HC (A3) Pipe Sizing
Suction, liquid and hot gas lines for a refrigeration system with a flammable HC refrigerant (A3): compressor, condenser, filter drier, sight glass, expansion valve and evaporators connected in parallel. Drag the evaporators into place and click a line to set its length, size or riser.
R290 · -10.0 °C / 40.0 °C · 18.00 kW
System Data
All refrigerants here are safety class A3 (higher flammability) per EN 378/ISO 817/ASHRAE 34. Changing the refrigerant resets the design pressures.
Evaporating and condensing temperatures are dew points (relevant for zeotropic blends with glide). The liquid temperature is the bubble point at the condensing pressure minus the subcooling; it sets the flash gas share and so the mass flow.
R290 (A3) · glide at evaporation 0.0 K · at condensing 0.0 K · liquid temperature 38.0 °C. Flammable (A3): the charge is limited by EN 378-1 and the product standards (IEC 60335-2-89/-40). Keep the charge low, avoid ignition sources and carry out a risk assessment (ATEX).
Useful superheat at the evaporator outlet. It counts as refrigerating effect, and the suction lines are sized for the lower density of the superheated gas.
Installed compressor capacity for comparison with connected evaporator loads. Enter compressor power for total heat rejection.
Directly controls pipe sizing — higher velocity yields smaller pipes.
Hot gas line
From the compressors to the condenser, carrying the whole circulated mass flow. Length 0 = no hot gas line. Tick Riser if the line runs upwards; its oil return is then checked.
Refrigerant charge
| Component | Inner volume (L) | Liquid (%) |
|---|---|---|
| Condenser | ||
| Evaporators | ||
| Receiver |
Pipes 1.82 kg + components 0.00 kg + other 0.00 kg = 1.82 kg. R290 (A3, LFL 0.038 kg/m³): limit 0.15 kg (m1 – always allowed).
The pipes are calculated automatically: the liquid line full of liquid, the suction and hot gas lines full of gas. Enter the components' inner volume (manufacturers' data) and the share that is liquid in operation, or enter the charge directly under Other charge. The limits follow EN 378-1:2016+A1:2020 annex C (m1 = 4 m³ × LFL, m2 = 26 m³ × LFL, m3 = 130 m³ × LFL) and the product standards IEC 60335-2-40 and IEC 60335-2-89. The check is a guide – national rules may be stricter.
Advanced – Margins & Pipe Material
Increases the length in the pressure-drop calculation — shows up in the Δp column in the “Main Headers”/“Evaporator Branch Connections” tables below, not in the pipe size or the cards at the top.
Adds ordering margin to the Bill of Materials and Insulation Schedule totals only (offcuts, mistakes) — a different thing from “Extra length for fittings” above, and does not affect the pipe size or Δp.
Standard refrigeration tube (ACR). Enough for R290, R600a, R600, R1270 and the blends; R170 (ethane) has high pressures — see the ⛔ mark.
Pipes that cannot take this pressure are marked ⛔ and never chosen automatically. The defaults follow from the refrigerant per EN 378-2 (ambient up to 32 °C): the saturation pressure at 55 °C on the high side (liquid and hot gas) and at 32 °C on the low side, as gauge pressure. They are reset when you change refrigerant. Adjust them to your own system.
Optional. Risers are sized for oil return with the criterion j*g ≥ 0.85; here you can set your own lower limit, e.g. the manufacturer's recommendation. The higher of the two is used. Empty = the criterion only.
Pipes smaller than this threshold will never be selected automatically.
Select insulation specification (thickness/color) per header for the material bill.
Evaporators
| Name | kW |
|---|
A pipe stub contains only ONE line (liquid or suction). A suction stub can be converted to an evaporator by assigning a kW load.
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Options · Units
Changes how values are shown and entered — all calculations still run in the background as before.
⚠ The charge 1.82 kg is above m1 = 0.15 kg: enter the volume of the smallest room with an evaporator to check the limit per EN 378-1, table C.2.
