Dual mode operation of a sub‐cooler vapor injection assisted direct expansion solar‐ambient hybrid source heat pumps in tropical climates

The solar radiation intensity is a significant factor affecting the performance of direct expansion solar‐ambient hybrid source heat pumps, as it leads to excessive superheating of the suction vapor and a subsequent reduction in the efficiency of the compressor. To overcome this problem, the system is designed with a sub‐cooler vapor injection (SC‐VI) mode for regulating the system operation in high solar radiation conditions. The system configuration presented here is aimed at low‐temperature heating applications, such as industrial water heating, drying and decentralized heating systems, which are extensively used in tropical regions, where electric resistance heating is the primary source of energy. The hybrid (solar‐assisted and controlled vapor injection) operation effectively optimizes the electrical energy consumption and indirect emissions. The SC‐VI mode is automatically triggered when the incident solar radiation is greater than 500 W/m 2 , ensuring reliable operation under different environments. The system operation was experimentally studied under different solar radiation, ambient temperature, wind speed, and relative humidity conditions throughout the year. The results demonstrate that the proposed system can achieve a compressor volumetric efficiency of over 0.83 even in the peak summer. Coefficient of performance (COP) ranges from 2.29 to 2.82, which is greater than the conventional system. The payback period is 18.18 months when compared with electric heating. Moreover, the sustainability analysis shows that the system reduces the carbon dioxide emission by 71%, with the estimated carbon dioxide emission of 42.33 tons over the system lifetime of 15 years.