Grantee Research Project Results
Final Report: Automated Hydroponic Green Roof with Rainwater Recycling Infrastructure for Residential and Commercial Buildings
EPA Grant Number: SU836133Title: Automated Hydroponic Green Roof with Rainwater Recycling Infrastructure for Residential and Commercial Buildings
Investigators: Hwang, Hyun-Min
Institution: Texas Southern University
EPA Project Officer: Page, Angela
Phase: I
Project Period: October 1, 2015 through September 30, 2016
Project Amount: $14,949
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Sustainable and Healthy Communities
Objective:
A large fraction of the urban areas is occupied by commercial and public buildings and residential houses. The conventional rooftop surfaces of almost all buildings and houses in the urban areas are covered by concrete, metals, and plastic shingles. On a hot and dry summer day, conventional roof surface absorb solar radiation and roof temperature can exceed ambient air temperature by up to 50 °C especially, in sunbelt states such as Arizona, California, Florida, and Texas. The absorbed heat can be transferred into the inside of buildings and houses that increase summer-time peak and overall energy demand for cooling. Electricity demand for indoor cooling increases 1.5-2.0% for every 0.5 °C increase in ambient air temperatures. It indicates that 5-10% of community-wide demand for electricity is used to compensate for the heat island effect when ambient temperature increases from 25 to 30 °C.
One of the major hurdles inhibiting adoption of green roofs is the lack of innovation to overcome these technical challenges. In order to address these technical issues, we will build a prototype model with a new and innovative green roof concept that is automated sustainable infrastructure, integrating rainwater harvesting unit, temperature and moisture monitoring sensors and solar panels for hydroponic systems and drip cooling system that require minimal maintenance. The intention of developing this prototype is to showcase effective models to promote the use of green roof and water infrastructure in urban areas to reduce energy consumption in addition to providing amenity and water quality benefits for communities and the environment.
The research objective of this project is to develop and evaluate attractive consumer-based and automated sustainable green roof with rainwater recycling infrastructure for commercial and residential buildings to reduce energy consumption and flash flooding and to remove heavy metals and organic contaminates from rooftop stormwater runoff.
Technical challenges we will address is 1) development of innovative green roof systems that do not require layers of conventional growth medium, 2) utilization of rainwater harvesting system coupled with geo-cooling system for irrigation and temperature control, and 3) development of fossil fuel free and low maintenance system through utilization of solar power and automated and sensor controlled irrigation system.
The primary technical challenge is application of hydroponic system to grow vines such as ivy plants that create shades over the roof surfaces. Hydroponic system is an innovative soil-free plant growing system and thus this system does not require a layer of growth medium that adds extra weight loads. Hydroponic system can also be also easily installed. The hydroponic system can ease the primary concern of building owners and house owners in adopting green roof.
Another technical challenge is installation of underground cisterns for rainwater harvesting for irrigation and geo-cooling of warmed water. When harvested rainwater is utilized for hydroponic system and/or conventional growth medium based green roof, we can avoid using any single drop of tap water. Cisterns installed in shallow ground can keep water temperature much cooler than the air during hot summer days so the cooled water stored in the underground cistern can be used to replace sun-heated water in hydroponic pipes that can protect plants from thermal damage and absorb further heat from the surrounding air. Utilization of the cooled water for drip cooling system can also help absorb more heat when the water molecules evaporate.
A pilot hydroponic plant growing pipes with automatic water circulation system was installed in the green house laboratory to test its feasibility for building a green roof. Three vine species (Scindapsus aureus, Hedera helix, and Hedera glacier) were kept in the laboratory for 5 weeks to check if they are feasible to grow in the hydroponic green roof system. Tomato, cucumber, and squash were also tested. An automated hydroponic-based plant growing system was installed in March 2016 on a roof of a 4-story parking garage building located on the TSU campus. A rooftop stormwater runoff collection system was connected to the hydroponic pipes. As an alternate system, an automated self-watering soil-based plant growing system was also installed to test its usefulness for a non-conventional green roof.
Summary/Accomplishments (Outputs/Outcomes):
Golden pothos (Scindapsus aureus) was not feasible to be grown in the hydroponic green roof system. Golden pothos seems not to survive when exposed directly to strong sunlight. The other two vine species (Hedera helix, and Hedera glacier) grew slowly and were replaced with blackie sweet potato vine (Ipomoea batata). Growth rate of this species in the hydroponic system were also not fast enough to build a green roof with significant shadow during the project period.
Automated self-watering soil-based plant growing system can be used as an alternate system to build green roofs. Plant species (Asparagus Densiflorus, Hedera Helix, and Ficus Annulata) that are not feasible to grow in hydroponic system can be grown in the self-watering system. Growth rates of these plants were also not fast enough to build significant shadow before the end of the project period.
This project showed that plants in hydroponic and self-watering pot systems can attract insects as shown in photos taken during the research period. It is an additional benefit of green roofs that provide habitats for many insects in urban areas and improve urban ecosystem health. Another promising benefit of hydroponic and self-watering pot systems is that urban green roof can also be used as vegetable gardens.
Reduction of roof surface temperature and contaminants was not measured because development of a hydroponic-based green roof was not successful. Utilization of cisterns and geo-cooling system was not made because the green roof was installed on the roof of the 4-story garage building that is too high to install geo-cooling system. Green roof installation was delayed because P3 project start date was October 1, 2016, which was not a good time to start a green roof. Plant growing season had passed and had to wait until spring 2016. The green roof was installed in March 2016. The remaining project duration was not long enough to build significant shadow using the hydroponic system.
Conclusions:
This project indicates that successful development of hydroponic-based green roof with significant shadow require a long period of time. It is necessary to identify plants feasible to grow in outdoor hydroponic systems to build significant shadow within a limited period of time. Additional research is needed to test whether they can survive mild winter for long-lasting hydroponic green roof. Installation cost for a hydroponic-based green roof estimated from this project is approximately $50,000 per 2,000 m2, which is only 9% of the cost for a soil-based green roof.
Installation of green roofs consisting of hydroponic and self-watering pot systems can be used as an useful education tool for K-12 schools and higher institutions. Installation of hydroponic- and self-watering pot-based green roof does not require difficult techniques. Installation cost is also very low, and thus these systems can be easily implemented as an educational tool.
Supplemental Keywords:
Self-watering pot, vine, urban insect habitat, urban vegetable gardensThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.