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The low thermal conductivity of PCMs limited thermal storage/release properties of latent heat thermal energy storage (LHTES) systems, and the performance enhancement of PCMs thermal conductivity, PCMs stages and operating conditions needed to be investigated simultaneously. This study selected polyethylene glycol (PEG) as PCM and expanded graphite (EG) as matrix to prepare composite PCMs (CPCMs). When the mass ratio of PEG:EG was 9:1 and CPCM density was 954.8 kg/m3, the thermal performance was excellent without leakage. Compared to the single-stage LHTES tank, the heat storage/release time of four-stage cascaded LHTES (CLHTES) tank was 1040/320s longer, the heat storage/release rate was 0.92/1.04 times and the maximum exergy efficiency was 10.6% higher. For the four-stage CLHTES tank, its heat storage/release rate was fast and efficiency was high at the inlet temperature of 75/10 °C and flow rate of 3 L/min. When the four-stage CLHTES tank was used in a solar heating system, a wider range of phase change temperatures (31.4–55.2 °C) and a longer delay time of temperature peak (2290s) were obtained. Therefore, the CLHTES tank with high thermal conductivity CPCMs could play a significant role in improving the storage/release performance of renewable energy sources. • High thermal conductivity composite phase change materials (CPCMs) were prepared. • The optimal mass ratio of PEG:EG and density were 9:1 and 954.8 kg/m3 respectively. • The CLHTES tank worked better at temperature of 75/10 °C and flow rate of 3 L/min. • The CLHTES tank with high conductivity CPCMs was suitable for solar heating system. [ABSTRACT FROM AUTHOR]

Combining phase change materials (PCMs) with building envelopes has emerged as an effective means to improve the thermal performance of envelopes and achieve the energy conservation and emission reduction in buildings. However, the PCM envelopes with constant phase change temperature and thermal conductivity typically work in a single season and have limited thermal regulation functions. This study proposed a double-layer heterogeneous phase change (DHPC) wall, composing two kinds of PCMs with different thermal conductivities and phase change temperatures. The thermal storage capacity, energy-saving rate and indoor thermal comfort of DHPC wall were analyzed under passive and active regulation strategies to evaluated its thermal performance in different seasons. In summer, the peak temperature of DHPC wall/box decreased by 6.6 °C/1.5 °C compared with the gypsum wall/box, which was further lowered by 1.7 °C/3.3 °C after introducing the cool water. In winter, the average temperature drop rate of gypsum/DHPC wall was 3.7/1.6 °C/h, and the thermal comfort interval duration of DHPC box increased to 92.8% ∼ 87.7% after introducing the hot water. Compared with gypsum wall/box, the attenuation factor and heat load level of DHPC wall/box decreased by 6.7% ∼ 27.3% and 4.0% ∼ 67.6% respectively, the heat storage coefficient increased by −4.2% ∼ 197.1%, and the energy-saving rate reached 9.0% ∼ 22.7%. The results showed that DHPC wall could efficiently meet the thermal requirements in winter and summer, and thus had broad application prospects. • A phase change wall with dual melting points and thermal conductivities was tested. • The seasonal thermal performance was evaluated under passive/active strategies. • The thermal insulation, storage and comfort were better under active strategies. • The thermal performance of proposed DHPC wall was superior to gypsum wall. [ABSTRACT FROM AUTHOR]