1. The cold storage has large loss of cooling due to poor insulation or sealing performance.
The poor thermal insulation performance is due to the insufficient thickness of the insulation layer of the pipeline, the warehouse insulation wall, etc., and the poor insulation and insulation effect. It is mainly caused by improper selection of the thickness of the insulation layer during design or poor quality of the insulation material during construction. In addition, during the construction and use process, the thermal insulation moisture resistance of the thermal insulation material may be destroyed, resulting in the insulation layer being damp, deformed, or even eroded. The thermal insulation capacity is reduced, the loss of the cold storage capacity is increased, and the storage temperature is significantly slowed down. .
Another important reason for the large loss of cold is that the warehouse has poor sealing performance, and more hot air invades the warehouse from the leak. Generally, if condensation occurs in the seal of the warehouse door or the seal of the cold storage wall, it means that the seal is not tight.
In addition, frequent switching of the warehouse door or more people into the warehouse together will also increase the cooling capacity of the warehouse. Try to avoid opening the door to prevent large amounts of hot air from entering the warehouse. Of course, when the warehouse is in frequent inventory or the quantity of goods is too large, the heat load increases sharply, and it takes a long time to cool down to the specified temperature.
2. The surface of the evaporator is too thick or excessively dusty, and the heat transfer effect is reduced.
Another important reason for the slow decline in the temperature of the evaporator is that the heat transfer efficiency of the evaporator is low, mainly due to excessive frost or excessive dust on the surface of the evaporator. Since the surface temperature of the cold storage evaporator is mostly lower than 0 ° C, and the humidity of the warehouse is relatively high, the moisture in the air is easily frosted on the surface of the evaporator, and even freezes, which affects the heat transfer effect of the evaporator. To prevent the surface of the evaporator from being too thick, it needs to be defrosted periodically.
Here are two simpler defrosting methods:
Stop defrosting. That is to stop the compressor operation, open the warehouse door, let the temperature rise, until the frost layer automatically melts, then restart the compressor.
Frosting. After the goods in the warehouse are carried out, the surface of the evaporator tube is directly washed with tap water having a relatively high temperature to dissolve or fall off the frost layer.
In addition to excessive frosting, the heat transfer effect of the evaporator is not good. The surface of the evaporator is too thick for long-term uncleaning, and its heat transfer efficiency is also significantly reduced.
3. There is more air or frozen oil in the evaporator, and the heat transfer effect is reduced.
Once the inner surface of the evaporator heat transfer tube is attached with more refrigeration oil, the heat transfer coefficient will be reduced. Similarly, if there is more air in the heat transfer tube, the heat exchange area of the evaporator is reduced, and the heat transfer is reduced. The efficiency will also drop significantly, and the rate of decline in the warehouse temperature will slow down.
Therefore, in daily operation and maintenance, attention should be paid to timely clearing the oil on the inner surface of the evaporator heat transfer tube and discharging the air in the evaporator to improve the heat transfer efficiency of the evaporator.
4. The throttle valve is improperly adjusted or blocked, and the refrigerant flow rate is too large or too small.
Improper adjustment or blockage of the throttle valve will directly affect the flow of refrigerant into the evaporator. When the opening degree of the throttle valve is too large, the refrigerant flow rate is too large, the evaporation pressure and the evaporation temperature also increase, and the warehouse temperature drop rate will be slowed down; meanwhile, when the throttle valve opening degree is too small or blocked, the refrigerant The flow rate is also reduced, the cooling capacity of the system is also reduced, and the rate of decline in the warehouse temperature will also slow down. Generally, it can be judged whether the flow rate of the throttle valve refrigerant is appropriate by observing the evaporation pressure, the evaporation temperature, and the frosting condition of the suction pipe.
Blockage of the throttle valve is an important factor affecting the flow rate of the refrigerant. The main cause of the blockage of the throttle valve is ice blockage and dirty blockage. The ice blockage is due to the poor drying effect of the dryer. The refrigerant contains moisture. When flowing through the throttle valve, the temperature drops below 0 °C, and the moisture in the refrigerant forms ice and blocks the throttle hole; the dirty plug is Due to the accumulation of more dirt on the filter inlet of the throttle valve, the refrigerant flows poorly and forms a blockage.
5. The refrigerant amount in the system is insufficient and the refrigeration capacity is insufficient.
There are two main reasons for the lack of refrigerant circulation. First, the refrigerant charge is insufficient. In this case, it is sufficient to fill in a sufficient amount of refrigerant. Another reason is that the system refrigerant leaks more. In case of such a situation, the leak point should be found first, and the connection points of each pipeline and valve should be checked. After the leak is repaired, a sufficient amount of refrigerant is charged.
6, the compressor efficiency is low, the cooling capacity can not meet the warehouse load requirements.
Due to the long-term operation of the compressor, the components such as the cylinder liner and the piston ring are seriously worn, the clearance is increased, the sealing performance is reduced, the gas transmission coefficient of the compressor is also reduced, and the cooling capacity is reduced. When the cooling capacity is less than the heat load of the warehouse, it will cause the warehouse temperature to drop slowly. The refrigeration capacity of the compressor can be roughly judged by observing the suction and exhaust pressure of the compressor. If the refrigeration capacity of the compressor drops, the common method is to replace the cylinder liner and piston ring of the compressor. If it still cannot be effective after replacement, other factors should be considered, and even disassemble and repair, to eliminate the fault factor.