Thermal performance of integrated collector storage solar air heater with evacuated tube and lap joint-type flat micro-heat pipe arrays

Abstract

To alleviate the problem of global warming and the energy crisis, this study proposed an integrated collector storage solar air heater that uses evacuated tubes as solar absorbers and paraffin as thermal storage material. In the proposed unit, lap joint-type flat micro-heat pipe arrays serve as heat conductors that transmit the solar energy absorbed by the evacuated tubes to the thermal storage tank or transfer the heat stored in the tank to the air flow channel. Outdoor experiments were carried out to obtain the thermal performance of the proposed device during charging and discharging. The effects of weather conditions, supply air flow rates, and inlet temperature on the thermal response of the integrated collector storage solar air heater were reported. The thermal storage efficiency during the experiment period ranged from 56.1% to 67.5% when the mean outdoor temperature ranged from −5.7 °C to 36.2 °C. The mean thermal extraction power and thermal released efficiency reached 1268.8 W and 98.5%, respectively. The results of the energy conversion process analysis and mathematical fitting showed that the mean charging efficiency was linear with the normalized temperature difference. The mean outlet temperature and mean extraction power were linear with the inlet temperature and exponential with the air flow rate. A conceptual design of an air heating system using the integrated collector storage solar air heater for a 9.9 m2 building was presented. The benefit pre-evaluation revealed that the system can reduce carbon emissions by approximately 5.8 tons over its life cycle.