PURPOSE: To provide a ventilating air conditioning system for keeping a negative pressure in a house to be air-conditioned, which is designed to keep the flow rate of supplied air and the negative pressure in the house constant by controlling the inlet angle of air flow to suction vanes of the exhaust line on the basis of pressure difference at the outlet side of a fan and at the inlet side of an exhaust air filter.

CONSTITUTION: Open air is introduced into a house 15 via an intake air filter 12 by means of a fan 14, and air in the house 15 is discharged to the outside via an exhaust air filter 17 and an exhaust duct 20 by means of an exhaust fan 18. A differential-pressure transmitter 21 detects the pressure difference at the air intake line to the house 15 and at the air exhaust line from the exhaust air filter 17, and a differential-pressure controller 22 controls the inlet angle of air flow to suction vanes 19 on the basis of the output signal of the transmitter 21. With such an arrangement, when clogging of the air filter 12 is caused, pressure distribution is changed as shown by the dotted line 30B in the drawing. On the other hand, when clogging of air filter 17 is caused, the pressure distribution is changed as shown by the one-dot chain line 30C. Here, since the negative pressure in the house 15 is increased in both cases, the capacity of the fan 18 is controlled by changing the inlet angle of air flow to the suction vanes 19 to meet with the increased negative pressure in the house 15.