For many years, R-22 was the refrigerant of choice for commercial and residential air conditioning and heat pump systems. Supermarket refrigeration systems, industrial centrifugal chillers, and industrial cooling applications also used R-22.
R-22 is classified as a hydrochlorofluorocarbon (HCFC), and its molecule contains chlorine, which makes it an ozone-depleting refrigerant. Its ozone-depletion potential (ODP) is 0.055. The R-22 molecule also contains hydrogen, fluorine, and carbon. Its global-warming potential (GWP) is 1,857.
Because of environmental concerns caused by its ODP and GWP, R-22 was phased out for new equipment in 2010, and its total production phaseout will happen in 2020. Because of this, there is a large installed base of R-22 air conditioning and heat pump systems that are candidates to be retrofitted to a different refrigerant in order to avoid the escalating cost of servicing an R-22 system.
R-410A has been the replacement hydrofluorocarbon (HFC)-based binary refrigerant blend for R-22 in new light commercial and residential air conditioning and heat pump applications. Other applications for R-410A include chillers and commercial refrigeration equipment. However, R-410A is not a retrofit refrigerant for R-22. If an R-22 system needs to be retrofitted to a different refrigerant, it is recommended to choose from a list of accepted R-22 retrofit refrigerants that have similar properties. However, there is not one “silver bullet” refrigerant blend that will be the perfect drop-in replacement for retrofitting R-22 systems. Each refrigerant blend has advantages and disadvantages. These advantages and disadvantages have to be balanced to make the best overall choice for your specific application. This month we’ll look at R-438A.
R-438A is versatile and can be used for retrofitting R-22 direct expansion (DX) systems in air conditioning applications (high temperature) and medium- and low-temperature refrigeration applications. R-438A is approved for sale in the U.S. under the Environmental Protection Agency’s (EPA’s) Significant New Alternatives Policy (SNAP) program.
R-438A is a blend consisting of R-32 (8.5 percent), R-125 (45.0 percent), R-134a (44.2 percent), R-600 (1.7 percent), and R-601a (0.6 percent). R-600 is the hydrocarbon (HC) butane and R-601a is the HC isopentane. These two hydrocarbons constitute a very small percentage of the total blend, but this small amount helps thin the mineral oil, so it has a lower viscosity, enhancing oil return to the compressor’s crankcase. This characteristic was intentionally designed into the blend to achieve mineral oil compatibility. Because of the small percentages of these two hydrocarbons, R-438A is not flammable. Its ASHRAE safety group classification is A1.
The evaporator and condenser temperature glide of R-438A is typically in the range of 6°-7°F. As with most refrigerant blends, R-438A is not recommended for use in systems with a flooded evaporator or a centrifugal compressor as the vapor/liquid composition difference associated with the temperature glide may adversely affect performance.
R-438A has a zero ODP. Its GWP, according to the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change, is 2,264.
R-438A has similar pressure and enthalpy characteristics compared to R-22 in low-temp, medium-temp, and air conditioning applications. It is compatible with mineral oil, alkylbenzene, and polyolester through all of these temperature ranges.
For most systems, R-438A may have 5-10 percent lower capacities with similar energy efficiency ratios (EERs) when compared to R-22. Because most R-22 systems in service today have excess compressor capacity, this small percentage in capacity loss will not be significant; the compressor simply runs a slightly longer cycle.
The mass flow R-438A is only slightly higher than R-22 to achieve the same refrigeration capacity, so existing thermal expansion valves (TXVs) can be used with minimal adjustment to the superheat setting.
Listed below is a brief summary of the retrofit procedures involved when replacing R-22 with R-438A:
• Establish baseline performance;
• Recover the R-22;
• Replace critical elastomeric seals/gaskets and the filter drier;
• Evacuate the system to 200 microns or below;
• Charge with R-438A. Since R-438A is a near-azeotropic refrigerant blend, it must be liquid charged. Initial charge should be approximately 85 percent of standard R-22 charge, but is system dependent;
• Start up the system, and monitor temperatures and pressures;
• Adjust the TXV to achieve desired evaporator superheat;
• Monitor the compressor’s oil level;
• Leak check the entire system; and
• Optimize control set points if needed.
R-438A can be used as a retrofit refrigerant blend in air conditioning and refrigeration applications with minimal system changes. Benefits of using R-438A in R-22 system retrofits include:
• No expansion valve or expansion valve power element change;
• No suction or liquid line set changes;
• No oil changes in most cases;
• Non-disruptive (no strainer plugging, especially with TXVs and evaporator pressure regulator valves);
• Needs a filter drier change but can use a standard filter drier;
• Minimal set point adjustments, if any;
• Only a 3-6 psi head pressure difference when compared to R-22;
• Only a 2-3 psi evaporator pressure difference when compared to R-22;
• Similar energy consumption when compared to R-22;
• In refrigeration retrofits, R-438A has a very low carbon footprint. Its GWP is 42 percent lower than R-404A; and
• Retrofit has low first cost for air conditioning and refrigeration applications.
Two important final notes: When retrofitting R-22 systems to R-438A (or any HFC refrigerant), it is recommended that critical elastomeric seals/gaskets, such as Schrader valves and liquid level indicators, be changed. Finally, always consult with the compressor manufacturer or follow their specific retrofit guidelines and procedures before performing a retrofit on any R-22 system or any other refrigeration system.
In upcoming articles, we’ll take a look at other R-22 retrofit options.
Publication date: 12/4/2017