Recent progress on developing anti-frosting and anti-fouling functional surfaces for air source heat pumps

•Anti-frosting and anti-fouling properties of functional surfaces were investigated.•Applications of functional surfaces to heat exchangers were examined.•Future studies for anti-frosting and anti-fouling surfaces were discussed. Developing anti-frosting and anti-fouling outdoor heat exchangers in air source heat pumps (ASHPs) can significantly enhance their thermal performance. Recently, fin surfaces with different wettability, including superhydrophilic, superhydrophobic, and slippery surfaces, have been highlighted due to their potentials to achieve the desired properties of outdoor heat exchangers. Anti-frosting and anti-fouling characteristics of superhydrophilic, superhydrophobic, and slippery properties on metal surfaces are investigated in terms of basic concepts, working principles and effects. The changes in surface wettability cannot only control behaviors of frosting formation and melted water during defrosting, but also affect contaminant accumulation and corrosion-initiated fouling on their surfaces. Applications of those surfaces to heat exchangers are also examined. The challenges and opportunities for successfully implementing the functional surfaces to heat exchangers of ASHPs are discussed.