Oh kids, it gives me the shivers to think of it! What a crazy world!
A cool concept
Apr 24th 2007 – From Economist.com
Hydrothermal cooling: How to use cold water from lakes and oceans for air conditioning
Geothermal heating—using the warmth of the Earth’s interior to heat water—is an old idea. Using the planet’s natural coolness, though, is something of a novelty. Nevertheless, as cooling and heating are merely two ends of the same process, it could save money and reduce carbon-dioxide emissions. As long, that is, as you can find a suitable source of cold.
Fortunately for Toronto, it sits next to a very large supply of the stuff, in the form of Lake Ontario. Canada’s largest city has been pioneering the idea that instead of using electricity to power air conditioning, a useful supply of cold can be directly extracted from the environment.
Three large pipes have been run 5 kilometres (3 miles) into Lake Ontario, to a depth of 83 metres. The water at that depth is a constant 4°C, its temperature protected by a layer of water above it, called a thermocline. The water is piped to a filtration plant and then to a heat-transfer station on the lakeside. Here the chill is “transferred” to another closed loop, consisting of smaller pipes that supply the towers of the city’s financial district. Built at a cost of C$230m ($200m) over four years, the system is run by the Enwave Energy Corporation.
One of the first buildings to be connected was the Toronto Dominion Centre, a distinctive set of office towers. Three of the five black buildings were designed by Ludwig Mies van der Rohe and built in the late 1960s and early 1970s. So was their air conditioning. Connecting them to the deep-water cooling project saves 7.5 megawatts of electricity.
The two newer towers, modelled on Mies van der Rohe’s designs, were also recently connected and this summer all five will be air conditioned by water from Lake Ontario. That will save another 2.5 megawatts. Another 12 megawatts will be saved from the connections to the Royal Bank Plaza and the Metro Centre, home to local government.
Some 36 buildings in the central business district have now been connected and a further sixteen have signed on to join the system. The project is expected to save the city 61 megawatts, enough to power 8,500 homes.
Toronto’s project is the largest of its kind in the world and the only one that combines cooling with drinking water. (The water taken from the lake goes on to reservoirs and provides about 15% of the city’s drinking water.) Other cities use similar cooling projects. The one in Stockholm uses seawater and is about two-thirds the size of Toronto’s. A much smaller system at Cornell University uses Lake Cayuga as a source.
Geneva would be an ideal candidate for the system, as Lake Geneva is both cold and deep. The city is investigating a scheme. Tokyo also has deep water, but has not yet done anything about using it.
Not all cities can benefit. Chicago, for example, initially appeared promising as it has harsher winters than Toronto and sits beside frigid Lake Michigan. But close to dry land, Lake Michigan is shallower than Lake Ontario. To get cold water, engineers would have to lay pipelines that were six times as long as Toronto’s. Officials in New York have explored using such a system, but ran into a similar problem: the neighbouring ocean is too shallow.
Using cold water for air conditioning saves more than just energy. Most office and apartment towers put the cooling units on the roof. Removing them means the space can be used for something else, such as a running track or a garden.
The three original Mies van der Rohe towers in Toronto have the cooling units built in between floors, so they appear as black, windowless bands from the outside. The owner is now working out how to convert that to office space, which in downtown Toronto is as precious as electricity.