The first is heating capacity. The suction flow of the heat pump compressor is directly proportional to the evaporation temperature. The lower the ambient temperature, the lower the suction flow and the poorer the heating capacity. In addition, when the evaporating temperature decreases, the heating of heat pump motor is constant, but the heat pump system mass flow rate is decreasing.
If the evaporation temperature is at -5°C, the mass flow rate is 50KG/S. When the evaporation temperature drops to -30°C, the mass flow rate may only be 20KG/S. At this time, the heating value of the heat pump motor is almost unchanged, but the flow of the refrigerant used to cool the motor is reduced, and the corresponding heating capacity per kilogram of refrigerant will increase, so the exhaust temperature will also increase. The density of the suction air will decrease after being heated, which is equivalent to the fact that the flow rate of the refrigerant decreases more, which is why the lower the temperature, the worse the heating capacity.
The second is reliability. I just said that when the evaporation temperature is lower, the suction flow of the heat pump compressor is reduced. At this time, the discharge temperature will increase and the heat pump compression ratio will increase. At this time, the lubricating oil in the compressor will easily expand, and then the viscosity will decrease. It will also cause the wear of the scroll to become serious, which will affect the stable and reliable operation of the main heat pump engine.There is also the running width. Any heat pump product has a safety interval when it is designed, which means that it is safe to operate within this interval, and once it exceeds this interval, accidents may occur. The compressor of the conventional heat pump is also designed with a safe operating range. If it is operated in an environment with a low evaporating temperature, it may not work as soon as the temperature drops. This is not just a question of reliability, but a question of availability.