Data Center Cooling Set Points Debated

What's the temperature in your data center? With many U.S. corporations focused on lowering their data center power bill, some vendors are recommending that data center managers raise the baseline temperature - known as a set point - inside their data center. Although nudging the thermostat higher can save money, some data center managers warn that it may leave less time to recover from a cooling failure.

Data center managers can save 4 percent in energy costs for every degree of upward change in the set point, according to Mark Monroe, the Director of Sustainable Computing at Sun Microsystems (JAVA), who said most data centers use set points between 68 and 72 degrees. Monroe did a survey of 14 of Sun's data centers, and found that eight had the temperature set at 68 degrees, five at 72 and one at 74.

"If you're running at 68 degrees, you're running at the bottom level of most of those ranges," Monroe said last week at AFCOM's Data Center World conference in Dallas. "There's no reason why you can't move to 78. This is a really simple thing to do."

Financial services firm Washington Mutual (WaMu) is among the companies that have raised their data center temperature as part of a green computing initiative to make their facilities more energy efficient.

It may not cost anything to turn the thermostat up, but some data center professionals worry about the impact of "hot spots" from high-density cooling installations. Confronted with a choice between paying a higher power bill or having servers overheat and malfunction, many data center operators prefer to err on the side of applying too much cooling, rather than too little.

Improved monitoring of data center conditions is one approach to moving set points higher. Air flow analysis using computational fluid dynamics (CFD) and placing temperature sensors on equipment are strategies that can give data center managers a detailed picture of thermal conditions in their facility.

Raising the set point is a key goal of Hewlett Packard's Dynamic Smart Cooling product, which is scheduled to launch next year and incorporates CFD, a sensor network, and a central server to monitor and adjust cooling. A similar approach is offered by DegreeC's AdaptivCool solution, which is already available.

"In some data centers the air coming out of the tiles is 50 degrees," HP infrastructure technologist Ken Baker said in a presentation on the product earlier this year. "It's a ridiculous level of overkill. Part of Dynamic Smart Cooling's technology is raising the set points. We're not taking (air conditioning) capacity out of the facility, we're just turning it down."

Sun's Monroe noted that equipment from HP, IBM, Sun and Cisco are all warranteed to work in environments up to 95 degrees. While that high a set point is impractical, Monroe argued that most facilities can raise their set points without compromising reliability. But he also acknowledges that raising set points can test the comfort level of many data center professionals. "This is a sensitive issue," Monroe said.

Audience members at Monroe's Data Center World sessions raised several concerns. One attendee noted that a higher set point leaves a shorter window of opportunity to address cooling failures. A new study by Opengate Data Systems found that a typical data center running at 5 kilowatts per server cabinet will experience a thermal shutdown within three minutes during a power outage. Higher density cabinets with 10 kilowatts will shut down in less than a minute. "Thermal runaways can wreak havoc on a data center causing instant data loss and lost revenue," said Martin Olsen, director of Product Management and Development for Active Power, the maker of UPS flywheel systems that sponsored the study.

Monroe said that if the facility is well managed, the benefits of raising the set point outweigh the risks. "If you have a thermal event, you're going to have to recover quickly," said Monroe. "I don't think those 3 or 4 degrees are going to make much difference."

Several attendees wondered about the impact of higher temperatures on data center humidity, which can be an important issue in the data center environment. Too much humidity can cause condensation on electronic components in a data center, while too little can result in static electricity that can damage equipment.

Monroe said the raised floor isn't the only area of the data center where temperature settings are being scrutinized for energy savings. "There is quite a bit of talk of raising the chilled water systems from 45 to 55 degrees," said Monroe. Recent studies on mechanical plant efficiency by Lawrence Berkeley Labs found that raising the chilled water temperature from 42 degrees to 55 degrees could improve chiller efficiency by 15 to 25 percent.