<p>Disclosed is an air conditioning system (10) wherein an outdoor unit (15) is connected to an indoor-side circuit (70) in which heating water on the usage side is circulated. A cooling circuit (21) is provided in the outdoor unit (15). When the air conditioning system (10) is running in cooling mode, a cooling cycle is carried out in which a heating heat exchanger (82) acts as a condenser, and a heat exchanger (23) on the heat source side acts as an evaporator in the cooling circuit (21). The heating water which is heated by the heating heat exchanger (82) is conducted to the top end of a thermal storage tank (37), while some of the heating water cooled by the heat exchanger (23) on the heat source side is conducted to the bottom end of the thermal storage tank (37). High-temperature heating water is stored in the section close to the top end of the space inside the thermal storage tank (37), and low-temperature heating water is stored in the section close to the bottom end of the space inside the thermal storage tank (37).</p>
