"ABSTRACT There is a growing trend to utilize economical ways to cool data centers@ which includes maximizing the use of ""free cooling"" techniques such as airside and waterside economizing. A new economizer cooling system is being developed and tested at this time and will be implemented in a number of data centers within the next year. This technique uses a heat wheel to transfer the heat from the computer room to the ambient environment with a minimal transfer of air and moisture. It has been shown to have the capability of cooling a computer room with a heat density of 600 W/ft? and a cabinet heat load of 70 kW. It can provide cooling throughout the computer room within the existing ASHRAE guidelines up to an ambient condition of 22??(72??. It has been demonstrated to handle a temperature rise through cabinets of over 28??(50??. It can accomplish all this with a mechanical efficiency as low as 0.03@ which for 550 kW load in the computer room only 17 kW of mechanical energy was being utilized."