Discussion on energy saving ways of cold storage
Release time： Author: administrator

Discussion on energy saving ways of cold storage

With the improvement of living standards, people demand for fresh food will also continue to increase, the average annual growth of our meat, fruits and vegetables, aquatic products, dairy products rate was about 11%, 25.8%, 12%, 24%, 7.8%, and as the cold storage refrigeration industry base will be further extended. As of December 2007, Chongqing city (including counties) to build large and medium-sized refrigerator with about 45 seats, a total capacity of about 120 thousand tons, of which 90960 tons of cold storage, high temperature storage 28500 tons. The March 2007 Shanghai total cold storage company 125, cold storage 137, the total capacity of 418 thousand and 100 tons, the frozen cold storage capacity of 314 thousand and 600 tons, chilled storage storage capacity is 96 thousand and 100 tons, an 7 thousand and 400 ton capacity, per capita storage volume of 99 liters. Shandong, Zhejiang cold storage capacity is more than 1 million tons. According to the China Refrigeration Institute data show that: by 2006, China's cold storage capacity of about 8 million 800 thousand tons, folded into a storage capacity of about 38 million cubic meters, the per capita possession of cold storage capacity of 29 liters. Take Chongqing as an example: Chongqing's per capita share of cold storage capacity is only 20 litres, lower than the national average, well below Shanghai's $99. The amount of frozen products shipped from to Chongqing each year is 40 to. As of December 2007, Chongqing City operating capacity of the cold storage gap is still 3 ~ 50 thousand tons, and with the improvement of people's living standards, the gap will further widen.

Thus, with the continuous increase of market demand, the construction speed and scale of the cold storage will continue to accelerate. However, the cold storage rate is low, production cost is too large by a considerable part of energy, is not conducive to the development of competition in the target market and China's economical society, which makes the discussion of cold energy utilization efficiency, strengthen the operation management and the system becomes very necessary to achieve energy-saving system.


1, cold storage industry energy consumption status
Overall, China's refrigerator industry started late, the existing refrigerator, belonging to the seven century, in 80s the construction of a high proportion, and the majority are still using cold storage centralized refrigeration system with ammonia as refrigerant, cooling equipment, metal consumption amount is large, the cooling effect is poor; production management confusion, equipment obsolete technology, automation the relatively low level of staff, service levels are relatively low, energy efficiency is relatively low, on the refrigeration industry, as shown in table 1.
From the table can be seen: China's overall power consumption of refrigeration enterprises is relatively large, the national average is much higher than the average level of the same industry, such as China refrigeration power consumption of the country with an average of 131kWh/m fand - A, which is more than 2 times the national average, is about 2.5 times the average level of Japan, even the refrigeration industry in the more developed than Shanghai, the same industry still has great difference, such as the Shanghai refrigeration enterprises power consumption of the average level of 76kWh/m - A is a British fand, advanced level of 4. 7 times or so, Japan's about 2.4 times.
According to the International Institute of refrigeration (IIR) requirements: in the next 20 years, should "make every refrigeration equipment to reduce the use of energy from 30 to 50% of the target, China will face enormous challenges, which makes the discussion on energy saving way, reduce the unit cooling capacity refrigerated products consumption, improve system efficiency, strengthen the warehouse management is particularly important, how to reduce costs, to achieve energy-saving system, the following approaches to the problems and energy saving from the technical level and management level to do some research.

