Modern highly glazed buildings require solar shading in order to obtain visual and thermal comfort for the occupants in addition to obtain a low energy use of the building. For the system to respond to the external conditions in an intelligent manner, automated operation is needed. When utilising an automatic solar shading system, it is important to use a control strategy that is accepted and preferred by the occupants. Consequently, the objective of this study is to investigate occupant satisfaction with respect to visual comfort under two blind strategies: one simple control strategy with closed slats when the solar shading is activated and one more detailed control strategy that utilises the cut-off angle of the slats or a minimum slat angle of 15˚ when solar shading is activated. Results from the study are helpful in the development of control strategies for blinds and are indications of how blinds should be treated in building design. Responses from 40 participants in a repeated measure design survey revealed that the detailed control strategy was significantly more popular among the test subjects than the simple control strategy. Comments by the participants gave strong indications that view to the outside influenced the choice of preferred control strategy. Even if the detailed control strategy was found to be the most preferred, the results indicate that it was not sufficient to avoid glare. Based on the results, both glare and view aspects should be incorporated in the building design to a greater extent than what is common practice today. It can further be recommended that more effort is put into finding optimal set points for activation of the solar shading and for controlling the tilt angle of the blind in order to obtain a more robust control strategy with limited overrule actions.

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a b s t r a c tModern office buildings are often designed with highly glazed facades, with an intention of being sufficiently day lit. However, extensive daylight supply has its backside, as glare might be a considerable concern. From a building design perspective it is important to be able to make reasonable predictions of discomfort glare from windows already in the early design stage when decisions regarding the façade are taken. This study focus on verifying if simple illuminance based measures like vertical illuminance at eye level or horizontal illuminance at the desk are correlated with the perceived glare reported by 44 test subjects in a repeated measure design occupant survey and if the reported glare corresponds with the predictions from the simple Daylight Glare Probability (DGPs) model. Large individual variations were seen in the occupants' assessment of glare in the present study. Yet, the results confirm that there is a statistically significant correlation between both vertical eye illuminance and horizontal illuminance at the desk and the occupants' perception of glare in a perimeter zone office environment, which is promising evidence towards utilizing such simple measures for indication of discomfort glare in early building design. Further, the observed response indicate that the participants in the present study were more tolerant to low illuminance levels and more sensitive to high illuminance levels than the DGPs model would predict. More and larger studies are needed to confirm or enfeeble this latter finding.

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