The application of cooling systems is a relatively efficient way to ensure the required thermal comfort conditions. One option is the application of cooled ceilings, where the heat load is removed using a ceiling structure with integrated cooling panels. These systems allow for a suitable way remove the heat load, but at the same time, compared to conventional air conditioning systems, they are characterized by a certain time dependence. The presented article describes experimental measurements carried out on days with high exterior heat exposure. Measurements evaluating the effect of the phase shift of temperature oscillations on the operation of the system were carried out using two cooling operating modes. According to results, it can be concluded that cooling systems based on cooling ceilings can be used effectively even with high external heat gains.