Air Conditioning Refrigeration Technology Development and Research Status

Business News Agency June 29th The current refrigeration technology has almost penetrated into various production technologies and scientific research fields, and has played a significant role in improving the quality of human life. It can be said that it is inconceivable that modern technological progress has left the development of refrigeration technology. In order to let the technical personnel of air-conditioning companies know the latest developments of air-conditioning and refrigeration technology in a timely manner, this article will use the relevant literature on air-conditioning and refrigeration technology in the near future as a basis to comprehensively report the main contents of the air-conditioning and refrigeration technology for your reference.

1. Research progress of refrigerants In general, the development of refrigerants can be divided into two phases. The first phase is from natural substances to artificially synthesized substances; then the second phase of refrigerant development will be Return to natural material.

Early refrigerants were substances that were readily available or made in nature, such as **, ammonia, CO2, and the like. However, these early refrigerants were ultimately due to the bulky efficiency of the refrigeration equipment, so they later withdrew from the conventional refrigeration system in the 1950s after the appearance of better-heated Freon refrigerants.

In 1929, U.S. General Company synthesized R12, and soon afterwards, series halogenated hydrocarbon compounds known as Freon such as R11 and R22 appeared. Due to its excellent thermodynamic properties, it was non-toxic, non-flammable, and extremely stable, and soon became a refrigeration. The protagonist of the agent was mass-produced and used, such as household refrigerators, automotive air conditioners, and small refrigerators, all of which use R12. By the 1970s, annual output of various halogenated hydrocarbons including refrigerants and blowing agents reached Millions of tons, and there is a continued increase.

However, Freon is a chemically very stable synthetic material that will not be decomposed by the natural world for a long time after it is volatilized into the atmosphere, but has spread to the stratosphere, with stratospheric and ozone layers in the atmosphere from 11km to 45km. When encountering in the stratosphere due to exposure to intense solar ultraviolet light, chlorine-containing Freon molecules (called chlorofluorocarbons, abbreviated as CFC) decompose free chlorine atoms, and chlorine atoms can catalyze the decomposition of ozone molecules, in the reaction the chlorine atoms It is continuously released, so the decomposition reaction continues, and the chlorine atoms cause the ozone layer to be destroyed, thinned, and disappear. Due to the extensive use of Fluoride, the ozone hole over Antarctica has been continuously expanded in recent years. It has also been reported that ozone holes have also appeared over the Tibetan Plateau, so replacement of Freon refrigerants is imperative.

2. International R22 Substitution Technology After the successful substitution of CFC, people paid more attention to HCFC. The first among them is undoubtedly R22 in the most widely used HCFC in the refrigeration and air-conditioning industry. Since its introduction in 1936, the refrigerant has swept the entire refrigeration industry with its superior comprehensive performance and was designed, manufactured, operated and maintained. Other areas have accumulated a wealth of successful experience.

However, because of the depletion effect of the ozone layer on the R22 and the higher greenhouse effect value, the 1992 International Conference in Copenhagen included it in the scope of gradual bans. The Vienna International Conference in 1995 banned the schedule, and according to the requirements of compliance, On July 1, 1999, the consumption of CFCs should be frozen at the average level from 1995 to 1997, reduced by 50% by 2005, and eliminated in 2010.

Strictly speaking, none of the single refrigerants have been found to outperform the R22 refrigerant. At present, the main alternatives for R22 include HFCS and natural working fluids. Although the research on HFCS refrigerants is relatively mature, non-azeotropic mixtures composed of HFCS refrigerants can theoretically use different boiling point of each component to achieve Lorentz cycle and improve refrigeration cycle efficiency. However, HFCS refrigerants still exist. A certain GWP value (global warming potential) is incompatible with the mineral oil used in R22 and requires the use of synthetic oils that are compatible with it, and the compatibility with desiccants, sealing materials, and other materials also needs further study. So more and more people have turned their gaze to natural working fluids.

The biggest advantage of natural refrigerants is that their GWP and ODP (Ozone Potential Energy) values ​​are approximately zero, they do not cause any harm to the environment, and they have excellent thermal performance and economy. At present, such mature refrigerants include R407C. , R32/134a, R410a, R134a, and hydrocarbon R1270 and so on.

