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How To Build A Cold Storage To Save Operating Costs

May 20, 2020

How to build a cold storage to save operating costs?


Compared with the ordinary refrigerator, the cold storage has a larger cooling area, and because of the large cooling area of the cold storage, the power consumption is relatively large. Today, Anyda Refrigeration will introduce how to make the cold storage more power-saving. Learning these skills can reduce the operation cost and save energy.


1. Reducing the heat load of cold storage

1. Enclosure structure of cold storage

The temperature of the cold storage is generally around -25 ℃, while the outdoor daytime temperature in summer is generally above 30 ℃, which means that the temperature difference between the two sides of the cold storage enclosure will be around 60 ℃, plus the daytime The sun's radiant heat makes the heat load from the wall and ceiling to the inside of the store considerable, and is an important part of the whole store's heat load. The thermal insulation performance of the reinforced envelope structure is mainly increased by thickening the insulation layer, applying high-quality insulation layers, and applying reasonable design schemes.

2. Insulation layer thickness

Of course, to thicken the insulation layer of the envelope structure, the one-time investment cost will increase, but compared with the reduction of the regular operating cost of the cold storage, whether it is considered from the economic point of view or from the perspective of technical management, it is more reasonable.

3. Two methods are commonly used to reduce the heat absorption on the outer surface

First, the outer surface of the wall should be white or light color to enhance the reflection ability. In the strong summer sun, the temperature of the white surface is 25 ° C to 30 ° C lower than that of the black surface;

The second is to do shading enclosure or ventilation interlayer on the outer wall surface. This method is more complicated in practice and has fewer applications. The method is to set up a peripheral protective structure at a distance from the thermal insulation wall to form an interlayer, and to set vents above and below the interlayer to form natural ventilation, which can take away the solar radiation heat absorbed by the external shield.

4. Cold storage door

Because the cold storage often requires personnel to enter and exit and load and unload goods, the storage door needs to be opened and closed frequently. If the insulation work is not done in the warehouse door, then a certain heat load will be generated due to the infiltration of high-temperature air outside the warehouse and the introduction of personnel heat. Therefore, the design of the cold storage door is also very meaningful.

5. Build a closed platform

It is cooled by a cooler, the temperature can reach 1 ℃ ~ 10 ℃, and is equipped with a slide-open refrigerator door, a soft sealing joint, the refrigerator can be directly leaned on the platform, and the door-to-door loading and unloading is carried out. Basically not affected by outside temperature. Small refrigerators can build door buckets at the entrance.

6. Electric refrigerator door (addition of cold air curtain)

The early single-leaf speed was 0.3 ~ 0.6m / s. At present, the opening speed of the high-speed electric refrigerator door reached 1m / s, and the opening speed of the double-leaf refrigerator door reached 2m / s. To avoid danger, the closing speed is controlled at about half of the opening speed. A sensor-type automatic switch is installed in front of the door. These devices are designed to shorten the door opening and closing time, improve the efficiency of loading and unloading, and reduce the residence time of operators.

7. Lighting in the library

Using high-efficiency lamps with low heat generation, low power and high brightness, such as sodium lamps. The efficiency of high-pressure sodium lamps is 10 times that of ordinary incandescent lamps, while the energy consumption is only 1/10 of inefficient lamps. At present, new LEDs are used as lighting in some more advanced cold storages, with less heat and energy consumption.

 

2, improve the efficiency of the refrigeration system

1. Use compressor with economizer

Screw compressor can be adjusted steplessly in the energy range of 20 ~ 100% to suit the change of load. According to estimates, a screw-type unit with a cooling capacity of 233kW and an economizer can save 100,000 kWh per year based on 4000 hours of operation per year.

2. Heat exchange equipment

Preferably use direct evaporative condensers instead of water-cooled shell and tube condensers, which not only saves the power consumption of the water pump, but also saves the investment in cooling towers and pools. In addition, the direct evaporative condenser requires only 1/10 of the water flow rate of the water-cooled type, which can save a lot of water resources.

