The Challenge
Developers of Arbor House, a 123−unit affordable housing complex in the South Bronx, needed to maximize space for rainwater harvesting to enable reuse in a 10,000 sf rooftop greenhouse, while mitigating stormwater pollution into New York City’s waterways. Goals included earning and maintaining LEED credits for water conservation and meeting strict regulations for mitigating combined sewer overflows (CSOs).
Funded by federal, state and city grants, this project promised to be the first in the United States to provide residents and the surrounding community with fresh produce grown on a building rooftop using stormwater for irrigation while keeping it out of the sewer system. Government stakeholders, whose participation was critical, increased pressure for meeting expectations.
The Solution
Arbor House uses Opti’s technology to reduce stormwater storage needs from two to one cistern while capturing, storing, and retaining rainfall during storms. Installed in 2017, Opti’s software controls the timing of water discharges from the single15,000−gallon cistern. Ahead of a storm, the Opti system draws down the stored water level to ensure rainfall is captured during the event. After, stored water is retained for reuse.
Operation and Maintenance
Opti’s software controls an outlet valve installed 12” from the bottom of the cistern. Opti software ingests the National Weather Service forecast to predictively draw down stored water, maximizing storage capacity. Arbor House managers use Opti’s web-based dashboard to monitor performance statistics, review historical data summaries, and enable automatic control of the outflow valve. The Opti platform also helps them prepare quarterly reports with performance data to achieve environmental compliance and maintain building LEED-Platinum and other certifications.
The Results
Within one year, Opti's active system increased efficiency by 4.6X compared to traditional passive management. By adding Opti adaptive controls, the developer was able to:
- Convert a passive system with two cisterns for storing 134,650 gallons to an Opti active system requiring one cistern for storing 15,560 gallons, reducing CAPEX
- Reduce the footprint needed by relocating the cistern under a parking lot, creating space for alternative use and additional revenue
- Prevent sewer overflows while reusing stormwater on-site to achieve LEED credits, reducing water bills and OPEX
