CO2 A/C !

Atilla the Fun · Post by **Atilla the Fun** » Sat Jun 21, 2008 2:45 pm

So I just read in my local newspaper that near-future cars will use carbon dioxide as the refrigerant. It's supposed to be 25% better, plus if CO2 gas a Global Warming Potential of 1, then R134a is GWP 1400 or so. This being the case, I see no point in converting my Fiero to R134a, as the CO2 should be available by the time my car is running.

Aaron · Post by **Aaron** » Sat Jun 21, 2008 5:48 pm

i kant reed good.

whipped · Post by **whipped** » Sat Jun 21, 2008 6:17 pm

Seems like it would be prone to breaking more. Don't you need about 2000psi to liquify co2? R134a is ~200psi.

Blue Shift · Post by **Blue Shift** » Sat Jun 21, 2008 7:52 pm

the room temperature pressure of a CO2 cylinder for paintball is ~900 PSI. It's within a reasonable range for refrigerant use, but you'd need some brawny lines and a brawny pump to handle it, I think. Probably make for good refrigerant, though.

I think they also use liquified CO2 to leach caffeine from coffee beans, and to dry clean stuff when carbon tetrachloride went away.

Atilla the Fun · Post by **Atilla the Fun** » Sat Jun 21, 2008 9:25 pm

The article said nothing about pressure, but I'll look for it tonight.

lucky · Post by **lucky** » Sun Jun 22, 2008 4:06 am

Blue Shift is right about the pressure. A full tank of CO2 for a paintball gun is 2/3-3/4 liquid at around 900psi. I've seen 1/4 steel brakeline used to feed it to a AutoMag, so I don't think lines for CO2 A/C shouldn't be that difficult/expensive.

Aaron · Post by **Aaron** » Sun Jun 22, 2008 11:26 am

I doubt they would be, however how safe is storing that for an extended period of time in an automobile? What happens in an accident, God forbid a bad accident? If the tank gets ruptured, it becomes a projectile, one with a lot of force.

Lastly, would the system still be essentially operable without maintenance? For example, would the CO2 lose its effectiveness, or can it be used over and over again like today's refrigerants? I guess what I'm asking is, will the bottle run out, or can you reuse the CO2 over and over again?

whipped · Post by **whipped** » Sun Jun 22, 2008 12:10 pm

There's no bottle. It would be just like a normal AC system, but with CO2 as the refrigerant.

I think they would probably have to eliminate any rubber hoses, but from what I heard, the top tier auto makers are moving towards that anyway due to stricter refrigerant emissions laws.

While a room temp bottle of co2 is 800 psi, a room temp bottle of R134a is 80 psi. But they still need a safety margin for the high temps effect on vapor pressure. So if an ac compressor typically reaches 200+psi on the high side, it wouldn't surprise me to see 2000+psi on a CO2 system.

Aaron · Post by **Aaron** » Sun Jun 22, 2008 12:16 pm

Oh ok.

Then I don't see a problem with the pressure, assuming all of the components can handle it.

Kohburn · Post by **Kohburn** » Mon Jun 23, 2008 9:17 am

Aaron wrote:I doubt they would be, however how safe is storing that for an extended period of time in an automobile? What happens in an accident, God forbid a bad accident? If the tank gets ruptured, it becomes a projectile, one with a lot of force.

Lastly, would the system still be essentially operable without maintenance? For example, would the CO2 lose its effectiveness, or can it be used over and over again like today's refrigerants? I guess what I'm asking is, will the bottle run out, or can you reuse the CO2 over and over again?

no it wouldn't become a projectile, it pops and peals open if its metal tank, and it cracks and leaks out very quickly and loudly if it s a carbon fiber tank. most likely they would use overrated tanks like scuba tanks that are good for up to 5000psi for safety sake.

phase changing CO2 from gas to liquid to gas again doesn't brake it down, it doesn't combine with anything in the system.

the high pressures required to liquify it and the risk of accidentally going to solid state (dry ice) inside the system are probably the reasons why i hasn't been done long before now.

Kohburn · Post by **Kohburn** » Mon Jun 23, 2008 9:23 am

with using CO2 you wouldn't need as big of lines as are used on the refrigerant systems because the energy released from the phase change of the CO2 is much greater (the energy to put it back to liquid is also greater) so a smaller volume of it is necessary for the same cooling effect.

smaller volume cn also mean a smaller a/c compressor. if they used the basic 8-900 room temperature pressure as the standard charge pressure then refilling could be handled with an upside down paintball tank to put liquid back into the system.

in fact asside from the high pressure belt drive compressor i could peice together a co2 based refrigerant system at home.

Atilla the Fun · Post by **Atilla the Fun** » Mon Jun 23, 2008 9:49 am

Putting a cog drive and a Gilmer belt on a compressor shouldn't be much of a challenge, I think the challenge is getting the compressor, condensor and evaporator to survive. This new refrigerant is called R744. Or is that 774?

lucky · Post by **lucky** » Mon Jun 23, 2008 4:08 pm

CO2 tanks are equipped with a burst valve because they are a high pressure, that would blow before the tank in any event. The tanks are built pretty ruggedly, I wouldn't worry about it being any kind of projectile or shrapnel. Best of all if it did rupture during an accident it would be like having an automatic fire suppression system.

Atilla the Fun · Post by **Atilla the Fun** » Mon Jun 23, 2008 6:34 pm

credit where it's due: the article is in fact in the new issue of Motor Trend, it has the black 2010 Camaro SS on the cover.

Atilla the Fun · Post by **Atilla the Fun** » Tue Jun 24, 2008 10:33 am

Oops! Road and Track.

p8ntman442 · Post by **p8ntman442** » Wed Jun 25, 2008 12:29 pm

you wouldnt need a tank, and you could run a very small piston type electric compressor at the evaporator, therefore having very little refrigerant under pressure, and almost no tubing in the engine bay.

figure .5 tons of cooling to cool your car in the summer. this is 6000 btu or ~4 hp to run.

Not bad. Id give anything to get rid of the AC lines under the hood of my cars.

whipped · Post by **whipped** » Wed Jun 25, 2008 12:49 pm

How would that work? 3500 watt electric motor for the AC? I don't think so. Starters use 1.3kw and you can't run them more than a couple seconds. Plus you'd still need to plumb the condenser somewhere.

The Dark Side of Will · Wed Jun 25, 2008 1:30 pm

There's a reason current A/C systems have the compressor belt driven...

Nashco · Post by **Nashco** » Wed Jun 25, 2008 2:45 pm

The Dark Side of Will wrote:There's a reason current A/C systems have the compressor belt driven...

Unless of course it's a hybrid and has a high voltage pack on board, then they get to do all sorts of fun stuff with electricity.

CO2 is a real PITA, it doesn't have much going for it unless you believe that you're doing the world some good by using it. Consider the greenhouse gasses created to make the parts that you'd use to retrofit, ship them, install them, etc. and then all of the sudden it seems kind of silly. If you're talking about a newly designed car that had it in mind from the get-go, then it makes a bit more sense, but even then it's a hard sell.

Bryce

Blue Shift · Post by **Blue Shift** » Sun Jul 06, 2008 12:10 am

CO2 is too easy, let's just use pure Nitrogren at a few thousand PSI. Or build a system that'll liquify atmospheric air, then expand it and blow it into the cabin. There ya go! :la:

Real Fiero Tech

CO2 A/C !

Would you try it?

CO2 A/C !