Optimization of Enclosed Aisle Data Centers With Induced CRAH Bypass

Abstract

Aisle containment systems reduce temperature nonuniformities in traditional air-cooled data centers and pave the way for higher cooling air temperature and more efficient operation of the cooling system and wider application of economizers. However, enclosing the aisle does not guarantee the lowest possible cooling infrastructure power. Enclosed air (EA) configurations require computer room air handler (CRAH) fans to provide the entire rack air flowthrough the perforated tiles, as well as the leakage flow that inherently exists in data centers. In this paper, we propose the installation of induction bypass (BP) fans beneath the cold aisle (CA) perforated tiles that draw air from the plenum, placing the latter under a slightly depressed pressure. In doing so, warm air from the hot aisle is drawn into the plenum, where it is mixed with a smaller amount of cold air from the CRAH. As a result, the CRAH fans operate at lower speeds and consume less power, but the air passing through the CRAH is cooled to a lower temperature so that the air supplied to the enclosed CA remains at or slightly below the server redline temperature (~27 °C). Detailed optimization based on hour-by-hour annual energy simulations for seven U.S. cities has shown that the proposed induced CRAH BP scheme can reduce combined chiller and air-moving power consumption substantially in EA data centers with or without an airside economizer.