A Hemispherical Sky Simulator for Daylighting Model Studies

American Journal of Applied Sciences, 2010

Problem statement: In recent years, daylighting simulation tools have been increasingly used by many architects, engineers and researchers to evaluate the day lighting performances of building design. Most of these tools employ CIE sky models for simulation. However, the accuracy and applicability of these tools for tropical sky are doubtable. The aim of this study was to validate the computer simulated result with scaled physical model results measured under real tropical sky. Approach: Daylighting model was constructed using scaled physical model to be tested under real sky measurement. The same model was configured in Desktop Radiance 2.0 to perform day lighting simulation experiments. All the measurements were carried out under intermediate and overcast tropical sky conditions in Malaysia; while related CIE sky conditions were used for simulations. Results: Due to the CIE sky conditions are very dissimilar from the actual tropical sky; simulated absolute value results such as external illuminance, absolute work plane illuminance and surface luminance recorded high mean differences from the measured results, with 81.63; 71.06 and 49.71%, respectively. However, relative ratios such as Daylight Factor (DF) yielded mean difference of 26.06% and luminance ratio was 29.75% only. The average mean difference was 44.37%. Conclusion/Recommendations: To compare the performances, relative ratios such as DF and luminance ratio showed better accuracies. For future research, validation on other parameters can be performed such as orientations, angle of the overhang, glazing, window sizes, colors, environment settings and electric lighting.

2005

A new type of sky and sun simulator has been developed in Belgium. This paper presents this new sky and sun simulator and the mirror box built as a complementary tool of this one. The simulator, made of 91 halogen lamps placed in a hexagonal shape, is based on the modelling of one patch of the Tregenza sky hemisphere distribution. Thanks to this concept, the illuminance evaluation of one geometric configuration made from one measurement set is usable for every sky model. The sun simulator, which is also made of halogen lamps placed in a hexagonal shapes is also described. This paper presents the parallax error measurements. The very intensive validation work is also summarised; it shows that the tools are powerful and present very low errors.

SHS Web of Conferences, 2019

To enable students to evaluate the impact of light on the scale models of their architectural projects, two physical simulation systems have been built: a mirror box and a sun and sky simulator. Both devices integrate LED-based light sources. We have integrated several models for the computation of the sky image: luminance models and colour appearance models. The integration of the recent and evolving LED technologies explains how our simulators are innovative.

The paper focuses on the validation of the popular simulation software Radiance; it investigates its accuracy and its limitations when used to calculate the daylight illuminance in clear sky conditions. The objective of the study is to examine the existence of any discrepancy and identify any systematic trend between actual and predicted results. The validation was conducted through a comparison between measured on-site data using the Luxmeter vs. Radiance's predicted results. Petrodar and NTC, both high-rise office buildings in Khartoum, were selected as case studies for the validation purposes. The study concluded that the diffuse daylight was simulated more accurately than the direct component. The variation between the measured values and simulated ones occurs at the points facing direct sunlight, and mostly when the sun comes at a low angle, this variation reached twice the measured in four cases. The study highlights the need for more refinement of the software when simulating direct component of daylight in clear sky conditions

Building Research and Information, 2008

Daylight coefficients are normalized contributions from discretized sky or ground segments, or preset solar positions, to solar quantities calculated at various building sensor points. Once generated, daylight coefficients can be folded against luminance efficacy and distribution models to calculate for instance time series of illuminances. Over the last 25-odd years, several daylight coefficient models have been published. The objective of this paper is to propose a standard daylight coefficient model for dynamic daylighting simulations (DDS), consolidating previouslypublished methods. This entails the definition of a standard daylight coefficient data format and accompanying software concepts for dynamic simulation purposes; dynamic in this context meaning variable with time due to changing sky conditions and shading device settings, in contrast to static modelling concepts such as daylight factors. The DDS standard model defines daylight coefficient data that is independent of building location and scene orientation, and generated using either simulation or measurement. DDS provides functionality to take into account independently-controlled daylighting sources (e.g. windows and skylights) and to query different daylighting quantities in a simulation context (e.g. illuminance at one or more sensors, annual daylight performance metrics). A Radiance-based intermodel comparison shows that DDS-based software outperforms the original validated Daysim approach, upon which DDS is based, notably in cases where sensors are subjected to sudden changes in solar exposure, e.g. in an urban canyon or for sensors located far from a window. It is the authors' intent that the proposed DDS standard daylight coefficient model, including the data format and accompanying software concepts, be adopted by daylighting and energy simulation software as a common mechanism for efficiently sharing daylight coefficient data for simulation purposes. Many concepts in this paper are presented with a wide audience in mind, yet the technical content will be more of interest to daylighting and energy simulation researchers and developers.

