At present, in the domestic air-conditioning design, the number of units for determining the capacity of the refrigeration unit and the selection of the model are often based only on experience. As a result, the initial investment of the equipment is greatly increased, and the installed capacity of the electrical civil engineering and construction is increased accordingly. Far more than the actual needs and even more than the above part of the refrigeration equipment idle for many years, the refrigeration unit operating efficiency is low, the cost is high, the accident occurs frequently. There are many reasons for this phenomenon. One of the main reasons is that the designer does not fully grasp the law of load change, and blindly considers the maximum load value as the only factor to consider when selecting the unit, and ignores the variation of the load at different times and different occasions. From the statistics of various aspects, there is very little time for the maximum load in the general air-conditioning cooling period in China, which is only a few percent of the annual running time. Most of the time of the refrigeration unit is the partial load. Under working conditions. Moreover, after calculating and analyzing the accumulated value of the air-conditioning cold load in each month of the cooling season, it is found that even the peak load maximum operating hours still occupy a considerable proportion. Because only by combining these two conditions, it is possible to obtain a satisfactory design by comprehensive consideration. Commonly used refrigeration units can be divided into piston type screw type and centrifugal type according to the compressor. Piston type refrigeration unit piston type belongs to medium and small-sized refrigeration unit. It is low in cost, small in size and low in efficiency. Therefore, it is still widely used in household refrigerators, air-conditioner air conditioners and small commercial air conditioners. However, with the continuous development of other new types of machines (especially screw type) and the high efficiency of the refrigeration technology, the inherent defects of the piston type, such as the small amount of cold and small structural complex consumables, many pairs of wet stroke sensitive load regulation performance. The difference can only rely on increasing or decreasing the number of cylinders for finite series adjustment, etc., which makes its use range shrink. The screw type screw-type refrigeration unit is a medium-cooling refrigeration unit. According to the number of rotors, there are single-screw and twin-screw units. In recent years, with the development and processing precision of the new tooth profile of the screw, the application of the high-precision rolling bearing, the use of the synthetic refrigeration system and the application of the automatic ratio adjustment technology of the internal volume ratio make the screw refrigeration unit continue to reduce energy consumption. The operating efficiency is greatly improved, and the value of the unit is close to the level of the centrifugal refrigeration unit. In addition, its original structure, simple components, less resistance to liquid hammer, strong running energy, stepless adjustment of partial load, less energy loss than centrifugal type, the application range of the screw unit is gradually expanded, and now it is medium Based on the cooling capacity, it extends simultaneously in both directions of size and cooling capacity, and has a tendency to replace the piston refrigeration unit. It can be seen that when the spool valve that regulates the cooling capacity of the compressor has just been adjusted from full load, the actual volume (dashed line) does not change continuously from sudden to continuous like the theoretical volume (solid line) due to the resistance of the bypass port. of. When the sliding valve slides to the limit position where the load rate is close, the exhaust chamber will communicate with the working volume, which will cause the high pressure gas in the exhaust chamber to flow back into the working volume of the person. Therefore, in order to prevent this from happening, generally only Allow the spool to move to the position of the load. Therefore, the screw compressor usually performs stepless adjustment of the amount of cooling between them. However, while the cooling capacity is adjusted, the power consumption is not proportional to the load change. The relationship between the power consumption of the screw compressor and the load can be seen. The two have different relationship curves with different evaporation temperatures. Red is the ideal proportional line. The lower the evaporation temperature, the higher the compression ratio, the less the power consumption is proportional to the load. Only when the evaporation temperature is higher and the compression is lower, the two are close to a proportional relationship. Moreover, the power consumption of each evaporation temperature has deviated from the ideal proportional line. Therefore, from the economical consideration of operation, it is generally preferable to operate the screw refrigeration unit above the load, and the following low-load operation is very uneconomical. In addition, the screw refrigeration compressor will produce under-compression and over-compression due to internal and external pressure ratios during operation, and both cases will generate additional power consumption. In response to this situation, an adjustable volume ratio mechanism has been developed, which makes the internal and external pressure ratios tend