Frost Management in Air Source Heat Pump Systems

Air source heat pumps (ASHPs) extract thermal energy from ambient air to provide heating in residential and commercial buildings. In cold or humid conditions, moisture in the air condenses and freezes on the evaporator coil, forming a frost layer that impedes heat transfer and increases pressure drop. Uncontrolled frost accumulation reduces the system coefficient of performance (COP), elevates energy consumption and may trigger frequent defrost cycles that further degrade efficiency and indoor comfort. Effective frost management comprises both passive and active measures: advanced heat exchanger designs minimise frost adhesion, while optimised defrosting strategies—such as reverse cycle operation, electric heaters or hot-gas bypass—restore performance at minimal energy penalty. Emerging control algorithms integrate real-time sensor data and weather forecasts to predict frost formation, adjust operating parameters proactively and tailor defrost timing. The global significance of this research lies in lowering carbon emissions through enhanced ASHP reliability and efficiency across diverse climatic zones.

Research from Nature Portfolio

Recent studies have introduced sophisticated computational frameworks to predict frost thermal conductivity and its influence on heat exchanger performance. By applying Gaussian Process Regression models with tailored kernel functions, researchers achieved near-perfect agreement between predicted and experimental thermal conductivity values under varying air temperature, humidity, flow rate and frost porosity. Sensitivity analyses pinpoint air temperature as the dominant factor affecting frost conductivity. These predictive tools enable engineers to estimate frost build-up and its thermal consequences without extensive laboratory trials, informing design optimisation and control strategies for frost mitigation.

Frost Management in Air Source Heat Pump Systems publication trend

The graph below shows the total number of articles in frost management in air source heat pump systems across all publications each year (not limited to Nature Index journals).

Technical terms

Frost thermal conductivity: A measure of the ability of the frost layer to conduct heat, influenced by frost density, porosity and microstructure.

Defrost cycle: A deliberate operational phase during which heat pumps reverse cycle or apply auxiliary heating to remove accumulated frost from the evaporator.

Coefficient of performance (COP): The ratio of useful heat output to electrical energy input, indicating the energy efficiency of a heat pump.

Gaussian Process Regression (GPR): A machine-learning technique that models complex dependencies between input variables and outputs, providing probabilistic predictions with quantified uncertainty.

References

1. Frosting Phenomenon and Frost-Free Technology of Outdoor Air Heat Exchanger for an Air-Source Heat Pump System in China: An Analysis and Review. Energies (2018).
2. An insight into the estimation of frost thermal conductivity on parallel surface channels using kernel based GPR strategy. Scientific Reports (2021).
3. Defrosting of Air-Source Heat Pumps: Effect of Real Temperature Data on Seasonal Energy Performance for Different Locations in Italy. Applied Sciences (2021).
4. Defrosting Performance Improvement of Air-Source Heat Pump Combined Refrigerant Direct-Condensation Radiant Floor Heating System with Phase Change Material. Energies (2020).