A water heater, insulated supply run, distant fixture branch and dedicated return with a circulator and balancing valve form this hot-water loop. Set heater outlet temperature, ambient temperature, initial loop temperature, recirculation flow and heat-loss conductance, toggle the circulator, and watch the return temperature evolve.
• A real-time 3D view with numbered, clickable parts: water heater; insulated supply run; remote fixture branch; dedicated recirculation return; return circulator and balancing valve. Scene tools include home view, focus-selected-part, auto-rotate, expand and show/hide labels, and drag-to-orbit with pinch-to-zoom. • Experiment controls: heater outlet temperature (45–65 °C); surrounding temperature (10–30 °C); initial mixed-loop temperature (10–65 °C); recirculation flow (1–10 L/min); loop heat-loss conductance ua (10–100 W/K); circulator enabled, plus a show flow/process markers toggle, pause/resume, single-step buttons (0.1 s and 1 s), a playback-speed selector and a restart experiment action. • Live readouts: mixed loop / return temperature; predicted equilibrium temperature; heat transfer to surroundings; heat exchange from heater; recirculation flow; physical elapsed time. A model response curve is drawn beside the 3D view and updates as you change controls. • A Curves & measurements tab with two live charts, the model equations as written in the simulator and snapshot readouts; an Experiments tab with 3 guided presets (warm the loop; switch off and cool; improve insulation) plus a model-verification bench, timestamped event log and copyable trial report. • A Learn & assess tab with 3 lessons (follow the system; connect the measurements; interpret the model), a 2-question knowledge check with reset, and a written model-scope statement.
The model treats the loop as a single 20 kg mass of water: Mcp dT/dt = ṁcp (Th − T) − UA (T − Ta). Heat enters from the heater in proportion to flow and leaves to surroundings in proportion to UA. The equilibrium temperature is T∞ = (ṁcp Th + UA Ta) / (ṁcp + UA), and the approach is exponential with time constant M cp / (ṁcp + UA).
More flow moves T∞ closer to the heater outlet; more heat loss pulls it toward ambient. Improving insulation, an experiment in the lab, raises the equilibrium.
With the circulator off there is no heat exchange with the heater, so the loop cools toward ambient. One animation second represents 30 physical seconds, and the simulator shows predicted equilibrium, heat exchange and loss in watts and physical elapsed time.
The loop is single and well mixed with constant heater outlet and ambient. It does not resolve plug-flow delay, pipe wall capacitance, microbial growth, scald risk, tank stratification or fixture mixing, and temperature is not a safety certification.
It circulates hot water past the fixtures so hot water is available quickly instead of waiting for cold water in the pipe to run out.
Heat leaks to the surroundings along the loop. Equilibrium settles where heat delivered by circulation matches the heat lost.
Lower heat-loss conductance UA reduces loss, so the equilibrium temperature approaches the heater outlet temperature.
No. Temperature is not a safety certification and the model does not cover scalding, Legionella risk or mixing valves.