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123 Zero build is a free tool for calculating the performance of a market-ready carbon neutral office building design. This application estimates the discounted payback for constructing a zero emissions office building in any U.S. location.

Use 123 Zero build to calculate the investment needed for photovoltaics to offset annual carbon emissions in your location. The payback calculations include estimated first costs for a highly energy efficient building, photovoltaic costs, discount rates and user-specified fuel escalation rates. Federal tax incentives also are included in the calculations. Local incentives to offset first costs can be added to the calculation by the user.

The calculations are based on Net Zero Co2urt, a very low-energy, market-rate, Class A office building in St. Louis, Mo., designed by HOK with The Weidt Group. The Net Zero Co2urt design is 73 percent more energy efficient than an ASHRAE 90.1-2004 benchmark office building and features use of photovoltaic panels, daylighting and solar hot water to achieve zero emissions status.

Net Zero Co2urt Design Parameters:
- 170,735 gross square feet
- 4 stories
- 15-foot floor-to-floor height with 60-foot-wide floor plate to optimize daylighting
- R-30 insulated roof
- R-40 walls
- 35 percent window-to-wall area ratio
- Low-E triple-pane glazing with argon fill and wood frames
- Building-wide lighting power density of 0.28 watts per square foot
- Underfloor air distribution with chilled beams and radiant heating with a frictionless water-cooled chiller and condensing gas boiler