Benchmarking energy consumption and CO2 emissions from rainwater-harvesting systems: an improved method by proxy

Life cycle analyses (LCAs) show the main operational energy contribution for rainwater-harvesting (RWH) systems come from ultraviolet (UV) disinfection and pumping rainwater from tank to building. Simple methods of estimating pump energy consumption do not differentiate between pump start-up and pump-operating energy or include pump efficiency parameters. This paper outlines an improved method incorporating these parameters that indirectly estimates pump energy consumption and carbon dioxide (CO2) emissions using system performance data. The improved method is applied to data from an office-based RWH system. Comparison of the simple and improved methods identified the former underestimates pump energy consumption and carbon emissions by 60%. Results of the improved method corresponded well to directly measured energy consumption and energy consumption represented 0.07% of an office building's total energy consumption. Consequently, the overall energy consumption associated with RWH systems is a very minor fraction of total building energy consumption.