Some countries are now competing to carry out research on alternative technologies for HCFC22. After several years of experimentation and evaluation, R22's mature HFCS alternatives are as follows:

A, R407c: R22 replacement is a louder candidate in many candidate alternative refrigerants. This is due to the fact that the thermodynamic properties of R407c are similar to those of R22. Their working pressure and cooling capacity are relatively close. This makes the replacement simple and easy, the original R22 machinery and equipment replaced by R407c after replacing the lubricant, adjust the system injection volume and throttling components, the compressor and the rest of the equipment can not be changed. However, using R407c, the cooling capacity and energy efficiency ratio of the machine are slightly lower than when using R22, and the biggest defect of R407c may be larger temperature slip. According to the latest data, R407c is promising in home air conditioners with a low refrigeration capacity range (5-20KW) and chillers with a high capacity range (20-350KW) in addition to screw compressors. .

B, R32/134a: This non-azeotropic mixture has the best thermodynamic properties at 30/70%. Many reports indicate that the cooling capacity of the optimized air-conditioning equipment after the system's injection volume and heat exchanger can use the mixed refrigerant can be equivalent to that of R22, and the energy efficiency ratio can also be increased by several percentage points. The disadvantage is that it is flammable under certain conditions, although it is not flammable under normal operating conditions.

C, R410a: Its thermal performance is very close to that of a single working substance. Although it is not very similar to the thermal properties of R22, it may be the most promising alternative to R22. The refrigeration system using R410a needs to be completely modified, but the modified machine becomes more compact. Its other advantage is that the liquid phase has a high thermal conductivity and a low viscosity, making it superior to R22's transmission characteristics. R410a has a higher energy efficiency ratio than R22 when optimized within the appropriate pressure range. With the same cost, the overall efficiency can be increased by about 5%, which is enough to compensate for the cost of retrofit design. Therefore, it can be used as a long-term substitute for R22. It has broad application prospects in ordinary air conditioners such as unitary or air-cooled, water-cooled integrated chillers (except large-capacity) and residential air conditioners with large cooling capacity.

D, R134a: Compared with R22, the pressure and the cooling capacity will be reduced. Most of the pipelines including the heat exchangers should be expanded to reduce the pressure loss, and the displacement of the compressor should also be increased. After replacing R22 with it, the cooling capacity of the system has greatly decreased, and the energy efficiency ratio has also decreased slightly. The cost of retrofitting of the system is high, so it is less likely to be used for small residential or commercial air conditioners, but it is more appropriate for large chillers, especially screw or centrifugal compressors.

E, R1270: Comparing the thermophysical properties and thermal cycling properties of R1270 and R22, hydrocarbon R1270 has a good environmental acceptance, the main thermophysical properties are similar to those of R22, and its latent heat of vaporization is higher than that of R22 and R290. , The heat transfer efficiency is high, and the flammability and explosiveness of R1270 can also be overcome through the perfection of safety measures in the production process and refrigeration equipment. Compatible with R22 system lubricating oil and other components, and with R22 volume cooling capacity is not much difference, no need to modify the compressor. With the advantages of high refrigerating capacity, high cycle performance coefficient, and greatly reduced charge, the overall consideration is an excellent refrigerant.

3. Although natural refrigerant HFC substitutes have solved the problem of depletion of the ozone layer, its high GWP is still an issue that cannot be ignored. If considered from the standpoint of environmental acceptability, natural refrigerants are undoubtedly the most thorough and perfect way to solve problems.

The school of natural refrigerants, represented by Prof. G. Lorentzen of Norway, has invested in natural refrigerants that are “natural and natural”.

The International Institute of Refrigeration (IIR) has held a biennial international conference on the topic of natural working fluids since 1994 and exchanged discussions on new discoveries and achievements in this field. At present, ammonia, propane and other hydrocarbons, and CO2 refrigeration technology are most likely to become long-term alternatives to R22 in natural refrigerants.

