Ventilation in existing buildings. Part Two: An approach to natural-like mechanical ventilation of existing buildings.

Describes a new ventilation strategy for retrofitted buildings. The system consists of two units including heat recovery, fan, filter, etc, which are installed in the window openings. They are operated in opposite directions which are periodically reversed. When desired, the unit is stopped and used as an airing panel. In laboratory tests the specified values were achieved. The heat recovery proved so efficient that no air heating was needed even at the lowest temperatures. Some noise and freezing problems were reported.