In the refrigeration system, the four major components constitute the refrigerant circulation, the compressor compresses the low-pressure vapor into high pressure, the throttling device throttles the high-pressure liquid to low pressure, the evaporator absorbs heat and evaporates on the low-pressure side, absorbs the indoor heat and cools, and the condenser releases heat and condenses on the high-pressure side, and discharges the evaporation heat and compression heat contained in the condensation heat to the outside.
In the condenser, the high-temperature and high-pressure steam from the compressor is condensed into a liquid, and a large amount of condensation heat is released, which is carried away by the external cooling medium such as air and cooling water. The amount of heat emitted by the condenser largely depends on the level of its condensing temperature, so how much should the condensing temperature be adjusted?
The condensing temperature is the saturation temperature of the refrigerant gas in the condenser when it is exothermic and condensed, which corresponds to the condensing pressure one by one, and increases or decreases together when it changes.
From the perspective of heat transfer, the condenser needs to release heat to the outside at a condensation temperature higher than the temperature of the external cooling medium, the larger the heat transfer temperature difference, the greater the heat release, the more liquefaction of the gaseous refrigerant, and the greater the circulation of the refrigerant. Therefore, the condensation temperature is first and foremost limited by the temperature of the external cooling medium, and cannot and will not be too low.
From the refrigeration principle, it can be seen that with the increase of condensing temperature and pressure, the power consumption of the compressor increases, the refrigeration efficiency decreases, and the energy consumption of the system increases significantly. Therefore, various measures are often taken in practice, such as increasing the heat exchange area of the condenser, reducing the temperature of the cooling medium, increasing the flow rate and velocity of the cooling medium, etc., so as to improve the heat exchange effect and make the condensation temperature and pressure not too high.
From the refrigeration system itself, it is not good for the condensing temperature and pressure to be too low, because the system needs to maintain a certain high pressure of condensation pressure to ensure a certain pressure difference between high pressure and low pressure, so as to meet the pressure difference requirements of refrigerant circulation and oil circulation in the system.
The reasonable temperature difference between the condensing temperature and the cooling medium, using air cooling with air as the cooling medium, generally requires the condensation temperature to be higher than the air temperature 8 12. When using water cooling with cooling water as the cooling medium, the condensation temperature is generally required to be 5 9 higher than the cooling water outlet temperature.
Under the standard condition, the outdoor air inlet temperature of the air-cooled heat pump unit is 35, and the condensation temperature can be estimated to be about 42 47 considering the heat transfer temperature difference of 8 12.
Under standard working conditions, the cooling water inlet temperature of the chiller is 32, the temperature difference between the inlet and outlet water is 5, the outlet temperature is 37, and the condensation temperature can be deduced to be about 42 46 considering the heat transfer temperature difference with the outlet water 5 9.
The level of condensing pressure can be read out by the high-pressure gauge installed in the exhaust of the compressor, so as to check the saturation pressure and temperature comparison table of the corresponding refrigerant, and the condensing temperature at this time can be obtained.
However, the adjustment of condensation temperature is different from the adjustment of evaporation temperature, which can adjust the evaporation pressure through expansion valves and compressors, while the former does not have this means.
The adjustment of condensation temperature is mainly to change the external heat exchange conditions, such as reducing the temperature of the cooling medium, increasing the flow rate and flow rate of the cooling medium, etc., and the actual work is to adjust the number of cooling towers, the speed of the cooling fan, the opening and bypass of the water valve, etc.
The ultimate purpose of reasonably adjusting the condensing temperature of the refrigeration system is to meet the heat exhaust and internal pressure difference needs of the refrigeration system, and on this basis, reasonably and appropriately reduce the temperature and pressure in the condenser to reduce the operating energy consumption of the system.
I Yi refrigeration