Abstract: An air conditioning system for buildings includes a plurality of air conditioners on the different floors, a cooling gravity type heat pipe connecting vaporizers in the air conditioners with a cold thermal source installed at the top of the building and a warming gravity type heat pipe connecting a condenser of the air conditioners with a hot thermal source installed in the basement of the building. The heat pipes are, respectively, provided with flow control valves at the inlet of each vaporizer and the outlet of each condenser. Each air conditioner is provided with a thermistor for detecting the temperature of the returning air and a liquid level detection switch for detecting the liquid level of the thermal medium in the vaporizer. The flow control valves are respectively controlled based on the detection signals issued by the thermistor and the liquid level detection switch.