A team of Yale researchers constructed the first thermoGreenWall™ as a sustainable feature at the Urban Ecology and Design Laboratory (UEDLAB) on Science Hill this past August. The team hopes the technology will be a sustainable alternative to cooling towers, which currently provide cooling and power needs worldwide.
thermoGreenWall™ (tGW) technology can be thought of as a hybrid of standard green wall and cooling tower technology, described Alex Felson, principal investigator and Director of the UEDLAB.
Green walls are essentially vertical gardens on the exterior of a wall. Their services include passively regulating a building’s cooling and heating needs, filtering air, and providing habitat. Green walls are also aesthetically pleasing.
Unlike standard green walls, the new technology actively rejects heat, providing an alternative technology to wet cooling towers that provide heat rejection needs for district chilled water production, building cooling, and power generation.
However, while a cooling tower uses chemicals and blowdown water to treat the buildup of pollutants, tGWs can treat water onsite through their substrates and vegetation, reducing the need for chemicals.
Additionally, cooling towers lose water to the atmosphere predominately through evaporation. tGWs repurpose the water before it is released by irrigating the green wall vegetation and adding co-benefits such as improved water and air quality. The technology can also be distributed across buildings and is scalable to different heat rejection demands.
Since 2009, UEDLAB has sought to integrate engineering and biological sciences with landscape architectural design. With the tGW project, funded through the National Science Foundation (NSF), the interdisciplinary research lab has been a pioneer in advancing green wall technology and utilizing green walls in novel ways to further the environmental sustainability of modern buildings.
The team holds a patent with Yale University and the original co-inventor and engineer, James Axley. The UEDLAB is now collaborating with the Yale Mechanical Engineering & Materials Science Department’s Corey O’Hern and his research group to further refine and model the system. In addition, Graeme Berlyn, a plant physiologist in the Yale School of Forestry & Environmental Studies (F&ES), is an NSF Co-Principal Investigator. Through the NSF funding, the team has employed four F&ES graduate students and more than 12 undergraduates, including six senior thesis projects at Yale.
The team is working with Yale Facilities to develop the project. They studied the Yale Campus cooling systems and worked with engineers on campus to form an initial design for the outdoor prototype.
The indoor and outdoor spaces offered by the UEDLAB made it an ideal location for constructing and testing the tGW. Using a hot water heat pump, the system removes heat from air in the lab space to heat potable water that is then recirculated outside to the constructed wall. Heat from the water is then released into the atmosphere through evaporation and convection.
The constructed system had its first trial run from August to November of 2016. The outdoor wall follows two years of research on an indoor green wall setup and a hydroponic system that tested plant performance in warmer climates. Since the start of the experiment, the team has been working on developing the smart technology for real world applications.
The team is testing the effects of inflow water temperature, substrate material, and types of plant communities on green wall performance and heat rejection capability. “The substrate has a lot of potential,” says Felson. “It acts as both a growing medium and as the surface material for active heat rejection.” The team is looking at substrates that have an increased surface area, absorb more nutrients, and hold higher volumes of water.
While most of the heat loss occurs through evaporation from the substrate, the team is also interested in exploring the role plants play in active heat rejection through stomatal openings, which plants use during photosynthesis and respiration. They are looking at various native wetland plants because their roots can acclimate to the quantity and temperature of the water that circulates through the constructed green wall.
This year, the team is performing co-benefit calculations that include water quality and microclimate performance to understand the technology’s public space value. The potential to regulate microclimate can help reduce the effects of urban heat islands, which are warmer areas in urban spaces due to human activities, weather, and building density.
During the first run of the system, hot water that circulates through the system affected the microclimate differently than a standard green wall offering the potential to further optimize heat rejection by fine-tuning plant-substrate interactions. The technology would present the opportunity to manipulate the microclimate through weather data and human user interests, said Acheampong Atta-Boateng, tGW team member.
Looking forward, the team hopes to construct a tGW near a campus cooling tower where they can test how it works using non-potable water.
Yale is committed to building a more sustainable world. By doing what we do best—integrating science, the humanities, and our community—Yale creates, tests and adopts innovative solutions to the environmental and social challenges we all face.
Learn more about the UEDLAB here.