Bitte wählen Sie ihr Lieferland und ihre Kundengruppe
Heat is transfered at surfaces of building envelopes by convection and by radiation. In this study radiation is considered more in detail. At first, basic concepts and laws of thermal radition are briefly presented. This chapter also deals with general raditive properties of real materials. Solar radiation is very importance for heat transfer at exterior surfaces of building envelopes. Several methods and mathematical models have been proposed for the evaluation of the intensity of solar radiation on the plane, when the azimuth angle of the normal of the plane and the tilt angle of the plane with respect to the horizontal are known. Heat transfer by radiation can be calculated applying theories of blackbody and of greybody. In practice, the energy exchange between two surfaces can be calculated by using radiative geometric configuration factors. According to these principles a computer program to calculate the radiation hea transfer has been developed. The special problem in heat transfer at exterior surfaces of building envelopes is the reradiation to the surface from the atmosphere in the night-time. In the computer program mentioned above, this has been taken into account using the concept of the effective re-radiation temperature. This is the temperature of that perfectly black surface surraunding a wall surface which would emit the same re-radiation as the actual surroundings. In the last chapter some application examples illustrating the effects of different calculating methods to the temperature field of building envelopes are presented. These examples have been computed with the finite element method program which has been developed at Helsinki University of Technology. In this investigation new subroutines have been developed which have been used in context of the main program mentioned above. (ERA citation 12:030973)