291. NATURAL AIR-CONDITIONING
By accident, my apartment has this strange natural air-conditioning. I noticed it when I first moved here. Every summer when it gets hot, I just open the front and back windows, and an incredible draft blows through. The blow rate is roughly equivalent to the medium setting on my 45 watt fan.
It blows constantly, always in the same direction, and I wondered about it for quite a while. The explanation seems to be this: Out back there's a black asphalt parking lot, which is usually about half full. The air rises off the asphalt, creating a convection current which draws in cool air from the shaded courtyard at the front of the building.
I spoke to some people, and apparently this technique has a long history. The romans used it, and it's a classic motif of middle-eastern architecture -- often enhanced by adding shade, trees and water in the courtyard, and tall convection chimneys.
These ideas are catching on in the architectural community. One example is the Eastgate Center in Harare, Zimbabwe:
From an article on the Eastgate design concept called Learning from Termites:
Mick Pearce's Eastgate, a mixed-use office and retailing high-rise built in Harare, Zimbabwe, in 1995, is particularly innovative in the way it responds to issues of sustainability. It is a biomorphic project modeled on a bioclimatic control of a typical termite mound that is to be found in the savannah of the countryside.Another example is Portcullis House in London, an office complex for members of Parliament. It uses no chillers and consumes less than 30% of the energy of a conventionally designed building. Note the convection chimneys:
...ventilation running costs for Eastgate are a tenth of those for a comparable air-conditioned building. It uses 35 percent less energy than the average consumption of six other conventional buildings in Harare, and the client has saved $3.5 million on a $36 million building due to the fact that no air-conditioning plant had to be imported.
Another low-tech scheme:
A plan to use cold water from deep in Lake Ontario as a natural coolant in downtown Toronto, Ontario buildings is a step nearer to reality. The Toronto District Heating Corp., the nonprofit utility behind the plan, has received a large equity investment by Canada’s fourth largest pension fund.A pdf from the IEA on this topic: Avoiding the need for Active Cooling - The systems/whole building approach
A new corporation, called Enwave, will be formed, to be held jointly by the City of Toronto and a subsidiary of the $36-billion Ontario Municipal Employees Retirement System (OMERS).
The investment by OMERS clears one of the biggest hurdles facing the project, which already has environmental approval from the provincial government.
The $120 million project will draw frigid water from more than 60 metres deep down in Lake Ontario, where it maintains a constant five degrees Celsius year-round. The water will be used to chill the water that presently cools downtown buildings, drastically reducing the amount of electricity needed.
A 2.6 km intake pipeline will be constructed, at an estimated cost of up to $45 million, to draw water from the lake, as well as a distribution pipe in the city's downtown core.
The plan could reduce carbon dioxide emissions by 40,000 tonnes annually and should be in use by 2010.Source
-- by JD