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New refrigerant (HFO-1234yf) coming...looks promising!

Chnaane on Fri April 18, 2008 1:29 PM User is offline

R134a has a phaseout schedule due to its global warming potential (GWP). I get a little snippy over the conspiracy theories (patent expiry, etc.) that get tossed around, but even so, the ultrahigh-pressure CO2 A/C systems that have been discussed from the start as the next stage in A/C refrigerants really haven't ever looked good to me. The very high system pressures require total redesign of just about every system component and predictable problems with sealing and related issues, not to mention the costs involved with much higher performance sealing systems.

This past week I was in Detroit at the SAE International Congress, and in the Monday issue of the SAE Congress Daily appeared this very interesting article, which I am posting here in its entirety. Boldface emphasis is mine:

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Honeywell, DuPont Offer Refrigerant to Meet Euro Regs

The world automotive A/C industry is being offered a new low-GWP choice to replace R-134a: HFO-1234yf (CF3CF=CH2), the hydrofluoroolefin that is the primary ingredient in the Honeywell blend "Fluid H". Although an effective low-GWP refrigerant, Fluid H drew objections because its secondary ingredient — CF3I — is a cardiac sensitizer and it raised stability questions. The blend also has some ozone depletion potential (ODP).

HFO-1234yf has a GWP number of 4, well under the European Union (EU) limit of 150. EU regulations require a phaseout of R-134a (GWP of 1300) starting on new models in 2011.

Deleting the secondary ingredient — CF3I — is said to resolve FLuid H issues. A recent presentation by Honeywell and DuPont, partners in a joint venture for a new refrigerant, said HFO-1234yf is toxicologically comparable with R-134a, which it matched or surpassed in all tests thus far including cardiac sensitization. HFO-1234yf has a pressure-temperature curve and other key characteristics very close to R-134a — it is thermally stable and compatible with R-134a components, and would be a near drop-in replacement for R-134a. A drop-in test by Toyota showed FHO-1234yf had slightly better cooling performance than R-134a.

CF3I is a fire retardant, so deleting it leaves HFO-1234yf with flammability questions. However, Honewell and DuPont claim flammability is so weak that HFO-1234yf could be used in conventional direct-expansion A/C systems, in which the refrigerant circulates through to the cabin, where an underdash heat exchanger (the evaporator) vaporizes and absorbs heat. Until now, the companies have long objected to the direct-expansion use of any flammable refrigerants, including the mildly flammable R-152a.

The companies previously presented results of HFO-1234yf flammability tests, including comparisons with R-152a and another mildly flammable one, R-32 (which has too high a GWP for EU consideration). R152a is being considered only for secondary-loop heat exchange, in which the refrigerant vaporizes underhood in an additional heat exchanger; this chills the nonflammable liquid that is then circulated through a passenger cabin heat exchanger. This is safer but adds cost and complexity, and there is a performance loss.

R152a is measurably more efficient than R-134a, compensating in part for the loss and presenting the opportunity for chilled liquid storage to maintain A/C cooling through a traffic stop in a hybrid [car] with the engine off. However, HFO-1234yf would have to be sufficiently safe to be circulated from underhood to the cabin or it would not get meaningful consideration. So the recent Honeywell/DuPont presentation addressed flammability in detail.

HFO-1234yf is flammable in concentrations of 6.5 to 12.3% in air, compared with 3.9 to 16.9% for R-152a. However, HFO-1234yf will not ignite even with a glowing hot wire and barely ignites with a butane lighter (R-152a ignites with both).

HFO-1234yf passes the ATM D 3065-01 test for flammability — an aerosol spray at a lit candle-type flame. Like a spray of essentially nonflammable R-134a, HFO-1234yf extinguishes the flame. The flammability envelope also is very small, as shown by CFD modelling of an HVAC system with a 550g (19.4 oz) charger of refrigerant, and venting valves triggered by a sensor detecting a leak. The model shows the flammability regions are small areas at the exits of the A/C registers and are gone within a second after the vents open. Flammable concentrations do not collect elserwhere in a passenger cabin, which significantly reduces the possibility that an ignition source with sufficient energy can be present in the flammability region during a leak, according to Honeywell/DuPont.

