So far, there has been a little imperfection in the analytical theory of radiation heat transfer. Although there is a calculation formula for non-transparent bodies, more universal calculation formulae for partially transparent bodies have not yet been found.
Today, various types of plastic films are most commonly used to cover greenhouses. However, plastic films are partially transparent to long-wave thermal radiation. Up to now, the radiation heat transfer in the buildings like solar greenhouses has been analyzed using the repeated reflection method.
Preceding authors calculated the radiation heat transfer of radiation systems containing partially transparent bodies such as glasses or films by using different methods, but they did not perform detailed quantitative and qualitative analyses of radiation components when radiation passes through partially transparent bodies. Also, the number of determinants increased considerably because different studies developed formulae with individual radiation components. Therefore, only computer-based calculations were able to determine heat fluxes of resultant radiation or transmission radiation, and some calculation time was required. Furthermore, studies on the determination of radiation heat fluxes using the multiple reflection method and the ray tracing method were more complex than using the effective radiation method. Introduction of computers into technical calculations enabled calculation of radiation heat fluxes in greenhouses by the repeated reflection method, but programming also required a lot of effort. In a word, it was more complex and less intuitive than the effective radiation method.
Kim Chol Gon, a researcher at the Faculty of Thermal Engineering, derived universalized formulae to briefly and explicitly calculate radiation heat fluxes in radiation systems with partially transparent bodies including solar greenhouses and solar collectors, using the effective radiation method (i.e., the radiosity method). Then, he proved that calculated characteristics of the daily temperature variation in a single-roofed solar plastic film greenhouse by using derived formulae are the same as those calculated by using the repeated reflection method.
These formulae can be fully applied to calculating radiation heat fluxes in all radiation systems with partially transparent bodies such as solar greenhouses and solar collectors. They can also be effectively applied to radiation heat calculations of public houses and buildings with windows.
For more information, please refer to his paper “The formula for calculating radiative heat fluxes in systems with partially transparent structures” in “Thermal Engineering” (SCOPUS).