Search

A novel high-dynamic range camera-based approach to measure the cumulative daylight dose in historic/conservation spaces has been devised and tested in a real-world setting under normal viewing conditions. The technique derives illuminance from the high-dynamic range-acquired luminance at numerous patches of the wall surfaces visible in the high-dynamic range image. These patches serve as proxy illuminance meters, thereby allowing the prevailing illumination field across the entire visible wall to be derived using a Kriging algorithm. The technique was validated under both controlled and in-situ conditions over periods of several months and shown to have comparable accuracy to the illuminance logging devices commonly used in historic/conservation settings. The set-up comprising a consumer digital camera and tethered computer proved remarkably resilient and allowed for continuous monitoring periods of six months or more. Application in a real-world setting revealed operational practicalities that would not have been found in a controlled environment.

This paper describes a pioneering in situ study of the daylight characteristics of a historic house interior. A combination of lux measurements inside and outside a historic showroom and recording ...

A new set of CIBSE weather files for building performance simulation was recently developed to address the need for better quality solar data. These are essential for most building performance simulation applications, particularly for daylighting studies and low-energy building design, which requires detailed irradiation data for passive solar design and overheating risk analysis. The reliability of weather data becomes paramount when building performance is pushed to its limits. Findings illustrate how principles of good window design can be applied to a case study building, built to the Passivhaus standard, and how its expected performance is affected by the quality of solar irradiation data. Analyses using test reference years were most affected by changes in the solar radiation model (up to 8.3% points), whereas for design summer years the maximum difference was 1.7% points. Adopting the new model caused overheating risk to be classified as more severe using test reference years than design summer years, prompting a discussion on the design summer year selection method. Irradiance data measured on-site were used as a benchmark to evaluate the new solar radiation model, which was found to significantly improve the accuracy of irradiance data within weather files and so the reliability of overheating assessments. Practical application: CIBSE weather files are widely used for compliance verification of building performance in the UK context. This paper tests how the introduction of a new solar radiation model in weather files will affect daylighting and overheating simulation results. Examples are given on how low-energy building design considerations driven by advanced simulation techniques can help reaching indoor visual and thermal comfort requirements.

Climate-Based Daylight Modelling (CBDM) gives designers the possibility to evaluate complex, long-term luminous environment dynamics. This complexity can be challenging to simulate, and even more challenging to communicate effectively through the use of performance metrics. A multiplicity of CBDM techniques and metrics has been developed over the last two decades, but these were rarely assessed against each other. This paper reviews four state-of-the-art techniques based on the Radiance raytracing engine and systematically compares them against a benchmark CBDM method. Four classroom spaces are used to carry out an inter-model comparison between performance metrics commonly used for compliance verification obtained from all analysed techniques. Additional sensitivity analyses assessed how changes in input variables influence such metrics. Results from the inter-model comparison showed that the representation of direct sunlight is markedly different between the various CBDM techniques, and that metrics based on horizontal direct sunlight are very sensitive to the choice of simulation method. This led to differences in predicted Annual Sunlight Exposure up to 39 percentage points. Metrics that consider both direct and inter-reflected light were found to be more robust, with variations from benchmark results within ± 15%. The analysis of the input variables showed that sensor grid spacing and time-step interpolation do not significantly affect any of these metrics. Changes in orientation and sky discretisation scheme had different effects depending on the metric and technique considered. The need for authoritative benchmarking systems when introducing new performance metrics for compliance verification or new simulation methods is also discussed.

Despite widespread research on daylighting, there are insufficient data to justify a definitive statement on daylighting design criteria. This paper reviews the requirements for daylighting codes a...

This paper describes a proposal for a daylight standard for CEN countries. It is now widely accepted in the research community, and increasingly so amongst practitioners, that the standards/guidelines for daylight in buildings are in need of upgrading. The essence of the proposal is that the ‘target’ for daylight provision should be founded on the availability of daylight as determined from climate files. The proposal is in fact a refinement of an approach originally described in a CIE document from 1970, and which appears to have been largely overlooked since then. The proposal states that a design should achieve a target daylight factor at workplane height across a specified percentage of the relevant floor area for half of the daylight hours in the year, where the target daylight factor is based on the provision of 300 lux. A key feature of the refinements are the formulation of the methodology such that the likelihood for misinterpretation and ‘game-playing’ is greatly reduced, if not eliminated altogether. The method, founded on cumulative diffuse illuminance curves, could be introduced relatively swiftly since it requires only modest enhancement of existing daylight prediction tools. In addition, the proposal will provide a sound ‘footing’ for eventual progression to evaluations founded on full-blown climate-based daylight modelling.

