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How does the Heat Pump defrost

  • By:Heyi
  • Date:2021/11/17

When customers use a heat pump to get heating, cooling, or make domestic hot water, frosting is a usual step in heat pump system operation. If a heat pump is well designed and under normal running, it can defrost by itself, even the user can’t feel the defrosting procedure. But if the frost issue cannot be solved automatically, there are some points below that we should consider:

1. Why does the air source heat pump ices up?

As we know the heat pump absorbs heat energy from the air, air source heat pump system the component that absorbs heat energy from air is a refrigerant evaporator. The temperature of the flowing refrigerant in the evaporator tube is very low, compared with the flowing refrigerant, the outside air temperature is higher.  So refrigerants can absorb energy from the outside air. During 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 around 0 °C, these accumulated dew form layers of frost.

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

During the heat pump low-temperature heating process, the 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 air source heat pump water heater improve the heat exchange efficiency of the heat exchanger, the heat pump should have a reliable defrost method.

3. How does the heat pump handle frost?

There are some methods below to avoid icing up.

a.Reverse cycle method

This method takes a device four-way valve. After the four-way valve activates, the direction of refrigerant flow is changed to allow the system to change from air source heating mode to the cooling mode for a certain time. The high-temperature gas discharged from the compressor is directly passed to the heat exchanger (evaporator) for defrost.

b. Hot gas bypass method

With this method, the refrigerant flow is not changed during defrosting. the heat pump will keep the heating 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 method

With this method, firstly the phase change material will store energy. When the evaporator is iced up to a certain level and needs to be defrosted, the energy stored in the previous phase change material will be released for defrosting.

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