Glossary M-R

concrete, concrete block brick, adobe, stone and other similar materials
the quantity of matter in body as measured by the ratio of the force required to produce a unit acceleration
mass-area-to-glazing-area ratio
the ratio of the total surface area of massive elements to the glazing area. Massive elements including in this definition are all floors, walls ceilings, or other interior objects with densities comparable to high-density concrete provided their surfaces are exposed and located in a room that is at least partially illuminated by direct solar gains
écart moyen (FR)
mittlere Abweichung (DE)
middelfeil (NO)
MBD mean bias deviation
Unit: %
Quantity defined by the formula: Used to characterize the bias of a model. Negative, if the model underpredicts, positive, if it overpredicts.
mean radiant temperature (MRT)
the area weighted mean temperature of all surrounding surfaces, i.e. sum of (s.t)/ sum of (s), where 't' is the temperature of each surface of angular area 's'. Also the temperature of a uniform black enclosure in which a solid body or occupant would exchange the same amount or radiant heat as in the existing nonuniform environment. It is an approximate indication of the effect that the surface temperatures of surrounding objects have on human comfort
mechanical system
a term widely used in commercial and industrial construction, referring to all the mechanical components of the building. i.e. plumbing, heating, ventilation, air conditioning and heat recovery
méridien (FR)
Meridian (DE)
meridiano (ES)
meridiano (IT)
meridian (NO)
Considering a great circle on the surface of the earth passing through the poles, a meridian is the half of this circle included between the poles.
meta analysis
a method of analysis which combines the results of a number of surveys to investigate the underlying processses
metabolic rate
micro climate
mixed systems
a solar heating system that combines two or more passive solar heating types
mixed-mode systems
heating or cooling systems which combine passive and mechanical systems
natural convection
heat transfer between a surface and adjacent fluid (usually air) and by the flow of fluid from one place to another, induced by temperature differences rather than by mechanical means, also called free convection. Compare with forced convection
natural convection air cooler
an air cooler depending on natural convection for air circulation
natural light
visible part of direct solar radiation. (Note: when dealing with actinic effects of optical radiations, this term is commonly used for radiations extending beyond the visible region of the spectrum.)
natural ventilation
Air which enters a building controlled, through open windows or other openings, due to wind pressue or temperature differences between the outdoor and indoor air
negative pressure
a pressure below atmospheric. In residential construction negative pressure often refers to pressures around the house that is less than the indoor or the pressures on e.g. the windward side of the house: such variations in pressure will encourage infiltration by cross ventilation
net load coefficient (NLC)
net reference load per degree of indoor-minus-outdoor temperature difference per day
net reference load
steady-state heat loss from a building, excluding the solar wall, assuming constant indoor temperature. Compare with net load coefficient (J)
facteur de transmission normale (FR)
normale Tansmission (DE)
transmitancia normal (ES)
fattore di transmissione normale (IT)
vinkelrett transmittans; vinkelrett transmisjonsfaktor (NO)
τn normal transmittance
Unit: 1
Ratio of the transmitted radiant or luminous flux to the incident flux striking the material in a direction perpendicular to its surface.
night insulation
movable insulation that covers a glazing at night and is removed during the day
night radiance
Heat radiance which appears at night: When the sky is clear at night a surface facing the sky sends and receives heat radiance to and from the sky. The radiant temperature of a clear sky is usually well below zero, particularly at night. Because of this the surface temperature can easily descend below the ambient outdoor air temperature
night ventilation
normal distribution
A frequency distribution that predicts the probability that a variable will take a certain value; the distribution is symmetrical about the mean value. Based on statistical theory, the normal distribution underlies much statistical analysis
(in daylight calculations) anything outside a building which prevents the direct view of part of the sky
épaisseur optique de l'atmosphère (FR)
Optische Dicke der Atmosphäre (DE)
Espesor óptico de la atmósfera (ES)
Spessore ottico verticale dell'atmosfera (IT)
Optische dichtheid van de atmosfeer (NL)
atmosfærens optiske tykkelse (NO)
Gestosé optyczna atmosfery (PL)
Atmosfärens optiska täthet (SE)


optical thickness of the atmosphere
Unit: 1
CIE. Quantity defined by the formula: δ(ε)=-ln(Φ’ee) Where Φe is the radiant flux of a collimated beam entering the upper limit layers of the atmosphere at an angle ε to the vertical, and Φ’e the attenuated radiant flux of that beam reaching the surface of the Earth. (In English, the term optical depth is sometimes used instead of optical thickness).
