Performance of Rainwater Harvesting Systems in Institutional Buildings under Different Reliability and Future Economy Benefits
The purpose of this study was to determine the most appropriate size of rainwater storage tank for Swinburne University of Technology Sarawak Campus (SUTS) based on the roof area and rainfall data and to compare its cost-effectiveness to a potable water supply. Daily rainfall data used in this study was obtained from meteorological station at Kuching International Airport, located about 6.3Km from SUTS. Water consumption data was obtained by translating the average monthly water bill provided by the SUTS facilities department. The simulation was conducted using a water balance model with yield-before-spillage (YBS) and yield-after-spillage (YAS) operating rules. The results were compared with Tangki Nahrim software. Additionally, cost analysis of rainwater harvesting system (RWHS) from the aspect of reliability, total cost, water-saving amount/year, payback period were further analyzed for choosing the optimum size of rain harvesting tank at different blocks in SUTS. The unit cost of harvested rainwater per m3 was evaluated with the water tariff charged by Kuching Water Board (KWB). Results show the optimal tank size for Block A&B and Block G is 60m3, while the optimal tank size for Block E is 30m3, with a reliability range of 83.5% to 89.5%. The capital cost required for Blocks A&B and G is RM51,310 each, while RM25,655 for Block E. With the installation of RWHS, the total annual water saving cost has amounted to RM8999.32. The payback period for these three blocks ranges from 12.9 years to 15.8 years, with a unit cost of RM1.87/m3 to RM2.29/m3. During the payback period, cost analysis revealed that the unit cost of water is slightly higher than the commercial water tariff rate. However, rainwater was freely supplied after that until the system's life span was reached. Thus, RWHS is the most cost-effective and long-term solution for reducing reliance on potable water supply.
Keywords: rainwater harvesting system, optimum tank size, reliability, yield-after-spillage, yield-before-spillage, Tangki Nahrim.
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