MachineCalcs

Refrigerant Line Size Calculator

Screen suction and liquid refrigerant line IDs from capacity, equivalent length, entered refrigerant properties, velocity targets and pressure-drop budgets.

HVAC 16 inputs 18 results

Calculator

Inputs

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Nominal or design evaporator capacity used to estimate refrigerant mass flow.
Btu/h
Cooling effect per unit refrigerant mass. Enter this from cycle/property data; the default is only a comfort-cooling example.
Btu/lb
Actual internal diameter of the selected suction/vapor line. Use tube data, not nominal OD.
in
Actual internal diameter of the selected liquid line. Use tube data, not nominal OD.
in
Straight length plus equivalent length for elbows, traps, fittings and valves in the refrigerant line.
ft
Positive when liquid must lift upward. The calculator adds liquid static head only for positive lift.
ft
Vapor density at suction line temperature/pressure. This is user-entered property data, not a built-in refrigerant table.
lb/ft³
Liquid density at the checked liquid-line condition.
lb/ft³
Dynamic viscosity in micro-Pascal-seconds for the suction vapor condition.
uPa*s
Dynamic viscosity in micro-Pascal-seconds for the liquid condition.
uPa*s
Absolute roughness used in the Darcy friction factor. Clean drawn copper is very smooth; fittings are handled through equivalent length.
in
Entered minimum suction velocity for oil return screening.
ft/s
Entered upper suction velocity target for noise and pressure-drop screening.
ft/s
Entered upper liquid-line velocity target.
ft/s
Maximum acceptable suction friction pressure drop for this line screen.
psi
Maximum acceptable liquid line drop, including friction plus positive vertical lift head.
psi

Results

Default result
Edit inputs
Refrigerant mass flow(m_dot)
8.723lb/min

Mass flow is capacity divided by entered net refrigeration effect.

Also computed

Suction velocity(v_s)Pass19.66ft/s

inside entered suction velocity window

Liquid velocity(v_l)Pass4.113ft/s

inside entered liquid velocity target

Suction pressure drop(dp_s)Pass1.042psi

34.7% of entered pressure budget

Total liquid drop(dp_l,total)Caution4.749psi

95.0% of entered pressure budget; little margin

Liquid friction drop(dp_l,fr)4.749psi

Liquid lift head(dp_lift)0psi

Positive vertical lift only; negative lift is not credited.

Friction drop vs Equivalent lengthFriction drop scales with equivalent length for the selected line IDs and mass flow. Liquid lift head is listed separately in the results.Friction drop vs Equivalent length02468020406080Equivalent length (ft)Friction drop (psi)
Friction drop scales with equivalent length for the selected line IDs and mass flow. Liquid lift head is listed separately in the results.
Method notes 3 notes
  • Formula: refrigerant mass flow = cooling capacity / entered net refrigeration effect.
  • Velocity uses v = m_dot/(rho*A). Pressure drop uses Darcy-Weisbach with user-entered density, viscosity, tube roughness and total equivalent length.
  • Final refrigerant line sizing must follow the exact equipment manufacturer long-line guide, oil-return requirements, traps, capacity derates, refrigerant classification, local code and qualified HVAC design practice.

Refrigerant line sizing starts by turning cooling capacity into refrigerant mass flow, m_dot = Q/NRE, using entered net refrigeration effect. The selected suction and liquid line IDs set velocity v = m_dot/(rho*A), and Darcy-Weisbach checks friction pressure drop against entered budgets while positive liquid lift adds rho*g*H. This calculator uses user-entered properties and targets; it does not replace manufacturer line-size or long-line tables.

