Recent advancements on indirect evaporative cooling and its applications: a review

According to the International Energy Agency (IEA), global energy use for space cooling has almost doubled since the year 2000 from 1000 to 1945 TWh, mainly due to global warming, rapid urbanisation and use of inefficient air conditioners. Without a major breakthrough in the efficiency of space cooling equipment, the electricity demand is expected to increase again by as much as 40% by 2030. This has increased the interest in finding alternative cooling methods for space cooling, preferably with low energy usage and minimum environmental harm. Evaporative cooling makes use of the enthalpy of the vaporisation of water, however, the humidified supply air causes discomfort to humans. Indirect evaporative cooling is more preferable as it is able to cool the air without a change in its humidity. It is particularly beneficial when compared to traditional vapour compression systems due to its ability to deliver cool, dry air with a relatively low energy input and without the need for harmful refrigerants. Recent developments in literature regarding indirect evaporative cooling have been reviewed in this paper. Numerical and experimental work from various areas of development include, but are not limited to: the use of solar desiccant systems; integration with other cooling components; parametric studies on performance; exergy and economic analyses; the use of coated heat exchangers; as well as hybrid nanofluids as a coolant liquid. Various configurations of evaporative cooling systems were reviewed with internal recovery options for regeneration. Within the study, performance of an indirect evaporative cooling configuration was investigated under Shiraz (Iran), Sevilla (Spain) and Riyad (Saudi Arabia) climatic conditions. Accordingly, energy savings potential of the considered system in comparison with vapour compression cooling was found to be 61% and 56% for Riyad and Shiraz respectively. On the other hand, it was found that using evaporative cooling was not favourable in terms of energy savings when compared to vapour compression in the Sevilla climate.