A novel approximate harmonic method for the dynamic cooling capacity prediction of radiant slab floors with time variable solar radiation

Abstract

The incident solar radiation from glass curtain walls shinning on the radiant floor cooling system enlarges its cooling capacity. In this study, an analytic expression using a novel approximate harmonic method is derived for the dynamic thermal response of the radiant slab floor with time variable solar radiation. The characteristic parameters, namely the decay rate and time lag which could be calculated by the thermal properties of the multi-layered radiant slab floor, are introduced to characterize the thermal response of the solar radiation waves. We compared the results calculated using the novel approximate harmonic method with that using a three-dimensional model of the radiant slab floor to evaluate the deviation of the novel approximate harmonic method. The results indicated that the dynamic heat transfer process calculated through the novel approximate harmonic method accords well with the three-dimensional model. Specifically, the transient floor surface temperature and cooling capacity in a design day calculated using the novel approximate harmonic method were close to that by the three-dimensional model with Root Mean Square Errors below 0.25 °C and 1.6 W/m2, respectively. According to the novel approximate harmonic method, the augment of the specific heat of the radiant floor increases the decay rate and decreases the fluctuation range of the cooling capacity influence by the time variable solar radiation.