Passive Solar House Designs and Plans
Direct Gain Passive Solar Designs
This is the simplest approach to passive solar heating. In this passive solar system, the living space is heated directly by the sun. You may have noticed that your home can be heated entirely by the sun during the spring or fall months. Most likely this is because you’ve got large windows somewhere on the south, south-east or south-west sides of the house, with relatively small windows or closed-off rooms on the north side.
Houses which are fully optimized for direct gain passive solar heating have their largest windows facing exactly south. This permits the maximum solar energy absorption in winter, and the minimum solar energy absorption in summer. Direct gain passive solar houses also require sufficient mass to absorb and store the heat. This means that the foundation must be of concrete, and the walls of concrete, brick or stone masonry. An interior water wall is also a good way to store solar energy for later distribution through the house. It must be situated within the house so that the sunlight hits it directly for most of the day. Thermal mass can also keep a house cool during the summer in hot climates.
For this passive solar system to work properly, the house must elongated on the north/south axis. The side of the house which faces exactly north usually has no windows. There is often a slope to the roof to maximize solar gain in the winter. This often makes the south wall significantly larger than the north wall. This design also often makes use of south-facing clerestories to allow more direct sunlight to enter the house.
Indirect Gain Passive Solar Designs
This passive solar system uses an intermediary mass to absorb solar energy, and then release it into the house. One type of indirect gain system uses thermal storage walls, and another uses roof ponds.
The thermal storage wall must face directly south. This is covered completely with transparent glass or plastic glazing, which is about four inches in front of the thermal mass. One way to design this is with masonry. The surface must have a dark coloration in order to absorb the maximum amount of solar radiation during the day. Adding vents to this side of the house allows heat to circulate into living spaces by convection, as well as by radiation.
Another indirect passive solar design is the water thermal storage wall, which transfers heat to the house by convection. The outside is typically painted black. The surface of the wall remains relatively cool since the heat is distributed evenly through the volume of liquid. The heat is then radiated into the living space.
A third design is the use of a roof pond. The liquid is contained within plastic bags, and placed within the roof which is directly adjacent to the ceiling below. This both heats the house in winter and cools it in summer. During the winter, the ponds are exposed to the sun during the day and covered at night. The reverse is done during the summer, which allows heat to escape from the ponds at night and guards them from gaining heat during the daytime.
Isolated Gain Passive Solar Designs
In this passive solar system, the thermal mass and solar collection areas are isolated from the main living areas. Heat is only drawn down into the living space if it is needed. The most common form of isolated gain is the natural convective loop. The heat is stored either in water or air with rock storage. As the water or air is heated it rises naturally and enters the top of a storage tank. This pushes cold air or water down into the collector.
Hybrid Passive Solar Design
By attaching a greenhouse or sun room to the south side of the house, the indirect and direct gain systems are combined. The greenhouse itself functions as a direct gain passive solar system. The living space absorbs heat from the greenhouse indirectly.
The Benefits of Passive Solar Systems
The benefits of passive solar systems are obvious. They provide an incredible energy savings on heating and cooling bills and reduce carbon dioxide emissions. Heating and cooling bills can be all but eliminated without the need for expensive solar panels or geothermal systems to be installed. It requires only alterations in design, and can be performed using traditional materials. Passive solar systems require little maintenance. The only real disadvantage is that the owner of the passive solar house has little control over heating and cooling. However, many solutions are available to resolve these problems. Passive solar designs can easily be used in concert with traditional and solar heating and cooling methods. As our technology improves, so should these passive solar methods.
I firmly believe that we should switch to constructing all new structures with a passive solar design. Especially government buildings should be designed in this manner, especially schools and government offices. Passive solar also is extremely useful for small buildings such as bus shelters. The savings both in terms of money and carbon dioxide emissions would be phenomenal.
It is also possible to retrofit buildings to passive solar. Although this is more difficult, since passive solar depends on the orientation of the building, many things could be done to reduce our fuel consumption and greenhouse gas emissions. These include the use of shading devices to block solar radiation from entering the home during hot summer months. Vines and trees which lose their leaves in the winter can be placed on the south side of the house. Also special eaves can block a significant amount of radiation during hot months, but allow the radiation to enter during the winter. This significantly reduces cooling bills, but doesn’t affect the heating bill in the cold months.
Architect-designed passive solar house designs and plans about on the web. Check out the additional resources to see them.
Source:
Edward Mazria, “The Passive Solar Energy Book.” Rodale Press, 1979.