Flow Diagram
Suction line
Liquid
Hot gas
Expansion valve
Tapped off another pipe
Drag an evaporator freely to position it. Click any pipe segment to set its length or manually override size.
Click here, then on a pipe run, to place a power meter.
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m
Size:
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Refrigerant charge and flammable refrigerant (A3)
| Part | Volume (L) | Density (kg/m³) | Charge (kg) | Share |
|---|---|---|---|---|
| Liquid line | 3.5 | 471.0 | 1.641 | 90 % |
| Suction line | 16.9 | 7.3 | 0.123 | 7 % |
| Hot gas line | 2.3 | 24.6 | 0.058 | 3 % |
| Condenser | 0.0 | – | 0.000 | 0 % |
| Evaporators | 0.0 | – | 0.000 | 0 % |
| Receiver | 0.0 | – | 0.000 | 0 % |
| Other | – | – | 0.000 | 0 % |
| Total | 22.7 | 1.821 | 100 % |
Limits for R290 (safety class A3)
Lower flammability limit LFL = 0.038 kg/m³ (EN 378-1 E / ISO 817)
m1 = 4 m³ × LFL = 0.152 kg · m2 = 26 m³ × LFL = 0.988 kg · m3 = 130 m³ × LFL = 4.940 kg
Limit: 0.152 kg (m1 – always allowed; EN 378-1:2016, table C.2 (AREA, Introduction to EN 378)). The charge is 999 % of the limit.
⚠ The charge 1.82 kg is above m1 = 0.15 kg: enter the volume of the smallest room with an evaporator to check the limit per EN 378-1, table C.2.
Measures
- The liquid line holds 90 % of the charge: shorten it and choose a smaller size (higher target liquid velocity, as far as pressure drop and flash gas allow).
- Place the unit close to the evaporators and choose components with a small inner volume (e.g. a microchannel condenser, a small receiver or none).
- Split the plant into several circuits, each below the limit.
- Go indirect: the HC unit in a machinery room or outdoors and a secondary fluid to the evaporators. Size the secondary network in Heating & cooling. → /hydronic/
- Put the compressor, condenser and receiver in a ventilated machinery room or outdoors (location class II or III, machinery room per EN 378-3).
Requirements and references
- Zoning: where flammable gas can occur, the area shall be classified per EN 60079-10-1 (ATEX directive 1999/92/EC), and equipment in a zone shall meet the ATEX directive 2014/34/EU. The calculator does not do the zoning.
- Machinery rooms, ventilation, gas detection and alarms: EN 378-3.
- Pipe joints and tightness: EN 378-2. Prefer permanent joints (brazed); mechanical joints shall be accessible and leak tested.
- Ignition sources: no ignition sources (switches, relays, hot surfaces, open flames) where refrigerant can collect after a leak. Most HC refrigerants are heavier than air and collect near the floor.
- The calculator does not replace a risk assessment. Check the limits against the standard text and national rules.
