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Solar shading meets thermal performance


When specifying solar control, not just any curtain walling bracket will do if the thermal performance of the building facade is not to be compromised, says solar shading and screening solutions provider Levolux


closer scrutiny. A glazed facade, formed from a modern curtain walling


W


system, will still be susceptible to excessive solar heat gain when it is exposed to direct sunlight for long periods. This can have a significant impact on the cooling loads of a building. While a degree of solar gain is appreciated in winter, if left unchecked, it will make a building overly dependent on air conditioning during the summer. As energy costs have soared over recent years, this has


changed the focus of architects not only on meeting the required building regulations and satisfying a client’s brief, but also on maximising the thermal performance of buildings. Buildings are increasingly designed with greater emphasis on


passive cooling techniques. This demands a more considered approach to curtain walling, as there is often very little flexibil- ity for it to accommodate external solar control devices. Shading performance for devices can vary enormously and


this is defined by a Solar Heat Gain Coefficient (SHGC) rating. For instance, a double glazed opening without any form of solar control will have a SHGC rating of around 0.65. The same double glazed opening fitted with moveable horizontal fins will have a SHGC rating of around 0.1. While it is important for an architect to consider the SHGC


rating of a shading device, attention should also be given to how the device is secured to the curtain walling. Any savings that


may be achieved by incorporating a shading device with a high SHGC rating can very easily be undermined if the bracket used does not incorporate an effective thermal break. Typical curtain walling brackets may satisfy load-bearing


requirements and may be compatible with a range of curtain walling systems, but perhaps the more important question is how they penetrate the curtain walling mullion. If the bracket does not incorporate a comprehensive thermal break, then it will be susceptible to cold bridging, acoustic and vibration transmission and interstitial condensation. Under Part L of the building regulations, a new commercial building must have a U-value of less than 2.2 W/m2


Perforated red screening, Citylabs (former Royal Eye Hospital), Manchester (above) and timber fins, University of Derby (left)


hile glass continues to be the predominant cladding material for commercial buildings, its thermal performance is now being placed under


K. One of


the key considerations for engineers when targeting a low U- value, is the thermal transmittance rating, or ‘χ‘, of materials used to form the building envelope. If a curtain walling bracket compromises the thermal break of the curtain walling, this will raise the U-value of the entire building envelope, possibly by as


Continued overleaf... respond online at www.architectsdatafile.co.uk


‘Buildings are increasingly designed with greater


emphasis on passive cooling techniques’


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