definitions - 32 Flashcards
This factor is the percentage of normal observers who may be expected to experience visual comfort in a particular environment with a particular lighting situation.
visual comfort probability VCP
are a complex interaction of light source and brightness, position of the task, reflectivity of the task, and position of the eye.
veiling reflection
a measure of speech intelligibility calculated from the number of words read from a selected list that are understood by an audience.
articulation index
the reduction of sound
attenuation
a single-number rating of a floor-ceiling’s impact sound transmission performance at various frequencies
impact isolation class IIC
a set of single-number ratings of acceptable background noise corresponding to a set of curves specifying sound pressure levels across octave bands.
noise criteria NC
a single-number rating of noise reduction
noise isolation class NIC
the arithmetic difference, in decibels, between the intensity levels in two rooms separated by a barrier of a given transmission loss.
noise reduction NR
:the persistence of a sound in a room after the source has stopped producing the sound
reverberation
the time it takes the sound level to decrease 60 dB after the source has stopped producing the sound
reverberation time
the unit of absorption; theoretically, 1 ft of surface having an absorption coefficient of 1.00
sabin
a single-number average over several frequency bands of a barrier’s ability to reduce sound.
sound transmission class STC
the difference, in decibels, between the sound power incident on a barrier in a source room and the sound power radiated into a receiving room on the opposite side of the barrier. The transmission loss varies with the frequency being tested.
Transmission loss (TL)
Sound has three basic qualities:
velocity frequency and power
inverse square law
The basic inverse square law is where sound intensity is inversely proportional to the square of the distance from the source.
is the bending of sound waves around an object or through an opening. Diffraction explains why sounds can be heard around comers and why even small holes in partitions allow so much sound to be heard.
diffraction
is the random distribution of sound from a surface. It occurs when the surface dimension equals the wave- length of the sound striking it.
diffusion
The drain that removes dirt that builds up in the floor pool of an evaporative cooling tower.
blow down
In sanitary drainage, any vent that serves two or more traps.
circuit vent
The ratio of useful light arriving at the work plane to the amount of light emitted by the source.
coefficient of utilization
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 performance
A decibel measured in the A scale, that is weighted to account for the special sensitivi- ties of the human ear.
dbA
A method of connecting windings on a three phase transformer, end to end, that results in a triangular shape.
delta connection
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.
diffuser
A unit of liquid flow used in sizing both supply and drainage pipes.
fixture unit
A valve that releases a definite amount of water into a plumbing fix- ture each time it is actuated.
flushometer valve
The basic unit of illumination arriving at a work plane. Is equal to one lumen per square foot.
footcandle
A thermometer that measures Mean Radiant Temperature (MRT).
globe thermometer
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.
heat pump
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/meter 2 or 10- 16 watts/ cm 2 .
intesity level IL
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.
inverse square law
A process of water soften- ing in which calcium and magnesium ions are replaced by sodium ions. This process is also known as the zeolite process.
ion exchange
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.
lumen
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.
mass law
The weighted average of all of the temperatures of all of the surfaces visible from a given position.
mean radiant temperature MRT
A one- number rating system giving the average sound absorption coefficient of a material at frequen- cies of 250, 500, 1,000 and 2,000 Hz.
noise reduction coefficient NRC
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.
NC curves
A subjective system of measuring loud- ness, based on the reference point of one equal to a sound pressure level of 40 dB.
sone
The loga- rithmic expression of the pressure exerted by sound waves on the receiver.
sound pressure level SPL
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.`
star connection
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.
thermosiphon
The reduction of sound that occurs when a given wall transmits sound from one room to an adjacent room, expressed in decibels.
transmission loss TL
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.
zeolite
An automatic valve that admits air into a supply pipe rather than allow- ing the pipe to suction or siphon polluted water back into the supply.
vacuum breaker
