Spring is here and you may need some coolness!

During the spring equinox, the sun is shining and the weather is warmer.

This week, the highest temperature in Beijing reached 20℃. Cold drinks such as ice cream and refrigeration equipment such as refrigerators and air conditioners have gradually entered our daily lives, and all of these are inseparable from the refrigerants that work silently behind the scenes.

Do you know the earliest refrigerator in the world? The bronze ice jar of the Warring States Period (Figure 1) is now in the collection of the National Museum of China. The "Zhou Li Ling Ren" records: "In spring, the jar is prepared. All the food and drinks are placed in the jar. All the wines and liquors are also placed in the jar. Sacrifices are shared with the ice jar." The ancients put wine in the jar and placed ice cubes in the space between the jar and the wall. In spring and summer, people could drink cool wine.

Figure 1 The world’s earliest refrigerator: a bronze ice jar from the Warring States Period [3]

1

What is refrigerant? What does it do?

Refrigerant (also known as refrigerant) is a substance used to absorb and transfer heat in a refrigeration cycle system.

In a typical vapor compression refrigeration cycle system (Figure 2), the refrigerant first absorbs heat in the evaporator (low-temperature zone) and then releases heat in the condenser (high-temperature zone). At the same time, the refrigerant is transferred from the evaporator to the condenser and transfers heat from the low-temperature zone to the high-temperature zone, thereby cooling the low-temperature zone.

In daily life, the high temperature zone and low temperature zone corresponding to the refrigerator (air conditioner) are the freezer/refrigerator (room) and the indoor environment (outdoor environment).

Figure 2 Schematic diagram of a vapor compression refrigeration cycle [1,2]

2

What types of refrigerants are there?

ASHRAE (American Society of Heating, Ventilation and Air-conditioning Engineers) Standard 34 lists more than 100 refrigerants, which can be classified according to different methods such as chemical composition, physical properties, application areas, and environmental friendliness. See Table 1 for details.

Table 1 Classification of refrigerants

The common classification method is to divide refrigerants into inorganic compounds, chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and hydrocarbons (HCs) based on their chemical composition. Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are commonly known as Freons (Figure 3).

Hydrochlorofluorocarbons (HCFCs) refrigerant R22

Hydrofluorocarbon (HFCs) refrigerant R32

Figure 3 Freon refrigerant products[4]

3

Why do we need refrigerants?

Refrigerants play an indispensable role in modern society (Figure 4), achieving temperature control by absorbing and releasing heat through refrigeration equipment represented by air conditioners, refrigerators, and chillers.

In daily life, the popularity of household air conditioners and refrigerators has improved people's quality of life and production efficiency. In the food storage and transportation industry, refrigeration and freezing technologies can maintain the freshness of food and extend the shelf life of goods. In the fields of healthcare and biochemistry, refrigerants are often used to ensure that the temperature for the storage and use of medicines, equipment and reagents is appropriate [5]. In ice and snow sports venues, the ice making and storage process cannot be separated from refrigerants.

Figure 4 Wide application of refrigerants

4

Does refrigerant have any harmful effects on human body and environment?

Some of the CFC refrigerants used in the early days were harmful to the environment, causing ozone layer depletion and global warming (Figure 5).

Therefore, the United Nations formulated the Montreal Protocol, and most countries, including my country, signed the protocol in August 1987 to gradually phase out and ban the use of CFC refrigerants. Specifically:

Chlorofluorocarbons (CFCs) damage the ozone layer , increase ultraviolet radiation, and affect ecosystems and global climate . They were listed as Class I controlled substances under the Montreal Protocol and were phased out and banned worldwide in 2010.

Hydrochlorofluorocarbons (HCFCs) are much less destructive to the ozone layer than chlorofluorocarbons (CFCs) and are currently the most important transitional substitute for the latter. Some of them are required to be phased out by 2020 or 2030 under the Montreal Protocol.

Hydrofluorocarbons (HFCs) do not destroy the ozone layer, but they have a great potential to cause global warming . The Montreal Protocol does not stipulate an expiration date for their use, and the Kyoto Protocol of the United Nations Framework Convention on Climate Change classifies them as greenhouse gases. In addition, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) may cause skin and respiratory symptoms due to their toxicity .

However, with the continuous development of new technologies and environmental awareness, these destructive refrigerants have gradually been replaced by new green refrigerants such as carbon dioxide and hydrocarbons (HCs), which are environmentally friendly, safe and healthy.

Professor Zhang Xinrong of Peking University used a carbon dioxide transcritical refrigeration system to develop the most environmentally friendly ice track in the history of the Winter Olympics[10], which was applied to the National Speed ​​Skating Oval “Ice Ribbon” (Figure 4d).

Figure 5 Ozone layer hole and global warming

5

What is the necessity of refrigerant recovery?

The use of refrigerants requires comprehensive consideration of many factors such as energy efficiency, environmental protection, safety, and cost.

In my country, refrigerants are the third largest source of non-CO2 greenhouse gas emissions after methane and nitrous oxide (Figure 6), with estimated annual emissions exceeding 500 million tons of CO2 equivalent, of which emissions from equipment use, maintenance and dismantling account for more than 90% of total emissions over its life cycle.

Refrigerant recycling can reduce atmospheric pollution, reduce the greenhouse effect, save costs and resources, and promote sustainable development.

However, at present, the annual recycling volume of refrigerants in my country is less than 3% of the annual usage, which is significantly lower than that in developed countries.

The main reasons for this problem include high recycling costs, lack of a refrigerant life cycle management system, and low environmental awareness among users and practitioners [13].

Figure 6: Percentage of non-CO2 greenhouse gas emissions in my country in 2014[14]

6

How is the development of domestic refrigerants?

