Glare Probability Research Articles

Eight-month experimental study of energy impact of integrated control of sun shading and lighting system based on HDR vision sensor

One fifth of the electricity consumption of Swiss buildings is due to electric lighting. Integrated control of sun shading and artificial lighting can mitigate this demand while maintaining user comfort. However, the drawback of existing building control approaches is that they do not consider one of the main aspects of human-centric lighting: visual comfort. An ‘on-the-fly’ measurement of a visual comfort index, Daylight Glare Probability (DGP), by a novel High Dynamic Range (HDR) vision sensor was introduced into the building control system optimizing the sun shadings position and electric lighting status. As the first approach, this novel solution was tested during a short-term experiment for 15 afternoons at the LESO solar experimental building. The long-term effect of such novel system was evaluated during an eight-month data monitoring campaign. This experiment was carried out in the same building in order to study the ability of a novel control approach to maintain optimal visual and thermal comfort conditions while reducing the energy performance gap of a room as well as its electric lighting demand. The experimental results showed that the advanced controller mitigated the performance gap during the heating season by 72% with regard to a simulated scenario where a standard occupant manually controls the sun shadings and electric lightings; and by 19% with respect to an experimented scenario with best-practice integrated automated shading and lighting system. This system reduced backup heating demand leading to lower CO2 gas emissions. At the same time, visual comfort constraints regarding DGP and workplane horizontal illuminance were respected for 88.1% of work hours.

Photon mapping in image-based visual comfort assessments with BSDF models of high resolution

Data-driven models replicate the irregular Bidirectional Scattering Distribution Functions (BSDFs) of optically Complex Fenestration Systems in daylight simulation. RADIANCE employs the tensor tree to store the BSDF at high directional resolution. Its application in backward ray-tracing is however challenging, since the density of stochastic samples must match the model resolution. BSDF proxy and peak extraction address this problem, but are limited to cases when either the fenestration geometry, or the shape and direction of the transmission peak are known. Photon Mapping is proposed to efficiently sample arbitrary BSDFs from the known sun direction. The existing implementation in RADIANCE is extended to account for light sources and their reflections in the field of view, that are of particular importance for visual comfort assessments. The method achieves a high degree of accordance with ray-tracing, and reduces simulation times by ≈95% with data-driven models of high resolution.Abbreviations: BRT: Backward Ray-Tracing; BSDF: Bidirectional Scattering Distribution Function; CBDM: Climate-Based Daylight Modelling; CFS: Complex Fenestration System; DGI: Daylight Glare Index; DGP: Daylight Glare Probability; FPM: Five Phase Method; GPGPU: General Purpose Graphics Processing Unit; LCP: Laser Cut Panel; OoC: Out-of-Core; PM: Photon Mapping; RMSE: Root Mean Squared Error

Daylighting availability, glare and insolation occupant’s exposure in side-lit room and internal shading devices use

This study aimed to compare building performance indicators regarding daylight glare probability, insolation and daylighting availability Further analysed the potential for glare mitigation through internal shading devices’ uses: roller shades and blinds. Through modelling and dynamic buildings’ simulation (climate-based), an occupant was considered in three positions along with the room’s depth (1.5 m, 3.5 m and 6.0 m). The weather data from Florianópolis, Brazil, was used as environmental conditions. Hourly data of daylight glare indexes, horizontal and vertical illuminances and direct incident solar radiation were transformed into annual frequencies. Regarding the insolation, it was identified occupation commitment at 1.5 m from the window, until 19% of the time occupied. Daylighting availability metrics reached antagonistic levels of suitability. The variations in view directions and positions from the window showed drastic reductions in the intolerable and uncomfortable glare levels, but the second change did not solve the problem. Through internal shading devices’ uses, the glare mitigation was evidenced, according to the solar orientation, the optical properties considered (reflectance and transmittance) and 04 operations proposed. Recommendations were made to protect occupants from glare and insolation but taking advantage of daylighting availability.

