Impact of ASHRAE environmental classes on data centers

Data centers consume a significant amount of energy in the US and worldwide, much of which is consumed by the cooling infrastructure, particularly the chiller plant and computer room air conditioners and air handlers. To enable energy efficient data center designs, ASHRAE added two new IT environmental classes, A3 and A4, with associated allowable inlet air temperatures of 40C and 45C respectively. IT equipment that meet these new allowable environmental envelopes can operate in data centers with minimal refrigeration cooling and instead rely on ambient free cooling. In this paper we investigate the impact of allowing a data center to operate up to the A3 limit of 40C on total data center energy use for 3 different types of servers in a chiller-less data center located in a variety of locations. The study finds that though facility power reduces as the demand for cold air reduces, the increase in IT power consumption, due to fan speed-up, can offset these savings and in some cases result in an overall increase in data center power. Thus the most energy efficient operating point is dependant on the specific energy use profiles of the infrastructure and the IT equipment. The higher allowable temperature can also result in higher failure rates and an increased risk of equipment or service loss due to data center cooling failures. This paper also presents a study on the potential for chiller elimination and chiller use reduction across the US, Europe and in India by operating in the various ASHRAE envelopes. For wet, water side economized data centers, A2 and A3 equipment is sufficient to almost completely remove the need for chillers in many geographic locations.