Passive Solar

What is passive solar design?

Well, it is really the best of all worlds when you can heat or cool your home by simply taking advantage of the sun’s incoming solar radiation. It is free, sustainable and smart! Instead of relying on electricity or natural gas to heat a building, passive solar designs make use of a renewable resource, resulting in a significantly lowered environmental footprint. The goal of passive solar heating is to capture the sun’s heat within a building and release it during periods where the sun is absent. This allows the building to maintain a constant comfortable temperature without the use of electricity or natural gas. There are two major considerations when designing a passive solar building. The first element is the building’s orientation and window placement. The second is the use of thermal mass to absorb, store, and release heat. 

Orientation and window placement

The ideal passive solar building orientation depends on your location in the world. Buildings in the northern hemisphere should be positioned on an east-west axis so that the longest dimension is facing south and there should be plentiful south-facing windows. This allows maximum solar heat energy to be absorbed by the building. For our Australian friends and others in the southern hemisphere, the orientation and placement of windows should be facing north.

Creating an effective passive solar design has its difficulties, as one must balance the incoming sunlight with the temperature needs of the building. Too much solar heat energy can cause the building to overheat. Passive solar cooling systems work to reduce unwanted heat gain during the day. One example of a solar cooling design system is the placement of overhangs or awnings on windows. These devices block some of the sun’s rays during the summer yet allow the sun to penetrate during the winter. This is due to the differing positions of the sun during the seasons.

Deciduous trees provide seasonal shade

Vegetation is another way to reduce unwanted heat gain. For example, the placement of deciduous trees in front of south-facing windows is a great way to prevent too much solar heat energy during the warm months, as the leaves of the trees will be able to block some of the sun’s rays. This passive design strategy allows for solar heat energy to penetrate the building in the cool months, as the leaves on the trees will have fallen, no longer shading the building.

Thermal mass to radiate heat

A crucial aspect of passive solar design is the use of materials which have high heat gain capacity and significant mass. These qualities allow solar heat to be stored during the day. Materials such as dark coloured brick, concrete, and masonry are often used for the walls and flooring of passive solar buildings. For example, the incoming sunlight from south-facing windows will strike the brick floors and walls of a building. This brick will then absorb and store the solar heat and radiate it back out at night when internal temperatures begin to drop.

A wall that is specifically built for these purposes is called a “Trombe wall” after the French engineer, Félix Trombe, an early pioneer of passive solar design.

Learn More about Passive Solar on the Live. Well. Green. podcast episode 26

Green building basics – passive solar design