'Free' Air Con from LPG vapourisation old uk.rec.lpg topic

[DodgeRover]

Going way back does anybody remember a post (or series of them) on the old LPG newsgroup about using the latent heat of vapourisation of LPG (i.e the bit we usually get rid of into the cooling system) to provide the cooling in an air con system. I'm pretty sure it was by someone called Austin Shackles or something similar who had a V8? minibus/ school taxi

I tried a search but while I could find some of the group archived I couldn't find it.

It sounded quite feasible at the time. Thanks

[classicswede]

I'm sure it was someone from upside down land. I do remember the thread but not the exact details.

[DodgeRover]

Found the thread (eventually)
http://uk.rec.cars.fuel.lpg.narkive.com ... g-the-cold

[rossko]

If you want to do the sums, you only need to know the rate at which you use LPG (how much per hour) and the propane latent heat of evaporation.
Last time I roughed it out, it was about 1kW at full throttle, more like 100W in cruise - uselessly small I reckon.

[DodgeRover]

Might just about be enough for me as I've only got the front 2 seats then a bulkhead in the van, will try and remember my basic A level physics and see what theoretical temperature drop that could give me. I probably use more LPG than average per hour a 2.0 pinto pulling 3 ton of van isn't the most economical thing....

[SimonHobson]

It's something I mused about on and off since the 110 is "somewhat thirsty". I estimated something like 1kW worth of cooling while "making progress".
My thoughts were to have a pre-vapouriser set to drop the pressure to (some value to be determined) so that the outlet temperature would be (say) -5˚C. If there isn't the heat input, then the outlet would be mostly cold liquid that the main vapouriser would then heat and evaporate. With a good heat input, the output of the pre-vapouriser would be cool vapour (and perhaps a bit of liquid).

I did have some ideas how to get the "cold" into the cabin - without taking the gas itself inside. As an alternative, I did think of making an ice box and freeze ice packs for the cool box and/or keep the chocolate nice and hard

[LPGC]

Seems a novel idea but I can't see there being a practical way of achieving the free air-con effect without running reducers at too low a temperature or using just the second stage of a reducer along with some kind of pre-reducer like SimonHobson suggested. The only semi-practical way I can think of is to design a heat exchanger to fit between existing air-con condensor and a normal reducer - solenoid controlled water flow through the reducer needed for if the air-con is ever turned off... Would help the efficiency of the existing ac.

[SimonHobson]

Seems a novel idea but I can't see there being a practical way of achieving the free air-con effect without running reducers at too low a temperature or using just the second stage of a reducer along with some kind of pre-reducer like SimonHobson suggested.

Actually it would need to be a full reducer, not just a second stage. If the cooling load isn't sufficient (or is turned off altogether), then you still need the full vapourise and heat capability. I know it varies with a number of factors, but I find I can run the Romano Super on full vapour feeding the V8 in the 110, and it was the same with an R90 in my V8 Disco. On the other hand, my mates RR would lose power any time the tank pick up got uncovered (such as when accelerating hard ) - until he threw the reducer off and fitted a Romano.

I did also toy with running a closed liquid loop (with strong anti-freeze) - and a heat exchanger to provide engine heat to regulate minimum temperature. But I figured it would be a bit cold and the reducer would tend to collect a lot more heavy ends (amongst other ills).

[LPGC]

I thought, with the system set up as you suggested SimonH, there wouldn't be much point in ever turning the aircon off as it would always be free.. Maybe on a freezing cold morning though eh!

From what you've said, would seem the Romano has a bigger first jet than your mates previous reducer?

I'm sure I once read somewhere that some BMW AC systems were designed to use propane as the refrigerant gas - sounds dodgy to me but I think the site was something official / authoritative.

Heavy ends might be a problem with any such system, but I suppose there could be a reheat system somewhere in the vapour line to at least protect injectors etc.

[Gilbertd]

I'm sure I once read somewhere that some BMW AC systems were designed to use propane as the refrigerant gas - sounds dodgy to me but I think the site was something official / authoritative.

Propane can be used in older, pre '95, AC systems that were intended to use R12 refrigerant. It cools just the same as R12, is compatible with the seals used in R12 systems and will mix with the compressor oil that is suspended in the refrigerant. It would only be a problem if you had a leak as it tends to be slightly more inflammable than R12......

