An experimental and theoretical investigation of the extent of bypass air within data centres employing aisle containment, and its impact on power consumption

A combination of laboratory experiments and a system model are used to carry out the first investigation into the potential for cold air to bypass IT equipment within data centres (DCs) employing aisle containment, and the effect of this bypass on DC electricity consumption. The laboratory experiments involved applying a differential pressure across commercially available server racks and aisle containment systems and measuring the resulting air flow. The potential to minimise bypass by sealing leakage paths and redesigning racks was investigated and quantified experimentally. A new system model is developed using a combination of manufacturer data, empirical relationships and experimental results to predict the impact of bypass on the power consumption of the various components of a DC's cooling infrastructure. The results show that, at typical cold aisle pressures, as much as 20% of the supplied air may bypass servers by finding alternate paths through the server rack itself. This increases the required flow rate from air conditioning units (ACUs). The system model predicts that: (i) practical measures undertaken to reduce this bypass could reduce total power consumption by up to 8.8% and (ii) excessive pressure differentials across the containment system could also increase power consumption, by up to 16%.