A Study on the Improvement of the Evaluation Scale of Discomfort Glare in Educational Facilities

The lighting environment is a factor that significantly affects the physical and psychological aspects of occupants of a building. In particular, educational facilities should be designed to provide adequate natural lighting because it has a profound impact on students’ health and learning performance. Although environmental certification systems include evaluation items for improving the indoor light environment, there is a lack of evaluation criteria regarding the corresponding issue of glare. Therefore, this study aims to help visualize areas where indoor glare problems occur, and to improve the evaluation scale of discomfort glare in environmental certification systems. A standard high school classroom in Seoul was analyzed to study glare issues in the educational space. DIVA for Rhino—Grasshopper, a light environment simulation program based on Radiance and DAYSIM program, was used to obtain reliable light analysis simulation results, and the daylight glare probability (DGP) measure was used to calculate discomfort glare. The results of the simulation and analysis suggest this is a method for improving glare evaluation measures that are lacking in indoor environmental certification standards. The visualized frequency of discomfort glare data is useful for planning the layout of the indoor space, opening, and shading design of a building to prevent glare problems.

Impact of different control strategies of perforated curved louvers on the visual comfort and energy consumption of office buildings in different climates

Highly glazed façades in office buildings are often affected by excessive solar heat gains and daylighting. The use of exterior shading devices is one of the most effective strategies for controlling daylighting and solar heat gains through glazed façades and for maintaining the thermal and visual comfort. Exterior shading systems can either be fixed or movable (tilting and/or retracting). The latter are frequently used with control systems. The objective of this study was to evaluate the impact of four control strategies applied to a shading device made of movable curved and perforated louvers on the visual comfort and total energy consumption (for heating, cooling and artificial lighting) of an office space using integrated thermal and lighting simulations. The investigated control strategies were: an incident irradiance control, a vertical eye illuminance based control, a cut-off angle control and a blocking control. The obtained results were compared to those of three systems with fixed (unmovable) louvers. Simulations were performed for four cities with different climatic conditions: Montreal (Canada), Santiago (Chile), Boulder (USA) and Miami (USA). The assessment of the visual comfort was based on the spatial daylight autonomy (sDA) and simplified daylight glare probability (DGPs). The results indicate that, for the cities of Montreal, Santiago and Boulder, the optimal strategy is the ‘vertical eye illuminance control’, together with the ‘incident irradiance control’ in the case of Santiago. These strategies minimize the total energy consumption of the office space while ensuring visual comfort. In Miami, the best strategy corresponds to the ‘blocking control’ for the south façade orientation while blinds with fixed louvers (tilt angle of 60°) perform better than the active control strategies studied for the west façade orientation. The real world implementation complexity of each control strategy is also discussed.

Performance assessment of the BTDF data compression based on wavelet transforms in daylighting simulation

The bidirectional transmittance distribution function (BTDF), which is used to characterize the light transmission of a complex fenestration system (CFS), commonly involves bulky volume of data that can be a challenge to data storage and transmission in lighting simulation tools and on compact platforms. This paper introduces a compression scheme that is based on planar wavelet transforms with three levels of decomposition to efficiently compress the BTDF data of CFSs and maintain fidelity in daylighting simulation. The root-mean-square error (RMSE) and transmittance error (TE) of compressed medium-resolution BTDF data using three different wavelet bases were evaluated for five different CFS samples at various compression ratio. Based on the results, the generic error from compression did not exceed 20% with CDF9.7 basis for compression ratio up to 200. In the case of rendering an image of a scene in which a CFS was installed at the upper daylighting section of an unilateral façade, errors began to be noticeable at a compression ratio above 70. The uniformity factor g1 was discovered to be relatively sensitive to compression (below 15% error), while the average horizontal illuminance and daylight glare probability (below 10% error) were immune to compression ratio below 100. Compression was also evaluated for a high-resolution BTDF data of external Venetian blinds in the simulation of work-plane illuminance (WPI). With a HDR imaging technique based sky luminance map, the WPI simulation had unnoticeable errors for compressed BTDF data within a compression ratio of 100.

