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Summary: Both cool roof and phase change thermal storage are promising technologies in decreasing building energy consumption. Combining these two technologies is likely to further enhance the thermal comfort of the building as well as reduce air condition loads. In this paper, the cooling performance and energy‐saving effects of four types of roof (normal roof, phase change material [PCM] roof, cool roof, and cool PCM roof [cool roof coupled with PCM]) were investigated under a simulated sunlight. Experimental results indicate that compared with normal roof, the other three roofs are able to narrow the indoor temperature fluctuation and decrease the heat flow entering into the room. Among them, cool PCM roof gave the best energy‐saving effect that can lower the indoor temperature and heat entering into rooms by 6.6°C and 52.9%, respectively. Besides, the PCM location, PCM thickness, and insulation thickness exerted great impacts on the cooling performance of the roof. Placing the PCM on the internal layer beneath the extruded polystyrene (XPS) insulation board can make the indoor temperature 1.2°C lower than that on the middle layer. Although thicker PCM panels or insulation boards can provide a better thermal insulation, 5 mm in PCM thickness and 20 mm in insulation thickness are enough to guarantee the indoor temperature of cool PCM roof system at a comfortable range (22°C‐28°C) for a whole day. These findings will give guidance in designing buildings with a light and compact roof structure to decrease energy consumption and improve comfort level. [ABSTRACT FROM AUTHOR]

• 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, Na 2 HPO 4 •12H 2 O-based composite (31.3°C) and CaCl 2 •6H 2 O-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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Prepares CPCM with g-C 3 N 4 as a novel porous matrix to composite with Mg(NO 3) 2 ·6H 2 O. • G-C 3 N 4 prevents liquid leakage and fully resolves the subcooling of Mg(NO 3) 2 ·6H 2 O. • Sealants covering the surface of the CPCM prevents dehydration of hydrated salt. • The coated CPCM have stable phase change characteristics after thermal cycling. Mg(NO 3) 2 ·6H 2 O is a promising thermal energy storage material owing to its suitable melting point and high latent heat; however, it suffers from poor thermal stability owing to dehydration. This paper presents a two-step encapsulation method to prepare a shape-stabilized Mg(NO 3) 2 ·6H 2 O composite phase change material (CPCM). First, Mg(NO 3) 2 ·6H 2 O is infiltrated into a novel porous matrix – the graphitic carbon nitride (g-C 3 N 4). The g-C 3 N 4 provides a microhousing for Mg(NO 3) 2 ·6H 2 O to prevent liquid from leaking out during the solid–liquid phase change. The g-C 3 N 4 also significantly reduces the sub-cooling degree of Mg(NO 3) 2 ·6H 2 O from 29.2 °C to 1.9 °C. The Mg(NO 3) 2 ·6H 2 O/g-C 3 N 4 composite with 80 wt% Mg(NO 3) 2 ·6H 2 O has a phase change temperature of 87.0 °C and a specific phase change enthalpy of 112.30 kJ kg−1. Second, the Mg(NO 3) 2 ·6H 2 O/g-C 3 N 4 composite is shaped into a cylinder and then macroencapsulated with commercial adhesive sealants (an epoxy resin structural adhesive and silicon sealant). The sealants provide a shell for the hydrated salt to prevent dehydration. After 100 thermal cycles, the composite phase change material only lost 0.84% and 6.25% in weight with coatings of epoxy resin and silicon sealant, respectively, which are much lower than the 22.92% for the uncoated composite phase change material. The specific phase change enthalpy of the composite phase change material barely changed after 100 cycles; however, the loss for the uncoated composite phase change material reached 22.47%. The joint effect of the g-C 3 N 4 matrix and the sealants improve the thermal stability and reliability of the Mg(NO 3) 2 ·6H 2 O. This sequential multi-scale encapsulation method is promising for solving the typical problems of hydrated salts. [ABSTRACT FROM AUTHOR]

• A solar water heating system using a new type of collector was designed. • SAT/GO/EG functioned as both solar-absorbing substance and thermal storage medium. • The solar-absorbing efficiency of SAT/GO/EG was as high as 63.7%. • The solar-to-thermal conversion efficiency of novel system was equal to 54.5%. Solar energy has been widely used in water heating systems. Latent thermal storage technology using phase change material (PCM) has also attracted great attention in energy storage field. In this study, two kinds of composite PCM- sodium acetate trihydrate/expanded graphite (SAT/EG) and sodium acetate trihydrate/graphene oxide/expanded graphite (SAT/GO/EG) were prepared using a physical hybrid method. The melting temperature and latent heat of SAT/EG were 57.9 °C and 218.1 J/g, respectively. GO showed a negligible influence on the thermal thermophysical characteristics of composite PCM. Exposed in solar radiation, two PCMs can experience phase change almost at same rate. The leakage tests were conducted on these PCMs with the purpose of confirming the density of PCMs. The highest densities at which the PCMs can keep good shape stabilities were 0.8 g/cm3 for SAT/EG and 1.0 g/cm3 for SAT/GO/EG, which indicates that traces of GO (less than 0.1 wt%) can improve the shape stability of compressed PCMs. A solar water heating system equipped with a new type of collector was constructed by employing SAT/GO/EG (1.0 g/cm3, 1628 g) as the solar-absorbing substance and thermal storage medium simultaneously. Under real solar radiation, the SAT/GO/EG can finish phase change and reach the temperature above 70 °C from 9:00 AM to 2:00 PM on a typical day in Zhuhai, China. The solar-to-thermal conversion efficiency of the system was calculated to be 54.5%. These results illustrate that SAT/GO/EG possesses excellent solar-absorbing performance and shows great promise in designing novel solar water heating system. [ABSTRACT FROM AUTHOR]