PLEA, 2013

Integrated daylighting and energy simulation tools aim to accomplish a thorough and accurate wholebuilding energy analysis in buildings and resolve the problems associated with discrete processes. OpenStudio and DIVA are two simulation tools that provide integrated daylighting and energy simulation. The objective of this study is to compare OpenStudio and DIVA software in daylighting performance simulation with results from physical experiment. Through this study Useful Daylight Illuminance (UDI) as an indication of useful annual climate-base daylight was calculated for a toplighting model in DIVA, OpenStudio and experiment. Identical Radiance parameters have been used for both simulations. The results show that the daylight quantities predicted by DIVA are closer to the measured experimental data collected from monitoring the physical model on a year-round basis.

Architectural Science …, 2007

Scale models are frequently used to evaluate daylighting performances of buildings. In order to get accurate results, there are several rules to respect for building these scale models. Some of these rules are universal and others depend on the measurement and observation devices, the type of sky under which the study is carried out and the objectives of the study. This paper, based on the authors experience and on a literature review, presents rules to respect when building a mock-up for daylighting studies. These rules are illustrated by project examples that were tested under the Belgian artificial skies (Single-patch sky and sun simulator, Mirror box and Mechanical sun).

Energy and Buildings, 1984

We derive an equation for zenith luminance as a function of turbidity and solar altitude based on analysis of large quantities of luminance and illuminance data measured in San Francisco, California, between September 1979 and August 1982. Using only average turbidity values to predict hourly zenith luminance as a function of solar altitude can produce large errors. We compare the equation derived from our data, which is valid over a wide range of turbidity and solar altitude, to other published models. We also compare the relationship between horizontal illuminance and zenith luminance from the clear sky and conclude that, when ideal clear days are compared, this relationship is similar to earlier work based on measurements in European climates. Finally, we compare our sky luminance distribution measurements to previous published luminance distributions using the diffusion indicatrix. Our results are intended to help improve daylight availability prediction techniques and define additional requirements for data collection.

Energy and Buildings

We derive an equation for zenith luminance as a function of turbidity and solar altitude based on analysis of large quantities of luminance and illuminance data measured in San Francisco, California, between September 1979 and August 1982. Using only average turbidity values to predict hourly zenith luminance as a function of solar altitude can produce large errors. We compare the equation derived from our data, which is valid over a wide range of turbidity and solar altitude, to other published models. We also compare the relationship between horizontal illuminance and zenith luminance from the clear sky and conclude that, when ideal clear days are compared, this relationship is similar to earlier work based on measurements in European climates. Finally, we compare our sky luminance distribution measurements to previous published luminance distributions using the diffusion indicatrix. Our results are intended to help improve daylight availability prediction techniques and define additional requirements for data collection.

1983

This paper reviews the differences between thermal and daylighting considerations for building design and their implications for using illuminance and irradiance data. Old and new mathematical models for luminance distribution and illuminance calculation are explained. Overcast, clear, and average sky conditions are discussed and their dependence on atmospheric factors is examined. ~ve focus in particular on the turbidity of the clear atmosphere and the luminance at the zenith. We conclude that more measured daylighting data are required for validating the equations that have been developed separately in various parts of the world.