Deep water source cooling (DWCS) or deep water air cooling is a form of air cooling for process and comfort space cooling which uses a renewable, large body of naturally cold water as a heat sink. 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. On the other side of the heat exchanger, cooled water is produced.
Water is most dense at 3.98 °C (39.16 °F) at standard atmospheric pressure. Thus as water cools below 3.98 °C it decreases in density and will rise. As the temperature climbs above 3.98 °C, water density also decreases and causes the water to rise, which is why lakes are warmer on the surface during the summer. 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.
Deep water source cooling is very energy efficient, requiring only 1/10 of the average energy required by conventional cooler systems. It does not use any ozone depleting refrigerant.
Deep water source cooling requires a large and deep water quantity in the surroundings. To obtain water in the 3 to 6 °C (37 to 43 °F) range, a depth of 66 m (217 ft) is required.
Cornell University's Lake Source Cooling System uses Cayuga Lake as a heat sink to operate the central chilled water system for its campus and to also provide cooling to the Ithaca City School District. The system has operated since the summer of 2000 and was built at a cost of $55–60 million. It cools a 14,500 ton (51 megawatt) load.
Since August 2004, a deep lake water cooling system has been operated by the Enwave Energy Corporation in Toronto, Ontario.It draws water from Lake Ontario through tubes extending 5 kilometres (3.1 mi) into the lake, reaching to a depth of 83 metres (272 ft). The deep lake water cooling system is part of an integrated district cooling system that covers Toronto's financial district, and has a cooling power of 59,000 tons (207 MW). The system currently has enough capacity to cool 3,200,000 square metres (34,000,000 sq ft) of office space.
The InterContinental Resort and Thalasso-Spa on the island of Bora Bora uses an OTEC system to air-condition its buildings. The system accomplishes this by passing cold seawater through a heat exchanger where it cools freshwater in a closed loop system. This cool freshwater is then pumped to buildings and is used for cooling directly (no conversion to electricity takes place). Similar systems are also in place in The Excelsior hotel and The Hong Kong and Shanghai Banking Corporation main building in Victoria, Hong Kong.
