Deep beneath the scenic surface of Lake Ontario, Toronto’s most valuable source of renewable energy is cold, cold water. As water is closest at 39 ° F (4 ° C) and sinks to the bottom, it can become a stable cooling water source for deep seawater cooling (DLWC). A highly successful DLWC system now provides refreshing and soothing air temperatures to many of Toronto’s hospitals, data centers, training campuses, public buildings and commercial and residential buildings.
The idea behind the technology is not that complex: Instead of focusing on energy-intensive compressors and coolers to dissipate heat from buildings, DLWC uses water from nearby Lake Ontario to whip the heat away. It is a system that is sustainable, low in carbon and energy sharing.
Connecting to the network can reduce water consumption and operating costs, provide more predictable energy costs and improve the building’s resilience. The environmental benefits also run deep; the system currently displaces 55 MW of energy per year from Toronto’s electricity grid.
The result of cooling deep lakes is less energy consumption than other sources and significant reductions in water consumption. The system is so successful that it saves the city 90,000 megawatts of electricity consumption annually, which can be equated with the energy needed to run a city of 25,000. It is expected that 30% of the city’s floor area will be connected to low – carbon heating and cooling by the year 2050.
The original DLWC system was completed in 2004 and provided energy to a limited number of customers in the city. However, the system became so popular that Toronto’s DLWC system has almost reached capacity, cooling over 100 buildings in the city center, such as City Hall, Scotiabank Arena, Toronto General Hospital, various hotels and a brewery.
Enwave owns and operates Toronto’s DLWC systems and shares infrastructure with the city of Toronto’s water supply. The city and Enwave operate under an existing energy transfer agreement (ETA) that facilitates the transfer of cooling energy from the city’s drinking water infrastructure to Enwave’s district energy supply through heat exchangers.
The partnership is an essential element of TransformTO, which outlines a path to achieving net zero emissions in Toronto. The road includes a set of long-term, low-carbon goals and strategies to reduce local greenhouse gas emissions and improve the city’s health, grow its economy and improve social equity. On October 2, 2019, the City Council voted unanimously to declare a climate emergency and accelerate efforts to mitigate and adapt to climate change, by adopting a stronger net zero emission reduction target in 2050 or earlier. Greenhouse gas emissions in Toronto were 38% lower in 2019 than in 1990.
The Deepwater Lake cooling system has a prominent place in the TransformTO plan, as it already saves 90,000 megawatts of electricity consumption annually – roughly enough to run a city of 25,000. Energy savings are around 90%, and as the necessary cold water is available all year round, the need for additional cooling is eliminated.
It is so popular that the city has almost reached capacity and has recently committed to an expansion that could run up to $ 100 million. “It’s a big investment,” said Carlyle Coutinho, president of Enwave Washington Post, adding that “it would be challenging to continue to grow commercially without increasing the base load.”
How the Deepwater Lake cooling system works
Traditional commercial water cooling systems often involve towers that evaporate water as a means of dissipating heat. DLWC avoids that evaporation, and Enwave estimates that the Toronto system saves about 220 million gallons of water annually – equivalent to 350 Olympic-sized swimming pools.
How does the DLWC system bring so many energy savings to Toronto?
- Inlet pipes extend 5 miles into Lake Ontario.
- The pipes draw water from a depth of 83 meters.
- Cold water is pumped to the Island Filtration Plant, which is operated by Toronto Water.
- The water moves itself through these pipes using relatively little energy.
- These 3 massive pipes are located about half a kilometer away from each other.
- A fourth pipe is in the planning phase. Once installed, it can add up to 60% more capacity.
- The cold water is treated for use as drinking water before being led to a pumping station.
- Large heat exchangers – rather than energy-intensive air conditioners and coolers – transfer thermal energy between two systems.
- Heat exchangers transfer heat or coolness between water circuits and are located where these water circuits meet – at each customer site, and where the lake’s water pipes meet the city’s pipes.
- Water identified for drinking water in the city is minimally heated.
- The water supplied to buildings in the center to replace traditional air conditioning has cooled.
- Once the seawater reaches the city, the DLWC system operates via a series of water loops.
- A loop moves the seawater;
- Another loop moves water within the center; and,
- Loops in each building interact with the system server.
- After the cooled water is circulated through and cooled the buildings, Enwave reuses the heat and returns the hot water to the pumping station to repeat the process.
The Deep Lake Water Cooling System cannot work anywhere
There are certain parameters that need to be in place for the DLWC system to fit well.
Location: Shallow, sloping sea shelves do not work as they cannot be placed efficiently.
Demand: Although it appeals to many communities, the DLWC system must have enough applications to justify a system.
Pre-investment: It costs a lot. Cornell University’s seawater cooling system cost $ 58.5 million. But it provides the university with a method of cooling that eliminates refrigeration equipment and its associated energy consumption, impacts on the environment from energy consumption, and any future problems with the new generation of refrigerants designed to replace CFCs. The city of Toronto invested $ 170 million in its project.
Other ways to utilize deep water are in the study stage; one is called a salt water air conditioner. Saltwater air conditioning (SWAC) uses sea instead of seawater as a refrigerant. The technology comes in two parts. First, the salt must be dissolved in water, then it must be regenerated so that it can be reused again and again. There are also problems with this approach, as it often uses ammonium nitrate, which is categorized as a hazardous substance.
Image taken from NOAA / open source
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