- Certification: in the EU, Implementing Regulation (EU) 2024/2215 now also covers hydrocarbons (Art. 2(1)(b)–(c)). Certificate A1: F-gases and hydrocarbons, any charge; A2: under 3 kg (labelled hermetically sealed systems under 6 kg); B: CO2; C: ammonia. Old category I/II certificates become A1/A2 only after updated knowledge (Art. 10). National rules apply too – e.g. Germany: ChemKlimaschutzV, in force since 17 April 2026 (existing certificates valid until 12 March 2029). Sweden: the new certificates cannot be issued yet, so the requirement cannot yet be applied to natural refrigerants (Naturvårdsverket, 2026-10). First refresher training by 12 March 2029 throughout the EU (Regulation (EU) 2024/573, Art. 10(9)). (EUR-Lex – (EU) 2024/2215, LfU Bayern – ChemKlimaschutzV, Naturvårdsverket – övergångsperiod; checked 2026-10-29)
Safety standard in other countries
- United Kingdom: BS EN 378 (the UK edition of EN 378, same charge limits). Hydrocarbons are outside the GB F-gas rules; the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR, SI 2002/2776) require a risk assessment and zoning where flammable gas can occur. (legislation.gov.uk – DSEAR, SI 2002/2776; checked 2026-10-25)
- Japan: High Pressure Gas Safety Act (Art. 5) and its Cabinet Order (Art. 2(5)(iii)–(iv), Art. 4) – propane, propene, isobutane, n-butane and ethane are flammable gases under the Refrigeration Safety Regulations (冷凍保安規則 Art. 2(1)(i)) and belong to "other gases": below 3 tons of refrigerating capacity per day outside the Act, 3 to under 20 tons per day a notification (届出) to the prefecture, 20 tons per day or more a permit (許可). The legal capacity (法定冷凍能力) is calculated from the compressor displacement, R = V/C (冷凍保安規則 Art. 5), not from the cooling capacity in kW; the commercial ton of about 3.86 kW is not the legal value. For flammable refrigerants Art. 7(1) requires explosion-proof electrical equipment, a gas detector with alarm and fire-extinguishing equipment. (e-Gov – 高圧ガス保安法, 施行令, 冷凍保安規則, Japanese Law Translation – High Pressure Gas Safety Act; checked 2026-10-29)
- USA: ASHRAE 15-2022 and UL 60335-2-89 (2nd edition, 27 October 2021), which EPA SNAP refers to (40 CFR 82 subpart G, appendix R; SNAP Rule 26, 2024). SNAP accepts hydrocarbons only in new equipment designed for them, not in conversions, with use conditions per sector. The limits for R290 in new stand-alone commercial refrigeration come from UL 60335-2-89, not from the CFR text: about 300 g with doors or drawers, 500 g open. (eCFR – 40 CFR 82 subpart G, EPA – SNAP Rule 26 (2024); checked 2026-10-29)
- Canada: CSA B52:23 Mechanical refrigeration code. It has legal force once a province adopts it, e.g. British Columbia (B.C. Reg. 104/2004: B52:23), Alberta (Alta Reg 49/2006, s. 6(b): CSA B52 as amended from time to time), Manitoba (2024) and Ontario (TSSA, from 1 October 2024). (CSA B52:23, SCC; checked 2026-10-29)
- Australia and New Zealand: AS/NZS 5149.1:2016 (+Amd 1:2018) for refrigerating systems – ISO 5149-1 with national modifications (MOD), so charge limits can differ from ISO/EN – and AS/NZS 60335.2.89:2020 Amd 1:2024 (commercial refrigerating appliances). The Australian ARC refrigerant licence covers fluorocarbon refrigerants; work with hydrocarbons may need an additional state licence – check the rules of the state. (AS/NZS 5149.1:2016, AS/NZS 60335.2.89:2020 Amd 1:2024; checked 2026-10-29)
- Switzerland: ChemRRV (SR 814.81) annex 2.10 bans or restricts refrigerants that are stable in air (fluorinated refrigerants, F-gases) and ozone-depleting substances; hydrocarbons are not covered and are often the alternative (tighter limits from 1 January 2027; transitional rules in no. 7 still allow some F-gas systems until 2028–2032). The exception refers to SN EN 378-1:2017+A1:2021, SN EN 378-2:2017, SN EN 378-3:2017+A1:2021, SN EN IEC 60335-2-89:2022/A11:2022 and IEC 60335-2-40:2022 (ed. 7): if these cannot be met with a natural refrigerant, BAFU may allow an F-gas. (Fedlex – ChemRRV, Anhang 2.10 (Fassung 2027), Fedlex – ChemRRV (SR 814.81), Anhang 2.10, BAFU – Kältemittel, BAFU – Stand April 2026; checked 2026-10-29)
