Experimental investigation on the thermal performance of double-layer PCM radiant floor system containing two types of inorganic composite PCMs

•Two inorganic composite phase change materials were introduced into the floor system.•A double-layer radiant floor system with two phase change layers was constructed.•The two composites based on expanded graphite exhibited different melting points.•The performance of test rooms with different systems in winter or summer was studied.•Two composites endow the test room better thermal comfort and lower power costs. Double-layer radiant floor systems that consist of two inorganic phase change layers placed at different positions, were first explored for regulating the indoor thermal comfort in winter and summer climates. Specifically, two hydrated salts having different melting points were respectively compounded with expanded graphite to obtain enhanced thermal conductivity. In the floor systems, Na2HPO4•12H2O-based composite (31.3 °C) and CaCl2•6H2O-based composite (20.2 °C) were used for the heat storage layer and the cold storage layer, respectively. It is found, in the winter climate, the room equipped with a radiant floor system consisting of an upper heat storage layer and a lower cold storage layer, realizes a thermal comfort duration of 2.2 times that of the reference room containing pebbles in the floor. Significantly, the radiant floor system constructed by just exchanging the positions of the two layers endows the room with a thermal comfort duration of 8.1 h in the summer climate, which is 1.7 times that of the reference room. Moreover, appropriately enhancing the thermal conductivity of the composites can promote energy savings by reducing the operating time of the active system. It is estimated that the double-layer radiant floor systems can save economic costs by shifting the peak load. [Display omitted]