as shown in fig1 so as to keep the interior of the partition panel 10 clean or the filter 17 can also be mounted on the air outlet 12 as shown in fig1 when a detachable air outlet panel 12 a or air inlet panel 13 a is applied the filter 17 can be mounted on or near the panel 12 a or 13 a so that it can be easily replaced or cleaned after the panel is removed fig1 a and 13b illustrate another embodiment of the invention in which an outside air supplying duct 19 is incorporated with the partition panel 10 the room or building is equipped with an outside air import duct 50 and other required devices such as a blower 51 and an air filter 52 so as to provide fresh air to the room the fresh air is delivered through the outside air import duct 50 to the outside air supplying duct 19 then it passes through the heat exchanger 30 and is discharged into the room from the air outlet 12 the outside air supplying duct 19 is located at the bottom of the partition panel 10 the cross sectional dimension of the outside air supplying duct 19 is as large as possible.