How to use automation technology to control energy saving in cold storage

How to use automation technology to control energy saving in cold storage

Warehouse temperature and evaporation temperature adjustment

　　(1) Warehouse temperature adjustment of multi-point temperature parameters

　　In the past, the temperature adjustment of the warehouse was controlled by instrument, which was mainly based on position adjustment. The evaporation temperature was often not adjusted, which made it difficult to achieve good energy-saving effects. The ideal control method for warehouse temperature is to use the average temperature of the warehouse, the inlet air and outlet air temperature of the cooler as input parameters, compile an appropriate control program, and adjust it through a computer control system. In this way, the temperature storage adjustment can meet the requirements of energy saving, and it can also meet the needs of high-precision temperature adjustment in some warehouses. At present, it has reached the accuracy requirement of 0.25°C, saving about 10%.

　　(2) Reduce the parallel operation of cold rooms with different evaporation temperatures Since the refrigeration compressors of the same system can only operate at the same evaporating temperature, if cold rooms with different evaporating temperatures are operated in parallel, the cold room with a relatively high evaporating temperature will be in a non-energy-saving operation state. The heat load of the cold room The higher the value, the less energy saving. This situation should be avoided as much as possible. In the Freon refrigeration system, adding a back pressure valve to the return pipe of the high-temperature storage and a one-way valve to the return pipe of the low-temperature storage is a typical approach that does not save energy.

　　(3) Variable evaporation temperature adjustment

　　 In a certain operating state, if the evaporation temperature can be adjusted with the thermal load of the warehouse and the refrigeration capacity of the refrigeration system as parameters, it will not only achieve the purpose of energy saving but also make the energy adjustment more reasonable. Generally speaking, the evaporator and compressor of the refrigeration system can basically meet the needs of the highest load. If the heat load in the cold room decreases and the cooling capacity cannot be adjusted in time, the evaporating temperature of the refrigeration system will be lowered accordingly, so that the cooling capacity and heat load of the compressor reach a new equilibrium point.

　　 The decrease in evaporating temperature in turn increases the refrigeration capacity of the evaporator. Facing the reduced heat load, it will inevitably result in frequent start and stop. For every 1°C change in evaporation temperature, the corresponding increase or decrease in electrical energy is about 3 to 5%. If the evaporating temperature is increased in time and the system is at another ideal balance point, it will not only avoid waste and save energy, but also reduce the frequent starting of the refrigeration compressor, which is an energy-saving measure that achieves two goals.

　　 variable flow adjustment

　　 In the past, the refrigerant flow of the evaporator of the ammonia refrigeration system basically did not have variable flow adjustment; the refrigerant flow of the evaporator of the Freon system, most of which only achieved simple proportional adjustment. Most of the air flow of the air cooler is not adjusted or only two-speed and the number of fans are adjusted. The adjustment of these two flow parameters is directly related to the cooling capacity of the warehouse cold distribution equipment and the temperature of the warehouse, and it is also one of the contents that the cold storage energy-saving automatic control should pay attention to.

　　 Set appropriate control accuracy and add over-limit control

　　Different warehouses, different inventory commodities and different storage periods have different warehouse temperature and control accuracy requirements. From the perspective of energy saving, as long as it does not affect the quality of the product, the warehouse temperature should be high instead of low, and the control accuracy should be low instead of high. There is no need to pursue too low storage temperature and high-precision control.

　　 For the warehouse temperature control of multiple cold rooms, in addition to the original warehouse temperature setting value, a warehouse temperature over-limit control value should be added. This two-factor warehouse temperature adjustment can ensure that when the refrigeration system needs to be put into operation, it will not be put into operation prematurely due to the deviation of the temperature of the other warehouse; it can also prevent the cold room or the refrigeration system from prematurely shutting down according to the actual situation at the time. Stop operation, make full use of existing energy and avoid frequent start and stop of equipment or systems.

　　Set up peak avoidance operation control

　　 Electricity shortage is a common phenomenon in all parts of the country. The huge difference in power consumption between peaks and valleys has exacerbated the shortage of electricity. For this reason, the peak-to-valley difference in electricity tariffs is gradually widening. On the premise of not affecting the quality of goods, cold storage is set up to avoid peak operation, which is conducive to the power grid to cut peaks and compensate for valleys, and helps overall energy conservation in the macro; it also helps to reduce the operating cost of the cold storage in the micro.

　　 Cold room relative humidity adjustment

　　The similarities between the relative humidity adjustment of the cold room and the temperature adjustment method need not be repeated. Generally, the relative humidity of the cold room is between 85-95%, but some cold rooms require a relative humidity lower or higher than this range. For example, some air conditioning libraries require a relative humidity of 98%, while some crop genebanks require a relative humidity of 98%. The relative humidity requirement is 40-45%. Ewing pays attention to energy-saving measures in high relative humidity adjustment and low relative humidity adjustment. The adjustment of humidity is beneficial to the storage/preservation of vegetables, fruits and other crops.

