Experimental investigation of CRAH bypass for enclosed aisle data centers

Abstract

Aisle containments in data centers help provide uniform server inlet air temperatures. This allows the cooling system to run at a higher evaporator temperature and more efficiently. On the other hand, CRAH units run at higher speeds to ascertain that racks receive sufficient air flow. Since CRAH fan power already constitutes an important component of data center power use, such increases in the fan power can overshadow the energy savings due to more efficient chiller operation. CRAH bypass configuration is proposed to achieve optimum operating condition for enclosed aisle data centers. This configuration utilizes fan-assisted perforated floor tiles to induce a fraction of tile flow from the room through bypass ports or leakage paths and help decreasing the amount of air flow passing through the large flow resistances of CRAH units. Experimental results show that there is an optimum operating condition for the specific data center test cell that is designed to represent an enclosed aisle data center utilizing the proposed CRAH bypass configuration. Here, the flow characteristics of major system components and experimental measurements have been used to calibrate a flow network model (FNM) for the design optimization and trade-off analysis of the proposed system. Calibrated FNM along with a thermodynamic model (TM) of the cooling infrastructure provides an estimate of the energy use at various fractions of CRAH bypass air and chilled water temperatures. This study introduces the design of the experimental setup for testing CRAH bypass configuration for enclosed aisles and for calibrating models to predict the cooling infrastructure energy saving potential of the proposed technique.