Daylighting control performance of a thin-film ceramic electrochromic window: Field study results

Control system development and lighting energy monitoring of ceramic thin-film electrochromic (EC) windows were initiated at the new full-scale window systems testbed facility at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, CA. The new facility consists of three identically configured side-by-side private offices with large-area windows that face due south. In one room, an array of EC windows with a center-of-glass visible transmittance T_v range of 0.05–0.60 was installed. In the two other rooms, unshaded windows with a T_v = 0.50 or 0.15 were used as reference. The same dimmable fluorescent lighting system was used in all three rooms. This study explains the design and commissioning of an integrated EC window-lighting control system, and then illustrates its performance in the testbed under clear, partly cloudy, and overcast sky conditions during the equinox period. The performance of an early prototype EC window controller is also analyzed. Lighting energy savings data are presented. Daily lighting energy savings were 44–59% compared to the reference window of T_v = 0.15 and 8–23% compared to the reference window of T_v = 0.50. The integrated window-lighting control system maintained interior illuminance levels to within ±10% of the setpoint range of 510–700 lx for 89–99% of the day. Further work is planned to refine the control algorithms and monitor cooling load, visual comfort, and human factor impacts of this emerging technology.     

A statistical approach for estimating diffuse illuminance on vertical surfaces

This paper presents a statistical approach for estimating vertical diffuse illuminance in a tropical environment. A two-year period (2003–2004) of vertical and horizontal diffuse illuminance data from four measuring stations in Thailand were used for the model development. These data were divided into three groups according to sky conditions, namely clear, overcast and partly cloudy skies. Vertical and horizontal diffuse illuminances in overcast conditions were directly related using regression analysis and an equation relating vertical diffuse illuminance to horizontal diffuse illuminance was established. A similar set of equations was established for vertical sunlit and shaded surfaces under clear sky condition. To obtain the vertical illuminance model for all sky conditions, the correlation equations for clear and overcast skies were linearly combined using cloud cover as a weighting parameter. The performance of this regression model was evaluated using a one-year period (2005) of measured data. The discrepancies between the calculated and measured vertical illuminance in terms of RMSD range from 15.1% to 22.4%, depending on sky conditions, the orientation of the receiving surface and the positions of the sun relative to the surface. The performance of the proposed model was also compared to that of 12 models reported in literatures. It was found that the proposed model has the lowest RMSD for clear, partly cloudy and overcast sky conditions.     

Research on minimum illumination as a function of visual performance

The objective of this research is to find minimum illuminance level such that a visual task (in this case is reading) still can be done properly. The reading object in this research is sentences (written in Bahasa Indonesia) and printed in Times New Roman font on a white A4 paper. Three factors are observed, i.e. font size, luminance contrast (between letters and paper), and reading distance.Measurements were made of the minimum illumination that was needed by subjects, such that they still can read the object properly. The experiment was done in a dark room and the illuminance level on the object from a lamp was adjusted by using a dimmer device.The results of this experiment show that the lowest minimum illuminance of 0.13 lx (for reading object with font size 16, luminance contrast of 0.93, and distance of 60 cm) and the highest of 15.32 lx (for reading object with font size 8, luminance contrast of 0.55, and distance of 100 cm). By using analysis of variance method, it can be shown that reading distance is the most influential factor for the minimum illuminance level, and then followed by dimension and luminance contrast.     

The New York Times Headquarters daylighting mockup: Monitored performance of the daylighting control system

