Can anyone tell me the reason that the low pressure line of home A/C
unit is insulated, and the high side line is not?? It seems to me
you would minimize the affects of external heat gain/loss by
insulating both lines, thus being able to fine tune the system a
Brad (AZ - very hot)
efficiency( Albeit not very much)- there's no need to insulate it unless
you have a situation where it runs for a distance in a very hot attic after
a hefty lift or something goofy like that where you could get flash gas at
the metering device.
If there is a temperature difference between ambient air and the liquid line
you WILL either have greater subcooling of less. Heat transfer doesn't stop
when it leaves the condenser.
Back it up? Ok, why do they say take your subcooling measurements at the
outlet of the condenser coil: if it didn't make any difference take it at
the reciever outlets. I know, line pressure friction loss ect, but heat
transfer is also a factor, the reciver doesn't have 'line friction loss' but
we try not to take our readings on the outlet of the reciever.
I've seen units not run because they GAINED temperature and LOST subcoolling
and then the units capacity was short. Happens all the time in steel mills,
attics etc. Happened at a Glidden paint plants computer room a few years
back. So the reverse is true as well too.
The key words were "Albeit not very much-" But in a foundry it can make
a difference if you don't insulate the liquid lines.
"Brad (AZ - very hot)"
From the perspective that Brad was in AZ -plus he even felt the need to
mention the fact that it was very hot- It is reasonably obvious that he was
concerned that heat on the liq line has an effect on efficiency...
"If you ""insulated"" the high side line you would probably ""lose some
efficiency"" ( Albeit not very much)"
You also confirm that heat can and indeed does effect subcool etc so you
too question jr's response
So within the context of Brads post Jr's quip is way off, which is why I
asked him to back it up..
If for no other technical reason, the low pressure suction line will sweat
from humidity in an attic and possibly drip water on the ceiling below it.
Foam insulation reduces the contact area of the suction line from the humid
air. It keeps the suction line from picking up unwanted additional heat in
an unconditioned space.
However, now that I notice you are in AZ, you don't have to worry much about
No, I am not an hvac person. I am just trying to get some
understanding of how this stuff works. I would think that you would
want the liquid line to be as cool as possible when it hits the
expansion valve. In the heat of the summer, the attic may be 150
degrees, which would be a bad thing if the line heats up enough. I
also have a fairly long run ~60ft in the attic.
I peronally haven't seen anyone have the liquid line insulated (in AZ
- residential), so I guess I have to assume that the subcooling is
sufficient to prevent any flashing.
I am sorry Brad I was being wise ass
If liquid line is subjected to hotter conditions then
condensing temperature then yes perhaps it would help to be
insulated that goes for any refrigeration system.
If sub-cooler is use then sub-cooler must be located as close
as possible to the TXV and liquid line should be insulated.
Sub-coolers in cap tube jobs are not much beneficial unless
is on refrigeration system at -20 or lower temperatures.
in domestic and commercial set ups sub-cooler is use to
keep suction line from freezing up or sweating and not for
efficiency as what some guys believe and I am not saying
that it does not help. What I am saying that OEMs
have put those sub-coolers in to system to super-heat
the suction line as I have stated and perhaps at same time
preventing any slugging to compressor.
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