The cooling capacity cannot meet the warehouse load requirements
(low compressor efficiency)
There are two main reasons for the lack of refrigerant circulation.
First, the refrigerant charge is insufficient, and only a sufficient amount of refrigerant is needed at this time;
Another reason is that there are many refrigerant leaks in the system. To catch up with this situation, you should first find the leak point, focus on checking the connections of each pipeline and valve, and then fill in a sufficient amount of refrigerant after repairing the leaked parts.
Lack of cooling capacity
(Insufficient amount of refrigerant in the system)
An insufficient amount of refrigerant in the system directly affects the flow of refrigerant into the evaporator. When the opening of the expansion valve is too large, the expansion valve is improperly adjusted or blocked. The refrigerant flow rate is too large, the evaporation pressure and evaporation temperature also increase, and the temperature drop rate of the warehouse will slow down; at the same time, when the expansion valve is opened too small or blocked, the refrigerant flow rate also decreases, and the cooling capacity of the system also increases with The decrease of the warehouse temperature will also slow down. Generally, it can be judged whether the refrigerant flow rate of the expansion valve is appropriate by observing the evaporating pressure, evaporating temperature and the frosting condition of the suction pipe. Expansion valve blockage is an important factor affecting refrigerant flow. The main causes of expansion valve blockage are ice blockage and dirty blockage. Ice blocking is because the drying effect of the dryer is not good, and the refrigerant contains moisture. When it flows through the expansion valve, the temperature drops below 0 °C, and the moisture in the refrigerant freezes into ice and blocks the throttle valve hole; dirty blocking is because There is a lot of dirt accumulated on the filter screen at the inlet of the expansion valve, and the refrigerant is not smooth and smooth, causing blockage.
Refrigerant flow is too large or too small
(improper adjustment or blockage of expansion valve)
Its heat transfer coefficient will decrease, once more refrigeration oil is attached to the inside and outside of the evaporator heat transfer tube. Similarly, if there is more air in the heat transfer tube, the heat exchange area of the evaporator will be reduced, the heat transfer efficiency will also be significantly reduced, and the temperature drop rate of the warehouse will be slowed down. Therefore, in daily operation and maintenance, attention should be paid to timely removal of oil stains on the inside and outside of the evaporator heat transfer tube and discharge of the air in the evaporator to improve the heat transfer efficiency of the evaporator.
Reduced heat transfer effect
(There is more air or refrigeration oil in the evaporator)
This is mainly because the frost layer on the outside of the evaporator is too thick or the dust is too much. Because the outside temperature of the evaporator in the cold storage is mostly lower than 0 ℃, another important reason for the slow drop of the storage temperature is the low heat transfer efficiency of the evaporator. The humidity of the warehouse is relatively high, and the moisture in the air is very easy to frost or even freeze on the surface of the evaporator, which affects the heat transfer effect of the evaporator. In order to prevent the outer frost layer of the evaporator from being too thick, it needs to be defrosted regularly.
Here are two simpler defrosting methods:
① Stop to defrost. That is, stop the operation of the compressor, open the door of the warehouse, let the temperature of the warehouse rise, and restart the compressor after the frost layer automatically melts.
②Chong cream. After moving the goods out of the warehouse, directly flush the surface of the evaporator pipe with tap water with a higher temperature to dissolve or fall off the frost layer. In addition to the poor heat transfer effect of the evaporator due to the thick frost, the surface of the evaporator is too thick due to the temporary uncleaning, and its heat transfer efficiency will also be significantly reduced.
Reduced heat transfer effect
(The surface of the evaporator is frosted too thickly or has too much dust)
Poor thermal insulation and thermal insulation effects, and poor thermal insulation performance are due to insufficient thickness of thermal insulation layers such as pipes and warehouse thermal insulation walls. It is mainly caused by improper selection of thermal insulation layer thickness during design or poor quality of thermal insulation materials during construction.
In addition, during the construction and use, the thermal insulation and moisture-proof function of the thermal insulation material may be damaged, resulting in the thermal insulation layer being damp, deformed, or even eroded.
Another important reason for the large cooling loss is the poor sealing performance of the warehouse, and more hot air intrudes into the warehouse from the leak. Generally, if there is condensation on the seal of the warehouse door or the seal of the cold storage insulation wall, it means that the seal is not tight.
In addition, frequent opening and closing of the warehouse door or more people entering the warehouse together will also increase the loss of cooling capacity in the warehouse. The door of the warehouse should be prevented from opening as much as possible to prevent a large amount of hot air from entering the warehouse. Of course, when the warehouse is frequently stocked or the stock is too large, the heat load increases sharply, and it generally takes a long time to cool down to the specified temperature.
lead to large cooling loss
(cold storage due to poor thermal insulation or sealing performance)
Components such as cylinder liners and piston rings are severely worn, and the compressor is temporarily running. When the matching clearance increases, the sealing performance will decrease accordingly, the gas transmission coefficient of the compressor will also decrease, and the cooling capacity will decrease. When the cooling capacity is less than the heat load of the warehouse, the temperature of the warehouse will drop slowly. The refrigeration capacity of the compressor can be roughly determined by observing the suction and discharge pressures of the compressor. If the refrigeration capacity of the compressor decreases, the commonly used method is to replace the cylinder liner and piston ring of the compressor. If the replacement still does not work, other factors should be considered, or even dismantling and inspection to eliminate the fault factors.
Post time: Feb-17-2022