A wavy fin-and-tube heat exchanger as an air heat collector in an air-source heat pump: Experimental results on the influence of frost on air-side pressure drop and thermal performance

• A modified friction factor correlation for frosting conditions is proposed. • A slight reduction in thermal conductance was detected during frosting. • Frost mass can be estimated by changes in the air humidity ratio. • The air mass flux ratio can be used to estimate the pressure drop during frosting. This study experimentally evaluated frost layer growth, air-side pressure drop, and thermal performance of an air heat collector of large-scale air-source heat pump under realistic operating conditions. Frost accumulation was monitored through mass measurements, humidity ratio changes, and visual observations. Real-time mass measurement improved the accuracy of frost monitoring. Image processing techniques were applied to estimate frost thickness from the recorded video footage. Two novel methods were developed to calculate the air-side pressure drop as a function of the frost thickness using existing density correlations. The first method uses the initial pressure drop and the air mass flux ratio increased to a power of 3.7. The second modifies the existing friction factor correlation and integrates it into the pressure drop equation. Both methods agreed well with experimental results, within ± 25 % accuracy over a specific period. Notably, only a slight reduction in the thermal conductance was observed. These novel methods provide tools for analyzing the effects of frosting, addressing a critical gap in performance prediction and supporting technological advancements in air heat collectors. This is essential as the electrification of heat production has accelerated the adoption of heat pumps systems.