Mtaffish:
I’ve done this one so many times in the past that I can recite it from memory. However, you fail to tell us all the basic data:
What is your desired evaporation temperature? This will fix the suction pressure on the compressor (assuming you are talking about a mechanical refrigeration system).
What is your available design condensing temperature?
What type of compressor and driver are you applying?
What are you applying the refrigeration effect to? Is it air conditioning? Is it a dairy milk operation? Is it an industrial plant application? Is it located in a remote area? Is it located in a refinery?
Presumably you know the answers to the above and all you require are the obvious, engineering, economic, and operational factors to identify in order to select the applicable refrigerant:
Grade the toxicity level; (Hydrocarbon =1; CO2 = 2; NH3 = 3)
Grade the availability level; (NH3 = 1; CO2 = 2; Hydrocarbon = 3)
Grade the flammability level; (CO2 =1; NH3 = 2; Hydrocarbon = 3)
Grade the environmental level; (NH3 = 1; Hydrocarbon = 2; CO2 = 3)
Grade the refrigerant cost level; (NH3 = 1; Hydrocarbon = 2; CO2 = 3)
Grade the COP level. (NH3 = 1; Hydrocarbon = 2; CO2 = 3)
In the last 20 years the answer for me has consistently been Ammonia (NH3). In my applications down to -25 oF it has been the optimum refrigerant in spite of its potential toxicity. With proper design and operating procedures I have never had an incident with it – both as a direct or in-direct refrigerant.
I hope this information and experience helps you out.
