Theoretical analysis to optimize heat extraction from a solar pond integrated with a carbon dioxide heat pump

Heat pumps integrated with renewable energy sources represent an efficient approach to residential heating and cooling, with minimal environmental impact and reduced carbon emissions. While these systems have been extensively researched, there is a necessity to broaden their scope by investigating novel approaches to energy capture and storage that are adopted to the specific characteristics of the region. This study analyzes the effects of different operating parameters on heat extraction from a solar pond integrated with a heat pump using carbon dioxide under transcritical conditions. Subsequently, an optimization examination is conducted to assess and determine the conditions required to achieve the maximum heat extraction rate and the minimum pumping power. The outcomes of this investigation demonstrate that the carbon dioxide mass flux and operating pressure exert a greater influence on the responses compared to the inlet temperature of carbon dioxide and the lower convective zone temperature of the solar pond. Additionally, within the investigated range of mass flux, the highest level of heat extraction occurs at operating pressures near the critical point of carbon dioxide, approximately 7.5 MPa. To meet the demand for maximum heat extraction from the solar pond, the optimal conditions result in an overall performance improvement of 2.61 times compared to the reference state. Furthermore, optimizing the system to maximize heat extraction from the solar pond while using the minimum pumping power results in a total performance enhancement of 4.13 times.