Discussion on the development of based on partially high-efficiency and energy-saving refrigeration technology
The 21st century has entered a period of rapid economic development. At the same time, refrigeration and air conditioning products have also become popular, and they exist in various production technologies, scientific research fields, and living spaces. The figure of refrigeration technology. It can be said that the development of refrigeration technology is all to meet people's needs and plays a very important role in improving the quality of human life. However, it cannot be ignored that while air conditioning and refrigeration technology promotes social and economic development, it also causes serious damage to our living environment.
1 The development history and application status of air conditioning and refrigeration technology
In prehistoric times, humans have discovered that during seasons when food is scarce, prey can be preserved for a longer period of time if kept in cold cellars or buried in snow. In China, in order to protect themselves from the scorching heat in summer, ancient emperors built ice kilns as early as 3,000 years ago in the Zhou Dynasty, which were called "Lingyin" at the time, to store natural ice in winter. For summer use, its managers call it "Lingren". This is also the most primitive ice storage technology. During the Warring States Period, with the advancement of technology, the "Bingjian" appeared. The "Bingjian" can be said to be the earliest refrigerator prototype in our country. But before the Tang Dynasty, the ancients only used natural ice and did not know how to make ice. However, there are certain difficulties in the storage of natural ice and it cannot meet people's demand for ice in summer. At the end of the Tang Dynasty, people used the heat-absorbing properties of saltpeter to make ice when it was dissolved in water, pioneering artificial ice making and solving people's demand for ice to a certain extent. In the 13th century, the Italian Marco Polo came to China and brought our country's refrigeration technology back to Italy, which spread ice-making technology throughout Europe.
Modern air conditioning and refrigeration technology originated in the United Kingdom, and the technology matured in the United States. In 1872, Boyle invented the ammonia compressor, and only then did refrigerators and other refrigeration equipment appear one after another. In the 1930s, various Freon refrigerants appeared, accelerating the development of refrigeration technology.
In the development history of refrigeration technology for more than 200 years, air conditioning and refrigeration technology in advanced foreign countries has developed rapidly. Most of the development of my country's air conditioning industry and air conditioning and refrigeration technology has been developed by introducing foreign technology. Under the current guidance of my country's reform and opening up that emphasizes low energy consumption, green and environmentally friendly sustainable development, the development of refrigeration technology in my country's air conditioning industry mainly focuses on the research and development of refrigerants. and the application of new technologies. Although after the signing of the " Montreal Protocol ", with the efforts of all parties, by reducing the use of HFCCS and HFCS refrigerants, new refrigerants such as R410A, R32, and R290 were vigorously developed.
2 Development trends and prospects of refrigeration and air conditioning
Currently, under the national policy of "energy conservation and emission reduction", an important issue in the refrigeration and air conditioning industry is the application of energy-saving and efficient new technologies and the research and development of new refrigerants. The author will briefly introduce the new refrigeration technology that has development potential in recent years, and briefly analyze its advantages and disadvantages.
2.1 Solar Refrigeration Technology
Solar energy is recognized as one of the most suitable, safest, greenest and most ideal alternative energy sources for mankind in the future. It has the advantages of convenience, huge energy, no pollution, and good safety. On the one hand, the use of solar energy to drive air conditioning systems can greatly reduce the consumption of non-renewable energy and electricity resources. On the other hand, the lower power consumption reduces the environmental pollution problems caused by burning coal and other conventional fuels for power generation. It is the current field of air conditioning and refrigeration technology. Research hotspots. Its working principle mainly relies on the photovoltaic effect and the Peltier effect. There are ways to achieve solar refrigeration: "light-heat-cold", "light-electricity-cold", heat-electricity-cold". Solar-driven refrigeration is based on the energy conversion method. The difference can be divided into the following two methods - photothermal conversion refrigeration and photoelectric conversion refrigeration.
2.1.1 Light-thermal conversion
This method is to conduct light-heat conversion and then use thermal energy for refrigeration. The main research is solar absorption refrigeration. , solar adsorption refrigeration and solar jet refrigeration, the above three refrigeration methods have achieved a series of research results in my country. Table 1 is a comparison of the technical characteristics and parameters of several types of solar thermal driven air conditioners.
Among the above-mentioned solar air conditioners, lithium bromide-water absorption air conditioners are currently the most widely used in demonstration applications, but they are not common in China and are more commonly used in the European market.
