Complex Fenestration Systems Research Articles

Interactive selection of optimal fenestration materials for schematic architectural daylighting design

Complex fenestration systems, such as prismatic and laser cut panels, are emerging as attractive options in architectural design thanks to their high potential to assist in energy and comfort issues. These systems can be used to redirect intense illumination from the sun but have complex transmissive properties that in turn depend on continuously changing illumination conditions due to the dynamic nature of natural light. The resulting non-intuitive interactions with the built environment make it necessary to develop tools that adequately represent these systems' behavior to the architect. The method presented in this paper enables simulation of the direct and indirect illumination from the sun and sky throughout each day for different months Preprint submitted to Automation in Construction 17 December 2007 of the year. The user can interactively explore the high-dimensional configuration space to select optimal materials early in the design process, using both qualitative and quantitative design criteria to make adjustments.

Efficient calculation of daylight coefficients for rooms with dissimilar complex fenestration systems

The daylight coefficient (DC) method is a powerful and efficient method to perform annual daylight illuminance simulation. A set of coefficients are calculated for a given room space and static fenestration systems prior to simulation start. Time series of indoor daylight illuminances are obtained by only knowing the sky luminance. However, for rooms with dissimilar dynamic complex fenestration systems (such as windows with movable shadings) whose optical behaviour (transmission, reflection and scattering) may change during simulation, the efficiency of the DC method may be compromised as another whole set of coefficients must be re-calculated. This study presents the development of a new methodology to compute the DC set for rooms with dissimilar complex fenestration components only once prior to simulation start. A validation study is carried out, in which the daylight illuminances in an office space equipped with a clear window and internal Venetian blinds are compared using predictions from the present model, the Radiance program, as a benchmark model employing detailed optical model of Venetian blinds, and the Daysim program employing a simple engineering blinds model. Findings from the validation study show that the present model yields overall accurate results when compared with the benchmark model for any window orientation, although some local illuminance differences are observed in areas under direct sunlight exposure.

Complex fenestration systems: towards product ratings for indoor environment quality

Complex fenestration systems (CFS) include windows featuring complex glazing such as translucent and transparent insulation, solar control films, patterned or decorative glass, in-between pane shades, etc. CFS are believed to exhibit superior energy performance, but may have adverse effects on environmental features important for building-occupant satisfaction requirements such as the outdoor view (connection to outside), indoor view (feeling of privacy), luminance (major factor for discomfort glare), and light diffusion quality (relates to uniformity of illuminance on work plane). This article is part of a larger effort to rate complex fenestration systems for energy performance and indoor environment quality (IEQ). In the end, IEQ ratings must be derived from direct studies of how building occupants perceive the indoor environment conditions created by the installed fenestration product. As a first step, this work tackles the theoretical development of new metrics to rate CFS with regards to IEQ, namely the view impairment index, luminance index, and light diffusion quality index. The new indices are applied to some typical CFS, namely a diffuse window, and a clear window combined with an interior shading screen, and integrated perforated Venetian blinds. The results show that the diffuse window may increase the luminance by more than 100% under clear sky conditions when compared with a clear window with a similar light transmittance. White colored Venetian blinds may increase the window luminance by up to 50% and reduce the outdoor view by up to 66% as compared with a clear window with a similar light transmittance.

Optical models of complex fenestration systems

The need for energy conservation in buildings has spurred innovations in window technologies. These products include windows combined with shading devices, and windows featuring complex glazing such as switchable glazing, diffuse glazing, translucent and transparent insulation, patterned or decorative glass, etc. Current fenestration simulation tools for energy performance product ratings do not cover complex fenestration products. This paper addresses the development of detailed calculation models to compute the optical characteristics of complex fenestration products made up of a mixture of clear and scattering glazing layers. The models take into account not only the optical properties of the individual glazing layers making up the window product, but also the haze and gloss properties of the glazing layers. Specific optical models are developed to compute the optics of a clear substrate with applied or laminated scattering film, and composite film made up of a number of homogeneous materials with known optical properties. A general optical model was also developed for screen-like glazing panes such as insect/shading screens, roller blinds, drapery sheets, honeycomb transparent insulation and fibreglass translucent glazing.

Modelling indoor illumination by complex fenestration systems based on bidirectional photometric data

Significant efforts to assess the bidirectional transmittance distribution functions (BTDFs) of complex fenestration systems (CFS) have been undertaken in recent years. This paper presents a methodology for including these photometric raw data sets into the daylighting simulation and design process. The method is based on computing the luminous intensity distribution on the inward facing side of façade elements from BTDF data (measured or calculated) and the outside luminance distribution as seen from the façade element. Fourier optical principles are applied to derive filter conditions for BTDF interpolation. Since the BTDF raw data sets are big in volume, data compression techniques are introduced and applied. Control algorithms for dynamic façade systems (i.e. time variant systems like automated blinds) are accounted for. The procedure is validated against analytical and numerical test cases. Limitations of the approach are being discussed. As an application example, the method is incorporated into lighting simulation engines and into a complex fenestration system database.

