Frost mitigation methods for heat pumps and refrigeration systems

At the IIR co-sponsored 18^th International Refrigeration and Air Conditioning Conference at Purdue, US, researchers from Oak Ridge National Laboratory presented a state-of-the-art review of the various frost mitigation strategies for air-source heat pumps (ASHPs) and commercial refrigeration units ^[1].

When the operating conditions are extremely cold and humid and the surface temperature of the heat exchanger is well below the freezing point (below the dew point temperature of the air), moisture from the air stream will freeze on the surface after condensation and frost will start to develop. Frost growth significantly degrades the performance of the system.

The authors point out that, in the case of refrigerated display cabinets, the electrical energy consumption for defrosting can range from 10% to 30% of the total consumption, with an average of about 20%.

They classified frost mitigation measures into three major types: upstream treatment of air, coil design adjustments and system adjustment.

The following table compares the various frost mitigation methods according to several criteria:

Table various frost mitigation methods

The authors conclude that:

Air treatment approaches seem to be the most promising for commercial refrigeration applications, but they are not viable options for heat pumps operating in cold climates.

Passive techniques such as adapting the fin geometry or modifying the surface morphology have been seen as major developments, however their application is limited by unacceptable durability, scalability and manufacturing challenges.

System level modification techniques have been successfully deployed in a range of systems with varying levels of impact. These techniques are most appropriate for heat pump applications, although several have been considered for commercial refrigeration systems as well.

All papers from the IIR 2021 Purdue conferences can be downloaded by using the following links:

Papers from the 18^th International Refrigeration and Air-Conditioning Conference

Papers from the 25^th International Compressor Engineering Conference

Papers from the 6^th International High Performance Buildings Conference

NB: Members of the IIR benefit from a reduction on these communications.

[1] Nawaz K. et al, A Critical Literature Review of Defrost Technologies for Heat Pumps and Refrigeration System: link.