jm-lrt-ec-mix-final.pdf (3.25 MB)
Download fileNeutral daylight illumination with variable transmission glass: theory and validation
journal contribution
posted on 2015-07-03, 10:27 authored by John MardaljevicJohn Mardaljevic, Birgit Painter, Ruth Kelly WaskettThe dynamic control of daylight is seen as key for the e ective exploitation of natural
illumination in buildings. Traditional control solutions are invariably used in a sub-
optimal manner: blinds/shades are left down for long periods and lights are left switched
on. A glazing with a transmissivity that varies continuously between clear and dark
extremes, and which can be controlled automatically, could be much more e ective in
providing a `well-tempered' daylit environment that meets occupants needs. Amongst
the di erent types of variable transmission glazing that have undergone extensive research
and development in the last few decades, those based on electrochromism appear to have
the best performance characteristics and the greatest market potential. Electrochromic
glazing generally exhibits a shift in spectral transmission as the glass darkens, e.g. causing
it to appear blue as it tints. Occupants however are believed to prefer a neutral spectrum
of daylight illumination without any pronounced hue. In this paper the authors show
that it is possible to maintain a neutral spectrum of illumination with EC glazing under
normal operation provided that just a small proportion of the EC glazing is kept in
the clear state. A theoretical model to predict the daylight spectrum resulting from
any arbitrary combination of clear and tinted glazing is described. Predictions from the
model are compared with measurements of the daylight spectra in an o ce with EC
glazing under various states of tint. The predicted spectra show excellent agreement with
the measurements. The model is applicable to any combination of clear and/or tinted
glass panels irrespective of the glazing type(s). The paper concludes with a discussion of
design considerations for the e ective deployment of EC glazing.
History
School
- Architecture, Building and Civil Engineering