The Hot Box (solar heater) // Calefaccion Solar

This house is nice and cool in summer because of the thick stone walls. Alas, that means that also in winter the house is cool, even when sunny and 20º outside, which is not pleasant. The house hardly has any windows at the sun side, so there is no heat coming in. That can be helped, with a solar heater. There are various types, but in principle it's a (wooden) box with a transparent front, and a black contraption on the inside, the "absorber". Air passed through the absorber heats up, and is led into the house. The transparent front can be glass, or a plastic or polycarbonate material. The idea is to isolate the collector from the cold outside air, to prevent heat loss.

The black absorber can be various types. Some people make a pipe of soda cans, painted black. Others use a sheet of black metal. Air passed behind that sheet heats up. A very efficient type is constructed with two or more layers of mosquito netting. Pass air through and it heats up.

If you're curious have a look at: https://rimstar.org/renewnrg/solar_air_heater_types_diy_homemade.htm en http://stonehavenlife.com/comparing-solar-air-heater-designs-performance/, en http://www.builditsolar.com/Experimental/AirColTesting/Index.htm for various types and an efficiency comparison.

I have chosen the "Screen solar air heater (matrix)", with two layers black mosquito netting. As the transparent material I have asked for a sheet of Makrolon 3000 x 2100 x 6 mm to be sawn in three 1 meter wide sheets, so I can build three individual solar heaters of 2.1 x 1 meters. Makrolon is sheet material for transparent roofs. The box is made of thin triplex (4 mm) and 20 x 20 mm wooden bars and some aluminium profile. Used 3 x 10 mm screws and D3 wood glue. A small fan and a 4 Watt solar pan0el for moving the air through.

Today it's ready for it's first test, at 17:00, so near sunset. Outside temperature: 14º C (50º F). Hot air temperature: 38º C (100º F).

Setting sun, eh! Very curious how it'll be in the full sun tomorrow!

I have not insulated the box, nor sprayed it black. I have material for 3 solar heaters, so I will experiment with insulation and black paint with those.

The box is oiled with Tung wood oil inside and outside. (Inside only once.)