Properties and Performance Indicators of Virtual Natural Lighting Solutions

Several studies have shown that in the built environment, natural light is highly preferred over electrical lighting for its positive effects on user satisfaction, health, and the potential on saving electrical energy. However, natural light is highly variable and limited by time and space. For example, significant fractions of working population in the world do their work during nighttime. Shift workers experience various discomfort issues, and increased long-term risk of some types of cancer due to a lack of synchronisation between the shift work schedule and the worker’s light-dark cycle. Many buildings also have several inside spaces, while admission of natural light into work places is strongly suggested. A possible way to overcome this problem is to develop and apply a Virtual Natural Lighting Solution (VNLS), which is a system that provides virtual natural light, with all of its qualities, which can be integrated inside new and/or existing buildings. One of the first challenges in developing such solutions is modelling their behaviour and predicting their impact on spatial use and performance of buildings. In order to model a VNLS, it is necessary to understand the relevant properties that the solution itself should have, as well as the relevant performance indicators which show how the solution affects performance of buildings where it is applied. For the case of VNLS, the performance indicators of a building will be described in terms of visual comfort, space availability, thermal comfort, and energy consumption. A study is presented, based on literature reviews, in which the properties of currently known artificial windows and skylights are compared to that of real ones. The comparison shows that each existing solutions addresses a subset of all aspects required for a VNLS. The paper concludes by summarising the relevant properties and performance indicators with their expected range of values, which will be the input for developing a computational model of VNLS

Development of virtual natural lighting solutions with a simplified view using lighting simulation

Computational building performance simulation can be employed to develop various future solutions. The development of Virtual Natural Lighting Solutions (VNLS), which are systems that artificially provide natural lighting and view comparable to those of real windows and skylights, is steered by modelling them as arrays of small light sources resembling a simplified view of a blue sky and green ground. The lighting simulation tool Radiance is employed to predict the space availability, uniformity, ground light contribution on the ceiling, and probability of discomfort glare. The input variables are "distance between windows", "tilt angles", "beam angles", and "total luminous fluxes of the sky elements". Sensitivity analysis shows that the total luminous flux positively influences the space availability, the beam angle positively influences the uniformity; and negatively influences average ground light contribution on the ceiling and average probability of discomfort glare. Most of the VNLS models with 114° beam angle perform better on the tested performance indicators than real windows under CIE overcast sky

Simulation study of a virtual natural lighting solutions prototype: validation and analysis

Introduction The benefit of natural light and view from windows in buildings has been widely reported (e.g. Berman et al., 2008; Aries et al., 2010). However, there are some situations in which natural light is absent, for example, due to hygienic or safety reasons. To answer this challenge, the concept of Virtual Natural Lighting Solutions (VNLS), which are systems that can artificially provide natural lighting as well as a realistic outside view with properties comparable to those of real windows and skylights, is proposed. This study aims to find how a certain VNLS prototype influences the indoor lighting condition and visual comfort. In particular, this study focuses on lighting measurement and simulation of a 'second generation' VNLS prototype. Two objectives are defined: (1) to validate the illuminance distribution results obtained from Radiance simulation (Ward & Shakespeare, 1998) with the ones obtained from measurement, by evaluating the interior lighting condition inside the test room; and (2) to determine the effect of various prototypes configurations on the space availability, uniformity, and visual comfort in the test room

Lighting performance of virtual natural lighting solutions with a simplified image in a reference office space

The objective of this study is to describe the approach of modelling VNLS and using the Radiance lighting simulation package to compare the lighting performance of various VNLS configurations in a defined reference office space. Prior to incorporating a realistic view component in the performance assessment, a simplified image is included in the simulation. The lighting performance is described in terms of the ability to meet the space availability demand, the illuminance uniformity on the workplane, and the ability to meet visual comfort demands, e.g. to produce minimal glare at predefined observer’s positions in the given space. Space availability is defined as "the percentage of workplane (at height of 0.75 m from the floor) meeting a certain minimum illuminance criteria". The building type discussed in this study is a reference office space with dimensions of 5.4 m × 3.6 m × 2.7 m (L×W×H). There are four vertical window configurations chosen from the earlier studies of Diepens et al (2000) and LBL (2010). Each window configuration is modelled with a simplified viewed image on its surface. No real windows are present in the modelled spaces

Space availability of buildings with virtual natural lighting solutions

Natural light is highly variable and limited in time and space. In situations where it is not or insufficiently available, Virtual Natural Lighting Solutions (VNLS) can be promising. This paper presents research based on computer simulation to explore the space-gaining potential of VNLS in offices, healthcare facilities, and industrial halls. The models are developed and simulated using the Radiance lighting simulation tool. The space-gaining potential of the virtual windows is determined by comparing space availabilities, i.e. the percentage of space with workplane illuminance more than a certain level, in situations with either real windows or virtual windows only. Criteria concerning visual comfort glare indices and luminance ratios are also considered. The paper demonstrates a comparison of space availability and visual comfort in some building types with virtual windows, compared to those of real windows with CIE overcast sky. The building type with the largest space availability and relatively low glare indices will be considered as the one with the biggest potential

Integrating Visual and Energy Criteria for Optimal Window Design in Temperate Climates

Building codes and certifications require maximal building performance in different aspects. However, focusing on achieving a single purpose can prevent obtaining additional ones. This work aims to help building designers balance energy and visual performance design criteria. The difficulty to achieve many goals resides in high degrees of complexity when many building features must be considered in an infinite number of possible design solutions. Multi-objective optimization techniques start to be applied in building science, but different appropiate assessment criteria applied to a single problem can lead to diverse valid solutions. A brief review was made of commonly used energy consumption and visual comfort and performance criteria. The study was made through whole-building computer simulations of a standardized test room. This provided a solution space with "compromise sizes" satisfying both energy and visual aspect objectives. However, unprotected windows cannot meet all these criteria. This makes the provision of sun-protecting elements necessary. A selection procedure based on design needs is detailed

Simulaties voor R&D: ‘Virtual Natural Lighting’ systemen

Mensen hebben een sterke voorkeur voor natuurlijk licht in gebouwen. Natuurlijk licht is echter zeer variabel en niet altijd en overal aanwezig. Er is dus behoefte aan ‘virtuele’ natuurlijke verlichting, die alle kenmerken van het ‘echte’ natuurlijke licht in zich heeft. De verwachting is dat een dergelijke lichtoplossing een echte natuurlijke lichtbron kan gaan vervangen in situaties waar natuurlijk licht niet of niet voldoende aanwezig is

Development of a heterogeneous catalyst for lignocellulosic biomass conversion:Glucose dehydration by metal chlorides in a silica-supported ionic liquid layer

An attempt is made to immobilize the homogeneous metal chloride/EMIMCl catalyst for glucose dehydration to 5-hydroxymethylfurfural. To this end, ionic liquid fragments were grafted to the surface of SBA-15 to generate a heterogenized mimick of the homogeneous reaction medium. Despite a decrease in the surface area, the ordered mesoporous structure of SBA-15 was largely retained. Metal chlorides dispersed in such ionic liquid film are able to convert glucose to HMF with much higher yields as is possible in the aqueous phase. The reactivity order CrCl2 > AlCl3 > CuCl2 > FeCl3 is similar to the order in the ionic liquid solvent, yet the selectivity are lower. The HMF yield of the most promising CrCl2-Im-SBA-15 can be improved by using a H2O:DMSO mixture as the reaction medium and a 2-butanol/MIBK extraction layer. Different attempts to decrease metal chloride leaching by using different solvents are described