Pocket HVAC
Pocket HVACWhat is an R-507A PT chart?
An R-507A PT chart lists the pressure R-507A boils and condenses at for each temperature. At 40°F that's 89.2 psig on the vapor (dew) side and 89.3 psig on the liquid (bubble) side. It's sold as Forane 507A, Genetron AZ-50 and Klea 507.
Anywhere liquid and vapor are together in a system, like inside the evaporator and condenser coils, the pressure and temperature are locked together, so one tells you the other. On the job, the chart turns gauge readings into saturation temperatures: the suction pressure gives the temperature the evaporator is boiling at, and the liquid line pressure gives the temperature the condenser is condensing at. Compare those with your line temperatures and you have superheat and subcooling.
R-507A is a blend of R-125 and R-143a, 50/50 by weight (safety class A1), made for low and medium temperature commercial refrigeration, like walk-in coolers and freezers and supermarket cases. It replaced R-502. It has a very high global warming potential (GWP), so new equipment is moving to lower-GWP refrigerants.
How it's calculated
Absolute pressure = gauge pressure + 14.696 psi (101.325 kPa, one standard atmosphere) Saturation data: R-507A: CoolProp 8.0.0, R507A Between table points (every 0.5 °C): ln(pressure) is interpolated linearly in 1 ÷ absolute temperature Blends have separate liquid (bubble) and vapor (dew) curves Glide = dew temperature − bubble temperature at the same pressure Printed chart rows are solved by CoolProp at each exact temperature
Sources
- Bell, Wronski, Quoilin & Lemort (2014), "Pure and Pseudo-pure Fluid Thermophysical Property Evaluation and the Open-Source Thermophysical Property Library CoolProp", Industrial & Engineering Chemistry Research 53(6)
- Lemmon (2003), "Pseudo-Pure Fluid Equations of State for the Refrigerant Blends R-410A, R-404A, R-507A, and R-407C", International Journal of Thermophysics 24(4)
- Arkema, Forane 507A Thermodynamic Properties (NIST REFPROP 9.0)
If a number doesn't match your chart, email me what you entered and what you expected, and I'll check it against the source. You can also read how the numbers are checked.
Checked by Paul Williams · Updated
Questions
What is the R-507A pressure at 40°F?
At 40°F, R-507A saturates at 89.2 psig on the vapor (dew) side and 89.3 psig on the liquid (bubble) side. At 100°F it's 242.1 psig vapor and 242.3 psig liquid.
Why are the two columns almost the same?
R-507A is an azeotrope: its two ingredients, R-125 and R-143a, boil off together, so it behaves almost like a single refrigerant. From -40 to 150°F its liquid and vapor pressures are never more than 0.3 psi apart, under 0.1°F of glide. Use the vapor column for superheat and the liquid column for subcooling, though on R-507A the difference won't show on a gauge.
Is R-507A the same as R-404A?
No. Both are A1 blends for commercial refrigeration and they run at similar pressures, but they're different mixtures: R-507A is about 2 to 4 psi higher at 40°F. Use the chart for the refrigerant on the unit's nameplate.
How accurate is this chart?
It comes from NIST's equation of state for R-507A (Lemmon, 2003) through CoolProp. It matches Arkema's Forane 507A tables, which use NIST REFPROP, to within 0.1 psi on every row from -40 to 150°F.