2.1.2 Light-to-electricity conversion
This method realizes light-to-electricity conversion first, and then uses electricity for cooling. At present, the commonly used photovoltaic power generation driving methods are divided into two types: photovoltaic direct supply mode and indirect driving mode. The schematic diagram is shown in Figure 1(a) and Figure 1(b).
Photovoltaic direct drive mainly consists of photovoltaic array, DC/DC voltage stabilizing equipment, and DC load. It mainly generates current through the photoelectric effect of the photovoltaic array, and directly outputs it to the DC load after passing through the voltage regulator. Compared with the indirect drive mode, the direct drive mode The driving mode has less energy loss due to fewer intermediate processes.
The photovoltaic indirect drive mode consists of a photovoltaic array, a charge and discharge controller, a battery pack, and an inverter. The principle is the same as that of direct drive. The difference is that a battery pack is added to store the electric energy emitted by the solar cell array when it is exposed to light. And supply power to the load at any time. For AC loads, an inverter needs to be added accordingly to convert the DC power from the battery into AC power. This mode of photovoltaic power generation requires 2 to 3 energy conversions, and the energy loss is about 6% to 8%.
In recent years, with the rise of the photovoltaic industry and the decline in photovoltaic power generation costs, the photovoltaic application market has continued to expand. Solar photovoltaic refrigeration technology has also developed accordingly, and there are more and more studies on photoelectric refrigeration. Photovoltaic refrigeration is produced by combining photovoltaic power generation and refrigeration technology. It is mainly developed on ordinary refrigeration equipment to make use of the consistency of the cooling load of the air conditioner and the power generation of solar cells. That is, the stronger the sunshine, the stronger the power. When cooling is needed, the greater the cooling capacity provided by the refrigeration system.
2.1.3 Research progress and problems of solar refrigeration technology
As for the light-heat conversion mode, since adsorption refrigeration is driven by low-grade thermal energy and uses environmentally friendly refrigerants, it has developed rapidly in recent years and has considerable potential. Application prospects, Germany's Solarnext Company, Japan's Nishyodo and Mayekawa companies have reported on their solar adsorption air conditioning products. However, chemical adsorption has performance attenuation, low thermal efficiency, and the heat transfer enhancement of the adsorbent often leads to the weakening of the refrigerant's mass transfer, which has always been a bottleneck for its development. At present, adsorption refrigeration has formed an industry. Compared with foreign countries, domestic development is relatively slow. In the EU, due to policy support, the adsorption refrigeration industry has been rapidly cultivated and has become an important carrier of solar air conditioning and combined cooling, heating and power generation.
In terms of photovoltaic refrigeration, in China, Yang Yufei of Beihang University proposed a vapor compression refrigeration system driven directly by photovoltaics. Due to the weak dehumidification capability, only a simulation model was built and no actual application verification was seen.
The "Q-HAP solar air conditioning technology" developed by Midea in 2010 and the solar variable frequency air conditioner launched by Gree in the same year made use of this technology. Gree Electric launched the photovoltaic direct drive variable frequency multi-spring in 2014, which organically integrates solar energy and permanent magnet synchronous variable frequency centrifuge to develop a photovoltaic direct drive variable frequency centrifuge. This centrifuge can directly use solar energy to provide power, improving solar energy utilization. , thereby optimizing building energy allocation, reducing building energy consumption, and reducing carbon dioxide emissions.
Abroad, Japan's Mitsubishi Chemical Corporation, ICL Co., Ltd. and Fruehofer Co., Ltd. jointly developed a photovoltaic air conditioner for trucks named One, which uses thin-film solar cells produced by Mitsubishi Chemical Corporation to charge the battery when the car is running. Activate the air conditioner when the car is stopped. It is estimated that a 10 t truck can reduce diesel consumption by approximately 1,500 L per year.
Although solar refrigeration technology has many advantages, it still faces many problems.
1) Since the source of solar energy is mainly controlled by natural conditions, once the weather conditions are poor, it is difficult to ensure sufficient cooling capacity, which destined the development of this technology to have considerable limitations. One direction is to use it in combination with other technologies, such as ice storage technology or backup of conventional refrigeration and air conditioning systems.But it will increase the initial investment, and the initial investment of solar refrigeration and air conditioning itself is 10 to 16 times higher than the investment of conventional air conditioning, making the investment payback period longer.
2) This technical system occupies a large area and is difficult to apply to high-rise buildings. The solar energy collection equipment and building must be optimized and designed.
