This study presents the development of a real-scale latent heat thermal energy storage (TES) device based on an air-PCM (phase change material) heat exchanger. The device uses the outdoor ambient temperature difference between night and day to refresh the indoor air and shift or completely avoid the use of air-conditioning in air-cooling in the building sector. The design is based on an extensive set of numerical simulations, performed by the commercial software ANSYS Fluent, focused on a parametric study allowing to identify the optimum value of different design parameters in order to have 10 hours of temperature shift. The numerical simulations were supported by experimental measurements done with a small-scale test rig. Additionally, the thermal response of the PCM to cooling and heating was also studied in a controlled temperature and humidity environment.