Modelling long-wave radiation heat exchange for thermal network building simulations at urban scale using Modelica

There are different options for modelling indoor and outdoor long-wave radiation exchange in thermal building models for simulations at urban scale. For improving these building models, a good trade-off between accuracy and simulation time is a major challenge. To evaluate different radiation models for thermal network building models, we compared four outdoor radiation and two indoor radiation models. For the comparison, we set-up three test cases on a generic room and a single family dwelling and analysed surface temperatures, heat demands, and simulation times. The results favoured an outdoor radiation exchange model according to the German Guideline VDI 6007 with modified parameter calculations. It includes important simplifications that lead to short computing time while keeping a sufficient accuracy. For indoor radiation exchange modelling at constant temperatures, a linear approach significantly reduces simulation time without any major accuracy losses.