A Trombe wall is a south-facing masonry wall covered with glass spaced a few inches away. Sunlight passes through the glass and is absorbed and stored by the wall. The wall has vents provided at both upper and lower parts for air circulation. The glass and airspace keep the heat from radiating back to the outside. Heat is transferred by conduction as the masonry surface warms up, and is slowly delivered to the building some hours later.
Trombe walls can provide carefully controlled solar heat to a space without the use of windows and direct sunlight, thus avoiding potential problems from glare and overheating, if thermal storage is inadequate. The masonry wall is part of the building's structural system, effectively lowering costs. On the outside, the wall is painted black to increase its absorptive capacity. The inside, or discharge surface of the Trombe wall can be painted white to enhance lighting efficiency within the space. However, the outside large dark walls sheathed in glass must be carefully designed for both proper performance and aesthetics.
Solar radiation is absorbed by the blackened surface and stored as sensible heat in the wall. Air, in the space between the glazing and the wall gets heated up and enters the living spaces through upper vents. Cool room air takes its place through the lower vents, thus establishing a natural circulation pattern. The distribution of heat into the living space can be almost immediate or delayed depending on air circulation. Furthermore, the delay can be varied depending on the thickness of the wall, and the time lag properties of the wall materials. If the vents are provided with dampers, the air flow can be controlled. Use of movable insulation in the form of a curtain, between the wall and glazing provides another mode of control.