to be consistent, reduces power consumption, improves the economics of the screw machine operation, and satisfies the user's transformation to a certain extent. Requirements for working conditions. Centrifugal refrigeration unit centrifugal type belongs to medium and large capacity refrigeration unit. It has large refrigeration capacity, small mechanical wear and small wearing parts, stable operation, easy multi-stage compression and multiple evaporative temperature cooling. It can be steplessly adjusted, especially in frequency conversion technology. After development, combined with the adjustment of the inlet guide vane, the adjustment range of the unit can be widened, and high efficiency can be maintained during partial load operation. The main disadvantage of the centrifugal unit is that the working condition can not be changed greatly, and the narrow range of adaptation is prone to surge at low load rate. Therefore, the centrifugal unit generally only performs stepless adjustment between loads, strictly speaking the lower limit of load. It is determined that the compression ratio of the current centrifugal refrigeration unit is related to the number of revolutions of the motor, and it is mainly used in the case where the capacity of the single unit exceeds. Since the most commonly used motor is a fixed speed motor, the centrifugal refrigeration compressor mostly uses an inlet guide vane to adjust the intake adjustment bypass adjustment and other means during partial load. Among them, the economics of intake regulation and bypass regulation are relatively poor. The former is often used in the case where the cooling capacity does not change much. The method of adjusting the inlet guide vane is simple in structure, and the economy is better than the former two. Therefore, the air conditioner centrifuge is fixed at a fixed speed. Most used. When the vanes are fully open, when the vanes are fully closed and when the vanes are all closed, when the unit is operating in the normal working area on the right side of the surge envelope, a compressor can pass through the inlet vanes as the system performance curve changes. Adjust the adaptation at any time, but obviously this is at the expense of some operational efficiency. When the performance curve of the unit enters the surge zone, it is impossible to adjust the inlet guide vanes by itself. At this time, it is necessary to use the bypass adjustment method to adapt to the working conditions. When the unit detects that its operating condition is in the area, it automatically opens the inlet guide vanes automatically. When it is in the area, it automatically adjusts the motor speed to the minimum. It only depends on the inlet guide vane adjustment to meet the needs when it is detected. In the area, the motor speed and inlet guide vane opening are adjusted simultaneously to achieve optimum operating efficiency. In this way, through the different combination adjustment methods of the above three regions, the normal operating range of the unit is increased, the surge area is reduced, the operating efficiency of the unit at each working condition is improved, and a large operation cost is saved. After three generations of development of centrifugal frequency conversion unit, the price ratio of the unit itself and the frequency conversion device is from the initial to the present one. The frequency conversion device can be placed on the unit as a small box from the initial to the present. Mature, cost-effective and higher, it can be expected that the frequency conversion centrifugal unit will be used by more and more users. However, the frequency conversion technology also has defects, that is, radiation will be generated externally in the frequency conversion process, which may adversely affect the human body in the vicinity. Western developed countries have already carried out research work, and China should also pay attention to and study it. . The centrifugal refrigeration unit can achieve good partial load characteristics by combining frequency conversion adjustment with inlet guide vane adjustment. It can be seen that at partial load, the compressor realizes stepless adjustment of the motor speed by frequency conversion, so that each working point on the right side of the surge envelope can maintain high operating efficiency, especially if the pressure changes with the speed, The highest operating efficiency can be achieved from load to full load. When the system performance curve out of the surge envelope, it must be combined with the inlet guide vane adjustment to expand the range of stable operation of the unit, improve the operating efficiency, and at the same time avoid the occurrence of surge. Air conditioning and refrigeration unit selection principle and method After understanding the annual load change law and the characteristics of common refrigeration units, the unit selection can be carried out. The selection generally includes the determination of the total capacity of the first phase of the refrigeration technology, the determination of the type of the unit, the comparison of the performance of the unit with the brand, the determination of the number of units and the capacity of the single unit. Each of these steps has taken into account factors such as the reliability and safety of initial investment in operation and maintenance. The total capacity of the unit is determined to determine the total capacity of the air conditioning and refrigeration unit to meet the air conditioning design load requirements of the air conditioning system. When determining the total