EPA mandate’s impact on PCA design

It has been a year since the Environmental Protection Agency instituted a number of changes to 40 CFR Part 82, Protection of Stratospheric Ozone. These changes are meant to sharply restrict the use of substances that allegedly harm the earth’s...


R-134a: The advantage to selecting R-134a is that as a single component refrigerant, it is not subject to any of the difficulties that arise with mixtures. However, R-134a has a 40% lower refrigeration capacity than R-22. In practical applications, using this refrigerant requires larger heat exchanger sizes and bigger compressors to provide the same capacity and efficiency attained with R-22. This requires more sheet metal, a larger equipment footprint, and higher manufacturing costs. This refrigerant cannot be used in existing R-22 systems as a “drop-in” replacement, but requires new, dedicated equipment. R-134a systems with the same cooling capacity as the R-22 equivalent cost about a third more.

R-404a: This refrigerant is a “low-temperature” mixture (three parts, including R-134a) and is most commonly used in food storage reefers or freezers. Low temperature in this case means sub-zero (32°F down to 2°F or lower).

R-407c: The advantage in selecting R-407C is its ability to be used as an alternate refrigerant in systems designed for R-22 for some environments. When retrofitting equipment that is in use, the R-22 refrigerant and mineral oil must be carefully and thoroughly removed before charging, as R-407C is not miscible with the mineral oils typically used in R-22 systems, requiring instead a synthetic lubricant. When used in systems designed for R-22, R-407C performs with about a 5% reduction in efficiency. A primary disadvantage of R-407C is that, as a zoetropic refrigerant, it experiences fractionation (the mixture does not maintain a constant composition across phase changes). Saturation temperatures may vary up to 9°F (a phenomenon known as temperature glide) in the refrigeration cycle because at a given pressure, the blend boils/condenses at different temperatures. This can be a particularly serious issue if the system develops leaks and performance diminishes. When re-charging the system, refrigerant cannot simply be added because the leak rates of the individual components are not equal due to the fractionation effect. The system must be completely evacuated. The previous charge must be recovered and disposed of or recycled. A complete re-charge of unused refrigerant is required to ensure the proper mixture and desired performance.

R-410a: The refrigerant blend R-410A is a nearly azeotropic refrigerant blend and does not experience fractionation upon change of phase, and very little temperature glide (\

 

Refrigerant Selection: Environmental Considerations

Refrigerant selection goes beyond the legal aspects pointed out in the previous paragraphs. PCA manufacturers share the same environmental responsibilities that are being imposed on the construction and commercial air conditioner manufacturers, including power consumption and “Total Equivalent Warming Impact.” Some European manufacturers are touting the advantage of R134a because of its low “Global Warming Potential.” However, if one is concerned about the environment, then one needs to consider three attributes of any refrigerant. These are:

1) Ozone Depletion Potential: A material’s ozone depletion potential (ODP) is a measure of its ability to destroy, compared to CFC-11 (R11), stratospheric ozone

2) Global Warming Potential: The global warming potential (GWP) of a greenhouse gas is an index of its ability, compared to CO2 (which has a very long atmospheric lifespan), to trap radiant energy

3) Total Equivalent Warming Impact: An air conditioner’s total equivalent warming impact (TEWI) is based on the refrigerant’s direct warming potential and the indirect effect of the energy that the air conditioner uses.

Any new air conditioner design must employ a refrigerant that provides the cooling required for the application, and all three of the refrigerant attributes shown above in order to be both a legal and also a responsible design. For any refrigerant, the ozone depletion potential (ODP) is by definition a discrete number and must be zero for new designs as mandated by national and international law.

The global warming potential (GWP) is also a discrete number by definition. Its primary significance in refrigerant selection is the direct warming potential component of the total equivalent warming impact (TEWI).

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