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Roof receives heat directly from the solar radiation and outdoor air, and the heat transfer of the roof is often greater than that of any external wall. The building roof is usually overheated in summer, causing a great increase in the air conditioning load and negative effects on indoor thermal comfort. Thus improving the thermal insulation performance of the roof is essential for reducing air conditioning energy consumption and improving indoor thermal comfort. In this paper, an innovative pipe-embedded ventilation roof with outer-layer shape-stabilized PCM (named VRSP for short) was proposed. The heat gain is stored in the PCM to migrate excessive heat during the day and released through air ventilation at night. A three-dimensional transient-state heat transfer model of the VRSP system was built by CFD. The effects of phase transition temperature range of PCM, thickness of PCM layer and airflow rate in the ventilation duct on the thermal performance of the structure in five representative climate regions of China were evaluated. Results show that the optimum phase transition temperature ranges of PCM in severe cold region, cold region, hot summer and cold winter region, hot summer and warm winter region and mild region are 31–33 °C, 34–36 °C, 36–38 °C, 34–36 °C and 29–31 °C, respectively. The optimum thicknesses of the PCM layer are 25–30 mm, 25–30 mm, 30–35 mm, 25–30 mm and 20–25 mm, respectively. The suitable airflow rates are 1.5–1.9 m/s, 1.6–2.0 m/s, 2.1–2.5 m/s, 1.9–2.3 m/s and 1.4–1.8 m/s, respectively. The conclusion provides valuable guides for the application of VRSP under various climate conditions. • A pipe-embedded ventilation roof with shape-stabilized PCM is proposed. • Effects of physical properties of PCM and airflow rates are investigated. • The new system is optimized for its applications in different climate zones. • Considerable energy-saving effects are observed in Kunming, Harbin and Beijing. [ABSTRACT FROM AUTHOR]

Roof with outer-layer shape-stabilized phase change material (RSPCM) is a building construction that incorporates shape-stabilized phase change material (PCM) into the out layer of the roof. The decrement factor of the roof and the peak temperature of the inner surface can be greatly reduced by using the PCM in summer. CFD numerical simulation is used to investigate the thermal performance of RSPCM. The effects of the phase transition temperature, layer thickness and phase transition temperature radius of PCM are studied numerically. Results show that the suggested PCM thickness is 30 mm and the temperature radius should be as small as possible. The optimum phase transition temperatures are 31–33 °C, 34–36 °C, 36–38 °C, 34–36 °C, and 29–31 °C respectively in severe cold region, cold region, hot summer and cold winter region, hot summer and warm winter region and mild region. The decrement factors at the corresponding optimum phase transition temperature are about 0.030, which are lower than that of the roof without PCM by over 85%. The peak temperatures of the inner roof surface are all decreased by over 3.7 °C. These results can be used as a guideline for optimum design to improve the dynamic thermal performance of roof structure in summer. • Heat transfer model of roof with outer-layer shape-stabilized PCM is built by CFD. • Effects of phase transition temperature and radius, and PCM thickness are studied. • Decrement factor, time lag and latent heat utilization of this roof are analyzed. • PCM thickness of 30 mm is recommended. • Optimum phase transition temperature of PCM are obtained for five climate zones. [ABSTRACT FROM AUTHOR]