Non-Invasive Calorimetric Sensor for Waterflow Event Detection in Premise Plumbing Systems

Non-invasive and low-cost sensors for waterflow event detection are required to determine p-values for the estimation of peak water demand during premise plumbing system design. This paper presents a low-cost calorimetric flow sensor for non-invasive detection of waterflow inside copper waterpipes. As a critical design parameter, the distance between a heater and two symmetrically placed temperature sensors was optimized to maximize the thermal coupling between the heater and water through the pipe wall. A printed circuit board with commercial high-resolution temperature sensors as well as precision 3D-printed heater bridge and sensor mount were designed with features to improve heat conduction symmetry and to minimize undesired direct heat conduction paths between the heater and temperature sensors. The sensor mount also allows ease of deployment on waterpipes. The assembled device showed excellent heat conduction symmetry with a temperature offset <0.054°C. Tests with emulated water on/off events successfully verified the operation and functions of the sensor.