Comparison of Different Glare Indices through Metrics for Long Term and Zonal Visual Comfort Assessment

Nowadays different indices are used for the assessment of the visual discomfort related to glare, such as Daylight Glare Index, Daylight Glare Probability, and Vertical Eye illuminance. Regardless of their effectiveness in detecting glare perception, all these indices are intended to be local and instantaneous, not summarizing the long term glare perception through the space (Carlucci et al. 2015). In this work, a set of metrics able to express both the time constancy, i.e. availability, and the spatial uniformity, i.e. usability, has been used for detecting discrepancies and inconsistencies between the glare indices when dealing with time and space distribution. Results confirm that different glare indices can lead to different conclusions not only when considering point and instantaneous values but also when analysing availability and usability. Moreover, the availability and usability representations, indirectly confirm themselves effective in providing a global assessment of the confined space analysed, even when visual comfort is concerned

Assessment Of Long-Term Visual And Thermal Comfort And Energy Performance In Open-Space Offices With Different Shading Devices

Solar radiation plays a significant role in reducing building energy consumption for air-conditioning and lighting and affects thermal and visual comfort conditions. Additionally, for the occupants of confined spaces, daylight strongly affects not only the human performance but also the general well-being, both from a psychological and physiological point of view. On the other hand, large windows on building façades may facilitate the entry of daylight and solar heat gains, increasing the risks of overheating or visual discomfort. In these cases, the proper use and control of shading devices is mandatory to prevent glare and direct solar radiation on the occupants, even while affecting the energy performance. The best balance between those contrasting requisites has to be defined by comparing the behavior of different combinations of glazing systems and shading devices, while considering the specific application context. In the assessment, different metrics are needed to analyze both comfort and energy aspects. In this paper, the effects of external and internal roller shades, both on thermal and visual comfort and on overall building energy demand, have been considered for the climatic conditions of Rome. An open-space office with windows distributed on a single façade or on opposite façades, and directed towards 2 orientations (South or South/North and East or East/West) has been simulated. The window area and the glazing system have been changed in order to evaluate the shading performance in several office configurations. The thermal comfort indoor conditions have been controlled by fixing adequate operative temperature set points. Shades with three different levels of solar and light transmission coefficients have been chosen for the comparison. To fulfill occupant visual comfort, the shades are controlled based on two set points: on a limit glare index of 22 DGI and on the maximum total solar radiation incident on the windows - 150 W m-2. An illuminance level of 500 lux during the hours of occupation is guaranteed by dimmable artificial lighting. Concerning the energy performance, the office primary energy demand for heating, cooling and lighting have been calculated. The assessment of the long-term comfort conditions has been conducted on a seasonal basis, taking into account both the thermal and visual comfort conditions. Regarding thermal comfort, the Discomfort Time weighted by the Predicted Percent of Dissatisfied (WDTPPD) and the radiant temperature asymmetry have been calculated in 9 points in the office including also the effect of the diffuse and beam solar radiation directly reaching the occupants. The visual comfort has been assessed through three climate-based metrics: the Spatial Daylight Autonomy (sDA), which describes the annual sufficiency of ambient daylight levels, the Annual Sunlight Exposure (ASE), which describes the annual potential risk of visual discomfort in interior work environments and the Daylight Glare Probability (DGP), which is the percentage of disturbed people. The dynamic simulation has been conducted in EnergyPlus 8, while the visual aspects have been analyzed with DaySim and equivalent lighting simulation codes

On The Representation Of The Thermal And Visual Behavior Of A Roller Shade Material: Comparison Between Different Simulation Models

Shading systems, if efficiently operated, can improve the internal environmental quality, namely both thermal and visual comfort, and reduce the energy consumption due to cooling needs. Roller shades represent one of the most commonly used types of shading systems, in particular in the tertiary sector. Not only they can be easily installed and maintained, but also they often represent the only design choice when existing buildings are considered. Although roller shades are characterized by a beam-beam and by a beam-diffuse transmittance, both changing according to the incidence angle, as the transmitted solar radiation decreases with the increase of it, they are typically modelled assuming equal reflectance and emissivity for both sides and perfect diffuser behavior, with transmittance and reflectance independent from the solar radiation incidence angle. Neglecting the daily variability of these properties can lead to underestimate their impact on the occupants comfort conditions. In this paper, different models for representing the roller shades behavior, embedded in two widely diffuse simulation codes have been compared with a set of measured data, recorded at the Bowen laboratories of the Purdue University (Indiana USA), combining thermal (Energy Plus) and lighting simulation (Energy Plus or DIVA for Rhino). The thermal properties of the building materials and the internal gains have been calibrated for the thermal simulation, in order to evaluate better the models capability of predicting the roller shades behavior. Then, starting from the simplest daylighting model, which assumes the roller shades as perfect diffusers, more complex characterizations have been considered and validated through the comparison with the measured data.