3. The evaporator end in the cold store prefers to use the cold fan instead of the evaporative exhaust pipe, which not only saves materials and has higher heat exchange efficiency, but also can be adapted to changes in the load of the store by changing the air volume if a stepless speed-regulated cooler is used. The goods can be run at full speed just after entering the warehouse, and the temperature of the goods can be quickly reduced. After the goods reach the predetermined temperature, the speed is reduced to avoid the power consumption and machine loss caused by frequent start and stop.

4. Impurities in heat exchange equipment

Air separator: When the non-condensable gas is present in the refrigeration system, the discharge temperature will increase due to the increase of the condensing pressure. The data shows that when the cooling system is mixed with air, its partial pressure reaches 0.2MPa, the system power consumption will increase by 18%, and the cooling capacity will drop by 8%.

Oil separator: The oil film on the inner wall of the evaporator will greatly affect the heat exchange efficiency of the evaporator. When there is a 0.1mm thick oil film in the evaporator tube, in order to maintain the set temperature requirements, the evaporating temperature will drop by 2.5 ° C and the power consumption will increase by 11%.

5. Removal of scale in the condenser

The thermal resistance of scale is higher than the tube wall of the heat exchanger, which will affect the heat transfer efficiency and increase the condensing pressure. When the scale of the water pipe wall in the condenser is 1.5mm, the condensing temperature will increase by 2.8 ℃ than the original temperature, and the power consumption will increase by 9.7%. In addition, scale will increase the flow resistance of the cooling water and increase the energy consumption of the pump.

Prevention and removal of scale can use electronic magnetic water descaling and anti-scaling, chemical pickling and descaling, mechanical descaling and so on.

 

3. Defrosting of evaporation equipment

When the thickness of the frost layer is greater than 10㎜, its heat transfer efficiency drops by more than 30%. It can be seen that the frost layer has such a great influence on the heat transfer. It has been determined that when the temperature difference between the inside and outside of the pipe wall is 10 ° C, the storage temperature is -18 ° C, and the heat transfer coefficient K value is only about 70% of the original value after one month of operation, especially the ribs in the air cooler The film tube, when there is a frost layer, not only the thermal resistance increases, but also the air flow resistance increases, and in severe cases it is sent out without wind.

Preferably select hot gas defrost instead of electric heating defrost to reduce power consumption. Compressor exhaust heat can be used as a source of defrost heat. The temperature of the frost backwater is generally 7 ~ 10 ℃ lower than the condenser inlet temperature. After treatment, it can be used as the cooling water of the condenser to reduce the condensation temperature.

 

4. Evaporation temperature adjustment

The reduction of the temperature difference between the evaporation temperature and the temperature in the warehouse will increase the evaporation temperature accordingly. At this time, if the condensation temperature remains unchanged, it means that the refrigeration capacity of the refrigeration compressor is increased. It can also be said that the same refrigeration capacity is obtained. Under the circumstances, the consumption of electric energy can be reduced. According to estimates, when the evaporation temperature decreases by 1 ° C, it will consume 2 ~ 3% more electricity. In addition, reducing the temperature difference value is also extremely beneficial to reduce the dry consumption of food stored in the warehouse.

 

5. Other energy-saving approaches

At night, on the one hand, electricity consumption can be saved due to the "valley period" of night electricity consumption; on the other hand, the power of the power plant generator set can be balanced so that it does not have large power fluctuations during the day. From a macro sense, It also saves energy. So it should be strongly advocated. Especially in the cold storage, quick freezing and ice making have high utilization value.

In addition, ice storage technology can be used. The ice produced at night produces a part of the cooling capacity during the day, which can bear a part of the load to a certain extent and reduce the power required by the system.


Automatic control of other equipment:

The use of electronic expansion valve can save 10% energy;

Defrost function on demand, can save 5% energy;

The temperature setting of the warehouse that is reset at night can save 4% energy;

Cooler fan operation control, can save 3% energy;

Cold storage door anti-condensation control, can save 2% energy;

Compressor unit and condensing fan control, can save 10% energy