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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
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 Oil Droplets
Refrigerant Vapor Molecule
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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 lubricationNoise 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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