Low GWP blends for domestic air conditioning

According to an IIR Informatory Note, the refrigeration and air conditioning sectors account for about 7.8% of global greenhouse gas emissions. ^[1] This contribution comes in the form of a direct effect, which is related to refrigerant emissions from refrigeration systems (37%), and an indirect effect,  related to CO₂ emissions from fossil fuel power plants producing electricity to power refrigeration systems (63%). The Kigali Amendment aims at reducing the direct effect. 

R134a, R1234yf, R410A, R407C, and other refrigerants are currently the best alternatives to ozone-depleting refrigerants (CFCs and HCFCs), especially for household and car heat pump applications. However, the global warming potential (GWP) of these refrigerants is considerably high. For instance, hydrofluorocarbon refrigerants R410A and R134a have zero ODP but high GWP values of 2100 and 1360, respectively.

Refrigerants with low GWP and best energy performance are required to reduce both direct and indirect contributions to environmental issues. However, most of the newer zero ODP, low-GWP alternatives suffer from one or more undesirable characteristics, such as greater flammability, toxicity, or lower volumetric capacity than widely used HFC refrigerants.

In a recent review article, the authors focused on ultra-low and low-GWP refrigerants providing system performance comparable to or better than that of existing refrigerants in residential air conditioning. ^[2]  According to the UNEP RTOC 2014, GWP₁₀₀ values are classified into five levels, with low-GWP refrigerants having a GWP₁₀₀ <300. ^[2]

According to the review article, HFC and HFO blends (R32/R1234yf, R32/R1234ze, and R32/R1123) can be good substitutes for currently used refrigerants.^[2] Furthermore, the authors found R744/R32/R1234ze(E) and R744/R32/R1234yf to be promising ternary mixtures. The addition of R744 offers improved system performance, particularly the volumetric flow, without increasing GWP.  

Technical difficulties in using low-GWP refrigerants were listed in the article, along with suggested measures to solve them. For instance, irreversible losses as well as pressure drops in the condenser and evaporator increase due to the lower volumetric capacity of the refrigerant blends. As a solution, the authors suggested reducing the irreversible losses by choosing an appropriate compressor size and suitable lubricant oil. Furthermore, larger tube diameters and refrigerant bypasses in the heat exchangers can be used to reduce the pressure drop.^[2] 

The IIR recommends a holistic approach to the selection of new refrigerants, using tools such as the Life Cycle Climate Performance (LCCP) which considers all GHG emissions or, preferably, the Life Cycle Analysis (LCA), which considers the whole equipment over lifetime.^[1] Moreover, safety standards, training of personnel to handle flammable refrigerants as well as accessibility of the technology at a global scale should be considered. 

Sources 

[1] Domanski P., Motta S. Y. Low-GWP Refrigerants: Status and Outlook. 48th Informatory Note on Refrigeration Technologies. http://dx.doi.org/10.18462/iif.NItec48.06.2022  

[2] Uddin K, Saha BB. An Overview of Environment-Friendly Refrigerants for Domestic Air Conditioning Applications. Energies. 2022; 15(21):8082. https://doi.org/10.3390/en15218082