Passive solar home design minimizes energy use of a home by taking advantage of a variety of factors (location, materials used, climate etc.). When it is well designed, the energy loads needed for heating and cooling are reduced. Those needs are met, either partly or entirely, by using solar energy.
Site location should be taken into account in order to maximize the energy efficiency of a home. When planning your home, you want the south side of the house to have a clear view of the sun. In some areas, zoning takes into account solar access. In these areas, you will be covered in case a neighbor wants to build a home that would obstruct sunlight. If you cannot find an area that protects solar access, purchase a lot that has a long south to north stretch. You can then use the northernmost part of the lot to build the house. You also want to make sure that the area to the south of your home does not have trees growing there.
How Does Passive Solar Design Work?
In order to be successful, a passive solar home needs to include the following elements: properly oriented windows, adequate thermal mass, the right distribution mechanisms and effective control strategies.
Windows and other sun-facing devices should be directed at a 30-degree angle from true south. In the heating seasons (winter, parts of spring and fall), they should not be obstructed by shade during the hours from 9AM to 3PM . During cooling seasons, the windows should be shaded.
Thermal mass is a term which refers to all of the materials in the home that can store heat (concrete, bricks, tiles, stones, etc.). Thermal mass is beneficial in colder climates and detrimental in warmer climates. During the heating season, thermal mass should have unobstructed access to sunlight in order to gather as much heat as possible. During cooling seasons, shading thermal mass reduces the load on your cooling system.
Distribution mechanisms refer to the mechanisms that transfer heat through conduction, convection and radiation in the home. Conduction refers to the heat transferred between two objects that are in direct contact with each other, such as a sun-heated floor warming your bare feet. Convection refers to the heat transfer that occurs within a single object, like air or water. Radiation refers to the heat transfer that occurs when a warmed up surface emanates heat into its surroundings, such as a sunny window. In a passive solar home, these distribution mechanisms take into account the three types of heat transfer and either encourage it or block it.
Control strategies use methods that keep the home’s energy neutral. These include roof overhangs, south facing windows and thermostats. Any method or mechanism that acts by sensing a change in temperature from the desired mean is part of a control strategy.
So all in all, a passive solar home includes the elements mentioned above in the form of:
- Air sealing and insulation
- Proper window positioning, glazing, and shading
- The proper thermal mass type and location
- Various cooling and heating systems
Direct, Indirect and Isolated Gain Homes
The three design types of a passive solar home take advantage of solar energy in different ways. In direct gain design, sunlight passes through the south-facing windows and it heats masonry floors and walls. This heats up the thermal mass during the day and during the night the heat is released into the home. In some cases, designers include water-filled containers in the rooms affected by the sunlight in order to increase the thermal mass and subsequent heat dispersal that occurs during the night.
The indirect gain design is a little bit more ingenious. Heat is transferred through the thermal mass, which is a southern facing wall behind a single or double layer of glass. The wall is dark-colored in order to absorb as much heat as possible. As it gets warmer, it radiates heat into the living space. The most common form this design takes is the Trombe wall.
Given that heat travels through masonry at an average rate of one inch per hour, it will take eight hours for the heat to reach the living space through an eight-inch wall. In order to stop heat from reaching the thermal mass during cooling seasons, this design takes advantage of the sun’s positioning, overhang placement, and glazing of the windows
Finally, the isolated gain design aims to produce an enclosure that is dedicated to gathering heat. In isolated gain design, heat is gathered in the thermal mass of an enclosed space, commonly known as a solarium or sunroom. It is then spread through the house by convection and conduction mechanisms.
Is Passive Solar Design For You?
Passive solar design can provide a ton of benefits, even if it is partially implemented. By using some of the methods described in this article, you can reduce your home’s energy load even further once insulation and a solar system are in place.