How does the Heat Pump defrost

  • By:Heyi
  • Date:2021/08/03


When user use a heat pump to get heating or make hot water, frosting is usual step in heat pump system running. When a heat pump is working normally, It  can defrost by itself, even the user can’t feel its defrost procedure. But when the frost problem cannot be solved, we will think about the following questions.

1. Why does the air source heat pump frost?

As we know the heat pump absorbs heat energy from the air, the component that absorbs heat energy from air is a refrigerant evaporator. The temperature of  flowing refrigerant  in the evaporator tube is very low, comparing with the flowing refrigerant, the outside air temperature is  higher.  So refrigerant can absorb energy from outside air.  in the procedure of refrigerant evaporation, the relatively hot air from the outside will form dew on the surface of the evaporator. When the temperature drops below 0 ° C, these accumulated dew form layers of frost.

2.What is the harm to the heat pump after frosting?

During the heat pump low-temperature heating process, frosting will inevitably occur in the evaporator, and the thickness of the frost layer will gradually increase with time passing, gradually the frost will decrease the energy exchange and reduce the heating capacity of the heat pump.

Therefore, in order to maintain the heat exchange capacity and improve the heat exchange efficiency of the heat exchanger, it is necessary to get a reliable  defrost method.

3.How does the heat pump handle frost?

They are below ways to make defrost.

a.Reverse cycle method

This method take a device four-way valve. After the four-way valve activating, the refrigerant flow direction is changed to allow the unit to change from the heating state to the cooling state. The high-temperature gas discharged from the compressor is directly passed to the heat exchanger for defrost.

b. Hot gas bypass method

During defrosting, the refrigerant flow is not changed, the heat pump keep the heating working state, and the high-temperature gas discharged from the compressor bypasses a part directly to the chamber heater through the bypass pipe for defrosting. The heat source for defrosting is the electric power consumed by the compressor and the heat storage capacity of the compressor casing.

c. Energy storage defrost

Let the phase change material store energy first. When the heat exchanger frosts to a certain level and needs to be defrosted, the energy stored in the previous phase change material is released for defrosting.






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