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Refrigerant Line Sizing

Refrigerant Line Sizing. Knowledge makes the professional. What’s the big deal with line sets?. What’s the big deal with line sets?. Improperly-sized line sets can cause compressor failures. 3 Physical Factors. Size of refrigerant charge Pressure drop Velocity.

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Refrigerant Line Sizing

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  1. Refrigerant Line Sizing Knowledge makes the professional DESIGN AIR UNIVERSITY

  2. What’s the big deal with line sets? DESIGN AIR UNIVERSITY

  3. What’s the big deal with line sets? • Improperly-sized line sets can cause compressor failures. DESIGN AIR UNIVERSITY

  4. 3 Physical Factors • Size of refrigerant charge • Pressure drop • Velocity DESIGN AIR UNIVERSITY

  5. 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. DESIGN AIR UNIVERSITY

  6. Don’t just match the connection size! DESIGN AIR UNIVERSITY

  7. Don’t just match the connection size! DESIGN AIR UNIVERSITY

  8. Connection size on unit May be correct liquid line size DESIGN AIR UNIVERSITY

  9. 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. DESIGN AIR UNIVERSITY

  10. Inside the Suction Line: Refrigerant Vapor Molecule Refrigerant Oil Droplets DESIGN AIR UNIVERSITY

  11. Velocity is important! • Approximately 1,200 feet per minute. DESIGN AIR UNIVERSITY

  12. Why? • Picks up refrigerant oil and returns it to the compressor. • If velocity is too low, oil is not returned. DESIGN AIR UNIVERSITY

  13. If suction line is too small . . . • The increased resistance to flow will: • Reduce the capacity and . . . • Reduce the efficiency. DESIGN AIR UNIVERSITY

  14. 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. DESIGN AIR UNIVERSITY

  15. What’s the right size suction line? • Large enough to minimize pressure drop. • Pressure loss reduces cooling capacity. DESIGN AIR UNIVERSITY

  16. 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! DESIGN AIR UNIVERSITY

  17. 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. DESIGN AIR UNIVERSITY

  18. Liquid Line Sizing • Must be large enough to minimize pressure drop. . . • But small enough to minimize excess refrigerant which can damage the compressor. DESIGN AIR UNIVERSITY

  19. What’s the right size liquid line? • Large enough to minimize pressure drop. • Keep liquid refrigerant from flashing to a vapor. DESIGN AIR UNIVERSITY

  20. If the liquid line is too small? • Loss of capacity • Damages expansion valve • Noisy evaporator • High superheat can damage compressor DESIGN AIR UNIVERSITY

  21. What’s the right size liquid line? • Small enough to minimize refrigerant charge. • Excessive refrigerant can damage the compressor. DESIGN AIR UNIVERSITY

  22. For example . . . • A 3/8” liquid line holds well over twice as much refrigerant as a ¼” liquid line. DESIGN AIR UNIVERSITY

  23. 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.” DESIGN AIR UNIVERSITY

  24. 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. DESIGN AIR UNIVERSITY

  25. At what cost? • 21 ounces of R-410A refrigerant @ $10.00 per pound = $13.13 + labor. • And the system performance is worse! DESIGN AIR UNIVERSITY

  26. 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 DESIGN AIR UNIVERSITY

  27. 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. DESIGN AIR UNIVERSITY

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