Methodology to optimize rainwater tank sizing and cluster configuration for a group of buildings

The behavior of a rainwater harvesting system depends on some variables that cannot be controlled, such as precipitation, building roof size and water demand. The selection regarding rainwater tank-size will affect the performance of the system and the cost-benefit ratio. The criterion employed for this selection is based on the need for volume-storage and typically, yield large-sized rainwater-tanks, especially when the amount of rainwater is higher during rainy seasons. This article presents a methodology for modelling the rainwater harvesting, storage, and water consumption, for different configurations of a set of buildings, called clusters, where all buildings collect, store and same collected water. This methodology allows for analyzing based on different indicators what is the best recommended configuration and tank sizing, based on configuration and storage ratio exhibited, thus avoiding the situation of being underutilized. The proposed methodology is applied to case of study at a university (Mexico). In this study case, the dynamics per day is modeled over a year, considering monthly rainfall averages, over 2 groups made up of 4 buildings with different collecting capabilities and consumption each, allowing for the analysis of 9 cluster configurations and 4 tank sizing dimensions. The results are analyzed by means of annual indicators such as: the decrease in the volume of water used from the public network, the days of autonomy of the system, and a coefficient R (which relates the volume spilled to the empty volume). This coefficient is then used selection regarding tank sizing and the most recommended cluster configuration.