- South Africa: SANS 10147:2014 (edition 5) is the standard for refrigerating systems, including those of air-conditioning plants. Under the Pressure Equipment Regulations (regulation 17) the work shall be done by an Authorised Refrigeration Practitioner registered with SAQCC Gas (through SARACCA). Registration is valid for 3 years. The ODS Regulations (GN R351 of 2014, amended 2021) forbid releasing ozone-depleting substances into the atmosphere (reg. 7) and using HCFC-22 or other HCFCs in new refrigeration or air-conditioning systems since 1 January 2015 (reg. 5(2)(c)). (SABS – SANS 10147:2014 (Ed. 5.00), SAQCC Gas – SARACCA; checked 2026-10-29)
- Chile: NCh3241:2017 for refrigeration and air-conditioning systems (based on ISO 5149-1:2014, ISO 817:2014 and ASHRAE 15) and NCh3301:2017 for installing and servicing systems with flammable refrigerants (A2L, A2 and A3). (INN – NCh3301:2017, MMA/INN – NCh3241:2017, NCh3301:2017; checked 2026-10-07)
- Colombia: NTC 6228-1 to -4 (ICONTEC, 2019–2021), based on ISO 5149. (Minambiente – NTC 6228-1; checked 2026-10-07)
- Rest of Latin America: ISO 5149-1 to -4 where the country has not adopted a standard of its own. (ISO 5149-1:2014; checked 2026-10-07)
ISO 5149-1 uses the same method for charge limits (m1, m2, m3 and room volume) as EN 378-1 annex C, which the app calculates with. Always check against the edition in force in the country.
Bill of Materials
Lengths include the waste allowance above, but not the fitting length allowance (which only affects Δp).
Insulation Schedule
Insulation types are selected under 'Advanced' in System Data.
Evaporator Branch Connections
"Own Load" is the evaporator's own kW value. "Load in Pipe" is the accumulated flow through that specific pipe — larger if other evaporators/pipes are tapped onto it. Never sum the "Load in Pipe" columns for a grand total; use "Own Load" instead.
Main Headers
Show calculation
Calculation per pipe section
| Pipe section | Mass flow [kg/s] | Density [kg/m³] | Inner diameter [mm] | Velocity [m/s] | Re | f | Length (+ fittings) [m] | Δp [kPa] | Δp per metre [Pa/m] | Note |
|---|---|---|---|---|---|---|---|---|---|---|
| Liquid, Main Stem: Condenser → Cold Room 1 | 0.06454 | 471 | 17.3 | 0.585 | 56,200 | 0.0206 | 6 (+1.8) | 0.75 | 125 | |
| Liquid, Main Stem: Cold Room 1 → Cold Room 2 | 0.03585 | 471 | 11.1 | 0.791 | 48,700 | 0.0214 | 6 (+1.8) | 2.22 | 371 | |
| Liquid, Main Stem: Cold Room 2 → Display Case | 0.01434 | 471 | 7.9 | 0.621 | 27,300 | 0.0245 | 6 (+1.8) | 2.19 | 366 | |
| Suction Line, Main Header: Compressor → Cold Room 1 | 0.06454 | 7.266 | 38.2 | 7.74 | 300,000 | 0.0148 | 6 (+1.8) | 0.658 | 110 | |
| Suction Line, Main Header: Cold Room 1 → Cold Room 2 | 0.03585 | 7.266 | 26 | 9.27 | 245,000 | 0.0155 | 6 (+1.8) | 1.45 | 242 | |
| Suction Line, Main Header: Cold Room 2 → Display Case | 0.01434 | 7.266 | 17.3 | 8.43 | 148,000 | 0.0171 | 6 (+1.8) | 2 | 334 | |
| Hot gas line: Compressor → Condenser | 0.06454 | 24.56 | 17.3 | 11.2 | 535,000 | 0.0142 | 10 (+3) | 16.6 | 1,660 | |
| Cold Room 1 – Liquid | 0.02868 | 471 | 11.1 | 0.633 | 39,000 | 0.0225 | 5 (+1.5) | 1.24 | 249 | |
| Cold Room 1 – Suction line | 0.02868 | 7.266 | 26 | 7.41 | 196,000 | 0.0161 | 5 (+1.5) | 0.803 | 161 | |
| Cold Room 2 – Liquid | 0.02151 | 471 | 11.1 | 0.475 | 29,200 | 0.0239 | 5 (+1.5) | 0.745 | 149 | |
| Cold Room 2 – Suction line | 0.02151 | 7.266 | 19.9 | 9.48 | 192,000 | 0.0163 | 5 (+1.5) | 1.74 | 348 | |
| Display Case – Liquid | 0.01434 | 471 | 7.9 | 0.621 | 27,300 | 0.0245 | 5 (+1.5) | 1.83 | 366 | |
| Display Case – Suction line | 0.01434 | 7.266 | 17.3 | 8.43 | 148,000 | 0.0171 | 5 (+1.5) | 1.67 | 333 |
Basis of calculation
- Method
- Darcy–Weisbach per pipe section; the size is the smallest tube that keeps the velocity at or below the target. Gas lines are marched in 50 steps with the density following the local pressure (isothermal); liquid lines use a constant density.
