Acronyms and definitionsA useful method of revising or testing yourself about a subject is to check whether you can ‘decode’ the abbreviations and acronyms of technical terms, and whether you can accurately define a technical term of principle. The following lists of acronyms and definitions from the text are intended to help your revision and self-testing.
ATD accumulated temperature difference
BAS building automation system
BER building emission rate
BOD biochemical oxygen demand
BRE Building Research Establishment
BREEAM Building Research Establishment Environmental Assessment
BS British Standards
BTU British Thermal Unit
CAD computer aided design
CCGT Combined cycle gas turbine
CCS carbon capture and storage
CCT correlated colour temperature
CHP combined heat and power
CIBSE Chartered Institution of Building Services Engineers
CIE Commission Internationale de l’Eclairage
clo clothing scale
COD chemical oxygen demand
COPH coefficient of performance (COPH) of a heat pump
DER dwelling emission rate
DH district heating
DLOR downward light output ratio
DRI driving-rain index
emf electromotive force (voltage)
EPBD Directive for Energy Performance in Buildings (EU)
ES Euro Standards
GWh gigawatt hour
ICT Information and communications technology
ISO International Standards
LCA life-cycle analysis
LED light-emitting diode
LPN Perceived noise level
MSI mean spherical intensity
NC noise criterion
NIHL noise-induced hearing loss
NR Noise rating
PMT thermal mass parameter
PNC preferred noise criterion
PSALI permanent supplementary artificial lighting of interiors
PSV passive stack ventilation
PTS permanent threshold shift (of hearing)
R sound reduction index
Re Reynolds’ Number
RH relative humidity
RMS root mean square
SAP Standard Assessment Procedure (energy performance rating)
SBEM simplified building energy model
SBS sick building syndrome
SEDBUK Seasonal Efficiency of Domestic Boilers in the UK
SEL sound exposure level
SI Système Internationale d’Unités
SIL sound intensity level
SON high-pressure sodium lamps
SOX low-pressure sodium lamps
SPL sound pressure level
SRI sound reduction index
STP standard temperature and pressure
SVP saturated vapour pressure
TER target carbon dioxide emission rate
toe tonne of oil equivalent
TTS temporary threshold shift (of hearing)
UGR unified glare rating
ULOR upward light output ratio
VOC volatile organic compound
VOC volatile organic compounds
Absolute zero: a temperature at which no more internal energy can be extracted from a body, which occurs at –273.16°C.
Admittance see thermal admittance.
Air temperature/height: air temperature drops by 6.5°C for each 1000 m increase in altitude.
Airborne sound: sound which travels through the air before reaching a partition.
Anode: positive electrode.
Apostilb: a unit of luminance; 1 apostilb = 1/ cd/m 2.
Atom: the smallest part of an element which can take part in an chemical reaction.
Bernoulli Theorem: the total energy possessed by the particles of a moving fluid is constant.
Calorific value is a measure of the primary heat energy content of a fuel expressed in terms of unit mass or volume.
Candela: the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 x 10 12 Hz and of which the radiant intensity in that direction is 1/683 W/ω.
Cathode: negative electrode.
Centre of pressure: the point where the line of action of a pressure force passes.
Chemical reaction: an interaction between substances in which atoms are rearranged.
Chlorofluorocarbon: mixture of organic compounds containing carbon, chlorine and fluorine.
CIE sky: a standard overcast sky in which the luminance steadily increases above the horizon.
Clear-sky radiation is a mechanism that causes surface temperatures to fall because a clear dark sky behaves more like a theoretical black body than does a cloudy sky.
Coefficient of performance of a heat pump: the ratio of heat output to the energy needed to operate the pump.
Colour rendering index (Ra): a number that indicates the accuracy by which a lamp shows surface colours; an ideal index being 100.
Compound: a substance containing two or more different elements which are chemically joined together to form a new material with new properties.
Conductance (C) is sometimes used to express the reciprocal of thermal resistance, where C = 1/R.
Conduction: the transfer of heat energy through a material without the molecules of the material changing their basic positions.
Conductor: material that allows a significant flow of electric current.
Convection: the transfer of heat energy through a material by the bodily movement of particles.
