Raising the temperature in server racks can make a data center more efficient. But what happens if the room gets too hot for people?
If you’re Google, the servers keep humming along while the humans retreat to climate-controlled sections of the building. That’s what’s been happening at Google’s data center in Belgium, which was the company’s first facility to rely entirely upon fresh air for cooling, instead of energy-hungry chillers. That approach has helped the facility become Google's most efficient data center.
For the vast majority of the year, the climate in Belgium is cool enough that this design works with no problems. When it gets hot in Belgium, the temperature inside Google’s data center warms beyond the facility’s desired operating range – periods that the company refers to as “excursion hours.”
Staff Retreats From Heat
During these periods, the temperature inside the data center can rise above 95 degrees. That’s when the humans leave the server area.
“We've been operating in Belgium since 2008 with no chillers,” said Joe Kava, Senior Director of Data Center Operations for Google. “We've had very few excursion hours, and they don't last long, so we let the site run right through them. We ask our employees to go in and do office work. It's too warm for people, but the machines do just fine.”
Google’s experience is the latest affirmation that servers are much tougher than we think. Many data centers feel like meat lockers, as servers are maintained in cool environments to offset the heat thrown off by components inside the chassis. Typical temperature ranges in data centers often range from 68 and 72 degrees.
In recent years, rising power bills have prompted data center managers to try and reduce the amount of power used in cooling systems. If you can raise the temperature, data centers can run with less cooling, or even none at all, as is the case at Google’s Belgium site.
Servers Handle Heat
Studies by Intel and Microsoft showed that most servers do fine with higher temperatures and outside air, easing fears about higher hardware failure rates. Dell recently said it would warranty its servers to operate in environments as warm as 45 degrees C (115 degrees F).
But this trend has implications for data center staff. Higher temperatures at the server inlet area also mean more heat in the hot aisle, where staffers work on cabling and other connections in the rear of the server. This is a special challenge when the hot aisle is contained to prevent waste heat from recirculating into the cold aisle.
The federal Occupational Safety and Health Administration (OSHA) sets guidelines on work conditions in the U.S., which call for specific ratios of rest time to work time for people working in environments where temperatures exceed acceptable working conditions, such as a contained hot aisle in a data center.
Some server techs simply dress for warmer conditions in the hot aisle. For some providers, the answer was shifting cabling connections to the front of the server, so techs could work in the cold aisle. Facebook's Open Compute design, for example, places cabling on the front of the server, allowing the company to leave the hot aisle dark.
On-Demand Cooling for Hot Aisle
Vendors are starting to offer equipment that can address conditions in the hot aisle. Tate, which makes flooring tiles for raised-floor environments, recently introduced the SmartAire T, an in-floor damper that can provide on-demand cooling in hot aisles. When maintenance is required, cool air can be briefly redirected into the hot aisle to make the area tolerable for staff.
Before entering the hot aisle, a technician uses a supply trigger, typically a switch located outside the hot aisle, to activate the SmartAire T units. Cool air then enters the hot aisle until a comfortable temperature is established. SmartAire T units maintain this temperature until the technician completes the assigned work and deactivates the units.