- Equations
Δp = f · (L/d) · ρv²/2 + ρ·g·hRe = ṁ·d / (A·µ)f = 0.25 / [log10(ε/(3.7·d) + 5.74/Re^0.9)]² (Re < 2300: f = 64/Re)L = L_pipe · (1 + 30 %)
- Friction factor
- Swamee–Jain (explicit form of Colebrook–White), roughness of the chosen pipe type
- Fluid data
- CoolProp (HEOS; blends as CoolProp predefined mixtures, composition per ASHRAE 34) 8.0.0
- Standards
- EN 378-1:2016 (C.2, E) · EN 378-2:2016 · IEC 60335-2-89:2019 · IEC 60335-2-40 · ASHRAE 34
- Notes
- Density in the table is the inlet value; superheated suction and discharge gas from saturated vapour density corrected for the superheat.
- Compared with Danfoss Coolselector 2 for R290, R600a and R1270 (12 cases, 36 sizes): mass flow within 0.05 %, Δp within 0.8 %.
Refrigerant pipe sizing – frequently asked questions
How do you size refrigerant lines for R290 and other HC refrigerants?
The calculator works out the mass flow from each evaporator's capacity and the refrigerant properties (CoolProp), then picks the smallest pipe that keeps the velocity below the target. Pressure drop is calculated with Darcy–Weisbach and shown in kPa and as saturation temperature drop (K). The results have been checked against Danfoss Coolselector 2.
What velocity should suction, liquid and hot gas lines have?
The defaults are 10 m/s in the suction line, 0.8 m/s in the liquid line and 12 m/s in the hot gas line. A higher velocity gives smaller pipes but more pressure drop, and suction risers also need enough velocity for oil return.
How much pressure drop is acceptable in a refrigerant line?
Common guide values are about 1 K saturation temperature drop in the suction line and 0.5–1 K in the liquid and hot gas lines. The calculator converts every pressure drop to K and warns of flash gas when the liquid line drop exceeds the subcooling.
How do I make sure oil returns up a suction riser?
Mark the line as a riser. The calculator then picks a size in which the gas is fast enough to carry the oil upwards (criterion j*g ≥ 0.85) and shows the minimum velocity. If even the smallest allowed size is too large, a double suction riser is suggested.
Which refrigerants are included, and how is glide handled?
R290 (propane), R600a (isobutane), R600 (butane), R1270 (propylene), R170 (ethane) and the blends R441A, R443A, R436A, R436B and R510A, all of safety class A3. Temperatures are entered as dew points; for zeotropic blends the glide, bubble point and liquid temperature are worked out automatically.
What is the charge limit for a system with R290 or R600a?
It depends on the refrigerant's lower flammability limit (LFL), the room volume, the location and the access category under EN 378-1 (Annex C), or on the product standard for factory-built units: IEC 60335-2-89 for commercial refrigerating appliances and IEC 60335-2-40 for heat pumps and air conditioners. The calculator estimates the charge and compares it with an indicative limit; it does not replace the standard. Small pipes and short lines mean a smaller charge. Always carry out a risk assessment.
Check the charge in the tool above →Heating, cooling & brine pipe sizing →
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