Deep water source cooling

It uses water at 4 to 10 degrees Celsius drawn from deep areas within lakes, oceans, aquifers or rivers, which is pumped through the one side of a heat exchanger.

The combination of these two effects means that the bottom of most deep bodies of water located well away from the equatorial regions is at a constant 3.98 °C.

It is similar in concept to modern geothermal sinks, but generally simpler to construct given a suitable water source.

For many buildings, the lake water is sufficiently cold that the refrigeration portion of the air conditioning systems can be shut down during some environmental conditions and the building interior heat can be transferred directly to the lake water heat sink.

The energy source is very local and fully renewable, provided that the water and heat rejected into the environment (often the same lake or a nearby river) does not disturb the natural cycles.

In Europe, lake-based heating and cooling could save 0.8 TWh per year, and is most promising in Italy, Germany, Turkey and Switzerland.

To obtain water in the 3 to 6 °C (37 to 43 °F) range, a depth of 50 to 70 m (160 to 230 ft) is generally required, depending on the local conditions.

Although deep water source cooling is referred to as "free cooling" in some literature, a considerable amount of energy (typically electrical) is expended to operate pumps with a sufficient head to overcome frictional, and minor losses in distribution piping, and any heat exchangers.

Estimated savings is an 80% reduction in fossil fuel previously required to operate a conventional electric cooling system.

Since August 2004, a deep lake water cooling system has been operated by the Enwave Energy Corporation in Toronto, Ontario.

Water drawn from the depths of Lake Ontario is not circulated directly through terminal air-conditioning units within buildings.

Chilled water within the buildings is part of a closed-loop district cooling system, pumped from a centralized location where the heat-exchangers are installed, back to the buildings where it can absorb heat from fan coil units installed to provide latent, and sensible space cooling.

[12] Honolulu Seawater Air Conditioning is majority owned by eBay founder Pierre Omidyar's Ulupono Initiative.