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531 Cards in this Set

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Absorption Coefficient
The percentage of incoming energy which is absorbed. In measur­ing radiant energy (light or heat) it is a unitless ratio which may vary depending on wavelength. In acoustics, it is called a sabin and may vary depending on frequency.
Absorption Refrigeration
A cooling process resulting from the absorption of vapor by a brine solution that is then heated to remove the mois­ture. The heat may be supplied by solar or other heating sources.
AC
The abbreviation for either air condition­ing or alternating current, depending on the context.
Acoustic Power Level
See Power Level.
Air Gap
An unobstructed vertical path, open to the atmosphere, separating the outlet of a faucet from the overflow rim of the fixture it serves. The purpose is to prevent a momentary vacuum in the supply pipe from siphoning water from the fixture back into the supply pipe.
Alternating Current
An electric current that reverses its direction at regular intervals, gener­ally 60 times per second in the United States. A plot of the voltage over time is a sine wave.
Ambient
Relating to a general or all surround­ing condition. In thermal processes, it refers to the air temperature, as distinct from that of surfaces or objects. In lighting, it refers to the background light level, and in acoustics, it refers to the background noise level.
ASHRAE
The abbreviation for the American Society of Heating, Refrigerating, and Air Conditioning Engineers, the source of most of the standardized information on the subject.
Aspect Ratio
The ratio of the longer to shorter dimension of an air conditioning duct, that affects duct friction, or of a room, that relates to light reflection.
Ball Drip
The automatic drain valve at the base of a dry standpipe.
Blow Down
The drain that removes dirt that builds up in the floor pool of an evaporative cooling tower.
BTU
The abbreviation for British Thermal Unit, a unit of heat energy, which is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
BTUH
The abbreviation for Btu's per hour, an energy flow rate.
Building Automation
The control by auto­matic equipment of many functions in a large building, usually including the HVAC system, the fire detection and alarm system, and building security.
CFM
The abbreviation for cubic feet per minute, which is the flow rate of air in a mechan­ical system or duct.
Chiller
A piece of equipment which cools water for use in an air conditioning system.
Chill Factor
A fictitious temperature assigned to a combination of actual temperature and wind velocity that has the same physiolog­ical effect as still air at the chill factor temperature.
Chlorination
The addition of small amounts of chlorine to a water source to kill bacteria.
Circuit Vent
In sanitary drainage, any vent that serves two or more traps.
Clerestory
A window above eye level that admits daylight, such as the high windows in a cathedral.
Code
An organized body of rules and regula­tions adopted and enforced by a governmental unit, such as a building code.
Coefficient of Performance
The ratio of the amount of heat energy delivered by a heat pump to the amount of energy supplied, or the ratio of the amount of heat energy removed by a refrigeration machine to the amount of energy expended in its removal. It is similar to effi­ciency, but often exceeds 100 percent, and is therefore expressed as a number, i.e., 2.7, which is typical for a heat pump.
Coefficient of Utilization
The ratio of useful light arriving at the work plane to the amount of light emitted by the source. The CU depends on the reflectivity of different surfaces and the aspect ratios of the ceiling, wall, and floor cavities.
Comfort Zone
The combination of thermal and environmental conditions within which a human is comfortable, often shown on a psy-chrometric chart.
Conductance (C)
The rate at which a specific thickness of a given material conducts heat.
Convection
The heat transfer process that occurs when a warm fluid rises, displacing cold fluid which then falls.
Cycle
One complete set of repeating events, typically used with alternating current or sound.
Cycles per Second (CPS)
A measure of frequency in electric current or acoustics, i.e., the number of cycles per second of a wave or oscillation. In acoustics, the term has been largely replaced by Hertz, where 1 cps = 1 Hz.
Daylighting
The use of natural light from out­side to replace or augment electrical light out­doors, which produces energy savings.
dBA
A decibel measured in the A scale, that is weighted to account for the special sensitivi­ties of the human ear.
Decibel (dB)
A logarithmic measure of sound intensity level.
Degree Day (DD)
The amount by which the average outdoor temperature at a particular loca­tion is below 65°F for one day. Degree days may also be summed and stated for a month or a year.
Delta Connection
A method of connecting windings on a three phase transformer, end to end, that results in a triangular shape.
Dew Point Temperature
The temperature of air at that the water contained in the air begins to condense and form dew. The dew point for a given air sample is always lower than or equal to its current temperature.
Diffuser
A device through which the air from a duct enters a room, or a device through which the light from a fixture enters a room.
Dry Bulb (DB)
The temperature of air as read on an ordinary glass thermometer.
Dry Pipe Sprinkler
A sprinkler system whose pipes are normally pressurized with only air, thus being invulnerable to freezing temper­atures. Upon actuation, the air is vented and supply pressure forces water through the sys­tem.
Economizer Cycle
An energy-saving strat­egy in which a part of the HVAC system is shut off while the rest is used, such as shutting off the refrigeration when the outside air tempera­ture is low, while the fan continues to operate.
Effective Temperature
A fictitious tempera­ture having the same physiological effect as air of a standardized temperature, humidity, and velocity.
Efficacy
The ratio of the lumens emitted by a lamp to the electrical power consumed by the lamp.
Emissivity
A factor that represents the rate at which a given surface material gives off or emits radiant energy. The emissivity varies from 0 to 1.0, where 1.0 is the theoretical emissivity of a perfect black box at the same temperature.
Enthalpy
The total of sensible plus latent heat stored in the air. It is also known as Total Heat.
Exit
A continuous and unobstructed means of egress to a public way. Its minimum width is generally 44 inches.
Fire Assembly
A complete fire-resistive assembly consisting of a fire door, fire damper, or fire window and its mounting frame and hard­ware. The entire assembly, not just its compo­nents, must be approved and labeled by a testing agency that inspects the materials and workman­ship during fabrication at the factory. Available ratings are 3/4, 1, 1-1/2 and 3 hours.
Fixture Unit
A unit of liquid flow used in sizing both supply and drainage pipes.
Flame Spread Rating
A numerical classifi­cation indicating the rate at which flame will spread in or on a given material, in which higher numbers flame up more rapidly.
Flushometer Valve
A valve that releases a definite amount of water into a plumbing fixture each time it is actuated.
Footcandle
The basic unit of illumination arriving at a work plane. One footcandle is equal to one lumen per square foot.
Forced Air System
A heating or cooling sys­tem that uses a fan to circulate heated or cooled air through ducts to the occupied spaces.
Forced Convection
The movement of a fluid by a fan or a pump, in order to force heat exchange.
Four Pipe System
A hot and chilled water system having separate return lines for each sup­ply line, and with no mixing of the two streams.
Frequency
The number of cycles that occur per second, either in alternating current or acoustics. In acoustics, the frequency deter­mines the pitch.
Frost Line
In a given location, the maximum depth in soil that is expected to freeze in cold weather. Water piping must ordinarily be buried below the frost line to protect against freezing.
Fusible Link
A piece of wax or paraffin that melts at a predetermined temperature, setting off a sprinkler head, an alarm system, or otherwise actuating a fire protection device.
Globe Thermometer
A thermometer that measures Mean Radiant Temperature (MRT).
Ground
An electrical conductor connected to the earth or to a pipe extending into the ground, used to dissipate hazardous currents into the earth.
Halon
A gaseous fire extinguishing medium that smothers fires, often used in automatic sys­tems in computer rooms.
Heat Pump
A refrigeration loop used to bring heat into a space instead of removing heat from it. The term is also used for an entire system of such units attached to a recirculating heat sink.
HEPA Filter
A high efficiency particulate air filter, which removes dust and other tiny parti­cles from a moving air stream.
Hertz (HZ)
The frequency of a sound, or of an alternating current, equal to the number of cycles per second.
High Intensity Discharge (HID)
A family of lamps consisting of a quartz envelope inside a glass envelope. The inner quartz tube can stand higher temperatures, and allows for the current to arc between the two electrodes exciting a plasma of mercury, metal halide, or high pres­sure sodium.
HP or BHP
Horsepower or brake horse­power, a unit of power, equal to roughly 746 watts.
Illumination
The intensity of light falling on a surface, usually expressed in footcandles.
Impact Isolation Class (IIC)
A rating of the degree of isolation of a floor against the trans­mission of impact noises.
Infiltration
The leakage of air through cracks around windows and other building elements.
Intensity Level
The intensity of sound at a given location, measured in watts per square meter, or more commonly in dB where the ref­erence level is 10~12 watts/meter2 or 10~16 watts/cm2.
Inverse Square Law
A physical principle that states that the intensity of a phenomenon is inversely proportional to the square of the dis­tance from the source to the measuring device. It holds true for point sources of light, and for sound in an open field.
Invert
The lowest point of the inside of a drain, pipe, channel, or other liquid-carrying conduit.
