Energy and water saving potential with rainwater-based evaporative cooling and toilet flushing

Journal article, 2025

Addressing the limited research on integrated rainwater utilization for cooling, this study assesses a dual-purpose rainwater harvesting system for indirect evaporative cooling and toilet flushing in three cities in Sweden during 2015–2023. Using climate data and a validated model, water and energy savings in residential and commercial buildings were evaluated. Simulation was conducted to reach 90 % of evaporative cooling water demand, redirecting water to toilet flushing during low cooling periods. Annual water demand ranged from 7 to 22 m³/(m³/s), covering 28–58 % of cooling demand. Energy savings reached 34 % with water savings between 13 and 28 %. Suggested system size yielded energy savings of 1–28 % and water savings of 8–28 %. The seasonal coefficient of performance varied strongly with operational time and cooling demand. This study provides crucial data on the synergetic benefit of such a system, bridging the knowledge gaps on their practical performance and potential on enhancing building resource efficiency.