Page 32 - Climate Control News November 2021

Data Centres
Low cost, high performance cooling
CONDAIR MANAGING DIRECTOR, IAN EITZEN, EXPLAINS HOW HUMIDIFIERS CAN BE USED IN DATA CENTRES TO PROVIDE LOW COST EVAPORATIVE COOLING.
Depending on the condition of the air stream, evaporative cooling can offer a temperature re- duction of up to 12°C. More and more air han- dling units are being developed with an evapora- tive cooling element to take advantage of this low cost, low energy form of temperature control.
Two main strategies have emerged for using cold water humidifiers to provide evaporative cooling in AHUs for data centres; direct evapora- tive cooling and indirect evaporative cooling.
Direct evaporative cooling uses the humidifier to spray or evaporate water into the filtered, in- coming air stream. This strategy is used to in- crease the cooling effect of free air cooling sys- tems, whereby a high volume of outdoor air is supplied to the data halls and an equivalent amount of warm air exhausted.
Direct evaporative cooling is ideal for use in dry climates, where the dry outdoor air offers the greatest potential for absorbing moisture from the humidifier, and therefore providing cooling to the incoming fresh air.
A consideration for employing this type of cooling strategy is the level of criticality placed on the introduction of outside air to the indoor environment. For critical data centre operations,
ADIABATIC EVAPORATION IS a process whereby water changes from a liquid to the va- pour phase. The heat required to evaporate the water is taken from the air stream.
The result is that air stream is cooled, whilst simultaneously increasing humidity. Adiabatic evaporation can be considered air humidifica- tion, as the moisture content of the air stream increases in the process. This process, often re- ferred to as evaporative cooling, can be de- signed specifically to provide low energy cool- ing of the air stream.
The use of evaporative cooling in data centre environmental control strategies is now relative- ly commonplace. The nature of evaporative cool- ing perfectly suits the requirements of a data centre’s climatic operating window.
Unlike a regular office temperature of around 23°C, a data centre’s upper temperature condi- tion can be as high as 28°C. When the outdoor climate conditions are suitable, data centre cool- ing systems may use the outdoor air rather than mechanical cooling in their data halls.
During the warmer months, when the outdoor air conditions are too warm to successfully low- er the indoor temperature to the desired set- point, evaporative cooling can be used to provide additional low energy cooling capacity.
A litre of cold water, when evaporated into the air, provides 0.68kW of adiabatic cooling. A sin- gle cold water evaporative cooler can supply around 1,000 litres of moisture while operating on less than 1kW of electricity, providing low en- ergy, high capacity cooling.
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