Simulating Daylight Propagation through Complex Fenestration Systems in a Urban Context Using Variable Sampling Subdivision Scheme

The use of Complex Fenestration Systems (CFS) within buildings can contribute to a significant reduction of cooling loads by the way of two assets: the redirection of daylight and the shading of sunrays. In order to back-up these features, daylight performance evaluations need to be performed individually in each case according to the geographical location, outdoor conditions, building orientation and design as well as indoor material properties. The use of computer simulations can make this assessment easier than on-site CFS monitoring requiring the availability of testing facilities, materials and equipment transportation as well as the physical installation of a CFS. Computer simulations can be carried-out using the RADIANCE lighting software, which allows the estimation of the daylight propagation through the CFS using monitored light transmission properties. Those features named BTDF data (Bi-directional Transmission Distribution Function) are assessed using a bidirectional gonio-photometer and stored in an internationally standardized format. In order to perform such simulations, BTDF data are assigned to a planar polygon that models the CFS and/or a window becoming a secondary light source in the virtual model. The accuracy of the simulation results is generally relying on the computer simulation parameters that drive the lighting calculation in the virtual model, as well as the BTDF data resolution assigned to the polygon mimicking the CFS. In an urban context moreover the shadowing effects due to adjacent buildings have a significant impact on the incoming daylight flux transmitted by the CFS. It is important accordingly, to subdivide such a polygon - which may be a large glazed area - in an optimal way in order to enhance the simulation accuracy. Computer simulations were carried-out for that purpose using a virtual model of an office room placed in an urban context. The BTDF data of a Laser-Cut Panel (LCP), made of a 6 mm thick acrylic panel with 4 mm spaced parallel laser cuts, were applied for that purpose to: i) a single pane representing a full-size office window and ii) subdivided polygons of the size of the LCP sample benefitting from BTDF monitoring. All results are compared in order to determine the influence of the polygon subdivisions referenced to the BTDF data on the final computer simulation accuracy.

Annual Performance Assessment of Complex Fenestration Systems in Sunny Climates Using Advanced Computer Simulations

Chantal Basurto Dávila, Jérôme Henri Kämpf, Jean-Louis Scartezzini

Complex Fenestration Systems (CFS) are advanced daylighting systems that are placed on the upper part of a window to improve the indoor daylight distribution within rooms. Due to their double function of daylight redirection and solar protection, they are considered as a solution to mitigate the unfavorable effects due to the admission of direct sunlight in buildings located in prevailing sunny climates (risk of glare and overheating). Accordingly, an adequate assessment of their performance should include an annual evaluation of the main aspects relevant to the use of daylight in such regions: the indoor illuminance distribution, thermal comfort, and visual comfort of the occupant’s. Such evaluation is possible with the use of computer simulations combined with the bi-directional scattering distribution function (BSDF) data of these systems. This study explores the use of available methods to assess the visible and thermal annual performance of five different CFS using advanced computer simulations. To achieve results, an on-site daylight monitoring was carried out in a building located in a predominantly sunny climate location, and the collected data was used to create and calibrate a virtual model used to carry-out the simulations. The results can be employed to select the CFS, which improves visual and thermal interior environment for the occupants.

2015

Daylight optimization of buildings and application of advanced daylighting systems in Central Mexico

Chantal Basurto Dávila, Apiparn Borisuit, Jérôme Henri Kämpf, Mirjam Münch, Jean-Louis Scartezzini

