Method of Calculation the Efficiency and Economic Viability of Rainwater Harvesting Systems

Abstract

Purpose: study the methodology for designing a rainwater harvesting system and evaluate its technical and economic viability for supplying water for washing vehicles in the garage of the State University of Rio de Janeiro (UERJ), Maracanã campus.   Theoretical framework: water supply in urban areas faces complex challenges, due to changes in minimum flows, pollution of water sources, demand growth, variability and uncertainties in the rainfall regime. Rainwater harvesting systems have become an alternative to supply non-potable demand, reducing the need for consumption by the public supply system.   Method: evaluation of rainfall in the region of Tijuca, Rio de Janeiro, to meet the demand for water for washing vehicles through a rainwater harvesting system. The calculations of the catchment area and volume of the reservoirs used data, with a historical series between 2009 and 2018, statistical adjustment of the Gumbel frequency distribution and a ten-year recurrence period.   Results and conclusion: An average percentage of 61 to 75% of demand was met, depending on rainfall variations and the capacity of the reservoir adopted. Average monthly savings of between US$ 200 and US$ 300 were found, corresponding to a period of 4 to 24 months for cushioning investments in the implementation of the system.   Research implications: The research contributes with data that reinforce the importance and efficiency of correctly sized systems, as an alternative source to meet non-potable demands. Originality/value: the article presents a specific methodology for sizing the main elements in a system (catchment area and reservoir volume) and configures excellent technical and economic viability in the proposed use.