Canadian Technology – Deep Lake Water Cooling

Toronto’s Deep Lake Water Cooling system may not be the first of its kind in the world, but the remarkable success and sheer size of the network nonetheless makes it worthy of mention in our series. The system, operated by Enwave Energy, uses water from Lake Ontario to cool buildings in Toronto’s downtown core. The process is reliable, renewable and up to 75% more efficient than conventional office air conditioning systems. Enwave’s current network is capable of cooling up to 3.2 million square metres (34 million sq ft) of office space along a chilled water loop 10 miles long. Deep Lake Water Cooling takes advantage of water's density characteristics, which inherently preserve a low temperature reservoir (stable at 4°C, the temperature at which water is most dense) at the bottom of deep water bodies. To capitalize on the massive cold water reservoir at the bottom of Lake Ontario, Enwave submerged three large intake pipes deep into the lake. The pipes extend along the natural slope of the lake floor, stretching 5 km from Toronto Island and reaching a depth of 83 m. Cold water retrieved from the lake is filtered and disinfected at the Toronto Island water treatment facility before being pumped to a heat exchange station in downtown Toronto. Here, heat extracted from buildings in Toronto’s downtown core is transferred from the closed loop cooling system to the lake water. Enwave’s closed loop district cooling network circulates chilled water to buildings in Toronto’s downtown core, eliminating the need for each building to operate separate water chillers. The cooling system is capable of continuously circulating water at over 30,000 gallons per minute and can accommodate peak flow rates of up to 72,000 gallons per minute. Each building on the network dissipates waste heat from their air conditioning systems to the chilled water, increasing the temperature of the cooling water in the process. After circulating through the downtown network, water from the cooling loop is returned to the heat exchange station at slightly above 13°C, having gained approximately 8°C during circulation. Here the cooling loop water is chilled by the cold lake water and prepared for recirculation. During the heat transfer process, the cooling water and the lake water are confined to their separate networks so there is no direct contact or cross contamination. The chilled cooling loop water is then re-circulated to buildings in the downtown core while the lake water is introduced into Toronto’s drinking supply. The network started operation in August 2004, becoming the first district cooling system to incorporate Deep Lake Water Cooling. The efficiency of the cooling system compared with conventional air conditioning chiller systems is credited with eliminating 40,000 tonnes of carbon dioxide pollution from the atmosphere each year (the equivalent of taking 8,000 cars off the streets of Toronto). Combining the Deep Lake Water Cooling system with Toronto’s drinking water intake has also alleviated the need for auxiliary heating to raise the drinking water temperature prior to distribution and avoids dumping waste heat into Lake Ontario. Summary by: Richard Murphy