What Does Thermal Mass Actually Do in a Building?
In a building, as in a refrigerator, mass really does only one thing. It delays the flow of heat. Delaying the flow of heat (say from indoors to outside, or from outside to indoors) can save fuel (and energy) in two ways. It can store energy in the form of heat (or “coolness”) that you’ve bought cheaply (solar energy source or off-peak electricity, for example) for use when that same energy is more expensive. In climates where daily temperatures swing above and below the human comfort zone, thermal mass can save energy by applying the day’s heat (gained during warm hours) against the night’s coolness. Thermal mass also improves the comfort of building occupants, particularly in solar homes, by reducing the range of temperature swings.
