Common phase change materials (PCMs) have serious shortages, and the most important one is the low thermal conductivity. This issue makes the phase change process a time-consuming period that decreases the performance of thermal storage units. This paper concentrated on improving energy and exergy performance with the aid of an air–PCM heat exchanger, which could be employed for free cooling of buildings. For the heat exchanger, the PCM of Rubitherm 22 °C high capacity (RT22HC) and the nanoparticles of multi-wall carbon nanotube were employed. The initial charging and discharging experiments showed that due to thermal conductivity enhancement, melting and solidification periods decreased using nano-PCM with three concentrations of 0.1, 0.2, and 0.5 mass% compared to the PCM without nanoparticles. Moreover, the highest exergy and energy efficiencies were obtained for the case of nano-PCM 0.5 mass% during the charging process and the values were 11.03 and 21.33%, respectively. Experiments with nano-PCM 0.5 mass% were accomplished during three continuous days. The results demonstrated that the heat obtained from nano-PCM 0.5 mass% encapsulations varied with weather conditions. In addition, the output energy and exergy rose with sunrise and fell with sunset. Finally, an economic analysis was carried out for cold climate conditions. The results indicated that the whole invested capital expenditures will return in the ninth year of exploitation.

Keywords