Theoretical Consideration for the Effect of Rainfall in the Mathematical Models for Simulation of Thermal Behaviour in Houses

Mathematical models for simulations of the thermal behaviour of houses have been, so far, based solely on the heat transfer due to radiation, conduction and convection. To the author's knowledge, no model has attempted to take account of the effect of rain and the consequent surface evaporation. This study shows the effect of rain to be quite considerable and as a result the inside temperature drop can be as high as a few degrees C, if the loss of heat is not compensated by heaters. Moreover, the temperature drop as a result of surface evaporation does not vanish when the rain stops, it continues to be present as long as the surface is wet, although the value gradually decreases with time. The effect of the increase in the thermal conductivity of the roof and the outermost layer of the external walls as a result of the penetration of moisture has also been considered. The effect, however, proved not to be of serious significance for the internal room temperatures.