A Trombe wall is a massive equator-facing wall that is painted a dark color in order to absorb thermal energy from incident sunlight and covered with a glass on the outside with an insulating air-gap between the wall and the glaze. A Trombe wall is a passive solar building design strategy that adopts the concept of indirect-gain, where sunlight first strikes a solar energy collection surface in contact with a thermal mass of air. The sunlight absorbed by the mass is converted to thermal energy (heat) and then transferred into the living space. Trombe walls may also be referred to as a mass wall, solar wall, or thermal storage wall. However, due to the extensive work of professor and architect Félix Trombe in the design of passively heated and cooled solar structure, they are often called Trombe walls. This system is similar to the air heater (as a simple glazed box on the south wall with a dark absorber, air space, and two sets of vents at top and bottom) created by professor Edward S. Morse a hundred years ago.
History of passive solar systems and evolution of Trombe walls In 1920s, the idea of solar heating began in Europe. In Germany, housing projects were designed to take advantage of the sun. The research and accumulated solar design experience was then spread across the Atlantic by architects such as Walter Gropius and Marcel Breuer. Apart from these early examples, heating homes with the sun made slow progress until the 1930s, when several different American architects started to explore the potential of solar heating. The pioneering work of these American architects, the influence of immigrant Europeans, and the memory of wartime fuel shortages made solar heating very popular during the initial housing boom at the end of World War II. Later in the 1970s, before and after the international oil crisis of 1973, some European architectural periodicals were critical of standard construction methods and architecture of the time. They described how architects and engineers reacted to the crisis, proposing new techniques and projects in order to intervene innovatively in the built environment, using energy and natural resources more efficiently. Moreover, the depletion of natural resources generated interest in renewable energy sources, such as solar energy. Parallel to global population growth, energy consumption and environmental issues have become a global concern - especially while the building sector is consuming the highest energy in the world and most of the energy is used for heating, ventilation and air conditioning systems. For these reasons, today's buildings are expected to achieve both energy efficiency and environmental-friendly design through the use of renewable energy partly or completely instead of fossil energy for heating and cooling. In this direction, the integration of passive solar systems in buildings is one strategy for sustainable development and increasingly encouraged by international regulations. Today's low-energy buildings with Trombe walls often improve on an ancient technique that incorporates a thermal storage and delivery system people have already used: thick walls of adobe or stone to trap the sun's heat during the day and release it slowly and evenly at night to heat their building. Today, the Trombe wall continues to serve as an effective strategy of passive solar design. The first well-known example of a Trombe wall system was used in the Trombe house of Odeillo, France in 1967. The black painted wall is constructed of approximately 2 foot thick concrete with an air space and a double glazing on its exterior side. The house is primarily heated by radiation and convection from the inner surface of the concrete wall, and the results from studies show that 70% of this building's yearly heating needs are supplied by solar energy. This is comparably efficient to a good active solar heating system. The Trombe wall converts solar radiation into heat at about 70-80% efficiency—significantly more efficient than photovoltaic systems, which have an efficiency of around 15-20%. Another passive collector-distributor Trombe Wall system was built in 1970, in Montmedy, France. The house with 280 cubic metres (9,900 cu ft) living space required 7000 kWh for space heating annually. At Montmedy-between 49° and 50° North latitude-5400 kWh were supplied by solar heating and the remainder from an auxiliary electrical system. The annual heating cost for electricity was approximately $225 when compared to an estimated $750 for a home entirely heated by electricity in the same area. This yields to a 77% reduction in heating load and a 70% reduction in the cost for winter heating requirements. In 1974, the first example of Trombe wall system was used in the Kelbaugh House in Princeton, New Jersey. The house is located along the northern boundary of the site to maximize the unshaded access to available sunlight. The two-story building has 600 square feet (56 m2) of thermal storage wall which is constructed of concrete and painted with a selective black paint over a masonry sealer. Although the main heating is accomplished by radiation and convection from the inner face of the wall, two vents in the wall also allow daytime heating by the natural convection loop. According to data collected in the winters of 1975-1976 and 1976–1977, the Trombe wall system reduced the heating costs respectively by 76% and 84%.
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