The RIBA conference that initiated this book included the introduction by Pilkington Architectural of their Triple Planar glass. This is a glazing system that eliminates the need for framing, with the junction between panes sealed with 10-12 mm of silicon. The importance of this system is that it can achieve a U-value of 0.8 W/m2K, which should make it highly attractive for commercial application when coupled with its aesthetic appeal.4
A wider market can be expected for Pilkington's electrochromic glass, marketed as Econtrol. This works by passing a low electrical voltage across a microscopically thin coating to the glass, activating a tungsten-bearing electrochromic layer which can darken in stages. Electricity is only used to change the state of the coating, not to sustain its level of transmittance. About 3 volts are needed to effect the change, and this could be provided by the building energy management system or be individually controlled by occupants, allowing for fine-tuning to immediate needs. PV cells integrated into a façade or roof could easily supply this level of power.
This system offers several advantages. Foremost is the fact that it can save energy. It avoids overheating and solar glare. Trials conducted in Germany indicated that it can save up to 50% of the energy required for air conditioning. Even when the glass is fully darkened, external views are maintained. The avoided cost of external shading must also be factored into the cost-benefit analysis.
The first building to feature Econtrol was a bank in Dresden. The electrochromic glazing on the southern elevation is over 17m high and 8 m wide. The glass can be switched to give five levels of light and heat transmittance.
Finally, in 2002, Pilkington introduced 'hydrophilic' glass to the market. This is a self-cleaning glass which goes under the name of Pilkington Activ. Layers are deposited on the glass during the float manufacturing process to produce the photocatalytic characteristics of the glass. After exposure to ultraviolet (UV) light in daylight, the coating reacts chemically in two ways. First it breaks down organic deposits - tree sap, bird droppings etc. - by introducing extra molecules of oxygen into the deposit. This has the effect of accelerating the rate of decay. Second, the coating causes the glass to become hydrophilic. This means that droplets of rain coalesce to form sheets of water which slide down the glass, removing dirt particles in the process. The really smart aspect of the product is that the coating stores enough UV energy during the day to sustain the process overnight.
The avoidance of cleaning costs, especially for commercial buildings, could offer considerable annual savings, especially where atria are concerned. For householders it could, in the long term, spell the end of the local friendly window cleaner.
Now that nanotechnology has taken a hold on glass manufacturers, all kinds of possibilities can be envisaged; for example, glass that responds instantly to changes in weather or that is an integrated photovoltaic electricity generator.
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