木構造房屋生命週期碳足跡與林木經營碳匯效益評估

Abstract

本研究為求找出人為活動的二氧化碳減量熱點，以盤點林業上下游的碳排放為旨，於上游的林地經營階段採用Individual model與Allometric equation建立符合個體生長曲線，且合乎林分測量的林地生長模式，對未來林地的生長做預測推估。於下游選擇建築產業，作為林業產品碳替代的標的，以生命週期評估的範疇帶入BICF法與台灣的資料庫，進行台灣木構造建築的二氧化碳計算，並以相同功能的鋼筋混凝土建築作為比較基線。並提出修改建議，將木材的碳儲藏效益計入原料部分，且於廢棄部分進行情境設計並扣除原計入的碳儲藏效益。 研究成果得出: 一、台灣的木構造建築四層樓案例，在總生命週期評估三十年內，碳排放量共1,411,647 kgCO2e；相同功能的鋼筋混凝土建築，在總生命週期評估六十年內，碳排放量共2,856,168 kgCO2e，兩者相差2.02倍。二、程式模擬出林地的林分生產率，隨時間變長且樹木變大後，會有減緩的趨勢，可以作為林業上游需要人為採伐，以釋放林地提供樹木新生空間的證據。綜合以上兩點定量結果，可以定性的歸納，台灣林業在木構造建築的碳替代效益，從上游到下游都是有益於二氧化碳減量的。

Buildings contribute significantly to Greenhouse gas emissions, because of the high-energy consumption and the material used. By finding out a way to reduce the Greenhouse gas (GHGs) emissions of building, we can slow down climate change. In addition, the carbon substitution of wooden products can store GHGs in the wood, and free land for planting new saplings to absorb more carbon. According to the ISO 14025 specification and the CFP-PCR the life cycle assessment of buildings in Taiwan is divided into five phases: Materials Manufacturing, Construction, Use phase, Maintenance and End-of-life. There is many research about reducing carbon emission in civil engineering, but most of this research did not consider carbon storage project to import the concept of carbon substitution. Thus, to sum up the carbon substitution totally, this research calculated the carbon substitutions of wooden building by life-cycle assessment (LCA) and also model the forestry in Taiwan. We established a model to take into account the storage benefits of carbon substitution. The model can estimate the carbon reduction from replacing reinforced concrete buildings (RC-building) with Cross-Laminated-Timber buildings (CLT-building). This study is based on the LCA of RC-building and CLT-building. The two parameters,「GHGs emission of non-wooden product」and「GHGs emission of wooden product」, were put into this model. Because of the multiple effects of forestry management, we let the 「GHGs storage in wooden product」become a part of Materials Manufacturing Phase in CLT-building. It reduces 232,137 KgCO2e emission in life cycle, and needs 85 m3 wood by using CLT-building instead of RC-building in a four-floor building.