R-454B PT Chart: Bubble and Dew Pressures, −40°F to 150°F

With the temperature box at 75°F, the tool reads that row straight off the chart: the bubble point is 208.40 psig and the dew point is 199.51 psig. No arithmetic is involved, because 75°F is one of the rows.

A gauge reading rarely lands on a row, so the pressure box interpolates. Take 120 psig on the dew side. The 45°F row has a dew pressure of 118.34 psig and the 46°F row has 120.59 psig, so 120 psig sits (120 − 118.34) ÷ (120.59 − 118.34) = 1.66 ÷ 2.25, or about 0.74 of the way from one to the next. That makes the dew point 45.74°F, shown as 45.7°F.

The bubble side works the same way between the 43°F row (119.86 psig) and the 44°F row (122.14 psig), which gives 43.1°F. Subtract one from the other and the glide at 120 psig comes out at 2.6°F. Each temperature is rounded to a tenth of a degree first, so the three numbers on screen agree with each other.

Every row was computed with the equation-of-state models in CoolProp 8.0.0, one row per whole degree Fahrenheit. The pressures are gauge readings, assuming a sea-level atmosphere of 14.696 psia.

The chart was spot-checked against Honeywell's published Solstice 454B pressure–temperature chart, at six pressures from 20 to 450 psig on both the bubble and dew sides. Measured as a share of absolute pressure (gauge plus 14.696 psi), every one of those twelve points is within about 1% of the reference charts checked. The biggest gap in psi was 1.92 psi, about 0.4%, on the bubble side at 450 psig, and the biggest as a percentage was 0.33 psi, just under 1%, on the bubble side at 20 psig. The methodology page explains how the comparison is made and lists the points on other charts that fall outside 1%.

When a pressure falls between two rows, the lookup draws a straight line between them and rounds the result to 0.1°F. CoolProp's mixture solver didn't converge on its first pass at nine of the hottest rows, between 134°F and 149°F. Those nine rows were solved again at their own temperatures, starting the solver from the nearest good row below. None of them were interpolated, so the chart runs unbroken to 150°F.