Hi all, back with another question. So I keep finding new variables that affect the efficiency of the refrigeration cycle differently. This time it is the thermal conductivity of metals used in construction of heat exchanging elements. Specifically I can't figure out which combination would result in a lower cost of production: ammonia with stainless-steel evaporator and condenser or R404a/R22 with copper (or some copper alloy) evaporator/condenser. Ammonia is a superior, natural refrigerant. But copper's thermal conductivity puts steel to shame. On balance, which combination would you pick?