Investigation method for the icing behavior on coated surfaces of evaporators in air-source heat pumps
Heat pumps are considered a key technology in the energy transition and have become widely used in the building sector in recent years. However, under real operating conditions the evaporators of air-source heat pumps (ASHP) are often exposed to icing, particularly at low ambient temperatures. When the surface temperature of the evaporator drops below the dew point, water vapor from the air condenses and freezes on the surface. This ice formation impairs system performance and energy efficiency by increasing flow resistance and reducing heat transfer. To mitigate these effects, various functional coatings have been developed to influence wetting and icing behavior. Despite the increasing availability of such anti-icing coatings, a systematic and reproducible method for their comparative evaluation under realistic ASHP operating conditions is still lacking. This paper presents an experimental investigation methodology that enables a quantitative and reproducible analysis of the icing behavior of coated evaporator surfaces. The method combines thermodynamic measurements with image-based evaluation to characterize frost formation and detachment. Dedicated test rigs operated in a controlled climate chamber allow precise adjustment of temperature, humidity, and airflow. The modular test design enables targeted analysis of individual icing and defrosting processes and supports the assessment of different coatings. The proposed methodology thus provides a resource-efficient and practical approach for identifying suitable coating candidates for real evaporator geometries and contributes to the development of more efficient and reliable heat pump systems.