Continue workflow

All HVAC
Next 1 Estimate line charge After manufacturer line size is approved, estimate added charge from line length and manual rate. Next 2 Convert airflow and load Use air-side capacity and temperature difference to sanity-check the cooling capacity basis. Next 3 Size ductwork Size air-side ductwork separately from refrigerant suction and liquid line sizing. Chart Use reference data Duct size worksheet

How to use this calculator

  1. Find manufacturer data. Use the equipment manual or long-line guide for approved nominal sizes, maximum length and property basis.
  2. Enter capacity and properties. Enter capacity, net refrigeration effect, vapor density, liquid density and viscosities for the checked condition.
  3. Enter actual line IDs. Use actual internal diameters from tube data, not only nominal outside diameter.
  4. Add equivalent length. Include straight tubing plus elbows, traps, valves and fittings as equivalent length.
  5. Read velocity and drop. Compare suction oil-return velocity, liquid velocity and pressure-drop budget before using the manufacturer-approved size.

How it works

This refrigerant line size calculator is a screening worksheet for a line set you are already considering. It does not publish a built-in refrigerant table or approve a nominal copper size. The first step is refrigerant mass flow:

m_dot = Q / NRE

where Q is cooling capacity and NRE is the entered net refrigeration effect. The selected suction and liquid line IDs then set line area:

A = pi x ID^2 / 4

v = m_dot / (rho x A)

Pressure drop is calculated with Darcy-Weisbach:

dp = f x (L / D) x (rho x v^2 / 2)

The friction factor comes from Reynolds number and the entered tube roughness. Positive liquid-line lift adds rho x g x H to the liquid-line friction drop. The line set size by tonnage and length reference and suction line size calculator shortcut summarize the same pressure-drop and oil-return checks before you open the full worksheet. For exact refrigerant sizing searches, use the refrigerant line size calculator by tonnage and length or the liquid line size calculator.

Worked example

Verified against the live calculator

A 3 ton comfort-cooling system has an entered net refrigeration effect of about 69 Btu/lb. That gives roughly 8.7 lb/min of refrigerant flow. With a 0.785 in suction ID and a 0.311 in liquid ID over 50 ft of equivalent length, the calculator checks whether suction velocity stays inside the oil-return window and whether suction and liquid pressure drops stay inside the entered budgets.

Frequently asked questions

How do you size a refrigerant line?

Start with the equipment manufacturer line-size table. This calculator screens the selected suction and liquid line IDs by estimating refrigerant mass flow from capacity and net refrigeration effect, then checking velocity and pressure drop against your entered limits.

Can I use tonnage alone to pick suction and liquid line sizes?

No. Tonnage is only one input. Refrigerant line sizing also depends on refrigerant, evaporating and condensing conditions, equivalent length, vertical lift, oil return, traps, pressure drop, capacity derate and the exact outdoor/indoor equipment combination.

Why does the calculator ask for net refrigeration effect and density?

Those properties turn cooling capacity into refrigerant mass flow and then into line velocity. They vary with refrigerant and operating conditions, so this page treats them as entered design data instead of embedding a stale property table.

Does this replace a long-line guide?

No. Use the manufacturer long-line guide for approved line sizes, maximum length, riser traps, oil-return details, added charge, accessories and capacity derates. This calculator is only a pressure and velocity screen for a selected line set.

How is liquid vertical lift handled?

Positive liquid-line lift adds static head, rho x g x height, to the liquid friction drop. Negative lift is not credited because final refrigerant piping still needs manufacturer and commissioning checks.

Method & assumptions

  • Uses entered refrigerant properties; defaults are examples, not a refrigerant property database.
  • Actual suction and liquid line inside diameters must come from tube data or the equipment manual.
  • Equivalent length should include elbows, risers, traps, valves, branch kits and fittings when the design method requires them.
  • Suction oil-return velocity targets, liquid velocity limits and pressure-drop budgets are entered by the user because they are refrigerant, equipment and application specific.
  • Does not check compressor model approval, maximum line length, long-line kits, traps, oil return under part load, capacity derate, superheat/subcooling, A2L safety, leak concentration, evacuation, charging or local code.
  • For charge arithmetic after line size is approved, use the refrigerant line charge calculator. For air-side checks, use duct sizing, duct friction loss, static pressure and grille sizing.

References

  • Formula basis: continuity, refrigerant energy balance and Darcy-Weisbach pipe pressure loss.
  • Use the current equipment installation manual, manufacturer long-line guide and refrigerant property data for final line selection.
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