A concept to evaluate dynamic daylight glare

Abstract

A method towards a dynamic daylight glare evaluation in the early stage of design was developed in this thesis, using existing glare metrics under multiple observer positions and gazes. The results pointed out that it is possible for a zonal characterization regarding glare sensation to be achieved with the combination of multiple existing metrics and a weighting system, named the adaptation possibility.
Initially, a literature review was conducted in order to specify the limitations of the existing glare metrics and the different practices used for glare evaluation. Then the thesis continued in the definition of the proposed methodology and the case study on which the method would be tested.
The proposed methodology for a dynamic and zonal glare evaluation would account for different gaze directions and observer positions, as well as, the adaptation possibility in terms of head rotation and glare duration. Multiple glare metrics were used in the method as the literature review indicated that, there is a need either for an enhanced glare metric that would meet the current limitations or for a combination of the existing ones. Thus, the existing glare metrics of DGP, DGPs and DGI were implemented in the method. For the extraction of one glare value per position, two indicators were created named the Total Point Glare (TPG) and the Space-Time Glare (STG) based on a point-in-time analysis and a period of time respectively. It is important to note that, the method included arbitrary assumptions which needed to be validated ‘in situ’.
The case study was that of a hypothetical library room in Stockholm with one fully glazed façade facing South. Additionally, the performance of different shading systems, such as venetian blinds and roller shades, were tested. After a direct sun analysis at eye level, a specific grid was formed indicating the different possible positions of the observer in the space. The observer would be able to rotate his head in each position and, thus, the study would account for multiple gazes with a fixed visual centre directed towards a computer screen. The time step of the analysis was that of 1 hour.
The results of the study indicate that provided glare free area under roller shades reached 100% during a small period of time. However, the glare free area coverage fluctuated a lot between extremes (from 100% to only 20% of the total space). Such rapid variations could potentially have a negative impact on visual comfort counteracting any temporary glare protection. On the contrary, the performance of the venetian blinds seemed to be more stable, even though the glare free area coverage did not reach 100% of the space.
It was found that, even though the method allows the placement of the furniture/partition at an early design stage, it is still quite expensive in terms of computational time. This issue could be solved in the future when supercomputers will be available to the general public and lighting simulation may rely on more efficient engines.
Since the method derived from researched rules of thumb and reasoneable hypothesis implemented in a virtual model, should be further investigated and validated with empirical studies with human subjects.
Regarding the case study, it was found that, different metrics could evaluate the space differently according to the parameter that they are based on (e.g. Contrast, beam illuminance, dim space conditions), indicating the importance to implement specific metrics under the corresponding circumstances. Different shading systems could provide different choices for the glare assessment. The examined statistic shading systems indicated that the venetian blinds could partially shade the glare source and regulate the contrast, while the roller shades limited the possibilities of adaptation at each case. It was interesting to observe that the DGP indicated low glare risk in 100% of the space under roller shades, while almost 100% problematic area under the venetian blinds.

Popular Abstract

Glare is a physiological phenomenon influencing visual comfort. While disability glare is easier to assess, discomfort glare has been rather difficult to be estimated. Most of the metrics found in literature are, to some extent, reliable predictors of glare. However, they refer to specific conditions for a point in time and a point in space with a certain direction of gaze. This implies that they are mostly useful during an advanced design stage. But how reliable would be a daylight glare evaluation of a whole space, based only on one view and a point-in-time analysis? More and more daylight researchers conclude that current glare estimation practices form a base for development. This thesis proposes a specific methodology for a dynamic and zonal glare evaluation during a period of time. The aim is not the development of a new glare metric, but rather the combination of the existing ones in an earlier design stage.


The proposed methodology considers different observer positions and gaze directions, while accounting for the adaptation possibility in terms of head rotation and glare duration. Three glare metrics were implemented, the DGP, DGI and DGPs, as they could enhance the total glare evaluation by describing the glare sensation either based on contrast and/or direct sunlight penetration. Eventually, two indicators were developed, the Total Point Glare (TPG), that outputs one glare indication value per position and point-in-time, and the Space-Time Glare (STG), that provided one glare prediction value per position during a longer period of time.
For the development of the aforementioned method, a virtual model of a hypothetical library room in Stockholm was used, having a fully glazed façade towards South. The performed analysis was grid-based, in order to simulate the possible movement of the occupant in the space. Additionally, the occupant could rotate his head so, that multiple gazes would be examined. The study considered the impact of two shading systems, namely venetian blinds and roller shades, on glare risk assessments.
Zonal glare analysis could drastically improve the design of space by evaluating different areas in terms of glare probability and glare free space availability. Even though the method allows the placement of the furniture/partition at an early design stage, it is quite expensive in terms of computational time. This issue could be solved in the future when supercomputers will be available to the general public and lighting simulation may rely on more efficient engines. Since the method derived from reasoned assumptions and hypothesis, should be further investigated and validated with empirical data.
The investigated glare indices presented a similar pattern regarding the critical zones of space. Different metrics could lead to different interpretation of the results, indicating the importance to implement specific metrics under the corresponding circumstances. Furthermore, regarding the tested shading systems, it was shown that the diffusive systems could maintain approximately the same illuminance levels. However, the provided glare safe area coverage would vary a lot during the day, counteracting the seemingly enhanced visual comfort.

• author: Tsianaka, Efthymia Eirini
• supervisor: Niko Gentile
• organization: Division of Energy and Building Design; Department of Architecture and Built Environment
• course: AEBM01 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Arts and Architecture; Technology and Engineering
• keywords: glare, daylight, zonal, long-term, adaptation possibility, TPG, STG, directional glare, weighting system, dynamic, visual comfort, fenestration system
• publication/series: Master thesis
• language: English
• id: 8964204
• date added to LUP: 2018-12-17 13:39:55
• date last changed: 2018-12-17 13:39:55