Deep lake water cooling
Deep lake water cooling is a technique for harnessing the deep layers of lakes to cool buildings.
Water is densest at 3.98 °C (39.164 °F, 277.13 K). Consequently during Winter, the coldest layers of a deep lake, in a temperate climate, will be at the surface. During the Spring and Fall the average temperature of a lake will cross the temperature at which water is densest. At this point all the water in the lake can mix, replenishing the oxygen at the lake's bottom.
As the lake water's average temperature rises in the Spring the warmest layers is at the surface, below which is a boundary layer, the thermocline. And below there is a layer of water that will remain at 3.98 °C (39.164 °F) until fall.
The Cornell system
The Toronto system
In 2004 the city of Toronto, Ontario, on Lake Ontario, initiated what has been described as the first large scale deep lake water cooling system. In the Toronto system the inlet pipes for the city's domestic water supply was replaced with pipes that were 83 metres below the lake's surface. Before the water goes the city's water customers it goes through a heat exchanger which is used to cool buildings in the city's downtown core. The waste heat is not dumped back directly to the lake. The water, which is still cool enough for use in customer's domestic cold water, is returned to the lake, through the city's water system. But it is no warmer than if no deep lake water cooling was used.
Other potential sites
Africa's Great Lakes don't have a cool winter to build a reservoir of cool water, so they are not potential sites of this technology.
- Julian Smith. The AC of Tomorrow? Tapping Deep Water for Cooling, National Geographic News, September 10, 2004. Retrieved on 2008-06-04.
- What's the City doing to shrink its footprint?, City of Toronto. Retrieved on 2008-06-04.
- How deep lake cooling works, Enwave. Retrieved on 2008-06-04.
- Fred Langan. Toronto turns to lake water for air conditioning, Christian Science Monitor, August 30, 2007. Retrieved on 2008-06-04.