**7. Conclusions**

As expected, the energy saving potential (ESP) of the air-PCM heat exchanger for cold storage in passive cooling of buildings depends on the climatic conditions. However, the differences between some locations were not as significant as could be expected. The energy saving potential in the case of Athens was only about 30% higher than the ESP in the case of Helsinki. The influence of the air flow rates on the ESP was rather significant. In the considered configuration of the air-PCM HEX and the investigated operating conditions, the ESP decreased rather significantly below about 400 m3/h.

The average utilization rate of the heat of fusion (URHF) was lower than 50% in all investigated cases. The main reason for that was the daily outdoor temperature swing that does not always overlap (straddle) the phase change temperature range of the PCM. Nonetheless, the URHF exceeded 90% on some days. In the case of Madrid (the location with the highest average ESP), the outdoor temperature set point of 20 ◦C for the utilization of cold during daytime had only a small influence on the overall ESP, which was very close to the theoretical maximum (without considering any set point). The main reason was the frequent occurrence of outdoor air temperatures above 20 ◦C during the utilization of cold, which made the set point condition inconsequential most of the time.

From the economic point of view, the considered way of cold storage (an air-PCM heat exchanger) was not economically viable even in the climates with the most favorable conditions.

**Author Contributions:** Conceptualization, P.C.; methodology, P.C. and L.K.; software, L.K. and M.Z.; formal analysis, P.C., L.K., and M.Z.; investigation, P.C., L.K., and M.Z.; writing, original draft preparation, P.C. and L.K.; writing, review and editing, P.C. and L.K.; visualization, L.K. and M.Z.; supervision, P.C.; funding acquisition, P.C. and L.K.

**Funding:** This research was funded by the project Sustainable Process Integration Laboratory (SPIL), funded as Project No. CZ.02.1.01/0.0/15\_003/0000456, by the European Research Development Fund and by the project Computer Simulations for Effective Low-Emission Energy funded as Project No. CZ.02.1.01/0.0/0.0/16\_026/ 0008392 by the Operational Programme Research, Development and Education, Priority Axis 1: Strengthening capacity for high-quality research.

**Conflicts of Interest:** The authors declare no conflict of interest.
