A Trombe wall is a very good example of a passive heat source, in the sense that there are no mechanical parts used for the simple version of the technology.
A trombe wall is a very thick wall, consisting of a glass pane secured to an inner wall, with a space between the two. The inner wall is usually a material with good thermal storage properties. When the sun hits the glass on the outer side of the wall, the heat radiates through to the inner wall which absorbs it.
The warmth is not only absorbed by the inner wall, but it is also transferred to the passing air from inside the building. This passing, cooler air comes into the space through a vent at the bottom of the inner wall, and as it rises through the space, it is heated by the heat coming through the glass. This warmed air then passes through another vent at the top of the inner wall and flows back into the building (as shown by the image below). These vents should be shut at night though, otherwise the cool air will find its way inside the room to which the wall is connected.
This system even works when the sun goes down and is not directly hitting the wall. The inner wall stores heat from during the day and releases this heat slowly throughout the night, so the building is constantly being heated.
If there were also a vent at the top of the outer wall, you could shut the inner walls vent in the summer, open the outer vent and voilà! You also have a free ventilation system.
Some simple improvements to this simple version of a trombe wall could be painting the inner wall black, or a dark colour to absorb more heat, or by using double glazed glass – trapping more air in the air space, maybe even a simple blind to help with reducing the heat loss at night. There are a fair few variations on the simple wall described above.
This method of maintaining a warm space is very economically friendly, as well as being environmentally friendly. If Victorian homes, such as homes seen in Bedford, had utilised this simple method of keeping your home warmer, perhaps the smog in the sky which we associate with Victorian times would have been rid of a lot sooner!
Written by Jade Turney – Building Tectonics.