Using Outside Air for Data Centers

Conventional wisdom holds that it takes one Watt of cooling to remove every Watt of ICT equipment inside the data center. Today's data centers can do a bit better than that, but cooling costs remain a considerable OpEx cost for facilities.

One approach that's generating increased interest is the use of dry-side economizers, which bring in outside air to cool the data center. Using outside air saves the power that is normally used by compressors and chiller plants to cool facilities; even bigger gains may be achieved by avoiding CapEx (Capital Expense) costs by eliminating the purchase of chiller plants entirely or at least reducing CapEx costs by installing smaller cooling plants.

At first blush, this approach may seem to only be of marginal value. However, higher density data centers (such as those with blade servers) may have a relatively large temperature increase between inlet and exhaust temperature. Even if the desired inlet temperature is only 75°F, a facility with a 50°F temperature rise would have an exhaust temperature of 125°F--most ambient temperatures are well below this temperature. Bringing in outside air could take less energy than cooling the recycled air--humidity considerations notwithstanding.

To look at the impact of using outside air to cool data center equipment, several data center operators have performed small-scale tests to see how data center equipment is impacted by outside air:

• Microsoft's test: http://blogs.msdn.com/the_power_of_software/archive/2008/09/19/intense-computing-or-in-tents-computing.aspx
• Intel's test: http://www.intel.com/it/pdf/Reducing_Data_Center_Cost_with_an_Air_Economizer.pdf and http://www.datacenterknowledge.com/archives/2008/09/18/video-intels-air-side-economization-test/

Air economizers look promising, based on these results.

--kb