February 2, 2008

Anything massive, once warmed, tends to stay warm. The Earth maintains a habitatable environment in the minus 459 degree cold of space because our atmosphere allows the planet to capture, distribute, and store energy from the Sun. The atmosphere, like the glass skin of a greenhouse, contains this energy, and thermal currents – the wind, the jet streams, and ocean currents distribute it over the Earth. This system is an example of thermal inertia.

The thermal inertia of Earth is best visualized by using the analogy of the flywheel. A flywheel takes a lot of energy to get up to speed, but once moving only a small thump on a regular basis is needed to keep it going. Each day’s sunshine is the thump that keeps the thermal flywheel going. In twenty-four hour rotation, the planet takes this one-sided blast of solar energy and distributes it through thermal currents, to create our solar system’s only habitable environment.

All that natural energy gave builder Michael Sykes an idea- “What if a house could store and release energy through convection currents, just like the Earth?” So, Sykes set out to design a house which has a miniature atmosphere surrounding a massive structure that can store energy.

Since the late 1980’s, his company —Enertia Building Systems, INC. — has been producing homes that heat and cool by design, rather than through mechanical systems like furnaces and air conditioners. Sykes makes his Enertia homes available nationwide as pre-cut, numbered kits.

The thermal performance of solid timber homes is well known to their owners. Once heated, they stay warm- far longer than a conventional stick frame house. Once cooled, they remain cool. These thermal storage properties, along with proper southerly orientation, allow an Enertia home to heat and cool itself through its design, rather by mechanical system.

Instead of being a tight box to contain heated air- like a conventional home- an Enertia house stores energy in its massive walls. Air that has been warmed through passive solar gain is confined to the outer envelop, and is used for moving energy into the massive internal walls. The heat experienced by occupants is radiant: warm walls and floor.

The thermal current that distributes the warmth is created by both convection and geothermal cooling. Three feet below the surface of the Earth, the temperature is a steady 50 to 55 Fahrenheit, so the basement is always cooler than the heated air above it. Warm air rises in the south of the house. As the warm air reaches the attic, it travels towards the cooler air on the north side of the house (since this side of the house receives no direct sunlight). This completes the loop and distributes heat to the north side of the home.

In the summer, the air that is heated in the outer envelope rises, and is allowed to escape …