Split-pane electrochromic window control based on an embedded photometric device with real-time daylighting computing

Well-designed electrochromic (EC) glazing control can improve the energy performance of buildings and visual comfort of occupants in highly glazed buildings. This paper designed and demonstrated a compact integrated EC glazing automation system to control tint states of a split-pane EC window according to variations of sky conditions. The control is based on monitoring the luminance distribution of the sky and real-time lighting computation for a building interior, using an embedded photometric device (EPD). It optimizes tint states of EC glazing to offer sufficient daylight provision and temper discomfort glare for occupants, which potentially mitigates excessive solar heat gain. ’In-situ’ experiments were conducted in a full-scale testbed to demonstrate the daylighting performance under various sky conditions. Experimental results showed 83% of the working time for work-plane illuminance (WPI) and 95% of the time for daylight glare probability (DGP) were constrained in comfort range (WPI∈[500, 2000] lux, DGP ≤ 0.35) by the automated EC glazing (controlled by EPD) under clear skies; 68% of the time for WPI and 94% of the time for DGP in confined range under clear skies with thin clouds; 62% of the time for WPI and 85% of the time for DGP in confined range under partly cloudy skies.

A method to evaluate glare risk from operable fenestration systems throughout a year

Nowadays buildings are being designed with large glazed areas mainly due to aesthetics considerations but also to achieve daylit spaces. However, large glazed facades are prone to cause glare problems for building users. To mitigate this risk, it is important to predict existing glare metrics dynamically and reliably in the early stages of the design of a facade. Current evaluation methods for dynamic glare are either computationally too expensive or not suitable for operable façade systems. In this study, a new method is proposed to calculate the Daylight Glare Probability (DGP) index in a computationally efficient fashion, while allowing the fenestration system to switch states during the annual simulation. The method is based on a matrix formalism to calculate the vertical illuminance at a view position, and also on the calculation of a luminance map of the field of view solely from the direct component of the light sources. A first validation of the proposed method is presented. An office setup in Freiburg is monitored with a luminance camera for different weather conditions and different façade systems. Additionally, the calculation of the DGP index by the proposed method is compared with the calculation of the DGP by backward raytracing with high rendering parameters. The proposed method has been implemented in a building simulation program, called Fener. A case study is presented to illustrate the new possibilities offered by the Fener tool. The glare risk of three different textile roller blinds, with similar visible transmittance but different openness coefficient, is assessed.

Integrated parametric design of adaptive facades for user's visual comfort

Abstract The idea of Adaptive Solar Facade (ASF), as a modular, dynamic, and flexible types of smart facades could be a promising approach in a comfort-centric design through the proper integration with the parametric design. Therefore, this paper is to investigate the development process of ASF grounded on parametric design tools with a focus towards its visual comfort indices through a controllable shading system. To that end, first, a comprehensive literature review was carried out to develop an origami-based dynamic system, and three numerical timing patterns were then applied using Grasshopper plug-in for Rhino. In addition, the environmental plug-ins of Honeybee and Ladybug were employed to determine indoor daylight quality via different geometrical and physical properties. Thus, 1800 design models were prepared, based on several variables including rotation motions, indoor view angles, time hours and transmittance properties in order to investigate the daylighting performance and glare probability in a single office space located in the hot-arid climate representative; Tehran, Iran. Furthermore, interactive correlations between the geometrical pattern and visual performance were investigated, leading to this fact that the proposed prototype can significantly improve the flexibility of the shading system to control visual comfort. As the conclusion, all datasets were integrated into an algorithmic workflow while converting its advantages and limitations into an optimization process. Finally, a full potential hexagonal adaptive system was presented to achieve the maximum visual comfort level based on the users' preferences that can be the basis for future investment on smart building envelopes.

