The use of solar energy in indirect systems consists in placing elements that receive radiation just behind the glazing. Solar radiation with a wavelength of 0,3 do 3,0 μm and heats it. The receiver emits heat waves of length from 4 do 30μm, which are stopped by the glass partition; the only intermediary here is air. Light absorbing elements, as in typical air collectors, there are sheets of different metals, plastics, various types of blinds and similar lightweight building partitions, which are placed behind the glazing in the southern elevations.
The small mass of these partitions makes, that the absorbed heat is immediately radiated, which causes large fluctuations in the temperature inside the room, so it's a flaw in the system.
A better solution is to place a thick one behind the glazing, maximum concrete wall, which heats up slower, but the heat is released longer and more gently. This solution was popularized in the 1960s by a French scientist, working at the National Center for Scientific Research in Odeillo (CNRS), prof. F. Trumpets. Since then, this simple, a very effective method, has become very common. To build the Trombe wall, materials with high density and heat capacity are used.
The best materials used to build Trombe walls are: concrete with stone aggregate, reinforced concrete, full clinker brick, stone and water.
Characteristics of partitions and materials used in passive solar systems
| Type of material and type of partition | Density
kg/m³ |
Specific heat kJ/kgK | Thermal conductivity coefficient W/(m²K) | heat capacity kJ/(m³.K) | Temperature compensation factor. m³/h |
| Concrete with stone aggregate | 3400 | 0,84 | 1,45 | 2016 | 0,0026 |
| Aerated concrete | 800 | 0,84 | 0,29 | 672 | 0,0016 |
| 400 | 0,84 | 0,14 | 336 | 0,0015 | |
| sawdust concrete | 1200 | 1,46 | 0,47 | 1752 | 0,0010 |
| 500 | 1,46 | 0,29 | 1168 | 0,0009 | |
| Zuzlobeton | 1800 | 0,84 | 0,87 | 1512 | ‘ 0,0021 |
| 1000 | 0,84 | 0,40 | 840 | 0,0017 | |
| Keramzytobeton | 1600 | 0,84 | 0,87 | 1344 | 0,0023 |
| 800 | 0,84 | 0,29 | 672 | 0,0016 | |
| reinforced concrete | 2500 | 0,84 | 1,63 | 2100 | 0,0028 |
| Masonry walls: | |||||
| - full brick | 1800 | 0,84 | 0,79 | 1512 | 0,9019 |
| - Hollow brick | 1400 | 0,84 | 0,64 | 1176 | 0,0020 |
| - made of silicate brick | 1900 | 0,84 | 1,05 | 1596 | 0,0024 |
| - made of magnesium brick | 1920 | 0,84 | 3,80 | 1613 | 0,0085 |
| - made of clinker brick | 1900 | 0,92 | 1,05 | 1748 | 0,0022 |
| Pinewood
and spruce |
550 | 2,72 | 0,17 | 1496 | 0,0004 |
| Plain stone | 2400 | 0,84 | 2,56 | 2016 | 0,0046 |
| Hearth slag | 1000 | 0,75 | 0,29 | 750 | 0,0014 |
| 900 | 0,75 | 0,26 | 675 | 0,0014 | |
| Keramzyt | 500 | 0,75 | 0,16 | 375 | 0,0015 |
| Water | 1000 | 4,18 | 0,58 | 4180 | 0,0005 |
| Air | 1,2 | 1,00 | 0,026 | 1,2 | 0,0780 |
The Trombe Wall performs functions: collector, hopper and emitter (radiator) heat Thanks to its mass, it can store heat for a day or two, and its response to high irradiation is small and phase-shifted.
For the construction of the Trombe wall, water in containers can be used in addition to solid materials. Water has much better properties than all other materials . It can be collected in dark opaque tanks placed behind glass, as did S. Bear in a house realized in Albuquerque USA (a wall of tin barrels filled with water with a capacity 208 1 each) or in transparent plastic tubes, as designed by the American company Kaltwalwall Corporation.
The requirements for the Trombe wall in our climate are as follows: 0,6 —1.0 m2 of wall per 1 m2 of floor for concrete walls or 0,45 — 0,85 m2 per 1 m2 of floor for water walls. Brick walls should be thick 25 — 38 cm, concrete 30 — 45 cm, and water - 15 — 30 cm. The walls should be moved away from the external glazing (2 windows) oh the least 12 cm (o 1/15 -1/20 of the collector height). To improve the efficiency of the walls, it is recommended to allow air circulation in the space between the glass and the wall. Openings in the wall allowing air circulation should have a total area of equal size 1/20 the entire surface of the wall. Close the top opening on cold days, to prevent reverse circulation.
In the latest variants of the Trombe wall, instead of cumbersome heat shields left down at night, the outer part of the wall is covered with selective layers. These layers do not impair the efficiency of solar radiation absorption by the wall, and prevent the wall from radiating heat towards the glass (outside). Their effectiveness is the same as thermal insulation (blinds). The Trombeła wall can also be a short-term heat storage. In such cases, its weight should be increased by no more than 10 do 20%.
In order to improve the efficiency of the wall, it is combined with materials undergoing phase changes, which increases the time and amount of stored thermal energy. With successive sunny days, the wall is able to accumulate more and more energy. American and French experiments conducted in the early 1980s confirm this, that the efficiency of such a wall is approx. 50% higher than traditional Trombe walls.
Calculations of profits from solar radiation were made for a single-family house in Zakopane, Warsaw and Mikołajki. this house, o 160 m2 of usable area and 29 m2 of the Trombe wall from the south, of a traditional form, only with increased thermal insulation of external walls, obtained from solar radiation, received through the Trombe wall: in Zakopane 20%, in Warsaw 14%, and in Mikołajki 15% meeting the heat demand.
Another way to absorb and store solar radiation is to build a water pool, which in the housing should have a heavily glazed southern wall, to reduce evaporation (cooling down) water in private swimming pools, it is very effective to cover them at night and on cloudy days with thermal insulation, which makes it easier to keep the water temperature within the range of 25 do 30°C.
Water tanks placed on the roof can also be used to absorb the sun's rays, on a non-thermally insulated ceiling structure. In lower latitudes, they are a good way to obtain heat in winter, and cooling rooms in summer; useless in our climate.