The experimental part of the study of the reverse cycle defrosting performance on a four-circuit outdoor coil unit in an experimental 6.5kW heating capacity residential ASHP has been reported in Part I of a two-part series. The experimental results indicated that downwards flowing of the melted...

When an air source heat pump (ASHP) operates in heating mode, frost can be accumulated on the surface of its finned outdoor coil. Frosting deteriorates the operation and energy efficiency of the ASHP and periodic defrosting becomes necessary. Currently the most widely used standard defrosting...

When the surface temperature of the outdoor coil in an air source heat pump (ASHP) unit is lower than both freezing point of water and the air dew point, frost can be formed and accumulated over outdoor coil surface. Frosting affects the energy efficiency, and periodic defrosting therefore is...

A study is presented on the characteristics of the air source heat pump (ASHP) under two kinds of typical mal-defrost phenomena. The definition of the “Mal-defrost phenomena” is put forward, and the possible origins of their occurrence are analyzed. It is concluded that the current defrost...

To quantify the performance drop of the air source heat pump (ASHP) system under a special kind of mal-defrost phenomenon appearing in moderate climate conditions, a field test was conducted for 8days at the initial stage of a heating season in Beijing, China. The mal-defrost was found with the...

When an air source heat pump (ASHP) unit is used for space heating at low ambient temperatures in winter, frost may form on its outdoor coil surface. Since the accumulated frost adversely affects its performance and energy efficiency, periodic defrosting of the outdoor coil is necessary....

Energy conserving is an important issue in greenhouse farming. Because greenhouse operations consume large amount of fossil fuel energy, energy conservation is necessary for securing famers’ income and alleviating global warming. Surplus air thermal energy (SATE) in greenhouses exists even in...

Electrification of heating by making use of the Electric Heat Pump (EHP) technology powered by increasing shares of electricity renewable sources is seen as a potential key approach to decarbonise the energy sector in many countries, and especially in the UK. However, the widespread use of EHPs...

Reverse cycle defrosting is the most widely used standard defrosting method for air source heat pump (ASHP) units. It was suggested in previous experimental studies that during reverse cycle defrosting, downwards flowing of the melted frost due to gravity over a vertically installed...

To investigate the impact of defrosting-water retention on the surface of heat exchangers of the air source heat pump (ASHP) performance during frosting–defrosting cycles, an experimental study has been conducted. Testing was carried out in a controlled-environment chamber with ASHP...