Automated ‘Eye-sight’ Venetian blinds based on an embedded photometric device with real-time daylighting computing

Optimal shading control can improve occupants’ visual comfort and increase energy savings on artificial lighting and cooling loads during warm seasons. A highly integrated automated shading system is presented in this paper. Designed to regulate daylighting according to the varying sky conditions in decentralized applications, it optimizes visual comfort for occupants and maximizes their view outwards. The shading control is based on real-time lighting simulation for a building interior based on sky (and landscape) luminance distribution monitoring. Its lighting simulation quality was validated in a daylighting test module showing a 10% root-mean-square error in both work-plane illuminance (WPI) and daylight glare probability (DGP). Conducted under various sky conditions during summer, autumn and winter, the shading control demonstrated its capability in regulating daylight provision, mitigating excessive solar heat gain, tempering discomfort glare, and maximizing outside view for occupants with minimal delay. The results showed that the WPI was maintained within the range of [500, 2000] lux in 96% of working time under clear skies and in between 79% and 88% of working time under partly cloudy skies. The expected mitigation of cooling loads due to excessive solar heat gain (SHG) was estimated to reach 47% during a warm climate, compared with no shading protection. The automated shading system was also demonstrated to successfully occlude glare due to secondary reflections on specular surfaces from surroundings.

Potential Benefits of PV-Shading System in Office Buildings and Semi-Continental Climate Conditions

Solar PV shading devices are good solutions to control daylight and reduce the unwanted solar gains, while generate electricity at the same time. Since thermal, electrical and daylighting performance competing each other, it is imperative to consider specific design criteria to optimize and allow energy efficient level of thermal and visual performance. In this context, the study focus on the optimum design of PV shading devices for typical office building with high fenestration ratio and climate conditions of Prague. TRNsys simulation environment was used for the evaluation of the power and thermal performance of the PV shadings considering various tilt angles, projection depth and orientations. Ecotect/Daysim software tools were used to evaluate the daylighting performance and lighting energy use. Useful Daylight Illuminance (UDI) and Discomfort Glare Probability (DGP) indices were also calculated for indoor visual comfort analysis according to the design configuration. Results were overall evaluated to reveal the potential energy benefits compared to the non-shaded case. The study serves as a guide for the optimum design of PV shading systems.

Analysis of the daylight performance of window integrated photovoltaics systems

Integrating photovoltaics into windows provides the possibility of including an additional function of energy production to a conventional building fenestration component. There is no doubt that electrical power can be generated on-site. However, the effect of PV windows on the indoor luminous environment of the space served by them has not been comprehensively researched. This paper investigated the daylight performance of integrating four types of photovoltaics (semi-transparent thin film Cadmium telluride (CdTe) solar cells with 10% and 50% transparency, crystalline silicon solar cells with and without crossed compound parabolic concentrators (CCPC)) to a window of a typical south-facing office under different Window-to-Wall Ratios (WWRs). Annual useful daylight illuminance (UDI), daylight uniformity ratio (UR) and daylight glare probability (DGP) have been analysed based on dynamic simulation using RADIANCE. The simulation results show that windows integrated with crystalline silicon cells and CCPC optics have the potential to provide best daylight availability when compared with standard double glazed windows and other tested PV window prototypes, if it is applied to rooms with large WWRs (e.g. 60% or 75% WWR) at high latitudes (e.g. city of Harbin). Its application also improves the uniformity of daylight spatial distribution and eliminates the risk of glare. Semi-transparent CdTe PV window with 10% transparency can also improve the percentage of working hours that fall into UDI 500–2000lux range, however, it will result in the most sharp illuminance contrasts within the room. Applying all of these tested PV windows can effectively reduce the possibility of glare.

