HVAC exhaust can boost rooftop crops

Researchers have found that planting vegetables crops near vents exhausting carbon dioxide-rich air can produce up to four times more growth.

The farming system, known as BIG GRO, takes a sustainable waste resource that exists in excess in cities – human respiration – and applies it to farming.  

Conducted on the roof of the Boston University campus between 2018–19, the study used air from indoor classrooms – which was enriched with CO₂ produced through respiration – to fertilise crops and increase plant growth. 

The study used two types of crops, spinach and corn. Spinach is most responsive to increased levels of CO₂, while corn is one of the less sensitive crops. Additional control crops were exposed to high wind speeds and to air without extra CO₂.

Indoor CO₂ levels were monitored to measure how much gas was being supplied to the crops; when classrooms were occupied, CO₂ levels spiked above the recommended 1000ppm for 37 per cent of the time. This delivered considerably more than the required 800ppm plants need to influence growth.

The spinach crops showed a four-fold increase in biomass when farmed beside CO₂ vents. When exposed to high wind speed as well, the crops still returned double the biomass of the crop grown without CO₂.

Despite being less sensitive to CO₂, corn grown near CO₂ vents was two-to-three times larger and greener, although researchers suspect another factor such as temperature may have influenced results.

While researchers have not confirmed whether the farming style impacts nutrient density, they do believe the findings could be useful in addressing environmental and food supply concerns.

“Leveraging under-utilised rooftop areas to grow crops will help overcome many environmental, economic, and social challenges cities around the world currently face,” say researchers. “Implementing this approach on rooftops across cities and increasing overall urban vegetation through farming will help address some environmental challenges facing cities, including producing hyper-local food more efficiently and sustainably, harvesting carbon, and helping integrate into the surrounding environment.”

Read the full research paper, Enhancing crop growth in rooftop farms by repurposing CO₂ from human respiration inside buildings.

Photo by Quaritsch Photography on Unsplash.