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How to Use the Refrigerant Piping Calculator
Choose the refrigerant, then use the tabs to pick the suction, discharge or liquid line. Each line has its own velocity and pressure drop limits.
Enter the refrigerating capacity in kW, tons or Btu/h, the evaporating temperature, the condensing temperature and the liquid subcooling.
Enter the straight length, the fittings allowance, the vertical rise and, for gas lines, the lowest load the system runs at.
Check the recommended tube, the velocity and the loss as a temperature, then read the notes. Add the project details and use PDF, CSV, Copy or Print.
Sizing refrigerant lines in ACR copper
A refrigerant line has two jobs that pull against each other. It has to be large enough that friction does not eat into capacity, and small enough that the gas, and the oil riding along with it, keeps moving. The calculator tests nine ACR copper sizes against both limits for a suction, discharge or liquid line, and recommends the smallest size that passes. The fluid properties come from the open-source CoolProp library rather than from rules of thumb.
How the calculator finds the flow and the loss
Mass flow is the capacity divided by the refrigerating effect, which is the enthalpy of the dew-point vapour leaving the evaporator minus the enthalpy of the liquid leaving the condenser. In the R-410A Suction Riser example, 10.5 kW of R-410A at 5°C evaporating and 45°C condensing has a liquid leaving at 39.9°C, 5 K below the bubble point, so the refrigerating effect is 156.8 kJ/kg and the flow is 67.0 g/s, or 241.1 kg/h. For each tube the page divides the flow by density and inside area to get velocity, finds the Reynolds number, and solves the Colebrook-White equation for the friction factor with a roughness of 0.0015 mm, the usual value for drawn copper. The Darcy-Weisbach equation then gives the loss over the equivalent length, which is the straight length plus the fittings allowance. A 30% allowance is a starting figure, so replace it with counted fittings when the drawing exists. To see how the friction factor moves with Reynolds number and roughness, try the Moody chart calculator. For blends, gas properties use the dew point and the liquid uses the bubble point.
Pressure drop is read as a temperature
A kilopascal means different things in different lines, because the saturation pressure of a refrigerant climbs at a different rate in each. For that reason line sizing guides state the limit as the change in saturation temperature that the pressure loss causes. Hussmann's line sizing data guide designs suction lines for no more than about 2°F (1.1 K), and Daikin Applied allows 2 to 3°F (1.1 to 1.7 K) per line. The calculator marks 1.1 K or less as OK, up to 1.7 K as marginal, and anything above as a failure. The table shows how much pressure that 1.1 K stands for. R-410A at 5°C gives up 29.2 kPa for every kelvin, so 1.1 K is 32.1 kPa, while R-134a at -30°C gives up only 4.1 kPa per kelvin.
| Refrigerant | kPa at 5°C evaporating | kPa at -10°C | kPa at -30°C |
|---|---|---|---|
| R-410A | 32.1 | 22.2 | 12.5 |
| R-32 | 32.9 | 22.7 | 12.7 |
| R-454B | 29.6 | 20.5 | 11.4 |
| R-22 | 20.5 | 14.1 | 7.8 |
| R-407C | 20.6 | 13.7 | 7.2 |
| R-134a | 13.7 | 8.9 | 4.5 |
| R-404A | 24.1 | 16.7 | 9.4 |
| R-507A | 24.8 | 17.3 | 9.8 |
| R-448A | 22.2 | 14.9 | 8.0 |
| R-449A | 22.1 | 14.9 | 8.0 |
Pressure equal to a 1.1 K change in saturation temperature at the dew point, from CoolProp.
Velocity: a floor for oil return and a ceiling for noise
Oil leaves the compressor with the gas and only comes back if the gas drags it along the pipe. Daikin Applied's refrigerant piping design guide gives minimum velocities of 2.54 m/s for horizontal suction and hot gas lines and 5.08 m/s for risers, while Hussmann's guide uses 3.6 m/s and 6.1 m/s. The calculator takes 3.6 m/s horizontal and 5.1 m/s in a riser, which sits inside that spread. At the top end it caps suction gas at 12.7 m/s (2,500 fpm), discharge gas at 15.2 m/s (3,000 fpm) and liquid at 1.5 m/s, close to the 1.54 m/s Daikin gives to avoid hammer when a solenoid closes. Velocity falls in step with flow, so the minimum is checked at the lowest load you enter, not at full load.
The suction line and its riser at part load
The R-410A Suction Riser example runs 15 m of suction line with a 3 m rise and a 50% minimum load. A 3/4 in. tube moves the gas at 8.3 m/s at full load and loses 0.75 K, which passes. At half load the gas slows to 4.2 m/s, below the 5.1 m/s riser minimum. Dropping the riser to 5/8 in. lifts the half-load velocity to 6.2 m/s, and over 3 m of riser it adds only 5.5 kPa, about 0.19 K. The page reports that split: the 3/4 in. tube for the horizontal runs and 5/8 in. for the riser. Daikin describes the same approach and advises against a double suction riser where a single one can be made to work.
