ACR Journal

CMYK / .ai CMYK / .ai CMYK / .ai acrjournal.uk 21 REFRIGERANTS • It is non-toxic and non-flammable with an A1 safety classification • It is heavier than air • It has high volumetric refrigeration capacity (around 6 x that of R404a) which means smaller compressors, components, pipework etc. • Typically pressure drops in liquid and suction lines are small • There is good heat recovery potential A key operating difference between CO 2 and other refrigerants is the low critical and high triple points. These can both occur in normal ambient conditions and as such must be considered in system operation. The high triple point puts a limit on how low the systems can evaporate. Also, as it occurs above atmospheric pressure, then it must be considered in refrigerant handling. The low critical point means at “condensing” or gas cooler outlet temperatures above this point we cannot condense the fluid back into a liquid. With other refrigerants these points are further apart and as such do not occur in what could be normal operating conditions, so CO 2 is unique in this respect. The first two tables above detail how CO 2 compares with some other commonly used refrigerants in terms of triple and critical points: The most widely adopted CO 2 refrigeration technology, particularly in the UK, is called transcritical. This name Refrigerant R744 R404A R134a Critical Point 31.1 o C/72.8 Bar 72 o C/34.7 Bar 101 o C/40.70 Bar Triple Point -56.6 o C/5.2 Bar -100 o C/0.03 Bar -103 o C/0.004 bar Refrigerant designation R404A R134a R513A R1234ze R290 R290 R717 R744 Family HFC HFC HFO blend HFO HFO blend HC Natural Natural Safety A1 A1 A1 A2L A1 A3 B2L A1 GWP 3922 1300 573 7 1273 3 0 1 Application MT/LT MT MT MT MT/LT MT/LT MT/LT MT/LT Temp. Gl. de 0 0 0 0 6,2 0 0 0 Region Number of Transcritical CO 2 Installations in 2008 Number of Transcritical CO 2 Installations in 2018 Number of Transcritical CO 2 Installations in 2020 Growth in % (2018 - 2020) Europe 140 >16,000 29,000 81% Canada >370 650 76% Japan >245 340 39% Australia >40 100 150% New Zealand >40 100 150% South Africa >110 >220 100% refers to the fact that when operating above the critical point we can no longer condense the refrigerant. At condensing temperatures below the critical point we operate “sub critically” which is similar operation to HFC systems. However, as transcritical operation can occur, system design and operation must cater for this. The table above details how uptake grew up to 2020, as detailed in Shecco’s World Guide to Transcritical CO2 Refrigeration Pt2: As mentioned previously, a major consideration for CO 2 refrigeration is the design and operating pressures of the system, which falls under the Pressure Equipment (Safety) Regulations (previously the EU's PED). Again, this can vary depending on application and manufacturer but we are starting to see some standardisation around design pressures and in the main these are at the higher end of the potential options to offer the greatest system resilience. Componentry to support these pressures is now readily available and Beijer Ref wholesalers Dean & Wood, RW, HRP and DWG are major suppliers to the market. In addition, our new Beijer Ref Academy in Yorkshire can equip engineers with the most up-to-date training available. Our hands-on courses have been constructed by engineers for engineers, with CO 2 and A2L packaged condensing units fully operational. One-day courses include CO 2 Introduction & Safe Handling (including install & commissioning SCM Booster Pack) and CO 2 Installation & Commissioning (Condensing Units). For more information, visit: https://www.beijerrefacademy.co.uk/