Arizona’s native cactus inspires sustainable office design

Pinal County Attorney’s Office in Florence, Arizona, uses biomimicry to create a building which replicates the native saguaro cactus and its natural response to surviving the intense desert heat.

The resulting design uses a “breathable” facade system, mounted off the building, composed of ribbed metal panels, mimicking the fins of the cactus. Although the metal panels absorb heat, the projected format of the facade gives ample air circulation and heat dissipation. At the same time, the office brings in copious amounts of natural light to enhance occupant wellbeing and health.

The team at the integrated design firm DLR Group researched the plant’s ability to protect itself from intense heat with its natural composition of self-shading vertical fins. The fins redistribute the heat, so no part of the cactus receives direct sunlight for more than 15 to 20 minutes at a time, cancelling out the possibility of sunburn.

The nature-inspired design interpreted the plant’s shifting shadows into the rigid metal fins, endowed with pops of color for aesthetic enjoyment of drivers crossing by. The system of panels works in a similar fashion as a cactus’s fins, as it allows the sunlight to fall in varying areas—letting heat redistribute for longer periods, until natural air convention can cool the ribs. Wherever windows were needed, the metal wall panel system carries angled windows projected out from it, and they serve as self-shading elements.

The glazing in the project has heat-reflecting capabilities, resulting in solar control, and a low-e coating with light management ability to balance visible light transmittance and glare reduction. The high-performance glass helped bring down mechanical system costs, causing long-term reduction in energy costs.

The team at the firm measured the results of relying on exterior shading. The result indicated, on a hot summer day in June, the conference room on the south side of the building saw a 22 percent decrease in solar gain during the busiest and hottest hours of the day, while the west side training room saw a 14 percent decrease. The team’s preliminary model also suggested a decrease of 39 percent in energy savings, compared to Zero Tool’s energy use intensity (EUI) median of 100 kJ/m2/year (kBtu/sf/year) for existing buildings of this type in the region.

Another factor which resulted in space and cost savings for the building were the design team’s creation of 90 percent complete design documents during the design phase. This allowed the building’s footprint to be brought down to the minimum. The mechanical system equipment, for instance, typically takes up 6 to 8 percent of a building’s total square meters (square foot), but in this project, savings of 204 m2 (2,200 sf) could be availed by bringing the mechanical space down to 4 percent. Another reduction in cost resulted from compressing the floor-to-floor height to 4.4 m (14.5 ft), cutting down on facade size and costs by 18 percent.

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