Costs and benefits of thermal energy storage for augmenting indirect/direct evaporative cooling systems

Most data center cooling systems are designed to match installed cooling capacity to peak cooling demand at the most challenging ambient condition which typically occurs for only a period of the diurnal cycle. Evaporative coolers are provide economical cooling but use large quantities of water and are generally constrained to the ASHRAE A2 limits [1]. Direct expansion `topping' systems are a common technology to extend the temperature-humidity range, however, direct expansion systems require substantial electrical power which negatively affects the operating costs. Phase change materials have potential for economical thermal energy storage. Used instead of direct expansion, thermal energy storage can reduce the cost of cooling energy. By storing cooling capacity, thermal energy storage enables time-shifting of cooling demands and extends the temperature-humidity limits for evaporative cooling beyond the ASHRAE A2 limits. An added benefit, thermal energy storage with indirect/direct evaporative coolers reduces water consumption.