Ion Exchange
A process of water softening in which calcium and magnesium ions are replaced by sodium ions. This process is also known as the zeolite process.
lonization Detector
A fire detector which detects the products of combustion (POC) even before they are visible to the naked eye.
K Factor
The thermal conductivity of one square foot of a material per inch of thickness, with a surface temperature difference of one degree F.
Kilowatt (KW)
A unit of electric power, equal to 1,000 watts.
KVA
A rating for transformers equal to the product of volts and amperes divided by 1,000. The product of the KVA and the power factor gives the power in kilowatts.
Latent Heat
The heat added to or removed from a substance when it changes its state. See Sensible Heat.
Light Shelf
An overhang, either outside or inside or both, that is used with a clerestory to reflect light up onto the ceiling, and reduce direct light adjacent to the window below.
Lumen
A unit of light, defined as the amount of light passing through one square foot at a distance of one foot from a one candlepower source.
Luminaire
A complete light fixture, includ­ing lamps.
Mass Law
The theoretical law that states that for each doubling of mass in a wall, there is a 6 dB drop in the amount of sound transmitted.In actual practice, it is usually closer to 5 dB.
Mean Radiant Temperature (MRT)
The weighted average of all of the temperatures of all of the surfaces visible from a given position.
NC Curves
A single-number system for spec­ifying a maximum SPL level in a given location, using standardized reference contours. The curves weight the frequencies to which the human ear is sensitive.
NEC
The abbreviation for National Electrical Code.
Neutral
The wire or conductor in an electrical system that is equidistant in voltage from the phase conductors of the system. It is not the same as ground.
Noise Reduction Coefficient (NRC)
A one-number rating system giving the average sound absorption coefficient of a material at frequen­cies of 250, 500, 1,000 and 2,000 Hz.
Occupancy
The purpose for which a building is intended to be used.
Occupancy Group
A designation for a group of several occupancies that have comparable fire safety considerations, and which are therefore grouped together by the code.
OSHA
The abbreviation for the Occupational Safety and Health Act, which regulates working conditions.
Passive Solar Design
The practice of orient­ing and sizing a building, its windows, and its internal masses in such a way that it responds to the sun and to the climate, without the use of mechanical equipment.
Perm
The unit of permeability for a given material, expressing the resistance of the mate­rial to the penetration of water or water vapor through it. One perm is equal to the flow of one grain of water vapor through one square foot of surface area per hour with a pressure difference of one inch of mercury.
Permeability
The property of permitting pas­sage of water or water vapor through a material without causing rupture or displacement.
Potable Water
Water that is suitable for drinking.
Power Factor (PF)
In an electrical circuit, the ratio of real power in watts to the product of voltage and current.
Power Level (PWL)
The logarithmic expression for the acoustical power at the source of a sound. It is also known as Acoustic Power Level.
PPM
The abbreviation for parts per million.
Psychrometric Chart
A graph showing the relationships between temperature, humidity, relative humidity, and enthalpy.
Reheat
The adding of sensible heat to a sup­ply air stream which has been previously cooled.
Relative Humidity (RH)
The ratio of the moisture content of the air to the maximum pos­sible content at the same temperature.
Reverberation
The persistence of sound in an enclosed space after the source has stopped.
Reverberation Time
The time it takes a 60 dB sound to completely die away in a closed room after the source has stopped.
Sabin
The unit of sound absorption equivalent to the absorption of one square foot of open window.
Sensible Heat
Heat that changes the temper­ature of a substance, and does not represent the addition of any moisture to the substance
Shading Coefficient (SC)
The ratio of the solar heat gained through a window with adding devices to the solar heat gained by a single pane double strength clear glass window. Shading devices, such as Venetian blinds, lower the SC.
Siamese Fitting
A Y-shaped hose attachment at the base of a building, which allows the fire department to connect a fire hydrant through a pumper truck to provide or augment water flow to a standpipe.
Smoke Developed Rating
A numerical rat­ing derived from a standardized fire test proce­dure. Larger numbers indicate a greater density of smoke.
Smokeproof Enclosure
A continuous enclosed stairway separated from the building at each floor by an open vestibule that allows smoke to vent away without entering the stair.
Soil
A sanitary drainage term referring to the waste from urinals, water closets, and fixtures of similar function.
Sone
A subjective system of measuring loud-ness, based on the reference point of one sone equal to a sound pressure level of 40 dB.
Sound Level Meter
A meter that measures the sound pressure level and gives a reading in dB.
Sound Pressure Level (SPL)
The logarith­mic expression of the pressure exerted by sound waves on the receiver. The reference pressure is 2 x 1O~5 newtons per square meter.
Sound Transmission Class (STC)
A single-number rating for the evaluation of a particular construction cross-section in terms of its transmission of airborne sound. The higher the STC rating, the more effective the construction is at stopping airborne sound.
Sprinkler System
A system used to extin­guish fires automatically by releasing water or other substances. See Dry Pipe Sprinkler and Wet Pipe Sprinkler.
Stack Vent
The portion of a soil or waste stack that is above the highest branch drain con­nected to the stack. Its sole function is to vent to the outside air.
Standpipe
A vertical supply pipe for firefight-ing. Dry standpipes are empty, and must be con­nected to a fire hydrant via a Siamese connection and a pumper truck. Wet standpipes are pressur­ized and filled with water, to serve attached hoses within the building, on each floor. Wet standpipes also have Siamese connections to allow the water flow to be augmented from fire hydrants.
Star Connection
A method of connecting the windings on a three-phase transformer in which one end of all three windings is connected to a common neutral center point, forming a Y shape. Same as Wye Connection.
Starter
A device that starts the arc in a neon or fluorescent lamp, or a contactor and overload relay used in starting some electric motors.
Steam Trap
A valve that permits passage of air or water, but not steam, often used with steam radiators.
Sweating
The method of soldering copper plumbing, or the condensation of water on cold pipes or building materials.
Thermosiphon
The method of using a heated surface and the resulting convection to move a fluid out of a space. In solar hot water heaters, the collector is below the storage tank, and the water is circulated automatically by convection when it is heated. Thermosiphoning may also be used to ventilate a building by sending the warmed air out the top, and siphoning in cooler air at the bottom.
Three Pipe System
A hot and chilled water system having a common return pipe for both supply lines. Ton The amount of cooling required to create a ton of ice in a 24 hour period, equal to a steady rate of 12,000 Btuh.
Transmission Loss (TL)
The reduction of sound that occurs when a given wall transmits sound from one room to an adjacent room, expressed in decibels.
Trombe Wall
A form of mass wall that trans­fers heat by causing convection into the room behind it, as well as conduction.
Two Pipe System
A hot or chilled water sys­tem having only a supply and return line. It can supply only heated or chilled water to a zone, but not both simultaneously.
U Factor or U Value
The thermal conductiv­ity of a particular wall section, expressed in Btu's per hour per degree Fahrenheit per square foot.
Vent Stack
A vertical pipe that vents several sanitary drainage lines, in order to break the siphoning suction which would occur when water drops through the system.
Watt
The basic unit of electrical power, equal to the product of volts and amperes in direct current systems, equal to 3.41 Btuh.
Wavelength
The length of one complete cycle or waveform, for light or sound waves. In light, the dominant wavelength determines the per­ceived color.
Wet Bulb Temperature (WB)
The tempera­ture attained by a glass thermometer whose bulb is covered with a wet sock and placed in an air stream moving at 1,000 feet per minute.
Wet Pipe Sprinkler
A sprinkler system that is continually pressurized with water. If a fusible sprinkler opens, water is immediately forced through the sprinkler head.
Vacuum Breaker
An automatic valve that admits air into a supply pipe rather than allow­ing the pipe to suction or siphon polluted water back into the supply.
Variable Air Volume (VAV)
An air condi­tioning system that accommodates thermal load changes by varying the flow of supply air into
Zeolite
A substance used in water softening, in which a filtering tank is recharged by passing a salt solution through it. The tank may then be used as a filter for the free ions associated with hard water.
Zone
A portion of a building controlled by a single thermostat, because its spaces have sim­ilar heating or cooling needs.
Absolute filter (H)
A high-efficiency mechanical filter built originally for removing radioactive particles and having an efficiency of 99.9% or higher.
Absolute humidity (H)
Weight of water vapor per unit vol­ume of air-steam mixture. Usually expressed in grains per cubic foot.
Absolute pressure (G, H)
The pressure above an absolute vacuum; the sum of the pressure shown by a gage {ox gauge) and that indicated by a barometer.
Absolute temperature (H)
Temperature measured from absolute zero; on the Fahrenheit scale, the absolute tem­perature is approximately °F + 459.6° and on the Celsius scale °C + 273°.
Absorption (AS)
The ability of a material to absorb acoustical energy. Measured in sabins.
Absorption (H)
An assimilation during which the absorbent undergoes a physical or chemical change ior both:. Absorbers such as lithium chloride and calcium chloride are used in dehumidifying. The process is also used in absorption refrigeration.
