A Trombe wall is a dark coloured masonry or concrete wall covered externally with a glass skin spaced in front to leave a small air space. Solar radiation passes through the glass and is absorbed by the mass wall. The mass is heated during the day and then releases its warmth to the interior during the evening and night hours. Ideally the glazing should have exterior insulating shutters for night-time use in order to prevent the heat gained from being returned back to the outside. Vents can also be placed in the wall to make use of convection currents to directly heat the room behind during the day.
The actual residence does not contain a trombe-wall.
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Trombe walls are named after the French inventor Felix Trombe, due to his work on them in the late 1950s. A typical Trombe wall consists of a 200-400mm thick masonry wall coated with a dark, heat-absorbing material and faced with a single or double layer of glass. The glass is placed between 20-150mm away from the masonry wall to create a small airspace.
Heat from sunlight passing through the glass is absorbed by the dark surface, stored in the wall, and conducted slowly inward through the masonry.
The glass prevents radiant heat from the warm surface of the storage wall from escaping. The heat radiated by the wall is therefore trapped within the air gap, further heating the wall surface. For a 400mm thick Trombe wall, heat will take about 8 to 10 hours to reach the interior of the building. This means that the room behind remains comfortable through the day and receives slow, even heating for many hours after the sun sets, greatly reducing the need for conventional heating and cooling. Rooms heated by a Trombe wall often feel more comfortable than those heated by forced-air systems because of the radiantly warm surface of the wall, even at lower air temperatures.
Architects can use Trombe walls in conjunction with windows, eaves and other building design elements to evenly balance solar heat delivery. Strategically placed windows allow the sun's heat and light to enter a building early in the morning while avoiding glare and excess heat gain in mid-afternoon. At the same time, the Trombe wall absorbs and stores heat for evening use.
If upper and lower air vents are included in the wall, the outer air gap can be used to set up convection currents to quickly heat air within the internal space. Making these vent operable allows the occupants control over instantaneous heating. These must be operable to some extent to prevent reverse cooling convention currents occurring at night.
Applying a spectrally selective surface or low-e coating to a Trombe wall may improve its performance by reducing the amount of infrared energy radiated back through the glass. The selective surface consists of a sheet of special metal foil glued to the outside surface of the wall. It absorbs almost all the radiation in the visible portion of the solar spectrum and emits very little in the infrared range. High absorbence turns the light into heat at the wall's surface, and low emittance prevents the heat from radiating back towards the glass.
Variations
Instead of transferring the energy by heating masonry, it is possible to use a water-wall. Due to convection currents within the water itself, heat is transferred through much quicker than a masonry wall which relies solely on conduction. This can be useful when a shorter delay in heat delivery is required. When using such a system, it is better that the air between the glass and wall remained completely trapped, acting to further increase the external surface temperature of the wall.
Summary
The Trombe wall probably requires the least effort to operate of all passive systems and is ideal for spaces where silence and privacy are desirable. Since it provides most of its heat to the space during the evening and night-time hours, it is ideal for use in living areas and bedrooms. You should, however, provide for some method of cleaning the internal area between the glazing and the storage portion of a Trombe wall. Like direct gain systems, Trombe walls are not normally affected by zoning ordinances.