Refrigerant Line Sizing by 826T9IJJ

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									 Refrigerant Line Sizing

Knowledge makes the professional



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What’s the big deal with line sets?




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What’s the big deal with line sets?

Improperly-sized line sets can cause
 compressor failures.




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3 Physical Factors


           Size of refrigerant charge

           Pressure drop

           Velocity



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Each manufacturer’s piping design
rules must be followed.

Where to look?

In the installation instructions.

Do not just install line sets that match
 the fitting size on the outdoor unit or
 indoor coil.

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Don’t just match the connection size!




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Don’t just match the connection size!




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Connection size on unit    May be correct liquid line size




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Suction line sizing

Must be large enough to minimize
 pressure drop which minimizes capacity
 loss. . .
But small enough to keep the velocity of
 the refrigerant high enough to pick up
 and carry the oil back to the compressor.

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Inside the Suction Line:

                     Refrigerant Vapor Molecule




                             Refrigerant Oil Droplets



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Velocity is important!




Approximately 1,200 feet per minute.

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Why?


Picks up refrigerant oil and returns it to
 the compressor.


If velocity is too low, oil is not returned.


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If suction line is too small . . .


The increased resistance to flow
 will:

  Reduce the capacity and . . .

  Reduce the efficiency.


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Why?


Because the lower the suction pressure
 is when the refrigerant gases return to
 the compressor, the less dense they are.

The compressor will pump less volume
 per cycle resulting in lower capacity &
 efficiency.
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What’s the right size suction line?


Large enough to minimize pressure drop.


  Pressure loss reduces cooling capacity.




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What’s the right size suction line?


Small enough to keep velocities up.


  A must for oil return to the compressor.
  Extra important on 2-stage equipment!


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What about traps in vertical
risers?

Not needed.
Undesirable, in fact.
They just add to the pressure drop.
Proper line sizing will result in proper
 velocity and good oil return.

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Liquid Line Sizing

Must be large enough to minimize
 pressure drop. . .

But small enough to minimize excess
 refrigerant which can damage the
 compressor.


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What’s the right size liquid line?


Large enough to minimize pressure drop.


  Keep liquid refrigerant from flashing to
   a vapor.



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If the liquid line is too small?

  Loss of capacity
  Damages expansion valve

  Noisy evaporator
  High superheat can damage compressor


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What’s the right size liquid line?


Small enough to minimize refrigerant
 charge.


Excessive refrigerant can damage the
 compressor.


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For example . . .

A 3/8” liquid line holds well over twice as
 much refrigerant as a ¼” liquid line.




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What happens if . . ?

. . . the manufacturer recommends a ¼
 inch liquid line for lengths up to 50 feet,
 but you install a 3/8 inch liquid line?


The condensing unit is factory charged
 for 15 feet of “properly-sized liquid line.”

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You must add refrigerant!


 0.6 ounces per foot for every foot over 15 feet.


 For example: 50 feet minus 15 feet = 35 feet.


35 x 0.6 = 21 ounces of refrigerant.

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At what cost?


21 ounces of R-410A refrigerant @
 $10.00 per pound = $13.13 + labor.


And the system performance is worse!


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What about compressor life?

Liquid refrigerant migrates to the
 coldest spot in the system.
Why put extra liquid into the
 crankcase?
   Washes out the lubrication
   Noise on start-up

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Repeat after me . . .

The equipment manufacturer is always
 right!
Bigger is not better!
Refrigerant line sizing is important!
Incorrect line sizing can cause
 compressor failure.
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