Some elements for assessing the radiated heat in urban areas

Heat island describes increase in air temperature between a city and its surrounding area. The air temperature increase significantly endangers the quality and health of life in a city. Radiation plays a crucial role in heating of open surfaces in a town. Solar radiation heats the surface that later cools itself radiating heat during the night. The presented model calculates the amount of daily sunlight for arbitrary location and arbitrary day of year. This is the basis for calculation of shades from buildings and estimation of the heat radiated to the street. This is an input for the second part of the model: calculation of the street surface temperature and heat exchange with the surrounding air. Heat exchange problems involving radiation lead to a non-linear formulation, which can be simplified with careful parameterisation, i.e., contribution of radiation should be expressed through radiated heat instead of direct influence of distant body temperature. That approach requires introduction of a non-linear convective heat transfer coefficient between the pavement and the open air. In order to determine model parameters, small experimental field with several differently paved areas has been established near the Faculty. Some of the recorded data is presented in the paper.