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REAL Alternatives Module 2 Design Differences for Alternative Refrigerants | 6 1. R744 (Carbon dioxide) The properties of R744 effect how the refrigerant is applied: See REAL Alternatives Guide 1, figure 2 Type Key facts GWP2 Sat temp3 Typical applications R744 Carbon dioxide, CO2 High pressures 1 ‐78OC Retail refrigeration, heat pumps, integrals All components must be suitable for a high pressure rating because of the high maximum operating and standstill pressures of R744; R744 has a lower practical limit than most HFCs because of its low toxicity. (Refer to Module 2 for more details on fixed leak detection); See REAL Alternatives Guide 2 The practical limit for a refrigerant represents the highest concentration level in an occupied space that will not result in escape impairing effects for the individual. For full information see the Safety Standard EN378‐1, F 3; R744 is an asphyxiant and a fixed leak detection system should be fitted if a leak in an enclosed occupied space such as a cold room, or in plant areas, could result in a concentration which will result in escape impairing effects. It is recommended that the alarm level is set at 50% Acute Toxicity Exposure Limit (ATEL) or Oxygen Deprivation Limit (ODL) as specified in EN378 for machinery rooms. This is the level above which there is an adverse effect that results either from a single or multiple exposures in a short space of time (usually less than 24 hours). For R744 the ATEL / ODL is 0.036 kg/m3, so the alarm should be set at 0.018m3 (approximately 20,000 ppm). Typically there will also be a pre alarm at 5,000 ppm because of the rapid rise in concentration in the event of a leak due to the high pressures of R744; Compressor displacement and pipe diameters are smaller because of the high cooling capacity of R744 compared to other refrigerants. For example the compressors displacement is approximately 1/5th of that needed for R404A; some examples of R733 systems The low critical temperature of R744 results in differences in overall system design. R744 is used in the following types of system: 2 GWP is from F Gas Regulation EU 517:2014 3 Sat temp is the saturation temperature at atmospheric pressure (1 bar g), except for R744 where it is the surface temperature of solid R744 at atmospheric pressurePDF Image | Alternative Refrigerants
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