Absorption coefficient (AS)
The fraction of sound energy impinging on a surface that is absorbed by that surface, usually denoted by a. Frequency sensitive.
Absorption refrigeration (H)
A process whereby a secondary fluid absorbs the refrigerant and, in doing so, gives up heat. Afterward, it releases the refrigerant, during which time it absorbs heat.
Acoustics (AS)
The science of sound, including its generation, transmission, and effects.
Acrylonitn'le-butadiene-styrene, ABS (PS)
A thermoplastic compound from which fittings, pipe, and tubing are made.
Active sludge (PS)
Sewage sediment, rich in destructive bacteria, that can be used to break down fresh sewage more quickly.
Adaptive reuse (G)
Converting existing buildings to new functions to avoid demolishing them; generally considered a sustainable design by avoiding the need to dispose of existing building materials and conserving the use of new materials along with the resources needed to produce and erect them.
Adiabatic (H)
A change at constant total heat; an action or process during which no heat is added or subtracted.
Aeration (PS)
An artificial method in which water and air are brought into direct contact with each other to furnish oxygen to the water and to reduce obnoxious odors.
Aerobic (PS)
Living or active only in the presence of free oxygen (said of certain bacteria).
Airborne sound (AS)
Sound that is transmitted through air by a series of oscillating pressure fluctuations.
Air change (H)
The quantity of infiltration or ventilation air, in cubic feet per hour or minute, divided by the volume of the room.
Airfoil fan (AS, H)
A fan with an airfoil-shaped blade that moves the air in the general direction of the axis about which it rotates.
Air gap (PS)
The unobstructed vertical separation between the lowest opening from a pipe or faucet conveying water or waste to a plumbing fixture receptor.
Alternating current, AC (E)
Flow of electricity that cycles or alternates direction. The number of cycles per second is referred to as the frequency.
Ambient (AS, H, I)
Encompassing on all sides. Thus ambient air is the surrounding air; ambient light is the lighting envi­ronment of a space; ambient noise is the surrounding sound in a space.
Ambient lighting (I)
Lighting throughout an area that pro­duces general illumination.
Ambient noise (AS)
The sound associated with a given envi­ronment, usually a composite of many sources.
American Standard Code for Information Interchange, ASCil (DP)
A system for referring to letters, numbers, and com­mon symbols by code numbers. The numerical value assigned for each binary digit of an eight-digit byte is, from left to right, 128, 64, 32, 16, 8, 4, 2, and 1.
American Wire Gauge, AWG (E)
The standard system for measuring the size of wires in the United States.
Ampacity (E)
The current, in amperes, that a conductor can carry continuously under conditions of use without exceed­ing its temperature rating.
Analog (DP, TC)
Varying continuously (e.g., sound waves). Analog signals have their frequency and bandwidth meas­ured in hertz. See Digital.
Anechoic (AS)
An acoustical environment free of any reflected sound; a free field.
Angstrom (I, TC)
A unit of length, 0.1 nm or 1CT10 m, often used to measure wavelength, but not part of the SI system of units. See Nanometer.
Apparatus dew point (H)
Dew point temperature of the air leaving the conditioning apparatus.
Aspect ratio (H)
In a duct, the depth of elbow along (paral­lel to) the axis of bend divided by the width in the plane of the bend.
Atmospheric pressure (G, H)
Pressure indicated by a barom­eter. The standard atmospheric pressure is 760 mm of mer­cury (29.921 in. of mercury) or 14.7 lb per square inch (in.2) at sea level.
Attenuation (AS)
Lessening or reduction, e.g., from 80 dB to 70 dB.
Aural (AS)
Pertaining to the ear or to the sense of hearing. A-weighting (AS) Prescribed frequency response defined by ANSI Standard SI.4-1971. Used to obtain a single number representing the sound pressure level of a noise in a manner approximating the response of the ear, by deemphasizing the effects of the low and high frequen­cies. See dBA.
Axial flow fan (H)
A fan with a disk- or airfoil-shaped blade that is mounted on a shaft and that moves the air in the general direction of the shaft axis.
Backflow (H, PS)
In plumbing or HVAC systems, water flow into water-distributing pipes from any source other than that for which the system is designed.
Backflow connection (PS)
In plumbing, any connection or arrangement which permits backflow.
Backflow preventer (PS)
A device to prevent backflow into a water supply line from the connection at its outlet.
Background sound (AS)
Noise from all sources in an envi­ronment, exclusive of a specific sound of interest.
Backup (DP)
A copy of a program or document that can be used if the original is destroyed.
Ballast
A device used with fluorescent and HID lamps to provide the necessary starting voltage and to limit the cur­rent during operation of the lamp.
Bandwidth (DP, TC)
The highest frequency that can be trans­mitted in an analog operation. Also (especially for digital systems), the information-carrying capacity of a system.
Baud (DP, TC)
Strictly speaking, the number of signal-level transitions per second in digital data. For some common coding schemes, baud equals the number of bits per second, but this is not true for more complex coding, where the term is often misused. Telecommunication specialists prefer bits per second, which is less ambiguous.
Baud rate (DP)
The number of bits per second. Baud rates are most commonly used as a measure of how fast data are transmitted by a modem.
Beam angle (I)
The angle between the two directions for which the intensity is 50 percent of the maximum inten­sity, as measured in a plane through the nominal beam centerline.
Bell-and-spigot joint (PF)
The joint commonly used in cast-iron pipe. Each piece is made with an enlarged diameter or bell at one end into which the plain or spigot end of another piece is inserted when the pipe is being laid. The joint is then made tight with cement, oakum, lead, or rubber caulked into the bell around the spigot.
Bellows (H, PS)
An expansible metal device containing a fluid that will volatilize at some desired temperature, expand the device, and open or close an opening or a switch, as in controls and steam traps.
Bimetal (H)
Two metals of different coefficients of expan­sion welded together so that the piece will bend in one direction when heated and in the other when cooled. Thus it can be used in opening and closing electrical circuits, as in thermostats.
Binary numbers (DP)
The base-2 numbering system of almost all computers, as opposed to the base-10 (decimal) numbers in common use.
Binary system (DP)
A numbering system using 2 as base, as opposed to 10 as base in the decimal system. For example, 1 in binary system is 1; 10 is 2; 11 is 3; 100 is 4; 101 is 5; 110 is 6; 111 is 7; 1000 is 8; 1001 is 9; and 1110 is 10. The binary system is used in almost all computers.
Bit (DP)
Abbreviated from "binary digit," the smallest possi­ble unit of information. A bit represents one of two things: yes or no, on or off, or, as expressed in the binary numbers used in computers, 0 or 1.
Blackbody (H, I)
A body that absorbs all the radiant energy falling upon it.
Boiler (H)
A closed vessel in which fuel is burned to generate steam. (A vessel that produces hot water should be called a hot-water heater^)
Boiler horsepower (H)
The power required to evaporate 34.5 lb of water at 212°F per hour, or the equivalent of 33,475 Btu per hour (Btuh).
Booting (DP)
The starting up of a computer by loading an operating system into it. (The name boot comes from the idea that the operating system pulls itself up by its own bootstraps.)
Branch circuit (E)
The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
Branch interval (PS)
In plumbing, a vertical length of waste pipe, usually one story high, to which the horizontal branches from that floor are connected.
Branch vent (PS)
A vent connecting one or more individual vents with a vent stack.
British thermal unit, Btu (G, H)
The amount of heat required to raise the temperature of 1 lb (0.45 kg) of water 1 degree Fahrenheit (0.565°C).
Broadband (TC)
In general, covering a wide range of fre­quencies. The broadband label is sometimes used for a network that carries many different services or for video transmission.
Buffer (DP)
An area of memory or a separate memory cache that holds information until it is needed. Buffers are used to speed up printing, redraw the screen, etc.
Bug (DP)
A mistake or unexpected occurrence in a piece of software (or, less commonly, in a piece of hardware).
Building drain (PS)
The section of the horizontal drainpipe connecting the drainage pipes inside the building with the building sewer outside the inner face of the building wall.
Building sewer (PS)
The pipe extending from the outer end of the building drain to the public sewer.
Building trap (PS)
A trap in the building drain to prevent air circulation between the building drainage system and the building sewer.
Bulletin board (bulletin board system), BBS (DP)
A com­puter dedicated to maintaining messages and software and making them available over phone lines at no charge. People upload (contribute) and download (gather) messages by calling the bulletin board from their own computers. BX (E) An electrical cable consisting of a flexible metallic cov­ering inside of which are two or more insulated wires for carrying electricity.
Byte (DP)
A group of eight bits that the computer reads as a single letter, number, or symbol. For example, 01000101 is a typical byte of the binary system.
Calorie (H)
In engineering, the large calorie is usually used; it is defined as one one-hundredth of the energy or heat required to raise the temperature of 1 kg of water from 0°C to 100°C. The small calorie is the heat required to raise the temperature of 1 g of water.
