From outside to inside, a Trombe wall consists of a layer or more of glass, a narrow air space, and a masonry wall coated with a dark, heat-absorbing material. Energy from the sun passes through the glass, gets absorbed by the dark surface, and is stored in the wall, where it can be distributed to the interior.
Mike Mahon, owner of Adaptive Building Solutions, is a strong proponent of the Trombe system. Before constructing these walls, he drew lessons from a project he’d heard about, in which the builders poured concrete into forms—as would be done for a basement wall—and stacked a second level on top. They had a tough time keeping the wall from leaning because it didn’t have structural supports, so here, Mahon and his crew used grouted concrete masonry units. They framed the floors, walls, and roof before tackling the Trombe walls. “That approach enabled us to build the walls with controlled precision,” Mahon says, adding that filling the cores creates density for increased thermal mass. The wall is capable of giving off radiant heat for 10 to 12 hours; had the crew left the CMUs hollow, they wouldn’t have nearly as much capacity to store and deliver heat.
After the walls were up, they installed a “selective surface”—in this case aluminum coil stock with an indium-tin-oxide coating on one side. The selective surface improves the wall’s performance by reducing the amount of energy reflected or radiated back through the glass—about 90% of solar energy is absorbed and conducted inward. “That coating is basically a one-way valve for energy,” explains architect Michael Klement, who designed this project.
Mahon points out that this component could be made less costly by simply painting the wall surface black. He also describes working with the tin-oxide…