rates were marginally higher – it’s not clear if the difference is statistical noise or significant – and the savings were phenomenal. It’s only four pages and worth reading: http://www.intel.com/it/pdf/Reducing_Data_Center_Cost_with_an_Air_Economizer.pdf.
We all need to remember that higher temperatures mean less engineering headroom and less margin for error so care needs to be shown when raising temperatures. However, it’s very clear that its worth investing in the control systems and processes necessary for high temperature operation. Big savings await and it’s good for the environment.
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