With ‘solar chimneys’ buildings can become completely energy self-sufficient. Or so Ben Bronsema and his colleagues are trying to prove in a small wooden cabin in Limburg.
With several researchers cramped together in a small wooden cabin, one would think the room would quickly become stuffy. Yet a nice steady breeze prevents this from happening. Air is somewhat mysteriously flowing through a small ventilation grid, which is odd, because there doesn’t seem to be any other openings in the room that could explain the drought; moreover, there is hardly any wind outside.
Upon closer inspection however, this cabin looks more like a high-tech research facility. Hidden behind a couple of computers and a heap of entangled wires is the inlet of a chimney shaft.
An 11.5 meter high ‘solar chimney’ sticks out above the cabin. Solar energy absorbed by the chimney causes the air inside the chimney to heat up and, accordingly, move upward. As a result, it entrains air from the space underneath, thereby creating a breeze inside the cabin.
This solar chimney is a test model for Ben Bronsema, a 75-year-old PhD student who has been working as a heating and cooling systems guest teacher at the faculty of Architecture since 1993. “Retire and take it easy? No, why? I don’t feel like it”, Bronsema says.
With the aid of a grant from the Dutch ministry of economic affairs, Bronsema is investigating the best ways to build solar chimneys for the ventilation of buildings.
For decades researchers have been figuring out the best way to design buildings to make use of this technique. The pioneers in this field are researchers from India. But whereas the goal in warm areas of the world is mainly to ventilate buildings when opening windows is not enough, Bronsema wants to use this technique to make buildings in cold and temperate regions climate neutral.
For one, buildings with integrated solar chimneys theoretically wouldn’t need to spend energy on air-conditioning during hot summers. Bronsema however believes that if the chimneys are equipped with heat exchange devices, then heat from the airflow coming out of the chimney can be recuperated and stored as hot water underground and used for heating during winter.
In a later stage, Bronsema, who has dubbed his research ‘Earth, wind and water’, wants to combine the solar chimney with a specially designed roof that exploits wind-induced under- and over-pressures to create ventilation. And he intends to experiment with a cooling and ventilation method that involves pouring small droplets of cold water down a shaft.
For the moment, Bronsema and Harry Bruggema, a researcher at Peutz, an engineering company in Limburg where the experiment is taking place, are constantly measuring variables such as inside and outside pressure, temperature, solar radiation and wind speed.
The two are collaborating with researchers from TU Eindhoven’s architecture faculty, whom they provide with data. Based on this data, the researchers in Eindhoven will try to develop a tool that architects can use to design climate neutral buildings.
“A tool for architects, yes indeed, that’s the ultimate goal”, says dr. Marija Trcka-Radosevic, of TU Eindhoven, laughing. “But first we have to fit the physics in very complicated simulation models.” That in itself is a huge challenge, she says.
But Bronsema has his hopes up: “Now architects who want to use solar chimneys must gamble on the best size and number of chimneys. Our tool will change that. It will indicate how many chimneys should be integrated in the walls of the building.”
The researcher doesn’t expect that whole facades, on a building’s sunny southside, will need to be covered with chimneys in order to obtain the desired climatic effect, which of course would result in very dark apartments or offices. “But yes, probably you would need to make many parallel chimneys”, he says. “But then again, less sunlight from the south coming in the building is not always a bad thing. During the summer lots of people prefer sitting in offices facing the east, because on the south-facing sides the sun is too harsh.”
written by Tomas van Dijk, 3 march 2010 – Delta Year issue 42, nr 8