3) As a high-energy-consuming product, solar photovoltaic cells will also produce corresponding pollution during the production process, and there are problems with the recycling of scrapped batteries. According to statistics, more than 40 kg of coal must be burned to produce a 1 m The annual power generation of solar panels is 250 kW·h; above), which is enough to make a 2.2 W light-emitting diode (LED) light bulb shine for 30 years based on working 12 hours a day.
4) Development of low-cost energy storage materials: low-temperature (0-15 ℃) and medium-temperature (60-120 ℃) energy storage materials are currently being developed by countries around the world.
5) Overcoming the shortcomings of unstable solar energy flow and low density, actively developing solar concentrating technology and developing solar combined cooling, heating and power systems are the focus of future research and development.
6) Improve solar energy conversion efficiency. Improve the heat collection efficiency of solar collector and improve the structure of the collector. Although using the solar collectors in solar air conditioners together with solar water heaters is a way to improve conversion efficiency, with the implementation of "coal-to-electricity" in northern my country in recent years, the increasingly popular air source heat pumps in the northern region will eventually replace solar water heaters. , so this approach is not a one-and-done solution.
7) Whether it is a solar cell or a solar collector, there will be performance attenuation problems due to surface dust, coating and aging of photovoltaic components. In addition, absorption refrigerators also have performance attenuation problems. Therefore, reducing performance degradation is also a research direction for solar air conditioners in the future.
2.2 Thermoacoustic refrigeration technology
Thermoacoustic refrigeration technology is a brand-new refrigeration technology in the 21st century. In the past 20 years, many physicists and mechanical engineers around the world have been committed to studying this new type of heat engine and refrigeration based on thermoacoustic theory. Machines have made breakthrough progress both in theory and engineering applications, and many studies have entered the practical commercialization stage. Compared with traditional vapor compression refrigeration, thermoacoustic technology uses sound waves to perform "natural pump heat". Its structure is beautiful and simple, and it can solve almost all the shortcomings of traditional refrigeration technology. Its outstanding features are that it has no obvious moving parts, uses environmentally friendly working fluid , and can utilize low-grade heat sources.
2.2.1 Principle of thermoacoustic refrigeration technology
The working principle of sonic refrigeration is based on the thermoacoustic effect. The thermoacoustic effect mechanism can be simply described as adding heat when the sound waves are dense and discharging heat when the sound waves are sparse, then the sound waves are strengthened; conversely the sound waves are When the sound wave is dense, it expels heat, and when the sound wave is sparse, it absorbs heat, and the sound wave is weakened. With the deepening of research, the design level and manufacturing process of thermoacoustic refrigeration are also constantly improving.
The main functional components of the thermoacoustic refrigerator include sound source, hot and cold end heat exchangers, thermoacoustic plate stack and resonant tube. The thermoacoustic effect mainly occurs in the plate stack interval. The gas working fluid between the plate stacks is compressed or expanded when it vibrates back and forth at the equilibrium position driven by the sound source, and undergoes heat exchange with the solid plate stack, transferring the heat from the low temperature end. Pump to the high temperature end. Figure 2 is its microscopic schematic diagram. Process 1: The outside world does work on the microsphere, causing it to move to the right and compress adiabatically. The temperature increases and the volume decreases. Process 2: Isothermal heat exchange between the micelle and the solid wall, and the volume becomes smaller at constant temperature. Process 3: The microcluster does work on the outside world, moves to the left and expands adiabatically. The temperature decreases and the volume increases. Process 4: Isothermal heat exchange between the micelle and the solid wall, and the volume increases at constant temperature.
2.2.2 Research progress and problems of thermoacoustic refrigeration technology
In terms of efficiency, the efficiency of thermoacoustic machinery has been comparable to that of traditional internal combustion engines and refrigeration machines; considering the cooling capacity, some companies have used thermoacoustic technology to burn 35% of natural gas is liquefied and the remaining 65% is liquefied. This device can provide 2 kW of refrigeration capacity at a temperature of -140°C; in terms of refrigeration temperature, thermoacoustic refrigeration covers almost all temperature zones from normal temperature to low temperature. Today, thermoacoustic technology is mainly combined with pulse tube refrigeration technology or Stirling refrigerators and is used in fields such as infrared imaging.
Thermoacoustic technology can be said to be a refrigeration method with great potential, which can not only meet people's daily needs for cooling capacity, but also meet the needs of energy conservation and emission reduction in the 21st century.
