| 摘要 |
An apparatus for controlling passive (natural) ventilation of air through a ventilation duct (H, fig 3), the apparatus comprises a housing containing a plurality of interchangeable filters A, B, C and being a separate component to the duct and is mounted within the duct and controls noise transmission, heat loss, condensation and air filtration through the duct. The filters may be received in channels F. During installation of the apparatus into the duct, a flexible seal E may engage with the duct to prevent air travelling through the duct circumventing (passing around) the apparatus. An air buffer D between two of the filters may reduce heat loss and improve acoustic properties of the apparatus and contains air of an intermediate temperature and pressure between that found inside and outside of a building. The intermediate temperature of the air reduces condensation formation.
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