Tuesday, December 14, 2010

Should You Increase CRAC Set Points to Save Energy Costs?

By David Gross

Energy management for data centers has been lighting up the press wire lately.   The fundamental economic premise behind most of the stories is that by monitoring temperature, air flow, and humidity at more places and more closely, a data center will get a great financial return by reducing energy costs.   But I'm finding that some of the vendor presentations present the savings at a very generic level, and while they might have a good story to tell, the suppliers need more detailed financial analysis, and more sensitivity analysis in their financial estimates, especially to highlight how the financial paybacks vary at different power densities.

Recently, consulting firm Data Center Resources LLC put out a press release claiming that by increasing CRAC (Computer Room Air Conditioner) set points, a data center could get a "six month" ROI on its investment in sensors, aisle containment systems, and airstrips that augment existing blanking panels.    Of course, there is no such thing as a six month ROI, but I'll grant them the point that they really mean a six month payback period.   However, as I've said many times, ROI is a meaningless metric, instead data center managers should be using IRR, and incorporating the time value of money into all such calculations.

Once these new systems are installed, Data Center Resources argues that you can start increasing the temperature (they did not mention anything about humidity) set point on the CRACs and reduce energy costs.  The firm claims each degree increase in the CRAC set point cuts 4-5% in annual energy expenses.   But given the wide discrepancies in data center power densities, the actual savings are going to vary dramatically, and before estimating an IRR, a data center manager would need to perform a sensitivity analysis based on growing server, power, and cooling capacities at different rates, otherwise this is all just a generic argument for hot aisle/cold aisle containment.

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