Generally speaking when it comes to refrigerants, chillers are divided into two categories: low/medium (L/M) and medium/high (M/H) pressure. L/M pressure chillers can benefit from the use of pure HFOs (R1233zd and R1234ze), resulting in a GWP close to zero. The flammability penalty is very low and manageable, especially for systems installed outdoors or in machine rooms. We can expect that for the short-to-medium term, this type of systems will adopt ultra-low GWP refrigerants. The upper GWP limit, for large L/M chillers, could reach 630, which corresponds to the GWP of HFO blend R513A, listed by the EPA-SNAP regulation of July 2015 while R134a will be delisted starting in 2024.
For M/H pressure chillers, the medium GWP alternatives are in the 125-750 GWP range but users must be willing to accept an A2L flammability classification. This, again, should be acceptable for systems installed outdoors or in machine rooms. The market will likely move to GWP alternatives which offer the best trade-off between system costs and performance. We foresee that the choice will fall to high density/high pressure refrigerants with a GWP around 500-750.