In 2008 we wrote about a relatively new approach to data center cooling called the "heat wheel" that was being deployed in a number of European data centers. The heat wheel - also known as a rotary heat exchanger or Kyoto Cooling - is a refinement of existing approaches that take advantage of outside air to improve cooling efficiency and reduce data center power bills.
The government of the state of Montana recently become the first data center in the United States to deploy a heat wheel system to cool its data center. The new facility in Helena includes three 16-foot heat wheels. Rather than introducing exterior air directly into the server room, the heat wheel briefly mixes the outside air and exhaust air to creates an "air-to-air" heat exchanger. The state says it expects the system its facility to give it one of the lowest data center cooling costs in the nation.
Proponents of Kyoto Cooling say it improves upon air-side economization (free cooling), the use of outside air to cool servers in the data center. Heat wheels have been used for many years in industrial air conditioning, but never in data centers. Like air-side economization, heat wheels could produce significant energy savings by reducting the need to use power-hungry chillers for air conditioning.
In evaluating the system, the state of Montana used weather data from 2007, the hottest year on record in Helena, and found that 80 percent of the time, the heat wheels would be sufficient to cool the data center. Fort about 16 percent of the year, the system would mix air from the wheels and standard commercial systems.