Evaluation of the Effect of Vegetation and Green Walls on Building Thermal Performance and Energy Consumption

The Council on Tall Buildings and Urban Habitat (CTBUH) and several members of the Illinois Institute of Technology (IIT) launched a proposal to study the energy-saving effectiveness of green wall façade systems. This research was funded by Wagner Institute for Sustainable Energy Research (WISER). Professor Lorch Osler, Director of the Landscape Architecture program at IIT, was the Principle Investigator (PI) of the research; Dr Antony Wood, the Executive Director at the CTBUH; along with Dr. Payam Bahrami, a Senior Research Associate at the CTUBH. Irina Susorova, a Ph.D. candidate in the College of Architecture at IIT, was the graduate student that worked on this research.

The project analyzed the ability of green wall systems, such as hanging gardens and “living walls,” to improve a building’s energy performance by decreasing heat transfer through facades. In order to do this, a model of green walls was to be built and validated with experimental data. Included in the research was an evaluation of the importance of plant, façade, and weather parameters for the façade thermal performance. It was also important to note energy savings in buildings using plants on their facades and formulate design recommendations for buildings with green walls.

The experiment consisted of measuring the façade thermal performance of an existing building covered with climbing plants located on the campus of the Illinois Institute of Technology. Siegel hall, whose south and east facades are covered with Boston ivy, was selected for the experiment. The building had a lot of open space around its south and east facades with a few tall trees with low-density foliage that cast almost no shadows onto the studied façade. Two exterior areas located on the south façade were selected for the measurements: an area densely covered with plants and an area free of plants. These experiments were conducted over the course of four days.

(©CTBUH Left: Detail of the studied façade covered with Boston Ivy. Middle: South façade of Siegel Hall on the campus of Illinois Institute of Technology with measuring equipment attached. Right: Close up of measuring equipment)

The results of the experiment were used for validating the model by seeing how well it can calculate the exterior surface temperature and temperature gradient of the façade. Knowing the temperature difference between the bare and vegetated facades allowed for calculations in other façade properties.

This research addressed important topics of urban ecology and energy consumption in buildings. The significance of green walls is that they can help reduce problems of urban ecology and of the excessive resource use. Green walls, due to the vegetation component, can offset greenhouse gases and reduce urban heat island effect, improve air quality and lower risk of some diseases, increase biodiversity of plants and animals in cities, and lower energy use in buildings.