Candela, cd (I)
The unit of measurement of luminous inten­sity of a light source in a given direction.
Candlepower, Cp (I)
Luminous intensity of a light source in a specific direction.
Candlepower distribution curve (I)
A curve, generally polar, representing the variation in luminous intensity of a lamp or luminaire in a plane through the light center.
Cathode ray tube, CRT (DP, TC)
The display technology used on virtually all computer monitors and television sets.
Cathodic protection (PS)
The control of the electrolytic cor­rosion of an underground or underwater metallic structure by the application of an electric current.
Central processing unit, CPU (DP)
The central part of a computer. The CPU includes the circuitry built around the CPU chip and mounted on the motherboard that actually performs the computer's calculations.
Check valve (FP, H, PS)
A valve designed to allow a fluid to pass through in one direction only. A common type has a plate suspended so that the reverse flow aids gravity in forc­ing the plate against a seat, shutting off reverse flow.
Circuit breaker (E)
A device designed to open and close a circuit manually or automatically on a predetermined overcurrent.
Circuit vent (PS)
A branch vent from two or more traps extending from in front of the last fixture connection of a horizontal branch to the plumbing vent stack.
Clean room (H)
A room in which the air is highly purified, particularly with regard to dust and other particulate mat­ter. Clean-room techniques are used in the processing of delicate materials and products.
Clock rate (or clock speed) (DP)
The operations of a com­puter are synchronized with a quartz crystal that pulses millions of times each second. These pulses determine, for example, how often the screen redraws an image and how often the CPU accesses RAM or a hard disk. The frequency of the pulses—how often they occur—is measured in megahertz (millions of cycles per second) and is called the clock rate or clock speed.
Close nipple (H, FP, PS)
A nipple with twice the length of a standard pipe thread.
Closed cycle (H)
A system in which the fluid is used over and over without introduction of new fluid, as in a hot-water heating or mechanical refrigeration system.
Coefficient of performance, COP (H)
In a heat pump, the ratio of the effect produced to the electrical input in consis­tent units.
Coefficient of utilization, CU (I)
The ratio of the luminous flux (lumens) from a luminaire, calculated as received on the work plane, to the luminous flux emitted by the luminaire's lamps alone.
Color-rendering index, CRI (I)
Measure of the degree of color shift objects undergo when illuminated by a light source, as compared with a reference source, normally incandescent.
Color temperature (I)
The absolute temperature of a black-body radiator having a chromaticity equal to that of the light source.
Community antenna television, CATV (TC)
Cable television, a broadband transmission system generally using 75-ohm coaxial cable that simultaneously carries many frequency-divided TV channels.
Compiler (DP)
Software that implements a program by trans­lating it all at once.
Condensate (G)
Water that has liquefied from steam or pre­cipitated out from air.
Condensate (H, PS)
Liquid formed by condensation.
Condenser (H)
Apparatus used to liquefy a gas.
Condensing unit (H)
An assembly attached to one base and including a refrigerating compressor, motor, condenser, and receiver, and the necessary accessories.
Conductance (H)
The quantity of heat (usually BTU) transmitted per unit of time (usually 1 hour) from a unit surface of material under a unit temperature (usually 1°F) differential between the surfaces. Unit abbreviation is Btu/hr-ft2oE
Conduction (H)
The transmission of heat from one part of a body to another part of the same body, or from one body to another in contact with it, without appreciable displace­ment of the particles of the body.
Conductivity (H)
The quantity of heat (usually Btu) trans­mitted per unit of time (usually 1 hour) from a unit surface (usually 1 sq ft) to an opposite unit of surface of one mate­rial per unit of thickness (usually 1 in., but occasionally 1 ft) under a unit temperature differential (usually 1°F) between the surfaces.
Continuous load (E)
A load such that the maximum current is expected to continue for 3 hours or more.
Contrast (I)
Difference in brightness between an object and its background.
Convection (H)
The transfer of heat from one point to another within a fluid (such as air or water) by the mixing of one portion of the fluid with another. If the motion is due to differences in density, from temperature differences, the convection is natural; if the motion is imparted mechan­ically, it is forced convection.
Convector (H)
A unit containing heating elements that allow air to be heated through natural convection without using external power.
Cooling tower (H)
A device for cooling water by evaporation in the outside air. A natural-draft cooling tower is a cooling tower in which the airflow through it is due to the natural chimney effect; a mechanical-draft tower uses fans.
Coprocessor (DP)
A chip that specializes in mathematics, graphics, or some other specific kind of computation. When the CPU is handed the kind of job the coprocessor special­izes in, it hands the job off to the coprocessor.
Counterflow (H)
In a heat exchanger, a situation in which the fluid absorbing heat and the fluid losing heat are directed so that the lower and higher temperature of the one are adja­cent to the lower and higher temperature of the other, respectively. Ordinarily, one fluid is flowing in the opposite direction from the other, hence the term.
Critical angle (I, TC)
The angle at which light undergoes total internal reflection.
Critical velocity (H)
The point above which streamline flow becomes turbulent.
dBA (AS) (TC)
Overall A-weighted sound pressure level expressed in decibels referenced to 20 micropascals. An A-weighting is a single number approximating the response of human hearing.
Dead room (AS)
A room whose boundaries and furnishings absorb a great amount of sound.
Debug (DP)
To search out bugs or defects in a piece of soft­ware and eliminate them.
Decay rate (AS)
The rate at which the sound pressure level (in dB) decreases when the source of the sound is eliminated.
Decibel, dB (AS, TC)
Ten times the logarithm to the base 10 of a quantity divided by a reference quantity; dB = 10 X logl0(X/Xref).
Degree day, DD (H)
The number of Fahrenheit degrees that the average outdoor temperature over a 24-hour period is less than 65°F.
Demand charge (E)
That part of a utility service charged for on the basis of the possible demand as distinguished from the energy actually consumed.
Demand factor, DF (E)
The ratio of the maximum demand to the total connected load of a system.
Demand load, DL (E, H, PF)
The load, in appropriate units, such as kW, Btuh, or gpm, that an electrical or mechanical system encounters.
Density (G)
The weight of a unit of volume—usually, pounds per cubic foot.
Developed length (H, PF)
The length along the centerline of a pipe and its fittings.
Dew point, DP (G, H)
The temperature of a gas or liquid at which condensation or evaporation occurs.
Dielectric fitting (H, PS)
A fitting having insulating parts or material that prohibits the flow of electric current.
Diffraction (AS)
Alteration of the direction of propagation of a sound wave in the vicinity of a boundary discontinuity on the edge of a reflecting or absorbing surface. Frequency sensitive.
Diffuse sound field (AS)
A sound field in which the intensity of the sound is independent of its direction; an area over which the average rate of sound energy flow is equal in all directions.
Diffusion (H)
The movement of individual molecules through narrow spaces by the molecular velocity and bouncing asso­ciated with individual gaseous or liquid molecules.
Digital (DP, TC)
Expressed in binary code to represent infor­mation. See Analog.
Diode (DP, TC)
An electronic device that lets current flow in one direction. Semiconductor diodes used in fiber optics contain a junction between regions of different doping. (Doping means adding impurity elements to pure semiconductors to improve their conductivity.) Diodes include light emitters (LEDs and laser diodes) and detec­tors (photodiodes).
Direct current, DC (E)
Flow of electricity continuously in one direction from positive to negative.
Direct expansion (H)
An arrangement wherein a refrigerant expands in an evaporator in the airstream as intended.
Direct-fired heater (H)
A fuel-burning device in which the heat from the fuel is transferred through metal to air, which is then introduced to the space to be heated.
Direct glare (I)
Glare resulting from high luminances or insufficiently shielded light sources in the field of view.
Direct sound field (AS)
A sound field in which the energy arrives at the receiver in a direct path from the source, with­out any contribution from reflections. See Reverberant sound field.
Directivity index, Dl (AS)
A measure of the directionality of sound from a specific source, in decibels. The difference between the actual sound pressure level of the source and the sound pressure that would exist if the same source were a point source radiating spherically. The directivity index is sensitive to frequency.
Discomfort glare (I)
Glare producing discomfort. This type of glare docs not necessarily interfere with visual performance or visibility.
Discomfort index (H)
Original name of temperature-humidity index (THI).
Disconnecting means (E)
A device by which the conductors of a circuit can be disconnected from their source of supply.
Diversity factor (E, H, PS)
The ratio of the sum of the indi­vidual maximum loads during a period to the simultaneous maximum loads of all the same units during the same period. Always unity or more.
Downspout (PS)
The rain leader (pipe) from the roof to the means of disposal.
Drainage fixture unit, DFU (PS)
A measure of probable dis­charge into the drainage system by various types of plumbing fixtures. By convention, 1 DFU is equivalent to 1 CFM.
