A chart of refrigerant pressure against heat content on which a refrigeration cycle can be drawn.
On a pressure-enthalpy diagram, pressure rises up the vertical axis and heat content (enthalpy) increases to the right. A dome marks the saturation region: liquid to its left, mixture inside, vapour to its right. The basic cycle draws as four lines: evaporation across the bottom, compression rising to the right, condensation across the top, and expansion straight down. Superheat is the stretch beyond the right of the dome at low pressure; subcooling is the stretch left of the dome at high pressure.
Exam work areas
C · Planning installs and retrofits E · Commissioning and start-up