As anyone who has lounged in a sunbeam can attest, the sun brings heat to a room. In some climates at some parts of the year, this is a good thing. In a climate that is cold, you want the heat and light of the sun to shine through your windows in the winter time. Ideally, you want the house to help store this heat and release it in the evening or on rainy days. In a climate that is uniformly warm, you want to use passive solar design to create living environments that ward off heat and light or store it for release into the outdoors in the evening. The overall aim of passive solar design is to use building design to equalize the indoor temperature throughout the day and night.
Passive heating is the use of design elements to increase the heating of a building in the wintertime. Passive heating also increases the ability of a particular building to retain heat. Passive cooling is the use of ventilation, shading, insulation and other natural cooling methods to reduce the heat in a building in the summertime. The use of thermal mass in the home can help with both of these objectives, heating the home when it requires heat and storing heat when the outside is too warm.
If you’ve been studying energy efficiency, you probably know about the role of insulation in your home. Insulation creates a fluffy blanket around your home, preventing energy from moving in and out. Thermal mass is not insulation, but it also creates an indoor environment that is a more ideal living temperature. Thermal mass is a part of the house that is used to store and radiate heat energy. Materials that are used for thermal mass include adobe, clay, mud, rammed earth, concrete, and wood. These materials can be part of walls or floors.
How does the thermal mass work? Even when the climate is cold in the winter, the sun still gives energy to the earth. In the day time, the sun shines on the thermal mass and the mass stores the energy. At night, it releases it back into the house. In warm climates, thermal mass collects heat energy and radiates it back into the outdoors as the outdoor temperature drops in the evening. Historically, homes in hot places have been fashioned from thermal mass materials such as adobe.
It is best to have the thermal mass directly exposed to the sun in order to absorb heat. The exact amount of thermal mass required to heat a building varies from place to place and from building to building. Different materials store different amounts of energy. Also, different buildings lose different amounts of energy. A general rule of thumb is that the area of thermal mass that is exposed to the sun should be about six times the area of windows that are exposed to the sun.
Using thermal mass in your home moves your home renovation or building project beyond insulation. Thermal mass creates a home that can keep itself at a comfortable temperature. Sound space age? Not really. Thermal mass is about clay, earth, water and wood.