Dry-bulb temperature, DB (H)
The temperature of air as measured by a thermometer.
Dynamic head (H)
The pressure equivalent of the velocity of a fluid. Customary units of head are usually feet or inches ofH2O.
Dynamic random access memory, DRAM (DP)
A memory chip that loses its memory when the computer is shut off.
Effluent (PS)
Treated or partially treated sewage flowing out of sewage treatment equipment.
Electronic cleaner (H)
An air cleaner in which matter in the airstream is electrically charged, then attracted to surfaces oppositely charged.
Electronic data interchange, EDI (TC)
A series of standards that provide for the exchange of data between computers over phone lines.
Emissivity (H, I)
The ratio of radiant energy emitted by a body to that emitted by a perfect blackbody. A perfect blackbody has an emissivity of 1, a perfect reflector an emis­sivity of 0.
Energy management system, EMS (H, E)
An automated control system designed to achieve higher energy efficiency or lower energy consumption in a building. An energy man­agement system is not limited to the operation of HVAC, lighting, and other power systems.
Enthalpy (H)
For most engineering purposes, heat content or total heat, above some base temperature. Specific enthalpy is the ratio of the total heat to the weight of a substance.
Entropy (H)
The ratio of the heat added to a substance to the absolute temperature at which the heat is added. Specific entropy is the ratio of total heat to weight of the substance.
Equipment-grounding conductor (E)
The conductor used to connect the non-current-carrying metal parts of equip­ment, raceways, and other enclosures to the system ground. (The equipment-grounding conductor is color-coded green.)
Equivalent length (H, FP, PS)
The resistance to flow of a dtict or pipe elbow, valve, damper, orifice, bend, or fitting, or some other obstruction, expressed in the number of feet of straight duct or pipe of the same diameter that would have the same resistance.
Equivalent sphere illumination, ESI (I)
The level of spherical illumination that would produce a task visibility equivalent to that produced by a specific lighting environment.
Ethernet (DP)
A relatively fast local area network (LAN) cabling system developed by Xerox. Ethernet components are also sold by other vendors.
Evaporative cooling (H)
Cooling by the evaporation of water in air when the wet bulb is considerably lower than its dry bulb. This method is widely used in dry climates.
Expansion joint (H, PS)
A joint designed to absorb longitu­dinal thermal expansion in the pipeline due to heat.
Expansion loop (H, PS)
A bend of large radius in a pipeline designed to absorb longitudinal thermal expansion in the line due to heat.
Face velocity (H)
The speed, in feet per minute, by which air leaves a register or a coil.
Fault (E)
A short circuit—either line to line or line to ground.
Feeder (E)
Circuit conductors between the service equip­ment and the final branch-circuit overcurrent device.
Feet of head (H, PS)
Pressure loss in psi divided by the factor 0.433.
Fiber optics, FO (DP, I, TC)
A technology in which light is used to transmit information from one point to another. The transmitting medium is constructed of thin filaments (strands) of glass wires through which light beams are trans­mitted. For illumination purposes, the light may be any one visible spectral wavelength. For data transmission, light must be of a single wavelength to be totally reflected (refracted) within the fiber. Light sources are usually gener­ated by laser or LED.
Field angle (I)
The angle between the two directions for which the intensity of light is 10 percent of the maximum intensity, as measured in a plane through the nominal cen-terline of the light beam.
Finned tube (H)
Tube or pipe containing fins used for heat transfer between water and air, usually by natural convection.
Fixture branch (PS)
In plumbing, the branch from the water-distributing pipe in the building to the fixture supply pipe.
Fixture carrier (PS)
A metal unit designed to support an off-the-floor plumbing fixture.
Fixture drain (PS)
The drain from the trap of a fixture to the point where it connects with another drainpipe.
Fixture unit, FU (PF)
An index of the relative rate of flow of water to a fixture (water supply fixture unit, WFU) or of sewage leaving a fixture (drainage fixture unit, DFU).
Flanking transmission (AS)
Transmission of sound from the source to the receiver by paths around barriers or other means intended to block the transmission of sound.
Flow rate (H, PF)
Cubic feet per minute (CFM) of air circu­lated in an air system or pounds of water per minute circulated through a hot-water heating system.
Flushometer valve (PS)
A device that discharges a predeter­mined quantity of water to fixtures for flushing purposes and is actuated by direct water pressure.
Font (DP, TC)
A collection of letters, numbers, punctua­tion marks, and symbols with an identifiable and consis­tent look.
Foot-candle, fc (I)
The illuminance on a surface 1 sq ft in area on which there is a uniformly distributed flux of 1 lm. Foot-Lambert, f L (I) A unit of luminance of a perfectly dif­fusing surface emitting or reflecting light at the rate of 1 lm per square foot.
Formatting (DP)
All the characteristics of text other than the actual characters that make it up. Formatting includes things such as italics, boldface, type size, margins, line spacing, and justification. Also another term for initializ­ing a disk.
Free field (AS)
A field free from boundaries that would otherwise tend to reflect sound. Frequency (AS, E) Number of complete oscillation cycles per unit of time. A unit of frequency often used is the hertz.
Furnace (H)
Either the combustion space in a fuel-burning device or a direct-fired air heater. In the latter case, not to be confused with a boiler.
Fuse (E)
An overcurrent protective device with a circuit-opening fusible part that is heated and severed by the pas­sage of overcurrent through it.
Galvanizing (PS)
A process whereby a surface of iron or steel is covered with a layer of zinc.
Gigabyte, (DP)
A measure of computer memory, disk space, and the like, equal to 1024 megabytes (1,073,741,824 bytes), or about 179 million words. Sometimes a gigabyte is treated as an even billion bytes, but plainly, that is almost 74 million bytes short. Sometimes abbreviated gig (more often in speech than in writing).
Glare (I)
The sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted. Glare may cause annoyance, discomfort, or loss of visual performance and visibility.
Ground (E)
A conducting connection, whether intentional or accidental, between electrical circuit or equipment and the earth.
Ground fault (circuit) interrupter, GFI or GFCI
(E) A device that senses ground faults and reacts by opening the circuit.
Grounded conductor (E)
A system or circuit conductor that is intentionally grounded.
Grounding conductor (E)
A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.
Halon (FP)
A bromtrifluoromethane gas that is effective in extinguishing fires.
Handshake (DP)
What computers do when communicating, in order to establish a connection and agree on protocols for the transmission of data.
Head end (TC)
The central facility where signals are com­bined and distributed in an airborne sound (AS) system.
Heat pump (H)
An all-electric heating/cooling device that takes energy for heating from outdoor air (or groundwater).
Hertz, Hz (AS, DP, E)
A measure of frequency (cycles per second).
High-density (or high-resolution) television, HDTV (DP)
Television with about double the resolution of present systems.
High-intensity discharge (HID) lamp (I)
A lamp whose light source is mercury, metal halide, or high-pressure sodium.
High-pressure sodium (HPS) lamp
HID lamp in which light is produced by radiation from sodium vapor.
Home run (E)
The wiring run between the panel and the first outlet in the branch circuit. (Looking upstream, the wiring run between the last outlet and the panel.)
Horsepower (E, H, PF)
A unit of power that equals 746 W, or 1 hp = 3/4 kW.
Humidity (H)
Usually, water vapor mixed with dry air. Absolute humidity is the weight of water (or steam) per unit volume of the air-water mixture.
Hydrogen ion concentration, pH (H)
The logarithm of the reciprocal of the gram ionic hydrogen equivalents per litei. On the pH scale 7.0 is neutral; smaller values to 0 are acid, progressively so; and higher values to 14 are alkaline, pi°~ gressively so.
Icon (DP)
A graphic computer symbol usually representing a file, folder, disk, or tool.
Illuminance
The density of the luminous flux incident on a surface; the quotient of the luminous flux divided by the area of the surface when the latter is uniformly illuminated. illuminance (lux or foot-candle) meter (I) An instrument formeasuring illuminance on a plane. Instruments that respond accurately to more than one spectral distribution are color-corrected.
Incandescent lamp (I)
A lamp in which light is produced by a filament heated to incandescence by an electric current.
Index of refraction (I, TC)
The ratio of the speed of light in a vacuum to the speed of light in a material, usually abbreviated n.
indirect lighting (I)
Lighting by luminaires distributing 90 to 100 percent of the emitted light upward.
Input/output, I/O (DP)
Signal fed into and transmitted out of a circuit.
Integrated circuit, IC (DP, TC)
An electronic device that contains hundreds or thousands of separate components, such as transistors, resistors, and switches. Encapsulated in a plastic enclosure, it is also called a chip.
Integrated services digital network, ISDN (TC)
A digital standard calling for 144-kbit/sec transmission, corre­sponding to two 64-kbit/sec digital voice channels and one 16-kbit/sec data channel.
Intensity, or I (AS)
The average rate of sound energy flow per unit of area in a direction perpendicular to the area, usually in W/m2.
