Abdul Matin Sarfraz writes on the National Observer website about the world’s largest deep lake water cooling network. While more than 100 buildings are connected, two hospitals are saving 15 million kilowatt-hours of electricity each year, enough to power more than 1,300 homes by parting with older chillers and rooftop towers that consume far more energy and water. Is there a similar scheme in a city near you?
Downtown Toronto keeps its cool thanks to Lake Ontario
When two of Toronto’s largest hospitals tapped the frigid depths of Lake Ontario for cooling, the impact was immediate.
Operating costs dropped by about half a million dollars a year, carbon emissions fell by up to 400 tonnes annually and water use declined by more than 200,000 cubic metres — equal to 84 Olympic pools.
Toronto’s deep lake water cooling network, the largest of its kind in the world, draws cold water from the lake, and passes it through heat exchangers and circulates the cool water through a closed loop, connecting downtown buildings.
Buildings draw cooling from the system, and return the water at slightly warmer temperatures for recycling. In the winter, the system works in reverse by capturing the heat produced during the exchange to aid in heating the buildings.
Toronto General Hospital made the switch in 2018, followed by Princess Margaret Cancer Centre in 2020. Both are part of the University Health Network (UHN), which operates several major hospitals across the city.
Tapping into the network allowed the hospitals to part with older chillers and rooftop towers that consume far more energy and water.
Michael Kurz, director of environmental compliance, energy and sustainability at UHN, said the shift has delivered cleaner, cheaper, and more reliable cooling.
Together, the two hospitals save up to 15 million kilowatt-hours of electricity each year — enough to power more than 1,300 homes, Kurz added.
Launched in 2004 and operated by Toronto-based Enwave Energy Corporation, the network connects to more than 100 buildings and runs through 40 kilometres of underground pipes beneath the city’s downtown core. Three three giant intake pipes extend five kilometres into Lake Ontario, to draw the water.
At a depth of about 80 metres, the water stays a steady four degrees Celsius year-round, making it an ideal cooling source.
The cold water is first treated at the city Island Filtration Plant before it enters the city’s cooling network. Then it passes through heat exchangers at Enwave’s John Streetand Pearl Street stations, where the lake’s chill is transferred to a closed water loop that circulates through downtown buildings.
According to Mark Quattrociocchi, partnerships manager at Enwave, the environmental gains are substantial.
By tapping the steady chill of Lake Ontario instead of running power-hungry cooling towers, the system slashes electricity demand during peak hours, which saves about 61 megawatts of electricity demand each year, Quattrociocchi said. It also reduces water use by 700 million litres annually and cuts carbon dioxide emissions by 79,000 tonnes, equal to taking 40,000 cars off the road.
“What we’ve built here is called district energy,” Quattrocciocchi said. “Instead of each building running its own equipment, we centralize cooling and heating, and deliver it through underground pipes. That makes it much more sustainable and cost-competitive.”
Conventional building cooling systems, use rooftop cooling towers to reject heat from chillers. These towers spray water into the air and use large fans to evaporate it, which means constantly adding new water and chemicals to keep the system running.
By switching to Enwave’s closed-loop system, the hospitals no longer use water for evaporative cooling. Instead, excess heat is transferred to Enwave’s system and ultimately absorbed by cold water at the bottom of Lake Ontario.
Heating from cooling
The network also helps heat the buildings when the temperatures drop.
“We push cold water out at about 39 to 41 degrees Fahrenheit, and when it comes back at around 56 degrees, we’re able to capture that recovered heat,” Quattrociocchi said. “We’ve implemented a heat pump plant at our Pearl Street Energy Centre. We upgrade the recovered heat and then distribute it back out as low-carbon heating through our Enwave Green Heat program.”
Alternatively, heat pumps can be installed in the customer’s building, Quattrociocchi said.“That way, they can extract the recovered heat on their own property and provide low-carbon heating to their system,” Quattrociocchi said.
Facilities such as data centres, ice rinks and some hospitals produce excess heat and require year-round cooling systems. In those buildings, Enwave can continue recovering heat even in colder months.
The health network is exploring that option too. “There’s potential to harvest the heat from the return side,” Kurz says. “We’re studying the business case for it, and it could further reduce emissions, especially since heating tends to be the bigger challenge.”
Kurz said UHN is committed to reducing its environmental impact, adding that “GHG emissions and resulting climate impacts are detrimental to public health.”
Expansion and growth
Quattrociocchi said when the project launched in 2004, only a handful of buildings were signed on. Since then, demand has grown steadily as Toronto moves toward its net-zero target for 2040.
Last year, the company completed a major expansion with the addition of a fourth intake pipe in Lake Ontario, boosting the system’s capacity by 60 per cent and creating space to connect up to 40 more buildings downtown.
The $100-million project, delivered in partnership with Toronto Water, was supported by Canada Infrastructure Bank funding. With the upgrade, Enwave estimates the system saves more than 60 megawatts of peak electricity demand from Ontario’s grid and about 832 million litres of water annually — nearly 350 Olympic pools.
Mayor Olivia Chow praised the expansion for “cooling more buildings while reducing emissions and helping us reach our climate goals.”
Safe for the lake
Experts say Lake Ontario’s depth makes the cooling system far less risky than if it were placed in a shallower lake. Lakes such as Erie — much shallower at only 64 metres deep — are more vulnerable to warming, sunlight penetration and harmful algal blooms, said Ed McBean, a professor in the school of engineering at the University of Guelph.
Because the Lake Ontario water is drawn from a depth of 244 metres, conditions that fuel cyanobacterial blooms in smaller lakes are “not likely of concern from the deep lake water cooling system,” said McBean, whose research focuses on water supply security and risk management.
“To date, this has been an operational system that has been functional for 21 years and hence, they have experience that has been a substantial success,” McBean said.
The city also regulates how warm the water can be when it’s returned, ensuring aquatic ecosystems remain protected.
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Energy in Demand - Sustainable Energy - Rod Janssen 