Passive building designs are different ways we can take advantage of solar thermal energy to enhance heating (and/or cooling) in a building and thereby reducing the need to use other energy sources for this purpose.
The main goal of passive solar building designs is to reduce overall energy consumption. This usually means that we try to maximize the Sun’s to ability heat a building during the winter, but also enhance cooling in the summer.
Passive Solar Fraction (PSF)
A building’s passive solar fraction is a measure of how much of the heating the Sun is responsible for. A passive solar fraction of 15%, which is considered sustainable, means that the 15% of a building’s energy demand for heating is taken care of by the Sun.
It is possible to achieve a passive solar fraction (PSF) of more than 75% in some parts of the U.S., but at what costs? Most people are not willing to
Then there is the problem of retrofitting compared to building from scratch. Looking into retrofitting an old building to enhance passive solar fraction often offers excellent benefits and should not be overlooked, but the greatest gains are made early in the planning stages (unless you are willing to conduct serious changes for an old building).
Greenhouses are excellent examples of passive solar building designs. They are optimized to enhance solar heating and lighting with roofs and walls made of plastic or glass. As a result, plants can be grown in areas of the World where the outside climate wouldn’t allow them.
However, a greenhouse would not exactly provide ideal conditions for a human being. Passive solar building designs for homes are vastly different and more complex than those for greenhouses. Let’s look at some of the best design strategies when building a passive solar home:
- The orientation of a building is crucial. You want the rooms where you spend the majority of your time in (living room, kitchen etc.) to face the direction of the Sun. This will both enhance heating and natural sunlight.
- Smart shading enables us to keep the sunlight from entering the house during the summer when we want cooling. The solar trajectory is much higher in this season. The image below illustrates this concept perfectly.
- Good insulation stops heat flow in and out of the building and helps to regulate indoor temperatures.
- Ventilation should also be a part of passive solar building designs. A solar chimney can be used to help natural ventilation and reduce energy demand.
- Thermal mass or heat storage is another important aspect of smart passive solar building designs. Implementing trombe walls, ventilated concrete floors and water walls are some of the common efforts to store heat from the day and slowly release it when the Sun isn’t shining. You want the thermal mass as close to the center of the building.