Modelling of radiation fluxes in urban areas and their relevance to thermal conditions of humans

The most important meteorological parameter affecting the energy balance of humans during sunny conditions is the mean radiant temperature. It considers the uniform temperature of a surrounding surface giving off blackbody radiation which results in the same energy gain of a human body given the prevailing radiation fluxes. The latter usually vary considerably under open space conditions.

The mean radiant temperature can either be obtained from separate measurements of solar (shortwave) and terrestrial (longwave) radiation fluxes or by integral measurements. Here the methods of measuring mean radiant temperature as well as problems associated with the accuracy of the input data for estimation purposes.

The model „RayMan“ for the calculation of short- and long-wave radiation fluxes on the human body is presented. The model estimates the radiation fluxes and the effects of clouds on short wave radiation fluxes. The model which considers complex urban structures is suitable for use and planning purposes in urban areas. The final output of the model is however the calculation of the mean radiant temperature which is required in the energy balance model for humans and thus for the assessment of urban bioclimate. The model is developed in line with the German VDI-Guideline 3786, Part 2 „Methods for the human-biometeorological evaluation of climate and air quality for urban and regional planing at regional level, Part I: Climate“.

Results emanating from the model are validated with existing micro-meteorological measurements in urban areas especially in Freiburg and Leipzig.