Correlated colour temperature (CCT) of a light source: the absolute temperature of a perfect radiator when the colour appearance of the radiator best matches that of the light source (unit: Kelvin (K) – the SI unit of temperature).
Critical temperature of a substance: the temperature above which a vapour is not able to exist.
Daylight factor meter: a specially calibrated light meter which gives direct readings of the daylight factor at any point.
Daylight factor: the ratio between the actual illuminance at a point inside a room and the illuminance possible from an unobstructed hemisphere of the same sky (unit: percentage).
Dew-point: the temperature at which a fixed sample of air becomes saturated (unit: °C or K).
Diffraction: deflection that occurs at apertures, at edges and in thin layers.
Diffuse reflection: reflection in which the light is scattered in various directions (compare specular reflection).
Electric current: the rate of flow of charge in a material (unit: ampere).
Electrodes: conductors which form the terminals of a cell.
Electrolyte: a compound that undergoes chemical change in an electric cell and releases energy.
Element: a substance which cannot be separated into anything simpler by chemical means.
Emissivity is the fraction of energy radiated by a body compared to that radiated by a black body at the same temperature.
Equivalent continuous sound level, L Aeq,T: that constant sound level which, over the same period of time T, provides the same total sound energy as the varying sound (unit: dB(A)).
Externally reflected component: the light received directly by reflection from buildings and landscape outside a room.
Fluid: a material whose particles are free to move their positions.
Frequency: the number of cycles of vibration per second (unit: hertz).
Frequency: the number of repetitions, or cycles, of output per second (unit: hertz).
Gauge pressure: the value of a particular pressure measured in units above or below the atmospheric pressure.
Glare rating: an index or numerical measure of discomfort glare which enables glare to be assessed and acceptable limits recommended.
Glare: discomfort or impairment of vision caused by an excessive range of brightness in the visual field.
Globe thermometer: a regular thermometer fixed inside a blackened globe of specified diameter (150 mm is one standard) that can be used to calculate other temperatures.
Greenhouse ‘effects’ of gases:
H 20 = 35–70%
CO 2 = 10–25%
CH 4 = 4–9%
* Carbon dioxide (CO 2): produced by the burning of fossil fuels and forests and by all organic decay. Chimneys, motor vehicle exhausts and forest fires are major sources.
* Chlorofluorocarbons (CFCs): families of chemical compounds manufactured for use in refrigerators and spray cans, and for insulation. Although inert at point of use, CFCs escape to the upper atmosphere, where they chemically react and deplete the ozone layer which we need for protection from excess ultraviolet radiation from the sun.
* Methane (CH 4) the main component of natural gas supplies. Methane is produced by decay of organic matter and also by the digestion of sheep and cattle.
* Nitrogen oxides (NO x) the various oxides of nitrogen, which are mainly produced by motor vehicle emissions.
* Water vapour: occurs naturally from the waters of the world, not including clouds, and accounts for most of the greenhouse effect on earth.
Hardness of water : the degree in which it is difficult to obtain a lather with soap (unit: milligrammes per litre of calcium carbonate (CaCO 3) irrespective of actual salts present).
Heat pump: a device that extracts heat from a low-temperature source and upgrades it to a higher temperature.
Heat transfer: mechanisms for heat transfer are conduction, convection and radiation.
Heat, heat energy, thermal energy: All these terms are used here to describe the same concept.
Heat: a form of energy, also called thermal energy (unit: joule).
Hot-wire anemometer: device used to measure air movement.
Hygrometers: instruments which measure the humidity of air.
Illuminance (E): lighting effect; the density of luminous flux reaching a surface (unit: lux (lx) where 1 lux = 1 lumen/(metre) 2).
Illumination vector: the quantity of light from a specified direction, such as horizontal illumination.
Impact sound: sound which is generated on a partition.
Index: single value made up from multiple values.
Insulation products can be grouped by form under the general headings given below:
Rigid preformed materials. Example: aerated concrete blocks.
Flexible materials. Example: fibreglass quilts.
Loose fill materials. Example: expanded polystyrene granules.
Materials formed on site. Example: foamed polyurethane.
Reflective materials. Example: aluminium foil.
Insulator: material that has few free electrons available to produce a flow of charge and so passes relatively little electric current.
