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R-22 (HCFC-22) is the most widespread refrigerant being used in India for room air-conditioners, split air-conditioners, packaged air-conditioners and reciprocating central plant systems. R-22 (HCFC-22) is currently also being used in a large proportion of positive displacement compressor based chillers and in some larger tonnage centrifugal chillers. These uses predate the Montreal Protocol, but will be phased out as part of the overall HCFC phase-out. In the U.S., HCFC-22 cannot be used in new equipment after Jan 1, 2010.

So what's so special or different in the new refrigerants, such as R-407C and R-410A that make them different from the user-friendly R-22?

R-22 is a HCFC, i.e, a Hydro-Chloro-Flouro-Carbon, that contains chlorine, and which when released in the atmosphere, causes ozone, O3 to be converted to O2, and thereby depletes the Ozone layer.

However, R-22 has zero potential to increase global warming.

R407C is one of the HFC blends that is intended for HCFC-22 replacement, but it is zeotropic and not suited for use in a flooded evaporator. R-407C has been used in reciprocating chillers with direct expansion evaporators.

R-407C Contains R-32, R-125 and R-134a (23/25/52 by weight in %).

The use of substitute refrigerants such as R407C and 410A, while having zero potential to deplete the Ozone layer, create a new set of issues which must be understood. The following sections explain these issues in layman's terms:

The Ozone Depletion Potential
The Global Warming Potential
Zeotropes and Non-Zeotropes
The lubricating oil issue
The Glide problem
The Heat Transfer Coefficient (HTC) issue
The Servicing issue
The Toxicity issue
The Flammability issue
The Training issue


The Ozone Depletion Potential:

R-22 refrigerant is allowed to be used in the USA till Jan 1st 2010 and till 2030 in India, as per the Montreal Protocol. Leaked refrigerant is not the sole cause of depletion of the ozone layer. The Ozone Depletion Potential (ODP) of R407C is 0, while that of R22 is 0.05.


The Global Warming Potential:

The 100 Year ITH Global Warming Potential in (kg CO2/kg) for the refigerants are similar:

HCFC-22 1,700 1,500
R-407C 1,530 1,525

GWP:

"The Global Warming Potential (GWP) of a gas relates the cumulative (integrated) warming over time caused by the emission of the gas to the cumulative warming caused by the emission of the same mass of CO2. The two basic factors that drive the GWP value are the “radiative forcing” (the infrared absorption of an incremental amount of the gas in the atmosphere) of the gas and the rate of decay of the gas in the atmosphere, compared to CO2. There are uncertainties in establishing quantitative values for both radiative forcing and atmospheric decay rate for both the fluorocarbons and CO2. As a result the IPCC estimated that the accuracy of the GWP values is+ 35%. As new data has been and continues to be developed, GWP values have been revised and are subject to future revision. A detailed presentation of the methodology for determining GWP is contained in [IPCC [2001]. The fundamental importance of GWP values to this study is that it permits the warming impact of fluorocarbon emissions to be compared to the warming impact caused by energy consumption (and the associated CO2 emissions) for the various applications that make use of HFCs."

Fluorochemical 100 Year ITH GWP (kg CO2/kg)
TEWI-3 Appendix B Climate Change 1995 WMO 19993 Climate Change 2001

HCFC-22 1,700 1,500 1,900 1,700

R-407C 1,530 1,525 1,984 1,653


Reference:
http://www.arap.org/adlittle/appendixb.html


Zeotropes and Non-zeotropes:

R407C is a non-azeotropic (zeotropic) refrigerant mixture of Contains R-32, R-125 and R-134a (23/25/52 weight-%) and exhibits a quite different condensation phenomenon from those of R22.


The Lubricating Oil issue:

R-22 refrigerant requires that the lubricating oil in the compressor may be mineral oil, whilst for R-407C, specifically synthetic Polyolester or POE oils need to be used, as R407C does not contain chlorine, and therefore cannot dissolve mineral oil.While these oils are considered to be superior oils, less liable to breakdown, however they are more hygroscopic – they must therefore be kept from contact with air as far as is practical.


The Glide problem:

Unlike R22, R407C is a mixture of three refrigerants, which boil at different temperatures. As a zeotrope, R407C exhibits a phenomenon known as ‘glide’, that is changing state (evaporating or condensing) over a range of temperatures. 'Glide' has an adverse effect on the performance of conventional, mixed flow, shell and tube heat exchangers. For best performance, R407C should be used in plant with counterflow plate heat exchangers. 'Glide' can also increase the risk of freeze-up, in the event of a loss of flow or a localised restriction in the evaporator.

Since R407C is a zeotrope, the mixture will fractionate should a leak occur from a part of the system that contains both vapour and liquid. Service techniques have to be adapted in the light of this characteristic. After a significant leak, a moderate loss of refrigerant R407Cwill require the entire charge to be removed, before the system can be pressure tested, repaired, and fully re-charged. In short, systems will no longer be able to be topped up.