A 9-month monitored field study of the performance of automated roller shades and daylighting controls was conducted in a 401 m² unoccupied, furnished daylighting mockup. The mockup mimicked the southwest corner of a new 110 km² commercial building in New York, New York, where The New York Times will be the major tenant. This paper focuses on evaluating the performance of two daylighting control systems installed in separate areas of an open plan office with 1.2-m high workstation partitions: (1) Area A had 0–10 V dimmable ballasts with an open-loop proportional control system and an automated shade controlled to reduce window glare and increase daylight, and (2) Area B had digital addressable lighting interface (DALI) ballasts with a closed-loop integral reset control system and an automated shade controlled to block direct sun. Daylighting control system performance and lighting energy use were monitored. The daylighting control systems demonstrated very reliable performance after they were commissioned properly. Work plane illuminance levels were maintained above 90% of the maximum fluorescent illuminance level for 99.9 ± 0.5% and 97.9 ± 6.1% of the day on average over the monitored period, respectively, in Areas A and B. Daily lighting energy use savings were significant in both Areas over the equinox-to-equinox period compared to a non-daylit reference case. At 3.35 m from the window, 30% average savings were achieved with a sidelit west-facing condition in Area A while 50–60% were achieved with a bilateral daylit south-facing condition in Area B. At 4.57–9.14 m from the window, 5–10% and 25–40% savings were achieved in Areas A and B, respectively. Average savings for the 7-m deep dimming zone were 20–23% and 52–59% for Areas A and B, respectively, depending on the lighting schedule. The large savings and good reliability can be attributed to the automatic management of the interior shades. The DALI-based system exhibited faulty behavior that remains unexplained, but operational errors are expected to be resolved as DALI products reach full maturity. The building owner received very competitive bids ($30–75 US/DALI ballast) and was able to justify use of the daylighting control system based on operational cost savings and increased amenity. Additional energy savings due to reduced solar and lighting heat gains were not quantified but will add to the total operational cost savings.     

Sky model blends for predicting internal illuminance: a comparison founded on the BRE-IDMP dataset

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 sky model blends is reproduced in a post-process of the illuminance predictions from the ‘narrow-range’ sky model types. The determination of an optimum sky model blend is described. The findings show that relatively simple blends of just two pure sky models (e.g. CIE overcast and intermediate) may be adequate for the prediction of time-varying illuminances founded on climatic test reference year data.     

An analysis of climatic parameters and sky condition classification

In modelling solar radiation, of the required data daylight illuminance, luminous efficacy, radiance and luminance sky distributions, are always analysed under various sky types. Sky conditions are frequently categorised into overcast, partly cloudy and clear using some common climatic data including cloud cover (CLD), sunshine hour (SH) and solar radiation. This paper presents the study of these climatic parameters and their applications in the classification of sky condition. Frequency of occurrence and cumulative frequency distribution of each sky indicator have been established to interpret the prevailing sky conditions in Hong Kong. Special features on defining the sky clearness are highlighted and the implications for energy-efficient building designs are discussed.     

Modelling and simulation of virtual natural lighting solutions with complex views

In situations where daylight is insufficiently available, Virtual Natural Lighting Solutions (VNLS) can be promising to turn currently unused floor space into spaces with enough daylight qualities. This article introduces VNLS models with complex image scenes pasted on a transparent glass surface in front of arrays of small, directional white light sources. The objectives are twofold: the first one is to understand the effect of changing input variables, i.e. beam angle, total luminous flux of the “sky” elements, and image scene itself, on the lighting performance of a reference office space. The second objective is to compare two techniques of modelling the view, i.e. transmissive and emissive approaches, using Radiance. Sensitivity analysis of the simulation results show that under every image scene, the total luminous flux of the “sky” element is largely influential to the space availability, whereas the beam angle of the “sky” element is largely influential to the other output variables, including discomfort glare. The findings lead to a suggestion of preferred elements in the image scene, to ensure large space availability and uniformity. The transmissive approach generally generates smaller values of space availability, and largely depends on the view elements of the image scene. In turn, the average probability of discomfort glare using the transmissive approach is smaller than that using the emissive approach.     

A field study of illuminance reduction

Many offices are illuminated at levels much higher than necessary for office tasks. Lowering ambient illuminance, while maintaining task illuminance, i.e., task-ambient lighting, can save energy without impairing visual performance. A downside of task-ambient lighting is rooms appear dark and gloomy. Maintaining brightness perception is the key to success in task-ambient lighting. To examine the practicality of brightness-enhanced task-ambient lighting for illuminance reduction a field study was conducted in a modern office setting. This study examined office workers’ responses to approximately one-third lower ambient illuminance than the initial illuminance and two measures designed to enhance brightness perception: higher correlated color temperature lamps (6500 K) and sparkle elements. Surveys showed that after an initial adaptation period, office workers were generally satisfied with the lower level of ambient lighting. They did increase their use of task lighting at their desks but this had little impact on overall energy consumption. The 6500 K lamp was effective at increasing perceptions of brightness in offices with the lower ambient light level. Over a longer period, the sparkle elements used did not significantly change workers’ perceptions of gloom.     

