Study on thermal insulation characteristics and optimized design of pipe-embedded ventilation roof with outer-layer shape-stabilized PCM in different climate zones

Abstract 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.