Refrigerant CO2 conquering the market
CO2 rediscovered
Because of its low greenhouse potential in comparison to artificially manufactured refrigerants, CO2 is considered to be extremely environmentally friendly. Carbon dioxide has been used as a refrigerant since 1850 and has a long tradition in refrigeration engineering. An increasing awareness for the environment – and associated with this, conservation of natural resources and protection of natural habitats – has seen a rediscovery of the positive properties of "natural refrigerants": Consequently, the extensive benefits of CO2 in system operation have also been rediscovered.
Cost savings in procurement and disposal
In terms of volume, smaller refrigeration system components can be used in CO2 systems. These components have a low procurement price and are readily available on the market. As a natural refrigerant, CO2 is environmentally compatible and, because of this, disposal and recovery measures are not legally stipulated.
Improved system efficiency with CO2
CO2 has very positive properties for refrigeration engineering that can be used optimally to improve the efficiency of refrigeration systems:
- High volumetric flow-related cooling power (5 to 7 times higher than ammonia) and, consequently, smaller compressor capacities and piping diameters
- High theoretical coefficient of performance (COP) at condensing temperatures below the critical temperature of CO2
- Low viscosity and, because of this, low pressure losses that result in only small temperature losses in the heat exchanger
- Low pressure ratios between the refrigeration system's low and high pressure stages, which results in very high compressor efficiency levels
- High heat transfer coefficient during evaporation and condensation (up to 60% better than with HFC)
- Good material compatibility with conventional materials and refrigerator oils
Some important properties of CO2:
Environmental compatibility and physical properties:
- Very low global warming potential (GWP = 1)
- No ozone depletion potential (ODP)
- Environmentally compatible and safe
- Non-toxic in small concentrations
- Non-flammable (CO2 is used as a fire extinguishing agent)
- Heavier than air
- Triple-point at 5.18 bar and -56.6°C
- Low critical temperature at 31.05°C
Historical overview
| 1866/69 | Used as dry ice |
| 1877 | Liquefaction of CO2 and initial uses as a technical gas |
| 1881/90 | Design and construction of the first refrigeration systems with CO2 |
| 1887- 1890 | Increased development of refrigeration machines, especially in the UK and the USA |
| 1895 | First steam table from MOLLIER |
| 1904 | First pressure-enthalpy diagram from MOLLIER |
| 1929 | Detailed p,h diagram with solid phase: PLANK, KUPRIANOFF |
| 1932 | Cascade systems NH3-CO2 for temperatures to -50°C |
| 1950 | 60% of all ship refrigeration systems with CO2 and 10% of small and large refrigeration systems |
| 1960- 1965 | Strong decline in the use of CO2 |
| 1989- 1993 | Rediscovery and initial proposals for system designs |
