Experimental study on frost growth and dynamic performance of air source heat pump system

Abstract The effect of the frost growth and frost morphology on the performance of an air source heat pump was investigated experimentally. The frost thickness, frost accumulation and the dynamic performance of the heat pump were measured. It is found that the frost growth can be divided into three stages according to the frost morphology. In the initial stage, condensed water freezes and forms a transparent thin ice layer on the fins and tubes firstly, then the granular ices appear and grow gradually on the ice layer, and the column-shaped ice crystals are formed at last. The growth rate of the frost thickness, the heating capacity and COP of the heat pump increase with the frosting time significantly until the column-shaped frost layer is formed. In the second stage, the column-shaped ice crystals grow in its radius rather than in its length, and the frost thickness growth rate decreases or remains to be constant. However, the heating capacity and COP of the heat pump are only slightly affected by frosting on the outdoor coils. In the third stage, the ice crystals mainly grow in its length, and become gradually of an acerose-shaped one, finally a fluffy frost layer is formed. The frost thickness growth rate is about 2–4 times of that in the second stage. The drops per minute in the heating capacity and COP are increased by several times of those in the second stage. In addition, it is found that the frost growth rate and the drop in the performance of the heat pump are highest when the outdoor air temperature is about 0 °C with various relative humidity. The experimental results are in agreement with the corresponding simulation data except in the third frosting stage.

[1]  W. A. Miller,et al.  Laboratory examination and seasonal analysis of frosting and defrosting for an air-to-air heat pump , 1987 .

[2]  Predrag Stojan Hrnjak,et al.  Frost, defrost, and refrost and its impact on the air-side thermal-hydraulic performance of louvered-fin, flat-tube heat exchangers , 2006 .

[3]  Dennis L. O'Neal,et al.  EFFECT OF FROST GROWTH ON THE PERFORMANCE OF LOUVERED FINNED TUBE HEAT EXCHANGERS. , 1989 .

[4]  Simon Song,et al.  Modeling for predicting frosting behavior of a fin-tube heat exchanger , 2006 .

[5]  Robert W. Besant,et al.  Fan supplied heat exchanger fin performance under frosting conditions , 2003 .

[6]  Shiming Deng,et al.  A study on the performance of the airside heat exchanger under frosting in an air source heat pump water heater/chiller unit , 2004 .

[7]  Wen-Ruey Chang,et al.  Performance of finned tube heat exchangers operating under frosting conditions , 2003 .

[8]  Nilufer Egrican,et al.  Frost formation on fin-and-tube heat exchangers. Part I—Modeling of frost formation on fin-and-tube heat exchangers , 2004 .

[9]  Alvin C.K. Lai,et al.  Dynamic behavior of a direct expansion evaporator under frosting condition. Part II. Field investigation on a shipping container , 2006 .

[10]  Dennis L. O'Neal,et al.  Performance of finned-tube heat exchangers under frosting conditions: II. Comparison of experimental data with model , 1993 .

[11]  Ren Yue.  Numerical Simulation on the Performance of Heat Pumps under Frost Conditions , 2005 .

[12]  Hakan Karatas,et al.  Frost formation on fin- and- tube heat exchangers. Part II—Experimental investigation of frost formation on fin- and- tube heat exchangers , 2004 .

[13]  Alvin C.K. Lai,et al.  Dynamic behavior of a direct expansion evaporator under frosting condition. Part I. Distributed model , 2006 .

[14]  Yi Jiang,et al.  Local variation of frost layer thickness and morphology , 2006 .