capacity, it is necessary to consider the insufficient cooling capacity that may occur when the actual operating conditions of the unit deviate from the designed operating conditions. Therefore, in general, the required cooling capacity for the unit should be increased. Of course, this is based on the basic correctness of the load calculation. Determining the type of unit The type of refrigeration unit to be used should be determined by the user and the designer according to the actual situation of the user. The basic principle is that the area where the power supply can be guaranteed is preferred to the refrigeration unit directly driven by electric power, such as centrifugal screw type. (Piston type is generally only considered when the cooling capacity is small). Because of economic and technical analysis, the performance of electric-powered refrigeration units is better than that of heat-driven refrigeration units. If steam or hot water is available, consider a steam-type or hot-water type arsenic refrigeration unit. If energy such as natural gas can be used, a direct-fired snorkeling refrigeration unit is also a viable option. For areas where it is necessary to provide both hot and cold loads, or where the difference between hot and cold loads in summer and winter is not too great, heat pump units are recommended. This saves boiler equipment and saves initial investment and operating costs. Under the premise of solving the problem of equipment emission and noise pollution, air-cooled refrigeration units are recommended for small and medium-sized cooling. The performance of the unit is determined compared with the brand. During most of the year, the unit is working under partial load. Therefore, it is very important to determine the partial load operation performance of the unit. This is actually a comprehensive consideration process. . For example, for the screw machine, it is to select the ordinary single-head slide valve adjustment, or to select the multi-head plunger adjustment with excellent partial load efficiency but low full load efficiency, or to select the internal volume ratio adjustment with strong adaptability. In this case, it is necessary to judge the unit's operating conditions, load characteristics, financial strength, technical reliability, etc., otherwise it is easy to have a situation where the unit performance is too different from the load demand. If the frequency converter of the centrifuge is used or not, it should be considered as such. After the basic performance required by the unit is determined, other factors can be considered, such as the safety and reliability of the price value operation, the service life and the operational noise. These factors are actually linked to the brand. The same is the screw machine adjusted by the slide valve. There are certain differences between different brands (such as price noise, etc.), which requires careful comparison of morality. Choose the brand unit that best meets your requirements. The refrigeration unit for civil comfort air conditioning does not need another equipment unit, but the possibility of alternate use and rotation between the units should be considered. In the same station, a combined solution of different types of units with different capacities can be used to save energy. Because it is determined that several units are selected, not only related to the total load, but also related to the law of load change. If a unit is used, when the total load is within, only one unit with a load rate less than one can be opened, and it can be seen that the proportion of this time is very large, so whether it is centrifugal or It is uneconomical for a screw unit to operate for a long period of time at such a low load rate, and if a centrifuge is used, it is prone to surge. However, if a unit with a combination of centrifugal or screw units is used, the situation is much better. The small-capacity unit can be operated within the total load, which greatly improves the operating efficiency. The lower limit of the load rate of the screw machine is generally selected as the sum of the total load, so that when they are at the lowest load rate, they can still operate normally at the total load and the remaining two units are selected for the same capacity because For centrifuges and screw machines, the medium and low load of multiple units is more energy efficient than the high load operation of some units. Therefore, the parallel cooperation of two units with the same capacity under partial load can achieve better operation than the full capacity operation of a single unit. effect. As can be seen from the above example, the number of refrigeration units and the determination of the capacity of each unit depends not only on the number of static loads, but also on how any of these loads are dynamically changed. It is not advisable to combine the dynamic characteristics of the load with the static quantity, and combine the performance characteristics of various refrigeration units to determine the number of units and the single unit capacity, so that the unit can be in optimal working condition in the future. Professional massage gun, super long life, reduce your muscle pain and stiffness, no matter you are before or after exercise, use our massage gun, let your body get relaxed. Warm up before exercise, stimulate muscle potential, relax during exercise to maintain the best state, recover after exercise to remove fatigue and pain. Daily massage, universal body, body comfort. Leg massage, say goodbye to chunky legs. 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