THERMAL MASS: ESSENTIAL TO PASSIVE SOLAR HEATING
“Thermal mass” is essential to passively solar-heating your home, according to David Brackhahn of FOXFIRE Construction, Pagosa Springs’ “off grid” building specialist. He has been involved in passive solar design and construction since 1976. He relocated his company to Pagosa Springs in the summer of 1997 after many years in Los Alamos, New Mexico.
Many "Pagosans", motivated by a respect for our environment, want to save energy and resources. With our mountain winters, heating our homes can be both economically and ecologically challenging. Some are concerned about continuing availability of conventional public energy resources. Designing structures that passively utilize the sun’s energy to provide space heating is a perfect solution, one that’s cost-effective, clean, and environmentally “friendly.”
“Passive” solar heating involves simple principles of design that allow maximum benefits without requiring active devices such as electric fans or pumps. Passive solar begins with situating and shading a dwelling properly in order to take full advantage of the natural movement and orientation of the sun during its daily and seasonal heating and cooling cycles.
In a passive solar home, the people become “active” as their understanding of this marvelous resource grows. Simple acts, such as the timely opening or closing of a shade or window, not only maximize comfort but give them a sense of security and peace of mind from working in cooperation with nature.
David points out that a common mistake people often make in trying to solar heat their homes is assuming that huge areas of south-facing glass is all you need. In reality, that alone will severely overheat your air temperature, making you uncomfortably hot during the day, yet providing you no heat at all after nightfall when it is most needed. That’s where “thermal mass” comes in.
Thermal mass is any heavy masonry material, such as adobe, concrete, hard tile, brick (or even water in sealed containers) which, when struck by available sunlight, will absorb heat and then gradually release the heat back into the house over a period of hours, even after sunset. Using sufficient thermal mass where the sun strikes, as in floors, structural and decorative walls, “bancos” (masonry benches), and planters, creates more stable cycles of heat gain and heat release, making your living environment more consistently comfortable. All you really need as back-up heat is a wood-burning stove for those cloudy days when your thermal mass can’t “recharge” from the sun.
Good passive solar design also includes calculated fixed overhangs above your solar-oriented windows. The positioning of windows and extent of the overhangs is calculated for your site’s specific degree of north latitude, allowing maximum winter sun into your house but shading it from hottest summer sun.