Energy Efficient Data Centers Using Evaporative Cooling and Air Side Economizers

Abstract

Information Technology (IT) data centers consume a large amount of electricity in the US and world-wide. Cooling has been found to contribute about one third of this energy use. The two primary contributors to the data center cooling energy use are the refrigeration chiller (about 50% of cooling) and the Computer Room Air Conditioning units (about 33% of cooling). This paper focuses on a data center configuration that eliminates the use of the chiller plant thereby yielding substantial energy savings. One method of eliminating the chiller plant is to directly pump outdoor air into a data center with some amount of conditioning (particulate filtration). This configuration is can be called Direct Air Side Economizer (ASE). Since computer equipment is usually designed with the assumption that the rack air inlet temperatures are in the 15–32 °C range, the use of ASE is constrained to use only in those geographies where the outdoor air conditions allow such direct air use. One method to reduce the sensible air temperature of the outdoor air that is being ducted into a data center room is water evaporation directly into the air stream. Such a method can be called Evaporative Air Side Economizer (EASE). This paper discusses the benefits of EASE data center configurations in the context of the climate in the USA and realizable energy savings compared with traditional chiller plant based cooling loops. Hour by hour outdoor air temperature data for a typical year and psychometric charts are utilized in conjunction with simple transfer functions to model cooling via evaporative media. Phoenix, a US city in a hot climate is used to illustrate the use of the relatively new method of data center cooling. A comparison to the traditional chiller plant based approach resulted in about 30% of energy savings at the data center level.