DATA CENTRES COOLING
An artist’s impression of Digiplex’s Air-to-Air modular data centre
Simple Schematic of A2A Principle Principle of how DigiPlex’s Air-to-Air works Air treatment pod OUT
Server room Sealed unit
tubes, removing heat from them before being discharged outside. In the second airstream, 35°C indoor air is drawn into the heat exchanger from the white space hot aisle. It then passes through the polymer
Cool fresh atmospheric air
IN Adiabatic cooling No external air contamination possible
Closed loop de-ox rack cooling
tubes, where heat is removed, cooling it to 24°C +/-2°C. The air is then supplied back to the white space cold aisle through the raised floor void. The evaporative cooling system operates
matched with three ATPs – two duty, one standby – to provide the necessary cooling. It is within these ATPs that the key
to the data centre’s exceptionally low power consumption is found. Each ATP incorporates a low maintenance cooling system that uses the evaporation of water as the principle source of cooling energy, as opposed to the more traditional, energy- intensive, mechanical cooling refrigeration systems based on chillers and computer room air-conditioning units. At the heart of the evaporative cooling
system is a heat exchanger. Here, heat is exchanged between two air streams – cool outside air and indoor air – without them mixing. The outside air enters at the base of the evaporator compartment and is drawn up over a series of ribbed polymer
56 54 CIBSE Journal September 2013
in three modes to remove heat in the most energy-efficient manner. In its simplest mode, the unit is run without supplementary cooling. It will do this when the outside air’s dry-bulb temperature (the atmospheric temperature shielded from radiation and moisture) is cool enough to remove sufficient heat from the heat exchange tubes to reduce the indoor air to its set point. If the outdoor dry-bulb temperature is
not low enough, the unit will switch to its second mode, as an indirect evaporative air cooler. In this mode, the heat exchange elements are drenched with a film of water to introduce adiabatic and evaporative cooling effects. To optimise the evaporator’s performance and to save on fan energy, the volume of outside air can be varied to match the heat load. The determining factor in this mode of operation is ambient wet-bulb temperature, which governs the point at which evaporation of water can take place. Where the wet-bulb temperature is only 1 or 2°C below the dry-bulb temperature, it will feel humid and the effect of evaporative
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