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NEWS

Measures to achieve energy saving in cold storage with automatic control

PubDate:2017-02-10Author:Drying heat pumpSources:Refrigeration encyclopediaViews:3858

1, on the warehouse temperature and evaporation temperature adjustment


1.1 Treasury temperature adjustment of multi-point temperature parameters


In the past, the temperature adjustment of the warehouse was controlled by the instrument, which was mainly based on the position adjustment. The evaporation temperature was often not adjusted, and it was difficult to achieve good energy-saving effects. The ideal control method for the warehouse temperature is to input the appropriate control program based on the average temperature of the warehouse, the inlet air of the chiller and the outlet air temperature, and adjust it through the computer control system. Such tempering adjustment can meet the requirements of energy saving, and can also meet the needs of high-precision temperature regulation of some warehouses. At present, the accuracy requirement of 0.25 °C can be achieved, and energy saving is about 10%.


1.2 Reduce the parallel operation of different evaporating temperatures in the cold


Since the refrigeration compressor of the same system can only operate at the same evaporation temperature, if the cold rooms of different evaporation temperatures are operated in parallel, the cold room with higher relative evaporation temperature is in an energy-saving operation state, and the cold heat load is The higher the higher the less energy is saved. This situation should be avoided as much as possible. In the practice of a dual-temperature cold storage system in a Freon refrigeration system, adding a back pressure valve to the high-temperature storage return pipe and adding a check valve to the low-temperature storage return pipe is a typical practice that does not save energy.


1.3 variable evaporation temperature adjustment


In a certain operating state, if the evaporating temperature can be adjusted by the thermal load of the warehouse and the cooling capacity of the refrigeration system, the energy saving can be achieved and the energy adjustment can be made more reasonable. In general, refrigeration system evaporators and refrigeration compressors are equipped to meet the highest load requirements. If the cooling load is reduced and the cooling capacity cannot be adjusted accordingly, the evaporation temperature of the refrigeration system will be reduced accordingly, so that the cooling capacity and heat load of the compressor reach a new equilibrium point.


The reduction of the evaporation temperature, in turn, increases the refrigeration capacity of the evaporator, and in the face of 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 of electrical energy is about 3 to 5%. If the evaporating temperature is raised in time to make the system at another ideal balance point, it will not only avoid waste, but also save energy, and reduce the frequent starting of the refrigeration compressor, which is a two-fold energy saving measure.


2, variable flow adjustment


In the past, the refrigerant flow rate of the ammonia refrigeration system evaporator has basically no variable flow regulation; most of the refrigerant flow of the Freon system evaporator is only simple proportional adjustment. Most of the air flow in the air cooler is not adjusted or only two speeds and the number of fans are adjusted. The adjustment of these two flow parameters is directly related to the cooling capacity of the cold storage equipment in the warehouse and the temperature of the warehouse. It is also one of the contents that should be paid attention to in the cold storage energy saving automatic control.


3, set the appropriate control accuracy and add over limit control


Different warehouses, different inventory items and different storage periods have different warehouse temperatures and their control accuracy requirements. From the point of view of energy saving, as long as it does not affect the quality of the goods, the temperature of the warehouse should be high and not low, and the control precision should be low and not high. It is not necessary to pursue low temperature and high precision control.


For the temperature control of the warehouse in multiple cold rooms, in addition to the original warehouse temperature setting value, the reservoir temperature overrun control value should be added. This two-factor warehouse temperature adjustment can make the refrigeration system need to be put into operation, and will not be put into operation too early because of the deviation of the warehouse temperature; it can also prematurely smash the cold or refrigeration system according to the actual situation at the time. Stop running, make full use of existing energy and avoid frequent start and stop of equipment or systems.



4, set to avoid peak operation control


The shortage of electricity is a common phenomenon in all parts of the country. The huge difference between the peaks and valleys of electricity use has made the power shortage even more serious. Therefore, the peak-to-valley price difference of electricity tariffs is gradually widening. Under the premise of not affecting the quality of the goods, the cold storage is set to avoid peak operation, which is conducive to the peak clipping of the power grid, and helps the overall energy saving on a macroscopic level; microscopically, it is also beneficial to reduce the operating cost of the cold storage.