As it has been illegal to manufacture R12 for a considerable number of years now, it leaves the owners of older cars with a problem. No AC or spend quite a bit converting the system to the current R134a refrigerant. You can get blends that are supposed to be compatible with the seals, etc in the older systems but all of the old refrigerant should be slurped out or you can end up with a system clogged with a goo. In the US it is possible, if you know where to go, to still get 'fake' R12, manufactured in Mexico and smuggled across the border labelled as something els,e but it is widely suspected that it consists simply of Propane with the stenching agent removed.

[SimonHobson]

I thought, with the system set up as you suggested SimonH, there wouldn't be much point in ever turning the aircon off as it would always be free.

It might be free, but you wouldn't always have a load for it or want it on full. Besides, if I was using it for an icebox, then once it's cold there'll only be a small load.

From what you've said, would seem the Romano has a bigger first jet than your mates previous reducer?

You'd be surprised how small the metering jet in a reducer is ! Yes, the Romano and OMVL R90 both seem to run fine on vapour with a 3.5 V8 in a 2ton vehicle. And just think how small the hole is down the 6mm pipe.

I'm sure I once read somewhere that some BMW AC systems were designed to use propane as the refrigerant gas - sounds dodgy to me but I think the site was something official / authoritative.

Propane (and other HCs) were widely used as refrigerants before the chemical companies came up with the CFC and HFC refigerants and persuaded everyone to switch away from the "bomb in your kitchen" flammable gasses. I ran the AC in my Disco on propane for some time - worked just fine. I believe propane is a drop in replacement for R22, but for R12 it would really be a 50-50 mix of propane and butane. Years ago when I was "researching" it - I found someone's dissertation for an Australian uni where they'd researched the relative efficiencies etc and come up with the above.

Heavy ends might be a problem with any such system, but I suppose there could be a reheat system somewhere in the vapour line to at least protect injectors etc.

Well that was partly my reason for keeping the whole reducer - vapourise any liquid that the AC/fridge load doesn't deal with, and heat all the vapour up to full temp.

[LPGC]

From what you've said, would seem the Romano has a bigger first jet than your mates previous reducer?

You'd be surprised how small the metering jet in a reducer is ! Yes, the Romano and OMVL R90 both seem to run fine on vapour with a 3.5 V8 in a 2ton vehicle. And just think how small the hole is down the 6mm pipe.

The metering jet size is very small on the many different types of reducer I've worked on... That's why I suggested not using that stage of the reducer.. If we have a 2 stage reducer and the first stage is the limiting factor of the reducer while running on liquid propane, then given liquid propane is many times more dense than propane vapour, then we could expect the reducer to flow only a small fraction of it's rated flow rate while running on vapour. The metering jet might not be the limiting factor of the reducer while running on liquid, but even if it is only open half duty when the reducer is at full load then the jet will still be very much the reducer limiting factor while running on vapour. I expect this is why a vehicle running on an LPG mixer system can run OK at light loads on an empty tank (with enough vapour pressure), but go very lean and run very poorly when the driver puts his foot down.

Don't some aircon systems have a variable flow jet on the evaporator? How about a closed loop evaporator jet control system set up to keep pressure on the vapour side of the jet the same as it would be in the primary stage of a 2 stage reducer?

[SimonHobson]

The metering jet size is very small on the many different types of reducer I've worked on... That's why I suggested not using that stage of the reducer.. If we have a 2 stage reducer and the first stage is the limiting factor of the reducer while running on liquid propane, then given liquid propane is many times more dense than propane vapour, then we could expect the reducer to flow only a small fraction of it's rated flow rate while running on vapour.

By metering jet, I mean the metering jet - ie the one that controls the vapour flow according to demand. It's surprisingly small ! However, from memory when I last overhauled on, both the Romano and R90 have liquid jets of a similar size to the metering jet - except both (well the "Super" version of the Romano at least) have a secondary vapour jet that kicks in under medium to high load

I expect this is why a vehicle running on an LPG mixer system can run OK at light loads on an empty tank (with enough vapour pressure), but go very lean and run very poorly when the driver puts his foot down.

Indeed, once you are drawing vapour then the game changes somewhat.

Don't some aircon systems have a variable flow jet on the evaporator?

