Toronto turns to lake water for air conditioning

Cold water drawn from Lake Ontario cools buildings and provides big energy savings.

By Fred Langan | Correspondent of The Christian Science Monitor

from the August 30, 2007 edition

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Toronto - The Toronto Dominion Centre is the most distinctive set of office towers in the city's financial district. Three of the five black buildings were designed by Mies van der Rohe and built in the late 1960s. So was their air conditioning.

The three original towers, which contain about 3 million square feet of office space, were among the first buildings connected to Toronto's Deep Lake Water Cooling System in September 2004, saving the local electric utility 7.5 megawatts of electrical demand every working day.

"This conservation measure takes the pressure off Toronto's electrical system," says Blair Peberdy, vice president of Toronto Hydro, the local utility. The city's electricity supply tightens during the hot summer months, he says, so "removing air conditioning from the grid helps the system."

The first stage of the project's construction ran three 63-inch diameter pipes along the city's lake bed about three miles out into Lake Ontario. There it draws water 272 feet below the surface. At that depth, the water's temperature is almost always constant, protected by a strata of water above it called a thermocline.

"Below the thermocline, the water stays at 39 degrees Fahrenheit almost the entire year. That's the natural phenomenon that is our renewable resource," says Kevin Loughborough, vice president, major projects, at Enwave Energy Corp., which owns and runs the Deep Lake Water Cooling project.

The water is piped to a filtration plant on Toronto Island, less than a mile off the city's shoreline. It then continues to a heat-transfer station on the mainland squeezed between the Rogers Centre and the downtown Gardner Expressway. Here the lake water runs along one side of a metal plate in a heat exchanger, transferring the water's "coolness" to water running through pipes on the other side of the plate.

The lake water is sent along to reservoirs, providing about 15 percent of the city's drinking water. Since the water comes from so far out in the lake, it is free from such contaminants as algae and geosmin, which cause an unpleasant taste and odor in Toronto's water in the late summer and early fall.

The water used to cool the city's buildings travels in a closed loop inside 48-inch pipes that run for 15 miles beneath the city, six stories deep.

The cool water passes though metal coils inside participating office buildings. Fans blow over the coils, forcing cool air into each building's central air-conditioning system.

Toronto's system is connected to 41 buildings in the central business district, and a total of 57 buildings have signed on to use the system. Built at a cost of $200 million over four years, the system has two shareholders: the City of Toronto (47 percent ownership) and OMERS, the Ontario Municipal Employees Retirement System (53 percent).

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