How to Colonize an Asteroid
The Solar Window
Box
This device provides a limited amount of heat only late in the afternoon, but it serves as an impressive example of the power of sunshine. While this particular design requires the assistance of gravity to operate, the addition of fans to force the airflow would allow a variation of this device to operate in space.
Do you remember the last time that you opened an automobile on a sunny day, summer or winter, when the windows had been closed, and it was toasty warm inside? That is the basic principle behind the solar window box. We are going to trap the energy of the sun and make it work for us.
The device consists
of a folded tube stuck through a window. The face of the tube exposed to
the sun consists of a glass window which traps the sunlight with via the
"greenhouse" effect.
This box can be constructed of old windows, scrap lumber, and cheap insulation. It does require a fair amount of caulk, but I built the one on my shed from scrap materials for about $35.00 (U.S.).
The beauty of this device is that it produces a generous flow of warm air when the sun shines upon it, but it has no moving parts. The solar window box will not work in space because it relies on gravity to operate, but gravity can be replaced, in this instance, by small fans to direct the flow of air.
Operation of the
solar window box is fairly simple. Sunshine enters the system through a glass
panel, and heats a metal plate, called a plenum. In the system I use, my
plenum is a hunk of 1/4" iron sheet, 3 feet long by about 2 feet wide. My
glass face is made from old storm windows. I use a sandwich of two windows
to increase the amount of insulation.
The warmed plenum heats the air just above it, and causes it to rise. The warm air pushes out the top of the tube, and a vacuum is created at the bottom end of the plenum. The vacuum causes heavier cold air to be pulled in through the bottom if the tube.
Note that there is about an inch of space below the plenum so that air can be heated from both sides. The plenum can be made from sheet iron, like mine, or a piece of corrugated aluminum. It should be painted flat black with a heat resistant paint, such as that used for grills or engines. The angle of the plenum is critical, and is based on your latitude and the angle of the sun at the time of year you want it to work best. I don't need any heat in my shed during the summer, so I have the angle such that the sun hits it best during the fall and spring. In the summer, the sun is at such a steep angle to the plenum that it does not provide much heat.
