Because the refrigeration capacity of refrigeration equipment in each cold storage will change under different working conditions, some will increase and some will decrease, so a certain margin is reserved in advance when designing, so as to prevent the refrigeration capacity of the whole device from being exerted normally because the refrigeration capacity of a certain component is reduced too much when working under a certain operating condition.
Changing trend of main components in case of working condition change:
1. Compressor: the relationship between the refrigeration capacity of compressor and evaporation temperature and condensation temperature, and its refrigeration capacity decreases with the decrease of evaporation temperature or the increase of condensation temperature.
2. Evaporator: The refrigerating capacity of the evaporator is not only determined by the difference between the storage temperature and the evaporation temperature, that is, the heat transfer temperature difference, but also related to the outlet superheat (dry type) or liquid level (full type) of the refrigerant. When the storage temperature is constant, its refrigeration capacity increases with the decrease of evaporation temperature.
3. Condenser: The refrigerating capacity performance curve of the condenser can be seen. When the evaporation temperature or condensation temperature drops, the refrigerating capacity decreases; In addition, when the cooling water volume decreases and the cooling water temperature increases, the cooling capacity also decreases.
4. Expansion valve: The refrigeration capacity of the expansion valve is related to the pressure difference between the inlet and outlet of the valve and the weight refrigeration capacity of the refrigerant under this working condition, so when the condensation temperature drops, the refrigeration capacity decreases, and when the evaporation pressure is too high or too low, the refrigeration capacity decreases.
Variation and adjustment of evaporation temperature
The change of evaporation temperature of refrigeration equipment in cold storage is related to the heat load of warehouse, heat transfer area of evaporator and volume of compressor. When one of these three conditions changes, the evaporation temperature and pressure of the refrigeration system will inevitably change.
Change of heat transfer area: Influence on evaporation temperature The heat transfer area mainly refers to the evaporation area of evaporator, and the change of heat transfer area mainly refers to the change of evaporation area. The influence of the increase and decrease of evaporation area on evaporation temperature is basically similar to that of the increase and decrease of heat load. When the evaporation area increases, the evaporation temperature will increase; When the evaporation area decreases, the evaporation temperature will decrease.
Changes in heat load: Changes in heat load often occur. When the heat load increases and other conditions remain unchanged, the evaporation temperature will increase, the low pressure will also increase, and the superheat of suction will also increase.
Refrigeration capacity of compressor: the influence of the change of compressor refrigeration capacity on evaporation temperature When the energy of refrigeration compressor is increased, the suction capacity of compressor will increase accordingly. Under other conditions unchanged, high pressure will increase, low pressure will decrease, and evaporation temperature will also decrease.
According to the knowledge of thermodynamics, there is a corresponding relationship between the temperature and pressure of refrigerant evaporation, so the adjustment of evaporation temperature can be realized by adjusting evaporation pressure.
Adjusting evaporation pressure can be realized by changing the opening degree of throttle valve or adjusting the gas transmission capacity of refrigeration compressor (compressor with gas transmission capacity adjustment). If the opening of the throttle valve is turned down, the circulating amount of refrigerant is reduced, the evaporation capacity generated in the evaporator is correspondingly reduced, and the evaporation pressure is correspondingly reduced. On the contrary, if the throttle hole is opened, the evaporation pressure will increase accordingly. If the gas transmission capacity of the compressor is changed, the evaporation pressure will also change.
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