Life Cycle and Energy Saving Assessment for Green Roof
|關鍵字:||綠屋頂;U-value;建築耗能模式;生命週期評估;節能減碳;成本效益評估;永續環境系統分析;Green roof;U-value;building energy simulation model;life cycle assessment;energy saving;GHG emission reduction;cost-benefit analysis;sustainable environmental systems analysis.|
本研究實測10公分薄層綠屋頂U-value約在0.42左右。節能效益依二方法的模擬結果，三案例約有12至15kWh/m2/yr間效益；減碳效益則約有5,964至7,293 kg CO2e/yr間的減碳效益；環境效益部份在一般屋頂壽命20年至10年，綠屋頂在人類、水體與陸域生物毒性等面向所減少環境衝擊量在1×〖10〗^6 至1.8×〖10〗^6kg 1,4-DB eq，約減少51%至75%；成本效益評估結果綠屋頂在一般屋頂壽命在15年以下有5-50元/m2/yr左右的經濟效益，若電價上漲，綠屋頂的經濟效益將更為明顯。|
To prevent the increasingly serious threat of global warming to life on earth, building energy saving and greenhouse gas (GHG) emission reduction has become a major issue for most cities. Green roofs can effectively reduce heat flux and sequestrate carbon by vegetative cover, thereby decreasing building energy consumption and GHG emissions. This study thus applied a building energy simulation model and a life cycle assessment (LCA) software to assess the environmental benefits of local green roofs based on their energy savings, GHG emission reductions, and life cycle and cost-benefit assessments. For evaluating the energy saving, the U-value of a green roof was measured first. With the measured U-value and the typical meteorological year of the study area, the one-dimensional heat flux (1D-HF) method and the EnergyPlus model were used to estimate the energy saving. The GHG emission reduction was computed based on the emission factor of local electricity and the carbon sequestration capability of a green roof. The difference between a conventional roof and a green roof for various life cycle environmental impacts was evaluated by Simapro. Finally, a life cycle cost-benefit analysis was implemented based on the market prices of roof materials, replacement costs, life spans, and economic values of energy savings and GHG emission reductions. The results obtained in this study are intended to evaluate the applicability of green roofs for buildings in local cities. The U-value of a local extensive green roof with 10cm substrate depth was measured and estimated to be 0.42. The energy savings of three studied cases are approximately 12-15kWh/m2/yr. The GHG emission reductions range between 5,964 and 7,293 kg CO2e/yr. While compared to the conventional roof with a life span of 10-20 years, the green roof LCA result shows about 1x106-1.8x106 kg 1,4-DB eq impact reductions for human ecotoxicity, aquatic ecotoxicity, and terrestrial ecotoxicity. The life cycle cost benefit analytical results show $5-50/m2/yr economic benefit over the conventional roof with a life span of 10-15 years. The economic benefit is expected to significantly increase after the government raises electricity tariffs in near future.
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