tapping suction line for secondary cooling device?

[elrey]

Is it possible to tap into the suction line after the evaporator and use the lower temp vapor to cool
a secondary (higher temp) chiller? Without changing the existing system.

http://creativeion.com/rey/vw/ic/tap_refrigerant.gif

Thanks,
Rey

[mark beiser]

You would have oil return and compressor cooling issues.

Unles you overcharged the system enough to flood the evaperator coil, there wouldn't be much cooling capacity at all in the vapor return anyway, since there is no liquid refrigerant to boil off.

[elrey]

You would have oil return and compressor cooling issues.

Unles you overcharged the system enough to flood the evaperator coil, there wouldn't be much cooling capacity at all in the vapor return anyway, since there is no liquid refrigerant to boil off.

Thank you for the reply!

Are you saying overcharging would increase cooling capacity or addresses oil return/compressor cooling issues?

I'm looking to keep maybe 2gal of water EWT of ~80 degF - 90 degF to ~60 degF flowing ~2-4 gpm

Thanks again,
Rey

[Wild Leg]

I think, what you are asking is, "Can I put a much larger evaporator in an existing system?"

The existing system must be capable of handling the additional heat load. It doesn't suddenly acquire more capacity with just one change.
The compressor must still be cooled and lubricated.
The metering device must allow enough refrigerant to flow to maintain proper superheat. The condenser must be large enough to reject the additional heat.
Essentially, if the system was properly matched before the changes, then it will not be properly matched afterward.

What size is this system?

[Edited by bwal2 on 10-26-2004 at 09:05 PM]

[beenthere]

To cool 2gpm of water from 80 to 60 would take 19,728 btu/hr.

Maybe you should buy a small chiller instead.

[elrey]

I think, what you are asking is, "Can I put a much larger evaporator in an existing system?"

Not quite. I want to intercept and utilize some of the
relatively low temp vapor leaving the existing evaporator
to chiller water.


To cool 2gpm of water from 80 to 60 would take 19,728 btu/hr.

Yes that would be ideal, but
the temp change could happen over time (several passes thru
secondary coil).

Forgive me, but this is not for a residential application.
This was the first forum I saw and posted.

App:
Automative air condition system. I'm trying to "leech" the suction line to chill water for an air-to-water intercooler
by means of a small coaxial tube-in-tube coil.

Thanks,
Rey

[Edited by elrey on 10-26-2004 at 09:49 PM]

[mark beiser]

Originally posted by elrey

You would have oil return and compressor cooling issues.

Unles you overcharged the system enough to flood the evaperator coil, there wouldn't be much cooling capacity at all in the vapor return anyway, since there is no liquid refrigerant to boil off.

Thank you for the reply!

Are you saying overcharging would increase cooling capacity or addresses oil return/compressor cooling issues?

I'm looking to keep maybe 2gal of water EWT of ~80 degF - 90 degF to ~60 degF flowing ~2-4 gpm

Thanks again,
Rey

No, I'm saying there won't be much cooling capacity in the vapor return line unless the system is overcharged enough to flood the evaperagor coil.
What you are wanting to do won't work.

[Wild Leg]

To cool 2gpm of water from 80 to 60 would take 19,728 btu/hr.


Rey, the a/c system on a car is rated for only somewhere around 15,000 btu/hr. Even a big car has only about 20k capacity.

If you wanted that much cooling, you would have to bypass the passenger compartment's evaporator completely.

I think "no" is still the answer.

Are you trying to build a precooler for the combustion air?

[h2045]

Same piece of pipe in and out,full of gas,no flow,ambient temp.

[binford]

Your best bet would be to put the A/C evaporator into the water tank. I know this option does not fall into "Without changing the existing system". But since it's also most winter do you want cold air blowing inside too?

[dnt]

MVAC systems can be as large as 3 to 4 tons and are setup to supply cooling under extreme conditons so you should have plenty of capacity on a full size car but you will not receive enough cooling from the vapor from the evaporator, you will need to tap into the high pressure line from the condensor to the expansion device and utilize a seperate TXV and a miniature evaporator so the high pressure liquid can be boiled off in the miniature evap to produce cooling. I know of a auto AC site that has some real knowledeable people try this http://www.ackits.com/forum/index.cfm

[absrbrtek]

Agree!! That picture depicts no flow through the secondary loop.
Originally posted by h2045
Same piece of pipe in and out,full of gas,no flow,ambient temp.