However, thermoacoustic technology also has some disadvantages that cannot be ignored. Theoretical analysis: 1) Thermoacoustic theory currently only has relatively accurate equation descriptions in linear thermoacoustic aspects, but there are only preliminary attempts in nonlinear aspects, and there is no complete quantitative analysis. Therefore, incomplete theoretical development restricts industrial application. 2) In terms of linear thermoacoustic theory, when deriving the thermoacoustic equation, Swift adopts assumptions such as small amplitude and short plate stacking, which inherently restricts the energy flow density of thermoacoustic machinery, that is, it is designed using linear thermoacoustic theory. The thermoacoustic mechanical energy density is destined not to be very high. In order to meet the industrial needs of high-energy occasions, only a larger volume can be designed. Therefore, the lightweight and low-cost characteristics of the thermoacoustic machinery itself are abandoned, and the competitiveness with traditional machinery is greatly reduced. From a practical aspect of industrial processing, taking thermoacoustic refrigeration as an example, the first problem is the driver: if a piston is used to drive it, the core competitiveness of thermoacoustic refrigeration (no obvious moving parts) will be abandoned, and it will also cause thermal Nonlinear phenomena in acoustic effects, if speakers are used, whether they are driven by coils, piezoelectric materials, or magnetostrictive transducers, there will be a problem of insufficient energy density.
Although the warm-up machine looks very simple in structure, the principles inside are extremely complex, especially when it comes to its driving source and product-sound waves. Because sound waves are a physical quantity, their anti-interference ability is too poor. A little difference in structure and unreasonable design will have a great impact on it, and there will be huge losses in utilization.
Therefore, as a technology with great potential, the main problem faced by thermal sound is theoretical breakthrough and innovation, and now a lot of research is on engineering, that is, optimization of design technology. Although this will produce unprecedented breakthroughs in the short term, such as improvements in cooling capacity, COP, etc., it does not fundamentally solve the problem.
2.3 Radiation refrigeration technology
2.3.1 Principle of radiant refrigeration technology
Radiation refrigeration means that hot objects pass through the infrared transparent window of the atmosphere and use black body radiation to radiate heat into the cold trap in the outer space, thereby achieving refrigeration. Way. As we all know, as long as the temperature of an object is above absolute zero, the object will radiate outward. Due to different surface conditions, molecular structure, temperature and other conditions of the radiating object, the radiation wavelengths are also different. The temperature of most objects on the earth's surface is between 20 and 50°C. The wavelength radiated by objects in this temperature range is basically between 8 and 13 μm. The thermal energy of objects on the earth's surface is through radiation heat exchange, converting its own heat into the form of 13 μm electromagnetic waves. The form is emitted through the "atmospheric window" into outer space where the temperature is close to absolute zero, achieving the purpose of cooling itself.
Figure 3 is a simplified diagram of a radiant refrigeration system. The function of the insulation material around the system is to prevent the surrounding high-temperature air from transferring heat to objects in the internal space through convection and heat conduction. Therefore, insulation materials must be added around the refrigerated space, especially a "transparent" cover on the top to prevent heat from being brought in by air convection. The "transparent" cover and insulation materials can "keep cold" the radiator, but the "transparent" cover must have a high transmittance in the 8~13 μm band , and the radiation outside the 8~13 μm band has a very high transmittance. High reflectivity.The solar radiation spectrum is mainly concentrated in the 0.4~4 μm band, so the cover can block most of the solar radiation, while the radiation in the system is mainly concentrated in the 8~13 μm band. In this way, the heat in the system can be radiated to the outside through the cover. space to achieve cooling effect. The commonly used cover material is PE film. The "transparent" cover, insulation layer and radiator form a basic radiant cooling system, which generates low temperatures inside.
Although the principle of radiant refrigeration has been known as early as the 1950s and 1960s, the research work on its application in air conditioning only has a history of about 50 years, and only about 20 years in China. However, as a means of building air conditioning without energy consumption, radiant refrigeration is in line with my country's "energy saving and emission reduction" policy, and has developed vigorously in recent years, showing strong practical significance. Someone once predicted that radiant refrigeration can bring about earth-shaking changes in the energy field, allowing humans to protect the environment while also making better and more efficient use of energy to achieve harmonious development of the two.
