Air-conditioning of the future – cooling buildings with deep lake water

You never know where a really good idea will come from. Take the innovative Deep Water Cooling system that has replaced air conditioning systems in many big Toronto buildings by using the very cold water at the bottom of Lake Ontario to cool buildings. It uses less than a tenth of the energy required by conventional air conditioning systems.


Robert Tamblyn, the Toronto engineer who dreamed up the system, got the idea when he worked at the downtown Eaton’s department store in the 1940s. He figured out that the store was cooling the women’s evening wear department by blowing air over pipes that carried the cold municipal water supply.

But it took many years before his idea was put into practice, and the story of how that happened was told in the Toronto Star in 2012 by two people who were involved – Don Stevenson, the Ontario deputy minister responsible for the legislation that established TDHC, and Richard Gilbert, a former Toronto councillor who served as the company’s first CEO from 1982 to 1989.

Enwave, which operates the system, started life as the Toronto District Heating Corporation (TDHC), a city-controlled corporation that linked the heating systems of 130 downtown buildings, using a central cooling plant that produced high levels of greenhouse gases.. 

In the 1990s, TDHC’s second president, Alex Bystrin, had shown how the installation cost of deep lake water cooling could be reduced by more than half by sharing facilities with Toronto’s water supply, and how partially privatizing the TDHC could generate the money needed for the project. That led to its transformation into Enwave Energy in 1999. It has since been fully privatized, bringing Toronto a windfall of $100 million after the sale of its share.

In 2004, the City of Toronto agreed to share its water utility infrastructure with Enwave, giving the company access to the cold water of Lake Ontario before it enters the city’s distribution system as drinking water. 

Impressive results

The results of 15 years of operation are impressive, and Enwave continues to innovate. The system has displaced 55 megawatts of energy per year from Toronto’s electricity grid, equivalent to powering eight hospitals, and saved 832 million litres of water per year – the volume of about 350 Olympic-size swimming pools. (Traditional commercial systems often use towers that evaporate water as a means of expelling heat.)

It also has brought great business results for institutions and businesses that are part of the system.

Cadillac Fairview, one of the first customers to connect its TD Centre’s six office towers and covered pavilion to the system, converted the space it had used for mechanical equipment into a highly sought-after penthouse that has attracted world-class tenants to the now LEED Platinum-certified complex.

In 2018, Brookfield Place – which consists of two office towers and a gallery and the Hockey Hall of Fame, making up more than 2.6 million square feet of office space – saved enough electricity to power a small community.

Growth in Toronto’s west end is now supported by Enwave’s investment in an innovative thermal battery that creates and stores energy at night, which is part of The Well, a visionary mixed-use development featuring more than 3 million square feet of office and residential space. 

From Enwave website.

Toronto General Hospital has freed up 20%-30% in capital funds, thanks to savings from using the system, and can now better focus on its mandate by channeling resources into patient care, research or life-saving equipment. For other nearby buildings, tapping into the hospital’s new system is a progressive way to avoid costly and difficult HVAC retrofits, Enwave says.

While Toronto’s system is the largest in the world, and is studying the possible expansion of its system, there are others. Since 2000, Cornell University has been using Cayuga Lake as a heat sink to operate the central chilled water system for its campus and provide cooling to the Ithaca City School District. A similar system which uses ocean water is being used by a resort on Bora Bora, several buildings in Hong Kong, Hawai’i, and in Sydney, Australia, according to Wikipedia.

While they may not have proliferated on the scale of other types of climate-friendly technologies, both kinds of systems are now up and running in dozens of locations around the world, from Hong Kong to Bahrain, Hermann Kugeler of Makai Ocean Engineering told the Washington Post recently. “I think the big thing is informing people that it exists,” Kugeler said. “People don’t know it’s an option.”



Robert Tamblyn inspired Toronto’s innovative Enwave cooling system. Toronto Star, Oct. 21, 2012

Deep lake water revolutionizes cooling and improves water quality for residents. Federation of Canadian Municipalities.

Toronto is home to the world’s largest lake-powered cooling system. Here’s how it works. Washington Post, Nov. 5, 2021.

Enwave website.