| REFRIGERANTS conditioning sector, who claim that the timeline of proposed reductions is practically impossible to meet. As reported8 recently by the UK Committee on Climate Change (CCC), following the UKs commitment to the 2008 Climate Change Act9 and the 2015 Paris Agreement,10 the UK government aims to reduce F-gas emissions to less than 3.4MtCO2e by 2035, from 11Mt in 2021, with most of the planned reduction coming from the UK F-gas regulation. UK F-gas emissions have fallen over the past few years, decreasing by 6% in 2021; however, emissions remain higher today than in the early 2000s, and only 26% lower than 1990 levels. The CCC has determined that the consumption of HFCs must decrease to 15% of 2015 levels by 2035 to meet the UK governments target. The UK F-gas regulation provides the mechanism to reduce this if, as CCC notes, it is successfully enforced. The CCC also recognises the risk that emissions may increase with the roll-out of heat pumps, which currently mostly use F-gas refrigerants, unless the UK government takes action to ensure that there is a shift to non-F-gas refrigerants (such as propane, R290 and CO2, R744). Although the UK government has committed to reviewing the UK implementation of the F-gas regulation, there is, as yet, no clear legislative timeline, and no indication as to whether it will follow the lead in the recent provisionally agreed changes to the EU F-gas regulation However, industry has not stood still. There has been a significant transition away from the use of R-410A (that was originally developed to displace the high-ODP refrigerants, such as the lower-pressure HCFC R22, chlorodifluoromethane) to HFC R32 and the HFO/HFC blends, such as R454B. The synthetic HFOs typically have a 100-year GWP of between just 1 and 4. R32 (difluoromethane) had a previously accepted GWP of 675, but this has recently risen to 771, while R454B has a GWP of 467 (see boxout, The changing GWP). One of the key goals is to produce refrigerants that have favourable thermodynamic properties, including relatively low saturated vapour pressures. Many very closely emulate the historically favoured refrigerant HCFC R22, as illustrated in Figure 1. Although these are all energy-efficient refrigerants, most have other less welcome attributes that are likely to limit their eventual application in building services. The recent report13 from UK government confirmed that there has already been a significant transition away from the use of R410A to R32 and HFO/HFC blends, noting 16,000 14,000 Saturated pressure, kPa CPD PROGRAMME 12,000 10,000 8,000 6,000 4,000 2,000 0 -5 5 15 25 35 45 55 Temperature, oC R290 (A3) R22 (A1) R454B (A2L) R410a (A1) R32 (A2L) R744 (A1) Figure 1: Comparative saturated vapour pressures for R22, R32, R410A, R290, R454B and R744 that R32 has proved to be an important alternative, with similar characteristics to R-410A, apart from it being a lower flammability refrigerant designated as A2L under BSI ISO 817.14 (R410A is designated as an A1, non-flammable refrigerant.) The F-gas regulation contains an upcoming ban on small split air-conditioning systems with less than 3kg charge using F-gases with a GWP of 750 or more, from 1 January 2025. Although the UK report indicates there is already some use of propane, it is very limited. However, there is a significant upturn in major manufacturers interest in natural refrigerants which includes propane, as well as CO2 and potentially ammonia (R717) for use in new air conditioners and heat pumps. This is motivated by the deleterious environmental impact of many synthetic refrigerants and the lower GWPs of propane and CO2 and, pragmatically, has been accelerated by regulatory requirements. As discussed more fully in the CIBSE Journal CPD Module 99 from December 2016, propane (as well as other HCs) typically exhibits low pressure drops and achieves system efficiencies that are equal to or exceed those of synthetic alternatives. The latent heat of vaporisation of propane is twice that of the most common HFC refrigerants, so providing a higher cooling/heating effect for the same refrigerant mass flow.15 Work by the Fraunhofer Institute and a group of manufacturers16 has determined that heat pumps are practically operable with a refrigerant charge of about 10g of propane per kW, as compared with about 100g of propane per kW required with typical designs. Systems are already evolving to reduce refrigerant use the example of the monobloc heat pump in Figure 2 has a 14.3kg charge to provide up to 195kW of heating and about a quarter of the refrigerant mass required for comparable R410A units. The thermodynamic qualities of propane enable operation at low evaporating temperatures and high condensing temperatures, allowing it to provide water temperatures beyond 65C (at sub-zero THE CHANGING GWP The recent IPCC Sixth Assessment report11 (AR6) includes the official GWP figures for R290. The 20-year GWP20 of 0.072 and the 100-year GWP100 of 0.02 are somewhat lower than the traditionally applied GWP of 3 that had been assumed. Previous estimations were related to the formula for propane (C3H8) that assumed the three carbon atoms would combine with oxygen (O2) in the atmosphere to produce three CO2 molecules, hence a GWP of 3. However, the much lower GWP now estimated by IPCC results from propanes short atmospheric lifetime, with a temperature dependent half-life of about 14 days, as it breaks down into carbonyl compounds (carbonyl compounds do not, in themselves, contribute any significant GWP). The decomposition of propane into carbon dioxide is a lengthy procedure and would take many weeks to complete,12 by which time most of the propane would have already broken down. In that same report, R32 had its GWP100 updated to 771 (from 675) by the IPCC. This will also make a small impact on the GWP of HFO/HFC blend refrigerants. 44 December 2023 www.cibsejournal.com CIBSE Dec 23 pp43-46 CPD Module 226 Swegon.indd 44 24/11/2023 16:12