an environmentally friendly high temperature refrigerant

[star882]

Out of curiousity, is there a lot of work being done to make a non ozone-depleting refrigerant for high temperature applications like heat pump water heaters and condensing (ventless) clothes dryers? I'm curious because I have heard that all the condensing clothes dryers for home use currently use R22. Once R22 is phased out, what will be used instead (that will not involve insane pressures)? R410a is already pretty high pressure for A/C, so it would be impractical for higher temperature applications. (It may still work for the water heater, since a rooftop A/C can easily reach and exceed 120F on a hot day.)

Come to think of it, what design challenges are there in designing a high temperature system? In the case of the clothes dryer, I have noted that the normal operating temperature is quite close to the overload point. (I own one of those clothes dryers, and my parents have complained about it not drying well. I have realized that they were stacking towels on the top, causing it to run hot and cycle the overload.)

[Johnny Rod]

Depending on the temps etc. and charge size could you use a hydrocarbon? R600a (Care10, isobutane) is easy to get hold of, and there are other HCs with higher (or lower) boiling points you could use. Other low-pressure refrigerants include R236fa which is an HFC, not sure of its GWP so don't know how long it could be used, and it is quite expensive.