Princeton Firestone Library

Academic | Daylighting
LOCATION: Princeton, NJ
SIZE: 3000 sq. ft.
OWNERS: Princeton University
ARCHITECT: Shepley Bulfinch
PHOTOGRAPHER: © Robert Benson Photography

DESIGN TEAM:Robert Osten
 Dan Weissman

This library renovation included the relocation of Princeton University’s books reading room to a 21-foot-wide by 140-foot-long, glazed atrium space, nestled between the original library building and a 1980s-era addition. The original glass and brise soleil assembly provided reasonable solar control, but simply could not accommodate the strict 500 lux maximum required by conservators, so we were brought in to develop a solution.

After studying various design iterations and calculations to produce static daylighting solutions  (including implementing baffles and altering the transparency of the panes), it became clear that a dynamic solution would be necessary to meet these complex requirements. Mechanical shades would be problematic, due to the sloped glass, noise, and maintenance concerns.  Electrochromic glazing can change tint to decrease light transmission, typically in four steps from clear to 1% transmission, and proved to be the perfect alternative. After visiting other installations, the team gave the green light to develop the project with Sage Glass.

Up to this point, Sage’s typical installations included relatively simple control strategies, such as the creation of a series of horizontal bands or blocks defined by program. However, it quickly became apparent that grouping the glazing into large zones of control would not meet our criteria. To address this, we created a dynamic shading mask that could follow the sun as it moves across the sky, blocking direct sunlight from hitting tables of rare books, while also maintaining at least 10% clear glass for quality color rendering. This scheme would maximize the amount of clear or minimally tinted glass at all times.

To convince stakeholders of the concept, the lead author constructed an algorithm in Grasshopper for Rhino to visualize the concept geometrically, diagramming how the skylight could change throughout the day and year. The data was also used to create photorealistic animations in a dynamically changing digital heliodon, producing visualizations that simply could not be performed with its analog counterpart. However, these visualizations were both useful and deceiving; the representations made it clear that the shapes created were not pure geometries, and as such, the client requested some simplification. The transitions in the video were also abrupt, not portraying the 2-15 minute transition times actually found with electrochromic technology, which viewers found distracting. More importantly, this first iteration did not account for quantitative analysis; up to this point, the Grasshopper definition was only able to change states based on solar angle and obstructions. It’s one thing to create a simulation that ‘looks’ like it’s dynamically shading the space, it’s quite another to actually calculate it.

Ultimately, a nested, looping algorithm provided a workable solution that allowed the Grasshopper definition to test and iterate until it met our criteria. The algorithm would then write the results to a spreadsheet and move on. Once completed, the spreadsheet was handed off to Sage Glass, which used the data to program the installation. The project was completed in the spring of 2017. This was just in time for the summer research period and a first round of user feedback, as the staff began to notice a particular area that was not shaded in the afternoons. Based on this feedback, we modified the scenes, and will be waiting patiently until the summer of 2018 to see if the changes were helpful.

This project perfectly merged quantitative and qualitative design to develop a daylighting solution that could meet the client’s visual and metric needs in this space.