Work out liquid-line subcooling from gauge pressure and pipe temperature using the CoolProp bubble chart.
How to use this calculator
Formula: subcooling (K) = bubble SCT (°C) − liquid-line temperature (°C). A 1 K difference is the same size as a 1°C difference.
Blends: always use the bubble column for subcooling (fully liquid). Never use dew for SC.
Gauges: manifold gauges read barg. Match your liquid-line pressure to the nearest bubble barg row on the table.
Nearest row only: this tool matches the closest tabulated bubble pressure. It does not invent a continuous equation of state. If your pressure sits between rows, treat the result as approximate and confirm on the site PT chart.
R448A / R449A: not included. CoolProp 8.0.0 has no named fluid for them; use the manufacturer's PT chart [SOURCE NEEDED: manufacturer sheet].
R744: omitted from this calculator (high-pressure CO₂ practice is better done on the site chart). Use the PT lookup drill if you need R744 saturation rows.
Interactive calculator
Matched bubble SCT
Matched bubble pressure
ΔP to nearest row
Subcooling
Practice only. Always confirm against the PT chart on site before charging or deciding on charge. This tool is not a charge ticket.
Sat. temp °C
Bubble barg
Bubble bara
Sources
Values calculated with CoolProp 8.0.0 (PropsSI, Helmholtz equation of state). Absolute pressure in bar; gauge = absolute − 1.01325 bar (standard atmosphere). Rounded to 0.001 bar for practice. The auditable source file is pt-data-coolprop.json in the same folder; this page embeds a copy. Always confirm against the PT chart on site before charging or setting valves.
Practice drill
Ten questions. Use the bubble column and the CoolProp values on this page. Pass mark 75% (8 out of 10).
Question 1 of 10Score: 0
Your result
Pass mark: 75% (8 out of 10).
Want more practice with gauges, superheat and subcooling? RDA Academy training covers reading PT charts on live systems. Details are on the website: rda-academy.co.uk