In an effort to reduce carbon emissions and the use of fossil fuels, some cities around the world have implemented a new type of air conditioning methodology known as deep water cooling. Deep water cooling takes advantage of the exceptionally cold water found far below the surface of many lakes and other bodies of water. This cold water, often only a few degrees above freezing, is drawn into the city's water system through large intake pipes, where some of it is diverted to water treatment plants for general consumption, but not all of it.
The exceptionally cold water passes through a series of parallel pipes, one containing the cold water destined for large air conditioning chiller and the other containing warm water returning from service. This system is closed, which means the untreated water used for air conditioning never mixes with the city's potable water supply. The cold water drawn from the deep water cooling pipe acts as a thermal sink or heat exchanger. The cold pipes absorb excess heat from the warm return pipes, making the water cold enough to cycle through the chillers again.
The frigid water used in a deep water cooling system does not become part of the closed coolant system itself. Its only purpose is to remove heat from the return pipes instead of using an expensive and environmentally damaging refrigeration system powered by electricity or fossil fuels. A city using deep water cooling technology can save significant amounts of money per year and also take advantage of a natural source of coolant for their swamp cooler air conditioning system.
Deep water cooling is not without its challenges, however. Many cities are not located close enough to a source of deep water to make intake pipes economically feasible, for example. Additional equipment must also be purchased and installed in order to introduce the cold water supply to an existing municipal water system.
The ideal city for a deep water cooling system would be a large metropolis near a significant body of water, such as Ontario, Canada. The city of Ontario does have three large intake pipes submerged in a deep section of Lake Ontario, and the cold water drawn from that depth does indeed work as a natural heat exchanger for the city's air conditioning system. Other cities are also studying the feasibility of deep water cooling, but the initial investment in equipment and the challenge of finding a suitable cold water source remains daunting.