低い周囲温度での空気熱源ヒートポンプの熱容量減衰の理由
We all know that it is inevitable that the heat generated by the air source heat pump will attenuate with the decrease of the outdoor ambient temperature. We can summarize several reasons for the attenuation as follows:
01. The drop in evaporating temperature will cause the suction pressure of the compressor to drop and the suction specific volume to increase, which will lead to a drop in the heating capacity per unit volume of the refrigerant. This is the main reason for the heat attenuation of the air source heat pump.
02. The drop in suction pressure will cause the compressor pressure ratio to increase and the lubrication effect to deteriorate; the volumetric efficiency of the compressor will drop, resulting in a decrease in the actual air delivery volume and a decrease in the heating capacity.
03. The increase in suction specific volume and the decrease in the volumetric efficiency of the compressor will lead to a decrease in the mass flow of the refrigerant, resulting in a decrease in the heat transfer coefficient of the refrigerant side of the evaporator and the condenser, and the heat absorbed by the evaporator and the heat released by the condenser ( equivalent to the heating capacity) is reduced.
04. The drop in suction pressure will lead to an increase in the dryness at the inlet of the evaporator, an increase in the dynamic viscosity of the liquid refrigerant and a decrease in the density of the gaseous refrigerant on the low pressure side, and an increase in the flow pressure drop in the evaporator and the suction line. If the suction pressure of the compressor is maintained unchanged, the evaporation pressure and its corresponding saturation temperature will increase, the effective heat exchange temperature difference of the evaporator will decrease, and the heat absorption of the evaporator will decrease, which will also lead to a decrease in the heating capacity.
05. When the surface temperature of the evaporator fins is lower than the dew point temperature of the humid air and lower than 0 degree , the surface of the evaporator is frost; 霜層の成長速度は、湿った空気の含水量の増加と蒸発温度の低下とともに増加します。 霜層の厚さが増すと、蒸発器の熱抵抗と風抵抗の両方が増加し、加熱能力が急速に低下します。
The air source heat pump must be defrosted periodically to operate normally, and the heating capacity during defrosting is zero or even negative, resulting in a decrease in the average heating capacity.
