In the old days, many homes and businesses had relatively few and small windows.
Nowadays, many offices and apartments feature glass facade coverage from floor to ceiling. With roof and wall insulation being more common, the portion of heat exchange occurring through windows has grown.
In a traditional building, heat loss through windows accounts for between 10 and 25 per cent of all heat loss throughout the building, according to Australian Windows Association executive director and chief executive officer Tracey Gramlick. When roof and walls are insulated, this rises to between 60 and 80 per cent, Gramlick says.
Not surprisingly, therefore, windows have emerged as a focal point in the push toward more sustainable buildings and cities. Whilst double glazed windows are now common especially in southern states, attention is turning to ‘smart windows’ which change colour and the amount of light they emit according to changes in temperature.
In May, Professor Hujin Zhao, director of Griffith’s Centre for Clean Environment and Energy at Griffith University, was awarded $513,210 through the Australian Research Council’s Linkage Projects scheme. This funding will be used together with other money and in-kind support from Confirmation Australia Pty Ltd to develop low-cost and scalable syntheses of functional nanomaterials which will enable the development of windows containing glass which is able to achieve this effect.
Zhao says the importance of windows must not be underestimated. Thanks to a combination of heat exchange through windows being 10 times greater than that through insulated walls and windows comprising a growing portion of building surface area in modern buildings, he said windows are now a significant factor in overall heat exchange. Given that HVAC in offices accounts for around 70 per cent of energy consumption, cost savings from reducing heat exchange through windows and thus reducing the degree of reliance upon HVAC are substantial.
Essentially, Zhao said, his project will develop a functional nanomaterial which will serve as a coating material and will change its crystal structure above a critical temperature so as to block heat from the external environment to enter into the building and vice versa to prevent heat inside from escaping outside whereby the temperature drops below a given threshold.
Zhao says there are a number of technologies through which this can be achieved. In his project, two approaches will be used. Under one method, thermochromic materials will be used which will change their colour when temperature changes. In the other, liquid crystals similar to those used in televisions to change the colour of the material are applied to the window. Essentially, this will involve a thin layer coating on the glass using a blend of graphene and other materials.
Zhao says these applications will enable the glass within the window itself to partially control building temperature and will reduce reliance on heating, ventilation and air-conditioning. Through these approaches, he says, energy consumption at a laboratory scale can be reduced by half, although he says likely savings at the industrial scale are difficult to estimate.
“Basically, when the outside is hot, you won’t need to turn your air-conditioner on as often as you do now with a normal glass window,” Zhao said. “(In contrast,) when the outside temperature is lower, you won’t need to turn your heater on as frequently as you normally do with a normal glass window.”
In terms of smart windows, Gramlick says benefits could be considerable. Whilst it is currently possible for building occupants to adjust the volume of light coming in during the day by adjusting the blinds, Gramlick says this is inefficient when many would find it easier to instead turn artificial lighting on and off. Whilst automated blinds and shading controlled by central plant have a role, Gramlick said these have limitations in terms of many systems continuing to operate (unnecessarily) and waste energy when the building is not occupied. If instead we can get technology that responds to the environment which is integrated into the glass itself, she says this would be a major step forward.
Apart from smart windows, Gramlick said advances in window technology and sustainability are happening across other areas. In respect of framing, there are high performing materials in terms of timber and uPVC. In terms of aluminium, thermal breakage systems involving framing with half sized extrusions which are put together with a thermal break which slows down the movement of heat through the aluminium profile are not new but are now more readily available. Internationally, Gramlick says work is happening to introduce nanotechnology into the intumescent paints currently used for fire retardant purposes which she says may see the frame itself become more efficient in terms of protecting heat.
Beyond that, Gramlick says the long-term focus involves integrated systems of framing and glass working together with shading, landscaping and orientation to minimise heat loss.
She says Australia needs to think about where it is going following the Paris Agreement and must set targets so that the building sector has clear guidance about the standards it needs to reach and the point at which we reach the maximum of what can be achieved through more efficient buildings and thus have to look more at energy sources including renewables.
Going forward, Australia better performing buildings from an environmental perspective.
Through smart windows, in combination with efforts in other areas, we have a magnificent opportunity to make this happen.