Christoph Reinhart

Monitoring manual control of electric lighting and blinds

This paper reviews, validates and extends present knowledge of the degree and kind of manual control strategies of blinds and electric lighting systems that are used in private and two-person offices. A new monitoring setup was applied from March to December 2000 in 10 daylit offices in Germany that featured manually operated electric lighting and automatically controlled external venetian blinds with manual override. The data shows that individuals consistently followed the same control strategy for their electric lighting and blinds. Groups of individuals tended to activate their electric lighting according to Hunt’s probability function, although there was a large spread between individual control levels. All subjects used their blinds to avoid direct sunlight above 50 W/m2, and incoming solar gains above 50 klux (~450 W/m2). They also were more willing to accept automatic blind opening than closing.

The simulation of annual daylight illuminance distributions — a state-of-the-art comparison of six RADIANCE-based methods

Abstract The present work discusses simulation results of annual indoor illuminance distributions for two office geometries situated in Freiburg, Germany, calculated with six different RADIANCE-based daylight simulation methods. These methods are the ubiquitous daylight factor method [P.J. Littlefair, Predicting annual lighting use in daylit buildings, Building and Environment 25 (1990) 43–54.], ADELINE 2.0 [M. Szerman, J. Stoffel, ADELINE 2.0, Radlink Technical Manual, IEA Solar Heating and Cooling, Task 12.], the classified weather data according to Herkel and Pasquay [S. Herkel, T. Pasquay, Dynamic link of light and thermal simulation: on the way to integrated planing tools, 5th Int. IBPSA Conf., Prague, Sept., 8–10, 1997, Vol. II, pp. 307–312.] and two simulation procedures based on daylight coefficients according to Tregenza, namely ESP-r version 9 series [J.A. Clarke, M. Janak, Simulating the thermal effects of daylight-controlled lighting, Building Performance (BEPAC), (1) (Spring 1998).] and a new accelerated method developed by the authors. The new method calculates 145 diffuse and three ground daylight coefficients in a single raytracing run which considerably reduces the required calculation times for an annual daylight simulation. An explicit calculation of the indoor illuminances under all 4703 annual hourly mean sky luminance distributions from the Freiburg test reference year (TRY) serves as a reference case against which the other methods are tested. The simulation results reveal that the accuracy of an annual daylight simulation method is not necessarily coupled with the required simulation time. The quality of an annual simulation rather depends on the underlying sky luminous efficacy model and whether the method considers the hourly mean direct and diffuse illuminances for each time period explicitly. The two methods relying on daylight coefficients exhibit the lowest relative root mean square errors (RMSEs) for the straightforward office geometry. The results for the advanced office show that internal illuminance contributions due to external ground reflections are only considered by the new method.

The ‘adaptive zone’ – A concept for assessing discomfort glare throughout daylit spaces:

Discomfort glare is an underutilized parameter in contemporary architectural design due to uncertainties about the meaning of existing metrics, how they should be applied and what the benefits of such analysis are. Glare is position and view direction-dependent within a space, rendering it difficult to assess compared to conventional illuminance-based metrics. This paper compares simulation results for five glare metrics under 144 clear sky conditions in three spaces in order to investigate the ability of these metrics to predict the occurrence of discomfort glare and to hence support the design of comfortable spaces. The metrics analyzed areDaylight Glare Index, CIE Glare Index, Visual Comfort Probability, Unified Glare Rating and Daylight Glare Probability. It is found that Daylight Glare Probability yields the most plausible results. In an attempt to deal with multiple positions and view directions simultaneously, the concept of an ‘adaptive zone’ is introduced within which building occupants may freely adjust their position and view in order to minimise the effect of glare. The spatial and directional extents of the adaptive zone depend on furniture layout and the freedom of occupants’ tasks. It is found that applying the adaptive zone concept to a sidelit office with manually operated venetian blinds reduces the predicted hours of intolerable discomfort glare from 735 to 18 occupied hours per year and increases the annual mean daylight availability from 40% to 72%.

Dynamic annual daylight simulations based on one-hour and one-minute means of irradiance data

Abstract This study investigates the influence of the short-term dynamics of daylight on simulation-based predictions of the annual daylight availability in a building. To this end annual indoor illuminance simulations are carried out for a two-person-office using the RADIANCE-based dynamic daylight simulation method DAYSIM. As of yet, all available daylight simulation methods are typically based on 1-h means of irradiance data and thus tend to neglect the short-term dynamics of daylight. In the first part of this study the dependence of the annual daylight availability on the underlying simulation time step interval is quantified. Assuming two different automated daylight-dependent artificial lighting strategies, the predicted annual artificial lighting demand is systematically underestimated by up to 27% on the simulations based on 1-h means instead of 1-min means of measured beam and diffuse irradiances. The general validity of these results is ensured by employing irradiance data from five stations world-wide. As measured 1-min means of irradiance data are generally not available for practical applications, the stochastic Skartveit–Olseth model, which generates 1-min means of irradiance data from hourly means, is adapted for daylight simulation purposes in the second part of this study. The utilization of modeled 1-min means of irradiance data reduces the above described systematic simulation errors to below 8% for both automated lighting strategies and all five stations. Accordingly, the modified version of the Skartveit–Olseth model is able to enhance the quality of dynamic daylight simulations — without any additional planning effort for the lighting designer.

