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R407A was originally developed as a non-ozone depleting replacement for R22 in medium to low temperature refrigeration applications.
In the race to replace R22, R404A dominated the supermarket industry for almost 30 years though it really should not have, developed about the same time R407A had a much lower GWP (2,107) than R404A (3,922) but by the time it was fully tested by compressor manufacturers R404A had firmly established itself as the refrigerant of choice for most supermarkets.
Unfortunately, although it is non ozone depleting R407A does have a quite high GWP (global warming potential) 2,107 when compared to CO2 having a GWP of just 1.
That means that just 1Kg of R407A leaking from a fridge is equivalent to almost 2 tonnes of CO2.
Although the GWP of R407A is fairly high it is still nearly half that of R404A so began to replace R404A in some supermarkets after the implementation of tighter controls which would outlaw the use of virgin R404A in systems containing more than the equivalent 40,000 Kg CO2 charge size (10.19 Kg R404A) by January 2021.
With tighter controls on using high GWP refrigerants users of R404A had to find a better solution with a lower GWP to conform to the changes in legislation. R407A is a viable lower GWP alternative albeit only a temporary solution. R407A’s GWP of 2,107 makes it almost half that of R404A, F-Gas compliant, similar cooling capacity and improved efficiency. It should be noted that R407A does not suffer the same high discharge temperature issues associated with R407F.
It should also be noted that since R407A began replacing R404A new lower GWP refrigerants are now available such as R448A GWP1,387 & R449A GWP 1,397.
Although new lower GWP refrigerants are better than R404A they are still only classed as interim replacements with a medium GWP.
One disadvantage of R407A is that it is a zeotropic blend with moderate glide.
R407A is made up from 3 different components— 20% R32 for heat capacity, 40% R125 to reduce flammability and 40% R134 to reduce overall pressure.
Glide is the difference between the boiling and condensing temperatures of the least and most volatile components. This is easily demonstrated with alcohol distillation.
The “mash” is a basic weak mixture of alcohol and water and is a great example of a zeotropic blend containing 86% water and 14% alcohol.
Water has a boiling temperature of 100oC and alcohol boils at 78oC so the mash has a glide of 12oC. When placed into a still and heated the alcohol begins to boil off first then as the temperature approaches 100oC the water begins to boil, as this happens the alcohol content of the mash begins to drop so it is no longer its original 86% - 14% composition, the mash has fractionated into a new composition blend.