Internally reflected component: the light received from surfaces inside a room.
Kata thermometer: device used to measure air movement.
Kinetic energy: the energy associated with a mass of liquid having a velocity.
Kyoto agreement objective : to stabilise greenhouse gases in the atmosphere at a level that will avoid dangerous climate change.
L A10: the noise level, measured as A-weighted sound level, exceeded for 10 per cent of a given measurement time.
Lapse rate: the decrease of temperature with altitude.
Latent heat: the heat energy absorbed by or released from a substance during a change of state, with no change in temperature.
Latitude: higher latitude means further north or further south.
Lenz’s Law: the direction of the induced current is such that it will always oppose the change that produced it.
Light loss factor: the ratio of the illuminance provided at some given time compared to the initial illuminance.
Linear thermal transmittance of a thermal bridge: the rate of heat flow per degree per metre of the bridge that is not accounted for in the U-values of the building elements around the thermal bridge.
Loudness level: the loudness level (LN) of any sound is numerically equal to that SPL, in decibels, of a 1000 Hz pure tone which an average listener judges to be equally loud (unit: phon).
Lumen: the luminous flux emitted within one steradian by a point source of light of one candela.
Luminaire: the ‘light fitting’ that holds or contains a lamp.
Luminance: surface brightness; a measure of the ability of an area of light source, or reflecting surface, to produce the sensation of brightness.
Luminous efficacy: the ability of a lamp to convert electrical energy to light energy and is measured by the ratio of light output to energy input.
Luminous flux: the rate of flow of light energy.
Luminous intensity: the power of a light source, or illuminated surface, to emit light in a particular direction (unit: candela (cd)).
Lux: 1 lux = 1 lumen/(metre)2
Molecule: the smallest part of a compound which can take part in a chemical reaction.
Natural frequency: the characteristic frequency at which an object tends to vibrate when disturbed.
Octave band: the range of frequencies between any one frequency and double that frequency.
Ohm’s Law: for a metal conductor, at constant temperature, the current flowing is directly proportional to the potential difference across the conductor.
Organic compound: one that contains atoms of carbon and hydrogen.
Overtones and harmonics: frequencies equal to whole-number multiples of the fundamental frequency.
Oxidation: the gain of oxygen in a chemical reaction.
Peak value: the maximum value of alternating voltage or current, measured in either direction.
Photometer: an instrument that measures the luminous intensity of a light source by comparing it with a standard source whose intensity is known.
Pitch: the frequency of a sound as perceived by human hearing.
Polymer: a substance with large chain-like molecules consisting of repeated groups.
Potential difference: a measure of the difference in charge between two points in a conductor (unit: volt).
Potential energy: the energy associated with a mass of liquid at a height above a reference level (datum).
Power density of a lighting installation: the total power rating of the installation divided by the total floor area of the installation (unit: watts/m2).
Power: a measure of the rate at which work is done, or at which energy is converted from one form to another.
Precipitation: the release of water from the atmosphere. Examples include rain, snow, hail and dew.
Pressure energy: the energy or the work associated with moving a mass of liquid by a force.
Primary cells: cells that cannot be recharged.
Psychrometers: instruments which measure the humidity of air.
Psychrometric chart: a set of graphs which are combined to plot the relationships between the different variables used to specify humidity.
Radiation: the transfer of heat energy by electromagnetic waves.
Reduction: the loss of oxygen in a chemical reaction.
Reflectance: the ratio of the luminous flux reflected from a surface to the flux incident upon the surface.
Reflection: reversal of direction which occurs at a surface.
Refraction: deflection that occurs at the boundaries of different materials.
Resistivity ( r): an alternative index of conduction in materials and is the reciprocal of thermal conductivity, so that r = 1/k. Similarly, the unit of resistivity is the reciprocal of the unit k-value unit: m K/W.
Reverberation time: the time taken for a sound, when stopped, to decay by 60 dB (unit: seconds).
Reverberation: a continuation and enhancement of a sound caused by rapid multiple reflections between the surfaces of a room.
Root mean square value of alternating current: that value of direct current that has the same heating effect as the alternating current.
Saturated vapour pressure: the vapour pressure of the water vapour in an air sample that contains the maximum amount of vapour possible at that temperature.