2 energy saving in cold storage design
2.1 reasonable design envelope
The heat transfer of the envelope structure and the heat insulation layer accounts for 20%-35% of the total heat load of the refrigerator, so reducing the heat load of the building envelope can achieve the purpose of energy saving. Envelope Q1=KA (Tw-Tf), the heat from the heat transfer formula, the heat transfer is related to three factors, namely, the heat transfer area of A (m) and heat transfer coefficient K (W/ m K) and the heat transfer temperature difference between the T (K). The temperature and temperature difference of heat transfer outside ambient temperature and food storage required by the Treasury, the heat transfer coefficient is mainly composed of inside and outside the enclosure wall of the convective heat transfer coefficients and envelope thermal resistance constitution, introduced the concept of shape coefficient of building S (shapecoefficientofbuilding), as the base area and all appearance and storage capacity than here assuming the envelope surface area is A, volume V, then the shape coefficient: S=A/V, when the construction of cold storage capacity under certain conditions to determine the best area.
Envelope heat load and the thickness of the insulation layer is inversely proportional to the increase of the insulation thickness will reduce operating costs of cold storage, but the initial investment will be increased, so it requires the construction of cold storage in the refrigerator according to the age determination of optimum thickness, also considering the influence of environmental temperature on the thermal insulation layer selection.
2.2 compressor energy saving
In the selection of cold storage design often by the maximum load to the compressor, and the initial design often does not adapt to the actual operation of the process, according to the work load of the compressor cylinder adjust or reduce the number of compressor units, the system load and the compressor cooling capacity, to prevent the "big horse car" phenomenon, increase energy consumption.
2.3 do a good job of heat exchange equipment
Quantity of heat exchange equipment in cold storage operation energy consumption is large, data show that: in the evaporation temperature of -1O DEG C, the condensing temperature decreased by 1K, the compressor unit refrigeration amount reduced power from 2.5% to 3.2%; the condensing temperature is 3O DEG C when the evaporation temperature is increased by 1K, the compressor unit electricity consumption decreased by 3.1% ~ 3.9%. Can reduce the energy consumption of heat exchanger is of great significance for energy saving. Reduce energy consumption of heat transfer equipment can be the following aspects:
(1) selection of condenser
Abroad is generally used as evaporative condenser, it eliminates the need for cooling tower and water pump and water cycle of investment, worthy of our attention is the cooling water flow of evaporative condenser and water-cooled condenser is only 1/10, the obvious energy saving.
(2) increase the evaporation temperature
Increasing the evaporation temperature, can reduce the temperature difference of heat transfer, reduce the power consumption of the compressor, increase the cooling capacity, the data show that for each compressor, the evaporation temperature rise of 1 degrees Celsius, the refrigerating capacity per kilowatt motor per hour will increase by about 2.4%, the general refrigeration device is designed according to the full load condition, but in the actual in many cases the operation is not full load operation, so the refrigeration capacity is reduced, increasing the evaporation temperature, reducing the temperature difference of heat transfer, can also achieve a cooling effect. Improve the evaporation temperature can also reduce the dry food consumption, to ensure the freshness of food, reduce the loss of nutrients, so in the case of allowing, according to the characteristics of the food, as far as possible to improve the evaporation temperature.
2.4 strengthen the energy saving door
The refrigerator door opening and closing will cause great loss of cooling capacity, the bad performance of refrigerator door may increase energy consumption of 15% or more, but many units did not realize the seriousness of the problem, do not pay attention to open and close the refrigerator door, causing a lot of hot air into the cold storage, hot humid air in the air conditioning evaporator and easy combination the surface frost, and will break the balance of the temperature distribution, increase the burden of the refrigeration unit. Reduce the cold loss of cold storage door should pay attention to the following aspects:
(1) the area of cold storage door should be reduced as much as possible in the design, with special attention paid to reducing the height of the cold storage door. It is proved that the cold direction of the cold storage door is much larger than the width direction;
(2) to improve the automation degree of the cold storage door, at present, the opening speed of the latest high-speed electric refrigerator door can reach 1m/s, the opening speed of the double fan cold storage door reaches 2m/s, and the cold storage door is opened and closed in time;
(3) increasing the air curtain to prevent the cold loss of the cold storage, and to achieve the intelligence of the air curtain and the cold storage door, that is to say, the cold air door is opened and closed at the same time.
2.5 lighting system energy saving
The lighting system not only wastes a lot of electrical energy in the cold storage, but also increases the heat load of the cold storage or the freezing room. The lighting in the cold storage is generally concentrated in the working channel, the illumination is about 150 ~ 200Lx. In accordance with the provisions of the design of cold storage in China: per square meters housing area by lighting caused by heat, cold rooms can be 1.8 ~ 2.3W/ square meters, operating personnel processing long time stay, packing room etc. can be 5. 8W / square meters, but in the actual operation is often greater than this value, strengthen the management of lighting system can set the pilot and control lights in the warehouse, to ensure the safe operation of the situation to the energy-saving, also can use automatic type double lamps, equipped with mobile sensor (motiondetectors), it can according to whether there is the mobile object database, to determine the dark and light lamps, the lamp can be made in lighting save power 50%.
