Direct Gain In Solar Passive Design

Direct solar gain is the simplest form of Passive solar heating.

The sun enters the house via a window or aperture and is absorbed into a floor or wall.

The thermal mass of the floor or wall retains the solar absorption as heat.

The surface area are typically darker in colour to absorb more heat.

The thermal mass is important to collect as much energy as possible combined with an appropriate absorption area.

Generally the use of masonry walls is ideal.

Water is an excellent source of thermal mass but is generally unsuitable in houses.

When designing the passive solar fraction (that is the amount of solar energy needed to heat the house) the thermal mass and aperture or window area critical.

The use of too little thermal mass can cause overheating.

Of course you may not be able to heat the whole house using passive solar and the amount will be governed by the geographical position of the house the amount of windows there orientation and other factors such as shading etc.

The general rule is that too little thermal mass causes overheating too much will not affect the passive solar performance. The use of solar gain is dependent on the other passive principles of air tightness insulation and use of suitable windows to ensure that the gains are not fried away as quickly as they are gained.

It is pointless in having solar gain without having the others in place.

In a retrofit the same principles apply so in a retrofit situation enhance insulation air tightness and window selection to minimise losses.