The azimuth of a particular surface or the major axis of a building. see azimuth
outside air
external air, atmosphere exterior to refrigerated or conditioned space, ambient (surrounding) air
overcast sky
A sky in which there is no direct solar radiation. NOTE: The measured temperature data and solar radiation tables for overcast skies within this Handbook refer to days when the cloud cover was 8/8 during all the daylight hours. Night-time temperature data are related to the same 'overcast' days, i.e. night-time cloud cover was not taken into account.
unit of pressure. House air tightness tests are typically conducted with a pressure difference of 50 Pascals between the inside and outside. 50 Pascals is equal to 5.008 mm (0.2 in) of water at 12.9oC
passive solar energy
Solar energy collected by non active systems e.g. windows, atria etc.
percent of possible sunshine
the actual number of hours of sunshine expressed as a percentage for the month (or other period of time)
percent radiation received
the monthly mean Global Radiation of a horizontal plane, expressed as a percentage of the monthly mean radiation on a horizontal plane outside the atmosphere
water vapour permeance is the rate of water vapour diffusion through a sheet of any thickness of material (or assembly between parallel surfaces). It is the water vapour flow to the differences of the vapour pressures on the opposite surfaces. Permeance is measured in perms (m².K/W)
water vapour permeability is a property of a substance which permits passage of water vapour. When permeability varies with psychrometric conditions, the 'spot' or 'specific permeability' defines the property at a specific condition
phase change materials
materials with a phase change point close to the desired room temperature which can be used either to reduce temperature fluctuations within a room or to store energy in the phase change process (usually melting) and re-releasing it to the system when its temperature falls below the transition point. Phase change materials may be surface mounted as in phase change tiles or storage based as in latent heat stores for active solar systems (see latent heat)
observateur de référence photométrique CIE (FR)
photometrischer Normalbeobachter CIE (DE)
observador fotométrico patron CIE (ES)
osservatore fotometrico CIE (IT)
fotometrische standaardwaarnemer (van der CIE) (NL)
CIE fotometriske standardobservatør (NO)
obserwator fotometryczny CIE normalny (PL)
CIE standardobservatör för fotometri (SE)
  photometric observer CIE standard
CIE. Ideal observer having a relative spectral responsivity curve that conforms to the v(λ) for photopic vision and that complies with the summation law implied in the definition of luminous flux.
vision photopique (FR)
Tagessehen; photopisches Sehen (DE)
visión fotópica (ES)
visione fotopica (IT)
fotopisch zien (NL)
fotopisk syn; dagssyn (NO)
widzenie fotopowe (PL)
fotopiskt seende; dagseende (SE)
  photopic vision
CIE. Vision by the normal eye when it is adapted to levels of luminance of at least several candelas per square meter (i.e. under daylight).
pixel (FR)
Bildelement, Pixel (DE)
pixel (ES)
pixel (IT)
pixel (NO)
A small discrete element which with other elements, consitutes an image.
predicted mean vote (PMV)
The average comfort vote predicted by a theoretical index (generally that of Fanger) for a group of subjects when subjected to a particular set of environmental conditions
positive pressure
a pressure above atmospheric. In residential construction positive pressure often refers to pressures around the house that is above than the indoor or the pressures on e.g. the leeward side of the house or above the roof: such variations in pressure will encourage infiltration by cross ventilation
predicted percentage dissatisfied (PPD)
The percentage of subject population who will be dissatisfied (uncomfortable) in a given environment as predicted by a theoretical index (generally that of Fanger). see PMV
preverence vote
The response by a subject as to their preference at the time of asking; this may be a preference for a warmer or cooler environment, or for a particular response on a comfort scale
in air conditioning: to heat the air before other processes
the normal force exerted by a homogeneous liquid or gas, per unit of area, on the wall of the container
Probit analysis
A statistical analysis whereby the proportion of people casting different comfort votes at a particular temperature can be estimated for a population from the results from a sample
The branch of psychology dealing with the relationship between our sensations and the stimuli from the physical world
the study of the interactions between temperature and water vapour in air. Includes relative humidities, wet and dry bulb temperatures, enthalpy, and so on
R value
the thermal resistance to heat flow across a sample material of a unit area and known thickness caused by a temperature difference across it. This is often used to give a comparative value of the effect of different insulating materials. (m².K/W)
luminance énergétique; radiance (FR)
Radianz; Strahldichte (DE)
radiancia (ES)
radianza (IT)
radiantie (NL)
radians (NO)
luminancja energetyczna (PL)
radians (SE)
Le radiance (in a given direction, at a given point of a real or imaginary surface)
Unit: W/(m² sr)
CIE. Quantity defined by the formula: Where dΦe is the radiant flux transmitted by an elementary beam passing through the given point and propagating in the solid angle dΩ containing the given direction: dA is the area of a section of that beam containing the given point: θ is the angle between the normal to that section and the direction of the beam.
