The refrigeration industry has many different types of refrigerants being used. Industrial refrigeration traditionally uses Anhydrous Ammonia (R717) or Carbon Dioxide (CO2), and the residential/commercial sector uses a wide variety of synthetic refrigerants. Why so many different types of refrigerants you may be thinking. Well, it didn't use to be that way less than a century ago. With an increase in special applications, temperature ranges, and regulators like the U.S. Environmental Protection Agency (EPA). This has created a wide variety of refrigerant types, and more are steadily being introduced.
Let's discuss Synthetic Refrigerants VS Natural Refrigerants.
Synthetic Refrigerants: Simply put, this means a substance that was "man-made". You see this term used frequently for automobile motor oils: synthetic motor oil = man-made VS conventional oil = crude oil.
Natural Refrigerants: Simply put, this means a substance was developed from naturally occurring elements in nature. For example, Anhydrous Ammonia (R717/NH3) is derived from the air because the air we breathe is roughly 78% nitrogen. Don't let this concept be misleading, the process of making Anhydrous Ammonia is more complex than it appears. One method is called the Haber-Bosch process, this does require a significant amount of fossil fuels to be used throughout the process. The creation of natural refrigerants (directly or indirectly) does leave a carbon footprint.
Now, are you ready to dive deep into some key characteristics that make refrigerants different from one another? We know you can't wait, so let's get into it!
Mixed Refrigerants: This is referring to synthetic refrigerants that are commonly used in residential and commercial refrigeration applications. Refrigerants that have “temperature glide” are called zeotropic or non-azeotropic. Zeotropic mixtures have components with different boiling points, a phase change over a range of temperatures (five to ten degrees usually) at a constant pressure (e.g. is any 400 series refrigerants). During the evaporation process, the most volatile component boils off first and the least volatile component boils off last. The opposite occurs during the condensation process. If one component boils at 90°F and the other at 100°F, that would be 10 degrees of glide. Terms like dew point and bubble point are used with zeotropic refrigerants when referring to the P-H Diagram.
The “bubble point” is located towards the end of the condensing process (left side of the P-H Diagram). Bubble point is where only a single bubble remains to be condensed, considering the volatile components of the refrigerant.
The “dew point” is located towards the end of the evaporation process (right side of the P-H Diagram). Dew point is where only a single droplet of liquid remains to be evaporated, considering the volatile components of the refrigerant.
Pure Refrigerants: These types of refrigerants are preferred for flooded & overfeed liquid feed type applications. Mixed refrigerants would boil at different temperatures and make their use not desired for maximum efficiency in flooded & overfeed liquid feed type applications. Anhydrous ammonia (R717) and Carbon Dioxide (CO2) are considered “pure” refrigerants because their ability to change phase at a constant temperature at a given pressure. Pure refrigerants superheat and subcooling points are simply calculated unlike mixed refrigerant blends.
Azeotrope Refrigerants: These types of refrigerants (e.g. R502 and R507) have a mixture of two components which have a constant boiling point and have characteristics like pure refrigerants. Anhydrous Ammonia is not categorized as an azeotrope refrigerant because it is a single molecule refrigerant (the single nitrogen atom and three hydrogen atoms are bonded together to form a single molecule). Anhydrous ammonia can be used with other azeotropic blends to create an azeotropic refrigerant e.g. ammonia and n-butane, ammonia and hydrofluorocarbons, and R723 – ammonia and dimethylether.
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