Advanced lighting simulation in architectural design in the tropics

This paper outlines a 2-year research program that the team attempted to apply one of the most powerful computational lighting simulation softwares, radiance, to assist in the daylighting design of an actual building in the tropics. The validation studies, which were carried out in the Asian Civilisation Museum (ACM) in Singapore, showed that radiance can be used to predict the internal illuminance with a high degree of accuracy under overcast sky conditions. The experimental application of radiance to daylighting investigation of the ACM further supports its capabilities as well as its accuracy. Using radiance to study two daylighting control options (curtains and louvers), it can be found that louvers are more effective than curtains as daylighting control devices, and that the angle of the louvers have more effect than their reflectance on daylight penetration and distribution.     

Verification tests of a mirror box type artificial sky without and with building scale model

A mirror box type artificial sky for simulating the CIE standard overcast sky has been designed and constructed, while the verification method has been developed and tested. Ratio between the mirror height above the workplane and the room length is 60:133 or 0.451, whereas the ratio between the mirror height above the workplane and the room width is 5:9 or 0.556. Taking the CIE standard overcast sky as reference, indoor illuminance ratios at various elevation angles relative to the zenith is found to be more consistent than luminance ratios. The largest error of illuminance and luminance ratios are respectively 10% and 43%, obtained at 0° elevation angle. Horizontal workplane illuminance values are on average 11,400lx, with illuminance uniformity U₀ and U₁ of respectively 0.92 and 0.86. Based on test results with a building scale model, four out of nine measuring points inside the model have small errors, four have medium error, and one has a large error of 25%. Most of the obtained errors are within the tolerable range of ±21% from the ideal values. Based on the conducted tests, the constructed mirror box type artificial sky is considered appropriate to be utilized for its purpose.     

Determination of vertical daylight illuminance under non-overcast sky conditions

In a dense urban region in which high-rise buildings are packed inside limited land areas, the daylight components reflected from ground and surrounding buildings play significant roles in daylighting design. The natural light available in an interior strongly depends on the amount of daylight reaching the window facades. Lately we proposed a calculation procedure, presented in form of simple mathematical expressions and diagrams, to determine the daylight illuminance on a vertical plane under overcast skies. This paper extends the study to non-overcast sky conditions. The performance of the proposed method was evaluated by comparison with the daylight illuminance simulated by a lighting software, namely RADIANCE, and with measurements under real skies. It was found that the data estimated by the proposed method were in good agreement both with the values simulated by RADIANCE and with the measured results. The paper offers to architects and building engineers a useful tool for estimating the daylight illuminance and in particular for determining and assessing various daylighting schemes and concepts during design and construction stages.     

A simple model of domestic lighting demand

This paper presents a new model of domestic lighting demand. The model is based on half-hourly data measured for a sample of 100 UK homes. It represents one sub-model in an end-user based distributed load model that is being developed to support investigations into the effects on low voltage urban electricity networks of future wide-scale uptake of solar technologies. To capture these effects and to serve applications involving renewable energy technologies (RETs) generally, the model is capable of representing load variations on very fine time-scales, down to 1 min intervals. Additionally, scaling factors are provided to enable prediction of long-term trends and to model some of the most important elements of diversity between connection points that are likely to impact on network performance and design below the 11 kV substation level.     

The use of shading systems in VDU task offices: A pilot study

We registered how eight subjects used their remotely controlled black Venetian blinds in eight individual offices, every 15 min, over a period of 30 weeks. This also included measuring parameters such as the illuminance on the window, the illuminance on the VDU screen, the ambient temperature inside the room, the presence of the worker and the state of the artificial lighting. During the same period, we registered the position of the blinds in seven other offices fitted with manually controlled fabric blinds, through webcam pictures taken every 15 min. There was no further monitoring inside these offices.With the data collected, several hypotheses regarding the use of Venetian blinds in offices were tested. It appeared that office workers were consistent in the way they used their shading system, however it was difficult to draw general conclusions on blind usage. The type of control of the shading system also seemed to be important. Remotely controlled black Venetian blinds were used three times more often than manually controlled fabric blinds. In addition, most of the time users adjusted the tilt of the slats of the Venetian blinds downwards, towards the external ground. We also came to the conclusion that the higher the quality of the VDU screen (in terms of emitted luminance levels), the more likely a worker was to tolerate high levels of diffuse reflections on it, hence taking more advantage of the daylight available.     

