Reducing energy usage in data centers through control of Room Air Conditioning units

Information Technology 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 and the Computer Room Air Conditioning units (CRACs). There have been recent changes in specifications for the data center environmental envelopes as mandated by ASHRAE (American Society for Heating Refrigeration and Air Conditioning Engineers), one of which specifically pertains to the upper and lower bound of air temperatures at the inlet to servers that are housed in data center rooms. These changes have been put in place in part to address the desire for greater cooling energy efficiency of these facilities. This paper primarily focuses on the methodologies to reduce the energy usage of room air conditioning devices by exploiting these recent changes in standards for the equipment environmental envelope. A 22000 square foot (6706 m²) data center with 739 kilo Watt of IT load is used as a representative example for numerical CFD analyses using a commercial software package to demonstrate methodologies to reduce the cooling energy use of Information Technology data centers. Several test case simulations are used to enable the calculation of room level air temperature fields for varying design conditions such as different numbers of operational CRACs or the volumetric air flow rate setting of the CRACs. Computation of cooling energy is carried out using available vendor equipment information. The relationship between the reduction in energy usage in CRAC units and the server inlet air temperatures are quantified and a systematic methodology for CRAC shut off is proposed. The relative magnitude of reduction in data center cooling energy use from shutting off CRACs or reducing CRAC motor speeds is also compared with scenarios involving increases in refrigeration chiller plant water temperatu- - re set point.