PURPOSE: To improve the thermal efficiency and to obtain a small-size device by integrally incorporating cool water coils for recooling an exhaust air increased in temperature and a fan for sucking the exhaust air through the cool water coils to return it to a chamber.

CONSTITUTION: A suction duct 2 extending downward upto the center of a device is connected to a suction port of a centrifugal fan 1 disposed in the center of the device. Two cool water coils 3, 3 for recooling the exhaust air are provided at the starting end of the suction duct 2. Each of the cool water coils 3 is disposed so that a suction port is inclined downward to some extent in the direction of the side wall of the device. On the front face of the suction port, an air filter 4 for catching dusts in the exhaust air is mounted. In this manner, the exhaust air is circulated within the device without being discharged outside a chamber. Thus, the thermal efficiency is increased, the duct to be connected to the cool water coils 3 is shortened in peripheral length, and the thermall loss is reduced.