Dynamic Simulation of the Green Roofs Impact on Building Energy Performance, Case Study of Antananarivo, Madagascar

Green roofs improve building energy performance and constitute an alternative to sustainable buildings. A green roof model is dynamically coupled with a building thermal model to assess its energy performance that takes into account the indoor air temperature dynamic changes. Under the climate conditions in Antananarivo, we compared green and conventional roofs. The present study shows that green roofs protect the roof structure under extreme temperature and large temperature fluctuations. For the case of Antananarivo, the amplitude of the temperature fluctuations at the top face of the support is reduced by 28 °C when using green roof. The impact of the green roof on indoor air temperature and energy demand is investigated. The vegetation decreases the maximum indoor air temperature and improves the building thermal comfort during summer days. It has no effect on the minimum indoor air temperature, but additional soil thickness can increase it. In addition, a global sensitivity analysis, which is carried out on the proposed model without considering any specific weather data, allows us to identify the most influential parameters on the energy demand. It has been found that green roofs have almost insignificant thermal impact in insulated buildings; however, their potential prevails over the building envelope and weather characteristics in the case of non-insulated building

Thermal Behavior of Green Roof in Reunion Island: Contribution Towards a Net Zero Building

International audienceA green roof is an option for improving a building thermal comfort. The investigation is here performed within the specific climate context of Reunion Island in south hemisphere. This type of roof system involves choice difficulties for plant species that are more favorable to establish that comfort. The objective of this work is to simulate the dynamic behavior of this system towards external requests in wet tropical zones and vis-à-vis influences of certain number of physical parameters related to this system. As long as possible, authors used the electrical analogy method to establish a mathematical model associated to the studied system. Based on this model, a Matlab computing code was finalized. Weather data of Reunion Island were used for simulations; the green roof potential and benefit were highlighted by surveying the temperature gain and the heat flux crossing the roof as well as the energy saving performance. Furthermore, the energy consumption being surveyed while doing sensitivity analysis with Fourier Amplitude Sensitivity Test method, the most influential parameters of the model were identified. Full scale experimental results are provided and consisting in monitoring green roof on the top of a public building. According to the results, we can assert that the green roof decreases heat flux entering through the roof during the day and restrains the restoration of accumulated heat at night. Indeed, the support on which the plantation ground bases affects the building thermal insulation. The experimental data are also conducted to prove the effectiveness of thermal insulation by green roofs in reducing temperature in the building between 5°C and 7°C in relation to plants type and the canopy Leaf Area Index (LAI). A comparison of experimental values and model results is done. Among other uses, this code can be used as a tool for choosing the plants and the drain materials to be experimented on the green roof. The results offer hints to optimize the design and thermal performance of extensive green roofs