Refrigerant pipe pressure drop calculator
Enter mass flow, pipe size/length and your refrigerant's density and viscosity at the actual operating condition, and get velocity, Reynolds number and pressure loss for a suction, discharge (hot gas) or liquid line — single-phase flow only.
How to use this calculator
- Pick the line type — suction, discharge or liquid.
- Pick the refrigerant — density and viscosity fill in at typical conditions, editable.
- Enter mass flow, pipe diameter and length, and any elevation change.
- Add fittings by their L/D equivalent length.
- Read the velocity, Reynolds number and pressure loss, plus the equivalent saturation temperature shift.
What this calculates — and its one big limitation
This calculates pressure loss for single-phase refrigerant flow only: superheated vapour in a suction or discharge (hot gas) line, or subcooled liquid in a liquid line — the condition a correctly designed system normally runs at. It does not model two-phase (flashing) flow, which needs correlations like Lockhart-Martinelli or Friedel that this site has no verified worked example to check an implementation against — shipping one without that check would be exactly the kind of unverified precision this site's other tools avoid. If your line is genuinely two-phase (e.g. a liquid line with a lot of flash gas from an underperforming subcooling margin), this tool's result won't apply to it.
The friction-loss physics itself is the same Darcy-Weisbach + Colebrook-White engine already implemented and verified elsewhere on this site (checked against published Moody-chart reference points) — pure fluid mechanics, not specific to air, reused here with refrigerant density and viscosity in place of air's:
v = ṁ / (ρ·A) velocity from mass flow
Re = ρ·v·D / μ Reynolds number
1/√f = −2·log₁₀( (ε/D)/3.7 + 2.51/(Re·√f) ) Colebrook-White
Δpfriction = f·(L/D)·(ρ·v²/2) Darcy-Weisbach
Δpstatic = ρ·g·Δh elevation change
Why refrigerant density and viscosity aren't auto-filled
Every other roughness/film-coefficient default on this site is a genuinely reasonable typical value across the range it's used for. Refrigerant vapour density isn't that — it depends on saturation pressure, which depends on saturation temperature, and the swing between (say) a −35°C low-temperature freezer suction line and a +10°C air-conditioning suction line is roughly a 5-10× difference in vapour density for the same refrigerant. Picking one "typical" number to auto-fill would mean silently guessing at the input that matters most to the result, not offering a reasonable starting point the way a duct roughness value is. Get the actual density and viscosity for your refrigerant at your real saturation temperature from your own P-h chart, refrigerant software (Danfoss Coolselector, RefProp, etc.) or manufacturer data, and enter those directly.
As a rough, illustrative sanity check only — not a design value — common refrigerant vapour densities in ordinary HVAC/refrigeration suction conditions are very roughly in the 5-40 kg/m³ range (lower at lower evaporating temperatures, and much higher for CO2/R744, whose operating pressures are far higher than the HFCs/HFOs in this list), while subcooled liquid densities for most common refrigerants fall roughly in the 900-1300 kg/m³ range at typical liquid-line temperatures. If your entered value is wildly outside these ranges for the line type you picked, double-check it before trusting the result.
Static (elevation) pressure change
Included as a separate term from friction loss, using the same Δp = ρ·g·Δh relationship used for any fluid column. It's usually a much bigger factor for liquid lines (refrigerant liquid density is 900-1300 kg/m³, not far off water) with a real vertical rise than for vapour lines, where the much lower density makes the same elevation change a small term by comparison — but the calculator applies it either way, since the formula doesn't care which phase it is.
Refrigerant selector's typical values
Picking a refrigerant and line type auto-fills the density/viscosity fields with a rough order-of-magnitude starting point (roughly ±0°C saturation for suction vapour, ±40°C saturation for discharge vapour and liquid) — a genuinely useful first number, but not pulled from a verified refrigerant property database the way the friction physics is verified against Moody-chart references. Treat it as a "something to calculate with immediately" placeholder and replace it with your own P-h chart or refrigerant-software value once you know your actual operating pressures — the note under the fields updates every time you change either dropdown, so it's always clear which reference condition was used.
Fittings and the equivalent temperature penalty
The optional Fittings section adds elbows/tees/valves to the friction calculation using the standard equivalent-length method (each fitting is treated as extra straight pipe, count × Leq/D × diameter) — generic published ballpark multipliers, not manufacturer-specific data, and it only affects friction loss, not the static/elevation term. The optional ΔTsat conversion turns the total pressure loss into an equivalent saturation-temperature penalty using a dp/dT slope you supply — useful because suction-line losses are usually judged in K of lost compressor performance, not in kPa.
Oil-return velocity guideline
Suction and discharge (hot gas) lines carry entrained compressor oil, which has to keep moving with the vapour to make it back to the compressor rather than pooling in a trap or a riser — this needs a minimum velocity, on top of the usual maximum (noise/erosion/pressure-drop-penalty) limit every line type has. Liquid lines have no equivalent minimum (liquid inherently carries oil along with it) but keep a maximum to avoid noise and the risk of provoking flashing at high velocity. The ranges checked here are typical published guideline ranges seen across refrigeration piping references, not a single citable standard's exact figures — a result outside the range is worth a second look against your own design guide, not an automatic fail.