Akira Shoujiguchi

Seeking an energy-efficient modular data center: impact of pressure loss on the server fan power

With the recent development of cloud computing, the amount of information to be processed in data centers has increased in recent years, which promotes the construction of new data centers. Modular data center, which is often packaged in standard shipping formats, has been introduced to construct and deploy data centers more quickly and less expensively than conventional data centers. To conserve cooling costs in modular data centers, a hot aisle/cold aisle arrangement of the IT racks is employed by dividing the top of the racks using the partition. However, dividing the top of the racks increases the pressure loss of the server fans, leading to the increase of the server fan power. To examine the impact of this effect on annual cooling power, we perform simulations of power consumption in modular data center that introduces outside air and louvers on the top of the racks. By varying the opening of the louver as a function of the outside air temperature and rack power, an operation to minimize the power consumption of the outside air fans and server fans is performed. We find that total cooling power in case where the louver is operated so as to minimize the total cooling power can be reduced than that in case where the louver is fully closed by about 5% (10%) for 10kW (20kW) rack power. We discuss that the popular method for calculating energy efficiency in data centers, i.e. Power Usage Effectiveness (PUE), defined by the ratio of total amount of energy used to the energy used in IT equipment, is probably incomplete metric. Therefore, we finally propose that a revised PUE that removes the server fan power from IT equipment energy, and it should be used to estimate the energy efficiency to avoid the wrong interpretation.