Passive Solar Design

Passive solar design is sustainable design capitalizing on the construction of the building, the way its site is set up, the environment around it, and its orientation to the sun to make the best use of the amount of sunlight to which it is exposed. These choices can cut down on electricity costs for the building while also helping to light, heat, and cool it.

In the northern hemisphere, buildings created on the principles of passive solar design usually have the longest walls running from east to west. This orientation allows heating from the sun in the winter and much less sun exposure in the summer. Such buildings also feature large south-facing windows, which are often insulated. Building materials that absorb and slowly release the heat of the sun are used in the flooring and walls. These materials include rocks, stone, or concrete; some even contain saltwater, which can collect the solar energy as heat.

Some passive solar-designed buildings can be located underground or built into the side of a hill. Because the temperatures found a few feet below ground are steady, this allows the building to be cool in the summer and warm in the winter.

Landscaping is another consideration, especially regarding the placement of trees and shrubs around a building. Deciduous trees, which lose their leaves in the winter, can be planted around the building to keep it cool during the summer by providing shade and in the winter more sunlight reaches the building.

Another key facet of passive solar building design is a roof overhang. Such overhangs are designed to allow sunlight to stream inside during the winter and shade windows from the higher sun in the summer. In areas where summer temperatures are high, especially in the South, putting roof overhangs on buildings can help keep buildings much cooler than they otherwise would be.

Types of passive solar design systems:

Direct Gain

Direct gain is the simplest type of passive solar design. In this system a large number of windows in a building are set up to face south (in the Northern Hemisphere). The glass is usually double-paned or even triple-paned. That is, the glass consists of two to three panes of glass with a pocket of air in between each pane. These panes are sealed inside one frame. Materials that can absorb and store the sun's heat can be incorporated into the floors and walls that are hit by the sun. These floors and walls release the heat at night, when it is needed the most to heat the building.

Passive Solar Cooling

During the summer months, the process is reversed. The thermal mass is prevented from receiving direct sunlight while absorbing the heat in the room, helping to keep the temperature cooler. Passive Solar Cooling can also be used to allow natural breezes into the buildings. These breezes can help cool down the buildings and provide fresh air. For large buildings the stack effect can be used – due to the fact that hot air rises, where a solar chimney can help draw air out from a building up a chimney.

Day Lighting

Day lighting provides natural light for a buildings interior. An open plan floor can also allow light to reach through a building. Using natural daylight rather then switching on artificial lights can help reduce energy demand, whilst also providing a better quality of light. It has been indicated that such natural daylight conditions also provide improved productivity at work and better health.

Thermal Energy Storage

Thermal energy storage (TES) may refer to a number of technologies that store energy in a thermal reservoir for later reuse. They can be employed to balance energy demand between day time and night time. The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment.

Often thermal storage utilizes a large wall oriented to the south in the Northern Hemisphere. This wall is placed behind double-glazed windows so that it can absorb sunlight. In some of these thermal storage systems, the wall contains a storage medium such as masonry or perhaps water.

The solar energy that is collected is stored during daylight hours so that it can be released when there is no sun.

Solar Greenhouse

Solar greenhouses are also known as sunspaces. They are a combination of both direct gain and thermal storage but are located in a greenhouse. The wall of the thermal storage system is placed next to the greenhouse and the home to which it is attached. This system primarily heats the greenhouse but also can provide heat to the house itself.

Roof Pond

As its name implies, the roof pond system consists of ponds of water placed on a roof. These ponds, which are exposed to the sun, collect the radiation from the sun and store it. The heat that is produced is controlled by insulating panels that are movable. During the winter these panels are open during daylight hours so that sunlight can be collected. During nighttime hours the panels are closed so that little or no heat is lost. The heat that is collected is released into the building to warm it. During the summer roof ponds are used in the opposite way. The panels are closed during the day to block the heat of the sun. At night they are opened to allow cooling of the building.

Convective Loop

The convective loop is also known as a natural convective loop. In this system, a collector is located below the building's living space. The hot air that is created from solar energy rises to heat this living space when needed.