By Chantal Martineau
Special to The Washington Post
Monday, August 29, 2005
Back in the 1940s, when Robert Tamblyn was working at Toronto's Eaton Centre department store, he noticed that it had tapped the city's water main -- illegally -- to rig up a system that fanned the chilly water through a network of pipes to cool the women's evening-wear department.
It was years before the city's water commissioner wised up. And years more before Tamblyn had the idea of applying the same concept in a bigger way.
"Air conditioning was a whole new word up here in the 1940s," says Tamblyn, the engineer many credit with developing an alternative technology -- lake-source cooling -- in North America.
He has helped devise large-scale, energy-efficient cooling systems for the city of Toronto and Cornell University's Ithaca campus. The city system, the largest of its kind, began operating last summer.
The first successful citywide venture was set up in Stockholm in 1995, but its capacity is less than half of Toronto's.
Unlike the department store's jury-rigged setup, Toronto's taps directly into the icy waters at the bottom of Lake Ontario.
It works by drawing water from 272 feet below the surface, where temperatures hover around 40 degrees Fahrenheit year-round. The coldness of the lake water is transferred via heat exchangers to a separate, closed water supply that loops around downtown Toronto and to participating office towers. Thirty-five buildings have already signed on to the project, including the Hudson's Bay Co.'s 1 million-square-foot retail outlet and 32-story head office. The company predicts it will save $416,000 a year on energy with the system.
Next year, several legislative buildings will be connected to the network.
Launched by Enwave District Energy, a public-private partnership, the new system will be able to cool more than 20 million square feet when it reaches full capacity. Participating buildings can expect to reduce the amount of energy used for cooling by an average of 75 percent, officials say.
Dennis Fotinos, Enwave's president, said the system will ultimately eliminate 40,000 tons a year of carbon dioxide emissions that conventional air conditioning would produce, and free more than 59 megawatts of electricity from the Ontario power grid.
"The more demands you can take off an already overburdened power grid in the northeastern U.S. and Ontario through initiatives like this, the less likely you're going to have power surges that cause blackouts," Fotinos said. "It's cheaper to reduce demand than build new supply."
Conventional air conditioning systems in high-rise buildings use electrically powered chillers in the basement to cool circulating water before pumping it upward and fanning it out over each floor. As the water rises, it absorbs heat, much of which is dissipated into the air by cooling towers on the roof before the water is returned to the basement to repeat the cycle.
With lake-source cooling, the chillers in the basement and cooling tower on the roof are obsolete. After heat exchangers use the lake water to lower the temperature of the cooling water, a central pumping station sends the cooling water around the city loop, branching off to each building. The cooling water eventually returns to each building's basement, where other heat exchangers extract some of the heat before sending it back to the pumping station to repeat the cycle.
The project got the green light several years ago, after Toronto residents began complaining about foul drinking water. The city's water commission gave Enwave permission to tap the lake to fulfill Tamblyn's vision of a cooling system under a deal that would also bring clean drinking water to the city through the 3.5-mile-long intake pipes the company wanted to build.
Enwave's long pipes draw water from depths untouched by the sun and most contaminants, allowing the city to save on purification. But at 40 degrees, deep-lake water would give people a doozy of a headache if they drank it directly, and it would cost a small fortune to heat up for bathing.
The system's central heat exchangers solve that problem by extracting the coldness from the lake water to cool the air conditioning supply and then sending the warmed lake water to the city's drinking-water supply. The cooling-water loop is a closed system, and the two supplies never mix.
At Cornell, W.S. "Lanny" Joyce, founder of its Lake Source Cooling Project, said the university began looking for alternatives after the 1987 Montreal Protocol restricted the use of chlorofluorocarbons widely used in air conditioning systems at the time.
"An institutional body like us, we figured we'd be around for at least another 135 years. So we needed a long-term solution," said Joyce, Cornell's manager of engineering, planning and energy management.
The university system was designed to last 100 years -- typical air conditioners have a life span of 15 to 20 years -- to justify the initial investment of $58 million. Since it started in 2000, the project has reduced campus cooling costs by 87 percent.
Lake-source cooling could raise its own environmental issues if it returned large quantities of warmed water to the lake, potentially harming marine life or promoting the growth of organisms that could cause contamination. Enwave avoids that by sending the warmed water to the drinking supply.
"The temperature of deep water doesn't fluctuate over the year, so it can be a consistent, low-energy source of cooling anytime of year," says Rob Watson, a senior scientist at the Natural Resources Defense Council in New York. "But if an entire city did this, you might have thermal pollution issues."
The high cost of setting up such systems, however, has kept them on the fringes of mainstream energy management.
Toronto's initial investment of $148 million mostly went toward laying three miles of piping beneath city streets and installing three intake lines to feed deep-lake water to the system.
Several U.S. communities along the West Coast are researching deep-source cooling, and Hawaii has an Ocean Thermal Energy Conversion plan underway. It will rely on seawater, which, because of tides and currents, must be drawn from far greater depths -- about 3,000 feet -- to get consistently cold temperatures.
But it takes more than a dense population next to a big, cold body of water for deep-source cooling to work.
"The factor that helps make it cost effective is if your local electricity costs are high," said Joyce, citing the Pacific Northwest as an example of a poor candidate for lake-source cooling because of cheap hydroelectricity there.
"Honolulu's electricity prices are at least twice the national average," he noted. "And they run nearly a full load every day of the year. They're the ultimate customer."