A ceiling ventilation inlet includes a housing having an air inlet aperture, an air outlet aperture, and a baffle supported for linear movement adjacent the air outlet aperture. A spring is positioned such that the baffle moves dependant upon air pressure difference between the confinement space and...http://www.google.es/patents/US5924922?utm_source=gb-gplus-sharePatente US5924922 - Method and apparatus for ceiling ventilation
