Thermal storage effect of radiant floor cooling system using phase change materials in the hot and humid climate of Indonesia

We proposed a novel radiant floor cooling system using phase change materials (PCMs) with night ventilation in the hot and humid climate of Indonesia. This study aims to clarify the measures to ensure the thermal storage effect of the proposed cooling system during daytime for a naturally ventilated room within a relatively narrow diurnal temperature range, focusing mainly on the thermal properties of PCMs. We analyzed the relationship between the indoor vertical air temperature distributions and heat flows of the proposed system using an experimental building in Tangerang, Indonesia. The results confirmed that the thermal mass of PCMs and the cooling strategy for the floor structure at night strongly contributed to maintaining a low floor surface temperature during the subsequent daytime. Calm wind conditions and warm nocturnal ambient temperature, which was 0.7-3.2 degrees C lower than the set-point solidifying temperature and is common in the tropics, prevented PCMs from solidifying in case of natural ventilation for the underfloor space. In contrast, forced ventilation for the underfloor space attaching PCMs was effective in ensuring sufficient solidification. Furthermore, 95% of the thermal storage capacity of PCMs might be utilized when the ambient temperature was 2-3 degrees C higher than the set-point melting temperature during the daytime. The phase change temperature for PCMs can be determined based on the average ambient temperature, whereas a relatively wide diurnal ambient temperature range, at least 4.7 degrees C, was required to ensure the latent heat thermal storage effect caused by the supercooling.