دانلود رایگان مقاله اثر تابش موج کوتاه و اجزای منعکس آن در میانگین دمای تابشی

Abstract

In outdoor as well as indoor environments, human thermal sensation strongly depends on the direct component of solar radiation incident on the body. Nevertheless, even though the direct component exerts the major contribute on this issue, especially in indoor environments and confined spaces, the diffuse and reflected components of the solar radiation also affects the thermal sensations of people. Despite this evidence, simple and reliable methods designed to take into account the effect of solar radiation on the indoor radiant field enveloping the human being in indoor environments are hardly available. This article aims to provide a contribute on this topic, proposing a model for the computation of the mean radiant temperature (MRT) in indoor environments in presence of solar radiation. The most innovative facet of the proposed model regards the computation of the effects of the radiation components reflected by the internal surfaces. Moreover, in order to try a preliminary validation of the model, an experimental campaign was also carried out and MRT values were measured in positions either directly irradiated by the sun or shielded from direct irradiation. The purpose of the measurements was to preliminarily analyze the extent of the accuracy with which the model might predict the rise of MRT due to solar direct irradiation.

5. Conclusion

The purpose of this paper is to propose a reliable and feasible relationship for the evaluation of the mean radiant temperature for a human subject placed in a confined environment, and irradiated by solar radiation, direct, diffuse and reflected as well. The application of the proposed algorithm, which allows to take into account the time and space variations of the climatic conditions defining the radiant field, requires the acquaintance with a series of parameters which are definitely assessable: the temperatures of the internal surfaces of the environment; the angle factors among the opaque and glazed surfaces of the environment and the subject; the rate of the diffuse and direct solar radiation entering the room through the glazed surfaces; the reflection coefficients of the indoor surfaces to solar radiation; the angle factors among the glazed and the opaque surfaces of the environment; the projected area factors of the subject in the solar beam direction. To sum up, the method is designed to realize a detailed evaluation of the mean radiant temperature which can be, in turn, exploited for thermal comfort optimization and energy efficiency purposes, allowing an optimal sizing and management of systems within the constraints defined by the comfort conditions. Moreover, in order to try to investigate the real effects of solar radiation, a series of experimental measures were carried out. They were specifically designed to analyze the effect of the direct solar component on the mean radiant temperature and to validate the predictions of the proposed model in this regard. As expected, the mean radiant temperature proved to be highly affected by solar irradiance and the proposed model seems to predict this behavior rather satisfactorily. As a matter of fact, notwithstanding the inertia of the probe could have a role in causing the detected discrepancies, the model predictions and the measured data follow similar time trend and the differences among the calculated and measured values are relatively small. This behavior could be explained on account of the fact that 5 min average experimental values were used in the comparison phase, so that the influence of the time variability of the radiative flux is reduced. In conclusion, the described preliminary experimental results show that the proposed model seems to predict adequately the mean radiant temperature value in presence of solar radiation, albeit particular occurrences seem to prove the need of further investigation on this topic. In this direction the future development of the research is planned.