Refrigerants Are Changing Again…What Are The Options?
The perfect refrigerant would be a safe compound (or blend of compounds) with no toxicity level, no risk of flammability aspects, has no compatibility problems with materials of construction, is inexpensive to produce, and provides a capacity greater than the existing refrigerants R-22 and 410A. Ideally they would be drop-ins that operate as efficiently, or better than the current refrigerants do in their existing systems. As I have heard in New Jersey, “forget about it.” All of the possible next generation options have plusses and minuses and must also satisfy the EPA’s regulative hurdles. Thus, trade-offs need to be understood when the refrigerant change is considered (See Table 1).
Next Generation Refrigerant HFO Options:
Hydrofluoro-olefin (HFO) refrigerants are made up of hydrogen, fluorine, and carbon. This refrigerant class has double-bonded carbon molecules in its structure. There are a number of HFO refrigerants currently under development or going through the approval process. Thus, there will be R-1234, with small letter alphabet soup after the numbers, available on the market soon. These refrigerants are listed as marginal for flammability and equipment cost however, they fall much closer to a passing grade for practical usage. Hence, their viability as replacement options remains. Two that are first out of the approval gate are HFO R1234yf (2, 3, 3, 3- Tetrafluoropropene) and HFO R1234ze (Trans-1, 3, 3, 3-Tetrafluoroprop-1-ene). The main concern from a contractor’s perspective is they will be expensive refrigerants because they are expensive compounds to produce.
Next Generation Refrigerant Option R-32
R-32 is a hydro-fluorocarbon (HFC) refrigerant that has a global warming potential (GWP) of 675 over the 100-year duration period that refrigerants are rated. GWP for R-22 (HCFC) is 1810, and for 410A (HFC) it is 2090. R-32 also has an ODP of 0, when coupled with its lower GWP, is a winner when compared to R-22 and R-410A. With relatively minor retrofitting, R-32 can be manufactured in existing R-22 facilities, and it is cheaper than the original R-22. So, why was R-32 not considered before? The answer: it has a flammability rating per ISO 817 and is listed as a 2L refrigerant in ASHRAE Standard 34. However, it has a relatively low burning velocity that is actually slightly lower than ammonia’s burning velocity. Thus, it is not explosive like butane, or pure hydrogen. A spark will not ignite R-32, it takes an open flame to ignite it. Since flammability is the only negative, and it represents a very small risk, R-32 is back as an option. R-32 would be the undisputed candidate except for one small detail, 2L refrigerants are currently not allowed for use in US building codes. Additionally, equipment instructions and industry usage standards need to be updated.
Next Generation Refrigerant Option CO2 (R-744)
Carbon Dioxide CO2 makes an excellent replacement refrigerant except for one small detail: the operating pressures required are so high, compressor efficiency suffers tremendously. Additionally, piping thickness needs to be greatly increased. Not a major stopper, but relevant working pressures at 2,000 psi make the systems more dangerous to work on.
Next Generation Refrigerant Option Ammonia
Due to the decreasing price of natural gas in the US, ammonia or lithium bromide based absorption systems may make a comeback. Thus, they remain on the list of possible refrigerants of the future.
Next Generation Refrigerant Option Propane (R-290)
Propane fails the flammability testing completely. However, since it passes all of the other requirements it is often included on the list of possible replacement refrigerants. Warning: R-290 has been marketed as a direct drop in replacement for R-22; but it is illegal to use R290 in HVAC equipment.
In conclusion, it looks like the next generation of replacement refrigerants will come from new HFO blends and/or once US codes are updated, R-32. Additionally, ammonia based absorption system’s may have some niche-markets where natural gas is cheap and readily available. At this time the manufacturers are planning their individual strategies. By following press releases, and available literature, contractors can monitor which way they are leaning. The best guess of this author is, they will figure out a way to get R-32 approved in the codes, and keep the HFO blends as a backup plan.
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