C047 -- Design Verification of the Impact of Electrochromic Glazing

Carson Headquarters was completed in Omaha, Nebraska, in May of 2021. The campus is composed of two towers joined at the center by an amenity hub. The largest building is six stories and encloses about 120,000 SF. It houses operations for Carson, a financial services brand that unites multiple sub-brands related to wealth management. Commercial tenants currently occupy the smaller tower, which is four stories and 80,000 SF. The entire campus is enveloped in SageGlass Harmony, an electrochromic glazing product. The decision to use electrochromic glazing occurred midway through design. Many specifications were in place, including HVAC systems. Presenter Kim Cowman led an engineering team that undertook rigorous modeling and analysis to understand the impact of the innovative envelope on thermal comfort and daylighting. Energy simulations compared glazing properties of ASHRAE 90.1 (2016 Climate Zone 5A), the manufacturer-provided values for SageGlass Harmony, and used the local typical weather file. The electrochromic envelope’s values indicated that it would shield much of summer’s solar gain, and its improved R-value reduced winter heat loss. After analysis, the design changed to specify 15 percent smaller air-handling units because of the reduced cooling and heating loads. The smaller units proved more than adequate. Data was collected by scientific instruments during a post-occupancy evaluation (POE) in July and August 2021, which was led by presenter Michael Kuhlenengal. For comparison, measurements were recorded for two weeks using the electrochromic envelope’s automated setting and for two weeks using a manual setting that could be adjusted by any employee, any time. Indoor temperatures stayed below thermal comfort levels prescribed by ASHRAE 55 and proved the smaller air handlers were more than up to the task. Carbon dioxide levels fell within WELL standards. Subjective attitudes were also collected from occupants using anonymized surveys, and a few comments indicated the space was occasionally too cold, further supporting the adequacy of the smaller air-handeling units. Lighting design also changed to account for greater access to useable daylighting. The electrochromic envelope removed the need for window coverings. Reduced energy required for electric lighting further improved the buildign’s energy profile although a few locations where measurements were documented appeared to be too dimly lit when the envelope darkened to reduce daylight penetration. In this paper, the authors will share details about the data collected from this real-world implementation of electrochromic glazing.