Thermal Performance of the Extensive Green Roof in Semi-Arid and Cold Climates

Abstract

Green roofs have recently gained popularity worldwide to reduce building energy consumption for heating and cooling. Many studies have shown the thermal benefits of green roofs in enhancing building energy efficiency in different climates, particularly in hot and temperate climates. However, studies in cold-climate regions are still limited, especially in cold and semi-arid regions. Therefore, this thesis aimed to provide region-specific knowledge by statistically analyzing the thermal performance of an extensive green roof and a reference roof in the City of Calgary, Alberta, in this climate context. In this thesis, data including roof temperature at several layers, heat flux, meteorological variables, media temperature, and moisture collected from 2017 to 2018, were used. Several statistical analyses were conducted to examine the thermal behaviour of the green roof and the impacts of media moisture on its thermal performance on hot, normal, and cold days. The results showed that the green roof mitigated spatial variations in temperature and heat flux and improved horizontal heat distribution on hot and normal days compared to the reference roof. Additionally, the green roof provided cooling effects by reducing temperatures at various common layers on hot days compared to the reference roof while offering warming effects on cold and normal days by increasing temperatures. The increased thermal resistance provided by the green roof further reaffirmed these cooling and warming effects. Moreover, the green roof decreased roof temperatures vertically from its top layer to the bottom layer, particularly during the daytime when the air temperature was higher, thereby absorbing and retaining more heat. Conversely, during nighttime, the green roof increased roof temperatures vertically when the air temperature was lower, thus retaining more heat inside the building. In addition, higher moisture content was found to be beneficial in reducing the temperature of the growing media at the bottom layer and reducing vertical temperature differences. These results confirmed the benefits of green roofs in reducing building energy consumption in the study case climate. Yet, there is a need for more elaborate quantification of the thermal benefits of green roofs at finer spatial and temporal resolutions.