Guidelines now allow a wider tolerance of both temperature and humidity and consequently the need to humidify has decreased in several contexts and in some applications is no longer a necessity .

As occurred with temperature however , there are only certain system layouts that push the conditions to the limit , following the ASHRAE guidelines . All data centres , particularly colocation centres that do not host their own ICT equipment , need to guarantee a high service level and find it difficult to adopt these requirements due to the related risks , such as electrical discharges and consequently opt for traditional designs and approaches to humidification and cooling .

Many operators feel a sense of uncertainty , torn between the new design criteria with the related risks , and the need to save energy , but can these seemingly opposing needs be reconciled ? One of the most effective humidification and cooling solutions involves the use of adiabatic high pressure spray systems , such as the CAREL humiFog . This technology entails adding moisture to an air stream , in such a way that evaporation absorbs some of the heat contained in the air , effectively resulting in a simultaneous increase in humidity and significant 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 centres in which the design conditions are close to the limits suggested within the guidelines , for example by ASHRAE . This is made possible by the layout of hot aisles and cold aisles , with careful design of air flows and good separation between the air entering the racks and the exhaust air .

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 ), whilst when the outside air is hotter and drier , evaporative cooling can be adopted , increasing humidity up to and above 60 % and reducing the temperature down to acceptable values , simply through the evaporation of water . The effectiveness of such systems depends significantly on local temperature-humidity conditions , nonetheless in much of continental Europe both free cooling and evaporative cooling can be exploited for most of the year , some data centres are designed to use mechanical cooling as an emergency backup system only .

The increasing popularity of the humiFog system demonstrates how humidification in winter can be provided by simply adopting the same evaporative cooling system used in summer , thus reconciling humidity control with energy saving , with provision of modulating operation and temperature and humidity control to manage air recirculation . The use of a matrix of nozzles and high pressure pumps to create minute droplets of water ensures optimum absorption . The inverter control and modulated atomised water production responds efficiently to varying load conditions with serial communication allowing working set point adjustment to suit different environmental conditions .

The choice of the system depends on numerous factors , ranging from available space to required efficiency and the need for modulation . In general , the solution needs to be evaluated in terms of TCO ( Total Cost of Ownership ) throughout the system ’ s working life , also taking into consideration its resilience in terms of continuous operation as well as water consumption , which in many areas may be a critical factor . Indeed , many data centres , together with the classic PUE for energy consumption also monitor WUE as regards water consumption .

In conclusion , the increasingly frequent adoption of adiabatic systems can help overcome the dilemma between humidity control and cost reductions , thanks to new , increasingly reliable technologies and reduced energy consumption . Fundamental for system optimisation is the CAREL integration with control open protocol systems .