For analyzing systems with high solar gains it is important that design tools have a reliable and accurate means of predicting the solar radiation on surfaces. Since solar radiation on a surface is often greatly influenced by self-associated facade obstructions, neighbor buildings and the surrounding landscape, a prerequisite of solar modeling is the ability to predict shaded and unshaded parts as a function of solar position and geometry. The objective of this thesis is to improve the shading and insolation calculations for simulating buildings simulations with TRNSYS.In order to select the appropriate shading and insolation algorithms for TRNSYS, a literature search was carried out on calculation techniques and their implementation in software applications for thermal building simulation. Based on the results of the literature search a computer program called TRNSHD was developed. In this program, surfaces are projected onto a plane and appear as a series of polygons. The heart of the program is a "polygon clipper" that determines the boundary of subpolygons when two or more polygons overlap one another. For a given geometric configuration, TRNSHD performs shading calculations of external surfaces. In addition, TRNSHD can determine the distribution of beam radiation that passes through a window and onto inside surfaces of a room. The results of an analysis with TRNSHD are sunlit fractions which are defined as the ratio of the radiation on a surface including shading effects to the radiation on the surface without shading. The radiation source can either be beam radiation or diffuse sky radiation. Although TRNSHD was developed for building simulations with TRNSYS, it is a stand-alone tool that is not restricted to either buildings or TRNSYS and thus can be used to solve other shading problems.For validation, the results of TRNSHD were compared with other algorithms. The major assumptions of TRNSHD and their effect on the results are discussed. The major assumptions concern the number of "patches" for diffuse sky radiation calculations and the frequency at which the beam radiation shading calculations are performed. The conclusion is that a total number of 72 sky patches are needed and a frequency of 24 hours (one average day) of each month is sufficient for an annual simulation. The comparative validation process showed that TRNSHD functions correctly and the results of TRNSHD are in good agreement with expected values. The external shading procedure for beam radiation has been validated against an ASHRAE algorithm for overhang and wingwall shading and against a proposed European standard. In addition, comparative calculations with another software application developed by the Danish Building Research Institute were performed. For validating the external shading procedure for diffuse radiation, results of TRNSHD have been compared to those of TRNSYS's TYPE 34 (overhang and wingwall shading) for different shading configurations. A comparison of TRNSHD with experimental measurements and computer simulatio...

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