Cool Storage is a well-known technique that been used to increase the energy efficiency of cooling systems. This paper represents a novel experimental work for the effect of internal capsules surface roughness on the performance of encapsulated cool storage systems. In this study, distilled water was used as a phase change material inside capsules. Internal surface roughness of 0, 3, 7 and 12 μm were tested using the same heat transfer fluid Characteristics. Heat transfer fluid (HTF) composed of 50–50 wt. of (water–ethylene glycol) was used with a fixed volume flow rate of 12 L/min LPM and four different inlet temperatures of −6, −8, −10 and −12 C. The solidified mass fraction, charging rate and energy storage were calculated and plotted versus the charging time to determine the surface roughness effect on the cooling performance of the system. Results showed that the internal surface roughness of capsules …