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ECONOMIZER: any mechanical device that adjusts to variable conditions to maximize energy efficiency; a control option in ventilation systems that makes optimum use of outside supply air, providing “free cooling”. During the economizer cycle, the system adjusts dampers according to the comparison between return air and outside air temperatures to meet the required air temperature.

ECZEMA: an acute or chronic non-contagious inflammatory condition of the skin that is characterized by redness, itching, and oozing vesicular lesions often caused by exposure to an irritant or chemical.

EDEMA: swelling

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.

EMISSION: the release of airborne contaminants from a source.

EMISSION RATE: a measure of the amount of a contaminant released from a source surface per unit time, expressed in units such as mg/m2-hr; or the concentration of a contaminant from a source that is present in the air space surrounding the source, expressed in units such as parts per million or m g/m3

EMISSION STANDARD: a voluntary guideline or government regulation that specifies the maximum rate at which a contaminant can be released from a source.

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EMPHYSEMA: A respiratory in human beings characterized by a loss of elasticity in the alveoli or lung sacs.

ENCAPSULATION: a mitigation technique that reduced or eliminates emissions from a source by sealing with an impenetrable barrier.

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 air stream 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.

ENVIRONMENTAL TOBACCO SMOKE (ETS): the combination of side-stream and mainstream smoke that is emitted from a burning cigarette; also called second hand smoke.

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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.

EQUILIBRIUM: the point at which the entry or creation rate of a contaminant equals the removal rate.

ERYTHEMA: an abnormal redness of the skin due to capillary congestion.

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.

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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.

EXHAUST: the indoor air that is removed from a building.

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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