The refrigerant has extremely low burning velocity. In a test using a tube 150cm (59 in) long and 38mm (1.5 in) diameter, the HFO-1234yf flame propagated less than 8cm (3.2 in) up the tube [before extinguishing itself]. A comprehensive risk analysis of the flammability is in progress.

As a single-compound refrigerant like R-134a, HFO-1234yf has no glide (temperature difference between vaporization and condensation), simplifying performance calibrations.

====
The article also includes pressure/temperature and physical-properties comparisons between R134a and HFO1234yf. The pressure/temperature curves are almost identical below 50°C, above which the HFO-1234yf exhibits slightly lower pressure for any given temperature. The degree and placement of this divergence looks to me very similar to that between R-12 and R-134a, in the direction that suggests the new refrigerant's pressure/temperature characteristics are closer to R12 than to R134a. The significance for older cars is obvious.

Here's the physical characteristics comparison from the article (with limited R12 data I've added from another source):

Boiling point Tb

1234yf: -29°C
134a: -26°C
12: -29.8°C

Critical point Tc

1234yf: 95°C
134a: 102°C
12: 112°C

Vapor pressure Pvap MPa (25°C)

1234yf: 0.677
134a: 0.665

Vapor pressure Pvap MPa (80°C)

1234yf: 2.44
134a: 2.63

Liquid density, kg/m3 (25°C)
1234yf: 1094
134a: 1207
12: 1292

Vapor density, kg/m3 (25°C)
1234yf: 37.6
134a: 32.4

====

Obviously, there remain questions not answered by this article. There'll surely be issues related to lubrication chemistry and possibly seal-materials compatibility. They may be easy to address (flush & fill system lubrication), moderately easy to address (flush & fill + replace certain O-rings and soft seals, maybe need a different desiccant in the filter-dryer) or they may be difficult to address (more complicated compressor compatibility issues, etc.). But the results of Toyota's drop-in test are very encouraging, I think. I will be interested to keep track of how this develops.

(I am sure it will do nothing to quell the patent-expiry conspiracy theories given the involvement of DuPont...)

TRB on Fri April 18, 2008 1:35 PM User is offlineView users profile

As with all the previous approved refrigerants. If this gets approved, we in the industry will adapt for it's use. But will have to wait and see how it plays out.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

bohica2xo on Fri April 18, 2008 1:37 PM User is offline

It might work in the EU, where they will put up with crappy systems, and have a mild clinmate.

The lower critical temp of 134a is bad enough here in the southwest USA, but that stuff is worse. Bring that "drop-in toyota test" here to Las Vegas in July, and sit in stop & go traffic on the strip for an hour at lunchtime...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Chnaane on Fri April 18, 2008 1:41 PM User is offline

I think it's early to be saying either "it will work great" or "it won't work at all".

mk378 on Fri April 18, 2008 1:46 PM User is offline

Remember the Chinese R-134a tainted with "unsaturated contaminants?" That's all this stuff is, unsaturated. Leave a double bond on the end of any molecule and it's ripe to polymerize. Making plasticy, rubbery stuff that doesn't belong in any A/C system.

Also lower Tc is never good, car A/C is almost always limited by the condenser and this doesn't help. If it lowers the mileage of the car even a little the increased CO2 from the tailpipe will readily offset any improvements from occasional leaks.

TRB on Fri April 18, 2008 2:03 PM User is offlineView users profile

Quote
Originally posted by: bohica2xo
Bring that "drop-in toyota test" here to Las Vegas in July, and sit in stop & go traffic on the strip for an hour at lunchtime...B.

They told us R134a was a drop in replacement 15 years ago also!

-------------------------
When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com


Edited: Fri April 18, 2008 at 2:27 PM by TRB

bohica2xo on Fri April 18, 2008 2:23 PM User is offline

Dammit 378, there you go with all dem chemistry facts again! LOL RefrigerantRubber will be the new eco-saviour...

I think I better go blow this keyboard out - maybe it will remove the sarcasam. A couple of cans of duster should do the trick.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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