Trombe wall

EXAMPLE 5 6 Solar Energy Storage in Trombe Walls... 

SOLUTION The passive solar heating of a house through a Trombe wall is considered. The temperature distribution in the wall in 12-h intervals and the amount of heat transfer during the first and second days are to be determined. Assumptions 1 Heat transfer is one-dimensional since the exposed surface of the wall is large relative to its thickness. 2 thermal conductivity is constant. 3 The heat transfer coefficients are constant. 

Analysis The nodal spacing is given to be Ax = 6 cm, and thus the total number of nodes along the Trombe wall is... 

We number the nodes as O, 1, 2, 3, 4, and 5, with node 0 on the interior surface of the Trombe wall and node 5 on the exterior surface, as shown in Figure 5-47, Nodes 1 through 4 are interior nodes, and the explicit finite difference lormulations of these nodes are obtained directly from Eq. 5 47 to be... 

The Dodal network for the Trombe wall discussed in Example 5 0. 

Note that the inner surface temperature of the Trombe wall dropped by I C and the outer surface temperature rose by 6.5°C during the first time step vrhile the temperatures at the interior nodes remained the same. This is typical of transient problems in mediums that involve no heat generation. The nodal temperatures at the following time steps are determined similarly with the help of a computer. Note that the dala for ambient temperature and the incident solar radiation change every 3 hours, which corresponds to 12 time steps, and this must be reflected in the computer program. For example, the value o( must be taken to be = 360 for / = 1 12, = 763 for i =... 

The temperatures at the nodes of a Trombe wall at various times... 

The rate of heat transfer from the Trombe wall to the interior of the house during each lime step is determined from Newton s law using the average temperature at the inner surface of the wait (node 0) as... 

Therefore, the house loses 785 kJ through the Trombe wall the first day as a result of the low start-up temperature but delivers a total of 38,514 kJ of heat to the house the second day. It can be shov/n that the Trombe wall will deliver even more heal to the house during the third day since it will start the day at a higher average temperature. 

Trombe Wall - A wall with high thermal mass used to store solar energy passively in a solar home. The wall absorbs solar energy and transfers it to the space behind the wall by means of radiation and by... 

The absorber may be a solid (e.g., concrete) wall with a black coating. In the case of solar dryers, this solution is justified if the wall is the dryer housing wall. Its operating principle is the same as that of the Trombe wall used in passive solar heating [56]. (For collector-integrated solar water heaters, see Refs. [105,108].)... 

FIGURE 15 Principles of a Trombe wall (passive) system. Abbreviations as in Fig. 12. 

With active systems, the controls are mostly automatic, heat flows are well contained, and heat transfer processes are accrrrately predictable. With passive systems, heat flows are more diffuse and complex interchanges occttr, which can be grossly influenced by user interference. Often the appropriate adjustment of controls (e.g., of shading devices or of Trombe-wall vents) by the user at the right time is reqtrired to achieve optimttm performance of the system. Both the competence and the attitude of the user can drastically influence the resrrlts. 

Thermal Mass The thermal energy that can be stored within the material of a body such as the inner section of a Trombe wall or the interior of a water-filled thermal window. 

Trombe Wall A two-part wall structure consisting of a transparent thermal capture outer wall and a dense, massive thermal storage inner wall. 

French engineer Felix Trombe (1906-1985) invented what came to be called the Trombe wall structure in the late 1950 s. The photoelectric effect that makes solar cells function was first explained by Albert Einstein in 1905, but it was not until the transistor revolutionized electronics in the mid-twentieth century that silicon became a sufficiently viable commodity to produce solar cells on a large scale. The physical principles that drive these different applications now form the foundation of the energy-efficiency movement. 

Trombe walls also use the principle of thermal mass. A Trombe wall consists of a thick solid wall of concrete or other dense material, open at the top and bottom to allow convective air circulation. A second outer wall of glass windows adjacent to the solid wall acts as the solar thermal collector. 

A Trombe wall captures solar energy to heat a massive inner wall that then radiates that heat into the interior of a building through air convection. Energy-efficient houses can be built from discarded tires that have been packed full of earth. 

Judkoff, R., Sokol, F., 1981. Performance of a selective-surface Trombe wall in a small commercial buildingReport TP-721-1158. Solar Energy Research Institute, Boulder, CO. 

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