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IAQ Glossary D


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DWV: Drainage, waste and vent.

DAMPER: A device used to control the volume of air passing through an air outlet, air inlet or duct.

DEATH: The absence of life. Apparent death is the end of life as indicated by the absence of heartbeat or breathing. Legal death is the total absence of activity of the brain, heart, and lungs, as observed and declared by a physician.

DECIBEL (db): A unit of measure of the intensity of sound. A decibel is one tenth of a bel; an increase of 1 bel is approximately double the loudness of a sound.

DECIPOL: a unit of perceived air quality. Air on mountains or the sea has a decipol = 0.01; city air with moderate air pollution has a decipol = 0.05- 0.03; acceptable indoor air quality has decipol = 1.4 (for 80% satisfaction)

DEGREE DAY: A unit, based upon temperature difference and time, used in estimating fuel consumption and specifying nominal heating load of a building in winter. For any one-day, when the mean temperature is less than 65oF, there exist as many degree-days as there are Fahrenheit degrees difference in temperature between the mean temperature for the day and 65oF.

DEHUMIDIFICATION: The condensation of water vapor from air by cooling below the dew point or removal of water vapor from air by chemical or physical methods.

DEHUMIDIFIER: (1) An Air cooler or washer used for lowering the moisture content of the air passing through it: (2) An absorption or adsorption device for removing moisture from air.

DEHYDRATION: (1) removal of water vapor from air by the use of absorbing or adsorbing materials; (2) removal of water from stored goods.

DEMAND CONTROL: A device that controls the kW demand level by shedding loads when the kW demand exceeds a predetermined set point.

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DEMAND CONTROLLED VENTILATION: a system having sensor-driven control units that turn on ventilation systems when gas concentrations (e.g., carbon dioxide) exceed a preset level.

DENSITY: The ratio of the mass of a specimen of a substance to the volume of the specimen.

DESICCANT: Any absorbent or adsorbent, liquid or solid, that will remove water or water vapor from a material. In a refrigeration circuit, the desiccant should be insoluble in the refrigerant.

DESORPTION: the phenomenon in which an adsorbed molecule leaves the adsorbent surface.

DEW POINT: The surface temperature at which moisture will condense out of the air onto a surface; varies with the relative humidity.

DEWPOINT, APPARATUS: That temperature which would result if the psychometric process occurring in a dehumidifier, humidifier or surface-cooler were carried to the saturation condition of the leaving air while maintaining the same ratio of sensible to total heat load in the process.

DEW POINT DEPRESSION: The difference between dry bulb and dew point temperatures (oF DB- oF DP).

DEW POINT TEMPERATURE: The temperature at which moist air becomes saturated (100% relative humidity) with water vapor when cooled at constant pressure.

DIFFERENTIAL: The difference between the points where a controller turns "on" and "off". If a thermostat turns a furnace on a 68o and the differential is 3o, the burner will be turned off at 71o.

DIFFERENTIAL PRESSURE: The difference in static pressure between two locations.

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DIFFUSER: A circular, square, or rectangular air distribution outlet, generally located in the ceiling and comprised of deflecting members discharging supply air in various directions and planes, and arranged to promote mixing of primary air with secondary room air.

DIFFUSION RATE: A measure of the tendency of one gas or vapor to disperse into or mix with another gas or vapor. This rate depends on the density of the vapor or gas as compared with that of air, which is given a value of 1.

DILUTION: a mitigation strategy that lowers the concentration of airborne contaminants by increasing the fraction of outdoor air in the supply air stream.

DIMORPHIC FUNGUS: A fungus with the ability to exhibit alternate growth forms, exhibiting yeast-like cells at 98.6oF (37oC), and exhibiting filamentous (mold) growth at room temperature.

DISINFECTANT: An agent that frees from infection by killing the vegetative cells of microorganisms.

DISPERSION: The general term describing systems consisting of particulate matter suspended in air or other fluid; also, the mixing and dilution of contaminant in the ambient environment.

DISPLACEMENT VENTILATION: a type of ventilation system that uses a plug flow of air to purge occupied spaces of contaminants. Typically such systems require large volumes of air moving at very low velocities. Because air moves directly through the space rather than mixing with the room air, supply air temperature at the air handler are closer to those of the desired conditioned temperature.

DOMESTIC HOT WATER: Potable hot water as distinguished from hot water used for house heating.

DOSIMETER (DOSE METER): An instrument used to determine the full-shift exposure a person has received to a physical hazard.

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DRAFT: A current of air, when referring to the pressure difference which causes a current of air or gases to flow through a flue, chimney, heater, or space; or to a localized effect caused by one or more factors of high air velocity, low ambient temperature, or direction of air flow, whereby more heat is withdrawn from a person's skin than is normally dissipated.

DROP: The vertical distance between the base of the outlet and the bottom of the air stream at the end of the horizontal throw.

DRY BULB, ROOM: The dry bulb (dew point, etc.) temperature of the conditioned room or space.

DRY BULB TEMPERATURE: The temperature registered by an ordinary thermometer. The dry bulb temperature represents the measure of sensible heat, or the intensity of heat.

DRY BULB TEMPERATURE, ADJUSTED: The average of the air temperature and the mean radiant temperature at a given location. The adjusted dry bulb temperature is approximately equivalent to operative temperature at air motionless than 80 fpm when the mean radiant temperature is less than 120oF.

DRY-SCRUBBING: the process of removing heavy concentrations of gaseous contaminants from an air stream using adsorbers of chemisorbers.

DUCT: A passageway made of sheet metal or other suitable material, not necessarily leak tight, used for conveying air or other gas at low pressures.

DUCT VELOCITY: Air velocity through the duct cross-section. When solid particulate material is present in the air stream, the duct velocity must exceed the minimum transport velocity.

DUST: An air suspension (aerosol) of particles of any solid material, usually with particle size less than 100 micrometers(um).

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DX COIL: A direct expansion coil. The refrigerant liquid turns to vapor in the coil, cooling the air (or water) flowing across the coil.

DYSPNEA: difficult or labored breathing.

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