The nuts and bolts of choosing a suitable refrigerant replacement. (Part II).
December 1, 2013 by DAVE DEMMA
In Part I in HPAC October 2013, we discussed the importance of having an R-22 strategy. Now it is on to the logistics of choosing a suitable replacement for converting existing R-22 systems, and a step by step process for implementing the conversion.
Table 2 shows the more common replacements for R-22, along with their chemical formulation. There is a limited supply of building blocks available to make suitable R-22 replacements. In fact, all of the common R-22 replacements are made by blending at least two of the following components: R-32, R-125, R-134A and R-143A. Some contain three of these components, and one contains all four. Along with these, there are several hydrocarbon compounds available, which when added to an HFC, will facilitate the use of mineral oil in the system (more on this later).
As stated in Part I, there are several factors to look at in making that choice:
• Thermodynamic properties of the conversion refrigerant
• Cooling capacity relative to R-22
• Refrigerant Mass Flow relative to R-22
• Efficiency relative to R-22
• Discharge temperature relative to R-22
• Pressures of the conversion refrigerant
• Conversion refrigerant oil requirements
• Has compressor manufacturer evaluated compressor performance and wear with conversion refrigerant
• Environmental concerns (GWP of the conversion refrigerant)
• Price and availability of the conversion refrigerant
The thermodynamic properties of the new refrigerant will determine the following:
• COP (efficiency) of the system
• Cooling capacity of the system
• Discharge temperature
• Required refrigerant mass flow rate (which will determine whether flow controls will need replacement)
In most cases it would be desirable to use an R-22 replacement that will provide performance and capacity close to that of R-22. The charts in Table 3 (Low Temperature), Table 4 (Medium Temperature) and Table 5 (Air Conditioning) show the comparative values for these four system parameters.
Capacity relative to R-22 is fairly self explanatory. Assuming that the R-22 capacity is 100 per cent, a value less than that means you will be suffering a capacity loss when using the particular refrigerant that capacity loss is attached to. The numbers in red are losses that are substantial and likely to eliminate the particular refrigerant as a valid choice for conversion.
Note that the capacity losses become more magnified as the evaporating temperature becomes lower. For example choose a refrigerant that has a capacity loss of approximately six per cent in an air conditioning application. On systems that are barely maintaining temperature with R-22, this would not be a good choice. However, if the system has enough extra capacity where a six per cent loss can be absorbed without loss in maintaining adequate comfort in the middle of summer, this might be an acceptable choice.
Now, take the same refrigerant in a low temperature application and you have a 19 per cent capacity loss. It might be a little more difficult to find an application that has enough extra capacity to absorb a loss of that magnitude.
The refrigerant mass flow rate will determine whether the existing flow controls (TEV and distributor nozzle) are sufficiently sized for the new refrigerant. While there are some refrigerants listed that have mass flow rates which are very close to R-22, there are others (in red) which would require replacing existing TEVs (and distributor nozzles in some cases). This becomes a very time consuming and expensive conversion. Refer to Table 6 and 7 for examples of potential conversions, and whether existing flow controls would require replacement. The application is a typical supermarket with a -20F evaporator temperature, a liquid subcooler providing 50F liquid refrigerant, and operating at 105F condensing temperature.
There are two things to consider with TEVs: Will the existing valve selection yield sufficient capacity with the new refrigerant, and will the new refrigerant use the same thermostatic element as R-22. R-404A and R-507 will require an element replacement, even if the original R-22 TEV body provides sufficient capacity after the conversion.
Now, it is true that every application is different. While the thermodynamic properties will determine how the existing R-22 selection will fare with the new refrigerant, how the original selection was made will also be a determining factor. In the above example, if the application above were 24 000 Btu instead of 18 000 Btu, the original TEV selection would have been a three-ton valve. This valve would be sufficiently sized for use with R-438A, slightly undersized for R-422D in the low ambient months, and sufficiently sized for R-404A/R-507 (but would require an element replacement).
It is recommended that all distributor nozzle and TEV selections be verified prior to the conversion. This becomes additional labour to verify what is currently in the system and then going through the exercise of determining the capacity with the new refrigerant.
Certainly choosing a refrigerant, which has a minimal capacity loss and similar mass flow requirements (meaning no distributor nozzle or TEV replacements) would be desirable.
There is much more to discuss and that will be done in a later issue. <>Dave Demma holds a degree in refrigeration engineering and worked as a journeyman refrigeration technician before moving into the manufacturing sector where he regularly trains contractor and engineering groups. He can be reached at firstname.lastname@example.org.
Reader comment in response to Part I (see HPAC October 2013, available online at www.hpacmag.com)
Reader: Dave some of your comments are in conflict. In the third paragraph you state: “…there is currently a good supply of R-22. There will be some R-22 available on January 1, 2020; however it is likely to be in limited supply. More importantly, it’s likely to be expensive.” Further along you say: “…do not panic. There is a good supply…”
Dave Demma: No doubt what was written in Part I appeared contradictory and confusing…so let me attempt to clarify. Being based in the U.S., my perspective on R-22 is much more influenced by what is happening here. The US Environmental Protection Agency (EPA) has revised their R-22 allocations for the importation/manufacture of new R-22 as appears in Table 1.
In 2012, the allocation for new imported/manufactured R-22 was set to be at 89.8 million lb. A temporary allocation ruling was released, with the proposed allocation for 2012 to be somewhere between 55.4 million lb. and 79.7 million lb. They went with the 55.4 million lb. amount. With such a severe reduction in allocation the price responded as one would expect…it quickly skyrocketed. In January of 2013, the allocation was further reduced to 39 million lb., causing further price increases. In April of 2013 the EPA released a permanent allocation ruling, bringing the current year allocation up to 62.7 million lb. That is a 60 per cent increase in supply and once again, the price responded as one would expect–with price reductions throughout the year.
In addition to the reduction in price, the increased allocation has caused a mini glut of R-22 in the U.S. While this is certainly a temporary situation, the fact is there is plenty of R-22 available right now. There will be a further reduction in allocation down to 51 million lb. in 2014, but this will s
till be greater than the original allocation given for the beginning of 2013.
We are awaiting the EPA’s final allocation ruling for 2015–2020. This will be the determining factor as to where prices will settle out in 2014. It will also indicate what we can expect the supply of R-22 to be as we get closer to 2020.
There is a good supply of R-22 now and the price is reasonable. However, it will not last and that is true whichever side of the border you are on.