Applying image recognition to frost built-up detection in air source heat pumps

Highlights: • Applying image recognition to frost built-up detection in ASHPs was studied. • A characteristic parameter of F was proposed to quantify the frosting degree on ASHPs. • The applicability of the novel frost built-up detection method was examined. • The novel method was further modified account for the impact of varying illuminance levels. When a space heating ASHP unit is operated in frosting conditions, accurate defrosting is necessary to ensure its operating efficiency and output heating capacity. Therefore, to improve the accuracy of defrosting initiation of ASHPs under frosting-defrosting operations, a study on applying image recognition to frost built-up detection in ASHPs has been carried out and the study results are presented in this paper. Firstly, the principle of a novel frost built-up detection method based on image recognition is presented. Secondly, a series of experiments to examine the applicability of the novel frost built-up detection method with respect to shooting angle, imaging pixels, illumination level, and the temperature of outdoor coil surface are carried out. Thirdly, the novel frost built-up detection method was further modified based on the experimental result obtained, and the verification of the modified novel detection method is reported. It is shown that the use of the modified novel frost built-up detection method could properly account for the impact of changing illuminance level on the accuracy of image recognition, to ensure the accuracy of frost built-up detection when ASHPs are operated in frosting conditions.