1. Introduction 2. Freezing of sessile non-deformed water droplet under natural convection at early frosting stage in an ASHP unit 3. Freezing of sessile deformed water droplet under natural convection at early frosting stage in an ASHP unit 4. Frosting on surface of horizontal cold plate under natural convection in an ASHP unit 5. Frosting on surface of non-horizontal cold plate under natural convection in an ASHP unit 6. Frosting on surface of horizontal cold flat plate under forced convection in an ASHP unit 7. Measurement and calculation of frost characteristics on cold surfaces 8. Experimental study of frosting on surface of finned tube heat exchangers in an ASHP unit 9. Numerical study of frosting on surface of finned tube heat exchanger in an ASHP unit 10. Frosting on surface of micro-channel heat exchanger in an ASHP unit 11. Reverse cycle defrosting for multi-circuit outdoor coil in an ASHP unit 12. Conclusions and future work