CIBSE ASHRAE Technical Symposium, Dublin, Ireland, 3-4 April 2014 Electrochromic Glazing: Avoiding the Blues John Mardaljevic PhD FSLL, 1 Ruth Kelly Waskett 2 and Birgit Painter PhD 2 1 School of Civil and Building Engineering, Loughborough University, Loughborough, Leicestershire, UK 2 De Montfort University, Leicester, UK 1 j.mardaljevic@lboro.ac.uk Abstract The dynamic control of daylight has been called the “Holy Grail” of the fenestration industry. Electrochromic (EC) glass is believed to be the leading contender in the race to manufacture a glazing technology that will achieve the accolade set down by Steve Selkowitz in 1998. With recent investment in the scaling-up of production capacity, EC glass is now set become a mainstream glazing product. As EC glass darkens (‘tints’) the peak in the spectral transmittance curve shifts to the blue. Whilst control of the luminous and thermal environment is highly desirable, occupants are believed to prefer daylight illumination that is perceived as neutral rather than tinted. Thus the question regarding the neutrality of the illumination spectrum is an important one that needs to be addressed. In this paper the authors show that it is possible to maintain an effectively neutral spectrum of daylight illumination in a space with EC glass in normal operation, provided that a relatively small proportion of the glass is left in the clear state. A theoretical formulation giving the overall spectral transmittance curves for any arbitrary combination of clear and tinted EC glazing in varying proportions is outlined. Applying the theoretical model it should be possible to configure and/or control an actual EC glass installation so that neutral daylight illumination results. The theoretical model is tested using measurements of the daylight spectra in an office space with EC glazing for various combinations of clear and tinted glass. 1. Introduction The use of daylight in office buildings is generally considered to be a greatly under- exploited resource. In large part this is because of the highly variable nature of daylight illumination. The natural, large variability in daylight means that users will often need to use shades to moderate excessive ingress of daylight. Most shading systems act as a “shutter” that is either open or closed, with users rarely making the effort to optimise the shading for both daylight provision and solar/glare control. And blinds are often left closed long after the external condition has changed. A glazing with a transmissivity that varies continuously between clear and dark extremes could offer a much greater degree of control over the luminous environment. The principle behind variable transmission glazing (VTG) is straightforward: the trans- mission properties of the glazing are varied to achieve an ‘optimum’ luminous and/or thermal environment. The various types of VTG can be grouped into three broad classes: chromogenic coatings, suspended particle device and micro-electromech- anical systems. In the chromogenic class there are four distinct types of formulations for coatings that have variable transmission properties. These are: electrochromic, gasochromic, photochromic and thermochromic. The agents causing the change in transmission are: voltage (electrochromic); concentration of pumped gas (gasochro- mic); localised illumination (photochromic); and, localised temperature (thermochro- mic). Thermochromic and photochromic are essentially passive devices which respond 1 of 9