Abstract: In a ventilation system for a building in which air is extracted by a fan arrangement, an inlet flap arrangement is provided for a ceiling opening which comprises a foamed material flap member mounted directly covering the ceiling opening. The flap member is controlled by a tension spring biasing it to a closed position so that its weight and air pressure act to open the flap. The angle of the spring relative to the position of the center of gravity of the flap member are controlled to provide the required opening characteristics. In one arrangement the flap member is shaped as a scoop so as to direct air along the ceiling when opened.

Abstract: An air to air heat exchanger particularly for contaminated air from an animal barn or the like includes a core formed by a plurality of thin-walled flexible plastics tubes supported at respective ends in tube sheets. The tubes are held under tension and arranged vertically in parallel rows and columns so that cold fresh air enters parallel to the rows horizontally beneath the upper tube sheet and then moved downwardly along the outside of the tubes to escape horizontally parallel to the rows above the lower tube sheet. The contaminated warm air passes from a plenum beneath the lower tube sheet upwardly along the inside of the tubes to an outlet at the top of the tubes. This direction of movement of the air causes a self-cleaning effect by condensate at the top of the tubes running down and cleaning the interior of the tubes of any collected contaminants. The design also enables the use of convenient inexpensive flexible tubes without allowing air movement to cause unacceptable flexing.