Intensity, or I (I)
The luminous flux per unit solid angle, expressed in lumens per steradian (lm/sr) or candela (cd).
Intensity level, IL (AS)
Ten times the logarithm of the ratio of the sound intensity to a reference sound intensity (Iref) of 10~12 W/m2 (9.29 X 10~14 W/ft2).
International Organization for Standardization, ISO (G)
An international organization that establishes standards on scientific and technology quantities.
Inverse square law (I)
The law stating that the illuminance at a point on a surface varies directly with the intensity of a point source and inversely as the square of the distance between the source and the point.
Invert (PS)
Lowest point on the interior of a horizontal pipe.
Isolux chart (I)
A series of lines, plotted on any appropriate set of coordinates, each of which connects all the points on a surface having the same illumination.
Kilobyte, K (DP)
A measure of computer memory, disk space, and the like, equal to 1024 characters, or about 170 words.
Laminar flow (H)
Flow occurring in fluid layers, in a conduit or space, with no eddy currents. Each particle of fluid flows directly from one end to the other or from top to bottom, or in some planned manner.
Lamp efficacy (I)
The ratio of lumens produced by a lamp to the watts consumed. Expressed as lumens per watt (lpw).
Lamp lumen depreciation, LLD (I)
Multiplicative factor in calculations of illumination for reduction in the light output of a lamp over a period of time.
LASER (TC)
An acronym for light amplification by stimu­lated emission of radiation. Laser light is directional, covers a narrow range of wavelengths, and is more coherent than ordinary light. Semiconductor diodes are the standard light sources in fiber-optic systems.
Laser diode (DP, TC)
A semiconductor diode in which the injection of current carriers produces laser light by amplify­ing photons generated when holes and electrons recombine at the junction between p- and »-doped regions.
Latent heat (H)
Inherent heat in the. form of fluid without a phase change.
Life-cycle cost analysis (G)
Accounting of cash flows for installation, debt retirement, maintenance, utilities, and salvage value of a system or component over the life of the element being analyzed; generally done to evaluate alterna­tive options.
Light-emitting diode, LED (AX, DP, TC)
Small lamp illumi­nated by the movement of electrons in a semiconductor.
Light loss factor, LLF (I)
A factor used in calculating illumi­nance after a given period and under given conditions. (Formerly called maintenance factor.)
Liquid crystal display, LCD (DP, TC)
A product that uses liq­uid crystals sealed in glass. The pixels contain individual transistors to generate alphanumeric and graphic images.
Live room (AS)
A room that has very little sound absorption from the boundaries and furnishings. Opposite of dead room.
Local area network, LAN (DP)
A network of computers and related devices that transmits data among many nodes in a relatively small area, such as one office or one building. See Wide area network.
Loop vent (PS)
A branch vent serving more than one fixture and looping back to connect with a stack vent instead of the vent stack.
Loudness (AS)
A subjective description of the level of sound. Typically, a 10-dB increase in sound pressure level is judged to be twice as loud as the level before the increase.
Low-pressure sodium (LPS) lamp, (I)
A discharge lamp in which a single wavelength of visible yellow light is produced by radiation of sodium vapor at a low pressure.
LP gas (H)
Liquefied petroleum gas, a gas of high heating content, stored under high pressure in liquid form. Delivered to consumers in containers where piped gas is not available, and used by gas utilities for peaking (when demand exceeds source of natural gas).
Lumen, lm (I)
The unit of luminous flux; the luminous flux emitted within a unit solid angle (one steradian) by a point source having a uniform luminous intensity of one candela (1 cd).
Luminaire (I)
A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps, and to connect the lamps to the power supply.
Luminaire dirt depreciation, LDD (I)
Multiplicative factor used in calculations of illuminance for reduced illuminance due to dirt collecting on the luminaires.
Luminaire efficiency (i)
The ratio of the luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.
Luminance (I)
The amount of light reflected or transmitted by an object.
Lux, Ik (I)
The metric unit of illuminance. One lux (1 lx) is one lumen per square meter (1 lm/m2).
Macro (DP)
A command that incorporates two or more other commands or actions. (The name comes from the idea that macro commands incorporate "micro" commands.)
Maintenance factor, MF (I)
A factor used in calculating illu­minance after a given period and under given conditions.
Makeup air (H)
Air brought into a building from the outside to replace that exhausted by a ventilating system.
Makeup water (H, PS)
Water supplied to replenish that lost by leaks, evaporation, etc.
Malleable iron (PS)
Cast iron heat-treated to reduce its brit-tleness. The process enables the material to stretch to some extent and to withstand greater shock.
Masking (AS)
The rendering undetectable of one sound of interest by other sounds.
Mbh (H)
Thousands of British thermal units (Btu) per hour (h).
MCM (E)
Thousand circular mil; used to describe large wire sizes.
Meg (DP)
An abbreviation for megabyte.
Megabyte, MB (DP)
A measure of computer memory, disk space, and the like, equal to 1024K (1,048,576 bytes). Sometimes people try to equate a megabyte with an even million characters.
Megahertz, MHz (DP, TC)
A million cycles, occurrences, alterations, or pulses per second. Used to describe the speed of computers' clock rates.
Memory (DP)
The retention of information electronically, on chips. There are two main types of memory: RAM, which is used for the short-term retention of information (that is, until the power is turned off), and ROM, which is used to store programs that are seldom, if ever, changed.
Menu (DP)
A list of commands to operate a computer. There are many types of menus: pop-up menus, submenus, etc.
Mercury lamp (I)
A high-intensity discharge (HID) lamp in which the major portion of the light is produced by radia­tion from mercury.
Metal halide (MH) lamp, (I)
A high-intensity discharge (HID) lamp in which the major portion of the light is pro­duced by radiation of metal halides and their products of dissociation, possibly in combination with metallic vapors such as mercury.
Modulator-demodulator, or modem (DP)
A device that lets computers talk to each other over phone lines. Modems are used to send digital signals through telephone lines, to be converted back to analog signals at the receiving end.
Mollier chart (H)
A form of graph, named for its inventor, covering heat properties of a fluid and having entropy as one coordinate and enthalpy as the other.
Multiplex (DP, TC)
To transmit two or more signals over a single channel.
Multiuser (DP)
Said of software or hardware that supports use by more than one person at one time.
Nadir (I)
Vertically downward directly below the luminaire or lamp; designated as 0°.
Nanometer (AX, G, I, TC)
A unit of length, 10"~9 m. It is part of the SI system and has largely replaced the non-SI unit angstrom (0.1 nm) in technical literature.
Nanosecond (DP, G, I, TC)
A billionth of a second. Used to measure the speed of memory chips, among other things. Abbreviated ns.
National Television Standard, NTS (TC)
The analog video broadcast standard used in North America and set by the National Television Standards Committee.
National Television Standards Committee, NTSC (TC)
Committee that sets television transmission standards in North America at 30 frames per second and 525 horizontal lines per frame.
Near field (AS)
The field in the vicinity of a real sound source wherein the sound level contours are different from those of a point source in a free field.
Needle valve (H)
A valve provided with a long tapering point in place of the ordinary valve disk. The tapering point permits fine gradation of the opening.
Net present value (G)
The theoretical inception cost or savings due to operation of an element or system including initial investment and cash flow from operations, generally discount­ing future cash flows to the present, thereby accounting for interest, inflation, and/or foregone profit.
Network (DP, E)
Two or more computers (or other computer-related devices) connected to share informa­tion. Usually, the term refers to a local area network.
Network operating system, NOS (DP)
A software program for a computer network that runs in a file server and con­trols access to files and other resources from multiple users.
Nipple (H, PS, FP)
A tubular pipe fitting usually threaded on both ends and under 12 in. long. Pipe over 12 in. long is regarded as cut pipe.
Noise isolation class, NIS (AS)
A single-number rating derived in ,the same manner as STC but based on NR (noise reduc­tion) rather than TL (sound transmission loss). It includes the acoustical absorption in the receiving room.
Noise reduction (AS)
The difference in decibels between the sound in one space and the sound in a second space atten­uated by some intervening medium; e.g., from one room to another.
Noise reduction coefficient, NRC (AS)
The average of the sound absorption coefficients in the 250-, 500-, 1000-, and 2000-Hz octave bands.
Octave (AS, AV)
An interval between two frequencies having a ratio of two to one (2:1).
Octave band (AS, AV)
A frequency band whose upper limit is twice the lower limit.
Ohm's law (E)
The relationship between current and volt­age in a circuit. The law states that current is proportional to voltage and inversely proportional to resistance. Algebraically, in DC circuits, / = V /R; in AC circuits, /= V/Z.
One-pipe hot-water system (H)
System that carries heated and cooled water to and from the radiators in the same "main" and in the same direction, with the hot water on top. This system is rare in modern-day applications.
