Radiative heat transfer considering the effect of multiple reflections in greenhouse structures

Abstract

In greenhouse structures, given the major role played by glazing systems with regard to losses and gains of energy in the system, an accurate prediction of the radiative heat transfer through the glazing material and in the interface between cover and ground is of great importance in energy simulations involving solar radiation. Note that the solar radiation is not only a function of the extinction coefficient (consequently the transmission coefficient), but also depends on the multiple reflections inside the glazing and between the glazing and its surroundings. Therefore, the objective of this study was to incorporate multiple reflections in the glazing and its surroundings, analyzing its influence on radiative heat transfer. In this paper, results show that the methods available in the literature that use only the multiple reflections on the glass cover can return an overestimation of energy transmitted of more than 58 %, while for methods that consider only the transmissivity of the glass this deviation could be even higher, with values of up to 85 %, using a reflectivity of the surroundings of 0.4. This paper also includes a sensitivity analysis, in which the transmitted energy are evaluated changing the quality of the glass and the reflectivity of the surroundings. Results show that the quality of the glass do not affect significantly the energy transmitted, but the reflectivity of the surroundings can considerably affect the prediction of energy gains of the system.