5, cold room relative humidity adjustment


The similarity between the adjustment of the relative humidity between the cold and the temperature adjustment method need not be repeated. Generally, the relative humidity of the cold room is between 85 and 95%, but there are some cold rooms that require relative humidity below or above this range. For example, some atmospheres require a relative humidity of 98%, while some crop germplasm banks have The relative humidity requirement is 40 to 45%. In the case of high relative humidity adjustment and low relative humidity adjustment, Ewing pays attention to energy saving measures. The adjustment of humidity is conducive to the storage and preservation of vegetables, fruits and other crops.


5.1 High relative humidity adjustment


For the regulation of high relative humidity requirements, firstly, the logarithmic mean temperature difference between the refrigerant temperature and the warehouse temperature should be minimized (2K is required), and if necessary, the refrigerant indirect refrigeration system can be used; Defrost and restore the defrost to the warehouse. These two measures are implemented through automatic control and are an effective energy-saving method.


5.2 Low relative humidity adjustment


For the adjustment of low relative humidity requirements, it is mainly necessary to control both aspects. The first is to control the dehumidification program on the basis of using the dehumidification method and the dehumidifier with as little heat as possible into the cold room, and reduce the heat load between the colds while achieving the relative humidity requirement. The second is to avoid unnecessary outdoor heat and humidity load when airflow organization control; once there is a low-temperature and low-humidity crop seed bank, the thermal and wet load from the outdoor intrusion into the warehouse accounts for about 35% of the original calculation load.


6, on the adjustment of the liquid supply mode


6.1 Direct expansion supply


Direct expansion liquid supply is the liquid supply method used in most halogenated hydrocarbon (including Freon) systems and individual ammonia systems. In the past, this liquid supply method basically used a thermal expansion valve to supply liquid. Due to the selection, adjustment, and problems of the product itself, energy saving cannot be achieved. The appearance of the electronic expansion valve combined with the temperature adjustment of the multi-point temperature parameter can better achieve energy-saving operation, generally saving 10%.


6.2 Gravity supply


Gravity liquid supply systems are widely used in old ammonia refrigeration systems and were gradually replaced by ammonia pump feed systems. Although the gravity liquid supply system is troublesome to operate but does not need to consume power transmission, it is undoubtedly an energy-saving operation with proper automatic control.


6.3 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 to increase the cooling capacity but also consumes electricity, if there is no reasonable configuration and proper self-control operation procedures It is difficult to achieve energy-saving operation. At present, many liquid pump recirculation systems have excessive liquid supply, but they cannot guarantee the minimum flow and lift of each pass, but it is difficult to ensure uniform supply of multi-layer cold storage. The flow rate cannot be basically changed according to the refrigeration load. And change, it is difficult to achieve energy-saving operation. For the liquid pump recirculation system, in addition to the configuration must be reasonable, it should also strengthen the research of the automatic control operation program, such as stratified liquid supply and variable flow control, etc., in order to achieve energy saving.


According to different cooling objects, different liquid supply methods are adopted to strengthen the corresponding self-control program research, especially to strengthen the direct expansion and gravity supply system of non-electric power transmission. It is also one of the ways to seek energy saving in cold storage.



7, evaporator dual flow regulation


In the automatic control of hot air defrosting, there is a double return air solenoid valve (or main valve), which is used to ensure safety and reduce the thermal load shock when the evaporator is restored to refrigeration. This practice can be extended to the refrigeration operation state of the evaporator and perfected to achieve reasonable operation and energy saving. According to the change of the heat load of the evaporator, the minimum load liquid supply, the return air solenoid valve and the large load liquid supply and the return air electromagnetic (main) valve are set, thereby correspondingly adjusting according to the actual load change. This method can not only make the cold room evaporator energy-saving operation, but also reduce the interference to other cold rooms and refrigeration systems of the system, which is conducive to energy-saving operation of the system.


8. About the air cooler (cooling fan) defrost control


The cooling fan is basically semi-automatic or timed defrost control. The problem is that the defrost command may not be timely or delayed, and the defrost process brings too much heat. In order to save energy, the defrosting of the chiller should be fully automatic. First, there must be a suitable and reliable frost layer sensor or differential pressure transmitter (in some cases, a current transmitter can also be used) to sense the best defrost time; then there must be a reasonable defrost procedure; Cooling fan fin thermometer to prevent excessive heating. The three-pronged approach will definitely enable the cooling of the air-cooler. In some assembled refrigerated warehouses, a wide range of electric heating defrosting chillers are used, and a computerized control system is used to change the fixed timed heating defrosting into on-demand defrosting, that is, memory memory is remembered for each actual defrosting situation. And analyze to determine the best defrost cycle. On-demand defrost is about 10% more energy efficient than regular defrost.