This paper describes a project to reduce the excessive daylight exposure of an oil painting, Hambletonian, Rubbing Down, displayed at Mount Stewart, Northern Ireland. Climate-based daylight modelling (CBDM) was used to understand the light exposure of Hambletonian and to assess the impact of control measures on the annual light exposure and viewing condition of the painting in the winter months. The computer model was used in conjunction with measured lux data to establish the base case light exposure and the effect of the control measures. Light control was implemented through the use of darker paint finishes on the walls and ceiling, which reduced the amount of reflected light reaching Hambletonian; and the addition of a mesh screen to the outside of the glazed dome above the painting. These interventions were cost-effective and straightforward to implement and manage. CBDM suggests the interventions reduced Hambletonian’s annual daylight exposure from 3.5 mlxhr to 0.63 mlxhr.

This paper describes a fundamental rethinking of the basis for the evaluation of the sun- light potential of spaces. It provides a robust methodology to answer the question: how much sunlight can enter a room? The measure proposed is the cross-sectional area of beam sunlight that passes through a window. The new measure { called the sunlight beam index { is described, and examples are given for a realistic residential dwelling. The sunlight beam index is determined for a full year on a time-step basis (e.g. every 15 minutes), but it can be aggregated into monthly or yearly totals. The annual total provides a single measure for: one window; a group of windows; or, all the windows for an entire dwelling.

The evolution of building facades towards increasingly smarter and more complex fenestration systems required an evolution in simulation capabilities too. While simulation software can reliably reproduce the system’s optical behaviour, the climate-based daylight evaluation of entire buildings needs to efficiently combine accuracy and computation speed. Five state-of-the-art Climate-Based Daylight Modelling (CBDM) techniques to evaluate a space with fixed venetian blinds are compared with each others. Multiple options to apply these techniques are also considered. The use of annual metrics based on global illumination led to a good agreement between all methods, while evaluating only direct sunlight exposed some profound differences between simulation techniques.

Energy-efficient building performance requires sophisticated control systems that are based on realistic occupant behaviour models. To provide robust data for the development of these models, research studies in real-world settings are needed. Yet, such studies are challenging and necessitate careful design in terms of data collection methods and procedures. This paper describes and critiques the design of a mixed methods approach for occupant behaviour research. It reviews the methodology developed for a longitudinal study in a real-world office environment where occupants’ experience with a novel facade technology (electrochromic glazing) was investigated. The methodology integrates objective physical measurements, observational data and self-reported experience data. Using data from one day of the study, this paper illustrates how the different sources can be combined in order to derive an in-depth understanding of the interplay between external daylight conditions, characteristics of the facade technology, occupant interaction with the technology and the resulting occupant experience. It was found that whilst the individual methods may be affected by practical limitations, these can be partially offset by combining physical measurements and observations with self-reported data. The paper critically evaluates the individual techniques, as well as the benefits of their integration and makes recommendations for the design of future occupant behaviour studies in real-world settings.

© 2015 Wiley-VCH Verlag GmbH & Co. KGaA. A major application area for electrochromic devices is architectural glazing, particularly that for office buildings which are often highly glazed. This chapter begins with an overview of daylighting in non-residential buildings and explains why the traditional control solutions, for example, blinds, often lead to the under-exploitation of the daylighting potential of the building. It reviews the control of daylight in buildings together with reasons why the traditional methods, for example, venetian blinds, are habitually used in a sub-optimal fashion, often negating the daylight potential afforded by the glazing design. Various types of chromogenic and variable transmission glazing (VTG) are outlined, and the potential for practical use in buildings together with operational factors and performance issues is discussed. The chapter concludes with a description of and preliminary findings from a case study evaluation of a pair of offices spaces in the United Kingdom fitted with EC glazing.

This paper introduces a new paradigm to assess daylight in buildings called ‘useful daylight illuminance’, or UDI. The UDI paradigm preserves much of the interpretive simplicity of the conventional daylight factor approach. In contrast to daylight factors however, UDI is founded on an annual time-series of absolute values for illuminance predicted under realistic skies generated from standard meteorological datasets. Achieved UDI is defined as the annual occurrence of illuminances across the work plane where all the illuminances are within the range 100-2000 lux. These limits are based on reports of occupant preferences and behaviour in daylit offices with user-operated shading devices. The degree to which UDI is not achieved because illuminances exceed the upper limit is indicative of the potential for occupant discomfort. The relation between achieved UDI and annual energy consumption for lighting is examined.

