Apple is using solar arrays, including a 100-acre solar energy farm in Maiden, N.C., to help power a data center there.
Apple allowed NBC's Today show inside the facility this week, and during the tour, a reporter asked what the temperature was there. "It's about 103 degrees in here," said Lisa Jackson, Apple's vice president of environmental initiatives and a former Obama administration EPA chief.
What wasn't explained is that Jackson and the reporter were walking down a hot aisle, and feeling the fan exhaust. The experience might have been different if they had walked down the cold aisle, where the rack fronts face the aisle.
Apple isn't disclosing details about its Maiden data center operations, except at the 30,000 foot level, so it's unknown exactly what temperatures it's operating at.
But it is possible to estimate a range.
The American Society of Heating, Refrigerating & Air-Conditioning Engineers (ASHRAE) sets temperatures and humidity guidelines for data centers based on what it knows about the equipment inside them. It recommends that data centers operate between 64.4 to 80.6 degrees Fahrenheit.
The recommended limit concerns the air intake temperature. The exhaust temperatures will be higher, how much higher will depend on the density and the quality of the air management, according to the Uptime Institute vice president Keith Klesner. But the temperature could be approximately 15 to 30 degrees Fahrenheit higher, he said in an email.
Dave Kelley, director of application engineering at Emerson Network Power's Liebert Precision Cooling, narrowed it down further. Typically, he said, "if you have 80 degrees Fahrenheit entering the IT equipment in the cold aisle, you will have 100 to 105 degrees Fahrenheit leaving in the hot aisle. All of these values are functions of how much work the IT equipment is doing. If it is not at full output, then the leaving temperature could be less," he said.
The points made by Klesner and Kelley, coupled with the 103 degrees cited by Jackson, suggest that Apple is running near or at the recommended ASHRAE temperature limit. To do so let's Apple save the most money on energy cost.
That strategy puts Apple in the forefront of data center operators in terms of temperature limits.
According to Uptime, while cutting edge-type data centers are pushing the thermal envelope, most data center managers are more conservative. A recent Uptime survey found that nearly half of all data centers reported operating at 71 to 75 degrees Fahrenheit. The next largest temperature segment, from 65 to 70 degrees, was 37%, it reported.
Data center managers may err on the side of caution because higher data center temperatures can increase risk of equipment failure, but it also requires sophisticated controls to avoid hot spots and other cooling problems.
ASHRAE also sets "allowable" temperature guidelines that go well above the recommended limits. Manufacturers can make equipment that can work at higher temperature ranges, all the way up to 113 degrees for equipment in the A4 class.
There are classes of equipment from A1 to A4, which represents the higher end of tolerance.
"Most operators will not operate to the allowable limit of the equipment but rather some temperature below that. In A4 class equipment, maybe they will select 105 degrees Fahrenheit," according to Don Beaty, a consulting engineer and publications chair of the society's Technical Committee 9.9 for mission-critical facilities, technology spaces and electronic equipment.
Patrick Thibodeau covers cloud computing and enterprise applications, outsourcing, government IT policies, data centers and IT workforce issues for Computerworld. Follow Patrick on Twitter at @DCgov or subscribe to Patrick's RSS feed . His e-mail address is firstname.lastname@example.org.