Study on the influencing factors of thermal performance of radiant heating floor with the intensive solar irradiation

Abstract

Radiant floor heating systems are widely used in buildings due to their great thermal comfort and energy-saving potential. In a building with many transparent envelopes, radiant floor units in some zones are usually irradiated by solar radiation, leading to overheating near the local floor surface. In order to quickly evaluate the heating performance of the radiant floor with the influence of solar radiation, a simplified model based on the thermal resistance network is established in this paper. Through derivation, the solar radiation effect coefficient (SREC) and the basic surface temperature are proposed, and then the floor surface temperature can be obtained from these two parameters. After experimental validation of this simplified method, the importance analyses of various factors affecting the SREC and the basic surface temperature are carried out, and the influence of each factor is summarized quantitatively. The results show that the pipe spacing has the greatest effect on the SREC, while the supply water temperature has the greatest effect on the basic surface temperature of the radiant floor. Moreover, the absorbed solar radiation intensity corresponding to the floor surface temperature equaling to the supply water temperature and the hot water stopping heating is defined as the critical value. As the temperature difference between the supply water and the indoor environment increases from 17 °C to 37 °C, the critical solar radiation intensity also increases from 180 W/m2 to 445 W/m2. If the absorbed solar radiation intensity is less than this critical value, increasing the pipe spacing, choosing a smaller pipe size, increasing the equivalent thickness and reducing the thermal conductivity of the radiant floor can all reduce the surface temperature of the radiant floor with the influence of solar radiation. The results of this study can put forward corresponding suggestions for the design and operation of the radiant floor to balance the cooperative heating relationship between the solar radiation and the heating system.