Evaluating the Energy and Thermal Performance of a Water-Cooled Condenser Using Reverse Osmosis Effluent in Residential Purifiers

Reverse osmosis (RO) water purifiers produce a large volume of reject water, which is typically discarded, leading to water wastage and resource inefficiency. This work proposes a novel approach to reusing RO effluent as a cooling medium in a water-cooled condenser integrated into a residential hot-and-cold water purifier. The system replaces a conventional air-cooled condenser with a water-cooled unit and was evaluated under controlled laboratory conditions (ambient temperature 25 °C). Experiments were conducted at various RO effluent flow rates ranging from 0.5 to 2.5 L per minute (LPM). Key performance metrics, including the coefficient of performance (COP), cooling time, and energy consumption, were measured and compared. Results showed that replacing a conventional air-cooled condenser with a water-cooled condenser configuration reduces energy consumption by up to 37.5% and shortens cooling times by up to 33%. Performance was maintained under intermittent RO effluent supply. However, an excessive flow rate (2.0 LPM) caused evaporator frosting and efficiency loss, indicating the importance of flow control. These findings demonstrate that internally reusing an RO effluent offers a sustainable, compact, and energy-efficient solution for next-generation water purifiers.