This paper examines the role of assumptions commonly made in validation studies for lighting simulation programs and quantifies the sensitivity of results to uncertainties in key model parameters such as sky conditions and surface reflectivity. Actually occurring overcast skies are often taken to approximate the CIE standard overcast sky for the purpose of comparing predictions against measurements in real buildings. The validity of this assumption is tested against measurements of the sky luminance distribution for real skies. Illuminance predictions are particularly sensitive to the assigned reflectance of surfaces when the direct component of illumination is small. A number of confounding factors that can lead to imprecise estimates of surface reflectivity for building facades are identified and a methodology to minimize their effect is proposed. This study reveals that commonly made assumptions with respect to sky conditions and moderate imprecision in model parameters can lead to erroneous assessments of program accuracy. The degree to which existing validation findings can be extrapolated to very different application scenarios is discussed in the context of reported conflicting assessments of program accuracy.

The evaluation of shading devices is generally carried out using a sequence of shadow-pattern images showing the progression of solar penetration for particular times of the day or year. This approach can reveal when solar penetration may occur, say at the summer solstice, but it cannot give a quantitative measure of the degree and likelihood of solar penetration over a representative period of a full year. This paper describes a new image-based technique to quantify the effectiveness of shading devices. It is founded on predictions of direct solar irradiation using hourly meteorological data for a full year. In addition to numerical output, the technique produces synoptic images that reveal the spatial and temporal variation of solar irradiation. There are no practical limits on the scene geometry and buildings with thousands of individual shading elements can be evaluated. The technique is designed to be both fast and highly scalable making it suitable for the evaluation of a large number of design variants. This is demonstrated in the paper using a parametrically defined model of a complex roof shading system based on the Changi Airport Terminal 3 design. The 3600 fins that comprise the roof shading system were generated using a parametric scheme where the fin orientation has a random component. A total of 42 design variants of the roof shading system were evaluated using the new technique.

This paper describes a novel approach for evaluating the total annual/monthly irradiation incident on building facades in urban settings. The analysis is founded on a physically-based rendering approach and uses data-visualisation techniques to generate ‘maps’ (i.e. false-colour images) of annual/monthly irradiation. The irradiation ‘maps’ are derived from hourly time-series data for 1 year and take accurate account of shading by, and inter-reflection from, other buildings and surfaces. The sun and sky irradiation images are evaluated separately. The sky contribution is calculated using realistic, non-isotropic models for the sky radiance distribution. The ‘maps’ can be used to confidently identify facade-locations where there is high irradiation, for example to aid the siting of photovoltaic (PV) panels. The technique can be applied to scenes of arbitrary complexity from a single building to fully ‘worked-up’ city models. The results of the analysis have been linked to a geographical information system (GIS)-based solar energy planning system. The system is targeted at city planners and one of its aims is to encourage the consideration of solar energy in the urban planning process.

The dynamic control of daylight is seen as key for the effective exploitation of natural illumination in buildings. Traditional control solutions are invariably used in a sub-optimal manner: blinds/shades are left down for long periods and lights are left switched on. A glazing with a transmissivity that varies continuously between clear and dark extremes, and which can be controlled automatically, could be much more effective in providing a ‘well-tempered’ daylit environment that meets occupants needs. Amongst the different types of variable transmission glazing that have undergone extensive research and development in the last few decades, those based on electrochromism appear to have the best performance characteristics and the greatest market potential. Electrochromic (EC) glazing generally exhibits a shift in spectral transmission as the glass darkens, e.g. causing it to appear blue as it tints. Occupants, however, are believed to prefer a neutral spectrum of daylight illumination without any pronounced hue. In this paper, the authors show that it is possible to maintain a neutral spectrum of illumination with electrochromic (EC) glazing under normal operation provided that just a small proportion of the EC glazing is kept in the clear state. A theoretical model to predict the daylight spectrum resulting from any arbitrary combination of clear and tinted glazing is described. Predictions from the model are compared with measurements of the daylight spectra in an office with EC glazing under various states of tint. The predicted spectra show excellent agreement with the measurements. The model is applicable to any combination of clear and/or tinted glass panels irrespective of the glazing type(s). The paper concludes with a discussion of design considerations for the effective deployment of EC glazing.

A true measure of the long-term daylighting performance of a building must account for the illumination that results from a wide range of sky and sun conditions. This paper describes how to predict...

