the existence of this narrow space the second embodiment is shown in fig2 and the locality which shall be controlled by the invention is defined by a ceiling walls and a floor not shown two walls are diagramatically shown in the form of two wall elements 101 and 102 and the wall element 101 can e g be a part of a wall facing to the north and the wall element 102 can be a part of a wall facing to the south the two walls thus consist of several wall elements which have parallel channels 103 placed horizontally the channels 103 can be connected in series or in parallel according to specific wishes but according to the shown embodiment the channels are in parallel from one end of the wall element to the other end and are connected in one end by a distributing main 104 in the wall element 101 and a distributing main 105 in the wall element 102 in the second end of the wall element there is a collecting main not shown by means of which the channels 103 open directly out to the ambient environment or can be connected to one more elements according to the size of the elements forming the wall of the building the wall elements 101 and 102 have a heat insulation.