Comprehensive evaluation of window-integrated semi-transparent PV for building daylight performance

Building-integrated semi-transparent photovoltaic windows (PV windows) have been considered as a potential candidate to replace conventional windows to improve building energy efficiency and hence reduce carbon emissions. With the integration of PV windows, the indoor luminous environment may be significantly affected. The presence of solar cells may cause undesirable shading, low illuminance levels and affect colour quality of the transmitted daylight. Therefore, it is important to comprehensively assess daylight performance of PV windows to ensure a comfortable luminous environment. In this study, the daylight performance of Cadmium telluride (CdTe) PV window with four different transparencies (i.e. 20%, 30%, 40% and 50%) applied to a cellular office space has been assessed in terms of daylight quantity and daylight quality. RADIANCE was selected to predict the annual daylight performance through advanced dynamic metrics including Useful Daylight Illuminance (UDI), simplified Daylight Glare Probability (DGPs) and Illuminance Uniformity (Uo). Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI), which are two attributes to characterise the colour quality of transmitted daylight were used to evaluate performance of the selected PV windows. CCT and CRI were calculated under three CIE standard daylight scenarios (CCT of 4000 K, 6500 K and 25000 K respectively). It is found that CdTe PV windows can significantly improve the homogeneity of daylight distribution on a task area located close to the window and reduce the risk of daylight glare when compared with the performance of a conventional double glazing. Moreover, the recommended CCT (i.e. 3000–7500 K) can be achieved with the employment of CdTe PV windows under 4000 K and 6500 K daylight scenarios. All of the CdTe PV windows examined were able to maintain CRI at a comfortable level i.e. above 90 under the three daylight scenarios.

A Novel Approach for the Definition of an Integrated Visual Quality Index for Residential Buildings

Visual quality is an important component of indoor environment quality and greatly affects inhabitants’ perception of the living space. Nevertheless, the lighting design of residential buildings is usually underestimated by both designers and standards. This paper presents an integrated index for evaluating the visual quality of an indoor environment in residential buildings. The main parameters considered are daylight access, probability of glare from daylight and electric illumination, maintained illuminance, and color temperature. These aspects are evaluated throughout a whole year using a fixed set of metrics and are combined using relative weights. It was decided to also consider qualitative parameters in order to give more importance to some psychological aspects of visual comfort. Finally, the building visual quality index is obtained by a weighted average of the results of each room with the addition of the qualitative parameters. The applicability of the index was tested through the simulation of a dwelling that will be built and monitored in the context of the Comfort for Sustainable Buildings in the Alps (CASA) research project. The building visual quality index proved to be useful during the design process, allowing for improvements in both electric illumination and daylight access through a comparison of different solutions. This study could represent a step towards the holistic evaluation of indoor environment quality.

Study on the overall energy performance of a novel c-Si based semitransparent solar photovoltaic window

This paper introduces a novel c-Si based building integrated photovoltaic (BIPV) laminate. It was produced by cutting standard crystalline silicon solar cells into narrow strips and then automatically welding and connecting the strips into continuous strings for laminating between two layers of glass. The overall energy performance of the BIPV insulated glass unit (IGU) including power, thermal and daylighting performance was investigated experimentally. The daily energy conversion efficiency of the active solar cell area was about 15% on sunny days, but it was less than 12% on cloudy days and overcast days. Due to the combined effect of both the semi-transparent PV laminate and the insulated glass unit, the solar heat gain coefficient (SHGC) of the BIPV IGU was as low as 0.25, which was much lower than commonly used glazing windows. Daylight analysis by means of high dynamic range (HDR) cameras and daylight glare probability (DGP) indicated that the BIPV IGU could reduce discomfort glare to some extent compared to clear glass windows. The net energy production of the BIPV IGU was estimated without considering the differences in HVAC energy use in this study. The artificial lighting energy consumption was about 431 W h/day while the average BIPV electricity production for the same period was 1940 W h/day. The net power generation was therefore 1509 W h/day for this BIPV IGU in Berkeley, California. Shading tests for the BIPV IGU were also conducted and the results revealed that the vertical configuration of solar cell wiring in the BIPV laminates was much more sensitive to horizontal shading patterns than vertical shading models. Thus, if shading was unavoidable in some cases, a reasonable arrangement of PV strings should be considered to bring down the energy loss as much as possible. Also, the impacts of environmental factors on the energy conversion efficiency of BIPV IGU were analyzed. Specifically, the power output declined by 0.42% of the peak power for each Celsius degree temperature rise. Thus, if more attention was paid to the heat dissipation issue of BIPV IGU, the overall energy conversion efficiency would be improved.