A particle tracking model was used to investigate the annual spring invasion of the North Sea by Calanus finmarchicus copepodites which overwinter in deep water off the Scottish continental shelf. Flow fields generated by a hydrodynamic model (HDM) were used to simulate the advection of zero drag particles representing the copepods. Particles were released simultaneously from a regular lattice of start positions at a given depth (D1), and ascended at a fixed rate (dD/dt) until they reached a final depth (D2) in the surface layers. The proportion of particles reaching target areas in the northern North Sea was relatively insensitive to a moderate degree of variation (±20%) around chosen default values of the vertical migration parameters (D1, D2 and dD/dt), derived from field data. The inclusion of horizontal diffusion velocities and diel vertical migration in surface layers did not significantly affect the results. Sensitivity to wind direction was investigated by applying flow fields from HDM runs with different wind forcing scenarios. For the default vertical migration parameters, only north-westerly winds resulted in particles entering the North Sea from release locations north of the Iceland–Scotland Ridge, where dense aggregations of overwintering copepods were encountered during field surveys. The particle tracking model predicted that the major routes for the spring Calanus invasion into the North Sea were the East of Shetland Atlantic Inflow and the Norwegian Trench Atlantic Inflow, which agreed with seasonal trends observed in Continuous Plankton Recorder data. Overall, despite its relative simplicity, particle tracking was confirmed as a robust tool to explore the causal mechanisms behind the annual invasion of the North Sea by C. finmarchicus emerging from diapause in the deep waters off the Scottish continental shelf.

Book Review of: Reinhart, C. Daylighting handbook I. Christoph Reinhart, 2014. ISBN: 9780692203637.

Daylight in buildings is the natural illumination experienced by the occupants of any man- made construction with openings to the outside. The quantity and quality of daylight in buildings is continually varying due to the natural changes in sun and sky conditions from one moment to the next. In urban settings, the dynamics of daylight illumination are ampli ed by the vertical extent of buildings and the density of the built form. Traditional schema for evaluating daylight in the built environment consider only one or perhaps a few `snapshot' conditions, e.g. a single overcast sky, or a sequence of shadow patterns for selected hours. This chapter describes the application of a technique called climate-based daylight modelling (CBDM) across various urban scales { from o ce spaces to large- scale city models. Climate-based daylight modelling is the prediction of various radiant or luminous quantities (e.g. irradiance, illuminance, radiance and luminance) using sun and sky conditions that are derived from standard meteorological datasets. Climate- based modelling delivers predictions of absolute quantities (e.g. illuminance) that are dependent both on the locale (i.e. geographically-speci c climate data is used) and the building orientation (i.e. the illumination e ect of the sun and non-overcast sky conditions are included), in addition to the building's composition and con guration. The examples described in this chapter include theoretical studies and two `live' projects.

The illuminance predictions from the lighting simulation program RADIANCE are compared with measurements taken in full-scale experimental rooms under real sky conditions for both overcast and clear skies. Results are presented for clear glazing and two types of light shelf. The model sky description is based on the real sky luminance distribution measured by a sky luminance mapping instrument. The sky luminance and room illuminance measurements are simultaneous allowing an extremely accurate representation of the real conditions in the model. Model representation of the measured sky brightness distribution is described.

This is the accepted version of a paper subsequently published in the journal, Lighting Research and Technology. The definitive version is available at: http://dx.doi.org/10.1177/1477153516658429

Closed access. This is an entry in the Encyclopedia of Sustainability Science and Technology.

Daylight distribution and the associated heat gain of a commercial building with curtain wall facade under different degrees of obstruction are studied. A new metric ‘useful daylight illuminance’ (UDI) is applied to analyze the time varying illuminance distribution on a work plane. The solar irradiance obtained from the daylighting simulation is input to a two-node thermal model for energy simulation. The indoor air temperature profile, cooling and heating load requirement and the associated electrical energy consumption based on a typical coefficient of performance (COP) are reported.

The drive towards sustainable, low-energy buildings has increased the need for simple, yet accurate methods to evaluate whether a ‘daylit’ building meets minimum standards for energy and human comfort performance. Current metrics do not account for the temporal and spatial aspects of daylight, nor of occupants comfort or interventions. This paper reviews the historical basis of current compliance methods for achieving daylit buildings, proposes a technical basis for development of better metrics, and provides two case study examples to stimulate dialogue on how metrics can be applied in a practical, real-world context.

A technique to measure arbitrarily complex luminous fluxes across large areas is presented. The technique is founded on high-dynamic range (HDR) imaging technology and can be achieved using a standard consumer digital camera and everyday materials such as printer-grade white paper. The same approach can also be used to determine the direct and diffuse components of illuminance. The technique has been named transmission illuminance proxy - high dynamic range imaging or TIP-HDRI.

