Good questions. Firstly there’s two parts to the refrigerant impacts. One is “Release”, that is, what happens to the refrigerant when it’s released. These are the direct affects (scope 1 in GHG accounting terminology) of releasing the refrigerant to the environment. This is equivalent to the emissions associated with combusting natural gas in a building (there’s literally resulting CO2 emissions at the actual building). This is usually where the largest impacts are. The other is the production impacts. If a “Low GWP” refrigerant takes a lot of energy to produce, or the supply chain results in a lot of fugitive emissions of high GWP gasses, the production impacts of that refrigerant may be quite high. This is what is driving the impacts of R1234z. Now, the refrigerant is still relatively new, and the production techniques are probably advanced beyond the EcoInvent data quality. Our data supplier (Life Cycle Strategies) noticed the high production impacts and investigated this. They related (largely) to fugitive emissions. He researched the current day production techniques and found evidence to suggest that fugitive emissions had been significantly reduced in the supply chain so he provided two materials, one with fugitive emissions and one without. Based on Life Cycle Strategies research, we would suggest using the “no fugitive emissions” version.
Your question is actually really timely. We are just releasing a new version of data with a wider selection of refrigerants and updated LCI impacts. This dataset should be available in a few days. If you’re interested in modelling refrigerants with greater accuracy please request V14 (edit: as of Dec 2021, the latest version of the data is v17) of the data for your project.