In my opinion it is all about situation. With the exception of the r22 phase out. The epa has said r22 is depleting our ozone, hence they are phasing it out and only a few refrigerants work in its place. 407c is a good retrofit, but 410A(higher pressure) is almost the new standard for creature comfort ac applications (but not a retrofit!!!) since they decided to phase out r22. Low pressure refrigerants are more for coolers/freezers. Others may chime in as well to further define, and I hope they do!

 

Low pressure refrigerants are more for coolers/freezers. Others may chime in as well to further define, and I hope they do!

I have never seen a low pressure cooler or freezer!

 

Low pressure machines a less likely to leak refrigerant than high pressure, low pressure machines are easy to service and in many cases a sensor or seal can be replaced without evacuating the refrigerant, low pressure machines don't need to ASME stamped etc. I prefer to work on low pressure!

 

when you say low pressure machine, what type of pressures do they run? So you can replace seals im guessing that are keeping refrigerant in, without pumping down/recovering? Im intrigued.

 

Really depends on the definition of low pressure refrigerant.

404A is low pressure relative to 410A.

 

Unless something has recently changed,pretty much all the way back since air conditioning was invented low pressure = bellow atmospheric pressure (14.7psia)

 

According to Mainstream Engineering, R410A is a high pressure refrigerant along with R22, R404A, etc. while R134A, R401A, R12, R500, etc are medium pressure. R11 and R123 are considered low pressure and R13, R23 and R503 are very high pressure refrigerants.

https://www.epatest.com/faq/608/#G3

I think the OP's question is one posed by his instructor so it's likely to best be viewed in a very broad sense, which would include all of these refrigerants, from low pressure to very high pressure. The question then is why one would select one over another for a particular application?

 

How and why an engineer might choose one refrigerant over another is basic to design. It's not something I've spent a lot of time on and maybe should have. I don't think pressure is first on a engineer's list of importance compared to a refrigerant's enthalpy, entropy, refrigeration effect, and all the other characteristics that make one different than another.
It's really a good question and I don't know what the food fight is about.
I remember way back I was reading that R22 systems don't use devices like soldering the liquid line to the suction or using heat exchangers to transfer heat to the suction and cooling the liquid because the refrigeration effect happened too fast for these things to be effective.
That's all that was said and I really wanted something more for an explanation at the time.
There seems to be a lot more than pressure in these choices. And there are hundreds of refrigerants.
So for the OP I hope some of y'all educated in the finer aspects of choosing refrigerants for applications can help out.

 

Well said. (If my "Like" button worked, I would use it for this post...) :gah:

 

Valdelocc man you are just looking for an argument

 

Nope, just messing with "beerbeer"