[docholiday]

It really is suicidal. No function, the problem is, that in the evaporator under normal operation you would have evaporated the refrigerant and leaving the coil with at least a little superheat. You need the refrigerant to change state in order to offer any cooling. Then even if you could make that work you would be dealing with a real potential for recondensing in the water coil when the water was cool and the ac load was high. There was a thread about EPR valves. Im not going to try to draw a diagram but here is the way.....


Liquid line splits with solenoids to enter each coil paralell.
Since your AC will probably have the lowest suction temperature/pressure you need to install an EPR on the air to air evap. On the water evap a CPR should be installed and the suction lines rejoin. There are many factors to consider such as are you planning to cool the water only when the ac is on, or will it be cooled all the time. Among others.

[rsmith46]

You don't need the liquid line solenoids or EPR & CPR if your only cooling the water when the A/C is on. Do need to feed the second evaporator with liquid and its own TXV.
I have seen it done where the primary evaporator used a TXV and the smaller secondary evaporator used a cap tube.

[elrey]

Thank you all for your time and insight. Because of your
advise/comments, I realize this will not work(as easily as hoped) and have dropped trying to use the A/C system.

I'm now considering pre-compressed NO2 to cool the water.
Of course, this might lead nowhere fast also.

Again, thanks for your help!!

Rey

[Edited by elrey on 10-28-2004 at 05:39 PM]

[elrey]

You don't need the liquid line solenoids or EPR & CPR if your only cooling the water when the A/C is on. Do need to feed the second evaporator with liquid and its own TXV.
I have seen it done where the primary evaporator used a TXV and the smaller secondary evaporator used a cap tube.


So how/where is the vapor from 2nd evaporator tied back into the system?

Thanks,
Rey

[clone477]

Sorry, to bring this back from the dead guys, but had a question for the knowledgable...

If keeping the blower fan on low, or even off for that matter, would basically cause the low pressure liquid to not evaporate(and remove heat) from the cabin evaporator, but instead, evaporate in the looped suction line thats emersed in the water tank. Correct?? Would this setup then function some what effeciently while still allowing no liquid refridgerant back to the compressor. Thanks for the info.

[beenthere]

Originally posted by clone477
Sorry, to bring this back from the dead guys, but had a question for the knowledgable...

If keeping the blower fan on low, or even off for that matter, would basically cause the low pressure liquid to not evaporate(and remove heat) from the cabin evaporator, but instead, evaporate in the looped suction line thats emersed in the water tank. Correct?? Would this setup then function some what effeciently while still allowing no liquid refridgerant back to the compressor. Thanks for the info.

The evap cool would freeze, and you would have no a/c when you wanted it, to say the least of the problems.

[billygoat22]

Why not get a small a/c system and add the new compressor to the accessories already on the engine? Then you would have a unit just for your application.

Fabricate a bracket and a new belt, mount the hardware. Less modification than tapping into the existing system, and could be optimized for the application.

[Shophound]

Existing MVAC systems use split coils all the time, such as in SUV's and minivans which require adequate cooling in the rear sections that the dash outlets could not handle.

What the OP was proposing, if there would even be any flow through that loop of stuff on the suction line, would be nothing but a superheater. The right way is to have two separate evaps with metering devices feeding the right amount of liquid to each coil. Condenser would need to be sized right to reject the additional heat, and the compressor sized to handle extra capacity of refrigerant.

Nissan had a minivan back in the 80's that had a small cooler in the console between the driver and passenger seats. It worked off the MVAC and was a small space. I never asked my friend that owned such a van how well it worked, but it seemed novel at the time.

[will 2]

Ditto what Billygoat said.

Heck, bring it into a ThermoKing shop, we/they could set it up to store icecream in your trunk if you'ld like.

[clone477]

I see what you guys are saying, looks like the best way would be to run a separate evap coil with its own metering device. I know the compressor would displace enough refridgerant(it was used in many older duel ac systems), and the condenser has already been upgraded from the old tube and fin design to parellal flow with 20% more surface area. Can anyone recommend a TXV that could be used with the existing fixed orfice tube design??