flux énergétique (FR)
Strahlungsleistung (DE)
flujo radiante (ES)
flusso energetico (IT)
stralingsstroom; stralingsvermogen (NL)
strålingsfluks (NO)
strumien energetyczny; strumien promienisty (PL)
stralningsflöde;stralningseffekt (SE)
&Phie radiant flux ; radiant power
Unit : W
Power emitted, transmitted or received in the form of radiation.
radiant heat transfer
the transfer of heat energy from a location of higher temperature to a location of lower temperature by means of electromagnetic radiation. Radiant heating is due to infrared radiation and its use is very prevalent in passive systems. see also infra-red radiation
Apparatus for heating of a room, which gives off heat to the space by radiation and convection
atmosphère de Rayleigh (FR)
Rayleigh Atmosphäre (DE)
atmósfera de Rayleigh (ES)
atmosfera di Rayleigh (IT)
atmosfeer de Rayleigh (NL)
Rayleigh atmosphere
An ideal atmosphere containing only air molecules (the earth atmosphere also contains aerosols, cloud droplets and ice crystals). Used by Rayleigh in 1871 to discover one of the most important example of a physical law of light scattering.
recirculated air
return air passed through the conditioner before being resupplied to the conditioned space. The air contditioning unit takes in outdoor air but also a part from the rooms
reference design
a detailed specification of the passive solar features of a hypothetical passive solar building used as the subject of performance analysis
reference temperature
a fixed indoor temperature in the definition of the net reference load. also the fixed indoor temperature in the reference nonsolar building used in the definition of solar savings
facteur de réflexion (FR)
Reflexionsgrad (DE)
reflectancia (ES)
fattore di riflessione (IT)
reflectiefactor (NL)
reflektans; refleksjonsfaktor (NO)
wspolczynnik odbicia (PL)
reflektans; reflexionsfaktor (SE)
ρ reflectance (for incident radiation of given spectral composition, polarization and geometrical distribution)
Unit: 1
CIE. Ratio of the reflected radiant or luminous flux to the incident flux in the given conditions. The reflectance is also called the albedo for a radiant flux.
reflectance of glazing material
radiant energy is reflected from both inside and outside surfaces of a sheet of parallel sided glazing. Multiple inter-reflections occur within the glazing. The ratio of the overall reflected radiant energy to the incident radiant energy is known a the reflectance. Its value depends on the angle of incidence. Energy interreflected from the inside face is dependent on the absorbitivity of the material and so is also dependent on wavelength. For any wavelength and angle of incidence, absorptance reflectance + transmittance = 1
reflectance of opaque materials
refractive index
a property of glazing materials that determines the reflection/refraction characteristics of the glazing
regenerative cooling
process of utilizing heat which is rejected or absorbed in one part of the cycle to function usefully in another part of the cycle by heat transfer
regression (linear)
A statistical technique by which the variation of a dependent variable can be predicted from the value of an independent variable (or variables) through a Regression Coefficient (or coefficients) plus a constant term. (y = a.x + b)
reheating of air
in an air conditioning system, the final step in treatment in the event the temperature is too low
relative humidity
the water vapour pressure in the air expressed as a proportion of the saturated water vapour pressure (ie the highest possible value) at the current air temperature
masse d'air optique relative (FR)
relative optische Luftmasse (DE)
masa optica del aire relativa (ES)
massa ottica relativa dell'aria (IT)
relatieve optische lu.htmlassa (NL)
relativ optisk luftmasse (NO)
gaestosv optyczna atmosfery wzgledna (PL)
relativ optisk luftmassa (SE)
m relative optical air mass
Unit: 1
CIE. Ratio of the slant optical thickness δ(ε) to the vertical optical thickness δ(0) of the atmosphere m=δ(ε)/δ(0). When the curvature of the atmosphere and atmospheric refraction are neglected, we have: m=1/cos(ε).
relative sunshine duration
ratio of sunshine duration to possible sunshine duration within the same period
resistance value (RSI)
thermal resistance value. Measurement of the ability of a material to resist heat transfer
the thermal resistance of unit area of a material of unit thickness to heat flow caused by a temperature difference across the material. (m²K/W)
production of carbon dioxide and heat by ripening of perishables in storage; also the breathing process of animals
room temperature
used colloquially to mean the ordinary temperature one is accustomed to find in dwellings. Technically it can mean the temperature of (l) a room in which a refrigerator is being operated or tested; (2) a room being conditioned for the occupant's comfort
écart quadratique moyen (FR)
Wurzel der mittleren quadratischen Abweichung (DE)
roten av midlere kvadratfeil (NO)
RMSD root mean square deviation
Unit: %
Quantity defined by the formula: Used to characterize the bias of a model in absolute terms.