The dynamic control of daylight is seen as key for the effective 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 effective in providing a 'well-tempered' daylit environment that meets occupants needs. Amongst the different 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 (EC) 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 electrochromic (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 office 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 effective deployment of EC glazing.
Abstract:Energy-efficient building performance requires sophisticated control systems that are based on realistic occupant behaviour models. To provide robust data for the development of these models, research studies in real-world settings are needed. Yet, such studies are challenging and necessitate careful design in terms of data collection methods and procedures. This paper describes and critiques the design of a mixed methods approach for occupant behaviour research. It reviews the methodology developed for a longitudinal study in a real-world office environment where occupants' experience with a novel facade technology (electrochromic glazing) was investigated. The methodology integrates objective physical measurements, observational data and self-reported experience data. Using data from one day of the study, this paper illustrates how the different sources can be combined in order to derive an in-depth understanding of the interplay between external daylight conditions, characteristics of the facade technology, occupant interaction with the technology and the resulting occupant experience. It was found that whilst the individual methods may be affected by practical limitations, these can be partially offset by combining physical measurements and observations with self-reported data. The paper critically evaluates the individual techniques, as well as the benefits of their integration and makes recommendations for the design of future occupant behaviour studies in real-world settings.
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