　　(1) High relative humidity adjustment

Relative humidity requires cold room adjustment. First of all, it is necessary to minimize the logarithmic average temperature difference between the refrigerant temperature and the warehouse temperature (2K is acceptable). If necessary, an indirect cooling system with a refrigerant can be used; in addition, air defrosting can also be used And restore the defrost to the warehouse. These two measures are implemented through automatic control and are effective energy-saving methods.

　　(2) Low relative humidity adjustment

　　 For the adjustment of the cold room with low relative humidity requirements, the main two aspects should be controlled. The first is to control the dehumidification program based on the selection of dehumidification methods and dehumidifiers that bring as little heat as possible into the cold room to reduce the heat load in the cold room while meeting the relative humidity requirements. The second is to avoid unnecessary outdoor heat and humidity loads during airflow control; there was once a crop seed bank with low temperature and humidity, and the heat and humidity load from the outdoor intrusion into the bank accounted for about 35% of the original calculation load.

　　 Liquid supply mode adjustment

　　(1) Direct expansion liquid supply

　　Direct expansion liquid supply is the liquid supply method adopted by most halogenated hydrocarbon (including Freon) systems and individual ammonia systems. In the past, this kind of liquid supply method basically used a thermal expansion valve to supply liquid. Due to the problem of model selection, adjustment and the product itself, it could not achieve the purpose of energy saving. The emergence of the electronic expansion valve combined with the multi-point temperature parameter adjustment of the storage temperature can achieve better energy-saving operation, generally saving 10%.

　　(2) Gravity liquid supply

　　 The gravity liquid supply system is widely used in the old ammonia refrigeration system, and was gradually replaced by the ammonia pump liquid supply system. Although the operation of the gravity liquid supply system is troublesome, it does not need to consume power for transmission. As long as it is equipped with appropriate automatic control, it is undoubtedly an energy-saving operation.

　　(3) Liquid pump supply

The liquid pump recirculation system is widely used in ammonia refrigeration systems; although the liquid pump recirculation system can increase the heat transfer coefficient of the evaporator and thus increase the cooling capacity, it also consumes electricity. If there is no reasonable configuration and proper automatic control operation program , It is difficult to achieve energy-saving operation. At present, many liquid pump recirculation systems have too much liquid supply but cannot guarantee the minimum flow of each channel. The head is too high but it is difficult to guarantee the uniform liquid supply of the multi-layer cold storage. The flow basically cannot be changed according to the cooling load. However, it is difficult to achieve energy-saving operation with changes. For the liquid pump recirculation system, in addition to the reasonable configuration, the study of automatic control operation procedures should be strengthened, such as layered liquid supply and variable flow control. Only in this way can the goal of energy saving be achieved.

　　 Adopting different liquid supply methods according to different refrigeration objects, strengthening the research of corresponding automatic control procedures, especially strengthening the research of direct expansion and gravity liquid supply system of non-electric power transmission, is also one of the ways to seek energy saving in cold storage.

　　Evaporator dual flow adjustment

　　 There is a double return solenoid valve (or main valve) in the automatic control of hot gas defrosting. Its function is to ensure safety and reduce the impact of thermal load when the evaporator resumes cooling. This approach can be extended to the refrigeration operating state of the evaporator and be improved to achieve the purpose of reasonable operation and energy saving. According to the change of the thermal load of the evaporator, z* small load liquid supply and return air solenoid valve and large load liquid supply and return air solenoid (main) valve are set, so that corresponding adjustments can be made according to the actual load changes. This approach not only enables the energy-saving operation of the cold room evaporator, but also reduces the interference to other cold rooms and refrigeration systems of the system, which is beneficial to the energy-saving operation of the system.

　　Air cooler (air cooler) defrost control

　　The defrosting of the air cooler basically adopts semi-automatic control or timing defrosting control. The problem is that the defrosting command may not be timely or delayed, and the defrosting process will bring too much heat. In order to save energy, the defrosting of the air cooler should be fully automated. First of all, there must be a suitable and reliable frost layer sensor or differential pressure transmitter (current transmitter can also be used in some cases) to sense the best defrost time; then there must be a reasonable defrost procedure; The air cooler fin temperature sensor prevents excessive heating. The three-pronged approach can definitely achieve the defrosting and energy saving of the air cooler. In some prefabricated cold storages, electric heating defrosting air coolers are widely used. Computer control systems are used to change fixed timing heating and defrosting to on-demand defrosting, which means that each actual defrosting situation is memorized through the memory function. And analyze to determine the best defrost cycle. On-demand defrosting saves about 10% energy compared with scheduled defrosting.