Most do. There's a temperature sensor bulb on the evaporator outlet which controls the inlet orifice valve. If you don't pull out enough heat energy, then instead of letting the evaporator get colder and eventually have liquid return to the compressor, the valve throttles the inlet liquid flow - less liquid in = less to evaporate = less energy needed to evaporate it.That is actually the reverse of what we are after though.

How about a closed loop evaporator jet control system set up to keep pressure on the vapour side of the jet the same as it would be in the primary stage of a 2 stage reducer?

Which is what I had in mind. Effectively put the 1st stage on <whatever you want to keep cold> and it'll cool that <something> down to the boiling point of propane at that pressure. But once you get down to that temperature, you'll have a mixed flow out and will still need the first stage in a water heated reducer - though I suppose you could do away with the control valve and open up the orifice since the pressure control is now upstream.

[SimonHobson]

Oh yes, ...
In many air-con systems, especially reversible ones, there is no metering valve - just an orifice or capillary tube.
If you pass a 2 phase mixture through a small orifice, then which vapour will pass through at a higher volume flow rate, it will be a lower mass flow rate than liquid. One of the few facts I recall from those sections at university

So in cooling mode, the capillary tube will restrict the mass flow rate if there is vapour in the flow line form the compressor & condensor (outdoor unit). Once the outdoor unit has extracted enough heat to supply liquid then the mass flow rate will increase and cooling will happen.
In heating mode, the reverse happens. The outdoor unit pumps hot vapour in, and the capillary restricts the mass flow rate until the indoor unit has extracted enough heat to condense into into liquid. The liquid evaporates again in the radiator of the outdoor unit taking in heat from outside.

[LPGC]

I know there are reversible systems etc, not sure what vehicles have them though... Is it some Mercs? I thought a lot of older aircon systems just had an orifice? Some luxury vehicles, limo's etc, have ac systems that can work for so long with the engine off - Is this using some kind of built up header of refrigerant on the front side of the pump?

Gilbert, interesting about propane and R12. Sorry I missed your post, I missed it before my last post so will acknowledge it now I've noticed it mate! If I can find a cheap enough mk2 facelift Granada I'm going to buy it, I had quite a few of them when I was younger and wouldn't mind another.. albeit with a different engine to the standard 2.8 - maybe a 4L Cologne from an Explorer, maybe with a Turbo or maybe a V8. I'd preferably get another with aircon, they use R12.

Which is the most efficient refrigerant gas then? I've read somewhere before that some American vehicles used to get vent temps of -8deg while in the desert in mid-day sun with the aircon switched to 'desert' (read dry air) mode...

[Gilbertd]

One of my neighbours runs the local branch of the Granny owners club and has a very tidy Mk2 estate with the 2.8 Cologne V6. I don't think the Explorer used the Cologne, as that was a German designed lump and the Exploder is a Ford US vehicle. I had one, briefly until I discovered it was diabolical for towing and it's an OHC engine not a pushrod job like the Cologne or the Dagenham designed Essex (never could work out why two divisions of the same company both designed a range of V4 and V6 engines around the same time that were actually very similar in design and both went into production). On my old '93 Range Rover Classic, I got some stuff called Johnsens Freeze 12 to put in the AC system and that worked really well. My '91 Maserati also an R12 system and I was using some stuff called Isceon 49 which went straight in and did the job. However, I think there has been some change in legislation because the company where I used to get it don't sell it any more. In fact, they don't even sell small cans of R134a any more even though they will sell you a charging hose! The Masser does have a slight leak though where a previous owner tie wrapped the hoses to keep them neat but one of them was too close to the back of the power steering pump belt so it ate through it. It's so cramped in the engine bay that it took me ages to find the leak and by the time I did, I couldn't get anything to put in the system to make it work again! It was while searching for something that I can put in there that I discovered about using Propane. Just need to make up a hose so I can charge the Masser AC from the fuel tank of the Range Rover......

[SimonHobson]

Which is the most efficient refrigerant gas then?

There's no such thing. All the different options have different characteristics - it's a matter of picking what's best for your situation.
Back when I was experimenting, it was either before the massive switch to R134a, or at least while R22 and R12 were still widely used.
Taking two gasses you'll probably be familiar with, propane and butane. As fuel gasses they come in red and blue cylinders (generally).

