PURPOSE: To eliminate danger for environment when organic heat medium is employed as a heat medium by a method wherein the title heat exchanger is provided with an exhausting facility, in which discharged and evaporated heat medium is condensed to recover it into a buffer tank while the vapor of non-condensed heat medium is removed by an adsorbing device to make it harmless.

CONSTITUTION: The deterioration of the pressure of heat medium in an expansion tank 7 is detected by a pressure detector 8 to open a control valve 9 and seal inert gas into the expansion tank 7. On the other hand, when the pressure of the heat medium in the expansion tank 7 is increased, the control valve 10 is opened to send the heat medium into a condenser 11 whereby the vaporized heat medium is condensed by the condenser 11 and is reserved into a buffer tank 12. The vapor of the heat medium, which is not condensed, is passed through an adsorbing tower 13 to make it harmless. When the heat medium is to be discharged, pressure reducing valves 16, 17 are opened to pour the inert gas between the evacuating valve 16 and a valve 15, then, the pressure reducing valves 16, 17 are closed and, thereafter, the discharging valve 15 is opened and the evacuating valve 16 is opened in accordance with the discharging amount of the heat medium whereby the heat medium is discharged perfectly by the pressures of a pump 6 and the inert gas. According to this method, the heat medium may be discahrged perfectly and safely.