Why is the "Ice Ribbon", the world's first Winter Olympics venue to use carbon dioxide refrigeration, so "silky"?

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Written by reporter Wang Xueying Edited by Ding Lin

New Media Editor/Song Meng

Scientific review:

Yang Yongan (Professor of Refrigeration and Air-conditioning Engineering Department, Tianjin Commercial University)

With the strong sprint of Dutch athlete Neus on February 8, the 20-year-old Olympic record in men's 1500-meter speed skating was broken. At the same time, the "Ice Ribbon" also continued its "record" of setting new Olympic records for many consecutive days.

▲On February 8, the men's 1500m speed skating final of the Beijing 2022 Winter Olympics was held at the National Speed ​​Skating Oval "Ice Ribbon". Dutch athlete Kai Nuis was in the competition. (Photo by Xinhua News Agency reporter Xue Yuge)

In addition to the outstanding performance of the athletes themselves, the National Speed ​​Skating Oval "Ice Ribbon" competition venue also played an important role in breaking Olympic records so frequently.

Have you ever wondered why the "Ice Ribbon" is so "smooth"? What are its unique features that are worth praising? Let's find the answers together in the following.

The National Speed ​​Skating Oval, known as the "Ice Ribbon", is a landmark venue for the 2022 Winter Olympics in Beijing. The "Ice Ribbon" has set many records. It is not only the largest all-ice surface design in Asia (with an ice surface area of ​​up to 12,000 square meters), but also the world's first Winter Olympic venue to use "CO2 transcritical direct evaporation refrigeration technology".

As a distinctive "Chinese solution" during the 2022 Winter Olympics, carbon dioxide transcritical direct cooling ice-making technology is regarded as one of the most advanced, environmentally friendly and efficient ice-making technologies. So, what is so powerful about this technology?

In fact, the principle of carbon dioxide refrigeration is similar to the refrigerant cycle in ordinary air conditioners: carbon dioxide is a gas at normal temperature and pressure, but after applying a certain high pressure, carbon dioxide will become a fluid in a critical state; these fluids are then sent to the areas that need to be refrigerated, and will absorb a lot of heat during their evaporation process, thereby achieving the purpose of cooling.

"The most critical feature of this technology is its atmosphere-friendliness and the fact that it will not cause ozone layer depletion. It will make a very great contribution to carbon peak and carbon neutrality," explained Yang Yongan, professor at the Department of Refrigeration and Air-conditioning Engineering at Tianjin University of Commerce.

For a long time, refrigerator manufacturers or winter sports venues have used Freon compounds as the main refrigerant. However, since 1971, as the scientific community gradually improved its understanding of Freon, people finally realized that Freon substances can cause environmental hazards such as ozone layer destruction and greenhouse effect. In contrast, carbon dioxide refrigerant, as a natural refrigerant, appears to be both environmentally friendly and safe.

Although carbon dioxide is a greenhouse gas, its greenhouse effect is much lower than that of the synthetic refrigerants such as Freon used in traditional refrigeration systems. For example, the R134a refrigerant commonly used in car air conditioning systems has a global greenhouse effect potential (GWP) of up to 1300, which is 1300 times that of carbon dioxide refrigerant (GWP value is 1).

Moreover, CO2 refrigeration is more energy efficient than traditional refrigeration systems. Yang Yongan pointed out that CO2 has excellent thermodynamic properties: "When the system is designed properly, its efficiency is close to that of conventional systems, and the system is compact and the size of the unit is small... The flow resistance (in the pipeline) is very small, so when it is used, the power of the working fluid pump is small and the pressure loss in the evaporator is also small." Therefore, CO2 refrigeration technology is more in line with the "green, energy-saving and environmentally friendly" concept of the Beijing Winter Olympics.

In addition to being more environmentally friendly, carbon dioxide as a refrigerant also has the advantages of being odorless, non-flammable, and non-combustible. It is safer than flammable refrigerants such as alkanes.

It is reported that in order to better utilize the advantages of direct cooling of carbon dioxide to make ice, the "Ice Ribbon" is equipped with an advanced intelligent energy management system, which can efficiently recover the waste heat generated by the refrigeration system and provide nearly 70°C hot water for scenarios such as venue dehumidification, ice surface maintenance and watering, and athletes' daily needs.

When the entire ice surface is in operation, the "Ice Ribbon" can save more than 2 million kWh of electricity per year in the refrigeration process alone, which is equivalent to the monthly electricity consumption of more than 6,000 households in Beijing. Since carbon emissions are close to zero during the entire refrigeration process, this is comparable to the carbon reduction achieved by planting more than 1.2 million trees.

As the speed skating venue for this Winter Olympics, the "Ice Ribbon" has extremely high requirements for the quality of the ice surface. Uneven ice temperature will cause the ice surface to be soft in some places and too hard in others. For speed skaters, too soft ice will slow down the speed, while too hard ice may make it difficult to stand on the ice, affecting the performance of the skaters.

Traditional ice rinks usually use indirect cooling methods (such as using Freon refrigerants or ethylene glycol coolants). However, since the coolants often do not release heat at a fixed temperature, the temperature difference of the ice in such ice rinks is generally as high as 1.5℃-2℃.

In contrast, the "Ice Ribbon" uses a carbon dioxide direct cooling ice-making system, which not only has a higher heat exchange efficiency, but also has a uniform ice temperature. The temperature difference on the ice surface can basically be controlled within 0.5°C, which helps to create the "fastest ice" for top events.

(This content is jointly produced by Beijing Science and Technology News and China Digital Science and Technology Museum)

Produced by: Science Central Kitchen

Produced by: Beijing Science and Technology News | Beijing Science and Technology Media

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