Analysis of the thermal and hydrological performance of green walls and green roofs in subtropical and temperate climates

Abstract

The search for energy efficiency and thermal comfort is widely discussed and constant in the academia. Numerous technologies, sustainable practices and policies have been developed aimed at reducing energy consumption and manage stormwater events and urban heat island. This research aimed to analyze the thermal and hydrological performance of a green walls and green roofs over 2 years of data monitoring. At first, since green infrastructure performance is significantly affected by regional climatic conditions, the meteorological parameters, such as temperature, relative humidity, solar radiation, wind speed, precipitation, and atmospheric pressure, of a Southern Brazilian city were assessed through the generation of updated weather files, in order to correct eventual inconsistencies in previous ones. Significant differences among the weather files were observed, specifically in precipitation volume, which was the parameter with more gaps and monitoring errors. In relation to the comparative analysis, both updated weather files (Test Reference Year and Typical Meteorological Year) presented dry bulb temperatures in consonance with the other files previously available. After this, climatological data was monitored from a green wall vegetated with the Wisteria floribunda species, installed at the Federal University of Santa Maria since 2017. The data were monitored for over 2 years every five minutes including wind speed, solar radiation, and internal and external temperatures conditions, and were used to calibrate a mathematical model that represents the heat flow through the exposed and vegetated walls. Through the examination of heat flux, it was observed that the vegetated wall led to a substantial reduction in conductive heat, reaching up to 83% during summer days. As a result of the plant layer's presence, the external surface temperature was significantly reduced by 8.6 °C. With the aim to analyze the hydrological behavior of green roofs in different climates, the data monitored in three green roofs in Brazil and three in Germany were crossed and compared. The findings indicated that green roofs demonstrate comparable cumulative retention capabilities, with a retention rate of 76.4% in Cfb (humid temperate climate) and 72.1% in Cfa (humid subtropical climate), despite variations in rainfall patterns. Additionally in humid subtropical climates, lower range classifications exhibited better retention performance, while in temperate climates, higher range classifications showed higher retention performance. These findings contribute to our understanding of the impact of adjacent microclimatic conditions.