Crank up the datacenter heat -- with care

ASHRAE says it's OK to make the datacenter warmer, but a higher temperature could have unintended consequences

Datacenter experts often share a similar nugget of advice as to how to reduce energy bills for the datacenter: Turn up the heat. The reason is, some datacenter managers have their datacenter CRAC units running far colder than is necessary to keep their machines sufficiently cooled. There's a clear financial benefit to boosting the temperature in your datacenter: Increasing the set point temperature by just one measly degree can reduce energy consumption by 4 to 5 percent, which translates to lower energy bills. For the environmentally conscious company, that also means a reduction in carbon emissions.

[ Learn more tips about how to beat the heat in the datacenter. ]

The next question, however, is how hot is too hot for the datacenter? Many datacenter operators turn to ASHRAE (American Society of Heating, Refrigerating and Air-conditioning Engineers) for guidance there. As of last week, the group officially expanded its recommended datacenter temperature range [PDF]: Previously, it was 68 to 77 degrees Fahrenheit. Now, it's 64.4 to 80.6 degrees. (Those temperatures should be measured at the server inlets.)

Moreover, ASHRAE altered its recommended approach to measuring humidity levels: It should now be measured by dew point and fall within 41.9 degrees Fahrenheit to 59 degrees. Humidity was previously measured by relative humidity, and the temperature range was narrower.

Before you crank up the heat to 80.6 degrees in the hopes of reducing those monthly utility bills, take note: The datacenter is a complex environment, and adjusting the temperature can have some unexpected or unintended results. For starters, a higher set temperature point doesn't automatically mean less energy waste. As ASHRAE puts it, "Neither the 2004 nor the 2008 recommended operating environments ensure that the datacenter is operating at the optimum energy efficiency."

For example, some datacenter gear is designed to speed up its fans to compensate for the higher inlet air temperatures. This could potentially offset the gains in energy-efficiency that you'd enjoy from raising the datacenter's temperature. ASHRAE advises that datacenter operators "review and determine, with appropriate engineering expertise, the ideal operating point for their system. This will include taking into account the recommended range and their site specific conditions."

That means that ongoing measuring and adjusting is a must if you really want to see your datacenter operating at maximum efficiency.

[ Read about how Microsoft has developed a system for monitoring datacenter perform that has helped the company cut costs. ]

Raising the temperature in the datacenter also can result in hot spots in areas where cool air doesn't reach an entire rack, a case for implementing "advanced monitoring of rack temperatures and datacenter airflow before nudging the set point higher," suggests Rich Miller at Data Center Knowledge.

[ Learn more about monitoring tools from companies such as HP and SynapSense. ]

Moreover, increasing the temperature in the datacenter means hotter hot aisles -- up to as high as 130 degrees Fahrenheit if you're hitting ASHRAE's recommended maximum temperature. That could spell uncomfortable working conditions for IT staff working at the back of a rack. blogger Mark Fontecchio has a suggestion to deal with the intense heat: "Simply to pull up a tile where you're going to work in the hot aisle, and replace it with a perforated tile. That way you can get a nice chilly gust of cold air blasting from your feet to counteract the furnace blowing in your face. Sure, putting perforated tiles in the hot aisle is considered a severe no-no in well-designed hot/cold-aisle datacenter configurations. But if it's temporary, and it can prevent the need to have an IV bag of fluids on site just in case of severe dehydration and overheating of employees, well, then it might be worth it."

The potential consequences of a higher datacenter temperature don't end there. When those server fans kick into high gear in response to a higher temperature, there's another potential consequence: more noise in the datacenter. Michael Patterson, a thermal engineer at Intel, told IT Knowledge Exchange that "[for] servers with (variable frequency drive) fans -- the increase in power comes mostly from the increase in fan power after 25 degrees Celsius [77 F]," he said. "Servers in 27 degrees Celsius [80.6 F] may have higher acoustics due to higher fan speed."

ASHRAE says an increase of 3.6 degrees Fahrenheit can result in a noise increase of between 3 and 5 decibels, enough to warrant scrutiny by datacenter managers to ensure that they're not causing harm to datacenter staff: "With regard to the regulatory workplace noise limits, and concern to protect their employees against potential hearing damage, datacenter managers should check whether potential changes in the noise levels in their environment will cause them to trip various 'action level' thresholds defined in the local, state, or national codes."

The bottom line here is that while ASHRAE has given a stamp of approval to running the datacenter at a higher temperature (though some will argue it's still not high enough), there are caveats. Turning up the heat takes some planning and follow-up to ensure a positive outcome.


Copyright © 2009 IDG Communications, Inc.