In which units is pressure represented on the pressure enthalpy (PE) chart?

Pressure on the pressure enthalpy (PE) chart is most commonly represented in pounds per square inch absolute (psia). This is because absolute pressure is crucial in thermodynamic calculations, especially when analyzing systems involving refrigerants.

Absolute pressure takes the atmospheric pressure into account, providing a true measure of pressure as it reflects the total pressure at a point, in contrast to gauge pressure, which omits atmospheric pressure and can cause discrepancies in thermodynamic interpretations.

Using absolute values ensures that any calculations involving enthalpy and energy changes are consistent and accurate. This is particularly important for HVAC/R applications, where proper refrigerant behavior needs to be modeled accurately to ensure system efficiency and effectiveness.