A comprehensive parametric analysis was conducted to evaluate the influence of the green roof design parameters on the thermal or energy performance of a secondary school building in four distinctively different climate zones in North America (i.e., Toronto, ON, Canada; Vancouver, BC, Canada; Las Vegas, NV, USA and Miami, FL, USA). Soil moisture content, soil thermal properties, leaf area index, plant height, leaf albedo, thermal insulation thickness and soil thickness were used as design variables. Optimal parameters of green roofs were found to be functionally related to meteorological conditions in each city. In terms of energy savings, the results showed that the light-weight substrate had better thermal performance for the uninsulated green roof. Additionally, the recommended soil thickness and leaf area index for all four cities were 15 cm and 5 respectively. The optimal plant height for the cooling dominated climates is 30 cm and for the heating dominated cities is 10 cm. The plant albedo had the least impact on the energy consumption while it was effective in mitigating the heat island effect. Finally, unlike the cooling load, which was largely influenced by the substrate and vegetation, the heating load was considerably affected by the thermal insulation instead of green roof design parameters.
This research initiative attempts to empirically determine, with reality-based (real instead of modeled) performance data from energy suppliers, the energy advantage associated with building high performance residence in Victoria, BC. In addition, this initiative created a much-needed benchmark for contractors to gain a firm understanding of the construction details required to achieve the various levels of the “Step Code” in the newest edition of the British Columbia Building Code. This was accomplished through a comparative energy analysis between a case-study high-performance “above-code residence” (ACR) to a “minimum code residence” (MCR) with the same floor plan. The ACR was built in 2015 before the step code was introduced, and therefore it was not determined what step level it achieved when it was built. It was not built to any particular performance standard, rather it was built using design details that were calculated to exceed Part 9 performance in effective R-value and airtightness. Upon investigation it was determined that the ACR achieved a performance level of “Step 3” bordering on “Step 4” performance. When compared to the MCR, it was found that the ACR has an energy advantage of 22.5 kWh/m2/year. However, many of the components in the ACR assemblies were either for aesthetic appeal (metal-roofing), or comfort (floor-cavity insulation), and therefore it was possible to remove these components (which is important for Part II of this study: An in-depth cost analysis between the two residences) while maintaining an energy advantage of 15 kWh/m2/year and step level 3 designation. This was dubbed the hybrid-residence as it employed a combination of above-code and minimum-code construction assemblies.
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