Water takes the heat off Hong Kong air-con

Using water to cool non-domestic air-conditioning systems could have reduced outside air temperatures by as much as 1.5°C during a heatwave in Hong Kong, researchers have found.

The study shows that water-cooled air-conditioning units are not only more energy-efficient, but also relieve the anthropogenic "urban heat island" effect, which sees cities have greater ambient temperatures than the countryside.

"We cannot ignore the effect of air-conditioning systems on the city environment," said Yi Wang of the University of Hong Kong.

As air-conditioning units cool us indoors, they expel heat outdoors. The amount of heat displaced can be enough to increase outdoor air temperatures measurably, contributing to the urban heat island effect.

And of course, if it gets warmer outdoors, even more air conditioning is needed indoors.

Not all air-conditioning systems are the same, however. Many rely on air to cool their condensing units, but those that are more energy-efficient use water. One method of water-cooling is known as direct cooling; it involves seawater being fed into the buildings that house condensers. Another type is centrally piped, with a tall cooling tower where air ascends amid a water cascade.

[...]