Thermal indices for the built environment
This page presents a summary of thermal indices used in the construction industry. For more information go to the articles for each item. To add more items, click 'Edit this article' above.
Degree days. The number of days and degrees that the outside air temperature is above or below a specified base temperature. See Heating degree days.
Emissivity. The amount of long wave infra-red radiation which a surface of known temperature (such as the façade of a building) will emit to its surroundings.
g-value (sometimes referred to as window solar factor, solar factor or total energy transmittance (TET)). The fraction of incident solar radiation transmitted by a window, expressed as a number between 1 and 0, where 1 indicates the maximum possible solar heat gain, and zero, no solar heat gain. NB The difference between g-values and solar heat gain coefficients is that they use a different value for air mass.
k value (or lambda value λ). A measure of the intrinsic thermal conductivity of a material, that is, how easily heat passes across it. This is a fundamental property independent of thickness.
Predicted percentage dissatisfied.
Psychometric charts. Graphs that can be used to assess the physical and thermodynamic properties of gas-vapour mixtures at a constant pressure.
R-value. A measure of the thermal resistance of a material of a specific thickness.
Shading coefficient. The amount of solar heat that passes through a transparent or translucent material compared to the amount of solar heat that passes through a sheet of clear float glass with a total solar heat gain coefficient of 0.87 (ie a sheet of clear float glass 3mm thick which has a shading coefficient of 1).
Solar heat gain coefficient. The fraction of incident solar radiation transmitted by a window, expressed as a number between 1 and 0, where 1 indicates the maximum possible solar heat gain, and zero, no solar heat gain. NB The difference between g-values and solar heat gain coefficients is that they use a different value for air mass.
Temperature. A measure of the average kinetic energy of molecules.
Thermal comfort. ‘…that condition of mind which expresses satisfaction with the thermal environment’.
Thermal optical properties. Characteristic radiant behaviour within the thermal spectrum.
U-value (or heat transfer coefficient). A measure of the thermal conductivity of a complete building element, including its surface conductivities.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Getting the most out of heat pumps and heating
How heat pumps work and how they work best.
Plumbing and heating for successful retrofit and renovation
Low temperature underfloor systems and heat pumps.
Cost-of-living crisis and home improvement plans
Starting on the right footing and top tips for projects.
Delays on construction projects
Types, mitigation and the acceleration of works.
From Chaucer to Fawlty Towers.
Electrotechnical excellence, now open for entries.
Net zero electricity grids BSRIA guide NZG 5/2024
Outlining the changes needed to transition to net zero.
CIOB Global Student Challenge 2024
Universitas Indonesia wins for second year running.
New project and cultural district described in detail.
The nature of EPCs, crticism and inaccuracies.
History, issues and redesign.
From waste recycling to energy performance the hierchy.
An introduction to WERCS and WEEE responsibilities
Dealing with 2 million tonnes of waste equipment a year.
Global BACS Market: analytics and optimisation
A BSRIA glance at building automation and control systems.
What it is and how to use it.
Types of insulating plaster by binder and insulant.
Investors in People: CIOB achieves gold
Reflecting a commitment to employees and members.
Scratching beneath the surface; a guide to selection.
ECA 2024 Apprentice of the Year Award
Entries open for submission until May 31.
UK gov apprenticeship funding from April 2024
Brief summary the policy paper updated in March.