Thermally activated building systems provide an effective method to combine thermal inertia and HVAC systems, and can be used to promote comfortable indoor conditions in summer. Ventilated slabs (VS) use supply air flow directly for heating or cooling, without the need for separate auxiliary systems. This paper proposes a detailed model of an office building equipped with VS under three different climatic conditions during one month in the summer. A Model Predictive Controller and a Genetic Algorithm, developed in MATLAB, are subsequently implemented to reduce energy consumption of the system while maintaining the room temperature set point. The outcomes of both short and extended sequences are presented after conducting modelling considerations. The dynamic behaviour of the room is highlighted, while the cooling demand is further evaluated using statistical indexes. The reduction in peak cooling load was noted in all instances, including during outdoor conditions that are unfavourable to free cooling strategies.