One-pipe steam system (H)
A steam heating system in which steam supplied to a radiator travels in the same pipe but in opposite directions as the cold water or condensate returns from the radiator. This system is rare in modern-day applications.
Open protocol (DP, TC)
A set of standard procedures that are agreed upon by all manufacturers so that data can be trans­mitted without obstructions.
Optic fiber cable, or OFC (DP, I, TC)
An information trans­mission medium consisting of a core of glass or plastic surrounded by a refractive cladding and a protective jacket. It transmits stranded and ribbon configurations. See Fiber optics.
Orifice (H, PS)
An opening. The term is commonly applied to disks placed in pipelines or radiator valves to reduce the flow of a fluid to a desired amount.
Orsat (H)
A device for measuring the percentage of carbon dioxide, oxygen, and carbon monoxide in flue gases.
Overcurrent (E)
Any current in excess of the rated current of equipment or the ampacity of a conductor.
Overcurrent device (E)
A device, such as a fuse or a circuit breaker, designed to protect a circuit against excessive cur­rent by opening the circuit.
Panel or panelboard (E)
A box containing a group of over-current devices intended to supply branch circuits.
Parabolic reflector lamp, PAR (I)
A lamp with internal reflector having the contour of a parabola to achieve beam control.
Partial pressure (H)
That part of the total pressure of a mixture of gases contributed by one of the constituents.
Pascal, Pa (AS)
Measure of pressure in the SI system ( = 1.45 X 10~4psi).
Payback period (G)
Elapsed time after installation of an ele­ment or system for savings in utilities and maintenance to equal the additional cost of its installation compared with another competing option.
Percentage humidity (H)
Ratio of weight of vapor in a mix­ture of air and water vapor to the weight of vapor when the vapor is saturated at the same temperature. Contrast with relative humidity.
Performance interaction (G)
The effects that one or mores ystems or subsystems have on other systems or subsystems; e.g., better insulation reduces HVAC loads and electrical system capacity to support the HVAC.
Phase alternate line, PAL (TC)
A television transmission standard vtsed mostly in Europe; 25 frames per second and 625 lines per frame.
Picture element, or pixel (DP, TC)
Any of the little dots of light that make up die picture on a computer (or TV) screen. The more pixels there are in a given area—that is, the smaller and closer together they are—the higher is die resolution of the screen. Sometimes pixels are simply called dots. The number of pixels on a screen is usually expressed by the number of hor­izontal and vertical rows, such as 640 X 480 or 1800 X 1280.
Pink noise (AS)
Sound that has equal energy in each octaveor suboctave band.
Pitch (AS)
A subjective description of sound quality referring to the principal frequency content. The sound pressure level of a tone.
Point source (AS, I)
A source of essentially zero dimensions that radiates sound or light uniformly in all directions.
Polarization (I)
The process by which the transverse vibra­tions of light waves are oriented in a specific plane.
Polyvinyl chloride, PVC (P)
An inert plastic material com­monly used for pipes. It has high resistance to corrosion.
Pounds per square inch pressure, psi (H, PF)
A unit measure of pressure, or force per unit area.
Power factor, PF (I)
The ratio of the working power to the apparent power of an AC circuit.
Presbycusis (AS)
A condition of deterioration of hearing acuity due primarily to aging.
Private branch exchange, PBX (AX, TC)
A private telephone system that usually interconnects with public telephone sys­tems to serve a business or an organization. It can also pro­vide access to a computer from a data terminal. PBX and PABX are used interchangeably.
Programmable ROM, PROM (DP)
A read-only memory chip that can be changed with a special device.
Propeller fan (H)
A fan with airfoil blades that move the air in the general direction of the axis of the fan.
Protocol (DP, TC)
A set of standard procedures that control how information is transmitted between computer systems.
Psychrometer (H)
A device employing a wet-bulb and a dry-bulb thermometer to measure the humidity in the air.
Psychrometric chart (H)
A graph used in air conditioning and showing the properties of airsteam mixtures. Pure tone (AS) A sound in which the instantaneous sound pressure wave is a pure sinusoid.
Raceway (E)
An enclosed channel of metal or nonmetal designed for holding wires or cables.
Radiation (H)
The transfer of energy in wave form from a hot body to a (relatively) cold body, independently of matter between the two bodies.
Radio frequency, RF (TC)
Electromagnetic waves operating between 5 kHz and the MHz range. Although off-air (over-the-air) and satellite TV signals operate far above these frequencies (54 MHz and up to many GHz), these TV signals are frequently incorrectly referred to as RF sig­nals in commercial applications.
Rapid-start (RS) fluorescent lamp
A fluorescent lamp designed for operation with a ballast that starts the lamp light output within a split second.
Reflectance (I)
The ratio of the reflected light to the incident light falling on a surface.
Reflected glare (I)
Glare resulting from specular reflections of high luminances in polished or glossy surfaces in the field of view.
Reflector (R) lamp (I)
A lamp with an internal reflector to redirect the light output to a controlled direction. Refraction (I, TC) The process by which the direction of a ray of light changes as the ray passes obliquely from one medium to another in which its speed is different.
Refrigerant (H)
A substance that absorbs heat while vaporiz­ing and whose boiling point and other properties make it useful as a medium for refrigeration.
Regenerative heating or cooling (H)
An arrangement whereby heat rejected in one portion of a cycle is utilized in another portion of the cycle.
Relative humidity, RH (H)
The ratio of the water vapor (by weight) in air to the water vapor saturated in air at the same pressure and temperature.
Relief vent (PS)
A vent designed to provide circulation of air between drainage and vent systems or to act as an auxiliary vent.
Residual pressure (FP)
Pressure remaining in a system while water is being discharged from outlets.
Resonance (AS, 6)
A state in which the forces of oscillation of a system occur at or near a natural frequency of the system.
Reverberant sound field (AS)
Sound that is reflected from the boundaries of and furnishings within an enclosed space. Excludes direct sound. (See Direct sound field.)
Reverberation (AS)
The persistence of sound in an enclosed space as a result of repeated reflection or scattering of the sound.
Reverberation time (AS)
The time required for the sound pressure level in a reverberant sound field to decay 60 dB after the source has been extinguished.
Riser diagram (E)
Electrical block-type diagram showing the connection of major items of equipment and components.
Romex (E)
One of several trade names for NEC-type non-metallic sheathed flexible cable.
Romex (NM) cable (E)
A cable composed of flexible plastic sheathing inside of which are two or more insulated wires for carrying electricity.
Room cavity ratio, RCR (I)
A number indicating the propor­tions of a room cavity, calculated from the length, width, and height of the room.
R-value (H)
Resistance rating of thermal insulation.
Sabin (AS)
Unit of measure of acoustical absorption. Named after Wallace Clement Sabin, U.S. physicist.
Saturated air (H)
Air containing saturated water vapor, with both the air and the vapor at the same dry-bulb temperature.
Saturated pressure (H)
That pressure, for a given tempera­ture, at which the vapor and the liquid phases of a substance can exist in stable equilibrium.
Saturated steam (H)
Steam at the boiling temperature cor­responding to the pressure at which it exists. Dry saturated steam does not contain water particles in suspension. Wet saturated steam does.
Seasonal energy efficiency ratio, SEER (H)
Measure of the efficiency of HVAC equipment on a seasonal, rather than a design-load, basis.
Self-contained cooling unit (H)
A combination of apparatus for room cooling complete in one package. Usually consists of compressor, evaporator, condenser, fan motor, and air filter. Requires connection to electric line.
Semiconductor (DP, TC)
A material that has an electrical resistance somewhere between that of a conductor (e.g., metal) and that of an insulator (e.g., plastic). Silicon and germanium are the two most commonly used semiconduc­tors. The flow of electric current in a semiconductor can be changed by light or by electric or magnetic fields.
Sensible cooling effect (H)
The difference between the total cooling effect and the dehumidifying effect.
Sensible heat (H)
Heat that raises the air temperature.
Septic tank (PS)
A tank designed to separate solid waste from liquid waste.
Service conductors (6)
The supply conductors that extend from the street main or from transformers to the service equipment of the premises supplied.
Simplex (TC)
Single element (e.g., a simplex connector is a single-fiber connector).
Sol-air temperature (H)
That temperature of the outdoor air that, in contact with a completely shaded building surface, would give the same rate of heat entry into the outdoor surface of the outdoor air, the actual intensity of solar and sky radiation incident upon that surface, and the actual wind velocity.
Sound power (AS)
The rate at which acoustic energy is radi­ated. Usually measured in watts.
Sound power level, PWL (AS)
Ten times the logarithm of the ratio of sound power, in watts, to the reference level
Sound pressure (AS)
The fluctuations of pressure about atmos­pheric pressure. Usually measured in micropascals (uPa).
Sound pressure level, SPL (AS)
Ten times the logarithm of the ratio of the mean square pressure to the square of a reference pressure (Prcf) of 20 uPa.
