January 2011

Volume 20, Number 1

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Market-Rate Net-Zero-Carbon Design Emerges from Exercise

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The long sides of Net Zero Co2urt face north and south, and have a 35% window-to-wall ratio that optimizes daylight without sacrificing energy performance.

Rendering: HOK

Designers at HOK and daylighting and energy consultants at the Weidt Group recently came together to see if they could design a market rate, net-zero-carbon-emissions office building. Their design exercise resulted in “Net Zero Co2urt,” a four-story, 170,000 ft2 (16,000 m2) office building for a downtown St. Louis site, and with an estimated payback period of 12 years for features going beyond a building meeting LEED Certified standards.

The Missouri climate of fairly harsh winters and hot summers was a challenge, as are regional costs for conventional electricity—among the lowest in the country at about $0.07/KWh. According to HOK, the modeled building uses 21.9 KBtus/ft2, producing 76% less carbon emissions than a conventional office building, and with only minor additional first costs—total construction costs as modeled would be $223/ft2. The building’s energy needs are met with a 52,000 ft2 photovoltaic array and 15,000 ft2 of solar thermal panels.

HOK and the Weidt Group offer five steps to net-zero-carbon design in their publication “The Path to Net Zero Co2urt.”

1) Assemble a resourceful team and establish an iterative design evaluation process.

2) Define environmental, comfort, and financial goals before beginning design.

3) Develop site and architectural strategies that reduce energy needs and optimize energy generation.

4) Design whole-building systems to “tunnel through” cost barriers.

5) Provide a plan that will equip the owner and tenants to occupy and operate the building with zero emissions.

The exercise required “integrated design on steroids,” according to Mary Ann Lazarus, AIA, global director of sustainable design at HOK. The team made extensive use of virtual meeting tools and modeling software, including tools developed by the Weidt Group that allowed the team to see their changing assumptions modeled almost instantaneously.

Because it had the ability to see quickly how its choices affected the overall performance of the building, the design team revisited design strategies multiple times in an iterative process. Also, as the team noted in its publication, “We need to know when we are making purely aesthetic decisions versus science-based decisions and be clear about which is which.” With the base buildings achieving a 73%energy use reduction, and the remaining energy needs provided by soar collectors on the roof, south-facing walls, and parking lot, Net Zero Co2urt would, if built, become one of the largest zero-emissions buildings in the country. Images, details, mobile phone apps, and a report can be found at www.netzerocourt.com.

– Allyson Wendt

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December 30, 2010