Optimizing Green Roof Design Parameters and Their Effects on Thermal Performance Under Current and Future Climates in the City of Toronto

Abstract

Buildings contribute 30% of total energy consumption worldwide and account for 28% of CO2 emissions. Green roofs (GRs) have shown potential in reducing cooling and heating loads of buildings, and thus, the related carbon emissions. The objective of this research was to analyze the thermal performance of extensive GRs and find suitable GR designs that reduce both cooling and heating building loads under both current and future climates in the City of Toronto. The effect of two design parameters, GR growing media depth and the insulation thickness of the roof, on building energy consumption were investigated. EnergyPlus was used to model GR energy balance for a secondary school building, the total energy consumption and the heating and cooling loads. Due to Toronto being a heating-dominated city, the use of insulated GR with a growing media depth of 200 mm was effective in reducing building total energy consumption. However, results showed that for insulation thicknesses of more than 120 mm under current climate and 80 mm under future climate, the total energy consumption of GRs increased compared to a reference (conventional) roof without GR. Therefore, use of highly insulated extensive GRs to? reduce building total energy consumption is not a suitable replacement for insulated conventional roof for secondary schools in the City of Toronto under current and future climates. Nonetheless, use of uninsulated extensive GRs are suitable choice in reducing the total energy consumption for retrofit schools with poorly insulated conventional roofs.