Development of electrochromic evacuated advanced glazing

Electrochromic evacuated advanced glazing has been developed, combining optimum dynamic control of the solar radiation penetrating into buildings with a high degree of thermal insulation. This was achieved by the optimisation of the electrochromic device materials (electrochromic, ion storage, protective layers, transparent conductors and polymer electrolytes) and by the refinement of a sealing method for evacuated glazing. Electrochromic evacuated glazing prototypes with dimensions up to 40 cm × 40 cm have been fabricated using vacuum techniques and chemical methods. The prototypes exhibit excellent optical and thermal performance, with a contrast ratio up to 1:32 (visible dynamic transmittance range T_lum,bleached = 63% and T_lum,colored = 2%), coloration efficiency up to 92 cm²/C and mid-pane U-values as low as 0.86 W m⁻² K⁻¹. Their durability in relation to real working environmental conditions has been assessed through indoor and outdoor testing. Such a glazing can be used in building applications to improve occupant thermal comfort, contribute to a reduction in space heating and cooling loads and allow for increased areas of fenestration thereby reducing artificial lighting loads. These factors reduce the energy demand for the building and therefore contribute to the reduction of carbon dioxide emissions.     

Possibility of using roof openings for natural ventilation in a shallow urban road tunnel

Naturally ventilated urban vehicular tunnels with multiple roof openings have increased in China. Unnecessary gas (polluted air or fire smoke) are expected to be exhausted out through openings. Whether its safety standards can be satisfied or not still needs to be verified. In this paper, a safe CO concentration was firstly discussed, and a heat risk level of very high to extreme up to 46 °C was given. Secondly, a real 1410 m tunnel was proposed, and a 1/10 scale model tunnel was reproduced. Ambient winds of 0.95 m/s in prototype and 0.3 m/s in model were considered. Under normal traffic test, a track circuit was constructed with model vehicles moving on it to form traffic wind, and once the air velocity was larger than 0.31 m/s, the airflows were found to be not relevant to the Reynolds number. The traffic winds were weakened by openings. For three of all tested traffic, the actual air velocities were larger than the required ones, so its air qualities were satisfied. In firing test, two sets of burning experiments were conducted with which the heat release rates (HRR) were 8.35 kW and 13.7 kW. Large amounts of smoke were exhausted out of openings, and the high-temperature was not significant. Full-scale numerical simulations were carried out to verify the experimental results respectively using Fluent 6.0 for normal traffic and FDS 4.07 for firing. The simulations were compared well with the experiments. Further FDS simulations show that the openings’ mass flow rates are influenced little by ambient temperature; with the increasing length of the buried section, much smoke accumulate inside leading to a high temperature; having 4–5 openings in one shaft group is oversize in the actual engineering design.     

Interactive fire spread simulations with extinguishment support for Virtual Reality training tools

Virtual Reality training for fire fighters and managers has two main advantages. On one hand, it supports the simulation of complex scenarios like big cities, where a fire cannot be simulated in the real world. On the other hand, fire fighting VR simulators allow trainees to experience situations as similar as possible to real fire, reducing the probability of accidents when they are practising exercises with real fire.The success of the Virtual Reality training tools also depends on how close to reality the simulation process is. This work provides fire spread algorithms for forest and urban environments, which can be used at interactive rates. Due to the interactive nature of the algorithms, the users are able to fight the fire by throwing extinguishing agents.Although the algorithms assume many simplifications of the problem, their behaviour is satisfactory. This is due to the efficient management of the cell states in a 3 m×3 m cell grid. Also the variables that have more influence on fire propagation constitute the core of the algorithms. The overall system deals with user extinguishment actions, natural and artificial firebreaks, variable wind conditions (even at a cell level) and non-contiguous fire propagation (embers and spotting fires). The unified forest/urban model leads to an object oriented architecture which supports the fire propagation algorithms. This also allows the system to compute efficiently mixed forest–urban environments.     