2.3.2 Research status of radiation cooling technology
Although the principle of radiation cooling is relatively simple, radiation cooling phenomena exist in nature, such as frost on leaves in the early morning of late autumn, the large temperature difference between day and night in the desert, and the presence of Saharan silver ants. Heat dissipation, etc., all utilize the principle of radiation heat dissipation. As early as the 1970s, some people tried to use outer space to dissipate heat, but there are still many problems until now. In the early years, radiative cooling technology was mainly used in satellites and infrared detectors. In recent years, the research direction has turned to civil buildings. , automobile and other industries. In 2014, Stanford University Shanhui Fan's research group published an article in "Nature", combining nano-optics and thermal radiation control, and proposed to achieve high reflection in the solar light band by designing multi-layer materials at the nanoscale. The strong emission effect of ~13 μm effectively realizes passive "unplugged" cooling under direct sunlight. This also declares that radiant cooling is possible under direct sunlight during the day, solving a problem in radiant cooling technology. However, the preparation process of this material is complex and the cost is high, which is not conducive to large-scale application. In 2017, based on Shanhui Fan, Xiaobo Yin and others from the University of Colorado in the United States randomly embedded resonant polar dielectric microspheres in a polymer matrix to prepare metamaterial that is completely transparent to the solar spectrum, and its Has an infrared emissivity greater than 0.93 in the atmospheric window. When a layer of silver metal is coated on the backing surface of the metamaterial, the metamaterial has a radiative cooling power of up to 93W/m2 under direct sunlight. More importantly, they found that this metamaterial can achieve large-scale commercial roll-type production and is a feasible energy technology and material for the development of radiant refrigeration. This technology solves the problems of complex radiation refrigeration material technology and high production costs. However, there is no mention of the service life of the film, maintenance and operation, whether the film surface needs to be kept clean to a certain extent, and possible light pollution.
Since the research on radiative refrigeration started late, its technical application cases are mostly used in the fields of satellites and infrared detectors; in some arid areas such as deserts, Gobis, grasslands in dry seasons, and islands lacking fresh water, fresh water is very scarce, and radiant refrigeration coatings The emergence of dew can help people collect dew on a large scale and alleviate the problem of water shortage. Pei Gang and others from the University of Science and Technology of China invented a comprehensive application device for solar heat collection and radiant refrigeration. The device can produce hot water and hot air during the day and cold air at night, effectively solving the problem of traditional flat-panel solar energy. The limitations of single functions of collectors and radiant cooling devices improve the utilization efficiency of the unit and building roof unit area.
2.3.3 Problems faced by the principle of radiation refrigeration technology
In general, the key to limiting commercial development at this stage is: 1) The development of new materials. To achieve commercial use, there must be high-performance, low-cost ultra-high-performance materials as the basis, and the metamaterial cannot cause harm to people or the environment. Although the radiator materials selected in previous studies have good cooling effects, some high infrared emissivity materials have pungent odors or are toxic. Materials with better refrigeration effects cannot be used commercially. 2) Radiant refrigeration technology can only achieve cooling, but not heating in winter. Users need additional auxiliary equipment for heating in winter, which brings an economic burden to users. Moreover, the temperature drop that the current technology can achieve cannot meet the cooling needs of ordinary users, let alone be used in cold storage and other places. 3) The radiation surface is greatly affected by air cleanliness. Too low air cleanliness will lead to a significant decrease in the radiation cooling effect.
2.4 Magnetic refrigeration technology
2.4.1 Principle of magnetic refrigeration
The principle of magnetic refrigeration mainly utilizes the magnetocaloric effect, also known as the magnetic card effect (Magnetocaloric effect) refrigeration. The so-called magnetocaloric effect refers to the thermal phenomenon caused by the orderly changes of magnetic materials under changing magnetic fields. When a magnetic material is magnetized, the temperature rises and releases heat to the outside world. When it is demagnetized, the temperature drops and absorbs heat from the outside world. When a cycle is used to connect the two processes of magnetization heat release and demagnetization heat absorption, by controlling the external magnetic field, the heat absorption and release of the magnetic material can be controlled, so that the magnetic material can continuously absorb heat from one end. The other end releases heat to achieve the purpose of cooling. At present, the commonly used magnetic refrigeration working fluids are mainly paramagnetic working fluids and ferromagnetic working fluids. This article will introduce the principles of magnetic refrigeration starting from paramagnetic working fluids and ferromagnetic working fluids respectively.