In the past few decades, my country's refrigerant industry has developed rapidly and has been in a stage of rapid growth. In recent years, the supply and demand relationship of refrigerants has gradually reached a balance.

my country has become a major producer (Figure 7) and consumer of refrigerants, and has also introduced a series of environmental protection policies and regulations related to refrigerants (Table 2) to promote sustainable development.

For example, the Regulations on the Management of Substances that Deplete the Ozone Layer were promulgated in 2010 to restrict the use and production of CFCs and other ozone-depleting air pollutants.

At present, domestic refrigerants are gradually developing towards a more environmentally friendly, energy-saving, intelligent and sustainable direction.

Figure 7 my country’s R22 and R32 refrigerant production from 2016 to 2020[15]

Table 2 Refrigerant-related policies and regulations

7

How is the development of refrigerants internationally?

Internationally, refrigerants are developing towards green, environmentally friendly, energy-efficient, and keeping pace with the times, which is mainly reflected in the following aspects:

Increased use of green and environmentally friendly refrigerants : Early chlorofluorocarbon (CFCs) refrigerants have been eliminated or banned, and more and more countries and regions are using green and environmentally friendly refrigerants to meet environmental protection requirements and reduce greenhouse gas emissions.

Energy-saving optimization of refrigeration systems : Improving the energy efficiency of refrigeration systems and reducing energy consumption can meet increasingly stringent requirements for energy conservation and emission reduction.

Application expansion of multifunctional refrigerants : In addition to traditional fields such as air conditioners and refrigerators, refrigerants are increasingly widely used in healthcare, life sciences, industrial manufacturing and other fields.

Development of refrigerant recovery and regeneration technology : Refrigerant recovery and regeneration technology has received more attention[16], and countries and regions such as Japan have even formulated mandatory regulations and policies.

Figure 8 Refrigerant recycling in various fields in Japan from 2003 to 2018 [16]

References:

[1] Wang Ruzhu, Ding Guoliang, Wu Jingyi, et al. Refrigeration Principles and Technology[M]. Beijing: Science Press, 2003.

[2] Shi Wenxing, Wang Baolong, Shao Shuangquan. Design of small air conditioning heat pump device[M]. Beijing: China Architecture & Building Press, 2013.

[3] Bronze Ice Mirror [EB/OL]. National Museum of China, [2023-03-14]. https://www.chnmuseum.cn/zp/zpml/kgdjp/202008/t20200824_247219.shtml.

[4] Refrigerant [EB/OL]. Shandong Huaan New Materials Co., Ltd., [2023-03-15]. http://www.sdhazl.com/cn/cold.html.

[5] Liu Jing. Principles of Cryogenic Biomedical Engineering[M]. Beijing: Science Press, 2007.

[6] Midea Refrigerator[EB/OL]. [2023-03-14]. https://www.midea.cn/1/1000000000400692349799.html.

[7] Helping export hairy crabs to Singapore, allowing “Chinese fresh produce” to go abroad [EB/OL]. [2023-03-15]. https://intl-img.sf-express.com/zh/xwgg/20171103/838.html.

[8] Cryopreservation: Applications and Advances[EB/OL]. Cell Science from Technology Networks, [2023-03-15].http://www.technologynetworks.com/cell-science/articles/cryopreservation-applications-and-advances-349021.

[9] The National Speed ​​Skating Oval "Ice Ribbon" successfully completed its first ice making[EB/OL]. Xinhuanet, [2023-03-15]. http://www.xinhuanet.com/politics/2021-01/22/c_1127015176.htm.

[10] Winter Olympics Dialogue | Interview with Zhang Xinrong from Peking University School of Engineering: Developing the most environmentally friendly ice and snow track in the history of the Winter Olympics [EB/OL]. Peking University, [2023-03-15]. https://www.coe.pku.edu.cn/newsfocus/topic/11285.html.

[11] GRAY E. NASA Reports Arctic Ozone Hit Record Low in March[EB/OL]. NASA, 2020-04-15.(2020-04-15)[2023-03-15] .http://www.nasa.gov/feature/goddard/2020/nasa-reports-arctic-stratospheric-ozone-depletion-hit-record-low-in-march.

[12] Past eight years confirmed to be the eight warmest on record[EB/OL]. World Meteorological Organization, 2023-01-11.(2023-01-11)[2023-03-15].https://public.wmo.int/en/media/press-release/past-eight-years-confirmed-be-eight-warmest-record.

[13] Tang Junjie, member of the National Committee of the Chinese People's Political Consultative Conference: Strengthening refrigerant recycling [EB/OL]. 2023 National Two Sessions, [2023-03-07]. https://www.spb.gov.cn/gjyzj/2022lhjytap/202303/320e80e1a6db4c62ba9de23762c7d39c.shtml.

[14] Tsinghua University Institute of Climate Change and Sustainable Development Project Comprehensive Report Writing Group. Comprehensive Report on Research on China's Long-term Low-carbon Development Strategy and Transformation Path[J]. Chinese Population, Resources and Environment, 2020, 30(11): 1–25.

[15] Gao Enyuan, Han Meishun. Analysis of China's refrigerant product market in 2020[J]. Refrigeration Technology, 2021, 41(S1): 51–59.

[16] Gao Huan, Gu Xin, Ding Guoliang. Analysis of the current status of refrigerant recovery and regeneration[J]. Journal of Refrigeration, 2021, 42(5): 17–26.

END

Source: Beijing Society of Refrigeration

Contributor: Zhang Xuan, Associate Professor, School of Mechanical and Vehicle Engineering, Beijing Institute of Technology

Selected for the Beijing Association for Science and Technology's 2023-2025 Youth Talent Support Project

Editor: Guru