architecture and engineering firm HOK proposes the circadian curtain wall, a façade of curved glass panels that responds to the sun’s path and the 24-hour circadian cycle. imagined for a building with an ovoid floor plate, the circadian concept boasts far greater inherent strength and wind resistance than flat-panel glass and allows for bigger window bays with fewer supportive aluminum mullions required to transfer wind load back to the primary structural frame. sustainability specialists at WSP built ecology collaborated with HOK on analyzing the performance of the façade and estimating operational energy savings.

all images courtesy of HOK

the circadian concept was born out of HOK’s ongoing research into building skins that reduce the use of carbon-heavy aluminum while also augmenting stiffness of the primary structure. besides reducing embodied energy, the curved windows offer 180-degree views flooding the building with natural daylight while connecting its occupants to the outdoors by extending the interior out past the building’s main footprint. as the sun moves through the sky, the façade’s bubbled glass provides self-shading on adjacent window glass that passively reduces solar heat gain.



the façade’s curved glass allows building occupants to walk out beyond the building’s main footprint to connect to the outdoors and daylight

the façade’s double skin offers additional benefits, including an extra level of thermal and sound insulation and a potential trombe wall effect to heat the building or mitigate cooling load. automated shades (housed in a cavity between the façade’s outer and inner skin where they’re kept clean and maintenance-free) provide additional glare and heat reduction during periods of intense sunlight. daylight and energy modelling for a 30-story building show that circadian curtain wall can reduce energy use by 16 percent; peak cooling load by 24 percent and peak heating load by 27 percent.



wind pressure analysis on traditional, flat-panel glass and the circadian curtain wall’s curved windows



a cavity between the façade’s exterior and interior glazing pulls heat off the building and provides a clean, maintenance-free housing for the automatic shades

the circadian curtain wall continues HOK façade specialist john neary’s research into building skins that increase energy efficiency while minimizing the use of carbon heavy aluminium



sketches of the circadian curtain wall



it is estimated the circadian curtain wall can save 300 to 400 tons of aluminum in a 1 million sq.ft. building with 300,000 sq.ft. of skin (when compared to using traditional flat-panel curtain walls)



inspired by the 24-hour circadian clock, the façade’s design maximizes building occupants’ exposure to daylight and the daily rhythms that influence human health



as the sun moves across the sky, the façade’s curved glass provides self-shading to adjacent windows – minimizing glare and heat gain



the circadian curtain wall’s shades deploy automatically depending on the location and strength of the sun – here fewer than half of the shades are deployed



WSP’s modelling analysis on a building with an ovoid floorplate shows that circadian curtain wall would reduce solar heat gain (top) while increasing interior daylight (below)

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edited by: sofia lekka angelopoulou | designboom