Design optimisation of internal shading device in multiple scenarios: Case study in Bandung, Indonesia

In daylighting design for buildings, provision of solar shading device is required to ensure satisfaction of the visual comfort criteria in response to the sky condition. However, since real sky is constantly changing, the optimum state of the shading device would ideally be adaptive and dynamic, thus no single optimum solution can be expected. In this case, computational daylight simulation is a powerful tool for exploring the potential and solving the optimisation problem. This research therefore aims to demonstrate the use of computational daylight simulation to optimise internal shading device, regarding various daylight metrics in a real open-plan office with a west façade orientation in Bandung, Indonesia, using Rhinoceros and Grasshopper. To simulate multiple sky condition scenarios, optimisation was performed for four ranges of diffuse solar irradiance, i.e. 1–80 W/m2, 80–159 W/m2, 159–289 W/m2, and 289–541 W/m2, considering input variables of type of blinds (horizontal or vertical), slat angle, and blinds material specularity. The optimum solutions were obtained using Pareto frontiers that have been filtered with the constraints, which were determined separately for each scenario. Results show that the spatial daylight autonomy (sDA300/50%), annual sunlight exposure (ASE1000,250), and percentage of daylight glare probability (%DGP>0.21) can all satisfy the design criteria.

Cross-validation and robustness of daylight glare metrics

This study evaluates the performance and robustness of 22 established and newly proposed glare prediction metrics. Experimental datasets of daylight-dominated workplaces in office-like test rooms were collected from studies by seven research groups in six different locations (Argentina, Denmark, Germany, Israel, Japan and the United States). The variability in experimental setups, locations and research teams allowed reliable evaluation of the performance and robustness of glare metrics for daylight-dominated workplaces. Independent statistical methods were applied to individual datasets and also to one combined dataset to evaluate the performance and robustness of the 22 glare metrics. As performance and robustness are not established in literature, we defined performance as: (1) the ability of the metric value to describe the glare scale (evaluated by Spearman rank correlation), and (2) the ability of the metric to distinguish between disturbing and non-disturbing situations (evaluated by diagnostic receiver operating characteristic curve analysis tests). Furthermore, we defined robustness as the ability of a metric to deliver meaningful results when applied to different datasets and to fail as few as possible statistical tests. Average Spearman rank correlation coefficients in the range of 0.55–0.60 as well as average prediction rates to distinguish between disturbing and non-disturbing glare of 70–75% for several of the metrics indicate their reliability. The results also show that metrics considering the saturation effect as a main input in their equation perform better and are more robust in daylight-dominated workplaces than purely contrast-based metrics or purely empirical metrics. In this study, the daylight glare probability (DGP) delivered the highest performance amongst the tested metrics and was also found to be the most robust. Future research should aim to optimise the terms of glare equations which combine contrast and saturation effects, such as DGP, PGSV or UGRexp, to achieve metrics that also perform reliably in dimmer lighting conditions than the ones explored in this study.