9, cold storage door control


The cold storage door has to be opened and closed, which is a regulation of every cold storage management, but no cold storage can be completely done, in addition to individual barbaric operations, there are also actual objective reasons. The best solution is also automatic control. If the door opening time is too long, it will be automatically closed. The heat load of the door opening loss is very large, and the energy saving effect is considerable.


The electric heating wire power of the cold storage door has two options: anti-condensation and anti-freeze. The configuration power of the cold storage door electric heating wire with different temperature is also different. Note that the optional heating power can save 2% energy.


10, warehouse lighting control


The lighting of the warehouse is 1.8~5.8W/m2 according to the design of the cold storage refrigeration design manual, but in actual engineering, it is often more than 10W/m2. If you forget to turn off the lights, not only the lighting energy is wasted, but also the heat load of the cold room and the cooling system. Adding a simple control avoids waste. When the cold storage door is closed for 5 to 15 minutes, if the illumination is still on, the illumination is automatically turned off. The time delay should exceed the maximum time for the worker to work in the first time, to avoid accidentally turning off the lights; in case of accidental turning off the lights, with the help of the warehouse light and cold storage door security settings, the safety of the personnel is still guaranteed.


11, on the condenser and condensation temperature adjustment


11.1 Sensing elements and adjustment objects for condensing temperature


Depending on the correspondence between the condensing temperature and the condensing pressure, the condensing pressure is usually used as a parameter for adjusting the condensing temperature. In the past, a high-pressure pressure controller was used as a sensor and a control signal was issued, and the adjustment effect was general. Pressure transmitters are now commonly used as sensors and computer control systems, simplifying the transmission, improving adjustment accuracy and increasing reliability. The object of adjustment is the operating state of the condenser and the input of the equipment. Taking the evaporative condenser as an example, the adjustable condenser operating conditions include dry running, wet running, and variable frequency operation of the fan and the water pump; the input of the condenser will also vary according to the load. For every 1K drop in condensing temperature, the energy saving effect is as valuable as the energy saving effect of each 1K increase in evaporation temperature.


11.2 Variable condensing temperature adjustment


Using the functions of the self-control components and the computer control system, the floating control of the condensing pressure can be implemented to avoid the condensing pressure being high or low, and the energy-saving operation effect can be achieved on the basis of ensuring the normal operation of the refrigeration system. Taking a quasi-centralized refrigeration system as an example, its unit and air-cooled condenser are controlled by a dedicated variable programr, which can save 10% energy.


12. About energy-saving operation of refrigeration compressors (mainly energy regulation)


The energy regulation makes the refrigeration capacity of the compressor change with the change of the heat load, which is one of the important contents of the automatic control of the cold storage energy saving. Different refrigeration compressors or units have different emphasis on energy-saving operation and energy regulation.


12.1 Screw refrigeration compressor


When setting the cooling capacity of the compressor, avoid the operating range of its low energy efficiency ratio; carry out the automatic adjustment of the internal volume ratio for the refrigeration system with a wide range of operating conditions; for the screw machine with economizer operation, discuss the implementation of the economizer Automatic adjustment of operating conditions.


12.2 Piston compressor


Reduce the number of cylinders working with a compressor as the energy adjustment unit, avoid the reactive operation of the piston, and avoid reducing the operation of the compressor C0P value; use the frequency conversion technology to achieve energy stepless adjustment, in the improvement of operating conditions Energy saving.


12.3 Adjustments for multiple online operations


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



13, on the frequency conversion adjustment


Frequency conversion technology for compressor energy regulation is one of the more popular methods. If the frequency conversion is too low, it will cause the oil pressure difference to decrease and the oil quantity to decrease. If the frequency conversion is too high, the oil circulation amount and consumption will increase, and the compressor valve failure will increase. The variable frequency drive should also note that its motor should be selected according to the maximum power.



14, real-time calculation control to ensure the best energy-saving operation of the system


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