　　 Cold storage door control

　　The cold storage door must be opened and closed immediately. This is a regulation of every cold storage management, but no cold storage can fully achieve it. In addition to individual brutal operations, there are actual and objective reasons. The best solution is also automatic control. If the door is opened for too long, it will automatically close. The heat load of opening the door is very large, and the energy saving effect is also considerable.

　　The power of the electric heating wire of the cold storage door has two options of anti-condensation and anti-freezing. The configuration power of the electric heating wire of the cold storage door with different operating temperatures is also different. Note that selecting appropriate heating power can save energy by 2%.

　　Warehouse lighting control

　　The warehouse lighting is 1.8~5.8W/m2 according to the cold storage refrigeration design manual, but in actual projects, it often exceeds this data and some even around 10W/m2. If you forget to turn off the lights, you will not only waste lighting power, but also increase the heat load of the cold room and refrigeration system. Add a simple control to avoid waste. When the cold storage door is closed for 5 to 15 minutes, if the lighting is still on, the lighting is automatically turned off. The delay time should be longer than the z* long time of the worker in one operation, so as to avoid turning off the lights by mistake; in case the lights are turned off by mistake, with the help of the warehouse lamp and the safety setting of the cold storage door, the safety of personnel operation is still guaranteed.

　　Warehouse lighting control

　　(1) Sensing element and adjustment object of condensation temperature

　　 According to the corresponding relationship between the condensation temperature and the condensation pressure, the condensation pressure is usually used as the adjustment parameter of the condensation temperature. In the past, high-pressure pressure controllers were commonly used as sensors and sent out control signals, and the adjustment effect was average. Nowadays, pressure transmitters are usually used as sensors and equipped with a computer control system, which simplifies the transmission device, improves the adjustment accuracy and enhances the reliability. The object of adjustment is the operating state of the condenser and the amount of equipment input. Take the evaporative condenser as an example. The operating states of the condenser that can be adjusted include dry operation, wet operation, and variable frequency operation of fans and water pumps; the input amount of the condenser will also change according to changes in load. For every 1K drop in the condensing temperature, the energy saving effect is as valuable as the energy saving effect of every 1K rise in the evaporation temperature.

　　(2) Variable condensation temperature adjustment

　　Using the functions of automatic control components and computer control systems, floating control of the condensing pressure can avoid high or low condensing pressure, and achieve the effect of energy-saving operation on the basis of ensuring the normal operation of the refrigeration system. Take the quasi-centralized refrigeration system as an example. Its unit and air-cooled condenser are controlled by a special variable programmer, which can save energy by 10%.

　　 Refrigeration compressor energy-saving operation (mainly energy regulation)

　　Energy adjustment enables the cooling capacity of the compressor to change with the change of thermal load, which is one of the important contents of the automatic control of energy saving in cold storage. Different refrigeration compressors or units have different emphasis on energy-saving operation and energy adjustment.

　　(1) Screw type refrigeration compressor

When setting the cooling capacity of the compressor, avoid the operating range with low energy efficiency ratio; implement automatic adjustment of the internal volume ratio for the refrigeration system with a large range of operating conditions; discuss the implementation of economizers for screw compressors operating with economizers Automatic adjustment of operating conditions.

　　(2) Piston compressor

The practice of reducing the number of cylinders of a compressor as the energy adjustment unit, avoiding the reactive operation of the piston, and also avoiding the operation of reducing the COP value of the compressor; adopts the frequency conversion technology to achieve stepless energy adjustment, which is in the improvement of operating conditions Energy saving.

　　(3) Adjustment of multiple parallel operation

　　 Try to use the number of compressors as the energy adjustment unit; try to keep each compressor in a high energy efficiency operation state; design a combination of different sizes of compressor heads, and invest in the corresponding energy combination according to the load change.

　　 frequency conversion adjustment

　　 frequency conversion technology is one of the more popular methods for compressor energy adjustment. If the frequency conversion is too low, it will cause the disadvantages of lower oil pressure difference and oil volume reduction; if the frequency conversion is too high, it will increase the oil circulation and consumption, as well as increase the compressor valve failure. The variable frequency drive should also pay attention to its motor should be selected according to z* high power.

　　Real-time calculation and control to ensure the best energy-saving operation of the system 　　 The optimal design of the refrigeration system and the best operation of the automatic control are very important for realizing energy saving in the cold storage. The real-time control task of energy-saving operation of cold storage can be completed by data collection, calculation control and monitoring system. The data collection calculation control system collects all relevant parameters of the refrigeration device, refrigeration system and working environment. The categories include temperature, pressure, pressure difference, liquid level, current, operating status, and fault conditions.