The capillary tube table for R22 enables refrigeration technicians to select the appropriate diameter and length for the capillary tube based on the evaporator temperature and cooling capacity.
Rules for Sizing Capillary Tubes with R22 Refrigerant:
- Capillary tubes rely on both their length and diameter to determine their total restriction.
- A percentage change in diameter can alter the flow more significantly than an equal change in length.
- Restriction can also be adjusted by lengthening or shortening the tube.
- The longer the tube, the slower the flow.
- Extremely long lengths to increase restriction and reduce flow are not only uneconomical but often ineffective.
- Shortening the tube increases flow until a critical point is reached, after which further shortening causes a significant flow increase.
- When the tube becomes very short, even small changes in length lead to large flow increases. At this stage, the tube behaves more like an orifice than a capillary tube.
General Recommendation:
Maintain the tube length between 5′ and 16′. While exceptions exist, staying within this range prevents many operational issues.
Parameters for Sizing Capillary Tubes with R22:
Evaporator Temperature:
The first parameter to consider is the evaporator temperature, which depends on the following:
| Equipment Type | Evaporator Temp. | Average Condenser Temp. |
|---|---|---|
| LBP (Low Back Pressure) | -23.3 °C (-10°F) | 54.4 °C (130°F) |
| MBP (Medium Back Pressure) | -6.7 °C (20°F) | 54.4 °C (130°F) |
| HBP (High Back Pressure) | 7.2 °C (45°F) | 54.4 °C (130°F) |
Electrical Power of the Compressor:
Usually measured in HP or W, this represents the maximum electrical power the compressor motor can use without damage.
Although not ideal for direct selection, electrical power is still commonly used instead of thermal load capacity.
Conversion:
1 HP = 746 W
| Compressor Power (HP) | Application (Evaporator Temp.) | Diameter (in) | Length (m) |
|---|---|---|---|
| 1/4 HP | HBP | 0.050 in | 3.0 m |
| 1/4 HP | MBP | 0.036 in | 2.5 m |
| 1/3 HP | HBP | 0.050 in | 2.0 m |
| 1/3 HP | MBP | 0.042 in | 3.0 m |
| 1/2 HP | HBP | 0.050 in | 1.5 m |
| 1/2 HP | MBP | 0.042 in | 2.0 m |
| 1 HP | HBP | 0.064 in | 1.5 m |
| 1 HP | MBP | 0.050 in | 2.0 m |
| 1 1/4 HP | HBP | 0.064 in | 1.5 m |
| 1 1/4 HP | MBP | 0.064 in | 1.0 m |
Cooling Capacity:
Cooling capacity is the true cooling performance of a compressor at a specific evaporator temperature. It is measured in Btu/h, Kcal/h, or W in some international models.
| Cooling Capacity | Capillary Diameter/Length | Evaporator Temp. (-10 °F) | Evaporator Temp. (25 °F) | Evaporator Temp. (45 °F) |
|---|---|---|---|---|
| 750 Btu/h (185 Kcal/h) | 0.028″ – 15 ft | 0.028″ – 14 ft | 0.028″ – 13.5 ft | |
| 1000 Btu/h (250 Kcal/h) | 0.028″ – 8 ft | 0.028″ – 7.5 ft | 0.028″ – 7 ft | |
| 1250 Btu/h (312 Kcal/h) | 0.028″ – 5 ft | 0.028″ – 4.5 ft | 0.028″ – 4.5 ft | |
| 1500 Btu/h (375 Kcal/h) | 0.031″ – 6 ft | 0.031″ – 5.5 ft | 0.031″ – 5 ft | |
| 2000 Btu/h (500 Kcal/h) | 0.040″ – 13 ft | 0.040″ – 12.5 ft | 0.040″ – 12 ft | |
| 3000 Btu/h (750 Kcal/h) | 0.040″ – 5.5 ft | 0.040″ – 5 ft | 0.040″ – 5 ft |
Note:
- Consider condensation temperature = 45 °C.
- Increase length by 2% for each °C rise in condensation temperature in extreme conditions.
