Thermal performance investigation of an integrated collector–storage solar air heater on the basis of lap joint-type flat micro-heat pipe arrays: Simultaneous charging and discharging mode

Highlights: • A novel ICSSAH was studied during simultaneous charging and discharging modes. • High volume flow rate improved the thermal performance. • The effect of cumulative solar radiation was investigated. • The daily thermal efficiency was 78.1% when the volume flow rate was 141 m³/h. -- Abstract: In this part of the investigation, the thermal performance of an integrated collector–storage solar air heater (ICSSAH) on the basis of a lap joint-type flat micro-heat pipe array during simultaneous charging and discharging mode is experimentally studied. Paraffin is used as a phase change material, and air acts as a heat transfer fluid in a built-out structure of ICSSAH. The thermal performance of ICSSAH is assessed under an outdoor experiment to explore the effect of seasonality, volume flow rate, and daily accumulative solar radiation. Thermal energy analysis is described and calculated in detail according to the experimental measurements. Results showed that the daily mean thermal efficiency in summer is significantly higher than the transition season. The smaller the volume flow rate is, the lower the thermal efficiency will be. However, the effect of solar radiation on thermal efficiency is small during the test conditions. The highest daily thermal efficiency at the volume flow rate of 141 m³/h is approximately 78.1% in the present study when the solar irradiance ranges from 0 W/m² to 874 W/m² and the ambient temperature varies from 27.8 °C to 35.4 °C.