Air conditioning gas

[GTSBoy]

Originally posted by slick
Then with regard to the 30L of LPG in your dual fuel car you would be able to point me to the clauses that say the LPG cylinder needs to be in a sealed compartment. And that a boot is not a suitable compartment on its own? As there are difficulties with sealing, venttilation and the presence of electrical equipment located in the boots of most cars. Also that all pipes adn associated connectors will be sealed in a sub-compartment and vented to the atmosphere away from things like the exhaust.

An you will note that no-one does it that way?

Another instance of the codes/standards/rules being impracticable (or near enough so in view of the costs involved).

When I spoke of gas codes I was talking about AG501 and the other real gas codes. Not the piddly little stuff that applies to motor vehicles. I don't usually work on combustion systems smaller than 5 MW. We spend half our time convincing paper pushers that the code(s) are either inadequate and so we have to put more safety equipment into a system, or that the codes are stupidly restrictive and were clearly written by a moron and that our system will be safe enough as is.

It is impossible to obtain a copy of any Australian Standard (or international equivalent) and design something that is safe and effective just by reading the code.

In fact NFPA 8503 (standard for safe design and operation of coal fired furnaces) actually has several clauses to exactly that effect at the front!! What a cop out.

cheers

[krawler]

Look at all the fridgies fighting, its funny cause it is...

Anyway.

Whether you've got a 134a system or a 12 system, you can regass both with SP34E. Its basically 95% 134a with a whisker of LPG in it. Because refrigerant is a fire retardent in itself, you dont have to sook about getting a fire in your car. And because of the LPG content its more efficient than 134a and helps assist in the return of oil to the compressor (more so a problem on commercial installs instead of automotive).

Moral of the story?
Ignore the mechanics and car aircon guys who insist on using 134a. Use SP34E. Then you dont have to retrofit anything and the only charge is an evacuation and regass. No new driers, no new oils, no nothing.

Another gas thats appeared is 34M which I believe is SP34E thats been mixed in a reactor. The moral of this little story is that even fi you get a leak that would normally dump just part of a blend out (leaving the system full of and inefficient gas made up of an incorrect blend) you dump a good mix so assuming its a small shaft seal leak (read: unavoidable) you just need a top up to make it work 100% again, instead of a top up only bringing capacity back to say 80% (if you wanted 100% again you need to dump all the gas, evacuate and recharge).

w00t.

[hamish]

OK, I'll chase up SP34E & 34M.

But I'd still happily use propane/butane if it were readily available.

[tandy ass]

Sorry to drag up this thread however I want a bit of clarifying and further info about air con systems.

Originally posted by slick
On the otherhand the evaporator has refrigerant running to it from the engine bay into the passanger compartment. When the airconditioning system is fully charged and operating the evaporator is flooded with liquid to make the system operate efficiently. This would mean that ~40-50% maybe more of the systems total charge is in the cabin when ever the system is operating.

Correct me if I'm wrong but dont air con systems remove heat by evaporating and deliver heat by condensing? Hence I thought there is SFA gas in the passenger cabin while there is a heat exchanger full of gas (in liquid form) in the engine bay. Or do I have something mixed up here?

About the refrigerant gasses. How do you measure how much is charged into a system. I'm more interested in the home/industrial air con systems, how do you know exactly how much is in them? Also, how are they evacuated of all air?

Cheers

[GTSBoy]

Bozz,

Taking your questions in reverse order.

You use a vacuum pump to pull the system down to a fairly hard vacuum. That ensures that there is very bloody little of anything in there before you start putting stuff back.

You measure how much you have put into the system by weighing your cylinder of gas as you fill (before - after = charge).

