Solar wall heating

With a transparent insulation element covering the outside of a massive wall, this part of the building can be converted to a solar wall heating area. Solar energy is converted to heat at the absorber and conducted with a phase delay of some hours - depending on thickness and building material -through the massive wall into the interior. This is the reason why windows and solar wall heating with transparent insulation fit very well together: the solar gains of a south-oriented solar wall reach the room mainly at night time and thus extend the period with passive solar heating considerably.

Suitable wall materials have a high density that is correlated with good conductivity and high thermal capacity. Examples are concrete, limestone and low porosity bricks. Gaseous concrete, high porosity bricks or wooden constructions with a density below 1000 kg/m3 are not suitable because the wall then cannot store enough heat, and only badly conducts the heat to the interior. This results in low efficiency and, worse, high absorber temperatures above 100°C, leading to thermal stresses and, eventually, destruction of the plastic transparent insulation materials.

The two principle variants of transparent insulation systems are shown in Figure 9.4.1. When a highly transparent exterior cover (type T for 'transparent') is used, most of the solar radiation is

Source: Fachverband TWD e.V. Gundelfingen, Germany

Figure 9.4.1 Principle types T and O for solar wall heating with transparent insulation (type O can be vented in summer for effective overheating protection)

Source: Fachverband TWD e.V. Gundelfingen, Germany

Figure 9.4.1 Principle types T and O for solar wall heating with transparent insulation (type O can be vented in summer for effective overheating protection)

absorbed on the surface of the massive wall behind. Here the wall should be painted with a dark paint (black, blue, green, dark red), thus influencing the system's performance with the choice of paint. A second opaque system (type O for 'opaque') includes the absorber similar to a thermal solar collector at the rear side of the product. The solar gains have to be transferred over an air gap, necessary because of building tolerances, to the wall by radiation and convection. The absorber colour cannot, then, be chosen freely.

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