Cold aisle, hot aisle and rack exhaust containment are all effective air management methods to separate the hot and cold air streams in data centres. However, both cold aisle and hot aisle containment require working in hot areas (the hot aisle). The rack exhaust system has the potential for higher densities (all aisles are cold); this is restricted by the exhaust duct volume. For hot aisle containment and rack exhaust containment the area available for overhead cable trays is reduced. With today’s low utilisation of IT equipment, the hot air is around 5°C (9°F) to 10°C (18°F) warmer than the cold air supplied to IT equipment. Given that the design delta T of IT equipment at full load is 25°C (45°F) to 30°C (54°F), the tendency to increase IT equipment utilisation and to increase air supply temperatures (to save energy), it is likely that in the future we will have hot air streams (e.g. in hot aisles) of around 50°C (122°F), quite uncomfortably high.

The UK Health and Safety Executive states: “Where the temperature ….would otherwise be uncomfortably high…. all reasonable steps should be taken to achieve a reasonably comfortable temperature, for example by: ….providing air-cooling plant.”

For future designs and for energy efficiency reasons we do not want to provide cooling in hot aisles, so therefore we should we be thinking of containing the hot air to be out of the working area, e.g. rack exhaust containment systems or similar.