For paramagnetic working fluids, when there is no external magnetic field, due to thermal motion or thermal vibration inside the paramagnetic working fluid, the internal magnetic moment orientation is random, so the corresponding magnetic entropy is large. Under isothermal conditions, when an external magnetic field is applied, the magnetic moment direction tends to be ordered along the magnetization direction. This process causes the magnetic entropy of the working medium to decrease, the degree of order to increase, and the magnetic working medium to dissipate heat to the outside world; under isothermal conditions, When the intensity of the external magnetic field is weakened, due to thermal motion or thermal vibration inside the paramagnetic working fluid, the magnetic moment tends to be disordered, the magnetic entropy increases, and the magnetic working fluid absorbs heat from the outside, thereby achieving the purpose of refrigeration, as shown in Figure 4 Show.
For ferromagnetic materials, when the temperature of the ferromagnetic material is below the Curie temperature TC, there is spontaneous magnetization inside the ferromagnetic material. When the temperature of the ferromagnetic material is above the Curie temperature TC, the material changes from ferromagnetic to Paramagnetism, the subsequent process is consistent with the refrigeration principle of paramagnetic working fluid, and will not be repeated here. The schematic is shown in Figure 5.
The process of realizing magnetic refrigeration can be briefly described through Figure 6: 1) The external magnetizing field acts on the magnetic working medium, the magnetic entropy of the working medium decreases, and the temperature increases. 2) Take away the heat of the magnetic working fluid through the heat exchange medium. 3) When the external magnetizing field is removed, the spin system within the magnetic working fluid becomes disordered again, and internal energy is consumed during the demagnetization process, causing the temperature of the magnetic working fluid to drop. 4) The magnetic working medium absorbs heat from the low-temperature heat source through the heat exchange medium, thereby achieving the purpose of refrigeration.
2.4.2 Current status of magnetic refrigeration research and its problems
Since Warburg discovered this phenomenon in metallic iron in 1881, research on magnetic refrigeration has never been interrupted. In recent years, room temperature magnetic refrigeration technology has made good progress in terms of magnetic refrigeration cycles, prototypes and numerical simulations. In theory, such as composite magnetic refrigeration cycles, active magnetic refrigeration cycles coupled with regenerative refrigeration, etc. Concept, with the deepening understanding of the operating mechanism, in terms of prototypes, the form of room temperature magnetic refrigeration prototypes is also constantly evolving, such as rotating regenerator/magnet systems, etc. In terms of numerical simulation, simulation models of different dimensions have been gradually constructed , Regarding magnetic refrigeration materials, scholars from various countries have currently conducted a large amount of research on room temperature magnetic refrigeration materials, mainly focusing on Gd metal and its compounds, Mn-based compounds and Heusler alloys.
Magnetic refrigeration technology is a new solid-state refrigeration technology that utilizes the magnetocaloric effect of materials. It has the characteristics of low vibration and low noise. Its heat exchange fluid uses environmentally friendly media such as deionized water. In recent years, room temperature magnetic refrigeration technology has made significant progress and has accelerated its practical application. Some scholars have initially combined room-temperature magnetic refrigeration technology with ground-source heat pump technology, and some related companies have released prototypes of refrigeration devices intended for commercialization.
Looking back at the development in recent years, room temperature magnetic refrigeration systems still face problems such as low efficiency of refrigerators when the temperature span increases, materials and magnetic circuits still need to be improved, and the cost of magnetic refrigeration systems is high. In terms of materials, the magnetocaloric effect of magnetic refrigeration materials is not large enough.
However, room temperature magnetic refrigeration technology is a new technology with good application prospects. It has a high level of technological maturity at this stage and is expected to replace current commercial, household, industrial and other special-purpose refrigeration devices in the future. It has a broad application market in the near room temperature range. As civil air conditioners gradually develop towards central air conditioners, it is expected that magnetic refrigeration technology will be used first in central air conditioners and automotive air conditioners.
3 Conclusion
Nowadays, humans have to face environmental resource issues. Solar refrigeration technology, radiation refrigeration technology, thermoacoustic refrigeration technology, and magnetic refrigeration technology are the current development directions of energy-saving refrigeration technology. Among them, thermoacoustic technology and magnetic refrigeration technology are relatively mature and are expected to be the first to achieve large-scale practical use. It is beneficial to reduce human pollution to the environment and consumption of conventional energy. As a high-energy-consuming industry, the air-conditioning industry must vigorously develop new green energy-saving and environmentally friendly technologies that the air-conditioning industry must consider in the future. In the context of energy conservation and environmental protection, the air-conditioning industry must take the lead in setting an example and contributing to energy conservation and emission reduction.
