One of the measures taken by governments to alleviate the effect of human activity on climate is to reduce energy consumption in countries. In the residential and tertiary sector, this action applies to seek more efficient systems for thermal comfort in buildings. 

To assess the energy efficiency of buildings it is necessary a computational simulation of it. An energy simulation involves a more detailed calculation of heat transfer processes existing in the building. One of the factors that influence the thermal behaviour of the building is the amount of direct solar radiation that reaches them.

This thesis analyses various methodologies used by existing simulation programs for calculating direct radiation and shadows on buildings. As a contribution to this field the method called "Shadow Volumes" is studied in this type of applications. With this method we obtained a much faster and more accurate calculations of shadows on buildings, and thus, a more accurate estimate of the radiation incident on them. 

Interoperability between different applications is studied in this thesis, too. Especially, the communication between thermal analysis building software and CAD applications for the geometric definition of it. Thus examines the use of the DXF format for communication between both applications.

Finally, it describes the methodology used in the thermal simulation software vpCLIMA, and how it applies the method "Radiant Time Series" to each of the factors involved in the thermal performance of the building.