Future of CAR AC refrigerats and R134A alternatives
Back in the old days most of the car AC used R12 gas or freon. The Freon or CFC gas was however bad for the environment. The CFC gas was responsible for creating holes in Ozone layer above Earth. After 1992, there has been a ban on CFC and the search is on for better environment friendly refrigerants. Now real life obviously have trade offs and it is seldom so easy to find a panacea. The gas most used in CAR AC system now a days is R134A. The R134A refrigerant is scheduled for a phase out in Europe but its usage continues in the rest of world. Now let's consider what kind of refrigerant car manufacturers would like to have
- The ideal refrigerant should work with existing systems
- The cooling efficiency should be high so that running cost is low
- There should not be any toxic effects
- Should not be highly Inflammable
Any replacement should not be inflammable because the evaporation unit is under the dash in most of the currrent cars. The way CAR AC systems work is that compressor pumps in refrigerant like R134A into the evaporation unit. The liquid under pressure starts boiling and turns into gas and int the process sucks in lot of heat. That way the evaporation unit removes heat (or adds cold) to passenger compartment. If the gas is highly inflammable then evaporation unit has to move out from the passenger compartment and that would mean a different packaging. Also an inflammable or highly toxic gas would also mean adding better electronic leak detectors that can detect even small leaks. All this means changes to existing packaging and hence extra costs.
Retrofitting may also be necessary because R134A requires higher operating pressure (see the R134A pressure temperature chart). As we have seen it is necessary for the refrigerant liquid to boil and for R134A boiling happens at a higher pressure as compared to old R12 or R22 refrigerants. R134A is less efficient and that means a costlier option. However the world is sticking with R134A as there is no viable alternative as yet!
All the refrigerants that were considered replacements of R134A still do not look as viable options . One kind of replacement is high pressure carbon dioxide refrigerant systems. The carbon dioxide systems are very expensive. R-152A was another option. R-152A however is mildly flammable refrigerant and that means changes to existing packaging. As we have seen we can not evaporation unit of car AC inside passenger compartment. R152A would need an under the hood only system. It would need a separate liquid coolant heat exchange system apart from the under-dash system. It may not be possible to adapt this change to existing factory cars without changes.
Recently emerging as a new choice for car AC refrigerant is soemthing called HFO-1234YF. HFO-1234YF was primary ingredient in a previous blend called Fluid H, by Honeywell. Taking out the second ingredient, a fire retardant but also a cardiac sensitizer among its issues, means that HFO-1234 YF alone raises flammability questions. Tests show that flammability of HFO-1234YF is far less significant than that of R-152A. As a result you can circulate this refrigerant through an underdash evaporator unit, the same as with an R-134A gas system. Direct circulation to an underdash evaporator saves one level of heat exchange, which has cost, packaging and efficiency advantages. HFO-1234YF cannot be ignited easily not even with high temperature producing things like a butane lighter or even an arc welder. That means flammability is taken under control. Toxicity tests have also been encouraging. Performance testing shows that HFO-1234YF is slightly more efficient than R-134A.
HFO-1234YF refrigerant has a pressure-temperature curve almost identical to that of R-134A. This mean it operates at same pressures as R134A and thus any gas leaks can be found with existing R134A leak detectors. The global warming level of HFO-1234YF is just 4, well below the european limit of 150.