Daytime artificial lighting in office buildings in India

The paper describes the results of a detailed subjective study on supplementary artificial lighting under (i) field conditions and (ii) controlled conditions in office buildings. Analysis of the data reveals that the amount of light required for the satisfactory performance of an office task varies from 100 to 200 lx. Hence 150 lx task illuminance with modelling vector lying between 1.5 and 2.5 gives an acceptable office interior luminous environment. The average value of 1.2 for the ratio of workplane illuminance at centre to rear of the room lays emphasis on the requirement of uniform lighting on workplanes. The acceptability of fluorescent lights (CCT 6800°K) has also been supported. A formula E_s = 110?0.88 E_n for E_n>30 lx has been suggested for the estimation of the quantum of artificial light required to supplement the available daylight for Indian conditions.     

Occupant related household energy consumption in Canada: Estimation using a bottom-up neural-network technique

A national model of residential energy consumption requires consideration of the following end-uses: space heating, space cooling, appliances and lighting (AL), and domestic hot water (DHW). The space heating and space cooling end-use energy consumption is strongly affected by the climatic conditions and the house thermal envelope. In contrast, both AL and DHW energy consumption are primarily a function of occupant behaviour, appliance ownership, demographic conditions, and occupancy rate. Because of these characteristics, a bottom-up statistical model is a candidate for estimating AL and DHW energy consumption. This article presents the detailed methodology and results of the application of a previously developed set of neural network models, as the statistical method of the Canadian Hybrid Residential End-Use Energy and Greenhouse Gas Emissions Model (CHREM). The CHREM estimates the national AL and DHW secondary energy consumption of Canadian single-detached and double/row houses to be 248 PJ and 201 PJ, respectively. The energy consumption values translate to per household values of 27.8 GJ and 22.5 GJ, and per capita values of 9.0 GJ and 7.3 GJ, respectively.     

Finite element simulation to design constructive elements: An application to light gypsum plaster for partitions

In the past decade finite element simulation has become a very useful methodological tool in the different science fields. This article offers a specific application of this powerful mechanism used for analyzing the mechanical behaviour of constructive elements in the design phase, prior to the laboratory tests’ stage. The aim of applying this simulation is to minimize the high cost the real scale fabrication of these elements entails.This research focuses on the analysis by finite element simulations (FES) of several construction elements used as interior partitions and made of plaster lightened with cork. The results of the study will allow us to determine the most suitable thickness values and proportions to ensure that the requirements stated by the standards and norms for light partitions are fulfilled. These parameters will later be useful for the final laboratory tests.Two simulation groups have been developed using the ANSYS application: firstly, a partition leaf of 200 × 260 cm is studied exposing it to a superficial load and to an eccentric load following the EUAtc common directives for the technical appreciation of light panels, 1973). Second, the behaviour of a panel with a through opening is tested with the simulation regarding the different hypothesis of the structure deformation supporting and surrounding it.Finally, it is proved that the element of thickness 7 cm and proportions stated at the beginning ensure a good performance regarding strain without producing any visible fissures, and therefore are suitable for a further laboratory test on real models.     

Optimal sun-shading design for enhanced daylight illumination of subtropical classrooms

This study investigates the feasibility of fitting windows with sun-shadings in order to minimize the lighting power costs in daylight-illuminated classrooms lit from a single side in subtropical regions. An IES-CPC model is created of a representative classroom in Taiwan, and a series of simulations is performed to determine the average illuminance value and the uniformity of the illuminance distribution in the classroom under various lighting conditions with no sun-shadings fitted to the window. The numerical results are found to be in good agreement with the experimental measurements obtained using an array of nine-channel photometers. Having confirmed the validity of the simulation scheme, the illumination properties of four different sun-shading designs are considered. The results show that a double-layered sun-shading represents the optimal sun-shading design in terms of achieving a uniform illumination distribution within the classroom. Given appropriate physical dimensions, this daylight access device achieves the minimum illuminance requirement of 500 lx and improves the lighting uniformity ratio from 0.25–0.35 to 0.40–0.42. Furthermore, using this sun-shading device, the required illuminance ratio of 0.5 can be obtained simply by switching on one of the three rows of lights in the classroom. Accordingly, the daylight access device not only improves the illuminance conditions within the classroom, but also reduces the lighting power cost by 71.5% compared to the case where all of the lights are turned on.