Nanorefrigerant is a mixture of nanoparticles and pure refrigerant, which can increase heat transfer characteristics in refrigeration and air conditioning equipment. The performance of four different Al2O3 nanorefrigerants and their pure fluids (R600a, R134a, R1234yf, and R1233zd(E)) is analyzed in a vapor-compression refrigeration cycle. The enthalpy of a nanorefrigerant in the refrigeration cycle is calculated by using the prediction method based on the density of nanorefrigerant. A numerical model is established for the thermodynamic analysis, and the results show that adding nanoparticles to the pure refrigerant enhances heat transfer in heat exchangers, increases cooling capacity, reduces compressor power consumption, and finally improves the performance of the refrigeration system. The COP improvement of R1233zd(E) + Al2O3 nanorefrigerant is the highest, and the COP improvement of R134a + Al2O3 and R1234yf + Al2O3 are close to each other. When the mass fraction of Al2O3 nanoparticles increases to 0.30%, the COP of R1233zd(E) and R600a increases by more than 20%; the maximum exergy efficiency is 38.46% for R1233zd(E) + Al2O3, and the minimum exergy efficiency is 27.06% for pure R1234yf. The results provide a basis for the application of nanorefrigerants in the vapor compression refrigeration cycle.

Centralized hot water systems are commonly installed in college student dormitories, representing a typical application for such systems. To achieve sustainable and environmentally friendly heating solutions, air-source heat pump hot water systems have gained attention for their high efficiency and energy-saving characteristics. By implementing heat pump technology, China could make significant progress towards achieving its carbon neutrality goals by reducing energy consumption and associated emissions. In this study, the heating performance of an air-source heat pump hot water system was tested in the field over the course of a year at a university in Chongqing, China. A simulation model was constructed using TRNSYS software, and a time-sharing control strategy was proposed to analyze the system’s operating characteristics and energy-saving performance. Results showed a 6% increase in unit annual average Coefficient of Performance (COP) and annual electricity savings of 10,027 kW·h, with an energy-saving rate of 8.77% after time-sharing control. The study highlights the significant economic and environmental benefits of adopting sustainable energy solutions, particularly in the context of increasing global greenhouse gas emissions.

In recent years, there has been great interest in developing cooling systems with humidity- and temperature-independent control capabilities that can operate efficiently at varying temperatures. This paper proposes a bi-loop double-evaporator ejection–compression cycle, which utilizes low-grade heat and is suitable for the construction industry. The proposed cycle involves the concurrent operation of a vapor compression cycle and an ejector refrigeration cycle that enables it to handle altered pressure levels and operate with varying compression ratios all the way to a common condenser pressure. Conventional computational fluid dynamics (CFD) approaches often model steam as an ideal gas with single-phase flow. In contrast, this research employs the wet steam model to optimize ejector geometry. The wet steam model takes into account non-equilibrium water vapor condensation, thus providing a more precise assessment of spontaneous condensation behavior and its impact on ejector performance. When compared to the conventional dry gas model, the use of the wet steam model dramatically decreases the entrainment ratio error from 16.24% for single-phase steam to 3.92% when compared to experimental data. This study concentrates on four critical attributes of wet steam, including Mach number, droplet nucleation rate, average droplet radius, and liquid mass fraction, to develop a strategy for enhancing ejector performance and efficiency. The study demonstrates that optimal area and primary nozzle diameter ratios for the steam ejector are 5 and 2.4, respectively. Increasing the area ratio mitigates condensation intensity, thereby reducing the liquid mass fraction in the diffuser. Overall, this paper provides valuable insights into improving and optimizing ejector performance, thus highlighting the importance of considering the behavior of spontaneous condensation in ejector design and modeling.