Thermal mass activation by hollow core slab coupled with night ventilation to reduce summer cooling loads

This study deal with the analysis of the effectiveness of free cooling ventilation strategies coupled with thermal mass activation to reduce peak cooling loads. A numerical simulation of the temperatures distribution of an office placed in Milan, Italy, during the month of July, is conducted on a Simulink® dynamical model. No air-conditioned system is present but two different free cooling systems are analysed and compared. Both systems act a primary ventilation during the day and a night ventilation during the non-occupancy period but the first is a traditional mixing ventilation system, the other is a thermal mass activation system, i.e. the outdoor ventilation air, before entering the room, flows through the ducts of the hollow core concrete ceiling slab. The performances of the two systems are investigated by means of time profile analyses of indoor operative temperatures and by means of frequency temperature distributions during the occupancy period. The cooling performances are measured by two different discomfort indexes: one represents the discomfort time percentage during occupation period, the other the discomfort weighted on the distance of calculated operative temperature from the acceptable temperature interval. This paper, in last analysis, tries to highlight the possibilities on cooling loads reduction and on thermal comfort increase in Mediterranean climate, connected to new strategies for thermal mass activation and night ventilation.