Experimental Validation of Autodesk® 3ds Max® Design 2009 and Daysim 3.0

Abstract This article compares daylight simulation results generated with two simulation programs, Autodesk® 3ds Max® Design 2009 (3ds Max Design) and Daysim 3.0 (Daysim), to indoor illuminance measurements in a sidelit space. The sidelit space was in a single location, but was configured with five fenestration and glazing options, and operated under a variety of sky conditions. The measurements form a set of ‘daylighting test cases’ that were recently developed to evaluate the simulation capabilities and limitations of different daylight simulation programs. Both 3ds Max Design and Daysim were given external direct and diffuse irradiances as simulation input, from which the programs predicted indoor illuminances on a grid of upward facing work plane sensors and downward facing ceiling sensors. 3ds Max Design is based on Exposure™ technology, a lighting analysis module that includes a ‘shader’ of the Perez sky model and that uses the mental ray® raytracer for the global illumination calculation. Daysim also uses the Perez sky model and is based on the Radiance backward raytracer combined with a daylight coefficient approach. The comparison of both programs with measurements demonstrated that 3ds Max Design simulated indoor illuminances for the daylighting test cases with reliability comparable to Daysim. Most mean bias errors and root mean square errors were in the range of those reported in earlier validation studies: both programs succeeded in reproducing measurements for a sidelit space with and without a lightshelf. While 3ds Max Design consistently underestimated the incoming light flux going through a translucent panel, Daysim results were lower than measurements for the internal venetian blind test case. The results suggest that the accuracy of both programs is sufficient for typical daylighting design investigations of spaces with complexity comparable to the five daylighting test cases.

Predicting the Daylit Area—A Comparison of Students Assessments and Simulations at Eleven Schools of Architecture

ABSTRACT In recent years, climate-based metrics, in particular daylight autonomy, have found their way into North American standards and green building rating systems. The authors showed in an earlier pilot study that subjective space evaluations by architecture students correlated well with daylight-autonomy-based daylit area simulations in a single north-facing studio space in Boston. For this article, the authors collaborated with educators at 11 schools of architecture and applied the method consistently to 13 spaces within the participating schools. The schools are located in Brazil (2), Canada (1), Egypt (1), and the United States (7). The authors also introduce the concept of a “partially daylit area” metric based on a minimum illuminance threshold for daylight autonomy of 150 lux. The two metrics correctly determined in 18 out of 24 cases which parts of the study space are fully or partially daylit. The authors accordingly propose a two-tier evaluation system to rate the daylight availability in spaces.

A rules of thumb-based design sequence for diffuse daylight

This paper proposes and validates a daylighting design sequence for sidelit spaces. Since the design sequence uses the daylight factor as a performance metric, it is aimed towards spaces that primarily receive diffuse daylight. It should be complemented by a design analysis that looks at direct sunlight for glare and energy considerations. The sequence interconnects and refines earlier proposed rules of thumb and is intended to be used during the earliest design stages when concepts regarding programming, floor plans, massing and window areas are initially explored. All steps within the sequence were ‘validated’ using Radiance simulations of over 2300 sidelit spaces. During step one of the sequence the effective sky angles are calculated and target daylight factors are defined for all potential daylit zones within a building. In step two a refined version of the ‘daylight feasibility study’ is used to help the design team to identify building zones with high daylighting potential based on a target mean daylight factor criterion. During step three suitable interior room dimensions and surface reflectances are determined using a combination of the Lynes’ limiting depth, ‘no sky line’, and window-head-height rules of thumb. Step four provides a more accurate estimate of the required glazing area for each zone based on the Lynes daylight factor formula which is also validated as part of this work. The effect of external obstructions is considered throughout the process. The paper closes with a discussion of the merits of the design sequence compared to the glazing factor spreadsheet calculation method promoted by LEED-NC 2.2.

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.

A Concept for Predicting Occupants’ Long-Term Visual Comfort within Daylit Spaces

ABSTRACT A new visual comfort concept is introduced to describe the long-term visual impression of space occupants. This concept, in contrast to instantaneous assessment of visual comfort, aims to describe an overall rating of visual quality in a space. A paired study consisting of occupant surveys and detailed 6-minute time step visual comfort simulations was performed for the studio spaces of Gund Hall in Cambridge, Massachusetts, which is occupied by approximately 500 students. Occupants reported four primary ways of experiencing visual discomfort: discomfort glare, insufficient monitor contrast, direct visibility of the sun, and direct sunlight on the workplane. Survey results were located spatially and in terms of orientation within Gund Hall, and a simulation model was calibrated based on furniture layout, measured material reflectances, and local measured weather data. The results of the study illustrate that it is possible to use current simulation-based visual comfort predictions to predict occupants’ long-term visual comfort assessments in a complex daylit space. By classifying occupant responses into two broad groupings of comfortable and uncomfortable, the prediction methodology correctly identifies reported comfort or discomfort from 73.2% to 86.5% of cases depending on time of day; however, more research is required for broader application of the long-term visual comfort model to other buildings. Through a spatial and temporal presentation of the simulation data, this new methodology can be used as feedback during the process of designing daylit spaces, avoiding visual discomfort, and increasing satisfaction within the built environment.

Learning by playing – teaching energy simulation as a game

Being able to read thermal simulation results and to adapt ones design accordingly has become an essential skill for graduating and practicing architects. This article proposes and evaluates an innovative way of how this skill can be taught via a 90-min in-class exercise or ‘game’ based on DesignBuilder/EnergyPlus. The game was tested in a class of 47 architecture students who competed to generate the lowest energy use intensity (EUI) for an office building in Boston. Design upgrades were associated with a cost premium and the overall upgrade budget was capped. The EUIs of the 10 final submissions were 22–31% below the base variant. While student essays revealed a clear preference for game-based learning vis-a-vis conventional teaching methods, the authors further propose that the game nourishes the emergence of an energy modelling ‘culture’ within schools of architecture that may lead to enhanced communication between architects and energy modellers.