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Thread: Suction line sizing.

  1. #1
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    Suction line sizing.

    Hey, so I知 having Trouble deciding what I want to do here. I知 installing a new system and running a new line set the.
    Air handler is in the attic and the system is a 3 1/2 ton Goodman. The manufacturer calls for any line set more then 25 feet needs a 1/18 suction line instead of the 7/8. I知 going maybe 35 feet.
    Do you really think 10 feet is going to make that much of a difference when it comes to operation of the unit? I know suction size matters for Capacity, oil flow, refrigerant dentistry etc. but I still think im going to be in that minimum 3% capacity loss area. Also the blower is a ECM Variable speed 1600CFM

    Thanks.

  2. #2
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    The market is competitive. If they could have gotten away with 35 then that would give them an edge in their competitors. They did not do this. I would go with the larger size.
    Quickly, I must hurry, for there go my people and I am their leader!

  3. #3
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    If the condenser is below the evap, then no need to increase size.
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  4. #4
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    Quote Originally Posted by HVAC Guy7 View Post
    I知 installing a new system and running a new line set. The Air handler is in the attic and the system is a 3 1/2 ton Goodman. The manufacturer calls for any line set more then 25 feet needs a 1/18 suction line instead of the 7/8. I知 going maybe 35 feet.

    Do you really think 10 feet is going to make that much of a difference when it comes to operation of the unit?
    If you look at Goodmans 鏑ong line Set Application publication, it states for 3.5 ton units, there is no capacity loss when using 7/8 suction line on line lengths up to 75 feet. At or after 75 feet, there is only a 1% capacity loss up to 175 feet of suction line.

    Remember, you need to calculate equivalent length by adding all the fittings (45コ and 90コ痴) in the total length. 90コ痴 are 2 feet each and 45コ痴 are .7 feet each.

    With that said, I doubt you will even get to 50 feet equivalent length with 5 x 90コ痴.

    Put an email address in your profile, or send me an email (address is in my profile), and I will get that publication off to you.
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  6. #5
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    Quote Originally Posted by beenthere View Post
    If the condenser is below the evap, then no need to increase size.
    ?

  7. #6
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    Thread Starter
    Thanks for your help I will look into that. From experience I think I should be fine anyway I just like to be 澱y the book as much as I can

  8. #7
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    Quote Originally Posted by ehsx View Post
    ?
    Well oil return comes to mind as for capacity the jury is still out on that.

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    Wow! 1-1/8 for a 3.5 ton, that痴 just poor engineering, plain and simple.
    "The only true wisdom is in knowing you know nothing" Socrates

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  11. #9
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    Quote Originally Posted by VTP99 View Post
    Well oil return comes to mind as for capacity the jury is still out on that.
    downflow?

    might decrease or limit if up-flow for oil return...

  12. #10
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    Quote Originally Posted by ehsx View Post
    downflow?

    might decrease or limit if up-flow for oil return...
    Right, gravity, oil return shouldn't be a problem with the condenser lower than the evaporator.
    As for the smaller line size and capacity rundawg already addressed that.

  13. #11
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    Quote Originally Posted by ehsx View Post
    ?
    No problem using 1 1/8" with oil return if the condenser is below the evap, gravity is working for you. But if a condenser is above the evap, the 7/8" is far better for oil return.

    1 1/8" velocity would be roughly 716 FPM, not good for oil return. Capacity loss of 178 BTUs per 100 foot(according to York line set chart).
    7/8" velocity would be roughly 1221 FPM, much better for oil return. Capacity loss would be 643 BTUs per 100 foot(according to York line set chart).
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  14. #12
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    Quote Originally Posted by beenthere View Post
    No problem using 1 1/8" with oil return if the condenser is below the evap, gravity is working for you. But if a condenser is above the evap, the 7/8" is far better for oil return.

    1 1/8" velocity would be roughly 716 FPM, not good for oil return. Capacity loss of 178 BTUs per 100 foot(according to York line set chart).
    7/8" velocity would be roughly 1221 FPM, much better for oil return. Capacity loss would be 643 BTUs per 100 foot(according to York line set chart).
    X2. The capacity loss is so minimal, just use the 7/8 if there is any doubt.

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    Goodman likes to see inverted trap on the suction/vapor line if Air Handler is mounted higher than OD unit...as you mention AH going in attic shows that in the install guide......also says open suction service valve first and not the liquid line....seeing you said you like to go by the book,...guessing you already know that thou.

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    I wonder why they want the suction valve opened first ?
    I know there has been some debate here on that.
    Personally I open the liquid line first.
    Think about a pump down system.

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    Quote Originally Posted by VTP99 View Post
    I wonder why they want the suction valve opened first ?
    I know there has been some debate here on that.
    Personally I open the liquid line first.
    Think about a pump down system.
    Liquid would enter the line set at temperatures way below your tp charts causing thermal shock to the evacuated portions. Opening the suction first allows only vapor to enter evacuated components and limits the drop in pressure/temperature in the condenser.

    If r-410a is below -60*f at atmosphere pressure where is it @ 50 microns? Can cause stress fracture even if freeze is not an issue.

    Pumpdown does not go anywhere near the same saturated temp.

  18. #16
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    Quote Originally Posted by VTP99 View Post
    I wonder why they want the suction valve opened first ?
    I know there has been some debate here on that.
    Personally I open the liquid line first.
    Think about a pump down system.
    Its to help prevent a large amount of oil being drawn out of the compressor from the the surge of refrigerant going into the liquid line.
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  20. #17
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    What ? The refrigerant in the condenser would be at ambient temperature.

  21. #18
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    Quote Originally Posted by beenthere View Post
    Its to help prevent a large amount of oil being drawn out of the compressor from the the surge of refrigerant going into the liquid line.
    Happens everytime a LLSV opens.

  22. #19
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    Quote Originally Posted by ehsx View Post
    Liquid would enter the line set at temperatures way below your tp charts causing thermal shock to the evacuated portions. Opening the suction first allows only vapor to enter evacuated components and limits the drop in pressure/temperature in the condenser.

    If r-410a is below -60*f at atmosphere pressure where is it @ 50 microns? Can cause stress fracture even if freeze is not an issue.

    Pumpdown does not go anywhere near the same saturated temp.
    No thermal shock worry. Its no different than if you did a repair, and then recharged the system. Your still putting liquid into the line while its under vacuum.
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  23. #20
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    Oh and for the record, every split system I've ever installed was done as I mentioned. Guess what ? Those systems are still running.

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