More than Heat Islands: Vertical Gardens as Thermal Radiation Shields

Research on vertical gardens tends to center on the various roles they have to play in the fields of the urban heat island effect, well-being, and urban biodiversity (among others). Nevertheless, there remains a gap in the knowledge of the specific properties of reflectivity for endemic plants in vertical gardens. This study builds on previous research, with a focus on endemic plants found in Ecuador, one of the most biodiverse countries in the world. Optical measurements were made using diffuse reflectance spectroscopy (both ultraviolet-visible and near-infrared) to quantify the reflectance properties of leaves from 10 different endemic plants that could be found in vertical gardens in the capital of Ecuador, Quito. The studied spectral range was from 300 to 2100 nm. For tests in the wavelength range from 300 to 1100 nm, a xenon lamp was used as the light source, while from 1200 to 2100 nm, an incandescent tungsten lamp was used. The results show that leaves exhibit reflectances of between 30 and 60% for the near-infrared region of the spectrum. This infrared reflectance enables the plant to serve as an effective heat shield against solar thermal radiation, reducing thermal gains for the surface behind the vertical garden. This is pertinent for buildings that are located in an area where high solar radiation is prevalent, where an effective protection against excessive heat loads from the exterior is essential. The impact of the research was to highlight the role endemic plants have in bioclimatic and passive design, in addition to the importance they play in increasing urban biodiversity.