Hot aisle / Cold Aisle server rack server layouts were conceived as a strategy for a more energy efficient cooling of a data centre. In this type of server room layout, each successive aisle is designated either a hot aisle or a cold aisle. In cold aisles the server racks are aligned so equipment inlets are facing each other on opposite sides. In the next aisle, both banks of server racks exhaust hot air.
Typically, cool air form the Air conditioning system flows in to the cold aisle, allowing the cold air to easily reach the server inlets at the front of the racks, flow through the IT equipment and exhaust into the hot aisle.
This method should increase energy efficiency by allowing for higher temperature set points by directing cooler air closer to the equipment inlets. By concentrating the cool air where it is needed most, the air conditioning units can run a few degrees higher than would other wise be necessary.