Improving cooling efficiency of servers by replacing smaller chassis enclosed fans with larger rack-mount fans

Abstract

As a common practice in the data center industry, chassis fans are used to direct air flow independent from neighboring servers. In general, smaller fans are less efficient compared to geometrically similar larger fans. In this study, a novel approach is proposed whereby chassis enclosed fans are replaced with a smaller number of larger fans installed behind a stacked array of servers which share airflow. As a baseline study, a CPU dominated 1.5U Open Compute server with four 60mm fans installed within its chassis is characterized experimentally for its flow impedance, fan speed dependent flow rate, effect on die temperature and power consumption at various compute utilization levels. Larger fans with a square frame size of 80mm and 120mm are selected and individually characterized for their air moving capacity and power consumption. Primary emphasis is placed on the 80mm fan case, with discussion of the 120mm fans included. CFD is used to simulate a system of stacked servers serviced by larger fans to obtain its flow characteristics and operating points. The fan power consumption of the larger fans is determined experimentally at these operating points replicated in an air flow bench. Comparing with the base line experiments, replacing smaller fans with larger units results in a significant decrease in fan power consumption without conceding flow rate and static pressure requirements.