How to make the cold storage more energy-efficient by means of automatic control (1)

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 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 a temperature adjustment can meet the requirements of energy saving, and can also meet the needs of high-precision temperature adjustment of certain warehouses. At present, the accuracy requirement of 0.25 ° C can be achieved, and energy saving is about 10%.

2, reduce the parallel operation of different evaporating temperatures

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.

3. How to adjust the evaporation temperature to make the cold storage more energy-saving by means of automatic control (1)

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, the refrigeration system evaporator and refrigeration compressor are basically equipped to meet the high load requirements of Zui. 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.

The large-scale cold storage project of Shanghai Fresh Supply Chain Company under the contract of Xueyi Refrigeration

Variable flow regulation

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.

Set 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. How to make the cold storage more energy-efficient by means of automatic control (1)

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.

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.

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.

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.

Liquid supply adjustment

1. Direct expansion of liquid 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%.

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.

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 too much liquid supply, but they cannot guarantee that the small flow and the lift of each pass are too high, but it is still difficult to ensure the uniform supply of the multi-layer cold storage. The flow rate cannot be basically based on the refrigeration load. Changes and changes, 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. 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 Zui small load liquid supply, the return air solenoid valve, 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. If you want to know the cold storage price you need, Shanghai Xueyi Refrigeration is a refrigeration engineering company engaged in cold storage installation, cold storage design, cold storage after-sales maintenance and repair. The cold storage construction team has many years of on-site construction experience. If you need to design and install cold storage and cold storage in the near future. Price, welcome you:

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