The discharge line
Run the same R-410A flow as a discharge line and the gas is much denser, 98.3 kg/m³ at the isentropic discharge state of 62°C, compared with 35.9 kg/m³ on the suction side. A 1/2 in. tube carries it at 7.3 m/s with a 1.06 K loss. Each kelvin at condensing pressure is worth 65.3 kPa, so the same 1.1 K allows far more pressure than in the suction line. Real discharge gas is hotter than the isentropic value, so it moves a little faster than shown. Keep the line sloped so oil can drain back, and size any riser for oil return at minimum load.
The liquid line, static head and flash gas
Liquid is dense, so velocity stays low and friction is small, but every metre of rise costs pressure. The R-404A Liquid Line example sends 25 kW of R-404A through 20 m with a 4 m rise. In 3/4 in. tube the liquid moves at 1.02 m/s, friction costs 13.6 kPa (0.31 K), and the rise adds 39.1 kPa, about 9.8 kPa for each metre at a density of 996 kg/m³. Together that is 1.18 K, which the 5 K of subcooling covers. If the liquid arrives below saturation pressure it flashes, and the expansion device starves. The same arithmetic gives 9.7 kPa per metre for R-410A liquid at 37.7°C, inside the 0.43 to 0.5 psi per foot (9.7 to 11.3 kPa per metre) that Daikin quotes for liquid risers. A 5/8 in. tube would carry the liquid at 1.53 m/s, just over the limit.
ACR tube sizes in the calculator
The nine sizes follow ASTM B280 ACR copper tube, which is sold by outside diameter. The wall thicknesses below are for hard-drawn straight lengths. Soft coil is made to its own wall schedule in some of these sizes, so confirm the inside diameter with the tube supplier before you size a coiled run close to a limit.
| Nominal size (OD) | OD (mm) | Wall | Inside diameter (mm) |
|---|---|---|---|
| 3/8" | 9.53 | 0.030 in. (0.76 mm) | 8.00 |
| 1/2" | 12.70 | 0.035 in. (0.89 mm) | 10.92 |
| 5/8" | 15.88 | 0.040 in. (1.02 mm) | 13.84 |
| 3/4" | 19.05 | 0.042 in. (1.07 mm) | 16.92 |
| 7/8" | 22.23 | 0.045 in. (1.14 mm) | 19.94 |
| 1-1/8" | 28.57 | 0.050 in. (1.27 mm) | 26.04 |
| 1-3/8" | 34.92 | 0.055 in. (1.40 mm) | 32.13 |
| 1-5/8" | 41.27 | 0.060 in. (1.52 mm) | 38.23 |
| 2-1/8" | 53.98 | 0.070 in. (1.78 mm) | 50.42 |
After the line goes in
The result is a design size, not a commissioning check. Pressure test the new line with dry nitrogen before you evacuate it, allow for the temperature change that moves the gauge reading, and watch for a drop over time. The pressure decay test calculator helps you read that drop. Once the system runs, confirm the liquid arrives subcooled, and keep in mind that valves, driers, oil traps and any extra charge for long lines follow the equipment manufacturer's data.
Frequently Asked Questions
State it as a change in saturation temperature, not as a pressure. Hussmann's line sizing guide designs suction lines for about 1.1 K (2°F), and Daikin Applied allows 1.1 to 1.7 K (2 to 3°F) for suction, discharge and liquid lines. This calculator marks a loss of 1.1 K or less as OK and up to 1.7 K as marginal. The pressure behind one kelvin depends on the refrigerant and the temperature: 1.1 K is about 32 kPa (4.7 psi) for R-410A at 5°C evaporating, 17 kPa (2.4 psi) for R-404A at -10°C and 4.5 kPa (0.7 psi) for R-134a at -30°C.
The calculator requires 5.1 m/s (1,000 fpm) in a riser and 3.6 m/s (700 fpm) in a horizontal run, checked at the lowest load the system runs at. Published guides differ: Daikin Applied gives 5.08 m/s for risers and 2.54 m/s for horizontal lines, and Hussmann gives 6.1 m/s and 3.6 m/s. Velocity falls in step with the flow, so a riser that works at full load can fail at part load. In the R-410A Suction Riser example, a 3/4 in. riser moves the gas at 8.3 m/s at full load and 4.2 m/s at 50% load, so the page suggests a 5/8 in. riser, which holds 6.2 m/s.
Enough to cover the friction loss plus the static head, which is liquid density times 9.81 times the rise, converted to a temperature with the slope of the saturation curve. In the R-404A Liquid Line example, 25 kW of R-404A runs 20 m with a 4 m rise in 3/4 in. tube. Friction costs 13.6 kPa (0.31 K) and the rise adds 39.1 kPa, so the liquid needs 1.18 K of subcooling to reach the expansion device without flashing. The 5 K entered covers it. Losses in the filter drier, solenoid and sight glass come on top and are not in the result.
Use ACR copper tube, made to ASTM B280 and supplied cleaned and capped. ACR tube is sold by its outside diameter, so a 3/4 in. size measures 3/4 in. across the outside, unlike plumbing tube, whose nominal size is 1/8 in. smaller than its outside diameter. The calculator tests nine sizes from 3/8 in. to 2-1/8 in. Check the working pressure of the tube against the pressure rating of your refrigerant and the code your authority enforces.