(1) R717: is a kind of cheap natural refrigerant with more than 120 years of experience. Its excellent thermal performance, its volumetric cooling capacity and energy efficiency ratio are all superior to R22; however, R717 has a high exhaust temperature, and it has certain The incompatibility of the material with the original lubricating oil is worrying. However, the emergence of new lubricating oils and other new technologies has provided possibilities for the expansion of ammonia. At present, there are already self-contained chiller units that use ammonia, and refrigeration technicians continue to work hard.

(2) R290: It is also a very cheap natural refrigerant that has been used for a long time in chemical production. The thermodynamic nature of propane is very close to that of R22, and therefore it may be a direct flushing refrigerant for R22. Compared with R22, propane has higher energy efficiency, lower exhaust gas temperature, and smaller volumetric refrigeration capacity. Its weakness is flammability. In recent years, the use of propane has grown, and relevant regulations for safe use have also been developed.

(3) CO2: Because of the high density and low viscosity of CO2, the flow loss of CO2 is small and the heat transfer effect is good. The enhanced heat transfer can make up for the shortcomings of its low circulation, increase the regenerator or use two-stage compression to achieve similar efficiency with conventional refrigerants, without the expansion machine, which is also the company developed CO2 small refrigeration or automotive air conditioning Research direction.

CO2 refrigeration technology has entered the threshold of practical application. CO2 heat pump water heaters developed by several major Japanese companies have been on the market for many years, and the annual output has reached 100,000 units. Japan Refrigeration Air Conditioning Association standards JRA-4050-2004 appliance heat pump hot water machine (carbon dioxide refrigerant) has strict requirements on the performance and installation of such products. In fact, a slight modification of the water heater can be turned into a heat-recoverable home air conditioner, so CO2 is used only for domestic air-conditioning. In terms of automotive air-conditioning, it can be said that all major auto companies in the world have carried out the development of CO2 air-conditioners, and they have been able to work together through a special coordinating agency. The International Automotive Engineering Society has continuously issued relevant reports. The European Union is currently talking about standards for CO2 air-conditioning, and is preparing to convert all European air-conditioning systems to CO2 systems in 2008-2010. The R134a car air conditioner is only transitional. Once the time is right, the shift to the CO2 system is a foregone conclusion. This "opportunity" is not only technical, but also policy-oriented and commercial.

4. In addition to the development of refrigerants in thermoacoustic refrigeration, there have been many advances in new refrigeration theory and practice, such as the research and application of thermoacoustic refrigeration technology.

Thermoacoustic refrigeration is a new refrigeration technology developed since the 21st century. Compared with the traditional vapor compression refrigeration system, the thermoacoustic heat engine has unparalleled advantages: instead of using environmental refrigerants, it uses inert gas. Or its mixture as a working substance, it will not cause damage to the environment caused by the destruction of the used CFCS or HFCS ozone layer and the greenhouse effect; its basic mechanism is very simple and reliable, no expensive materials are needed, and there are great advantages in cost; they do not need to oscillate The piston and oil seal or lubricate, and the characteristics of no moving parts make its life greatly extended. Thermoacoustic refrigeration technology almost overcomes the shortcomings of traditional refrigeration systems and can be the development direction of the next generation of refrigeration technologies.

The working principle of all the thermoacoustic products is based on the so-called thermoacoustic effect. The thermoacoustic effect mechanism can be simply described as adding heat when the acoustic wave is dense, and when the acoustic wave is sparse, the acoustic wave is strengthened; if the acoustic wave is dense, the thermal energy is discharged. When the sound waves are in sparse, the sound waves are weakened.

Of course, the actual thermoacoustic theory is far more complicated than this. Of course, the design level and manufacturing process of thermoacoustic cooling are also constantly improving. At present, the U.S. has the largest investment in the field of sound, and has the largest number of research institutions, and has made many breakthroughs.

In the early 90's of the 1990's, Thermoacoustic Refrigerator was developed by Prof. Garrett of the US Naval Postgraduate School (NPS). Around 2000, a solar-powered thermoacoustic refrigerator was developed.