The IT team at the US Department of Energy's National Renewable Energy Laboratory in Golden, Colorado, has built a data center that pipes air underground for a cheap and effective cooling solution. The NREL's Research Support Facility building that houses the data center is an Leadership in Energy and Environmental Design Platinum, or LEED, building designed to be "net zero" on energy usage. LEED is an internationally recognized "green" building certification system that uses metrics for water efficiency, CO2 emissions reduction, and energy savings.
Their data center rarely utilizes air conditioning and instead employs two separate systems to remove heat and cool the equipment. The NREL cooling system starts with outside air that travels through an underground channel and is cooled to roughly 54 degrees which it is pumped into the data center. The hot air from the data center is then pumped through the building for heating during the cooler months.
Remarkably, their data center has reportedly achieved a Power Usage Effectiveness rating of 1.15. The PUE metric is calculated by adding together the power required for the cooling system, the power management system, and the actual computer equipment, and dividing that number by the power required to operate just the equipment. The cooling and power management systems required to run their data center only requires one-tenth of a watt for every watt used by the actual computer hardware.