The intensive use of daylight in buildings is beneficial at many levels: it provides sufficient levels of illumination to perform working activities throughout the day and it reduces the use of artificial light, which in turn leads to lower electricity consumption [1-3]. The spectral composition of daylight often leads to higher visual comfort in humans, compared to electric lighting. There are also illuminance and spectrally-dependent light effects on the human circadian system, which regulate hormonal rhythms, alertness and (visual) performance across 24 hours [4-6]. The main objective of this work was to assess luminous performance in office buildings and to test optimizations by virtually applying different daylighting strategies by computer simulations.We first assessed the daylight distribution in two different office rooms, set-up as test modules on the EPFL campus in Lausanne (46° 32'N, 6° 39'E). One of these test modules is equipped with a standard double-glazing; the second one comprises anidolic daylighting systems [7], which convey diffuse daylight and sunlight deeper in the room, and reduce glare risk. In both rooms, we also assessed vertical spectral irradiance in the visible range, which gave us additional information with respect to photo biological properties of the available daylight. We then measured the real daylighting situation in an office room located in the city of Zacatecas, Mexico (22°47'N 102°34'W), which is equipped with a standard double-glazing window. In a next step we tested, whether the daylight distribution for this room could be improved by virtually applying different complex fenestration systems (such as prismatic panels and laser cut panels) by using computer simulations. The results of these simulations showed higher indoor luminous performance with the two advanced daylighting systems. This new method may contribute to an improved and tailored design of daylight availability in real buildings at different geographical locations.

EPFL2011

On advanced daylighting simulations and integrated performance assessment of complex fenestration systems for sunny climates

Chantal Basurto Dávila

The inclusion of daylight in buildings represents several benefits: its use not only signifies a reduction in the building energy consumption through the compensation of electric lighting, it also has positive effects in the execution of human activities. Through its spectral composition, it contributes to create a better interior atmosphere for visual comfort, leading to a better performance on working tasks. It also influences biological human cycles, which has an impact on human alertness, mood and well-being. Compared with electric light, its intensity and dynamic variations have a stimulating effect by providing a connection with the exterior environment. However, for buildings located at low latitudes (between 23°N and S), the inclusion of daylight implies the admission of sunrays, which affect the visual comfort and perception of the indoor environment by altering the interior luminance distribution increasing the risk of glare. An additional unfavourable effect is the increment of the interior thermal loads which represent a risk of overheating for the occupants. In those regions, common practices such as: the reduction of the window size, the use of tinted glazing and solar protection are usually applied to buildings in the search of overcoming such problems. However, the use of such strategies also implies a reduction of the admission of daylight inducing the use of electric light, which is incongruent in countries with large amounts of this natural resource. The use of Complex Fenestration Systems (CFS) may represent a solution given their characteristics: daylight redirection and direct solar rays protection. The latter would contribute to control the admission of solar gains while maintaining a good visual interior environment. However, the appropriate selection of CFS requires a careful evaluation of their features and performance regarding their suitability to the building location. This thesis explores the potentiality of using CFS to improve the interior daylight distribution in buildings located at low latitudes while maintaining a satisfactory visual and thermal interior environment for the occupants. In order to do this, the existing daylight situation of two office rooms located in the central-north of México (Zacatecas 22° 783' N., 102° 583' W, Altitude: 2543m) were monitored from 2011 to 2013. Illuminance and luminance were measured on periods of the year that are crucial for the interior luminous environment (summer and winter solstices together with spring equinox), in order to characterize the existing daylighting situation and to study the dispersion of results obtained using a virtual model which reproduces the features of both offices. The performance of five CFS was then tested using computer simulations in order to assess their suitability to the local sky conditions. For this, three main factors were taken into account: the improvement of the interior daylight distribution, the risk of glare and overheating. The effects of the CFS in a room regarding such conditions were simulated using RADIANCE and Energy Plus using BTDF data (Bidirectional Transmission Distribution Function that characterizes the CFS’s lighting transmission properties) assessed by the use of a gonio-photometer. The assessment was performed first during the winter and summer solstices as well as spring equinox and secondly then on annual basis. The latter was done in order to take into account the daylight variation characteristics of two locations with prevailing clear sky conditions. The results obtained allow determining the CFS that better contributes to a better interior luminous environment in each building without compromising the thermal and visual comfort of the occupants.