A Simplified Approach for the Annual and Spatial Evaluation of the Comfort Classes of Daylight Glare Using Vertical Illuminances

A simplified approach to calculate the daylight glare comfort class (imperceptible, perceptible, disturbing, or intolerable glare) on annual basis and for a grid of points in a space is presented. This method relies on the calculation of the vertical illuminance (Ev) for each grid point only, which is compared to an Ev threshold value for each daylight glare comfort class. These Ev threshold values are determined through a comparison with the Daylight Glare Probability (DGP) values on an annual basis through a fault-detection technique, for a reduced number of points. Compared to an annual calculation of exact DGP values on a certain grid, this approach is able to evaluate the daylight glare comfort classes only, but it is less time consuming. The paper presents and critically discusses this simplified method by means of its application to different case-studies: south and west oriented office in Turin (Lat 45.1° N), in which the DGP is assessed for three points in the space, considering glazing with different transmission properties (specular or scattering) and visible transmittances, as well as three operable internal shading systems (one venetian blinds and two roller blinds, for solar or glare control). For the presented case studies, the average error in the classification of the space according to daylight glare comfort classes is below 5% when comparing this simplified approach to related DGP values.

Investigation of an integrated automated blinds and dimmable lighting system for tropical climate in a rotatable testbed facility

Performance of automated blinds and auto-dimming lighting system in providing lighting energy savings and occupant visual comfort was studied in a rotatable testbed facility located in tropical Singapore. The automated Venetian blinds system, consisting of a daylight-redirecting top portion and a glare-controlling bottom portion, was controlled by an in-house developed control algorithm designed specifically for tropical climate of Singapore to introduce maximum daylight while minimising Daylight Glare Probability (DGP). The auto-dimming lighting system used Digital Addressable Lighting Interface (DALI) controller to control T5 fluorescent and LED luminaries. Energy consumption by the lighting system, working plane illumination distribution and DGP were monitored by a network of sensors and high-dynamic range (HDR) camera systems. Compared to non-dimmable T5 lighting, LED lamps provided about 24% of lighting energy savings. Auto-dimming technology showed about 46% lighting energy savings. LED lamps coupled with auto-dimming showed around 80% lighting energy savings. Without window blinds, the working plane illuminance exceeded the recommended 3000 lx level during certain time of the day and DGP exceeded 0.35. The automated blinds effectively eliminated glare discomfort, and with the automated blinds working in conjunction with the auto-dimming, significant lighting energy savings was achieved without compromising the illuminance level at the working plane. 75% of lighting energy savings was achieved for North orientation and 63% for East orientation. Façade orientation was found to have a significant impact on the lighting energy savings potential, with the North orientation achieving higher daylight savings due to higher daylight redirection possibility throughout the day. The lighting energy savings potential is higher for clearer sky conditions due to higher daylight availability. Implementation of daylight re-directing shading system has significant lighting energy savings in the tropics. These lighting energy savings can be captured by deploying an auto-dimming system. With careful design of the system and control algorithm, the lighting energy savings can be achieved while maintaining good visual comfort.

Overall energy assessment of semi-transparent photovoltaic insulated glass units for building integration under different climate conditions

Semi-transparent photovoltaic (STPV) windows, which can not only generate electricity in situ, but also effectively reduce solar heat gain while utilizing natural daylight, have gained increasing popularity due to their energy and environmental benefits. However, the poor thermal insulation performance of single-glazed STPV windows has restricted their application in cold climate regions. PV insulated glass unit (IGU) is an alternative for STPV window applications. This paper presents a comprehensive assessment on overall energy performance of PV-IGUs with different PV glazing transmittance and rear glasses in comparison with conventional IGUs in five different climate zones in China. The results show that PV-IGUs can achieve energy savings in all the representative cities. The largest energy savings are observed in Kunming where heating and cooling demands are low but annual solar radiation level is high. In cold climate regions like Harbin, the PV-IGU with higher transmittance and rear low-e glass consumes less net source energy in comparison with that with lower transmittance and rear clear glass. Although the lighting energy demand of PV-IGU is larger than conventional IGU, the daylight quality of the room with PV-IGU is better due to the higher useful daylight illuminance (UDI) and lower daylight glare probability (DGP).