The BRE-IDMP validation dataset contains simultaneous measurements of sky luminance patterns and internal illuminances in two full-size office spaces. This benchmark dataset has been applied previously to test the illuminance predictions from a lighting simulation program under real sky conditions. Sky luminance patterns were mapped into the lighting simulation so that the absolute accuracy of the program could be evaluated without the uncertainties that are introduced when sky models are used. For this follow-on study, the BRE-IDMP dataset is now used to quantify the divergence between the sky model generated luminance patterns and the actually occurring conditions based on the resulting internal daylight illuminances. The internal illuminances were predicted using three ‘narrow-range’ models (CIE overcast, CIE clear and intermediate) and the Perez All-Weather model. Predictions from the narrow-range models were used to investigate formulations for sky model blends. The illuminance effect of arbitrary sk...

This article describes a methodology to compare the energy benefit that may result from the adoption of two very different facade technologies in non-domestic buildings. A comparison is made of the energy benefit that might result from: (a) replacing conventional glass with electrochromic (EC) glazing; and, (b) installing PV panels across the opaque sections of vertical facade. The energy benefit from electrochromic glazing is predicted on the basis of displaced electric lighting usage against standard glazing with blinds, whereas the energy benefit from facade PV panels is equal to their delivered electrical output. The evaluation setting is a `typical' six metre deep perimeter office space with vertical glazing. Office orientations for each of the four cardinal compass points are considered. Performance evaluations are founded on a full year's hourly meteorological data for fourteen locales across the world. The predicted energy benefit from electrochromic glazing and facade PV are related to the total annual vertical irradiation incident on the building facade. The findings indicate that the energy benefit that results from replacing standard glazing with electrochromic glazing may exceed that of facade PV for the majority of cases studied. Surprisingly, electrochromic glazings are found to provide the greatest energy benefit for those cases at the lower end of the experienced range in total annual vertical irradiation. The effectiveness of widespread deployment across multiple facades for each locale is examined. The likelihood that electrochromic glazing alone can offer sufficient solar protection without recourse to additional shading is assessed using the recently formulated useful daylight illuminance (UDI) scheme.

This paper describes the application of a new paradigm, called useful daylight illuminance (UDI), to assess daylight in buildings. The UDI paradigm is designed to aid the interpretation of climate-based analyses of daylight illuminance levels that are founded on hourly meteorological data for a period of a full year. Unlike the conventional daylight factor approach, a climate-based analysis employs realistic, time-varying sky and sun conditions and predicts hourly levels of absolute daylight illuminance. The conventional approach produces a single number – the daylight factor as a percentage – for each evaluation point in the space. In contrast, a climate-based analysis results in an illuminance prediction for every daylight hour of the year for each point considered. The UDI paradigm offers a way to reduce the voluminous time-series data to a form that is of comparative interpretative simplicity to the daylight factor method, but which nevertheless preserves a great deal of the significant information content of the illuminance time-series. The UDI paradigm informs not only on useful levels of daylight illuminance, but also on the propensity for excessive levels of daylight that are associated with occupant discomfort and unwanted solar gain. In a conventional analysis of daylight provision and solar penetration, the two phenomena are assessed independently using methods that are idealised (daylight factor) and qualitative (shadow patterns). The UDI paradigm offers a simple methodology whereby daylight provision and levels of solar exposure are quantified using a single evaluative schema. Thus, it is also well-suited for teaching purposes. Application of the UDI paradigm is demonstrated using an analysis of design variants for a deep-plan building with a light-well. Comparison is made with the conventional daylight factor approach, the LEED daylight credit and measures of daylight autonomy.

The objective of this document is to promote the use of dynamic daylight performance measures for sustainable building design. The paper initially explores the shortcomings of conventional, static daylight performance metrics which concentrate on individual sky conditions, such as the common daylight factor. It then provides a review of previously suggested dynamic daylight performance metrics, discussing the capability of these metrics to lead to superior daylighting designs and their accessibility to nonsimulation experts. Several example offices are examined to demonstrate the benefit of basing design decisions on dynamic performance metrics as opposed to the daylight factor.

Scale model illuminance measurements in sky simulator domes are inherently subject to parallax errors. The magnitude of these errors under a number of Commission Internationale de l’É clairage (CIE) clear sky configurations is quantified using computer simulation techniques. In practical operation of a sky simulator dome, a second parallax error in the normalization measurements for horizontal illuminance is likely to compound the parallax error in the other illuminance measurements. This additional parallax error is accounted for in the simulations. The concept of a parallax-bounded volume is introduced. This is the volume of the dome which, on the basis of parallax alone, must contain a scale model if it is not to be subject to errors in the measurement of illuminance beyond a given tolerance. The findings indicate that, on the basis of a credible design goal for the sky simulator dome, high accuracy illuminance predictions (610%) are practically unattainable.