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Trombe walls |
by Norman Aceron Garcia
A Trombe wall is a passive solar building design feature used as an alternative to conventional fossil-fuel heating. Also called a solar wall, it is made from thick masonry with high thermal mass to passively store solar energy in a building. It was popularized by French architect Felix Trombe in 1964, but its application dates back to ancient times when early humans use thick adobe or stone walls to capture the sun’s energy and slowly release the heat at night when it is cold.
A standard Trombe wall is a south-facing masonry structure separated from the exterior environment by glass and an air space. It absorbs heat from the sun during the day and then slowly releases it in the direction of the building’s interior at night. It is typically 25 to 40 cm (10 to 16 inches) thick and is usually made of concrete, stone or adobe coated with a dark, heat-absorbing material on its exterior surface that absorbs solar heat from the southerly winter sun. To minimize heat loss to the outdoors, a single or double layer of glass is installed 20 to 50 mm (¾ to 2 inches) away from the masonry wall. This air space allows warm air to steadily conduct inward through the masonry structure.
Heat conducts through a masonry wall at a very slow rate of 25 mm (1 inch) per hour. Hence, the interior wall does not start radiating heat into the interior until late afternoon or early evening, when windows no longer permit direct solar heating. This means that the heat absorbed by the 20 cm-thick masonry wall at 12 noon will penetrate the interior living space by around 8:00 p.m. The time delay coupled with the decline of temperature differences, permits the utilization of varying daytime solar energy as a steadier source of heat during the night.
It can reduce heating costs as the house’s fossil fuelled heating system (furnace, boiler, space heaters, etc.) will be operated at reduced times. During prolonged overcast days however, the Trombe wall can become a source of heat loss, since there is minimal heat conducted from the exterior towards the interior. Installing an insulation panel on the interior side, between the collector space and the masonry wall, mitigates the heat loss during prolonged overcast days.
A Trombe wall is a passive solar building design system, which means it does not require any maintenance because it has no moving parts. The construction is relatively simple, inexpensive, and can be easily integrated into an existing home or into new house construction. By decreasing the need to heat the home from traditional fossil-fuelled equipment, you are reducing your home’s carbon footprint and thus making your home more environment friendly.
Norman Aceron Garcia, P.Eng. is an accredited professional in Leadership in Energy and Environmental Design specializing in Building Design + Construction. In 2015, Norman founded Mr. Peg Property Inspections, a social enterprise that advocates green building design and climate change adaptation strategies.