The evaportaor (in the cabin) converts liquid refrigerant to gas. So there is a lot of the mass of the total charge in there. (As per what Slick posted). The condensor takes the high pressure refirgeant gas and pulls the heat out of it that it got from being compressed, and hence converts it back to liquid. So there tends to be a bit of liquid phase in that core too, and of course the whole plumbing from the condensor to the evaporator (and a good chunk of the evap core) is full of liquid too.

cheers

[tandy ass]

GTSBoy, I thought that was what the TX valve was for, to limit flow and hence convert the liquid to a gaseous state, absorbing heat in the process. Isn't this at the entry point of the internal heat exchanger? I thought the compressor intake was gaseous from the heat exchanger in the cabin and output liquid, going to the heat exchanger in the engine bay.

2) Where do you get a suitable vacuum pump :p

[GTSBoy]

Bozz,

Not quite. TX stands for thermal expansion. The TX valve is feedback controlled by the evaporator temperature. If you have ever looked at one closely you will see the little copper tube that runs from the core to the TX valve. As the core temp rises that tube's internall pressure increases and opens the TX valve a little more, which lets more liquid into the core where it evaporates.

(In actual fact, there is a fair amount of the phase change that happens at the TX valve and so very cold gas goes through the evaporator and warms up. As load goes up, more and more of the refirgerant makes it through as liquid and evaporates at the core.)

The compressor most definitely puts out hot gas. If you get any liquid into a compressor it can destroy the compressor totally in just a few revolutions...same as hydraulic lock in an engine. The condensor takes the heat out of the hot gas and because it is at high pressure, liquifies the gas at the sort of temperature that you could expect at the front of a car in summer (30 - 75 C or therabouts depending on pressure).

If the TX valve gets stuffed and stays too open it will push a lot of liquid refrigerant through the evaporator...more than there is heat available to evaporate it and you will get liquid at the compressor inlet. Not good.

cheers

[GTSBoy]

2) From a fridge mechanic I suppose.

[Turbo4WD]

mate of mine who lives in NSW was playing around with LPG in a car which had lost its R134A. He said with the LPG it was not as cold as with the 134A. Is there any trick for filling with LPG and geting the right levels ect?

[sprint32]

I'm very interested in this LPG idea as a home instalation not only because my A/C is no longer effective, but also using it in a water to air intercooler instead of water. Has anyone tried this before? What were the results? could it be effective?
I want to do this on my r32 gtst, but could be really advantageous to mr2 drivers!!!

[GTSBoy]

I'm at a loss to understand how you would use LPG in an intercooler, unless you were thinking about running an actual air conditioner set up to do the cooling. But the size of teh air con system needed to cool that much air over such a large temperature would probably cost you 50 HP at the front pulley to run.

I don't recommend people using LPG to fill their air-con themselves (unless they have done a refrigeration course, of course.). I have no problem with getting it done by a fridge/air-con mechanic. It only costs a little bit of cash to get it done.

cheers

[sprint32]

Yes, Imeant to use it to cool the air.
So it cant be done? thats cool. I didnt think it would be worth it.
But it was worth a try. Besides, i think water runs more efficient anyway. It takes four times the energy to increase a set volume of water than it does the same volume of air.
All this refrigerant stuff is pretty new to me, I just wasn't sure about the efficiency of these gasses.
I'll just use an air-con core to cool the water then. should be better than the small units everyone always seems to use.

[The Pupat]

You'll wanna use something like an oil cooler not an air-con core.

The air-con core is designed to flow gas not fluid.

[postman]

wasn't there a thread not that long ago about diesel's in the US using LPG to cool the charge air down, similar to methanol injection?

[sprint32]

water and gas are fluids. aircon condenser tubes flow better the most radiator tubes so they have a slightly higher flow rate. however, being one continuous tube instead of many shorter tubes, it will have slightly more friction as a whole, hense the large size of the tubes to keep the flow rate up.
as a consequence of the water taking so long to travel through the entire core it should exit the cooler with a lower temperature.( although obviously not lower than ambient.) just my little way of creating something with overkill incase of masive heatsoak.lol.

any thoughts guys? I hope my theorys are sound.