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GLOSSARY ‘D’ to ‘E’
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. 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 dewpoint 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 which controls the kW demand level by shedding loads when the kW demand exceeds a predetermined set point. 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. 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 psychrometric 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. 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: The process of increasing the proportion of solvent or diluent (liquid) to solute or particulate matter (solid). 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. 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. DRAFT: A current of air, when referring to the pressure differencewhich 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 (dewpoint, 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. DUCT: A passageway made of sheet metal or other suitable material, not necessarily leaktight, 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). DX COIL: A direct expansion coil. The refrigerant liquid turns to vapor in the coil, cooling the air (or water) flowing across the coil. ECONOMIZER: A system that uses the maximum outside air for ventilation and free cooling, as long as dehumidification is not necessary. EFFECTIVE AREA: The calculated area of an outlet based on the averaged measured velocity between the fins. EFFECTIVE TEMPERATURE: The uniform temperature of a radiantly black enclosure at 50% relative humidity, in which an occupant would experience the same comfort, physiological strain and heat exchange as in the actual environment with the same air motion. ELECTRONIC PRECIPITATOR: Also called Electronic Air Cleaner (EAC); uses a high voltage between two conductors to remove particles (dust, etc.) from the air flowing through it. EMPHYSEMA: A respiratory in human beings characterized by a loss of elasticity in the alveoli or lung sacs. ENDOTOXINS: Harmful substances that are contained within the cells that produce them, or are integral constituents of cellular structure and are not released until the cell disintegrates. ENERGY: Expressed in kilowatt-hours (kWh) or watt-hours (Wh), and is equal to the product of power and time. energy = power X time kilowatt-hours = kilowatts X hours watt-hours = watts X hours ENTHALPY: The total quantity of heat energy contained in a substance, also called total heat; the thermodynamic property of a substance defined as the sum of its internal energy plus the quantity Pv/J, where P = pressure of the substance, v = its volume, and J = the mechanical equivalent of heat. ENTRAINMENT: The capture of part of the surrounding air by the airstream discharged from an outlet (sometimes called secondary air motion). ENTRAINMEMT VELOCITY: The gas flow velocity, which tends to keep particles suspended and cause deposited particles to become airborne. ENTROPHY: The ratio of the heat added to a substance to the absolute temperature at which it is added. EPIDEMIC: A sudden increase in frequency of a disease, above the normal expectancy, in a population of human beings. EPIDEMIOLOGY: The field of science that concerns itself with the determinants of disease and with the factors that influence its distribution. EPIDERMIS: The outer layer of human skin, composed of a thin layer of epithelial cells. EQUAL FRICTION METHOD: A method of duct sizing wherein the selected duct friction loss value is used constantly throughout the design of a low pressure duct system. ETIOLOGICAL: Pertaining to the cause of a disease or abnormal condition. EVAPORATION: Change of state from liquid to vapor. EVAPORATION RATE: The ratio of the time required to evaporate a measured volume of a liquid to the time required to evaporate the same volume of a reference liquid (ethyl ether) under ideal test conditions. The higher the ratio, the slower the evaporation rate. EVAPORATIVE COOLING: The adiabatic exchange of heat between air and a water spray or wetted surface. The water approaches the wet-bulb temperature of the air, which remains constant during its traverse of the exchanger. EVAPORATOR: The heat exchanger in which the medium being cooled, usually air or water, gives up heat to the refrigerant through the exchanger transfer surface. The liquid refrigerant boils into a gas in the process of the heat absorption. EXFILTRATION: The movement of air out of a building, through cracks and other openings, such as around windows and doors. EXOTHERMIC: A reaction in which heat is given off as in a fire, or in the combination of water and lithium bromide. EXOTOXIN: Harmful substance produced within cells, but excreted from intact cells into the surrounding environment. EXTRINSIC ALLERGIC ALVEOLITIS: A swelling from of pneumonia that is caused by an immune reaction in an allergic patient. The reaction may be brought about by a variety of inhaled organic dusts, often those containing fungal spores. A wide variety of symptoms may occur, including difficulty breathing, fever, chills, malaise, and muscle aches. The symptoms usually develop 4 to 6 hours after exposure. Kinds of extrinsic allergic alveolitis include bagassosis, farmer's lung, humidifier or air conditioner lung, mushroom worker's lung, suberosis. Also called hypersensitivity pneumonitis.
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