The piping designer is concerned with several factors when the size of refrigerant piping must be considered.
These factors are interrelated so that a change in one factor affects the others. The piping must be large enough to transfer enough refrigerant without a large pressure drop. However it should not be so large to penalize the piping costs or hinder a proper velocity for proper oil transfer. Oil is necessary to lubricate the compressor. The oil is atomized at the compressor and enters the piping system. The piping should be installed to promote the movement of oil back to the compressor. Horizontal piping is pitched in the direction of gas flow. Vertical gas risers require sufficient velocity to transport oil up the column. Gas risers in excess of 25 feet (7meters) require intermediate traps to capture oil in the off cycle.
Good practice for refrigerant pipe sizing falls within these guidelines for R-22 refrigerant.
The velocity in refrigerant liquid piping should not exceed 360 ft/min (5 m/sec). This reduces the possibility of noisy piping systems, and possible joint leaks from vibration. The pressure drop in liquid lines is generally limited to 6 lbs/sq. in. (40 kPa). This pressure drop limits the temperature rise from the heat of friction to 2°F (1°C). To adjust for a condensing temperature other than the standard ARI condition of 105°F for a water cooled condenser.
Load(tons) X (0.005 X Condensing Temp. °F + 0.45) = Adjusted Load (tons)
Load(kw) X (0.005 X Condensing Temp. °C + 3.52) = Adjusted Load (kw)
Since the oil to lubricate the compressor is soluble in liquid refrigerant, oil transport is not considered in the line if the refrigerant flow is proper.
The pressure drop in suction lines is typically limited to 3 lbs/sq. in. (20 kPa) to limit the temperature rise to 2°F (1°C) due to heat of friction. The velocity of the refrigerant in suction lines is important. Refrigerant oil should flow in the direction of gas flow in the off cycle (back to the compressor). To transport oil the minimum velocity in horizontal lines should be 500 ft/min, while vertical risers should have a minimum velocity of 1000 ft/min. To adjust for a condening temperature other than the standard ARI condition of 105°F for a water cooled condenser.
Load(tons) X (0.005 X Condensing Temp. °F + 0.45) = Adjusted Load (tons)
Load(kw) X (0.005 X Condensing Temp. °C + 3.52) = Adjusted Load (kw)
The pressure drop in hot gas lines is typically limited to 6 lbs/sq. in. (40 kpa). Transport oil lines are pitched in the direction of flow and velocities are within the same requirements as suction lines.
| Size | Globe | Angle | Short | Long | Line Flow | Branch Flow | Solenoid | Site |
|---|---|---|---|---|---|---|---|---|
| In.(mm) | Valve | Valve | Elbow | Elbow | Tee | Tee | Valve | Glass |
| 1/2 (13) | 70 (21) | 24 (7.3) | 4.7 (1.4) | 3.2 (1) | 1.7 (0.5) | 6.6 (2) | 70 (21) | 1.7 (0.5) |
| 5/8 (16) | 72 (21.9) | 25 (7.6) | 5.7 (1.7) | 3.9 (1.2) | 2.3 (0.7) | 8.2 (2.5) | 72 (21.9) | 2.3 (0.7) |
| 3/4 (19) | 75 (22.8) | 25 (7.6) | 6.5 (2) | 4.5 (1.4) | 2.9 (0.9) | 9.7 (2.9) | 75 (22.8) | 2.9 (0.9) |
| 7/8 (22) | 78 (23.7) | 28 (8.5) | 7.8 (2.3) | 5.3 (1.6) | 3.7 (1.1) | 12 (3.7) | 78 (23.7) | 3.7 (1.1) |
| 1-1/8 (29) | 87 (26.5) | 29 (8.8) | 2.7 (0.8) | 1.9 (0.6) | 2.5 (0.8) | 8 (2.4) | 87 (26.5) | 2.5 (0.8) |
| 1-3/8 (35) | 102 (31) | 33 (10) | 3.2 (1) | 2.2 (0.7) | 2.7 (0.8) | 10 (3) | 102 (31) | 2.7 (0.8) |
| 1-5/8 (41) | 115 (35) | 34 (10.3) | 3.8 (1.2) | 2.6 (0.8) | 3.0 (0.9) | 12 (3.6) | 115 (35) | 3 (0.9) |
| 2-1/8 (54) | 141 (42.9) | 39 (11.8) | 5.2 (1.6) | 3.4 (1) | 3.8 (1.2) | 16 (4.8) | 141 (42.9) | 3.8 (1.2) |
| 2-5/8 (67) | 159 (48.4) | 44 (13.4) | 6.5 (1.9) | 4.2 (1.2) | 4.6 (1.4) | 20 (6.1) | 159 (48.4) | 4.6 (1.4) |
| 3-1/8 (79) | 185 (56.3) | 53 (16.1) | 8.6 (2.6) | 5.1 (1.6) | 5.4 (1.6) | 25 (7.6) | 185 (56.3) | 5.4 (1.6) |
| 3-5/8 (92) | 216 (65.8) | 66 (20.1) | 10 (3) | 6.3 (1.9) | 6.6 (2) | 30 (9.1) | 216 (65.8) | 6.6 (2) |
| 4-1/8 (105) | 246 (74.9) | 76 (23.2) | 12 (3.6) | 7.3 (2.2) | 7.3 (2.2) | 35 (10.6) | 246 (74.9) | 7.3 (2.2) |
| 5-1/8 (130) | 292 (89) | 96 (29.2) | 14 (4.2) | 8.8 (2.6) | 7.9 (2.4) | 42 (12.8) | 292 (89) | 7.9 (2.4) |