Daylighting performance of an electrochromic window in a small scale test-cell

Abstract In this paper, the results of an experimental investigation aimed at assessing the performance of electrochromic (EC) windows with respect to daylighting control in buildings are presented. The research is performed under real weather conditions by a small scale test-cell equipped with a small area double glazing unit (DGU) where one pane consists of an EC device with visible transmittance τv ranging from 6.2 to 68.1% and the other of an ordinary clear float glass (τv ≈90%). Experimental tests are carried out as a function of time, weather conditions, test-cell orientation and switching strategies. These data are integrated with spectrophotometric measurements. Results show that the angle selectivity of the glazing combined with its active switching effect allows a wide range of selectable transmission states to suit the latitude and orientation of a building in relation to the local climatic conditions. For south facing windows and under the involved climatic conditions EC glazing driven by a dynamic control strategy can be very effective in reducing discomfort glare caused by high window brightness. Glare reduction can be realized contemporarily maintaining the work plane illuminance to adequate level for computer based office tasks so without compromising much of the available daylight. Furthermore, since EC glazing is never switched to heavily darkened states (τv >20%), colour rendering of inside objects should be always acceptable, although internal illuminance level could be slightly lower than to what users prefer in relation to the correlated colour temperature of the incoming light. These results change when considering west orientation for which high-luminance direct sunlight patches are registered on the work-plane even for EC glazing switched to its lowest transmitting state letting suppose that EC windows cannot provide full control of uncomfortable direct sunlight effects without integration of additional shading devices.

[1]  F. Simone,et al.  Preliminary test of a large electrochromic window , 1999 .

[2]  Claes-Göran Granqvist,et al.  Electrochromic tungsten oxide films: Review of progress 1993–1998 , 2000 .

[3]  R. Sullivan,et al.  Effect of switching control strategies on the energy performance of electrochromic windows , 1994, Other Conferences.

[4]  A. Roos,et al.  Evaluation of predictive models for the angle-dependent total solar energy transmittance of glazing materials , 2001 .

[5]  Eleanor S. Lee,et al.  Subject Responses to Electrochromic Windows , 2006 .

[6]  J. Scartezzini,et al.  Comparing daylighting performance assessment of buildings in scale models and test modules , 2005 .

[7]  Stephen Selkowitz,et al.  Daylighting control performance of a thin-film ceramic electrochromic window : Field study results , 2006 .

[8]  Ali A Nazzal.  A new daylight glare evaluation method introduction of the monitoring protocol and calculation method , 2001 .

[9]  P. Stone,et al.  The effects of environmental illumination on melatonin, bodily rhythms and mood states: a review , 1999 .

[10]  S W A Cannon-Brookes,et al.  Simple scale models for daylighting design: Analysis of sources of error in illuminance predictiont , 1997 .

[11]  Toshie Iwata,et al.  EXPERIMENTAL STUDY ON DISCOMFORT GLARE CAUSED BY WINDOWS PART 3 : Development of a method for evaluating discomfort glare from a large light source , 1996 .

[12]  A. Kruithof.  Tubular luminescence lamps for general illumination , 1941 .

[13]  Eleanor S. Lee,et al.  Application issues for large-area electrochromic windows in commercial buildings , 2000 .

[14]  R. G. Hopkinson.  A study of glare from very large sources , 1960 .

[15]  I. L. Bailey,et al.  Large area glare sources and their effect on visual discomfort and visual performance at computer workstations , 1992, Conference Record of the 1992 IEEE Industry Applications Society Annual Meeting.

[16]  Ian L. Bailey,et al.  The Influence of Spectral Composition on Discomfort Glare for Large-Size Sources , 1994 .

[17]  S. E. Selkowitz,et al.  Visual quality assessment of electrochromic and conventional glazings , 1996 .

[18]  F. Simone,et al.  Solid state electrochromic device: behaviour of different salts on its performance , 2000 .

[19]  Aslihan Tavil,et al.  Energy and visual comfort performance of electrochromic windows with overhangs , 2007 .

[20]  R. Dogniaux,et al.  Glare from windows: current views of the problem , 1982 .

[21]  Charles Anderson,et al.  Angular-dependent optical properties of low-e and solar control windows—: Simulations versus measurements , 2001 .

[22]  Jan Wienold,et al.  Evaluation methods and development of a new glare prediction model for daylight environments with the use of CCD cameras , 2006 .

[23]  Nicolas Morel,et al.  On-site performance of electrochromic glazings coupled to an anidolic daylighting system , 2007 .

[24]  Michele Zinzi,et al.  Office worker preferences of electrochromic windows: a pilot study , 2006 .