Heliotropic Shading: Daylighting a Rare Books Reading Room with Electrochromic Glass and Parametric Analysis

ABSTRACT

This paper introduces the design process and successful deployment of an electrically tintable glass, known as electrochromic glazing, for a fully daylit atrium sheltering a rare books reading room at a university library. The project demanded a novel design process where analysis and simulation data from a parametric model were directly used to program the final control system, merging quantitative and qualitative design workflows to develop a daylighting solution that could meet the client’s visual and metric requirements. The final daylighting design employs a dynamic “heliotropic” shading control system that follows the sun path both geometrically, as well as photometrically, maintaining illuminance levels from daylight at the task plane below a specified threshold at all times throughout the year. This solution used an electrochromic glazing product that offered four transmission levels ranging from 60% VLT to 1% VLT, providing the shading required to support the archival needs for engaging with rare and light-sensitive artifacts while maintaining as much clear or minimally tinted glazing as possible to support the visual and experiential qualities of the space. The project was designed between 2015–2016 and installed 2017–2018.

KEYWORDS:

• Daylighting design
• electrochromic glazing
• sustainability
• high-performance buildings
• visual comfort
• lighting for sensitive works

Acknowledgments

Thanks to Robert (Bob) Osten and Keith Yancey at Lam Partners who secured the project and assisted in the design. Bob was critical in selecting glazing specifications in the early iterations, and both Bob and Keith, along with Jack Risser, provided support through the more computationally complex phases of the project. Thanks to Jason Donahue, Jonathon Baron, and Kristina Osborn at Shepley Bulfinch who brought in Lam Partners and had faith in our design proposals. Fredrick Fisher and Partners served as the Design Architect and supported the project development along with the client, James Wallace, Margaret Kehrer, and Darlene A. Dreyer, at Princeton University. Phil Spande and Helen Sanders at Sage Glass led the manufacturer to accept and deploy the technology, and Phil answered many questions on the technical functions of the system. Ahoo Malekafzali Ardakan, at Sant Gobain, also provided technical information and feedback. Finally thank you to Christoph Reinhart at MIT for sage advice and guidance on how to crack this nut, Jon Sargent, Alstan Jacubiac, and Holly Samuelson, for peer review, and Azadeh Omidfar Sawyer for constant collegiality and general support on all things daylighting.

Fisher Marantz Stone served as the Electric Lighting Designer on the project. Professional photography by Robert Benson.

The author has previously presented the project at DIVA Day 2017, IES Research Symposium 2022, and numerous academic guest lectures.

Disclosure statement

No potential conflict of interest was reported by the author(s).