Study shines a light on shading
The study, undertaken by Newcastle-based retailer Classic Blinds and the University of Newcastle in collaboration with German awning manufacturer Markilux, involved the creation of two temperature-regulated rooms in which various internal and external shading products were installed and their effectiveness tested.
Stephen O'Keeffe, managing director of Classic Blinds said the project had emerged as a response to a saturated market in which “dubious claims” were often made about products’ capabilities, adding it was hoped the research would help consumers clearly understand the value of their investment in window furnishings. He also indicated that commonly used measurements such as R-values, did not enhance consumers’ understanding of products’ capabilities. An R-value is a measure of thermal resistance comprising the ratio of the temperature difference across an insulator and the heat flux through it.
“The purchase of a high-performing, high-quality product is a significant financial investment, so our industry needs to ensure that claims about window furnishings and their efficiency are backed by accurate information,” said O’Keeffe.
“The statement, for example, that a product is ’70 per cent more effective than timber at reducing heat’ is a bold claim that should be based on quantitative evidence. A claim that, for instance, a product will ‘reduce energy bills by 86 per cent’, is potentially very misleading.”
Consumers also needed to understand that other variables would affect the efficiency of the products, he said, for example how the window is fitted, the effect of gaps and convection on thermal efficiency; and the potential for fitting and measuring errors to also reduce the efficacy of window furnishings.
Commissioned from the University of Newcastle by O’Keeffe, one of the study’s objectives was to create a ‘star’ system, to provide clear information about how effective a window covering was and comparisons on light and thermal efficiency with other products.
“When a customer asks, ‘Is a Western Red Cedar shutter better at stopping heat ingress than an aluminium shutter?’ or, ‘Is it better to have a roller blind fitted within the reveal or face-fit?’, this ‘star rating system’ will allow fast and easy comparisons of the most common window coverings,” said O’ Keeffe.
He also pointed out that the use of different colours in different products created a “massive” variation in efficiency between window coverings of the same type but different colour.
“This research compared Satin Black and Satin White versions of test coverings. A customer may eventually choose a different colour, such as Dark Brown or Gloss White, but now they are able to consider the potential range of efficiency of their chosen window covering.”
In terms of the seriousness of the undertaking, O’Keeffe pointed out that the investment in building the test chambers and measuring equipment was considerable, but it ensured that temperature results were accurate to within +/- 0.5 of one degree.
“At its most simple, the testing was done by creating two identical, thermally-stabilised ‘rooms’. The entire test environment was stabilised with 24-hour air-conditioning to 22C. Two simple heat sources were applied to the rooms with precisely the same amount of heat and a window covering was placed in one of the test rooms to test against the control room.”
Prior research conducted by the University of Newcastle had shown that the maximum heat gain through windows was only about 40 per cent of the heat gain of a building; the rest of the heat coming through the walls, roof and slab.
“The best possible reduction in heat gain in a building using window coverings alone is therefore 40 per cent.”
In these tests, an ‘ultimate window covering’ (UWC) – a polystyrene panel 60mm thick – was chosen as a control to block the test window and set a benchmark. The reduction of heat gain in the test chamber using the UWC was 39.7 per cent– very close to the achievable maximum of 40 per cent.
Subsequent thermal testing on window coverings showed that Western Red Cedar reduced heat gain by about 32.1 per cent - a very, very good result. By comparison, slimline aluminium venetians tested at 18.5 per cent.
“All the window coverings tested, both internal and external, reduced heat to some degree, but in order to create a star rating system that would be meaningful for consumers, they had to be compared against other materials.”
Testing showed that for internal window furnishings, lighter colours were better at reducing heat than darker colours. The research also showed that some materials have more variation between colours than others. For example, for a thermally-resistant material like Western Red Cedar, the difference in thermal efficiency between black and white versions is far less than in a material like aluminium. Upon testing external fittings, awnings, the research revealed the reverse. A black awning will absorb more heat and not as much light will penetrate, but a white awning will allow the light to bounce around between the awning and the glass, transferring energy to the glass and allowing heat to transmit.
To emphasise the importance of providing clear information to consumers, O’Keeffe pointed out that there had been claims that one product included in the testing would save 86 per cent from an energy bill.
“The product showed a thermal reduction of 31.1 per cent, which is good and comparable to a Western Red Cedar shutter. While the product is thermally efficient, the concern here is the claimed reduction on an electricity bill. To quantify and verify such a claim, an enormous number of variables would have to be known, and many such claims are, at best, misleading.”
“As an industry, we should never make claims to customers that we can save ‘x’ per cent from their energy bills. All we can say is that ‘x’ will be a more effective product than ‘y’.”
O’Keeffe confirmed that the results of the study had been peer reviewed by the University of Newcastle and the report finalised.
“Interestingly enough, using standard R-value techniques, in other words a guarded hot box, doesn’t take into account any incident radiation. R-values are calculated on the heat flux via two stable thermal environments; colour has virtually no effect.”
“The thermal conductivity of window coverings, and R-value indirectly, seems to be less significant because the window allows heat to be reflected back to the external environment and the radiation is a major driver of the thermal performance of tested products.”
“The thermal performance of window coverings is then much more influenced by the colour of the window coverings, as the darker colours absorb more heat within the internal side of the chamber and then conduction and convection play a more significant role than the radiation for lighter colours."
O’Keeffe concluded that any calculations or computer models based on R-values and not colour would be “pretty meaningless.”
A beneficial by-product of the study is that it enabled Classic Blinds and Shutters to further develop the way it fits window furnishings and make investment in the design, testing and patenting of an ‘eco frame system’, which seals around the edge of the shutter panel and closes within its own frame. This keeps the heat between the back of the shutters and the reveal by removing any convection currents. This system is now available.
The results of the research are available via the Classic Blinds website www.classicblinds.com.au. Other retailers are encouraged to download them and for use on products in their showrooms.
This research is the first of its kind in Australia and was made possible with the assistance of the University of Newcastle, and generous provision of products from Markilux, Helioscreen, Bartlett’s Blinds and Open Shutters; special thanks to these companies for their support. Other products, including imported Chinese-manufactured items, were purchased for testing as necessary. Classic Blinds has undertaken to continue testing products upon request.
released: Monday, June 15, 2015
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