Strategies for reducing and detecting frost formation on air source heat pumps
Air source heat pumps (ASHPs), the most widely used heat pump type in residential buildings across Europe, suffer efficiency losses in cold, humid conditions due to frost accumulation on their evaporator surfaces. Frost forms in stages: humid air first condenses into water droplets, which then freeze and accumulate into an insulating frost layer that reduces heat transfer, increases pressure drop, and necessitates defrosting. These effects lower the system’s coefficient of performance (COP). This work explores both passive and active strategies to mitigate frost formation and improve frost management. Passive approaches include surface functionalization through laser structuring and coatings, aiming to reduce condensation, water accumulation and control frost distribution under mild conditions. In harsher conditions, where frost formation is unavoidable, reducing ice adhesion strength becomes more critical—potentially allowing mechanical methods such as piezoelectrically induced elastic waves to dislodge ice with minimal thermal input. An experimental setup has been developed to observe frost formation in situ on various surfaces under defined conditions. The tests presented in this article include bio-inspired microstructure such as superhydrophobic surfaces and topographies found on Arctic scallop shells, assessed for its potential to influence frost thickness and ice adhesion. Surface properties such as laser structure, contact angle and contact angle hysteresis are being correlated with observed icing behavior. In parallel, we investigate piezoelectric detection strategies for water and ice to enable predictable, demand-specific defrosting. Conventional time- or temperature-based control often leads to premature or delayed defrost cycles. By using sensors, defrosting can be triggered more efficiently, reducing unnecessary energy consumption. The combined approach of detecting and reducing frost formation offers promising insights into smarter anti-ice strategies for next-generation ASHP systems.