With water and wastewater systems accounting for at least 30% of public water consumption, and with about a quarter of all water in the built environment wasted, the role of water in the energy transition needs more attention.

But while the need to move away from fossil fuels is widely recognized, local infrastructure and grid planners are still figuring out how decarbonization and water conservation can work hand in hand to build a faster path to net-zero.

This energy-water nexus is one of the cornerstones of a global climate emergency that is often said to be about “water in all the wrong places”. And district energy is emerging as an important part of the solution.

Decarbonizing with District Energy

District energy systems on either side of the Great Lakes and the U.S.-Canada border are working to become more sustainable on both fronts—conserving water while also reducing greenhouse gas (GHG) emissions. District energy has been heating and cooling buildings in cities and on campuses for more than 140 years, widely enough that you may have experienced one of these systems without even realizing it.

It’s used in downtown business districts, university and college campuses, health care settings, airports, army bases, and research campuses—anywhere you find a cluster of buildings, with one system providing services to hundreds, sometimes thousands, of structures.

As the world’s energy systems turn toward renewable energy sources, district energy systems are keeping pace. Using industrial-size heat pumps, sewer and data centre waste heat recovery, geothermal, and geo-exchange, these systems have been central to building owners’ and municipalities’ carbon reduction strategies, with some of them achieving carbon-free status.

Two of these systems have managed to incorporate elements of the natural world nearby to become more sustainable while providing reliable, efficient cooling for the people who live and work in the buildings.

Diving Deep in Lake Ontario to Cool Toronto

In Toronto, Enwave Energy Corporation uses cold water from Lake Ontario to air condition downtown buildings via the world’s largest deep lake water cooling (DLWC) system. By eliminating the need for chillers and compressors, the system cuts electricity use and brings chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs)—ozone-depleting chemicals typically used in traditional air conditioners—to zero.

Instead, the Toronto DLWC system draws cold water (3.9°C/39°F) from nearly 100 metres below the surface of Lake Ontario, using heat exchangers to extract the cold and provide space cooling via a district chilled water network.

Participating buildings include Scotiabank Arena, home of the National Hockey League’s Maple Leafs and National Basketball Association’s Raptors, Toronto City Hall, commercial and residential buildings, hospitals, data centres, and college and university campuses—a total of 180 buildings, or 40 million square feet of real estate. It also serves as the primary supply for the city water system.

Compared to traditional chillers, DLWC systems can reduce electricity use by about 80%, and Enwave’s system saves an estimated 832 million litres/220 million gallons of water annually—equivalent to nearly 350 Olympic size swimming pools. The Toronto system also displaces 55 MW of electricity demand, the equivalent of powering eight hospitals, reducing strain on the provincial grid during summer peak periods.

Cooling the Chicago Loop with River Water

Chicago’s district cooling system, operated by CenTrio, is the largest carbon-zero cooling system in North America. It serves about 40% of the buildings in Chicago’s downtown core, including its famous Downtown Loop, providing air conditioning to 110 buildings with a combined 53 million square feet of space.

The system also boasts the largest ice battery in the country, a method of thermal storage in which huge volumes of ice are produced and stored overnight until the cold water can be pumped to connected buildings throughout the day, when the hustle and bustle of the city resumes. At peak production, this system of five interconnected plants can hold 10.4 million gallons/39.4 million litres of ice.

The icemaking process also conserves water using a natural resource right at the centre of the city—the Chicago River. Instead of consuming potable, treated drinking water stored in cooling towers, CenTrio swapped in ultra-filtered river water, reducing the burden on Chicago’s water system by 250 million gallons/950 million litres per year.

The Future of Heating and Cooling

As the world makes the transition away from fossil fuels toward renewable energy, district energy systems are emerging as an important part of the energy mix. With a strong track record of reliability stretching back more than a century, through innovative technologies and a focus on sustainability, district energy can play a key role in how our cities and campuses are heated and cooled for decades to come.

Rob Thornton is President and CEO of the International District Energy Association