Hygric design and control of radiant floor cooling

In humid climates, cooling the floor may lead to fungus growth and condensation. To inhibit fungus growth, the relative humidity of the cooled surface should not be higher than 80%. This condition sets an upper limit for the cooling power, depending on the humidity of the (naturally-ventilated) room air. In this paper the performance of a radiant cooling floor is analysed using a dynamic room model in the Matlab/Simulink environment with combined heat and moisture transfer in the construction. The water supply temperature is optimised, taking into consideration physical parameters such as the increase of air humidity due to internal sources and the physical heat and moisture properties of the material layers in the cooled floor and other relevant heat and moisture related building characteristics. Furthermore, a simple controlled system is analysed that interrupts the water supply as soon as the surface humidity exceeds the maximum allowed. The results show that the maximum achievable cooling power is predominantly determined by only two parameters: the increase of air humidity due to internal sources and the heat resistance of the floor covering. By controlling the system, the average cooling power is typically increased with 15 % and less sensitive to the water supply temperature. 1