Refrigeration Cycle on the P-H Diagram

One of the most important skills needed for the professional engineer in the HVAC and Refrigeration field is navigating the refrigeration cycle on a pressure-enthalpy diagram. The following sections will show each specific part of the refrigeration cycle on the pressure-enthalpy diagram and it will also highlight the important points and calculations needed.

Throughout this explanation the refrigerant R-134a is used as an example. It is recommended that the engineer get a copy of the P-H diagram for R-134a and the other common refrigerants. These diagrams can be found in the ASHRAE Fundamentals book. A sample R-134a diagram is shown below, with a sample refrigeration cycle, identifying (Step 1) Evaporator, (Step 2) Compressor, (Step 3) Condenser and (Step 4) Expansion Device.

Pressure Enthalpy Diagram with Refrigeration Cycle for the Mechanical PE Exam