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DATA CENTRES


Nigel Hillier, managing director of Carel UK talks about adiabetic cooling as a solution that ticks all the boxes.


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umidity control in data centers has always been considered necessary in terms of preventing electric discharges. The use of traditional technology based on heating water to boiling point – isothermal humidifiers – is however costly in terms of energy consumption, while also requiring increased cooling capacity. Over time these factors have led to a debate over the need to control humidity in data centers. ASHRAE has been working for many years on guidelines that allow a wider tolerance, in terms of both temperature and humidity. Consequently, the need to humidify has decreased in several contexts. Recently, ASHRAE has been further lowering the minimum humidity limit to the extent where humidification is no longer necessary.


As occurred with temperature, however, there are only certain system layouts that


34 November 2017


push the conditions to the limit, following the ASHRAE guidelines. Many data centers, above all colocation centers that do not host their own ICT equipment and need to guarantee a high service level, find it difficult to adopt these requirements due to the related risk. Consequently, they opt for traditional designs. This is particularly true for many existing data centers whose operators are worried about low humidity and the corresponding risk of sparks forming due to electrostatic discharges.


The result is that many operators feel a sense of uncertainty, torn between the new design criteria with the related risks, and the need to save energy.


Can these seemingly opposing needs be reconciled? One of the most effective solutions involves the use of adiabatic humidifiers: this technology entails adding moisture to an air stream, in such a way that evaporation absorbs


some of the heat contained in the air, with the result being a simultaneous increase in humidity and decrease in temperature. This effect is exploited for the purpose of providing cooling with very low energy consumption, and is referred to as evaporative cooling.


Evaporative cooling is increasingly used in new generation data centers in which the design conditions are close to the limits suggested by ASHRAE: this is made possible by careful design of air flows and good separation between the air entering the racks and the exhaust air (layout with “hot aisles and cold aisles”).


The higher operating temperature and humidity allow the use of outside air (free cooling) via air handling units when the outdoor temperature is favourable (for example, below 25°C), while when the outside air is hotter and drier, evaporative cooling can be adopted, increasing humidity up to 60% and higher while bringing the temperature


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