Hot Aisle Containment Systems (HAC)
The Cool Shield hot aisle containment systems (HAC) channel the heat from the server exhaust directly back to the returns on the cooling units.
First and foremost, hot aisle containment contains the hot exhaust air. This prevents warm air from re-circulating over the top of server cabinets and mixing with the supply air.
HAC Systems: How They Work
Typically, the perimeter of the hot aisle is enclosed with a vertical partition from the top of the server cabinets to the drop ceiling return. An aisle containment door is installed at both ends to facilitate access into the aisle. If there is no ceiling return, a duct system can be used to channel the exhaust air to one or more CRAC units directly. Since the hot exhaust air is removed from the room, the cooling units can be set to deliver supply air at a comfortable temperature for servers without the need to over-cool.
Returning warmer air to the CRAC/CRAH units actually increases their capacity. A 20-ton cooling unit may be able to deliver 25 or even 30-tons if the return air temperature is high enough. Besides increasing capacity, this will also improve efficiency, especially if the cooling units have variable speed fans. The increased capacity reduces wear on compressor and allows fans to operate on a more efficient spot on the energy curve.