Damper: A device for controlling air flow, usually in a duct.

Dehumidify: To remove water vapor from an airstream in a duct.

Delta P: See pressure drop. Delta ( ) is the Grrek symmbol for change.

Denier: The weight in milligrams of 450 meters of fiber. Within fibres of the same specific gravity, denier can indicate fiber size. For example: a 12 denier round polyester fibre is 0,001328 in. (36 microns) in diameter.

Desorption: The opposite of adsorption. A phenomenon where an adsorbed molecule leaves the surface of the adsorbant.

Differential Pressure: See pressure drop.

Diffusers: Terminal devices that distribute conditioned air throughout a space. Diffusers can be aspirating (mix air from the space with the conditioned air) or non aspirating.

DIN: The German Institute for Standardization (Deutsches Institut fur Normung e.V.). This institute establishes standards for testing and classifying air filters.

DOP: Dioctlyphthalate (diethylhexylphosphate), an oily liquid used in aerosol form as a challange for efficiency and leak testing HEPA Filters.

Draft Gage: See Manometer.

Dry-Scrubbing: The process of removing heavy concentrations of gaseous contaminants from an airstream by the use of specially designed adsorbers or chemisorbers.

Draw-through: An HVAV system with the fan located downstream of coils, air washer and filters.

Duct: Round or rectangular conduit through which air is carried from a central air conditioning system to various spaces in the building.

Dust: An aerosol of particles of any solid material, usually with particulate size less than 100 microns.

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