General Model of Radiative and Convective Heat Transfer in Buildings: Part Ii: Convective and Radiative Heat Losses

Abstract

The present paper represents the second part of the serial publication, which deals with convective and radiative heat transfers in buildings. The algebraic computational method for combined convective-radiative heat transport in buildings has been proposed. The convective transport of heat has been formulated by means of the correlation functions of the Nusselt number. The radiative heat transfer has been specified by using the radiosity method explained in the first part of the serial publication. The system of transcendent equations has been formed to couple the convective and radiative heat transports. The transcendent system has been solved iteratively, which has facilitated to obtain the optimized surface temperatures as well as the optimized values of the coefficients of heat transfer. On the basis of these optimized values, a more precise overall heat loss has been computed and compared with the results obtained from the thermal standard. The strong and weak points of the both used numerical methods have been discussed.

General Model of Radiative and Convective Heat Transfer in Buildings: Part I: Algebraic Model of Radiative Heat Transfer

“…But the real amount of heat loss depends on the quality of thermal insulation, the temperature difference between interior and exterior, external coefficients of heat transfer and external emissivities. The complete computations of heat losses that include inner convective and radiative transfers along with external convective and radiative transfers are accomplished in the second serial paper [30], which thematically continues the present paper.…”

“…All this should serve as a preparation stage for the development of a more general model for the estimation of heat losses of inner spaces of buildings, in which the heat transfer is realized by radiation and convection. The general model of combined radiative and convective heat transfer is formulated and applied in the separate serial paper [30] thematically related to the present contribution.…”

Numerical study of heat losses of building walls containing reflective foils

“…The radiosity technique has been applied and extended by many other authors, among them, for example, Oppenheim, 26 Ecker and Drake, 27 Gebhart, 28 Sparrow, 29 Sparrow and Cess, 30 Wiebelt, 31 Love, 32 Gebhart, 33 Howell, 34 Clark and Korybalski 35 and Ficker. 36,37 Since the radiosity method has been recently discussed very thoroughly and illustrated by means of practical examples, only basic relations are recalled here without further details to avoid overlap with previous publications. 36,37 The radiosity method is actually a three-step numerical procedure.…”

“…36,37 Since the radiosity method has been recently discussed very thoroughly and illustrated by means of practical examples, only basic relations are recalled here without further details to avoid overlap with previous publications. 36,37 The radiosity method is actually a three-step numerical procedure. In the first step, the matrix of view factors (F ij ) is determined.…”

“…Recently, this problem has been analysed by means of separate computations related to the building with and without radiative losses. 37 In those computations, among others, the following parameters were used: Tsky=−30oC , Ta=−15oC and the speed of the external air v=20 m/s (windy day). Surprisingly, the heat losses of those two computations were almost identical, that is, 3453.3 W versus 3546.9 W, which is a negligible difference amounting to 2.7%.…”