It is a common phenomenon that the temperature of the supermarket freezer does not drop and the temperature drops slowly. Now I briefly analyze the reasons for the slow temperature drop, hoping to bring some help to my colleagues in the work.
1. Due to the poor heat insulation or sealing performance of the freezer, the loss of cooling capacity is large
The reason why the thermal insulation performance is poor is that the thickness of the thermal insulation layer of pipes, thermal insulation boards, etc. is not enough, and the effect of thermal insulation and thermal insulation is not good. It is mainly caused by the improper selection of the thickness of the thermal insulation layer during design or the poor quality of thermal insulation materials during construction. . In addition, in the process of construction, the thermal insulation and moisture-proof performance 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, and more hot air intrudes from the leak. Generally, if condensation occurs on the sealing strip of the door or the heat insulation seal of the freezer, it means that the seal is not tight. In addition, frequent opening and closing of doors or more people entering the warehouse together will also increase cooling loss. Opening the door should be avoided as much as possible to prevent a large amount of hot air from entering. Of course, when the stock is frequently purchased 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.
2. The frost on the surface of the evaporator is too thick or there is too much dust, and the heat transfer effect is reduced
Another important reason for the slow temperature drop is the low heat transfer efficiency of the evaporator, which is mainly caused by the thick frost layer or excessive dust accumulation on the evaporator surface. Because the surface temperature of the freezer evaporator is mostly lower than 0 °C, and the humidity is relatively high, the moisture in the air is easily frosted or even frozen on the surface of the evaporator, which affects the heat transfer effect of the evaporator. In order to prevent the surface 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 compressor, open the door, let the temperature rise, and restart the compressor after the frost layer melts automatically.
②Chong cream. After removing the goods in the freezer, directly rinse the surface of the evaporator discharge 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 heat transfer efficiency of the evaporator will also be significantly reduced due to the excessive dust accumulation on the surface of the evaporator because it has not been cleaned for a long time.
3. There is more air or refrigeration oil in the evaporator of the supermarket freezer, and the heat transfer effect is reduced
Once more refrigeration oil is attached to the inner surface of the heat transfer tube of the evaporator, its heat transfer coefficient will decrease. Similarly, if there is more air in the heat transfer tube, the heat transfer area of the evaporator will be reduced, and its heat transfer will be reduced. Efficiency will also drop significantly, and the rate of temperature drop will slow down. Therefore, in daily operation and maintenance, attention should be paid to timely removal of oil stains on the inner surface of the evaporator heat transfer tube and discharge of 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 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 throttle valve is opened too large, the refrigerant flow rate is too large, the evaporating pressure and evaporating temperature also increase, and the temperature drop rate will slow down; at the same time, when the throttle valve is opened too small or blocked, the refrigerant flow rate The cooling capacity of the system is also reduced, and the temperature of the warehouse will also slow down.
Generally, it can be judged whether the refrigerant flow rate of the throttle valve is appropriate by observing the evaporating pressure, evaporating temperature and the frosting condition of the suction pipe. The blockage of the throttle valve is an important factor affecting the flow of refrigerant. The main reasons for the blockage of the throttle valve are ice blockage and dirty blockage. Ice blockage is due to the poor drying effect of the dryer, and the refrigerant contains moisture. When it flows through the throttle valve, the temperature drops below 0 °C, and the moisture in the refrigerant freezes into ice and blocks the throttle valve hole; dirty blockage is Due to the accumulation of more dirt on the filter screen at the inlet of the throttle valve, the flow of refrigerant is not smooth, resulting in blockage.
Precautions for using the freezer:
1. The freezer for long-distance transportation should be placed for 2 hours before it can be powered on to prevent the system from being damaged due to excessive pressure. For the first use, let the empty cabinet run for 1 hour, when the temperature in the box drops to the required temperature in the cabinet, and then put the items in.
2. The items should be separated when they are put in. Too tight squeeze will affect the air-conditioning circulation.
3. The freezer should not be close to the heat source to avoid direct sunlight and affect the cooling effect.
4. During the automatic defrosting process of the freezer, the temperature in the cabinet will rise in a short time. When the hot air outside the cabinet meets the food on the cold surface, the surface of the food will condense, and most of the dew will be removed when the refrigerator is turned on, and a small amount of dew will remain on the food, which is a normal phenomenon.
5. The needle valve on the evaporator of the freezer is used for system testing and refrigerant filling, and should not be opened at ordinary times to prevent refrigerant leakage.
6. The freezer shall not store flammable, explosive and volatile liquids and gases.
7. The shelf structure of the freezer can bear a weight of no more than 50kg per square meter (it needs to be evenly distributed), and too much will damage the shelves.
8. The ground should not have subsidence and should be kept level, otherwise it will affect the drainage, and poor drainage will affect the normal cooling and damage the fan.
Post time: Jan-13-2022