Propane will still boil off at -40˚, butane stops boiling off at around 0˚C - as I found out by experience when I borrowed a caravan and it turned out to be a cold night. Took me a little while to realise why I couldn't get enough of a flame to boil a kettle, let alone run the heater So if you need your cold end very cold, not much point picking butane (though it would go below 0˚C with some suction - but on the other hand, if you are working at higher temperatures then it'll be fine.
As said, propane boils off at very low temperatures - so for a given set of conditions you'll be working at higher pressures than with butane. On the other hand, if you need to work at lower temperatures then that would balance out.

As I mentioned earlier, some ozzie research paper showed that propane was a drop in replacement for R22 which was widely used in industrial/commercial fixed systems. A 50-50 mix of propane and butane is a drop in replacement for R12 which was the "standard" choice in automotive systems. I ran my Disco with neat propane for years - I figured that it would be less efficient for several reaons :
1) The evaporator would naturally run at a lower temperature - but the control valve would restrict the flow so this would not be an advantage.
EDIT: In any case, you don't want the evaporator too cold - it'll just freeze the condensate and block the air flow with a big lump of ice.
2) The condenser would also run at a lower temperature (for a given pressure) and so would be less efficient at removing the heat.
3) The system wouldn't run at higher temperatures (and hence pressures) if the condenser got hot as the high pressure switch would trip the compressor off.
But, it cost me pennies to fill up from teh same red cylinders I fuelled the car with - vs something like £70 the fist time I had the system filled after fitting it (and before I learned about propane and stuff) For that difference in cost, I was happy to take the loss in effectiveness - not that it didn't do it's job

[LPGC]

One of my neighbours runs the local branch of the Granny owners club and has a very tidy Mk2 estate with the 2.8 Cologne V6. I don't think the Explorer used the Cologne, as that was a German designed lump and the Exploder is a Ford US vehicle. I had one, briefly until I discovered it was diabolical for towing and it's an OHC engine not a pushrod job like the Cologne or the Dagenham designed Essex (never could work out why two divisions of the same company both designed a range of V4 and V6 engines around the same time that were actually very similar in design and both went into production)

I was a member of the Granny owners club back in the 90's
The Explorers used the 4L OHV Cologne engine, produced in Germany, until year 2000.. I've read about a Cortina powered by a 4L OHV Cologne with twin turbo's making 700bhp (Cortina tubbed out and back axle changed to a Volvo unit). If I were to go ahead and chose the 4L Cologne it would be for easy installation and standard bolt pattern, could also copy the Cortina's engine spec and choose from many gearboxes, C3, C4, Cosworth Scorpio spec box, etc.

As I mentioned earlier, some ozzie research paper showed that propane was a drop in replacement for R22 which was widely used in industrial/commercial fixed systems. A 50-50 mix of propane and butane is a drop in replacement for R12 which was the "standard" choice in automotive systems. I ran my Disco with neat propane for years

So hmmm... An R22 / R12 aircon pump would work OK as an LPG transfer pump?

[SimonHobson]

So hmmm... An R22 / R12 aircon pump would work OK as an LPG transfer pump?

No.
1) It's designed to pump vapour and won't take kindly to pumping liquid
2) It's designed to run with free oil in it's sump, which gets carried around the system with the refrigerant. Pump LPG through it and you'll wash the oil out and leave it unlubricated which I rather think doesn't make for a long life.

[LPGC]

So hmmm... An R22 / R12 aircon pump would work OK as an LPG transfer pump?

No.
1) It's designed to pump vapour and won't take kindly to pumping liquid
2) It's designed to run with free oil in it's sump, which gets carried around the system with the refrigerant. Pump LPG through it and you'll wash the oil out and leave it unlubricated which I rather think doesn't make for a long life.

1. Maybe get around the vapour pumping by drawing vapour from the bulk tank you use to fill a vehicle instead of liquid? The high pressure side of an R12 system is liquid isn't it (see liquid pumping through sight glasses on the HP side anyway)...?
2. Ahh yes I was aware that all aircon systems have a lube oil mixed with the gas. Not much getting around that problem but I wonder with all the talk of a bit of oil in all LPG etc how long an aircon pump would last if operated at reduced rpm...

I have a working old AC pump from an old 1990 BMW750... Wonder if it's worth a try if I connect fittings and drive it via a belt and electric motor...?