Bi-directional transmission properties of Venetian blinds: experimental assessment compared to ray-tracing calculations

An accurate evaluation of daylight distribution through advanced fenestration systems (complex glazing, solar shading systems) requires the knowledge of their Bidirectional light Transmission (Reflection) Distribution Function BT(R)DF. An innovative equipment for the experimental assessment of these bi-directional functions has been developed, based on a digital imaging detection system. An extensive set of BTDF measurements was performed with this goniophotometer on Venetian blinds presenting curved slats with a mirror coating on the upper side.In this paper, the measured data are compared with ray-tracing results achieved with a virtual copy of the device, that was constructed with a commercial ray-tracing software. The model of the blind was created by implementing the measured reflection properties of the slats coatings in the ray-tracing calculations. These comparisons represent an original and objective validation methodology for detailed bi-directional properties for a complex system; the good agreement between the two methods, yet presenting very different parameters and assessment methodologies, places reliance both on the digital-imaging detection system and calibration, and on the potentiality of a flexible calculation method combining ray-tracing simulations with simple components measurements.     

Design of a time-efficient video-goniophotometer combining bidirectional functions assessment for transmission and reflection

A detailed knowledge of the light distribution characteristics through advanced window systems is required to improve the visual comfort of the building's occupants while controlling the propagation of daylight in rooms and the solar gains. An innovative bidirectional goniophotometer has recently been set up for this purpose, using digital image capture and the projection of the emerging light on a diffusing screen. It therefore provides a continuous investigation of the bidirectional transmission figures in a time-efficient way. This instrument was converted into a double-purpose device, allowing both transmission and reflection measurements, which induced several strong constraints due to the conflict of incident and emerging light flux in reflection mode: on one hand the incident beam had to be restricted to the sample area only; on the other hand, as the screen obstructed the incoming light flux in some positions, a special opening in the latter was required. The practical answer to these constraints, detailed in this paper, proved to be reliable, appropriate and efficient.     

Control of visual conditions for open-plan offices

This paper reports insights about energy savings in buildings dedicated to tertiary activity. The goal is to employ as much as possible natural light flows to minimize the artificial light source consumption. Although the solar energy is power-efficient to light and heat a room, this natural source remains complex to manage and can generate inconveniences related to occupants visual comfort. The authors propose a global solution to deal with visual comfort by controlling the daylight contribution to the indoor light atmosphere. This control structure is based on the use of an innovative sensor of light conditions and it was implemented within an experimental room equipped with classic Venetian blinds. This paper focuses on the control laws to apply in order to meet visual needs for current tasks performed in offices.     

Exploring the synergy of building massing and façade design through evolutionary optimization

In performance-based architectural design optimization, the design of building massings and façades is commonly separated, which weakens the effectiveness in performance improvement. In response, this study proposes a hybrid massing-façade integrated design generation and optimization workflow to integrate the two elements in an evolutionary design process. Compared with the existing approaches, the proposed workflow emphasizes the diversity of building design generation, with which various combinations of building massing forms and façade patterns can be systematically explored. Two case studies and a corresponding comparison study are presented to demonstrate the efficacy of the proposed workflow. Results show that the optimization can produce designs coupling the potential of building massings and façades in performance improvement. In addition, the optimization can provide information that supports early-stage architectural design exploration. Such information also enables the architect to understand the performance implications associated with the synergy of building massing and façade design.     

Development of a cost-effective solar illumination system to bring natural light into the building core

This paper describes a novel and cost-effective way of providing direct sunlight to the core areas of a multi-storey building. In this system, sunlight is collected by a structure, called the solar canopy illumination system, which attaches to the building directly above the windows on each floor. The sunlight is then redirected by the optical components within the canopy and distributed within the building through a series of special-purpose light guides. These guides pipe the sunlight into the building, and also efficiently incorporate electric light sources so that they can provide supplemental lighting as necessary. This system combines several important energy-saving features and uses components that can be low cost in volume manufacturing. As a result, the system has the potential to be truly cost-effective based on the energy savings. The widespread adoption of such a system could substantially reduce energy consumption worldwide which would make a significant contribution toward greenhouse gas mitigation.     

Determination of the origin of the illumination vector due to vertical windows under Moon-Spencer sky conditions (uniformly overcast)

This paper provides a procedure of easy approximation to obtain the direction of the illumination vector for a window under an overcast sky.When working with uniform skies, it is simple to demonstrate that the direction of the illumination vector is determined by the centre of the window and the illuminated point.However, when a luminance distribution is produced such as that specified by the Moon-Spencer law, the origin of the vector is no longer the centre of the window, but some point within a fragment of the window. In this paper, this fragment of window is delimited.     

Daylighting with external shading devices: design and simulation algorithms

In this paper, simplified algorithms to assess the indoor natural illuminance on a prefixed point with external fixed shading devices are presented. The main aim of the proposed approach is to simplify calculations for the two basic cases of dynamic analysis, required by advanced hourly simulation packages, and first-stage building design.