(i) Superheating at the compressor suction:

• Superheating the refrigerant vapour at the compressor suction ensures that only dry vapour (no liquid) enters the compressor, preventing liquid slugging (which would damage the compressor valves, pistons/ scroll).
• It ensures the compressor operates on dry vapour, improving the volumetric efficiency and protecting the compressor.
• A controlled degree of superheat (set by the TXV) ensures the evaporator is fully used (all the liquid is evaporated) and the compressor is protected.

(ii) Undercooling at the condenser outlet:

• Undercooling (subcooling) the liquid refrigerant below its saturation temperature at the condenser outlet ensures that only liquid (no flash vapour) enters the expansion valve.
• This increases the refrigerating effect (the enthalpy difference across the evaporator is increased), improving the system's cooling capacity and efficiency.
• It prevents flash gas in the liquid line, which would reduce the refrigerant flow and the cooling capacity.

On a pressure-enthalpy (P-h) diagram, the refrigeration cycle is plotted. The refrigerating effect (cooling load) is the enthalpy difference between the evaporator outlet and the evaporator inlet (the horizontal distance of the evaporation line).

• Superheating at the compressor suction: The superheat moves the compressor suction point to the right on the P-h diagram (higher enthalpy at the same pressure). This increases the refrigerating effect slightly (the evaporator outlet enthalpy is higher), but the main benefit is protecting the compressor. The superheat is controlled by the TXV.
• Undercooling at the condenser outlet: The subcooling moves the condenser outlet point to the left on the P-h diagram (lower enthalpy at the same pressure). This increases the refrigerating effect (the enthalpy difference across the evaporator is larger), increasing the cooling capacity for the same refrigerant flow.
• Thus, both superheating and undercooling increase the refrigerating effect (cooling load) on the P-h diagram, improving the system's efficiency and capacity, while superheating also protects the compressor.