Insulating air con pipes

[glenhendry]

We have high under bonnet temps, and we have wagons that are hard to cool after becoming hot in the sun (due to large interior volume; a ute cab, in comparison, is easy). The air con compressor pushes cooled gas through the refrigerant pipes but they run through the engine bay, they must lose some of that precious coldness. There are lots of forums saying not to insulate them as condensing water will get trapped and rust the pipes. I dont believe that as they are aluminium. It looks easy and cheap to do, and the cold gas will reach the evaporator unit colder.

My question is, why weren't they insulated in a $100k luxury 4wd which cared about the performance of their air conditioning? I presume someone cleverer than me in thermodynamics decided not to?

Note: I got my air con gas refilled the other day and the air con man was AMAZED at how much gas was in our P38. Often its 300mls or 400mls or 500mls for large cars. P38 has 1400mls!! Interestingly, my brothers L322 Vogue only has ~500mls.

[bee utey]

Not so, the compressor pumps hot vapour which is condensed to less hot liquid inside the condenser, then passed through the engine bay to the evaporator. The cooling effect happens at the expansion valve (TX valve) which is usually close to the evaporator under the dash. Any cool pipe under the bonnet is the return from the evaporator and lagging it will add little to the overall performance.

[mistajoel]

^^ this guy knows his stuff. They insulate conventional air con pipes to stop them from sweating... like a cold glass of water on a hot day.. imagine that in your walls. the insulation stops humid air from touching the pipes.

Nothing would be gained from insulating the pipes under the bonnet of a car.

__________________
I only bother worrying when it stops leaking oil...usually means it's run out..

'96 Disco 300tdi

[mistajoel]

Note: I got my air con gas refilled the other day and the air con man was AMAZED at how much gas was in our P38. Often its 300mls or 400mls or 500mls for large cars. P38 has 1400mls!! Interestingly, my brothers L322 Vogue only has ~500mls.


The amount of gas needed is directly related to the length of pipes running between your compressor, condenser and evaporator... The more pipes, the more gas... must be a fair amount of plumbing in your car :)

__________________
I only bother worrying when it stops leaking oil...usually means it's run out..

'96 Disco 300tdi

[Blknight.aus]

and the size of your condensor and the size of the evaporator, capacity of the pump...

if insualting the pipes made an easily noticable difference to your AC's capability then somethings wrong.

yes, in theory it will make a little difference if your AC pipes are close to your exhaust but in reality the temp of the refrigerant in the High pressure side is over the average temperature of the engine bay

[scarry]

^^ this guy knows his stuff. They insulate conventional air con pipes to stop them from sweating... like a cold glass of water on a hot day.. imagine that in your walls. the insulation stops humid air from touching the pipes.

Nothing would be gained from insulating the pipes under the bonnet of a car.

__________________
I only bother worrying when it stops leaking oil...usually means it's run out..

'96 Disco 300tdi

True,but not quite right.

Recently,(couple of yrs ago now) regulations for some new commercial buildings mean insulation on A/C pipework has been increased.This is to reduce energy and increase efficiency.
I think this is minimal,and not worth the extra work etc etc.

Just another stupid reg we have to abide by:mad:

Also in a conventional A/C with a sealed unit,cold return gas is critical to keep the compresser operating parameters within limits.Un insulated pipework will cause the return gas to heat up and cause the compresser to operate hotter than design,which will eventually cause the oil to break down,and compresser failure.

An off engine drive compresser,or for that matter any open drive A/C or refrig compresser can tolerate higher return gas temperature due to it's design.

As said insulating the return gas line on a vehicle A/C will make minimal,if any difference at all.

i would be more concerned about keeping the condenser coil as clean as possible,as a dirty condenser will make the system very inefficient.

[rick130]

True,but not quite right.

Recently,(couple of yrs ago now) regulations for some new commercial buildings mean insulation on A/C pipework has been increased.This is to reduce energy and increase efficiency.
I think this is minimal,and not worth the extra work etc etc.

Just another stupid reg we have to abide by:mad:

Also in a conventional A/C with a sealed unit,cold return gas is critical to keep the compresser operating parameters within limits.Un insulated pipework will cause the return gas to heat up and cause the compresser to operate hotter than design,which will eventually cause the oil to break down,and compresser failure.

An off engine drive compresser,or for that matter any open drive A/C or refrig compresser can tolerate higher return gas temperature due to it's design.

As said insulating the return gas line on a vehicle A/C will make minimal,if any difference at all.

i would be more concerned about keeping the condenser coil as clean as possible,as a dirty condenser will make the system very inefficient.

Now this bloke knows his stuff ;)

Losses and gains can be calculated using an enthalpy/entropy chart (or a computer) but they are minimal.