Building energy consumption accounts for 30% of global final energy consumption, and electricity and heat used in buildings account for over two-thirds of the world's energy-related emissions. Therefore, research into energy-efficient heating, ventilation, and air-conditioning (HVAC) technologies is critical to ensuring global sustainability. Air source heat pumps (ASHPs) use electricity to convert low-grade energy to high-grade energy, providing significant energy savings over direct fuel heating. However, in low-temperature and high-humidity environments, the frosting issues on ASHPs' outside heat exchangers are widespread, decreasing heating performance and energy utilization efficiency. In recent years, superhydrophobic surface modification has garnered more investigation and attention as an effective frost control strategy. However, the superhydrophobic surface applied to the finned-tube heat exchanger and its frost suppression mechanism still needs to be further explored. At the same time, there is still a research gap in the application of superhydrophobic finned-tube evaporators to ASHP units, and their operating characteristics and performance analysis should be investigated. This dissertation reconstructed the microstructure of aluminium-based surfaces changed the phase transition conditions of traditional metal heat and moisture exchange surfaces, and took the ASHP units as the application object to realize the dropwise condensation and frost self-suppressing performance, and to further improve the system operation efficiency and reduce the emission of ASHP equipment. The primary research contents of this dissertation are as follows:

1) A superhydrophobic surface construction method based on chemical etching and self-assembly of low surface energy materials was proposed for aluminium-based finned-tube heat exchangers. Through response surface method and variance analysis, the impact of process parameters during the surface preparation on the wettability of aluminium fins was discussed, and an optimal parameter scheme that balances super hydrophobicity and durability of the surface was proposed. The modified aluminium fins underwent investigation using field emission scanning electron microscopy, three-dimensional topography analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The reaction mechanism of the preparation procedure was elucidated. The reliability of superhydrophobic finned-tube heat exchangers was confirmed by exposing them to high and low-temperature exposure tests, corrosion resistance tests, and mechanical friction tests, simulating actual operating conditions.

2) A condensation/frosting test visualization experimental platform based on flat fins was established, and the behaviour characteristics of the whole process of water vapour condensation, droplet freezing and thawing, and frosting/defrosting on flat fins with different wettability were obtained. Based on the kinetics of phase transformation and surface physicochemical theory, the mechanism of the effect of surface properties on the phase transformation driving force and nucleation energy barrier in the condensation process was elucidated, and the inhibition mechanism of superhydrophobic surfaces on each stage of the frosting process was revealed. Compared with bare Al surfaces, the maximum diameter of droplets was reduced by more than 80%. At the same time, the low adhesion and self-propelled jumping characteristics of superhydrophobic surfaces were conducive to realizing dropwise condensation, and the surface droplet coverage fluctuated below 30%. The frozen droplets on superhydrophobic surfaces exhibit overall peeling characteristics during the melting process, and the droplet thawing time could be reduced by 61% and 73% compared to hydrophilic surfaces and bare surfaces, respectively. Conducted frosting/defrosting experiments on flat plates under different cold plate temperatures and inlet air velocities, and analysed the frosting/defrosting characteristics and mechanisms of surfaces with different wettability under forced convection conditions.

3) A visualization wind tunnel platform for frosting/defrosting testing of ASHP evaporators was constructed. Based on the single frost cycle performance test with environmental control on the evaporator side, the operating characteristics of fixed-frequency ASHP units with evaporators of different wettability were clarified. The heating capacity and frosting/defrosting characteristics of the units under different indoor and outdoor conditions were analysed. Compared with commercial hydrophilic evaporator units, the maximum heating capacity of superhydrophobic evaporator units increased by 17.4% to 52.3%, and the total frost mass during the experiments was reduced by 58.7% to 76.3%. In multiple frosting/defrosting cycles of the superhydrophobic evaporator unit, the fluctuations of the maximum heating capacity, total heating capacity, and COP for each cycle were 0.8%, 2.5%, and 2.6%, respectively, proving the superhydrophobic finned-tube evaporators’ durability in the actual operation process of ASHP units.

4) Based on the standard enthalpy difference laboratory with indoor/outdoor environmental control, performance tests were conducted on the common household variable frequency ASHP units with finned-tube evaporators of different wettability surfaces. The climatic characteristics of typical cities in different building thermal design regions were analysed, and various experimental conditions were set according to the winter outdoor climate parameters to simulate the actual operating environments of different regions. During the test period when the superhydrophobic unit completes a frosting/defrosting cycle, in intermittent heating mode, the COP of the units could be improved by 28.1%~60.6% compared to the hydrophilic evaporator unit. Based on the climatic parameters of typical cities in the heating season, the frosting periods of the evaporator in different regions were analysed, and the electricity consumption of a unit during the heating season was calculated based on experimental data. From a perspective of the COP over the entire heating season, ASHP units with superhydrophobic evaporators perform the best energy-saving characteristics in the 3A and 5A regions which have relatively lower average outdoor temperatures in the HSCW region. The electricity consumption per square meter could be reduced by more than 10%. For the non-central heating residential buildings in the 2B areas, ASHP heating still has the advantages of energy-saving and environmental protection, and the superhydrophobic evaporator still makes a considerable contribution to the efficiency improvement of the ASHP unit. From the perspective of carbon reduction, the application of superhydrophobic evaporator units in the HSCW eastern regions will yield greater benefits.

This study helps to clarify the anti-frosting/defrosting characteristics and energy-saving effects of superhydrophobic finned-tube evaporators during the operation of ASHP units, providing experimental data support, key technologies, and theoretical support for the application of superhydrophobic evaporators in ASHP systems.