Renne and his team placed wireless temperature sensors on 388 server racks to gain a better understanding of hot and cold air spaces in the new high-density layout. They used vinyl curtains to enclose hot aisles so that hot and cold air couldn't mix as freely. They installed a cogeneration system that captures heat waste and turns it into electricity to power chillers.
No more sweaters in July
The new cooling design reduced hot and cold air mixing and increased the Delta T to nearly 22 degrees. With more efficient expulsion of hot air and better use of cold air, the overall datacenter no longer had to be kept at a chilly 55 degrees. The new room temperature target: 67 degrees.
Economizers could now use outside air in the 70-degree range. "This literally gets us through spring," Renne says. And during summer months, economizers can continue to blend outside air with cool air generated from air conditioners to achieve 67 degrees (although the datacenter will still need recirculated cool air during the hottest days).
By using economizers more often, NetApp not only keeps its new high-density datacenter cool but stands to save about 930,000 kWh annually, or 15 percent less energy usage from the old datacenter. This translates into $105,000 savings every year.
So how much did this new cooling design cost the company? Not much. Total capital expenditure, says Renne, was $167,000 -- not including the $140,000 rebate from PG&E, the local utility, as an incentive to do this kind of project. "ROI was in three months," Renne says.