Although R22 will be banned from use servicing existing equipment in Europe on January 1, and is on an accelerated phase-out in the rest of the world, it is still one of the most widely used refrigerants.
Lower GWP refrigerants are available but most struggle to match the efficiency of R22 in unitary air conditioning systems for the wide range of evaporation temperatures from -40°C to +10°C. Its thermodynamic properties also provide high performance at high ambient temperatures in excess of 40°C.
There are concerns over the contribution that the relatively high GWP of R410A might make to global warming if developing countries follow the developed countries in switching from R22 to this refrigerant. In addition, R410A is not very efficient in high ambients in countries like India where maximum daily temperatures often exceed 40ºC and demand for unitary ac is expected to increase eight-fold by 2030.
Even in Europe, the agreed phase-down of HFCs by CO2e will put increasing pressure on R410A. Daikin and other major air conditioning manufacturers have already begun introducing R32 in smaller split systems and in China some manufacturers are switching to propane.
According to a new report for the European Commission by the leading German environmental research consultancy Öko-Recherche, the switch to propane, R32 or R32/HFO blends could have a dramatic impact on efforts to reduce global warming.
Öko-Recherche is a Frankfurt-based independent environmental research institution and consultancy and is best known for producing the 2011 F-gas review report for the European Commission which formed the basis of the changes now being introduced on January 1.
This new report for the European Commission – Alternatives to HCFCs/HFCs in unitary air conditioning equipment at high ambient temperatures – maintains that if by 2030 60% of the developing countries’ demand for an alternative for R22 in unitary air conditioning was met by R290 and 40% by R32, the global warming impact could be reduced to 40% of the current level caused by R22. Further, if R32/HFO blends were introduced instead of pure R32, a further reduction to 20% could be achievable.
The R32/HFO blends briefly referred to in the report are Honeywell’s L20 (R444B) and LTR6A, a refrigerant being developed and tested by Mexichem. L20, a blend of R32 (41.5%), R152a (10%) and R1234ze(E) (48.5%) has a GWP of 331. The lesser-known Mexichem refrigerant similarly blends R-32 and R-1234ze(E) with a small amount (7%) of CO2. It has a GWP of 207.
In high ambient temperatures both are said to perform in high ambients at an efficiency of 98% of R22, a loss that could easily be compensated for by system design.
All of the refrigerants mentioned are flammable to some degree. Highly flammable (A3) in the case of propane (R290) or the new classification of “mildly flammable” in the case R32 and the blends.
International safety standards restrict the use of these gases by charge size. In the case of propane Öko-Recherche sees it is unsuitable for use in systems greater than 9kW or above 7 kW in high ambients.
The recently revised standard ISO5149 will allow greater maximum charges sizes for the “mildly flammable” A2L refrigerants, making 10-12kg charges possible. The Öko-Recherche report states: “In terms of the safety, A2L refrigerants are suited to completely cover the single-split subsector >5kW and also the multisplit subsector, in direct (DX) mode.”
While R410A performs well at the normal temperatures found in typical industrialised countries, its efficiency decreases notably compared to R22 at higher ambients.
In contrast, propane has a critical temperature close to R22 and should perform well at high ambients. Comparisons of the COPs at condensing temperatures of 65°C show that propane has only a slightly lower performance than R22 (~2.5%) and the discharge temperature is described as substantially lower.
Pure R32 is closer to R22 than R410A but still shows a difference of almost 9%. The high discharge temperature of R32 is seen as another drawback. This could be minimised by the use of liquid or vapour injection but could result in a loss of capacity or efficiency.