2.6 try to use mechanized operation
The mechanical operation can reduce the increase of cold heat load caused by the operating personnel, so as to reduce the burden of the refrigeration unit, the system is conducive to energy saving, this will be the future development direction of intelligent cold storage, cold storage should also arouse people's attention, refrigerator intelligent detection and fault diagnosis software, can realize intelligent detection and fault analysis of power system, so as to discover and solve the problems of speed, improve system reliability.
3 energy saving in cold storage operation management
3.1 regular inspection and maintenance of the envelope
The maintenance of cold storage structure should also be paid attention to. Infrared detection technology has been applied in many industries. Using infrared thermography can be non-contact detection of the infrared energy (heat), and convert it into electrical signals, thereby generating thermal images and temperature values on the display, can accurately quantify heat detect, fault can also accurately identify the area of fever and strict analysis. In this paper, the author uses the infrared thermal imager to check the maintenance structure of several cold storage in Chongqing. It is indicated that a large number of cold storage buildings are seriously cold due to disrepair.
3.2 reasonable use of night boot time
(1) the effective use of the peak valley electric current according to the electric periods of the implementation of electricity charges different standards, the provinces also adjusted according to actual situation, the peak valley difference of cold storage, high energy consumption, can use the night run storage, to avoid the peak period.
(2) the reasonable use of day and night temperature difference between day and night temperature is large, according to statistics, the condensation temperature of 1K per drop, can reduce the compressor power consumption by 1.5%, the unit shaft power refrigeration capacity will increase by about 2.6%. At low ambient temperature, condensing temperature will also decline, according to the literature, the marine climate area diurnal temperature can reach 6 ~ 10K, continental climate temperature can reach 10 ~ 15K, the southern area of diurnal temperature can reach 8 to 12 DEG C, so increase the night starting time, in favor of such cold.
3.3 timely release oil
The surface of the heat exchanger of oil will lead to evaporation temperature and condensation temperature rise due to the heat transfer coefficient of steel is about 20 times of oil, when the attachment of 0.1mm oil film surface of the condenser, the ammonia refrigeration capacity decreased by 16%, 12.4% increase in electricity consumption; oil film evaporator reaches 0.1mm, the evaporating temperature will drop 2.5 degrees Celsius 11-12%, power consumption will rise. The actual operation should be timely discharge of oil. The automatic control method can not only reduce the labor of workers, but also control the precise oil discharge time and the amount of oil.
3.4 to prevent non condensable gas into the pipeline
Because the air adiabatic index (n=1.41) greater than the adiabatic index of ammonia (n=1.28), in the presence of non condensable gas in refrigeration compressor exhaust ruptured condensing pressure and compressed air and additional increase, research shows that: when the refrigeration system of refrigeration system in a mixture of the non condensable gas, the pressure reaches 0.2MPa, power system the refrigeration capacity will increase by 18%, down 8%.
3.5 reasonable matching cooling water system
Due to seasonal changes in market demand, cold storage during operation, the general load changes, the condensing temperature changes, the cooling water is also changing, data show that the electricity accounted for the refrigeration system of electricity 15 ~ 25% cold water cooling system, so we should adjust the cooling water pump operation units timely and reasonable, to reduce the cold energy consumption.
3.6 timely defrosting
The heat transfer coefficient of steel is about 80 times of the heat transfer coefficient of frost, if the evaporator surface frost, will increase the thermal resistance of the pipeline, the heat transfer coefficient decreased, resulting in reduction in cooling capacity, so when the back running time the system should be timely defrosting, avoid unnecessary energy consumption increase, resulting in the increase of operating expenses.
3.7 adjust the condensing pressure
The total energy consumption of the refrigeration device of the water cooling condenser includes the energy consumption of the compressor and the energy consumption of the pump. Under certain conditions, the increase of cooling water has little effect on the condensation pressure. If the cooling water is enough, the increase of water has little effect on the condensation pressure. Therefore, in a certain range, can reduce the amount of cooling water, appropriate to increase the condensing pressure, so that the pump energy consumption, energy saving.
4 Conclusion
Energy saving will become the theme of social development in the future, and the energy saving potential of cold storage, this paper from China's current development speed and the scale of the cold start, and pointed out that China's foreign trade with the difference from the technology and operation management focuses on the energy saving way of cold storage, low temperature logistics library will be the social development the trend in the future, automation and intelligence should be the development direction of the future of cold storage, cold storage enterprises should enhance the social consciousness of competition, continuous improvement and development of China's refrigerator industry sound under the condition of market economy.

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