Passive Solar Design

Glazing large areas is a balancing act between heat gain and heat loss. If too much glass is used, the interior can overheat on sunny days but lose more heat on cloudy days resulting in a net loss. But if designed correctly, an area of glazing positioned on the south side of a house can bring passive solar heating gains, which helps to improve the thermal efficiency of the building. This works by retaining the heat which is naturally produced from sunlight. The sun emits heat radiation at short wavelengths, which passes through the glass easily, and this in turn warms the internal surfaces of the building. The building then re-radiates the heat back at much longer wavelengths, which doesn’t pass so readily through the glass, so consequently it is trapped warming the interior. Passive solar heating works at its best when the north side of the building is made out of a dense material such as masonry, which will effectively store the heat and release it slowly. The windows on the north side should also be restricted in numbers and size, to limit the loss of heat by that route. Further improvements can be made by shading the glazing with large roof overhangs. This not only protects it from the worst effects of the weather but also stops over heating by the summer sun when it’s high in the sky, whilst permitting the winter sun to enter when its orbit is lower in the sky.