On the global performance of offices with different Complex Fenestration Systems

Complex fenestration systems influence indoor comfort conditions and energy consumption in a complex way. If all the involved aspects are not considered jointly since the design phase, buildings can show a deep gap between their planned and real performance, especially when dealing with low energy buildings (Vanhoutteghem et al., 2015). This can be avoided by identifying the design configurations able to provide a trade-off between contrasting requisites: improving comfort conditions while minimizing energy use. This work analyzes and compares different design solutions for an open space office from a global performance perspective. Dependence on the building characteristics and operation strategy has been assessed by comparing two different windows sizes, three glazing systems, and three different approaches to control the shading devices, for a South oriented fa\ue7ade in the climate of Rome. The study has been conducted combining a RADIANCE/DAYSIM lighting simulation with EnergyPlus for the thermal comfort and energy analysis. A set of metrics, able to express both the time constancy and the spatial uniformity of visual and thermal comfort conditions, has been evaluated together with the energy demand for heating, cooling, and lighting. The results show how a global approach allows obtaining a more comprehensive building performance evaluation and, consequently, identifying design solutions capable of enhancing both energy efficiency and occupant comfort

Comfort metrics for an integrated evaluation of buildings performance

The capability of expressing all the different aspects of the building's performance, besides and beyond the mere energy behavior is becoming more and more important, because of the increased expectations related to either new construction or the renovation of existing buildings. Even though building energy performance is one of the main aims of an appropriate design process or of a suitable management strategy during the operation phase, it can be strongly undermined by the underestimation of the role of the indoor environmental quality. Poor thermal or visual comfort not only affects occupant satisfaction, well-being and productivity, but also induces actions and operations that ultimately compromise the energy efficiency targets. In order to support the design approach, including, since the very beginning, the comfort conditions among the design requisites, a set of metrics is proposed in this work, considering either time constancy or spatial uniformity of a single comfort aspect -or of different aspects at the same time. These metrics have been applied to a simulated reference environment, in order to test their ability to represent the performance of the envelope components when comparing building configurations characterized by high solar and daylighting gains and different window and shading configurations

Comfort and energy performance analysis of different glazing systems coupled with three shading control strategies

Shading control strategies are often required to optimize the balance between solar gains, daylight availability, glare protection, and view to the outside. Automated shading operation, when properly designed, may avoid performance losses due to manual operation while maintaining indoor environmental comfort. In this work, the integrated performance of different glazing systems coupled with three control approaches for roller shades is presented for a typical office space. The first control is a standard open\u2013closed operation based on a workplane illuminance range, while the other two are able to set intermediate shade positions according to the solar position to maximize daylighting. The third control addresses excessive daylight on the workplane by imposing a workplane illuminance threshold to reduce the risk of daylight discomfort glare. Daysim, based on Radiance and the daylight coefficient method, was used to calculate the annual illuminance profile over the workplane, and Evalglare was used to calculate glare indexes. EnergyPlus was used for thermal comfort and energy analysis. The results were processed through aMATLAB code for transferring required information from one tool to another. Moreover, to assess the global performance of the shading controls and fenestration configurations studied, visual and thermal comfort were evaluated through a set of metrics able to express both the availability (the fraction of time with acceptable comfort conditions at specific positions) and the spatial usability (the fraction of space simultaneously within comfort range at specific moments). The energy performance was also quantified in terms of primary energy demand for heating, cooling, and lighting. The results showed that it is possible to balance daylighting, thermal and visual comfort, and energy use. This can be achieved by simultaneously selecting shading controls that allow adequate daylight without causing glare, and glazing properties with good thermal performance that allow adequate daylight (high visible transmittance) but limit solar gains (lower solar transmittance or solar heat gain coefficient [SHGC]) for moderate and cooling-dominated climates

Long-term and spatial evaluation of the integrated performance of a window-shade system in an open space office located in Rome

The building façades, as a boundary between external and internal environments, play a central role in energy reduction and suitable comfort conditions maintenance. Their evaluation requires an integrated assessment approach, focused on occupants’ thermal and visual comfort, in time and space, as well as on maximizing daylight and achieving energy saving goals. In this paper, dynamic simulation is used to evaluate the integrated performance of different fenestration systems in an open space office located in Rome. The illuminating analysis has been performed using DIVA, and the results, processed by means of a Matlab code, have been used as an input for Energy Plus thermal and energy analysis. Then, the Energy Plus outputs have been post processed to calculate the solar radiation influence on occupants thermal comfort. Some new metrics have been introduced in such a way that it is possible to assess the comfort performance with comprehensive indicators

Dynamic Commercial Façades versus Traditional Construction : Energy Performance and Comparative Analysis

Driven by architectural trends and the need to maximize daylight, commercial building façades have become more transparent. High-performance façades include spectrally selective glazing systems, dynamic elements and insulated spandrel sections. Nevertheless, it is generally accepted that, compared to standard, traditional opaque construction, modern transparent envelopes result in increased overall energy use in these buildings. In this paper, the building façade is treated as a part of the building perimeter zone, which also includes electric lighting controls, shading attachments, HVAC components, and indoor environmental controls. Consequently, the objective is to balance the need for daylighting and view versus the need for controlling of solar gains and maintaining human comfort, while reducing energy demand for air conditioning and lighting. Key parameters in solving this problem are (1) technological advancements in glazing products, (2) utilization of dynamic building envelope components, and (3) lighting and HVAC controls. In order to demonstrate the potential of high-performance façades, a typical office building with large perimeter zones is used as an example. The basic model consists of standard brick exterior walls with 20% punched windows. Then, a comparative analysis is performed for a more transparent envelope with dynamic systems including shading and electric lighting controls, for the climates of Chicago and Rome. An integrated thermal-lighting model with flexible dynamic system controls, verified with commercial software, is expanded to simulate more complex façade controls for reducing glare problems while maximizing useful daylight. The results show the advantages of transparent façades with active systems, compared to traditional building envelopes. The more transparent building results in lower operational costs and source energy use, although total site energy use can be higher for heating-dominated climates