Deadline-Aware, Energy-Efficient Control of Domestic Immersion Hot Water Heater

Typical domestic Immersion water heater systems are always turned on during the winter, it heats quickly rather than efficiently and ignores predictable demand windows and ambient losses. We study deadline-aware control, where the aim is to reach a target temperature at a specified time while minimising energy. We introduce an efficient Gymnasium environment that models an immersion hot-water heater with first-order thermal losses and discrete on and off actions ${0, 6000}$ W applied every 120 s. Methods include a time-optimal bang-bang baseline, a zero-shot Monte Carlo Tree Search planner, and a Proximal Policy Optimization policy. We report total energy (Wh) under identical physics. Across sweeps of initial temperature (10–30 °C), deadline (30–90 steps), and target temperature (40–80 °C), PPO achieves the most energy-efficient performance at a 60-step horizon (2 h) it uses 3.23 kWh, versus bang-bang’s 4.37–10.45 kWh and MCTS’s 4.18–6.46 kWh, yielding savings of 26\% at 30 steps and 69\% at 90 steps. In a representative trajectory (50 kg, 20 °C ambient, 60 °C target), PPO consumes 54\% less energy than bang-bang and 33\% less than MCTS. These results show that learned, deadline-aware control reduces energy under identical physics where planners provide partial savings without training, while policies offer near-zero-cost inference once trained.