• The cooling of liquid refrigerant after condensation is called sub-cooling of refrigerant.
• The sub-cooling of the refrigerant increases the refrigerating effects per kg of the refrigerant circulated in the system without any change in the work of compression.
• Therefore, sub-cooling is always desirable to reduce the operating cost of the system.

In the p-h diagram we see that, sub cooling in a vapour compression cycle increases the refrigeration effect from 1 – 4 to 1 – 4’. Whereas the required work 1–2 is remain same.

Hence, the correct option is (A).