Keeping out the sun with switchable glazing

Electrochrome EControl glazing was used for IT instruction rooms of a school. Windows were provided in different sizes. Now there is constant light when working on computers.
Images/Graphic charts: EControl-Glas GmbH & Co. KG

Installing electrochrome solar control glazing provides for controlling heat and light reaching a building from outside.

Large areas of glazing in the outer skins of buildings offer undisputed advantages. They make for bright rooms inside with lots of light. Also, the use of daylight results in less energy being used for artificial lighting. On the other hand, and particularly in summer, they also let penetrate much heat energy into the building. In many cases sunshade glazing alone is not sufficient to prevent inside temperatures from going up. In such cases, additional devices will be needed to keep out the sun and reduce energy consumption for cooling purposes.

Planners of solar control solutions for offices and administrative buildings will also have to consider that people inside should still have almost unlimited viewing of their outside environment, despite any shadows. Such solutions should also rule out any glare effects reaching work stations. Traditional sunshade equipment, such as blinds, venetian blinds and awnings can only provide part of the solution.

Keeping out the sun at the touch of a button

New electrochrome sunshade glazing offers a very interesting alternative to mechanical sunshade providers, because they offer dynamic solar control. They also make for unlimited transparency at any time and largely rule out glare. Over and above the functional advantages of such types of glazing, dispensing with classical sunshade equipment also opens up new prospects for architects when designing the outer skin of buildings.

Electrochrome glazing allows for daylight supply as requested. The design of these new types of glazing available today with their system of dynamic layering is the same as that used for traditional insulation glazing. There is a float glass panel on the inside, and an electrochrome composite structure is positioned on the outside section of space between panels, consisting of another two float glass sections. Layers of extremely thin coating on the inner sides of these two panels are capable of taking up and releasing ions. Polymer sheeting capable of conducting lithium ions is placed between these two panels. When electricity (< 5 volts) is fed into this system, this will activate the ion exchange, the glass panel changes its colour to blue, thus reducing transparency to light as well as the overall transmission of energy. Pre-defined intermediate stages may also be chosen between the terminal settings of “bright” and “dark”.

Electricity is fed into every individual panel, and all panel sections are linked to a control unit. This allows for individual control. On the other hand, groups of window panels may be controlled via a single unit, so that entire sections of a building’s façade with up to thirty windows may be controlled at the touch of a single button. Infinitely variable control of this change of colour is possible when linking these electronic devices to the bus system of a building’s control panel. For a panel of 100 by 100 centimetres the change-over from the brightest to the darkest setting takes about 12 minutes. This colour-change process does not produce any noise. Users inside hardly notice it.

Convincing results

Total energy transmission (g) of electrochrome glazing available today ranges from 12 to 36 per cent (following EN 410). The heat insulation factor (Ug) of 1.1 W/m2 K for the heat protection-type glazing of the inside panel reaches the standard for today’s heat insulation glazing. Ug values of up to 0.5 and g values ranging from 10 to 35 per cent may be achieved when employing triple insulation glazing.

Elektrochrome glazing may be equally well built into windows and façades as it may be used for roof glazing and winter gardens. Panels may be made to different size specifications and they can also be employed for glass structures requiring higher sound insulation or security parameters. Specific requirements, as for overhead glazing, can also be met. In such cases, this type of glazing may be integrated into structures meeting appropriate regulations.

There are a few things to consider before thinking of installing electrochrome glazing. First, even when set at dark, there is a risk of glare caused by direct sunlight. Also, hard shadows should be avoided as far as possible because once electrochrome glazing is in place, permanent shade falling on parts of it results in different degrees of transmission and this modifies the darkening effect. You will find additional information on electrochrome glazing at www.econtrol-glas.de.

Latest developments at glasstec 2008

glasstec 2008 will demonstrate the performance parameters of electrochrome glazing as well as recent advances for switchable glazing when involving alternative technologies, such as employing gas or heat to change the colour of glazing as well as thermotropy, photochromy and liquid crystals (polymer-dispersed liquid crystals - PDLC and suspended-particle devices - SPD). Exhibits in the fair halls as well as an expert symposium in the context of the Specila Show “glass technology live“ will present latest insights between 21 and 25 October 2008.