The debugging examples of supermarket refrigerated showcase

The debugging examples of supermarket refrigerated showcase illustrate the operation process and requirements of the refrigeration system debugging. Example: There is a refrigeration device, the refrigerant is R12, and the temperature of the supermarket refrigerated showcase is required to be -10℃, and the cooling water temperature of the condenser during commissioning is 30℃. Start the compressor to put the refrigeration device into commissioning operation. When the supermarket refrigerated showcase is at a relatively high temperature, adjust the expansion valve of the supermarket refrigerated showcase to the point where you can see that the evaporator outlet begins to frost. Then it will run for a while. At this time, the value of the low pressure can generally be around 0.098MPa (gauge pressure) (the corresponding evaporation temperature is around -12°C). It should be pointed out that the opening of the expansion valve should not be too large, too large is likely to cause liquid hammer, but the valve opening cannot be adjusted too small, because too small will result in too small cooling capacity and slow cooling speed. During this time, we should pay attention to the changes in low pressure and the frosting of the evaporator, because with the gradual decrease of the storage temperature, the low pressure value and frosting will change somewhat. After the operation is relatively stable, adjust the expansion valve until the frost layer is condensed to the end of the air return pipe (that is, the suction port of the compressor), but it is best not to allow frost to condense on the compressor cylinder, otherwise it will easily cause liquid shock. In the process of adjusting the expansion valve, the adjustment amount cannot be too large at one time. Generally, adjust 1/4~1/2 circles at a time, and after adjustment, let it have about 20 minutes of running time. After repeated adjustments for many times, when the temperature of the supermarket refrigerated showcase drops to -10°C, the low pressure value is 0.49MPa (gauge pressure, that is, the evaporation temperature is -20°C). While adjusting the expansion valve, pay attention to the high-pressure operating value. According to the relationship between the condensing temperature and the cooling water temperature, in the case of 30℃ cooling water, the reasonable condensing temperature should be 5-9℃ higher than 30℃, correspondingly The condensing pressure is around 0.784MPa. If the high pressure can work around 0.784MPa, the frosting of the evaporator is continuous and uniform, and the suction temperature is -5～0℃ (if there is a gas-liquid subcooler, keep it at 15℃. The superheat is should). If there is no suction thermometer, it can be seen that the frost has just condensed on the suction port of the compressor. So far, it has basically met the design requirements.

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