The AC of Tomorrow? Tapping Deep Water for Cooling

Julian Smith
for National Geographic News
September 10, 2004

To anyone who's taken a dip in Lake Ontario, it seems like a no-brainer: Use the lake's icy waters to keep nearby cities cool. Last month Toronto did just that, announcing that its 170-million-dollar (U.S.) deep-lake water cooling system, the largest of its kind, was up and running.

Also known as "lake-source cooling" or "deep-source cooling," the process uses water pumped from the frigid depths of adjacent lakes or oceans to cool municipal buildings.

The technology is described as a clean, renewable, and sustainable alternative to conventional air conditioning and is used around the world. But such systems can have their critics.

Toronto's Hollywood-style unveiling featured music, dancers, and film star Alec Baldwin. But most of the action was below the surface in nearby Lake Ontario.

The Canadian city's new cooling project draws water from three miles (five kilometers) offshore and 270 feet (83 meters) down, where the temperature of Lake Ontario stays near 39.2 degrees Fahrenheit (4 degrees Celsius) throughout the year. Water is pumped to an island-based filtration plant and then sent through heat exchangers at an onshore pumping station.

The heat exchangers allow the lake water to cool a separate, self-contained water circulation system, which flows through buildings in downtown Toronto. The lake water, meanwhile, ends up as drinking water for the city.

Enwave, a Toronto energy company partly owned by the city, developed the system. According to the company, the new cooling system will eventually be able to cool 30 million square feet (2.8 million square meters) of office space, while using 75 percent less energy than conventional air-conditioning.

Chris Asimakis, Enwave's chief operating officer, says that when Toronto's system reaches full capacity, the city will conserve 59 megawatts of energy—the amount of power required to cool 12,000 homes by traditional means.

The project will keep 44,100 tons (40,000 metric tons) of carbon dioxide out of the air, according to the company's Web site. The greenhouse-gas savings is equivalent to keeping 8,000 cars off the road.

Enwave says the system will not only trim use of ozone-depleting refrigerants such as CFCs but also keep buildings cool even during blackouts when fully commissioned.

"People were skeptical at first," Asimakis said. "But eventually the local environmental community gave us their unanimous support."

The project currently cools ten Toronto buildings, including the tiny Steamwhistle Brewery and three skyscrapers in the Toronto Dominion Center, a financial-and-business office center.

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