Radiation exchange between persons and surfaces for building energy simulations

Thermal radiation within buildings is a significant component of thermal comfort. Typically the methods applied for calculating view factors between a person and its building surfaces requires great computational time. This research developed a view factor calculation method suitable for building energy simulations. The method calculates view factors by numerical integration of projected area factor. Over time the projected area factor of a person has been simplified by geometrical shapes. These shapes were compared with more complex equations on precision and calculation time. The same was done for the resulting view factors, where the results were compared with view factors found by ray tracing. While geometrical simplifications of the human body gave the fastest calculations, the complex equations gave the most accurate results. Non-rectangular surfaces and obstacles were treated by comparing intersection points with the edges of the surface, making the method applicable to rooms with complex geometry. The method for calculating view factors is robust and applicable to building energy simulation tools. Calculation time can be long depending on the complexity of geometry, grid-size and the choice of method for the projected area factor, but view factor calculations are done only once for a whole year simulation.