Comprehensive energy and economic assessment of CRAH bypass method in air-cooled data centers

The computer room air handling (CRAH) bypass (BP) method is a method to reduce the fan energy consumption in data centers. To provide a fraction of the server airflow, CRAH BP fans typically operate across an order of magnitude lower pressure drop across floor tiles compared to that across CRAH units. However, at a higher fraction of BP airflow, CRAH units are subject to low-temperature operation, which poses an optimization problem. Earlier studies indicated the potential to reduce the total cooling energy consumption in air-cooled data centers by using the CRAH bypass method. This study provides the most comprehensive assessment of the CRAH BP method in the literature for air-cooled data centers based on detailed thermodynamic modeling using hour-by-hour annual energy simulations. The parametric modeling and optimization results in this study address energy and economics of induced and forced BP methods in open and enclosed-aisle data centers considering both economized and non-economized operations. Despite the significant energy-saving potential of the CRAH BP method, economics plays a pivotal role in the feasibility of such an investment. The results and following discussions provide design considerations for the successful application of the CRAH BP method in air-cooled data centers.