Hitting the bounds of chemistry: limits and tradeoffs for low-GWP refrigerants.

We explore the possibilities for low-GWP refrigerants through two approaches. First, we explore the performance of hypothetical refrigerants to define the limits of what is allowed by thermodynamics. In the second approach, we apply property estimation methods and screening parameters to identify best candidates from a database of 100 million chemicals. We find that the optimal thermodynamic characteristics are quite rare; additional fluids are eliminated because they are unstable or highly toxic. We then estimate the cycle performance (considering the basic cycle, economizer cycle, and a cycle with a liquid-line/suction-line heat exchanger) of the remaining candidates and apply efficiency as an additional screening criterion. The end result is not thousands of low-GWP candidates, but a handful, and even these present tradeoffs. We argue that these represent all the viable candidates for single-component, medium- and high-pressure refrigerants — in other words, we have hit the limits of what chemistry allows.