Key technical characteristics of CO2 — Refrigerant R744
Key technical characteristics of CO2 that are relevant to its application as a refrigerant include:
- CO2 systems have high operating pressures, even higher than R410a, and need to be designed to suit.
- CO2 has low toxicity and as is in fact part of respiration process. Even so, care must be taken to ensure that CO2 levels do not rise in occupied spaces
- CO2 is heavier than air, as with fluorocarbons, and therefore tends to accumulate in low-lying areas.
- Copper pipe-work suitable for most commercial CO2 applications. Generally high-wall thickness copper as used for R410a is well suited to CO2.
- Oil solubility in CO2 is good, and hence direct expansion (DX) applications are easy
- CO2 has a low critical temperature, unlike any other know refrigerant. This implies that in many applications CO2 refrigeration systems operate in the so-called «trans-critical» area, which has both benefits and challenges.
- At pressures below 520 kPa, liquid CO2 cannot exist and solid dry ice is formed. This creates specific handling issues relating to servicing procedures (charging) and the design and location of safety relief valves.
- CO2 is well suited as a low temperature refrigerant, both for industrial freezing applications and for commercial freezer display cases.
- CO2 is also a uniquely well suited gas for heat pump applications
- CO2 can replace HFCs in a cascade in combination with any high stage refrigerant or as CO2-only system.
- Immediate highly feasible applications include:
- Cold storage, small and large scale
- All supermarket refrigeration systems
- Blast, spiral and plate freezers
- Industrial, commercial and domestic heat pumps
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