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Focusing on R744 ; the use of carbon dioxide as refrigerant was first suggested by Alexander Twinning in a British patent in 1850 . It was then first applied in the manufacturing of ice in the US when Thaddeus Lowe modified hydrogen pumps to compress CO2 in 1866 . In Europe , Carl von Linde built the first CO2 compressor in 1882 .
CO2 had its peak of use in the middle of the 1920s after it was successfully used to freeze meat on long shipping routes , for the first time by J & E Hall on a trip from the Falkland Islands to the UK in 1886 . J & E Hall further developed a two-stage CO2 compressor and later supplied refrigeration equipment to the National Skating Palace .
In the first half of the 20th century , CO2 was increasingly replaced with more efficient ammonia systems . Air cooled condensers required higher temperatures to a CO2 system and complicated subcritical operation . With the development of CFCs and their use in all refrigeration and air conditioning sub-sectors , the use of CO2 decreased more and more until it ended in the early 1960s .
CO2 as refrigerant experienced a revival in the 1990s because of its low environmental impact when used as refrigerant and its favourable properties regarding a variety of applications . CO2 has particularly good performances for low-temperature applications , e . g . in freezer plants . It has high heat transfer rates and can therefore provide rapid cooling .
The first modern CO2 system was developed in Scotland , where a small ammonia plant was used to condense CO2 , which then circulated as a secondary refrigerant in a thermo-siphon system without a compressor . It is now being used in low-temperature applications , heat pumps for heating water and has gained some traction in the motor industry .
The chemical properties of CO2 refrigerant are : |
Symbol : |
R744 ( degree of purity : 4.5 » ≥99.995 |
purity ) |
Aggregation state : |
Gaseous ( 1,013.25 hPa , 20 ° C ) |
Colour : |
Colourless |
Smell : |
Odourless |
Flammability : |
Non-flammable gas or solid |
Toxicity : |
Non-toxic |
The physical properties of CO2 : |
Melting point : |
-56.67 ° C at 5.185 bar / 518.5 kPa |
Boiling point : |
None at normal pressure 1,013.25 hPa |
Gas density : |
1.9767 kg / m ³ ( 0 ° C , 1,013.25 hPa ); 1.8474 |
kg / m ³ ( 15 ° C , 100 kPa ) |
Relative gas |
1.5289 ( ratio of dry air ) |
density : |
Critical point : |
31.0 ° C and 7,383 kPa |
Triple point : |
-56.67 ° C and 518.5 kPa |
Sublimation : |
-78.5 ° C at 101.325 kPa |
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RACA Journal I April 2025 www . refrigerationandaircon . co . za