Scalar illuminance: the total illuminance caused by light from all directions, including reflected light.
Secondary cells: cells that can be recharged.
Sensible heat: the heat energy absorbed by or released from a substance during a change in temperature.
Service illuminance: the mean illuminance achieved during the maintenance cycle of a lighting system, and averaged over the area being considered.
Sky component: the light in a room that is received directly from the sky.
Sol-air temperature: an environmental temperature for the outside air which includes the effect of solar radiation. The rate of heat flow due to the sol-air temperature is equivalent to the rate of heat flow due to the actual air temperature combined with the effect of solar radiation.
Solar radiation: intensity of solar radiation decreases as latitude increases.
Sound absorption: a reduction in the sound energy reflected by the surfaces of a room.
Sound exposure level: that constant sound level in dB(A) which, during one second, provides the same total sound energy as the measured noise.
Sound insulation: the reduction of sound energy transmitted into an adjoining air space.
Sound intensity: the sound power distributed over unit area (unit: watts per square metre). It decreases in inverse proportion to the square of the distance from the source.
Sound level meter: an instrument designed to give constant and objective measurements of sound level.
Sound path/sound ray: the directional track made by the wave vibrations as they travel through a material such as air.
Sound power: the rate at which sound energy is produced at the source (unit: watt).
Sound pressure (p) is the average variation in atmospheric pressure caused by the sound (unit: pascal).
Sound reduction index: a measure of the insulation against the direct transmission of airborne sound.
Specific heat capacity of a material: the quantity of heat energy required to raise the temperature of 1 kg of that material by 1 degree Kelvin or 1 degree Celsius.
Spectrometer: an instrument that disperses light into its component wavelengths and measures the amount of light energy radiated at each wavelength.
Specular reflection: direct reflection in one direction only ( compare diffuse reflection).
Steradian: the solid angle at the centre of a sphere which cuts an area on the surface of the sphere equal to the size of the radius squared.
Temperature: the condition of a body that determines whether heat shall flow from it (unit: degree Kelvin).
Thermal admittance: the ability of a material or construction element to exchange heat when subject to variations in temperature, such as over a 24-hour period (Unit: W/m2 K).
Thermal bridge: a portion of a structure with higher thermal conductivity that increases heat flow and lowers the overall thermal insulation of the structure.
Thermal comfort: ‘that condition of mind which expresses satisfaction with the thermal environment’ (BS EU ISO 7730).
Thermal conductivity: a measure of the rate at which heat is conducted through a particular material under specified conditions.
Thermal conductivity: a measure of the rate at which heat is conducted through a particular material under specified conditions.
Thermal mass parameter: an overall figure for the thermal mass of a building that is derived from the admittance of individual elements.
Thermal resistance: a measure of the opposition to heat transfer offered by a particular component in a building element (Unit: m2 K/W).
Threshold of hearing: the weakest sound that the average human ear can detect.
Threshold of pain: the strongest sound that the human ear can tolerate.
Traffic Noise Index LA10: an average of the 18 hourly L10 values taken between 0600 and 2400 hours on a normal weekday.
Transmittance see linear thermal transmittance
Uniform sky: a standard overcast sky which is taken to have the same luminance in every direction of view.
Utilisation factor: the ratio of the total flux reaching the working plane compared to the total flux output of the lamps.
U- Value: a measure of the overall rate of heat transfer, by all mechanisms under standard conditions, through a particular section of construction (Unit: W/m2 K).
Vapour barrier/check: a layer of building material which has a high resistance to the passage of water vapour.
Vapour diffusivity (permeability): the reciprocal of vapour resistivity.
Vapour pressure: the partial pressure exerted by the molecules of a vapour (unit: pascal).
Vapour resistivity/resistance (rv): a measure of the resistance to the flow of water vapour offered by unit thickness of a particular material under standardised conditions (unit: GN s/kg m).
Vapour: a material in the gas state which can be liquefied by compression, without change in temperature.
Vector/scalar ration: a measure of the directional strength of light at a particular point.
Velocity: the distance moved per second in a fixed direction (unit: metres per second).
Vernacular: in the local style.
Wavelength: the distance between any two repeating points on a wave (unit: metre).
Y-value see thermal admittance