The Heat Transfer Coefficient (HTC) issue:

"In this study, condensation heat transfer coefficients (HTCs) were measured on a horizontal plain tube, low fin tube, and Turbo-C tube at the saturated vapor temperature of 39 °C for R22, R407C, and R410A with the wall subcooling of 3–8 °C. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation HTCs were up to 50% lower than those of R22. For R407C, as the wall subcooling increased, condensation HTCs decreased on a plain tube while they increased on both low fin and turbo-C tubes. This was due to the lessening effect of the vapor diffusion film with a rapid increase in condensation rate on enhanced tubes. On the other hand, condensation HTCs of R410A, almost an azeotrope, were similar to those of R22. For all refrigerants tested, condensation HTCs of turbo-C tube were the highest among the tubes tested showing a 3–8 times increase as compared to those of a plain tube."

Reference


The Servicing issue:

"Clean installation practices, effective leak testing and de-hydration and the weighing of additional refrigerant requirements remain vital. But all of these procedures have long been associated with R22 and indeed any other refrigerants."

"Concerns have been expressed that a moderate loss of refrigerant will now require the entire charge to be removed, before the system can be pressure tested, repaired, and fully re-charged. In short, systems will no longer be able to be topped up. Once again, this is no different to the procedures required with R22 but supports the case for ensuring that the system is leak free at installation.

There are seriuos issues relating to the use of R407C refrigerant, especially when servicing work needs to be carried out at site post-installation. The vendor has to ensure that:"
It will however be necessary to add R407C as a liquid, to ensure that the correct mix is added.

"In operation, R407C provides a number of indications that, if applied to R22 would indicate that the system were overcharged. Although slight, the following changes may be anticipated:

Higher head pressure
Lower compressor superheat
Lower refrigerant temperature difference across the condenser.
Also there may be frosting at the evaporator inlet."


Equipment

1. All equipment used with the new refrigerant and oil must be compatible.
2. Vacuum pump should be compatible however provided that oil is regularly changed it can be universal.Leak testers that rely on a reaction with chlorine (i.e. halide) will not work with R407C.
3. Gauges should be universal however do provide a means of contamination between oil types. Purge and blow through with OFN if in doubt.
4. Reclaim unit – dedicated to refrigerant.
5. Reclaimed refrigerant cannot and should not be re-used, which is difficult for the customer to monitor.
6. R407C has to be charged in the liquid state. This implies that some sort of chilling device (usually ice), would be required in case the unit needs to be re-charged at a site.
7. The condensing pressure of R407C is about 10% higher, providing a derated performance. Guage manifolds for service must be suitable for this higher pressure.
8. R407C being an HFC refrigerant, is extremely susceptible to mixing of impurities (oil, water, pipe during brazing) as compared to R-22 refrigerant.

Reference:
http://www.aquaair.org/R22-R407C-Differences.html


The Toxicity issue:

Refrigerants are divided into two groups according to toxicity:

Class A signifies refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 ppm;

Class B signifies refrigerants for which there is evidence of toxicity at concentrations below 400 ppm.

R-22 is non-toxic, and no data is available about the non-toxicity of R407C below a concentrationm of 400 ppm, implying that R407C is toxic above 400ppm on prolonged exposure, though the toxicity levels of both refrigerants has been defined as A1 based on Safety Group Classification.

Classification of R-407C: R32/R125/R134a (23/25/52)- A1


The Flammability issue:

Refrigerants are divided into three groups according to flammability:

Class 1 indicates refrigerants that do not show flame propagation when tested in air at 21°C and 101 kPa;

Class 2 indicates refrigerants having a lower flammability limit of more than 0.10 kg/m3 at 21°C and 101 kPa and a heat of combustion of less than 19 kJ/kg;

Class 3 indicates refrigerants that are highly flammable as defined by a lower flammability limit of less than or equal to 0.10 kg/m3 at 21°C and 101 kPa or a heat of combustion greater than or equal to 19 kJ/kg.

Mixtures, whether zeotropic or azeotropic, with flammability and/or toxicity characteristics which may change as the composition changes during fractionation, shall be assigned a safety group classification based on the worst case of fractionation.

Reference:
http://www.fluorocarbons.org/en/applications/refrigeration.html


The Training issue:

Train-the-Trainers in Good Practices in Refrigeration Train-the-Trainers in Good Practices in Refrigeration. The Networking activity is managed by the Network and Policy Manager based at UNEP DTIE in Paris, France.
http://www.uneptie.org/ozonaction/news/mpaw.htm

Action pack for Schools:
http://www.uneptie.org/ozonaction/information/mmcfiles/4820-e-EdPack_1_guide_low.pdf.pdf

Check out the R407C - The Engineers Guide. Mitsubishi Heavy Industries
www.3dair.co.uk/download-files/r407c-guide.pdf