* Ratio to R22 system.
While no replacement refrigerant is ideal everywhere, each option has particular situations where it generally is preferred:
Ammonia — for systems that do not require a cooling medium below -28ºF, have room for the vapor-handling capacity and sufficient compression ratio. Ammonia’s low molecular weight limits compression ratios available in turbocompressor-driven systems.
Propane — for systems with some extra power available and a small amount of surplus vapor-handling capacity. Lubricant separation from propane requires larger lubricant knockout drums than with R22 systems.
Propane/propylene mixtures — for systems that have excess vapor-handling capacity, can tolerate higher discharge pressures, and would benefit from cooler refrigerant temperatures. Propane/propylene mixtures have similar lubricant separation concerns as pure propane systems.
Of course, individual circumstances and other technical and economic factors will dictate actual selection. Major factors to consider include lubricant systems, safety and availability. Propane/propylene mixtures, in particular, can be difficult to get in some areas and of varying composition depending upon the supplier.