Kelvin

Choose a tube series and judge its pressure rating

Size a layout in the tube you'll install, and judge each tube's rating against the design pressure at the standstill temperatures you enter.

Pipework, equipment and charge · Updated 7 Oct 2026

  1. 1

    Under Pipe sizing, choose the series in Tube. ACR copper to ASTM B280 is built in and is the default; the others are copied from Kelvin's reference library when you choose them.

  2. 2

    Enter Standstill, high side and Standstill, low side: the temperatures each side of the system can reach while it stands.

  3. 3

    Read each segment's pressure check in the ledger's Rule column.

How a rating is judged

  • At standstill each side of the system equalises, so a line's design pressure is the refrigerant's saturation pressure at that side's standstill temperature. Suction lines are on the low side; discharge and liquid lines on the high side. For a blend Kelvin takes the bubble pressure, the higher of the two.
  • The design pressure is set against the tube's rated working pressure at 70 °C, or up to the temperature its maker rates it to. It's never judged on the pressure the line runs at.
  • Enter the temperatures from AS/NZS 5149.2, which sets the standstill ambient for each side. Kelvin doesn't hold its tables, so neither has a default.
  • On a CO₂ low side the standstill pressure is set by its relief valve, so enter the saturation temperature at that relief setting.

What the check says

  • Pass: the design pressure is within the tube's rating.
  • Over tube rating (critical): the design pressure is above it.
  • Hotter than rated (warning): within the rating, but the line runs hotter than the temperature the rating holds to.
  • Pressure not judged: no standstill temperature is entered for that side. A layout saved before these were asked for reads this way until you enter them.
  • A standstill temperature past the end of the refrigerant's saturation data gives no design pressure, and the rating stays not judged.

Series with several walls

  • Where a series lists more than one wall for a size, Kelvin takes the thinnest wall whose rating covers the line's design pressure, or the thickest when none does. With no standstill temperature entered it chooses on the pressure the line runs at. A Wall cell under the size lets you choose one.
  • Where a run rises part of the way on a smaller bore, the check is against the weaker of its two tubes, and the rule says which.
  • A series the reference library doesn't hold yet is listed as not in the library yet, and choosing it is refused with the reason. It's never quietly sized in ACR instead.
  • The sizes are copied into the layout when you choose the series, so a later library edit doesn't change a saved layout.

Note

After a change of series, a size you entered that the new series doesn't have goes back to its auto size.