The Power of Thermal Mass

Posted on February 28, 2008
Tag(s): Green Building, Money Saving, Energy | | Email this

Thermal mass materials like stone or concrete floors have the ability to absorb and store energy from the sun. The advantage of integrating thermal mass in a home is reduced mechanical heating and cooling costs.

The concept of utilizing passive solar energy works optimally when a home is designed properly with windows facing south. The number, size and location of windows, or glazing, must be balanced in regard to the amount of thermal mass.

How it works: solar energy heats up the air in a room, collects in the mass materials, and then radiates that heat back into the room at night as it becomes cooler than the wall and floor surfaces. That’s because heat naturally moves in the direction of warmer to cooler. In winter, windows should be covered after the sun goes down, with insulated drapes to retain the heat in the room.

Thermal mass also has the power to cool a space, as well as the capability to reduce extreme indoor temperatures. During the summer, thermal mass has a lower initial temperature than the surrounding air and acts as a heat sink, therefore cooling the room. Appropriate shading devices or venting strategies also aid in cooling a space during the daytime.

Actually water is the best means of thermal mass, but of course it is not structural. A water-filled container, known as a “tube wall”, can be an ideal way to heat and cool interior spaces. It must have southern exposure and receive direct sunlight.

A “trombe wall” (pictured here) is made of dark-colored masonry or concrete and is a south facing, high thermal mass wall that is covered with glass to allow sunlight to pass through into the wall. The north face of the wall faces the living area. During the day the sun heats the south face of the wall and warms it. The heat is released back into the interior living space when the sun is no longer shining. Again. an appropriately-sized overhang is necessary to block out the high summer sun, yet still allow the low winter sun to penetrate through the trombe wall.

Source: US Dept of Energy