|
System Description:The Trombe wall is basically a system where thermal mass, solar gains and glazing properties are combined in order to achieve thermal comfort passively. The system is usually composed by a thick and heavy wall that works as thermal mass, facing the winter sun side of a building, with an external glazing and separated by a thin layer of air. Its operation is based on the greenhouse principle. The radiation from the sun passes through the glass layer and hits the wall. Most of this radiation is absorbed by the wall that acts as thermal storage and release inward slowly. The glass also prevents the heat, radiated by the wall facade, to escape. Thus, this heat remains constrained in the air gap, further increasing the temperature of the wall. In order to be effective, the wall mass is crucial. It has to be enough in order to absorb and store the heat during the day and then starts to release it inside the building during the night. This process helps to mitigate the internal temperatures, making the room comfortable during the day and the night [1].
The system described above is the classical Trombe wall, there are also several variations and implementations that can be done. The typical variations of the Trombe wall are described below in the last paragraph. |
Typical Uses:The Trombe wall is a passive heating system, it can contribute to reach the internal thermal comfort in winter in cold climates. In a full scale experiment made by the NREL in July 2004 [2], they observed that the Trombe wall contributed 20% of the total heating of the building and its average efficiency, defined as heat delivered divided by solar radiation incident on the external wall, is 13%. Depending on the external climate and the desired internal comfort the Trombe wall might be integrated with another heating system. Thus, the Trombe wall is typically used as a complementary system in buildings in cold climates to save energy during the winter period. Typical applications of this system are in sustainable and energy efficient buildings and they can be found almost in every country where heating is needed. Furthermore, one of its variation is the solar chimney that improve natural ventilation and decrease the cooling loads for the cooling season.
|
System Limitations:There are several limitations for a typical Trombe wall, its performances do not depend only on how it is constructed, but also on external factor such the external temperature or the incident solar radiation. Therefore, it can contribute to give thermal comfort in the building but it has to be integrated with other non-passive systems, able to provide heat when it is needed.
Another limitation is that full height Trombe walls, completely block the direct sun light coming into the building, thus an electrical lighting system is needed in the back room also for the day time, comporting a supplementary energy consumption. Even if Trombe walls reduce the energy consumption of the building during the heating season, if they are not well designed they can work as additional cooling loads in cooling season. Thus, increasing the needed energy for cooling. As mentioned before, there are several variations of the wall, made to avoid these problems. |
Typical Materials:A typical Trombe wall consists in a 4 to 16 inches thick, masonry or concrete wall with a dark, heat-absorbing material (or painting) on the exterior surface and
faced with a single or double layer of glass. The parameters that must be considered when designing the wall are its thermal capacity, that is directly related to its mass (thus its thickness and the material it is made of). Other material with high thermal capacity could be used.
In order to improve the system's performances, the glazing must have a high g/U ratio, where the g value is the coefficient to measure the solar energy transmittance of glass and the U value is a measure of heat loss through the glass. The air gap between the wall and the glazing is usually from 3/4 to 6 inches thick. [3] |
Construction Issues:There are not real construction issues for the Trombe wall, common materials can be used and the system itself it is pretty simple. However, it is important to make a previous analysis, because as said above, its performances depends on some design factors, such as the mass and the material of the wall or the type of glass used. Thus, during the design phase, it is necessary to calculate carefully these parameters, and it is not always an easy calculation. Another issue could be that the air gap is not easily accesible, and, specially in vented Trombe walls, it get dusty and have an impact on the internal air quality. For this variation is important to think how to clean this space before building it. Each other variation have different construction issues.
|
Variations:
|
Vented Trombe wall - Day
Low E-coating effect
Water-wall
|
Vented Trombe wall - Night
Overhang effect
Solar chimney
|
References:
[1] P. Torcellini and S. Pless, Trombe Walls in Low-Energy
Buildings: Practical
Experiences, NREL/CP-550-36277, July 2004;
[2] http://sustainabilityworkshop.autodesk.com/buildings/trombe-wall-and-attached-sunspace;
[3] http://en.wikipedia.org/wiki/Trombe_wall:
[2] http://sustainabilityworkshop.autodesk.com/buildings/trombe-wall-and-attached-sunspace;
[3] http://en.wikipedia.org/wiki/Trombe_wall: