China uses a large amount of copper, but the pricing power of copper is not only in the hands of foreign companies, but also the price increases every year, and the price will hit a new high in 2024. It is estimated that copper prices are likely to exceed 90,000 yuan or even 100,000 yuan per tonne. In the face of cost pressure, many industries are eager to achieve "copper substitution", such as cables, conductive bars, batteries, photovoltaics, magnet wires, etc. As a large copper user in the home appliance industry, the air conditioning industry has had such an idea since it first felt the industrial chain crisis brought about by the rise in copper prices. About 20 years ago, many domestic air conditioning brands chose to try "aluminum instead of copper".
Continuously deepen the research and expand the application of "aluminum application" technology
The "copper substitution" of the air conditioning industry is mainly aluminum, and many other industries also choose to replace it with aluminum, and some industries choose stainless steel with larger application volume and lower price because of product needs. For example, aluminum wire cables, aluminum wire motors, stainless steel valves, etc., the aluminum application of some products has even been developed for more than 10 years.
20 years ago, China's air-conditioning industry was still growing, and there was a lack of solid technical reserves and solid experimental verification for the application of aluminum in air-conditioning products, especially the lack of research on the reliability of individual enterprises.
In fact, air-conditioning companies have not given up the research of "aluminum application" technology, and have always firmly believed that this is a major trend in materials and processing technology. Because copper is a strategic resource, China's reserves are not abundant, and the key pricing power is in the hands of foreign companies, and the trend of copper price increases is becoming more and more intense, and the price is hitting a new high every year, which directly threatens the safety of the industrial chain and the stability of product prices.
Although the price of aluminum is also rising this year, there is still a price difference of four or five times compared with copper, and 70% of the world's aluminum ore storage belongs to China, which controls the pricing power. At the same time, aluminum is very close to copper in terms of performance, and has the advantages of lightweight, easy recycling, and low transportation costs, so from the national level, the application of aluminum has great advantages for the safety of the industrial chain, the ecological health of the industry, and the stability of product prices.
In fact, the "copper substitution" technology has made great progress in the home appliance and automotive industries, and has entered large-scale application. In the refrigerator industry, for example, almost 100% of aluminum heat exchangers are already used; In the automotive air conditioner, the all-aluminum micro-channel heat exchanger has also been 100% realized; In the valve parts, stainless steel has become the mainstream; Even on the car charging harness, an aluminium conductor scheme is used. Not long ago, Xiaomi SU7, which was frequently searched, used aluminum wire charging harness, and it was also mentioned in the official response of Xiaomi Auto that most new energy vehicle OEMs use aluminum conductor solutions. It can be said that in terms of "copper substitution" technology, all products that use copper are actively developing this technology, and aluminum and stainless steel are two important alternative materials.
In the air conditioning industry, many foreign companies using "copper substitution" technology products have begun large-scale production, Japan's Daikin, Hitachi, Mitsubishi, South Korea's LG, Samsung, the United States Reynolds, Trane, Carrier and other air conditioning companies in recent years have launched all-aluminum heat exchanger air conditioning indoor and outdoor units.
In the process of aluminum application in the domestic air conditioning industry, although it is difficult, relevant parties are also making efforts. For example, in December 2021, the China Household Electrical Appliances Research Institute established a research working group on aluminum application in the air-conditioning industry and issued an initiative: actively carry out technical research on the application of aluminum in air-conditioning products, actively adopt climate-friendly refrigerants, and continue to promote the development of energy-saving technology for air-conditioning. In March 2023, the working group released the first White Paper on Aluminum Application in the Air Conditioning Industry. In July 2023, the group standard "Test Method for Corrosion Resistance of Aluminum Heat Exchangers for Room Air Conditioners" led by the China Household Electrical Appliances Research Institute was officially released. On July 3, 2024, the 8th "Aluminum Application Research Seminar in the Air Conditioning Industry" will be held at the China International Aluminum Industry Exhibition.
There are abundant solutions, but there are still technical difficulties to be solved
In the air conditioning industry, the most popular technical research on "aluminum applications" mainly refers to the partial or full aluminum of heat exchangers. The technical difficulty of "aluminum application" of the connecting pipe of the internal and external units of the air conditioner is not large, and the industry has already had a solution; The application of stainless steel valves has also been widely promoted; The heat exchanger is the most important component of the air conditioner, which has a great impact on the performance of the whole machine, and the aluminum heat exchanger, especially the all-aluminum heat exchanger, is the main research and popularization direction of the industry. It is worth mentioning that aluminum foil is currently the largest type of aluminum used in air conditioning.
At present, all-aluminum heat exchangers are mainly divided into aluminum tube-fin heat exchangers and microchannel heat exchangers. For all-aluminum heat exchangers, because of the problem of impurities in aluminum materials, the most prominent reliability interference factor is corrosion, mainly pitting corrosion and electrochemical corrosion. In response to this problem, air-conditioning enterprises adopt the isolation of copper and aluminum heat exchanger production lines when building production lines, and carry out dust-proof treatment; In the production, the processing equipment related to the aluminum heat exchanger should be made of aluminum as much as possible to reduce the contact of copper and iron and other elements, reduce the cross-bending, tee design, etc., and do not use cleaning agents with chlorine elements.
In addition, the frosting and defrosting problems during the heating of aluminum heat exchangers are also a major problem faced by the air conditioning industry in the past. At present, the company has improved the drainage effect by using elliptical tube fin microchannel heat exchangers, vertical fin microchannel heat exchangers, hydrophilic aluminum foil, etc.
The vertical fin microchannel heat exchanger replaces five rows of 7mm copper tube aluminum fins with a single row of 32mm flat tubes, which is very efficient in heat transfer, which can solve the problem of insufficient heating performance of the all-aluminum heat exchanger, and at the same time, the refrigerant filling capacity can be reduced by 20%~30%. In addition, the vertical finned microchannel heat exchanger does not need to be tilted and the flat tube is in a horizontal position to solve the problem of condensation and frost drainage.
The above are only some of the solutions for the current all-aluminum heat exchanger for air conditioners, and not all. But this is enough to show that compared with 20 years ago, the aluminum application research of Chinese air-conditioning enterprises has been rich enough, and the large-scale production of all-aluminum heat exchanger household split air conditioners can be realized soon.
However, the obstacles to the large-scale application of all-aluminum heat exchanger household split air conditioners still exist, and four technical points need to be solved urgently. First, the aluminum forging industry needs to increase the content of pure aluminum in aluminum ingots, and high-purity aluminum can improve the mechanical properties and corrosion resistance of aluminum alloys. Second, the aluminum heat exchanger has good corrosion resistance to anthills, but its pitting corrosion, intergranular corrosion, electrochemical corrosion and other problems are more prominent. Third, the automatic brazing equipment of aluminum tube heat exchanger, as well as the automatic assembly equipment of micro-channel heat exchanger, are still in their infancy in China, and require the participation and investment of all walks of life. Fourth, the industry's demand for aluminum rods, aluminum foil and other products continues to rise, aluminum processing costs are fluctuating upward, once large-scale application, how to stabilize the balance of supply and demand will become a new topic.
The most important thing is that the impact of the "black heart tube" incident in the air conditioning industry 20 years ago on today's consumers' acceptance of "aluminum application" technology is still a problem for the industry to consider. In this regard, a person in charge of the enterprise said: "20 years ago, China's air conditioning industry once promoted the simple judgment method of 'who has the most important air conditioner and whose quality is good'. This was not a problem at the time, but now to promote the 'application of aluminum', how to make consumers accept the change that 'air conditioning can not only look at the material and weight', enterprises and industries should fully consider and do a good job in guiding the work when doing product promotion. ”
The development of the industry should not fall into the entanglement of "aluminum instead of copper", because no matter the use of copper and aluminum, the ultimate goal is to present consumers with better products, and the use of copper and aluminum is the technical direction that can coexist.
Time has passed, and the first year of aluminum application may be today. At the "7th Aluminum Application Research Seminar in the Air Conditioning Industry" held in Wuhan in 2023, Minister Li Feng of Midea Building Technology introduced: "Midea Building Technology began to study aluminum heat exchangers in 2012 and began to be applied in batches in 2017. Since 2017, we have been researching microchannel heat exchangers, and in 2020, we have begun to apply them to the North American roof machine series, mainly indoor and single-cooling outdoor units. "Not only Midea buildings, but also major air-conditioning companies, including Hisense, Haier, and TCL, have already begun to have technical reserves and applied them to export machines. 2024 is likely to be the first year of aluminum application, and more companies will open the application of all-aluminum heat exchangers.
(This article was first published in "Electrical Appliances" magazine, the author is Su Liang)