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Trombe wall
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== Design and construction == Trombe walls are often designed to serve as a load-bearing function as well as to collect and store the sun's energy and to help enclose the building's interior spaces.<ref name="Meltzer1985"/> The requirements of a Trombe Wall are glazing areas faced toward the equator for maximum winter solar gain and a thermal mass, located 4 inches or more directly behind the glass, which serves for heat storage and distribution. Also, there are many factors, such as color, thickness, or additional thermal control devices that have an impact on the design and the effectiveness of Trombe Walls.<ref name="Mazria1979"/> Equatorial, which is Southward in the Northern Hemisphere and Northward in the Southern Hemisphere, is the best rotation for passive solar strategies because they collect much more sun during the day than they lose during the night, and collect much more sun in the winter than in the summer.<ref name="Lechner" /> [[File:INTERIOR DETAIL OF 55-GALLON WATER FILED DRUMS THAT FORM THE CORE OF THE PASSIVE SOLAR HEATING SYSTEM OF THIS HOME... - NARA - 555315.jpg|thumb|A water wall with 55-Gallon Water Filled Drums, Corrales, New Mexico, US.]] The first design strategy to increase the effectiveness of Trombe Walls is painting the outside surface of the wall to black (or a dark color) for the best possible absorption of sunlight. Moreover, a selective coating to a Trombe wall improves its performance by reducing the amount of infrared energy radiated back through the glass. The selective surface consists of a sheet of metal foil glued to the outside surface of the wall and it absorbs almost all the radiation in the visible portion of the solar spectrum and emits very little in the infrared range. High absorbency turns the sunlight into heat at the wall's surface, and low emittance prevents the heat from radiating back towards the glass.<ref name="Torcellini">{{cite web |last1=Torcellini |first1=Paul |last2=Pless |first2=Shanty |title=Trombe Walls in Low-Energy Buildings: Practical Experiences |url=https://www.nrel.gov/docs/fy04osti/36277.pdf}}</ref> Although the Trombe walls are usually made of solid materials, such as concrete, brick, stone, or adobe, they can also be made of water. The advantage of using water as a thermal mass is that water stores considerably more heat per volume (has a greater heat capacity) than masonry.<ref name="Meltzer1985"/> The developer of this water wall, Steve Baer, names this system “Drum Wall”.<ref name="Michels1979"/> He painted the steel containers similar to oil drums and filled them almost full of water, leaving some room for the thermal expansion. Then stacked the containers horizontally behind an equator-facing double glazing with the blackened bottoms facing outside. This water wall involves the same principles as the Trombe walls but employs a different storage material and different methods of containing that material.<ref name="Myers1984" /> Like the dark colored thermal mass of the Trombe walls, the containers that store the water are also frequently painted with dark colors to increase their absorptivity, but it is also common to leave them transparent or translucent to allow some daylight to pass through. Another critical part of Trombe wall design is choosing the proper thermal mass material and thickness. The optimum thickness of the thermal mass is dependent on the heat capacity and the thermal conductivity of the material used. There are some rules to follow while sizing the thermal mass.<ref name="Mazria1979"/> [[File:Effect of Wall Thickness to Fluctuation.jpg|thumb|Effect of Wall the Thermal Mass Thickness on Living Space Air Temperature Fluctuations. Mazria, E.]] [[File:Half Trombe Wall.jpg|thumb|A half-height wall allows controlled direct gain for daytime heating and daylighting while also storing heat for the night.]] The optimum thickness of a masonry wall increases as the thermal conductivity of the wall material increases. For instance, to compensate for a rapid heat transfer through a highly conductive material, the wall needs to be thicker. Accordingly, since the thicker wall absorbs and stores more heat to use at night, the efficiency of the wall increases as the conductivity and thickness of the wall increase. There is an optimum thickness range for the masonry materials. The efficiency of the water wall increases as the thickness of the wall increases. However, it is hard to notice a considerable performance increase as the walls get thicker than 6 inches. Likely, a water wall thinner than 6 inches is also not enough to act as a proper thermal mass that stores the heat during the day. In the early Trombe wall design, there are vents on the walls to distribute the heat by natural convection (thermocirculation) from the exterior face of the wall, but only during the daytime and early evening.<ref name="Mazria1979"/> Solar radiation passing through the glass is absorbed by the wall heating its surface to temperature as high as {{Convert|150|F|C}}. This heat is transferred to the air in the air space between the wall and the glass. Through openings or vents located at the top of the wall, warm air rising in the air space enters the room while simultaneously drawing cool room air through the low vents in the wall. In this way additional heat can be supplied to the living space during periods of sunny weather. However, it is now clear that the vents do not work well in either summer or winter.<ref name="Lechner" /> It becomes more common to design a half Trombe Wall then combine it with a direct gain system. The direct gain part delivers heat early in the day while the Trombe wall stores heat for the nighttime use. Moreover, unlike a full Trombe wall, the direct gain part allows views and the delight of winter sunshine. [[File:19880412080NR Hopfgarten (Thüringen) Solarhaus am Weinberg.jpg|thumb|A building using Trombe wall as a passive solar strategy in Hopfgarten, Germany.]] [[File:Pared de muro trombe.jpg|thumb|A school with Trombe wall in Salta, Argentina.]] To minimize the possible drawbacks of the Trombe wall system, there are additional thermal control strategies to employ to the wall design. For instance, the minimum 4-inch distance between the glass and the mass allows cleaning the glazing and the insertion of a roll-down radiant barrier as needed.<ref name="Lechner" /> Adding a radiant barrier or night insulation between the glazing and the thermal mass reduces nighttime heat losses and summer daytime heat gains. However, to prevent overheating in summers, combining this strategy with an outdoor shading device like shutter, a roof overhang, or an interior shading to block excessive solar radiation from heating the Trombe wall would be the best.<ref>{{cite web |last1=Feist |first1=Wolfgang |title=First Steps: What Can be a Passive House in Your Region with Your Climate? |url=http://www.solaripedia.com/files/170.pdf}}</ref> Another strategy helps to benefit from the solar collection without some of the drawbacks of the Trombe walls is to use exterior mirror-like reflectors.<ref name="Lechner" /> The additional reflected area helps Trombe walls to benefit more from the sunlight with the flexibility of removing or rotating the reflector device if the solar collection is undesired. When three different Trombe wall facades with single glass, double glass, and an integrated semi-transparent PV module are compared in hot and humid climate, the single glass provides the highest solar radiation gain due to its higher solar heat gain efficiency.<ref>{{cite journal |last1=Kundakci Koyunbaba |first1=Basak |last2=Yilmaz |first2=Zerrin |title=The comparison of Trombe wall systems with single glass, double glass and PV panels |journal=Renewable Energy |date=September 2012 |volume=45 |pages=111–118 |doi=10.1016/j.renene.2012.02.026}}</ref> However, it is recommended to use the single glass with a shutter for the evening and night times, to offset its heat losses. High transmission glazing maximizes solar gains of the Trombe wall while allowing to recognize the dark brick, natural stones, water containers, or another attractive thermal mass system behind the glazing as well. However, from an aesthetics perspective, sometimes it is not desirable to distinguish the black thermal mass. As an architectural detail, patterned glass can be used to limit the exterior visibility of the dark wall without sacrificing transmissivity.<ref name="Torcellini" /> The largest Trombe wall in the Northeastern United States is located in NJIT’s Mechanical Engineering Building, at 200 Central Avenue, Newark, NJ.
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