An air conditioning device for at least one room intended to receive persons, in particular a room for passengers of a public transport vehicle, including: - central means for conditioning the temperature of a heat transfer liquid, - a circuit for circulation of the heat transfer liquid, passing through the central conditioning means, and comprising at least one pump for circulating the heat transfer liquid, - at least one air conditioning unit, intended to be housed in the room, comprising: • an enclosure having an air inflow opening from the room and a conditioned air outflow opening towards the room, • a heat exchanger, connected to the circulation circuit, characterized in that: - the air inflow and outflow openings being both laid out at the floor of the room, so that natural convection related to the presence of persons in the room will give the possibility of generating an ascending movement of the air from the air outflow opening in the room, - the air conditioning unit comprises a ventilation member, housed in the enclosure, able to have the air circulate in the enclosure from the air inflow opening to the air outflow opening, and - the heat exchanger is able to exchange calories between the heat transfer liquid and the air circulating in the enclosure under the effect of the ventilation member. - central means for conditioning the temperature of a heat transfer liquid, - a circuit for circulation of the heat transfer liquid, passing through the central conditioning means, and comprising at least one pump for circulating the heat transfer liquid, - at least one air conditioning unit, intended to be housed in the room, comprising: • an enclosure having an air inflow opening from the room and a conditioned air outflow opening towards the room, • a heat exchanger, connected to the circulation circuit, characterized in that: - the air inflow and outflow openings being both laid out at the floor of the room, so that natural convection related to the presence of persons in the room will give the possibility of generating an ascending movement of the air from the air outflow opening in the room, - the air conditioning unit comprises a ventilation member, housed in the enclosure, able to have the air circulate in the enclosure from the air inflow opening to the air outflow opening, and - the heat exchanger is able to exchange calories between the heat transfer liquid and the air circulating in the enclosure under the effect of the ventilation member. • an enclosure having an air inflow opening from the room and a conditioned air outflow opening towards the room, • a heat exchanger, connected to the circulation circuit, - the air inflow and outflow openings being both laid out at the floor of the room, so that natural convection related to the presence of persons in the room will give the possibility of generating an ascending movement of the air from the air outflow opening in the room, - the air conditioning unit comprises a ventilation member, housed in the enclosure, able to have the air circulate in the enclosure from the air inflow opening to the air outflow opening, and - the heat exchanger is able to exchange calories between the heat transfer liquid and the air circulating in the enclosure under the effect of the ventilation member.