The chilled air enters the front of each rack (cold aisle in Figure 8-4) over the entire height of the rack. The air takes away the heat from the equipment as it flows around and inside it, and is later ejected into the other side (hot aisle). The equipment must be facing toward or away from the forced air, as required for optimum cooling.
The racks can be located next to each other with small inter-rack gaps that must be large enough for them to be removed or serviced. The cold and hot aisles alternate. Each cold or hot aisle is shared by two adjacent rack rows.