Goniophotometry and assessment of bidirectional photometric properties of complex fenestration systems

This paper seeks to provide an overview of the currently available assessment tools for bidirectional transmission or reflection distribution functions (BTDFs and BRDFs) of complex fenestration systems (CFS). In the first part of the paper, the existing experimental devices (goniophotometers) developed specifically for CFS measurement are described. All but two are based on a scanning process to investigate the emerging light flux distribution, the alternative approach being based on digital imaging techniques. A critical analysis of their advantages and shortcomings is proposed to provide both researchers interested in replicating them and more generally potential users of BTDF or BRDF data with a lucid idea of the available options. The second part presents an alternative to physical measurements, made possible by using computer simulations based on ray-tracing techniques. In this case, every component of the modelled system must be of well-known geometric and material properties. Two virtual goniophotometer models are described and their validation results are analyzed. Whether they have been generated experimentally or through simulation, BTDF and BRDF data need to be processed into transmission or reflection functions that are directly related to sky and room conditions for them to be usable. The third part of the paper introduces a new BT(R)DF database management system whose aim is to become a reference resource for viewing and interpreting these complex data. The main visualization features of its interface are presented, that include a special focus on flexibility and on providing intuitive graphical information, in a similar way as for luminaires selection in electric lighting design.

Experimental validation of simulation methods for bi-directional transmission properties at the daylighting performance level

The objective of this paper is to assess the capability of existing lighting simulation methods to predict the performance of Complex Fenestration Systems (CFS), whose potential in daylight and sunlight control make them an increasingly popular alternative to conventional glazing. The research was conducted in two phases. First, collect reliable reference data by taking illuminance measurements inside a black-box under a measured and controlled external luminance distribution, the black-box's only aperture being covered with a complex glazing sample. Two types of materials were used: a Serraglaze™ element and a Laser Cut Panel (LCP). Several simulation methods were then investigated and validated against this reference case. For the first method, measured BTDF for both material samples were integrated into different simulation tools to determine the resulting indoor lighting conditions under the external luminance distribution chosen for the reference case. The same method was then applied with calculated BTDF data, based on ray-tracing calculations. Finally, one of the CFS (the LCP) was modeled using the backward ray-tracer RADIANCE so that the inside illuminance distribution could be deduced without requiring BTDF data. The comparison between the experimental reference data and the simulation results showed that the effect of the CFS on the room's illumination could be predicted with acceptable accuracy for most of the tested methods (generally within 10–20%). The simplicity of the testing scenarios allowed error sources related to simulation to be highlighted and helped determine the extent to which an accurate physical description of the samples could influence the results. Based on this study, recommendations were made for a better use of existing simulation methods.

Inclusion of the specular component in the assessment of bidirectional distribution functions based on digital imaging

To describe complex fenestration systems such as novel solar blinds, new glazing or coating materials, daylight and sunlight-redirecting devices, a detailed description of their optical properties is needed, given by their Bidirectional Transmission (or Reflection) Distribution Functions (commonly named BTDFs and BRDFs). These functions are angle-dependent at both the incidence and the emission levels, and are defined as the ratio of the luminance of a surface element in a given direction (after diffuse transmission or reflection) to the illuminance on the sample. However, these functions are capable of describing the specular as well as the diffuse components of emerging light, and their mutual knowledge is necessary to properly assess a glazing or shading system’s daylighting performances and benefit from their potential as energy-efficient and users’ comfort strategies. Although the analytical expression of a BT(R)DF differs whether it is related to specular or diffuse light, a simultaneous assessment of the two components can be achieved under certain conditions. These conditions are analyzed for the particular data acquisition procedure developed for a novel type of bidirectional goniophotometer, based on digital imaging.

04/00903 Performance evaluation of the BSRC multi-purpose bio-climatic roof: Waewsak, J. et al. Building and Environment, 2003, 38, (12), 1297–1302

Proper daylighting designs in interior spaces may reduce the energy costs of electric lighting and improve the productivity of occupants. This paper reports the potential advantages of a multifunctional complex fenestration system with embedded micro-mirrors in daylighting by simulation. The system consists of a polymer layer with an array of embedded parabolic micro-mirrors, which was attached to a glass pane of glazing. By appropriate geometrical design, the embedded micro-mirrors may combine the function of keeping a clear view through the glazing due to the microscopic size of the embedded mirrors, and improving daylighting quality and quantity because of the redirection of daylight by micro-mirrors. In order to fully explore the potential advantages of the daylighting system with embedded micro-mirrors, three configurations were investigated: micro-mirrors in the upper third of a double glazing, micro-mirrors in the upper two-thirds of a double glazing and micro-mirrors in the whole glazing. Metrics based on illuminance, uniformity, glare and directivity were used to assess daylight performance for a south-facing façade in Lausanne (46°30′N and longitude 6°37′E), Switzerland. Compared with a standard low-e double glazing, the daylighting system with micro-mirrors could induce more daylight in the rear of a room and improve the uniformity of the daylight distribution. By integrating micro-mirrors in the upper two-thirds of the glazing, the risk of glare was reduced for a sightline parallel to the glazing on the spring equinox and on the winter solstice. For the case with micro-mirrors in the whole glazing, the directivity of daylight along the depth of the room was significantly improved from the harsh range to the preferred range at noon, suggesting a comfortable visual situation.