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Insulation of Liquid Lines in Low Ambient Applications

Hay Mike T., Sherly here!I noticed you said,and I quote,,",T&E" chart!So I went into my CARRIER books as you suggested.


  • Brad White_9Brad White_9 Member Posts: 2,440
    To insulate or not?

    Professor, et. al:

    It is our specification standard to insulate the suction line on all refrigerant systems for performance and sweat avoidance and to insulate the hot gas lines for safety and performance. We do not ordinarily insulate the liquid line as this usually affords a little more condensing surface and is in the range of mild temperatures.

    We have a number of low-ambient R-410a ductless split system going in, serving 24/7 interior technical loads. Does leaving the liquid lines bare cause you any concern? Specifically over-cooling the refrigerant in a zero degree or lower design condition. It is not like we will have an additional change of state (can only go to solid and have much bigger problems! :))

    The units are low-ambient controlled to -20F using fan speed and wind baffles. Oh, for inverter control but another subject.

    Thanks for all replies!

  • TechmanTechman Member Posts: 2,144

    Hi Brad!The part I can partly answer is that every ductless splits that I'worked on has both lines insulated because the metering device is in the outdoor unit.Also I've recently went to two inverter tecnology classes .Daikin and Mitsubishi.Hope this helps,even a little!
  • Brad White_9Brad White_9 Member Posts: 2,440
    Hey Techman!

    Yes, it does help. I mis-spoke in that these are not ductless split systems but more conventional units substituted. Standard indoor fan coil evaporators with TXV's indoors, so a little difference.

    All this time I thought that the suction and liquid lines were insulated together on ductless split systems as a "bundling" convenience for the manufacturer. I did not know the TXV's were in the condensing unit. Something new I learned today!

    The Daiken and Mitsubishi (City Multi) systems rock, don't they?

  • Empire_2Empire_2 Member Posts: 2,343
    Hello Brad.

    We will generally insulate any LL over 25 ' of exposed surface area. It really not a concern it the summer months, but winter where the temps can plummet and it might be a good Idea. Technically additional sub-cooling of the liquid is a good thing and will result in greater net refrigeration affect, but to what extent will this hinder the operation of the system if the line is expose to say,...0* air or some kind of a surface. One thing to keep in mind is that the velocity on the LL is generally hi and sensible loss of sub cooled liquid may be negligible. If I look, I can find the velocity tables if you like......

    Also,...Techman...If you get time, plot out a 410A system with say 20 SC and add another 5 to 20* for exposed line. See what comes up on the P&E charts. I bet the TXV would be able to handle the additional subcooling......Now Fixed bore accurator would be a different story. You would surely see the suction pressure drop. I didn't mean to call you Sherly....:-)

    Mike T.
  • Empire_2Empire_2 Member Posts: 2,343

    I meant P&E.........Brain must have gotten stuck.. I did go back and correct it for you...:-)

    Mike T.
  • TechmanTechman Member Posts: 2,144

    Hay Mike T.Sorry about the unneeded change, I was busting your shoes,I was making fun of your use of T&E,because that IS how Carrier approaches the subject and I notice that you and Carrier seem to be an item.Next week I'll be going to a Carrier 3-day class on their 3-V control system.MY 1972 Carrier training literature says "T&E" right on the cover page!Enjoy your evening! Off to VOTE!!!!
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