Energy efficient economizer based data centers with air cooled servers

This paper focuses on alternative highly energy-efficient data center configurations with air-cooled servers that eliminate the use of chillers. In the first method, outdoor air is directly pumped through one side of an indirect air-to-air heat exchanger with air flow through the other side being passed through the data center to cool the air-cooled server racks. This method is called Indirect Air Side Economizer (IASE). In the second method, an external wet cooling tower or a dry cooler is used to reject the data center heat load to the ambient from a circulating liquid loop that is routed inside the data center for use inside a heat exchanger cooled rack. In this method, an air-to-liquid heat exchanger is used at the rack level to transfer the rack heat load dissipated by the servers from the exhaust air stream into the circulating water loop. In some cases, the external dry cooler may be enhanced to include evaporative cooling of outdoor air to reduce its' dry bulb temperature to be closer to the outdoor wet bulb temperature. These methods are called Dry Cooler with Rack Heat Exchanger (DRHx) and Evaporative Dry Cooler with Rack Heat Exchanger (EDRHx). This paper discusses these data center configurations in the context of their cooling power use and realizable energy savings compared with traditional chiller plant based cooling loops. Hour by hour outdoor air temperature data for a typical summer day in conjunction with simple transfer functions are used to predict the server inlet air temperatures with the use of different cooling configurations. Power use at the electronic equipment is also discussed.