Superheat and subcooling calculator
For 28 refrigerants, on CoolProp’s saturation tables. Either half works alone.
Refrigerant
Superheat
- Saturation
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- Choose a refrigerant
- Superheat
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Subcooling
- Saturation
- —
- Choose a refrigerant
- Subcooling
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What it works out
- Superheat
- Suction line temperature − the dew point at the suction pressure
- Subcooling
- The bubble point at the liquid line pressure − liquid line temperature
- Pressure alone
- The saturation temperature at that pressure, for reading a gauge like a P–T chart
Dew point and bubble point
A single-component refrigerant, such as R-32 or R-134a, boils at one temperature at a given pressure: its saturation temperature, where the dew point and the bubble point are the same. A zeotropic blend, such as R-454B, R-407C or R-449A, boils across a range. At a given pressure its liquid starts to boil at the bubble point and the last of it boils off at the dew point; the difference is its glide.
So superheat is measured from the dew point: only above it is the refrigerant all vapour. Measured from the bubble point, a blend with a few kelvin of glide could read as superheated while it still carried liquid. Subcooling is measured from the bubble point for the same reason: only below it is the refrigerant all liquid. Under each result the calculator names the point it used, and a blend’s glide at that pressure.
Where the figures come from
- Saturation
- The public refrigerant tables: bubble and dew pressures every 2 K, computed with CoolProp 7.2.1dev (open-source software under the MIT licence).
- Between rows
- Interpolated linearly in the logarithm of pressure against the reciprocal of absolute temperature. Checked against CoolProp’s own solution at 127,338 pressures across every table, the largest difference was 0.012 K; Kelvin’s tests hold it within 0.02 K. Results are shown to 0.1 K.
- Not extrapolated
- Below a table’s first row, above its last, above a critical point, and across rows CoolProp didn’t solve, the calculator says so instead of giving a figure.
- Gauge pressure
- Absolute pressure less a standard atmosphere, 101.325 kPa. A gauge reads against the air around it; where that differs much from a standard atmosphere, enter the absolute pressure if you have it. 1 psi = 6.894757 kPa.
- Not here
- R-448A and R-450A: CoolProp can’t form them, and Kelvin holds no other source it may republish, so their pages carry no table and the calculator doesn’t offer them.
- Your readings
- Worked out in your browser: nothing you type is sent anywhere. The last refrigerant and pressure unit are remembered on this device.
Printable
An A4 pressure–temperature chart for each refrigerant, in kPa and bar gauge, bubble and dew for a blend: every printable P–T chart.
Design with these refrigerants in Kelvin
Kelvin’s Free plan includes the refrigerant library, P–h diagrams, single-stage cycles and draft reports. Paid plans carry a system on through pipework, equipment, charge, energy and cost to issued reports.
Verify before relying on these figures
The saturation temperatures are computed with CoolProp from published equations of state and interpolated between its 2 K rows. They must be verified by a qualified professional before they’re relied on.