The National Institute of Standards and Technology (NIST) has identified 60 substances that may be useful as new refrigerant fluids. These substances were chosen out of the 56,203 fluids that were tested and considered. The reason these substances were identified is due to their low climate change potential in addition to low boiling points, which is necessary for use in refrigeration equipment. The results were summarized in the latest NIST Tech Beat.
The researchers found the substances through the use of a new computational tool they developed which identifies potential refrigerant fluids with low “global warming potential” (GWP). In other words, the program looks for fluids that have a low tendency to trap heat in the atmosphere. The program found approximately 1200 chemicals that fit the low GWP profile. Out of these, 60 had low enough boiling points to work in common refrigeration equipment.
The most commonly used refrigerants today are hydrofluorocarbons (HFCs). The widespread use of these refrigerants began when chlorofluorocarbons (CFCs) were phased out due to their depleting effect on the ozone layer. However, HFCs have a very high GWP, remaining in the atmosphere for many years. A widely used HFC is R-134a (1,1,1,2-tetrafluoroethane). This fluid is already being phased out in Europe due to its GWP level of 1430. Europe is now requiring a GWP of 150 or less for use in automobiles.
“What industry is trying to do is be prepared, because moving from a GWP in the thousands or tens of thousands to a GWP of 150 is an enormous challenge, both economically and technologically,” says NIST chemist Michael Frenkel. “We decided to leverage the tools NIST has been developing for the last 15 years to look into the whole slew of available chemicals.”
The new low GWP chemicals include fluorinated olefins that do not persist in the atmosphere for long periods of time due to their quick reaction time with atmospheric compounds. The new computational method “estimates GWP by combining calculations of a compound’s radiative efficiency (a measure of how well it absorbs infrared radiation) and atmospheric lifetime, both derived from molecular structure. Additional filtering is based on low toxicity and flammability, adequate stability, and critical temperature (where the compound’s liquid and gas properties converge) in a desirable range”.
The NIST has additional funding from the U.S. Department of Energy to narrow down these results even further in order to perform more detailed refrigeration cycle modeling.