With climate change leading to record summer temperatures, access to cooled spaces can mean the difference between life and death for many. However, air-conditioning can be prohibitively expensive and is energy—and greenhouse-gas emission—intensive. As of 2018, cooling systems accounted for roughly 10 percent of global energy consumption and 12 percent of residential energy expenditure in the United States. As an alternative, some areas have invested in deep water cooling systems (DWCS) as a low energy way of keeping buildings cool. DWCS use sea or lake water as a coolant rather than relying on electric-powered AC systems. DWCS work by running a closed loop of water through the buildings being cooled. The water chills the buildings and absorbs excess heat. The water then is cycled through a cooling station where it is rechilled by sea/lake water that has been pumped to the surface. The sea/lake water is either returned to the sea/lake or continues on to be processed in desalination centers or drinking water treatment facilities.
Toronto is currently home to the world’s largest deep lake water cooling system—the largest deep seawater cooling system has just launched in Tahiti. Launched in 2004, Toronto now used DWCS to cool over 100 buildings in the downtown area, including Toronto General Hospital, City Hall, and the Scotiabank Arena. Due to its popularity, the system has nearly reached capacity and Enwave, the company that runs it, has committed to a (CAN) $100 million expansion, adding a fourth pipe to the three that already pump water in from Lake Ontario. Enwave estimates that the system saves 90,000 mega-watt hours of electricity annually—enough to power a 25,000-person town—and 220 million gallons of water annually when compared to traditional cooling systems that rely on evaporation to dissipate heat.
DWCS save energy and reduce emissions, but they are not without their drawbacks. The initial cost of installing a DWCS system is high. Toronto’s system initially cost Enwave (CAN) $170 million to install and the Honolulu Seawater Air Conditioning LLC, after spending 16 years and $25 million obtaining regulatory approval, recently ended their DWCS plans due to an increase in estimated construction costs from $275 million to $400 million. Location and geography are also critical. The body of water used needs to be deep enough to ensure a permanently cold bottom level. Much of the ocean shelf along eastern United States, for example, is too shallow for deep water cooling. The amount of water that can be safely withdrawn for cooling also varies. While large bodies of water such as the great lakes and the ocean are effectively limitless as a cooling resource, smaller water bodies can only have so much water withdrawn before the returning warmed water effects the overall temperature. In the locations where it is feasible, however, deep water cooling can serve as an energy efficient way to cool a single large building, college campus, or a whole downtown area.
