Investigation of defrosting water retention on the surface of evaporator impacting the performance of air source heat pump during periodic frosting–defrosting cycles

Experimental study on the performance of air source heat pump system with multiple parallel outdoor units

“…The reverse‐cycle defrosting method is widely used in small air conditioner, heat pump, and cooling system, but its shortcomings are obvious: The sudden reversal of the four‐way reversing valve would not only cause a sudden change in the vapour suction and discharge pressure but also make a great impact to the pipelines and compressor . Huang et al carried out experimental study to compare the dynamic characteristics during the reverse‐cycle defrosting and hot gas bypass defrosting.…”

A modeling study on alleviating uneven defrosting for a vertical three-circuit outdoor coil in an air source heat pump unit during reverse cycle defrosting

“…Air source heat pump (ASHP) units used as cooling or heating source for building heating, ventilating and air conditioning installations have been increasingly and widely applied over the recent decades in many parts of the world [2,3]. However, when an ASHP unit operates at a low temperature and high humidity environment, frost can be formed and accumulated over the surface of its outdoor coil [4,5]. The outdoor coil is usually of multi-circuit structure on the refrigerant side in order to minimize its refrigerant pressure loss and enhance the heat transfer between refrigerant and outdoor air [4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

“…However, when an ASHP unit operates at a low temperature and high humidity environment, frost can be formed and accumulated over the surface of its outdoor coil [4,5]. The outdoor coil is usually of multi-circuit structure on the refrigerant side in order to minimize its refrigerant pressure loss and enhance the heat transfer between refrigerant and outdoor air [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Frosting adversely affects the operational performance and hence the energy efficiency of an ASHP unit, therefore periodic defrosting is necessary [6].…”

“…Currently, reverse cycle defrosting is the most widely standard defrosting method used for ASHP units [5,[8][9][10][11][12][13][14][15][16][17][26][27][28]. During reverse cycle defrosting, a space heating ASHP unit actually cools a space, degrading indoor thermal comfort while consuming electrical energy for melting frost [9].…”

An experimental study on defrosting performance for an air source heat pump unit with a horizontally installed multi-circuit outdoor coil

“…From the definition of surface tension [22], it is concluded that the total mass of retained water is directly proportional to the total area of circuit downsides. During defrosting, the retained water would consume energy [23], and thus delay the defrosting process. As shown in…”