How to save energy in cold storage?

• Reduce the heat load of cold storage

1、Cold storage enclosure structure

Low-temperature cold storage temperature will generally be in -25 ℃ or so, and in the summer outdoor daytime temperature is generally 30 ℃ or more, that is, in the cold storage enclosure structure on both sides of the temperature difference will be about 60 ℃, coupled with the solar radiation heat during the day, so that from the wall and ceiling to the library heat transfer to the formation of the heat load is considerable, is an important part of the heat load of the entire library. Enhance the thermal insulation performance of the enclosure structure mainly through the thickening of the insulation layer, the application of high-quality insulation, and the application of reasonable design programs.

2、Thickness of heat insulation layer

Of course, to thicken the heat insulation layer of the enclosure structure, the one-time investment cost will be increased, but compared with the reduction of cold storage often running costs, whether from the economic point of view or from the technical management point of view to consider, or more reasonable.
Two methods are commonly used to reduce the heat absorption of the outer surface
The first is to use white or light color on the outer surface of the wall to enhance the reflective ability. In the strong summer sunlight, the temperature of the white surface is 25℃ to 30℃ lower than that of the black surface;
The second is to make a sun-shading enclosure or a ventilated mezzanine on the surface of the external wall. This method is more complicated to construct in practice and is less commonly used. The practice is to set the outer enclosure structure at a distance apart from the heat-insulating wall, so that it forms a sandwich, and set vents above and below the sandwich to form natural ventilation, which can take away the solar radiation heat absorbed by the outer enclosure.
3、Cold storage door

Due to the cold storage often need people in and out, loading and unloading of goods, the library door needs to be opened and closed often. If there is no good heat insulation work in this part of the warehouse door, then due to the infiltration of high temperature air outside the warehouse and the heat brought in by the personnel will also produce a certain heat load. Therefore, the design of the cold storage door is also very meaningful.

4、Construction of closed platform

Cooling with chiller, the temperature can reach 1 ℃ ~ 10 ℃, and there is a slide-open refrigerated door, soft sealing joints, refrigerated trucks can be directly against the platform, the implementation of door-to-door loading and unloading, operation, so that the basic in and out of the library is not subject to external temperature effects. Small-sized cold storage can build door bucket at the entrance door.

5、Electric refrigerated door (with cold air curtain)

Early single speed of 0.3 ~ 0.6m / s, the current high-speed electric refrigerator door opening speed of 1m / s, double refrigerator door opening speed of 2m / s. In order to avoid the danger of closing speed control in the opening speed of about half. The front of the door is equipped with a sensor-type automatic switch. These devices are designed to shorten the opening and closing time, improve the loading and unloading efficiency, and reduce the operator's dwell time.

6、Lighting in the warehouse

Adopt high efficiency lamps with low heat generation, low power and high brightness, such as sodium lamps. High-pressure sodium lamp efficiency is ordinary incandescent 10 times, and energy consumption is only 1/10 of the low-efficiency lamps and lanterns. currently in some of the more advanced cold storage in the use of new LED as lighting, heat and energy consumption is smaller.

• Improving the efficiency of the refrigeration system

1. Use compressor with economizer

The screw compressor can be infinitely adjusted in the energy interval of 20~100% to suit the change of load. It is estimated that a cooling capacity of 233kW with economizer screw unit, according to the annual operation of 4,000 hours of calculation, a year can save electricity 100,000 degrees.

2. Heat exchange equipment

Priority is given to direct evaporation condenser instead of water-cooled shell and tube condenser.
This not only eliminates the power consumption of the pump, but also saves the cooling tower, pool investment. In addition, the direct evaporation condenser requires water flow is only 1/10 of the water-cooled, can save a lot of water resources.

3. The evaporator end of the cold storage is prioritized to use the chiller instead of the evaporator tube.

This not only saves material, heat transfer efficiency is higher, and if you use the infinitely variable speed chiller, you can change the air volume to adapt to the changes in the load of the warehouse. Goods just into the warehouse can run at full speed, quickly reduce the temperature of the goods; to be the goods to reach a predetermined temperature to reduce the speed, to avoid the frequent start and stop caused by power consumption and machine loss.

4. Treatment of impurities in heat exchange equipment

Air separator: the presence of non-condensable gases in the refrigeration system leads to the discharge temperature due to condensing pressure increases. Data show that when the refrigeration system is mixed with air when the partial pressure reaches 0.2MPa, the system power consumption will increase by 18%, the cooling capacity decreased by 8%.

Oil separator: evaporator wall oil film will greatly affect the evaporator heat transfer efficiency. When the evaporator tube has 0.1mm thick oil film, in order to maintain the set temperature requirements, the evaporating temperature should be reduced by 2.5 ℃, power consumption increased by 11%.

5. Condenser in the removal of scale

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

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

• Defrosting of evaporation equipment

When the thickness of the frost layer is >10㎜, its heat transfer efficiency drops more than about 30%, and it can be seen that the frost layer has such a great influence on heat transfer. Determined, when the tube wall inside and outside the measured temperature difference of 10 ℃, the library temperature in -18 ℃, pipe work for a month, its heat transfer coefficient K value of about only 70% of the original value, especially in the ribbed tube chiller, when there is a frost layer, not only the thermal resistance to increase, but also increase the resistance of the flow of air, and in severe cases, it is to the no wind sent out.
Prioritize the use of hot air defrost instead of electric heating defrost, reduce power consumption. Compressor exhaust heat can be used as a heat source of frost. Frost return water temperature is generally lower than the condenser water temperature 7 ~ 10 ℃, after processing can be used as a condenser cooling water, reduce the condensing temperature.

• Evaporation temperature adjustment

The evaporating temperature and the temperature difference between the temperature inside the warehouse is narrowed, the evaporating temperature can be increased accordingly, at this time, if the condensing temperature remains unchanged, it means that the refrigeration compressor refrigeration capacity, it can also be said that in the case of obtaining the same amount of refrigeration can be reduced to reduce the consumption of electrical energy. According to the estimation, when the evaporation temperature is reduced by 1 ℃, it is 2~3% more power consumption. In addition, reduce the value of the temperature difference to reduce the dry consumption of food stored in the warehouse is also extremely favorable.

• Other energy-saving ways

Night power can be used on the one hand because of the night power “valley” to save electricity, on the other hand, can balance the power plant generator set power, so that it will not have a large power fluctuations in a day, from the macro sense, but also to save energy. So it should be strongly advocated. Especially in the cold storage of quick-freezing and ice-making two aspects of the use of high value.
In addition to the use of ice storage technology, the ice produced at night in the daytime to produce a part of the cold, can to a certain extent to take part of the load, reduce the power required by the system.

• Automatic control of other equipment

The pro-expansion valve can save energy by 10%; on-demand frost melting function can save energy by 5%; the temperature setting of the storage set back at night can save energy by 4%; chiller fan operation control can save energy by 3%; anti-condensation control of the cold storage door can save energy by 2%; compressor and condensing fan control can save energy by 10%; the comprehensive energy-saving effect of the above 6 measures can reach 15-34%.

Improve the cold storage chain, product pre-cooling, etc., quick-frozen food pre-cooling before storage, food pre-cooling for every 1 ℃, can shorten the quick-freezing time of about 1%.
Currently commonly used pre-cooling methods: air pre-cooling, vacuum pre-cooling, cold water pre-cooling.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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