Optimisation of rainwater tank design from large roofs: A case study in Melbourne, Australia

Abstract

Rainwater tanks for larger roof areas need optimisation of tank size, which is often not carried out before installation of these tanks. This paper presents a case study of rainwater tank evaluation and design for large roof areas, located in Melbourne, Australia, based on observed daily rainfall data representing three different climatic regimes (i.e. dry average, and wet years). With the aim of developing a comprehensive Decision Support Tool for the performance analysis and design of rainwater tanks, a simple spreadsheet based daily water balance model is developed using daily rainfall data, contributing roof area, rainfall loss factor, available storage volume, tank overflow and irrigation water demand. In this case study, two (185 m3 and 110 m3) underground rainwater tanks are considered. Using the developed model, effectiveness of each tank under different climatic scenarios are assessed. The analysis shows that both the tanks are quite effective in wet and average years, however less effective in dry years. A payback period analysis of the tanks is preformed which reveals that the total construction cost of the tanks can be recovered within 15-21 years time depending on tank size, climatic conditions and future water price increase rates. For the tanks, a relationship between water price increase rates and payback periods is developed. The study highlights the need for detailed optimisation and financial analysis for large rainwater tanks to maximise the benefits.

Potable Water Savings by Using Rainwater for Non-Potable Uses in Houses

“…According to [15] calculations based on average annual rainfall produce unrealistic results, particularly in very large rainwater tank capacities. The concept of seasonality index studies this inter annual variability, separating the years into dry, average and wet, and evaluates if the variability affects the results.…”

Rainwater Harvesting in Large Residential Buildings in Australia

“…In single-family households, an expected payback period was found to be between 33 to 43 years depending on the tank size, while in a multi-family building a payback period was 61 years for a 20 m 3 tank. Imteaz et al (2011) found that for commercial tanks connected to large roofs in Melbourne, total construction costs can be recovered within 15 to 21 years depending on the tank size, climatic conditions and future water price increase rate. Tam et al (2009) investigated the cost effectiveness of rainwater harvesting systems in residential areas around Australia and found that these systems can offer notable financial benefits for Brisbane, Sydney and the Gold Coast due to the relatively higher rainfall in those cities as compared to Melbourne.…”

Proposal for a rainwater utilization project for non-potable purposes in vertical tank

“…Existem inúmeros trabalhos de pesquisa sobre o dimensionamento de reservatórios de armazenamento para uso em da água pluvial [38][39][40][41][42][43][44], e referências citadas, muitas vezes eles não são comparáveis a dificultada pela enorme disparidade entre as condições e restrições que influenciam e análise do desempenho específicos e as conclusões sobre a eficiência e confiabilidade do sistema, a saber: precipitação anual, área de precipitação total, a capacidade de armazenamento e consumos diários. Para contornar este revés, o conceito de análise não dimensional foi introduzido e aplicado em alguns estudos [38,44].…”