Investigation of thermal energy storage use to increase solar energy utilization in an ejector assisted two-source heat pump

To address the growing energy demand of countries, energy efficiency and renewable energy are the most critical components of energy strategies. Among various sectors, the energy demand in buildings has significantly increased. More than half of the energy demand in residential buildings is associated with space and water heating aand therefore, improving the efficiency of space and water heating and integrating renewable energy sources can make a significant contribution. Heat pump technology is an attractive option for heating residential buildings due to its low electricity consumption compared to electric heaters. In this study, the performance of an ejector enhanced, solar- and air-sourced heat pump system was analyzed using a thermal storage unit. The system was designed to operate under winter conditions, targeting low environmental impact and high energy efficiency. The effects of different heat exchanger and tank temperatures on COP and COP improvement were investigated, and optimal operating conditions were determined. Additionally, the performance of R1234yf and R717 refrigerants was compared. The results showed that there is a specific optimal heat exchanger temperature for each tank temperature. R717 provided higher COP values at low temperatures, offering advantages in terms of energy efficiency. A daily analysis conducted for the Istanbul region demonstrated that, despite winter conditions, PV/T collectors effectively charged the thermal storage unit with a thermal efficiency reaching up to 40%. The 30 m² PV/T collectors also provided instantaneous electricity production, reaching up to 1 kW, which reduced the amount of energy drawn from the grid and contributed to the system's environmental sustainability. Exergy analyses revealed that the highest losses occurred in the PV/T unit. The findings of the study indicate that ejector-supported heat pump systems have significant potential to enhance energy efficiency and reduce environmental impacts. Future improvements, such as the integration of phase-change materials in the thermal storage unit, performance testing under different climatic conditions, and the use of next-generation refrigerants, are recommended to broaden the application scope of these systems.