In situ experimental and theoretical studies of the performance and the fouling impact of shower greywater heat recovery systems

• In situ tests in real operation conditions has been conducted for 14 months on a commercial drain water recovery plates heat exchanger. • Real performances have been evaluated by considering fouling, unsteady effects and user profiles. • Heat exchanger fouling dynamics and biofilm development have been characterizedand and moddeled. • The overall efficiency of the heat exchanger considering fouling and unsteady effects is 66% and the fouling reduces the nominal efficiency of 8%. • The overall system efficiency taking into account shower heat losses (between shower head and drain) is 52%. This paper begins with a theoretical analysis of shower water heat recovery systems, assessing 3 key indicators in particular: the V40 indicator (volume of water that can be produced at 40 °C), the efficiency of the heat exchanger and the efficiency of the complete system . A benchmark was also carried out on commercial systems available, with a classification by type. Finally, a comparative and critical analysis was carried out on tests standards. Next, a model of fouling by biofilm development is proposed, then validated and calibrated experimentally. Then, this work presents the results of a in situ gravity grey-shower-drain water heat recovery system (plates) test campaign over 14 months and a theoretical analysis of this type of system, studying the different types of connections and the impact of influencing parameters (flow rate, temperature, user profile). This work provides experimental data on actual performance and characterizes fouling of this type of exchanger through biofilm development and show the good performance of these systems that can provide a significant impact on the whole energy balance of buildings. The average efficiency of the recovery heat exchanger, taking fouling into account, is 66 %, i.e. 8 % less than the nominal efficiency. Finally, the efficiency of the overall system was evaluated at 52 %, which means that DHW consumption in a dwelling can be drastically reduced with this type a low-tech system. This study also shows the significant impact of the fouling on the performance that requires to treat this question to ensure a sustainable operation over time.