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PAU Series

2-2. Refrigerant

This section describes the role and type of refrigerant used in the refrigeration cycle.

(1) What is a refrigerant?

To put it simply, a refrigerant plays the role of a heat carrier. Using the refrigeration cycle, the refrigerant which played an important role in the section “2.1 Refrigeration Cycle”, can be used to transfer heat from a low temperature to a high temperature location.

(2) Type of refrigerant

Ammonia, carbon dioxide, fluorocarbons, etc., are used as refrigerants, but fluorocarbons are the most commonly used refrigerants in air conditioning equipment and industrial cooling systems.
The invention of chlorofluorocarbons (fluorocarbons) as refrigerants has led to the dramatic development of refrigeration technology. Fluorocarbons transfer heat efficiently and are non-toxic and odorless. Their use as refrigerants in cooling equipment has spread rapidly because they are non-flammable, non-explosive, non-ignitable (except for some), and chemically stable without being corrosive.
However, it was found that the chlorine in chlorofluorocarbon-based refrigerants such as CFC (specific fluorocarbons) and HCFC (alternative fluorocarbons) has reached the stratosphere of the earth, destroying the ozone layer which prevents the transmission of ultraviolet rays into the atmosphere. As a result, their manufacture and use were completely prohibited (in 1995). Subsequently, the increasing use of HFCs (new alternative substances) as alternative refrigerants is being reviewed as they were also found to have an impact on global warming. Currently, research and development of substances to replace chlorofluorocarbon-based refrigerants is being carried out in the field of refrigeration technology. Among these are substances such as isobutane and carbon dioxide (CO2), etc., which are natural refrigerants attracting much attention because they exist naturally in nature.

Classification Refrigerant number Ozone layer destruction coefficient
(ODP)
Global warming potential
(GWP) *
Remarks
CFC R12 1 10900 Production stopped in 1996
HCFC R22 0.055 1810 Production scheduled to stop in 2020
Currently, the production volume is under control
HFC R134a 0 1430  
R32 0 675  
HFC
Mixing
R407C 0 1770  
R410A 0 2090  
HFO R1234yf 0 <1 With a low global warming coefficient, it is now commonly used as a substitute for fluorocarbons.
Minor combustibility
Natural refrigerant R717
(ammonia)
0 1 Has an odor and is toxic.
R744
(Carbon dioxide)
0 1  

*100-year integral value assuming a base of 1.0 for CO2 (IPCC 4th Report)

(3) Environmental impact of fluorocarbons

(1) Ozone depletion

In the mid-1970s, it was pointed out that chlorofluorocarbons (CFC), which are artificially produced substances, could destroy the ozone layer. Many of the fluorocarbons which were once used in air conditioners, refrigerators, sprays, etc., were released into the atmosphere in large quantities. As fluorocarbons possess properties that make it difficult for them to decompose near the ground, they reach the stratosphere due to atmospheric flow. When transported to the stratosphere at an altitude close to 40 km, fluorocarbons are decomposed by strong solar ultraviolet rays to produce chlorine. This chlorine works as a catalyst to break down ozone one by one. Besides fluorocarbons, there are several other substances that destroy the ozone layer, one of which is bromine released by halon and other substances which are used as fire extinguishing agents.

(2) Global warming

Carbon dioxide and other greenhouse gases contained in the atmosphere possess the property to accumulate heat radiating from the earth's surface, such as the oceans and continents etc., into the atmosphere and return it to the earth's surface again (greenhouse effect).
Since the start of the Industrial Revolution in the mid-18th century, the concentration of greenhouse gases in the atmosphere has increased rapidly due to the mass consumption of coal, oil and other fossil fuels by industrial activities, release of large amounts of carbon dioxide into the atmosphere due to the mass production of cement etc., and a decline in forested areas, which serve to absorb carbon dioxide in the atmosphere. The rapid increase in greenhouse gases has enhanced the greenhouse effect of the atmosphere and increased the absorption of heat in the atmosphere, resulting in a rise in the air temperature since the mid-20th century.
This is believed to be the cause of global warming.
The main greenhouse gases are carbon dioxide, methane, nitrogen oxide, and freon gases.

Carbon dioxide is a greenhouse gas that has the largest impact on global warming. Methane is a greenhouse gas that has the second largest impact on global warming after carbon dioxide. Methane is generated when withered plants decompose in wetlands, ponds, and paddy fields. In addition, it is also generated when natural gas is mined.
Although the absolute amount of fluorocarbons is small, the global warming coefficient is very high. The impact exerted by the specific fluorocarbon R-12 is more than 10,000 times that of carbon dioxide, resulting in a huge impact despite the amount being small.
As global warming progresses, glaciers will melt, sea level will rise, and submerged areas will increase, resulting in abnormal weather on a global scale such as El Niño, droughts, heavy rains, heat waves, cyclones and so on.

 

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