Technical and Financial Feasibility Analysis of Rainwater Harvesting Using Conventional or Green Roofs in an Industrial Building

Abstract

Given the high annual water consumption for non-potable uses (1112.08 m3, 65%) of an industrial building with a large roof area (4638 m2) located in the Northeast of Portugal, this study aims to evaluate the technical and financial feasibility of a rainwater harvesting system for these uses, considering the existing conventional roof (scenario 1) and adapting a green roof to the existing roof (scenario 2). This evaluation was based on the impact of the two scenarios on the building’s water savings. Under scenarios 1 and 2, the expected water savings were 64.47% and 59.43%, respectively. Therefore, the expected reduction in the annual water bill was €3867.07 + VAT (scenario 1) and €3564.63 + VAT (scenario 2). For scenario 1, considering a reservoir with 70 m3 for non-potable purposes, such as washing the building’s floor and use in industrial machines, and an initial investment of €41,109.13 + VAT, the single payback will be 11.29 years. The single payback for scenario 2 largely exceeded the lifetime of the green roof. However, as they are considered interesting solutions to reduce the negative externalities of industrial settlements, financial incentives could be proposed for the implementation of the green roof in this typology of buildings.