How Does The Passive Solar Home Absorb Temperature Changes?

Sunlight enters the home through windows and skylights, and it warms the air, the surfaces that it touches, and the walls and floors. Builders who use passive solar design principles seek to increase the amount of sunlight that enters a house by situating the building so that a long wall with large windows faces the sun, and they seek to hold onto the energy that has entered the house by using good insulation to prevent the loss of heat through the walls, and by using materials that will absorb and store the heat so that it can be released later, when it is needed.

The U.S. Department of Energy, on its Energy Efficiency and Renewable Energy (EERE) website, says, "The simplest passive design is the direct gain system in which the sun shines directly into a building, heating it up. The sun's heat is stored by the building's inherent thermal mass in materials such as concrete, stone floor slabs, or masonry partitions that hold and slowly release heat."

The El Paso Solar Energy Association, on its website, explains the concept of thermal mass. "Thermal mass materials have the ability to conduct and store energy, both heat and cold, and to release that energy back into the living space when it's needed. Heat always moves to colder surfaces. In the solar home, the free solar energy first heats up the air. Since the mass floors and walls are cooler, the heat is absorbed and conducted into these materials. Later, when the sun has set and the room air temperature falls, it will reach a point where the mass materials are warmer than the room air temperature. Since heat seeks out cold, the stored energy will now return to the room. The more mass in the home, the more energy that can be stored."

Frederick Bernard, the owner of Acorn Builders, a custom home designer, builder, and remodeler, says, "Back in the 1970s, builders were experimenting with adobe clay bricks, with concrete walls, and with other sources of 'heat sinks' in Arizona, New Mexico, and other parts of the southwestern United States. A heat sink is any building material that absorbs heat. In those days, they were actually trying to get the sun to shine right on the mass material-- the term is 'thermal mass' because it's a mass used to collect heat. So these thermal masses were designed to have the sun shine right on them. Over the past 30 years, they've come to realize that the sunlight that heats a room of a house will absorb into the concrete of the floor, and if you have a solid wall in a room, maybe one brick wall in each room, that has passive solar heat coming into it, that wall will store the heat for the night time when the sun is not shining."

Good design can also help prevent heat loss. Bernard says that "in windy climates, you might design a vestibule in the entryway of your house with two sets of doors where you open one door and then shut it--kind of like you see in a commercial building."