綠屋頂生命週期與節能效益評估

Abstract

全球暖化日益嚴重，建築物之節能減碳已成為都市重要議題。由於綠屋頂可降低屋頂熱量傳輸及具有碳吸附功能，為有效之建築物節能減碳措施，除此之外，綠屋頂亦具有其他環境效益。本研究因而以建築耗能模式及生命週期分析工具評估綠屋頂於台灣地區施行之效益。本研究針對國內數棟案例建築物之綠屋頂就其節能減碳、生命週期及成本效益進行評估。 建築物節能部份，本研究先量測綠屋頂之U-value與並使用標準氣象年氣象資料，以1D-HD法及Energy Plus建築耗能軟體模擬綠屋頂下的能耗差異，以評估其節能效益，節能結果亦與綠屋頂植物之二氧化碳吸收效果合併評估其減碳效益。在生命週期評估部份，依案例建築物綠屋頂與一般屋頂材料組成採用Simapro軟體分析綠屋頂在生命週期期間對環境之影響，並依與一般屋頂環境衝擊差異分析綠屋頂的環境效益。且依市場價格推估一般屋頂及綠屋頂建構、維護更換成本，最後進行成本效益評估，以探討都市建築物建置綠屋頂之適宜性。 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.