As many architects and building engineers will know, thermal transmittance is usually expressed as a U-value as this is the industry standard measure of the rate of heat loss through any sort of building component. Most engineers will express the process in terms of Watts per square metre, per degree Kelvin, or as W/m2K as well a U-value. When it comes to the thermal bridge analysis of an aluminium door facade or window frame, the U-value of the glazing and of the product as a whole is commonly given. This is because many aluminium frames are now fitted with a polyamide insulation profile. Therefore, clients and inspecting authorities want to understand fully how the addition of a polyamide thermal break is reducing heat loss in winter and preventing overheating in summer. Of course, since standard window products placed in different positions of a building will perform differently, new calculations are required for every design alteration. Furthermore, where bespoke aluminium-framed products are specified - perhaps for a facade, a curtain wall or an atrium – technical analysis is required from the start. In both cases, often the speediest method of gaining a good understanding of the expected performance is with specially designed software for thermal bridge calculation.
Architectural Modelling for the Simulation of Radiation and Convection
Partly because of the American Institute of Architects' (AIA) commitment to drastically reducing carbon wastage in buildings through heat loss by 2030, there has been a significant uptake in modelling the future performance of windows in many construction projects. Commercially available software has been available to designers since it was first developed in 2002. Nowadays, the demands of many architectural projects for using aluminium-framed glazing in ever-more imaginative ways is so great that the simple two dimensional modelling software of the early days is no longer deemed to accurate enough. Although 2D modelling software can be great for demonstrating to clients the need to locate windows in optimal positions, by allowing them to see heat flow lines, three dimensional software is often regarded as superior in terms of its accuracy. According to the AIA, the most commonly used software package in the United States for simulating radiation through windows and walls is Sefaira which accounts for about 30 per cent of the market. Sefaira allows for 3D visualisations of daylight simulations and can be used for the optimisation of air cavities as well as producing data for projected surface condensation. EnergyPlus, used as a thermal plug-in with DesignerBuilder or OpenStudio, is another popular choice as is IESVE.
"I especially like the fact that I can compare different versions [of the software]... with almost no effort, and thus quickly come to an optimal solution." - Markus Brunner, architect and energy consultant.
Professional Software Applications for Optimal Results
It is important to note that AIA's own studies have pointed out that although projects which have used modelling software outperform those which have not, in terms of their carbon neutrality, many modelled projects still fall behind the ambitious targets laid out under the 2030 challenge. What may account for this is that many of the software applications used, however sophisticated they might be, are programmed for general design use. Professional software is really needed to gain a truly accurate understanding of how aluminium windows and doors will perform in a given space and this means it often needs to be run by experts, sometimes the window manufacturers themselves. According to Arild Gustavsen et al, 2D and 3D modelling needs to exceed the current ISO standards in order to give a really accurate prediction of future performance. Usefully, specialist software applications are around which can model aluminium thermal break profiles with a stunning degree of success in their pro-level versions. Available as a free trial version, for example, Flixo provides indicative ratings for architects as well as being able to be used by expert window engineers to determine the U-values of a window, or a facade element, in accordance with the component assessment method required under EN ISO 10211 and EN ISO 10077-2.
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