Rainwater harvesting: model-based design evaluation

Abstract

The rate of uptake of rainwater harvesting (RWH) in the UK has been slow to date, but is expected to gain momentum in the near future. The design of two different new-build rainwater harvesting systems are evaluated using a state-of-the-art continuous simulation modelling approach. The RWH systems were shown to fulfill between 36% and 46% of WC demand. It was found that design methods based on simple approaches (such as used in these two cases) generate tank sizes substantially larger than the simulation model. Comparison of the actual tank sizes and those calculated using the simulation model established that the actual tanks installed are oversized for their associated demand level and catchment size. The importance of catchment size was demonstrated, a factor neglected in the simpler methods commonly used in practice. Financial analysis revealed that RWH systems within large commercial buildings may be more financially viable that smaller domestic systems. A recommendation for a transition from the use of simple tools to simulation models is made.