Economic Evaluation for Existing Rainwater Harvesting Systems

• Main Authors: Yang, Tzu-Chun, 楊子群
• Other Authors: Liaw, Chao-Hsien
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/esbhcw

碩士 === 國立臺灣海洋大學 === 河海工程學系 === 107 === Due to global climate change, the United Nations treats rainwater harvesting systems as an adaption alternative toward water shortage problem. In domestic, Water Resources Agency, Ministry of Economic Development, has listed rainwater harvesting as an alternative new water resources in the water law. But, research in the subject of economic assessment of rainwater harvesting systems is rare. The purpose of this study is to establish the economic assessment framework of rainwater harvesting systems and apply this framework to the cases completed in 2018 in the project titled Smart Management in Water Resources and Water Conservation Technology (107). These results can be used as a reference for the government in promoting and installing rainwater harvesting systems in the future. In the study, the life cycle base concept is used to calculate the benefits and costs in the stages of system construction and operation. For calculating the benefit-cost analysis, the Net Present Worth, the Benefit/Cost Ratio and Payback Period methods are used to establish the economic benefit assessment framework of rainwater harvesting systems. The cost part can be divided into "direct" and "indirect" costs of the rainwater harvesting systems. Direct costs include facilities of rainwater collection, transport, storage, pump, treatment, monitoring etc. Indirect costs include business tax, air pollution tax, supervision service fees etc. The benefits part can be divided into "direct" and "indirect" benefits of the rainwater harvesting systems. Direct benefits include water saving fees and sewage discharge reduction fees. Indirect benefits include electricity saving and carbon emission reduction fees. For those cases, no monitoring rainwater usage data is collected and calculating the theoretical rainwater usage is laborious due to large number of cases. Therefore, in the study, figures and tables for relationship between average number of rainwater storage use vs. water storage volume and water supply reliability vs. water storage volume for selected roof areas, rainwater demand and areas are constructed to estimate the amount of rainwater use. Finally, the sensitivity analysis is carried out by increasing selected percentage of current water price and wastewater discharge fee to explore the variation of benefit/cost analysis. For the base case, the unit price for calculating benefits is listed as followings: unit price of water equals NT$ 7.35 per m3, unit sewage discharge fee equals NT$ 5 per m3, unit electricity fee equals NT$ 4.27 per KWH and unit price for carbon emission equals NT$ 388 per ton. From the results, 41 cases with a benefit/cost ratio between 0.01 and 0.50, 21 cases with a benefit/cost ratio between 0.51 and 1.00, 14 cases with benefit/cost ratio is greater than 1. The average payback period is 37.04 years. For carrying sensitivity analysis, water price was raised to between NT $ 17 and 22 per m3 and the wastewater discharge fee was raised to between NT$ 11 and 14 per m3and the electricity fee and unit price of carbon emission charges remained unchanged. The results show that 11 cases with a benefit/cost ratio between 0.01 and 0.50, 18 cases with benefit/cost ratio between 0.51 and 1.00, 44 cases benefit/cost ratio greater than 1. The average payback period is 29.4 years. Therefore, as price of water, wastewater, electricity increase, rainwater harvesting system will become more attractive and vital.