Abstract: A ventilation plant for recovering heat from the outlet air and preheating the inlet air consists of a valve housing (10) including two fans (15, 16) for controlling the flow of air in two duct pipes (17, 18) connected to the surrounding atmosphere. An accumulator tube (17A, 18A), coupled into these two pipes, comprises a number of loosely inserted rolls (21) of pleated metal foil to achieve a great number of axial ducts communicating (24, 25) with one another at the roll ends. In one position the valve (26) leads the inlet air through one of the duct pipes and out through an outlet (13) in the valve housing at the same time as the outlet air is led into the other duct pipe and out to the surrounding atmosphere, or vice versa.

Abstract: A heat exchanger in combination with two duct system for bringing in relatively cold outside air into an enclosure while exhausting relatively warm room air from the enclosure. The heat exchanger is positioned so as to recover heat from the exhaust air into the incoming cold fresh air. A valving system switches the incoming cold air with the warm exhaust air in the flow paths of the heat exchanger. This solves the problem of moisture from the exhaust air condensing on the walls of the ducting system for the exhaust air.