I was away this weekend, when i got here this morning I discovered that my furnace had stopped working sometime over the weekend. It was 35 degrees in my office, 38 degrees warmer than outside! It didn't take long to get the furnace fixed and the heat running, but it took all morning to bring the house up to temperature, and all day before I felt warm again.
Ironically I was working on a design for a home that morning that the owner wants to heat passively and we spent some time on the phone (at my desk with coat, gloves and hat), discussing the merits of "thermal mass" in his new home. Thermal mass describes the capacity of a material to absorb and hold heat. Dense materials make good thermal mass, a warm rock after the sun sets is a great example of thermal mass heat storage. In good passive solar design you want to incorporate concrete, stone, tile and so on, in sunny spaces to absorb the heat of the sun during the day. This helps prevent overheating and dissipate the heat during the night, moderating the temperature of the house. In the southwest where they experience heavy cooling loads in the day and heating in the night time proper use of thermal mass in the design can dramatically improve the energy efficiency and comfort of the home. Its no accident that historically the southwest (and other hot/dry climates have made extensive use of brick, clay, and adobe in their construction.
As I worked this morning impatiently waiting for the concrete floor, plaster walls, timbers, walls and furniture to stop absorbing all the heat I was pumping into the room it was not lost on me just how dramatic the impact of good thermal design can have on our comfort. When designing your new home, office or addition pay attention to the orientation of your house, windows and how to take advantage of the physical properties of the materials in your home to benefit your comfort, your energy efficiency, and ultimately the sustainability of life on our planet.