Sound transmission class, STC (AS)
A single-number rating system designed to provide a cursory estimate of the sound-insulating properties of a wall or partition.
Sound transmission loss, STL (AS)
The difference in deci­bels of the sound pressure level on the receiver side of a partition or barrier from that on the source side, with the receiver side being free-field conditions.
Specific heat (H)
The heat absorbed by a unit weight of a substance per unit temperature rise of the substance.
Specific humidity (H)
Weight of water vapor, in grains or pounds, per pound of dry air.
Specific volume (H)
The volume occupied by a unit of air. Usually given in cubic feet per pound.
Specular reflection (I)
Mirrorlike reflection.
Split system (H)
Historically, a combination of warm-air heating and radiator heating; the term is also used for other combinations such as hot water-steam and steam-warm air. It is also applicable to a DX cooling system when the evap­orator (cooling) section is separated from the condensing (heat rejection) section.
Stack (PS)
The vertical main of a system of soil, waste, or vent piping extending through one or more stories.
Stack vent (PS)
The extension of a soil waste stack above the highest horizontal drain connected to the stack.
Standard air (H)
Air at 70°F and 29.921 in. of mercury and weighing 0.07488 lb per cu ft.
Standing wave (AS)
A sound wave that has a fixed distribu­tion in space, the result of progressive waves of identical frequencies. It is characterized by the existence of nodes or partial nodes and antinodes at fixed points in space.
Static pressure (H)
The pressure exerted by a fluid in all directions; the pressure which would tend to burst the con­tainer; the pressure exerted by the fluid if stationary.
Steam trap (H)
An apparatus for allowing water or air to pass but preventing passage of steam.
Storm sewer (PS)
A sewer used for conveying rain or surface or subsurface water.
Streamline flow (H)
Also termed viscous or laminar flow. In a streamline flow, the fluid particles are moving in a straight line parallel to the axis of the pipe or duct. With streamline flow, the friction varies directly as the velocity.
Structure-borne sound (AS)
Sound transmitted through solid material by means of vibration waves in the material.
Subcooling (H)
Cooling of a liquid refrigerant below the condensing temperature at constant pressure.
Subsoil drain (PS)
A drain that receives only subsurface or seepage water and conveys it to an approved place of disposal.
Sump pump (PS)
A mechanical device for removing liquid waste from a sump.
Superheated steam (H)
Steam at a temperature higher than the boiling temperature corresponding to the pressure at which it exists.
Supply fixture unit, SFU (PS)
A measure of the probable hydraulic demand on the water supply by various types of plumbing fixtures.
Surcharge (PS)
Rising of water levels above sewer inlets owing to instantaneous loads in excess of flow capacity, gen­erally a temporary phenomenon.
Sustainability (G)
Quality of an activity, policy, design, or design element to enhance functionality, improve habitability, conserve resources, and reduce harm to the environment.
Swing joint (H, PS)
An arrangement of screwed fittings and pipe to provide for expansion in pipelines.
Switchboard (E)
A large panel containing switches, overcurrent devices, buses, and, usually, instruments.
Task cooling (H)
Provision for local comfort conditioning, generally in a small area, where requirements are different from those of surrounding spaces.
Task lighting (I)
Provision for local illumination in appropri­ate areas where requirements are different from those of surrounding spaces.
Tee (H, FP, PS)
A pipe fitting that has one side outlet at right angles to the run.
Therm (H)
A unit of heat equal to one hundred thousand (100,000) Btu.
Thermocouple (H)
Two dissimilar metals joined together to produce an electromotive force that varies with the temper­ature. Used to measure temperature.
Timbre (AS)
A characteristic of sound whereby the listener is capable of distinguishing between two sounds even though they are of equal level and pitch.
Tone (AS)
A sound having a pitch and capable of causing auditory sensation.
Tons of refrigeration (H)
A common commercial measure of refrigeration capacity, especially of the cooling capacity of air conditioning apparatus, the equivalent of the heat required to melt one ton (2000 lb) of ice (heat of fusion is 144 Btu per pound) in 24 hours, hence, 288,000 Btu per day or 12,000 Btu per hour.
Total heat (H)
The sum of sensible heat and latent heat in a substance or fluid above a base point, usually 32°F (0°C).
Total internal reflection (TC)
Total reflection of light back into a material when the light strikes the interface with another material having a lower refractive index at an angle below a critical value.
Total pressure (H)
The sum of the static pressure and velocity pressure of a fluid.
Transformer (E)
A device used to raise or lower electrical voltage by means of an electromagnetic core and windings.
Trap (PS)
A fitting or device designed to provide a liquid seal that will prevent a fluid from passing back to where it came from.
Tubeaxial fan (H)
An airfoil (propeller) or disc fan within a cylinder and including driving mechanism supports either for belt drive or direct connection.
Tungsten-halogen lamp
A gas-filled tungsten incandes­cent lamp containing a certain proportion of halogens.
Turbulent flow (H)
Flow in which the fluid particles are mov­ing in directions other than a straight line parallel to the axis of the pipe or duct.
Twisted pair, or TP (E, DP, TC)
A type of wire made of two insulated copper conductors twisted around each other to reduce induction (and thus interference) from one conduc­tor to the other. The twist, or lay, varies in length to reduce the potential for interference from signals between pairs in a multipair cable. The lay usually varies between 2 and 12 in. Closer lay provides better attenuation between the con­ductors. TP cables are classified as unshielded (UTP) and shielded (STP). The latter includes a metal sheath sur­rounding the pairs within the protective jacket.
U coefficient (H)
Rate of heat transmission in Btuh/sq ft-°F.
Ultrasonic (AS)
Sound above the audible range.
Uninterruptible power supply, UPS (DP, E)
A power supply or system that provides a steady source of electrical power even when the normal (utility) power supply is interrupted. The system usually contains a storage battery floating on line with an inverter to convert battery power from DC to AC. Other UPSs may utilize a DC motor-driven AC gen­erator set.
Vacuum breaker (PS)
Check valve open to the atmosphere when the pressure in piping drops to atmospheric pressure.
Vaneaxial fan (H)
An airfoil (propeller) or disk fan within a cylinder, equipped with air guide vanes either before or after the wheel and including driving mechanism supports for either belt drive or direct connection.
Vapor barrier (H)
A material intended to prevent the passage of water vapor through a building wall or a pipe so as to pre­vent condensation within the wall or within the insulating material.
Vapor pressure (H)
The equilibrium pressure of the vapor of a liquid in contact with the liquid.
Veiling reflections (I)
Regular reflections superimposed on diffuse reflections from an object that partially or totally obscures the details to be seen by reducing the contrast. Veiling reflections are sometimes called reflected glare.
Velocity pressure (H)
The pressure exerted by a moving fluid in the direction of its motion. It is the difference between the total pressure and the static pressure.
Ventilation (H)
The art or process of supplying outside (so-called fresh) air to, or removing air from, an enclosure.
Venturi (H)
A contraction in a pipeline or duct to accelerate the fluid and lower its static pressure. Used for metering and other purposes.
Viscosity (H)
The property of a fluid by which it resists an instantaneous change of shape or arrangement of its mole­cules. Broadly, resistance to flow.
Visual comfort probability, VCP (I)
The rating of a lighting system, expressed as a percent of people who, when view­ing from a specified location and in a specified direction, will be expected to find the system acceptable in terms of discomfort glare.
Voltage, V (E)
The electric pressure in an electric circuit, expressed in volts.
Voltage drop, VD (E)
The diminution of voltage around a cir­cuit, including the wiring and loads. Must equal the supply voltage.
Voltage to ground (E)
For grounded circuits, the voltage between the ungrounded conductor and the ground; for ungrounded circuits, the greatest voltage between the given conductors.
Warming-up allowance (H)
An addition to the capacity of heating system (as calculated for heat loss) to provide for quick pickup in the morning.
Water hammer (PF)
Banging of pipes caused by the shock of closing faucets or other flow-control devices.
Water hammer arrester (PS)
A device, other than an air chamber, designed to provide protection against excessive surge pressure.
Wavelength (electromagnetic) (D, I, TC)
The distance between nodes of an electromagnetic wave, such as radio, TV, light, or radar; given by L (length, m) = 3 X 10'//, where/is the frequency, in hertz.
Wavelength (sound) (AS)
The distance between nodes in a sound wave; given by L (length, ft) = 1130// where/is the frequency, in hertz.
Wet-bulb temperature, WB (H)
The temperature of the an­as measured by a wet-bulb thermometer. Except when the air is saturated, the wet-bulb temperature is lower than the dry-bulb temperature in inverse proportion to humidity.
White noise (AS)
Sound that has equal energy in every pass band of equal bandwidth.
Zonal cavity method (i)
A lighting design procedure used for predetermining the relation between the number and types of lamps or luminaires, the room characteristics and the average illuminance on the work plane. The zonal cavity method takes into account both direct and reflected flux.