Definition
Adiabatic, or evaporative, cooling uses the energy absorbed when liquid water turns to vapour to chill an air stream. Warm air is drawn across wetted media or a fine water spray; as the water evaporates it pulls heat out of the air, dropping its temperature before it reaches the equipment. Because evaporation does the work instead of a compressor, the technique is far less energy-hungry than mechanical refrigeration, which is why large operators lean on it heavily.
Direct versus indirect
In direct evaporative cooling, outside air passes through water-soaked pads and the now-cooler, more humid air goes straight to the hardware. In indirect systems the evaporative effect cools one air or water stream that then chills the supply air through a heat exchanger, keeping the moisture out of the equipment space. Direct systems are simpler and cooler; indirect systems protect humidity control at the cost of some efficiency.
The water-for-energy trade
Evaporative cooling shifts cost from electricity to water, which is captured by the Water Usage Effectiveness (WUE) metric. Adding an adiabatic stage to a chilled-water plant can shave power use but introduce millions of litres of annual water consumption, so the choice is intensely local: it shines in hot, dry climates with cheap water and looks far worse where water is scarce. Modern designs with higher supply temperatures often run dry, without evaporation, for a majority of the year and only spray water during peak heat.
It works best within the warm envelopes of the ASHRAE Thermal Guidelines and complements an Air-Side Economizer (Free Cooling).
In Simple Terms
Adiabatic, or evaporative, cooling uses the energy absorbed when liquid water turns to vapour to chill an air stream. Warm air is drawn across wetted…