ADVERTISEMENT

Big Chill

An ambitious new project uses lake water to cool off city slickers
pipes for DLWC



ENWAVE
Staring at a lake on a hot day, many people might think the most straightforward way to cool off would be to jump into it. But the city of Toronto recently unveiled a much more intricate way to use Lake Ontario to cool some of its citizens. Beginning on July 15, an elaborate set of pipes began dredging cold water from the bottom of the lake to cool downtown buildings. According to Enwave, the company responsible for the $170-million project, it will reduce overall annual power usage by more than 40 megawatts and greenhouse gas emissions by nearly 40,000 metric tons--the equivalent of taking 8,000 cars off the road--once it is fully operational.

The new system is an example of Deep Lake Water Cooling (DLWC), an alternative to airconditioning systems dependent on fossil fuels and electricity. The idea is not novel. As Lanny Joyce, program manager of the Lake Source Cooling Project at Cornell University in Ithaca, N.Y., points out, cities have had to rid themselves of excess heat since the industrial revolution. Indeed, a number of Scandinavian cities, including Stockholm, use bodies of water as heat sinks and have been doing so for more than a decade. Seattle recently commissioned a study that investigated the potential of DLWC for a new development area; small systems in San Francisco and Vancouver are in place, and a site in Hawaii is also under construction.

The process relies on a simple premise: heat flows from hot to cold. A closed loop of chilled water flows through buildings, taking with it heat removed by air conditioning. Often, expensive chillers use refrigeration to remove this excess energy. But with DLWC, the cold lake water whisks the heat away. For example, in Cornell's set up, water drawn from Cayuga Lake is between 39 and 41 degrees Fahrenheit, but when it returns it is slightly warmer, averaging about 47 degrees F during the winter and 56 degrees F in the summer.

The Toronto project is more ambitious in scope. In the planning stages for more than 20 years, the development includes a new intake pipe for the city's drinking water supply. Water removed from 80 meters below the surface of Lake Ontario is pumped through three pipes to the Toronto Island Filtration Plant and treated to meet drinking water standards. Next, it travels to an energy transfer station and moves through heat exchangers to chill Enwave's closed water-supply loop that is distributed to customers. The two water supplies don't mix, and the lake water, now warmer and potable, moves to the John Street Pumping Station to be distributed to consumers. Meanwhile, the chilly water in Enwave's closed loop is distributed to their network of customers, with the cold water doing the work that used to be the domain of old-fashioned mechanical chillers.

Since its July 15 start-up, the system has been cooling nearly a dozen downtown buildings, including banks and office towers. ¿Everybody's thrilled because the water's colder than we had expected, slightly, and the heat exchange is working well,¿ Enwave's COO Chris Asimakis reports. ¿It's nothing but good news so far; the customers seem happy.¿ To date, however, Enwave has only signed up enough businesses to utilize about 34 percent of the system's total capacity.

Part of the resistance, Asimakis surmises, stems from the unknown nature of the project. ¿Everyone's familiar with chillers,¿ he says, referring to the devices that use chemical refrigerants, such as chlorofluorocarbons (CFC) until they were banned in 1993 by the Montreal Protocol, to control temperature and humidity. He points out that businesses signing up with Enwave can view the move as insurance against rising electricity costs, because the dependency on ever-present lake water leads to price stability. In addition, the heat exchangers used by the buildings on the Enwave loop last 50 years, on average, whereas a chiller's lifetime is estimated to be 20 to 25 years at most. Citing the example of the CFC ban, Asimakis further notes that many companies had to replace or retrofit their chillers to comply with the new regulations. For Enwave customers, the company manages the infrastructure and would be responsible for any such concerns in the future.

The start-up costs associated with DLWC are impressive, and in many cases, prohibitive. The report commissioned in Seattle, for example, notes that the price tag is more than what developers would consider feasible at this time. In the case of Cornell University, Joyce observes that the school had one advantage over industrial interests: ¿Cornell has been around for almost 150 years, and expects to be around for at least 100 more,¿ he remarks. A company that lacks such security is less likely to want to absorb the large initial costs. Even with some long-term security in place, the decision to switch to DLWC was not an easy one, Joyce says. In the high-flying mid-1990s, selling people on a system that required between 10 to 13 years before costs could be recouped was difficult, but in the end the university decided that it was worth it to reduce its overall environmental impact. To date, Cornell has decreased the energy utilized for air conditioning (about 10 percent of the total campus electricity use) by 86 percent, thanks to the Lake Source Cooling Project.

When it was first proposed, the Cornell project did encounter some initial resistance from a group of Ithaca inhabitants who were concerned enough about the added heat's potential effects on the lake's ecosystem to file a lawsuit in an attempt to stop the project. (The case was dismissed.) In Seattle, concerns about the health of the salmon population were also raised during the study. But the envionmental benefits of DLWC often outweigh the worries. "Some roadblocks have been thrown up, but none have not been permitted" once officially proposed says Bob Klug, a senior systems analyst for Seattle City Light who wrote the grant applications for the city's feasibility study. "[DLWC] is as green as can be."

The old adage, ¿location, location, location¿ also plays a huge role in DLWC, with geography being the biggest limitation on which cities, towns and companies can even consider employing the system. In addition, the approach requires district cooling, a central system that pools the cooling requirements of a number of buildings, in order to work. But if the Toronto project is a success, it could make other lake-adjacent energy users sit up and take notice.

Rights & Permissions
Share this Article:

Comments

You must sign in or register as a ScientificAmerican.com member to submit a comment.
Scientific American Holiday Sale

Give a Gift &
Get a Gift - Free!

Give a 1 year subscription as low as $14.99

Subscribe Now! >

X

Email this Article

X