Glossary

Air permeability
The unintended leakage of air through gaps and crack in the external envelope of a building.

Conduction
The transfer of heat between substances that are in direct contact with each other.

Convection
The transfer of the heat in fluid or air, caused by the movement of the heated air or fluid itself. In a building warm air rises and cold air settles to create a convection loop and is termed free convection.

g-value
The measure of the total energy passing through the glazing when exposed to solar radiation.

gtot
The measure of the total energy transmittance of the glazing in combination with the blind or other shading when exposed to solar radiation. Also known as the Solar Factor.

Glare
The condition of vision in which there is discomfort or a reduction in the ability to see significant objects, due to an unsuitable distribution of or range of luminance.

Light Transmittance (Tv)
The proportion of visible light transmitted through the shading material.

Lux
The measure of illuminance on a surface (1 lux = 1 lumen/m2).

Nanometers (nm)
A unit of one billionth of a metre, which is used to measure the wavelength of the light emitted by the sun.

Natural Ventilation
The supply of adequate fresh air to space within a home through windows, trickle vents etc. Removal of air may take place by natural or mechanical means.

Openness Coefficient
The ratio between the area of openings in the fabric/material and its total area.

Qi
It results from heat transfer by convection and longwave infra-red radiation of that part of the incident solar radiation which has been absorbed by the glazing. It is the absorbed heat that will not go back through the glass.

Radiation
The emission or transfer of energy in the form of electromagnetic waves or particles transferring energy from a warm body to a cold body without heating the air in between.

Standard Assessment Procedure (SAP)
A software that calculates the energy performance of dwellings. It has been developed by the Building Research Establishment (BRE) for the Department of Energy and Climate Chance (DECC). SAP assess the cost per year to provide a home with heating, lighting and hot water and presents the cost per square metre of floor area.

Simplified Building Energy Model (SBEM)
A software that calculates the energy performance of buildings that are not dwellings. It was developed by the Building Research Establishment (BRE) for the Department of Communities and Local Government (DCLG). SBEM estimates the amount of CO2 emissions produced by the building per square metre of floor rather than the cost.

Solar Gain
The solar radiation that enters the building through glazing hits objects and is converted to heat. This reduces the need to artificially heat the space.

Solar Reflectance (Rs)
The measure of the fraction of solar energy reflected by the fabric. A high value means that the fabric performs well at reflecting solar energy.

Solar Transmittance (Ts)
The measure of the fraction of the solar energy transmitted through the fabric. A low value means that the fabric performs well at reducing solar energy transmission.

SUV
Outside shading UV classification of the ability of an outside shading product to reduce UV transmission to those beneath it.

U-value
A measure of thermal conductance which is the ability of a material to transfer heat.