My goal in this project is to design an object that will show how a building can be designed to take advantage of the sun to heat itself, and can naturally ventilate and cool itself using the chimney or stack effect. The principle is based on the fact that hot air rises, specifically from the ground floor of a building up to the top floor. The air is heated by the sun, and as it rises creates a vacuum, pulling in fresh air from below and from the sides. This principle is the basis on which buildings with a double wall on the south facade are designed. Hot air rising between the two walls draws air from inside the building out, which in turns pulls in cool air from the north side. Also, the double wall acts as a buffer in the winter, increasing separation between the cold outside air and the warm inside air.
The BRE Building of the Future
International Netherlands Group (ING) Bank, Amsterdam,
The demonstrator object will be built much like a regular building. Essentially it will be a box, with a double layered wall on one side, with openings in the interior wall as well as on the back side of the box to draw air across the box, simulating natural ventilation. A fan will be located in some way at the top of the double wall to show the hot air escaping as it is heated by the sun and rises. Alternatively, smoke could be used to show the flow of air across the box and up the double wall.
The result: it worked perfectly! I used a simple box, about 12" X 17" X 8", cut out one side, and cut four small operable openings in the other side. On the sunny-side, a black wall of foamcore is recessed about 2" into the box, and also has four openings cut into it, aligned with those on the back. The box was then covered with plastic wrap, and three "chimneys" were installed on top, each with its own damper. Immediately after constructing it, I took it outside for a test. Even though the temperature was -10, and it was around 4pm, the heat rising out of the chimney cast a shadow on the wall behind, and I could feel the heat rising off the top.
Opening different numbers of windows and chimneys changed the flow of air, and that is what I hoped to observe. On our actual group test day, we used a thermometer to measure outside and exhaust temperatures. It was -5 outside and the exhaust on this bright and sunny day was +35; a fourty degree difference! Although I had a fan installed, the flow of air was never enough to turn it, which is basically what I expected. In a real building a fan would be used on days where the wind or solar-heating isn't strong enough to exhaust air out of the chimneys.
The results of this test show a couple of things; the sun can be great for heating and ventilating a building, but it can also greatly overheat a building if not properly considered in its design.
The front of the demonstrator, showing the three chimneys and the black wall with its openings.
A close up of the three chimneys--only one has its damper open, and that seemed to be the most effective method. The back of the demonstrator with the two bottom flaps open.
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