Thermal
Building Envelope – The physical separator between the internal environment of a building and the external environment, including resistance to air, water, heat, light, and noise transfer.
Façade – Typically the vertical element of a building envelope, between the Floor and Roof, which provides resistance to air, water, heat, light, and noise transfer. The façade will typically encompass Wall and Glazing. (Façades may also be non-vertical/angled).
Façade Performance – A benchmark overall performance value for the façade alone, constituting opaque wall and glazed elements and excluding the roof and the floor. This provides the option to improve the Overall Thermal Performance of the façade as Selected Façade Performance.
Floor – The element on the lowermost part of a building envelope, which provides resistance to air, water, heat, light, and noise transfer.
Glazing – The transparent/translucent components of the façade. This denotes the framing and structure that supports these components.
Overall Heat Loss Method – Maximum acceptable level of transmission heat loss through the building envelope in terms of the maximum average U-Value of all elements contributing to heat loss.
Overall Performance – A benchmark overall thermal performance value for the envelope of the entire building to include walls, glazing, floor, and roof.
Roof – The element on the uppermost part of a building envelope, which provides resistance to air, water, heat, light, and noise transfer.
R-value – Measurement of thermal resistance, which relates to a building element and is a measure of the resistance to heat passing through that element when unit temperature difference is maintained between the ambient air temperatures on each side. It is expressed in m2K/W or ft2 °F hr/ BTU.
Thermal Performance – The measurement of energy transfer through the building envelope, between the internal environment of a building and the external environment.
U-value – Measurement of thermal transmittance, which relates to a building element and is a measure of the rate at which heat passes through that element when unit temperature difference is maintained between the ambient air temperatures on each side. It is expressed in W/m2K or BTU/ft2 °F hr.
Wall – The opaque components of the façade.
Solar
Shading Factor – A value that represents the ratio between the area of glazing that is shaded and that which is unshaded. It indicates the amount of solar heat gains that will be transferred through the glazing. Shading will typically be provided by a shading device or surrounding feature.
Solar Heat Gain – Solar Heat Gain is the heat from the sun being collected and contained per unit floor area of space. It is measured in W/m2 or BTU/ft2 hr. Factors which influence this are the performance of the glazing, tints or coatings, patterned glass (depending on coverage and transparency of the pattern), internal/external shading devices, shading effects of neighboring buildings, trees or external features etc.
Solar Over Heating – Heat Gain that exceeds a benchmarked level that will cause occupant discomfort/increased cooling loads.
Solar Radiation – Radiant Energy of the sun which will vary depending on location, season, time of day, landscape and weather. Most of this radiant energy is either in short wave or infrared form. A smaller proportion is Ultraviolet rays. The sun can also be at various angles to a surface. The lower the angle, the more diffuse/scattered the rays will be through the atmosphere.
Solar Transmittance – Property of glazing that controls the amount of solar heat gains into the space It is typically represented as Solar Heat Gain Coefficient and will range from 0 – 1. The lower this figure is, the more effective the glazing will be at blocking solar heat eg. 0.1 will allow less Solar Heat through than 0.9. Modern glass which blocks Solar Transmittance does not necessarily mean that light will also be blocked.
Daylighting
Average Design Daylight Factor – A ratio of the internal daylight level of a space to the external daylight level, per unit floor area of the perimeter zone. It is calculated at design stage and is measured as a percentage.
Diffuse Transmittance/ Visual Light Transmittance – Coefficient of daylighting that can be transmitted through a glazing material, which includes the effects of dirt (denoted by Maintenance Factor). The higher the diffuse transmittance, the more daylight will pass through. This is affected by several factors; the number of glass panes in the assembly, coatings and the glazing type (clear or bronzed etc). Tinted glass can reflect a lot of light so that only 10% may pass through. Clear glass may allow 90% light through.
Maintenance Factor –Adjustment for percentage loss of daylighting through dirt on the glazing, compared to clean glazing in Rural/Suburban/Urban environments.
Reflectance – Area weighted average reflectance of internal surfaces (ceiling/floor/walls/windows) depending on their color (light/medium/dark).
Surrounding Features – Buildings, structures, or other obstructions that will reduce the angle of sky and therefore, the amount of daylighting internally.
