Domestic hot water optimizing potential in existing or renovated multifamily residential buildings

In a Swiss case study of the ReCO2st research project, hot water optimization demonstrated a high potential for energy savings with low investment costs. The optimization started with the end user to reduce first hot water consumption. Energy-efficient showerheads and faucets reduced hot water consumption by 10 to 25%, notably from 65.2 [l/p.day] to 48 [l/p.day] for the period of September to October 2019. A multi-criteria selection of showerheads involved end users considering other qualitative aspects like rinsing efficiency, overall feel of use, noise, and material robustness. Strict control of pipe and storing tank insulation reduced storage and distribution losses. Day and night storage temperature setpoints, water recirculation time, switching off this process after 11.00 p.m., temperature differential of start and stop loading setpoints, creating long loading cycles, ensure that the pipes are not always hot. Reducing Legionella cycles at 60 degrees to once a day avoided the need for continuous high temperatures. The combination of all these soft measures in the Swiss case study resulted in a reduction of energy consumption for hot water of 20-30%. This is equivalent to the installation of expensive solar panels for hot water. A detailed two- year monitoring of the building's hot water consumption shows the contribution of each optimization measure. The encouraging results show that without perfect control of the entire process, it is impossible to avoid a performance gap between planned and actual energy consumption.