Paper No 088 – Frosting and Defrosting Behavior of Evaporators – 13th IEA Heat Pump Conference, Jeju, Korea
Air-to-water heat pumps - being essential to reach the ambitious climate goals – don’t come without challenges: Evaporators of air-to-water heat pumps are prone to severe frosting in humid climatic during late fall, winter and spring. To sustain a reasonable CoP, de-frosting strategies are employed to remove the frost layer and restore normal operation. De-frosting, however, also reduces efficiency due to downtimes and heat loss due to reverse operation. Frosting and de-frosting of evaporators is characterized using overview and detailed image capturing. The frost growth is additionally quantitatively assessed using a digital high-resolution scale. Together with the thermodynamic data of the heat pump and the control parameters of the climatic chamber a full transient data set is available and analysed deriving frosting and de-frosting correlations. The extensive data set is an important base for numerical simulation: Frost growth and weight increase can be used to validate three-dimensional frosting models necessary to simulate and - in a second stage - optimize evaporator designs. Furthermore, the thermodynamic behaviour during frosting and de-frosting is an important input to onedimensional system models of heat pumps.