Combining reliability and cost benefit analyses of rainwater harvesting system for commercial buildings
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Date
2019
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Publisher
Universiti Teknologi Malaysia
Abstract
The present work aims to evaluate the performance of small and large commercial buildings rainwater harvesting systems (RWHS) in Johor Bahru, Malaysia. The selected small and large commercial buildings are AEON Taman Universiti and AEON Bukit Indah, respectively. Daily rainfall data of 29 years (1975 to 2003) recorded at Senai International Airport were used in this analysis. Water consumption at both buildings were monitored daily and combined with secondary data obtained from the AEON’s offices. Mass balance model was adopted as the simulation approach. In addition, the economic benefit of RWHS in terms of percentage of reliability (R), net present value (NPV), return on investment (ROI), benefit-cost ratio (BCR), and payback period (PBP) were examined. Effects of rainwater tank sizes and water tariffs on the economic indicators were also evaluated. Future water tariffs were predicted from historical data (1965 to 2015) using a simple regression equation. The study area receives high annual rainfall ranging from 1860 to 2892 mm, high number of rain days ranging from 160 to 228, and consistent rainfall pattern throughout the year. The water in those buildings was used for toilet flushing, plant watering and general cleaning, chiller system, and potable uses. The total daily consumption amounted to 214 m3 and 536 m3 for small and large buildings, respectively. The non-potable usages make up 68% (for small building) and 70% (for large building) of the total consumptions. The reliability of the RWHS for the small and large buildings were up to 93% and 100%, respectively, depending on the size of rainwater tank. The economic benefits of the proposed RWHS were highly dependent on the tank size and water tariff with the optimum PBPs for small building range from 6.5 to 10.0 years whereas for the large building from 3.0 to 4.5 years. Interestingly, RWHS for the large building offers better NPV, ROI, BCR, and PBP compared to the small system. In supporting RWHS implementation, a software for estimating reliability and economic benefits of RWHS has also been successfully developed in this study.
Description
Thesis (PhD. (Civil Engineering))
Keywords
Water harvesting, Rainwater, Industrial water supply