P-H diagrams can be used to compare the performance of different refrigerants by analyzing their thermodynamic properties, such as enthalpy, entropy, and pressure. By plotting the P-H diagrams for different refrigerants, engineers can compare their performance characteristics, such as refrigeration capacity, energy efficiency, and operating pressures. This enables the selection of the most suitable refrigerant for a specific application, taking into account factors such as environmental impact, safety, and cost.