EFFECT OF WALL THICKNESS ON THE SOLAR GAIN

Utilized passive solar gain covers considerable part of heat losses, especially in well insulated buildings. At the same time the thermal insulation of the wall in such a building, e.g. approaching the “Passivhaus” standard is about 20 cm thick. Unless a light weight building is spoken of further 20-30 cm loadbearing layer and the surface finishing should be added resulting in a total thickness of 45-60 cm. The thick wall narrows the cross section through which the direct solar beam may enter the room thus decreases the solar gain. The movement of the solar beam during the day and season can be followed on the base of the sun path diagram. One could say that on the other hand a massive loadbearing layer - especially if it is on the inner side - increases the heat storage capacity, thus increases the utilized part of the solar gain. Series of thermal simulation proves that the effect of heat storage capacity is less important in comparison with the cross section through which the solar beam enters the room. In other terms a light weight building with thin walls performs better than a massive one with thick wall providing the U-value is the same in both cases. In this paper the results of simulation will be presented. Certainly the wall should fulfill many requirements including load, weather-proofness, thermal insulation, building technology. Solar beam is only one of the many aspects. Nevertheless simple geometric tricks may lead to a good compromise, e.g. bevel edge reveal which is not perpendicular to the façade. No doubt in this case the thermal bridge losses around the window perimeter will be higher however this will be compensated by the solar gain.