Quantifying the Influence of Thermostatic Mixing Valves on Showering Behaviour, Water Consumption and Domestic Hot-Water Energy Demand

Showering represents a major component of residential water consumption and domestic hot-water energy demand. Although thermostatic mixing valves (TMVs) are widely used to improve thermal comfort and reduce the risk of scalding, their influence on showering behaviour and associated resource savings remains poorly quantified. This study proposes a conceptual model linking shower duration to temperature adjustment activities, flow interruptions during soaping, and user responses to hydraulic disturbances. Model parameters were estimated through two experimental campaigns involving 40 volunteers and 200 instrumented showers, complemented by an online survey of 1,000 French respondents. Four faucet technologies were compared under controlled laboratory conditions: a thermostatic mixing valve, a mechanical mixer tap, a two-handle mixing tap and a pressure-balance valve. The results showed that TMVs significantly reduced the initial temperature adjustment duration compared with all other faucet technologies, with reductions ranging from 45% to 60%. TMVs also led to significantly lower mixed-water temperatures, averaging 2.05 °C below those observed with conventional faucets. While no significant reduction in total shower duration was observed during experimental testing, the analysis revealed that TMVs substantially decrease adjustment-related activities during showering. The proportion of users interrupting water flow while soaping was estimated at 66%, whereas 41% of respondents reported being affected by hydraulic disturbances in their dwelling. Based on representative French showering conditions, the proposed model predicts annual savings of approximately 1.6 m³ of water and 96 kWh of energy per person. Extrapolation to the French residential building stock suggests a theoretical saving potential of 69 million m³ of water and 4.1 TWh of energy per year. These findings demonstrate that TMVs can reduce the environmental footprint of showering while maintaining user comfort and highlight their potential as a large-scale water- and energy-efficiency measure in residential buildings.