Solar radiation modelling in a complex enclosure
Introduction
Several thermal balance models have been developed over recent years, particularly for solar heating applications concerning dwellings equipped with ordinary window sizes. The earlier simulation programs were not able to give the precise distribution of different heat fluxes inside these dwellings. So, as there was a growing interest in the passive solar design for highly glazed dwellings or highly glazed commercial buildings, it became necessary to improve the simulation models. The first improvements appeared with the works of Depecker et al. (1984), Baleynaud (1987), and Grenier (1987). More recently, new algorithms for the solar radiation transmitted through windows with variable radiative coefficients dependant on incident angle have been developed by Pfrommer (1995) and Wall (1997), making it possible to determine the time-varying solar energy distribution in a room and to calculate, for example, the internal radiation heat transfer, the back loss of the reflected radiation, etc.
Kraus et al. (1993) separated the short wavelength fluxes originating from solar exchanges and the long wavelength fluxes coming from other radiative exchanges inside enclosures. But the dynamic localisation and distribution of solar patches, when it was calculated, was not used in the final calculations. The authors finally assumed that the direct solar radiation entering the room was received by the inner surfaces homogeneously to satisfy a one dimensional calculation model of dwelling. The same approximation was also used in recent comfort studies developed by Yilmaz (1987) and Belsmajor (1996).
For this reason, and also because computer capabilities have increased notably, we now propose a more refined model. The main aim of this model is to give the precise dynamic distribution of the diffuse and direct solar components on the natural environment of highly glazed dwellings and for complex enclosures containing obstacles (furniture or occupant), Fig. 1.
Section snippets
DESCRIPTION OF THE COMPUTER MODEL
Glazed spaces, such as veranda or atrium buildings have become a common feature in architecture. As this type of glazed space can be greatly affected by outside temperature or insulation it is necessary to calculate them in a detailed way. The following diagram shows that this problem is theoretically complex (Fig. 2).
First of all, we have to take into account the fact that a large part of the transmitted radiative energy can be lost by retransmissions, by reflections or directly through glazed
VALIDATION OF MODEL
The experimentation was carried out for a classical rectangular enclosure composed of a concrete floor, five identical wooden walls and wooden ceiling, and a window (Fig. 4). Each surface of the enclosure was covered with a specific paint whose radiative properties were 0.3 for solar absorptivity and 0.9 for emissivity. Thermocouples with an accuracy of ±0.2 K were buried at different surface positions and thicknesses inside these walls. A meteorological station was installed on the roof,
RESULTS
Choosing a typical and largely glazed office room (Fig. 8), different types of results are given by the model.
CONCLUSION
This study has shown that the new model is able to calculate the time varying distribution of solar fluxes for a complex enclosure possibly containing an occupant.
For this application case the relative importance of the solar patch on the fluxes absorbed by the occupant has been demonstrated. In fact, the influence of the diffuse radiation is greater and leads to possible radiative asymmetry. But we must also keep in mind that the direct beam creates local overheating that can modify parameters
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