Shaping the slats of hospital patient room window blinds for daylighting and external view under desert clear skies

Provision of daylighting and external view in hospitals is crucial as they create a positive healing environment. They could help in reducing patient stress, fatigue and length of stay, while increasing patient and staff safety and satisfaction. However, in desert locations that are typically characterized by year-long clear skies, control of solar penetration is essential. Window blinds were used to decrease patients’ visual discomfort and improve illuminance levels. The shape of blind slats influences daylighting performance and exposure to external view. The objective of this paper was to identify the shapes of horizontal blind slats that best suit a common hospital patient room layout design under the predominantly clear-sky of Cairo, Egypt. The paper utilized parametric tools and simulation software to systematically test possible slat shapes. A total of 77 slat shapes were examined. The objective was to fulfill year-round daylighting adequacy on the bed surface and the room area, and to maximize patient’s access to external view. The shading system examined in this paper was an internal horizontal blind that looks similar to Venetian blinds, but fixed with no movement. The shape of all slats of the tested blinds was simultaneously adjusted for examination. The effect of changing slat shapes was examined by evaluating daylighting performance in terms of Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE) on both the bed surface and the room surface planes. Exposure to external view, expressed as External View Factor (EVF) was also addressed. The two tips of each slat were kept fixed in position. The position of an intermediate point on the slat surface was systematically adjusted in the horizontal and vertical directions creating curved blind slat shapes. Results revealed that the sDA on the room surface plane was the limiting factor in determining acceptable slat shapes. The range of acceptable slat shapes according to the sDA on the bed surface criterion was larger than that of the whole room area. In addition, all tested slat shapes provided acceptable ASE performance. Blinds with flat or gently curved slat shapes scored better results in both daylighting and external view exposure. Position of the intermediate point of the slat – in most of the accepted cases – fell in a narrow vertical range around the horizontal base line. Changing the position of the intermediate point horizontally in either direction resulted in a marginal effect on the performance of the accepted cases. It was observed that the closer the intermediate point to the center of the slat, the better was the performance