Remote manual control depends on internet availability and the functioning of the house based systems. When that fails autonomous mode steps in. The autonomous operation mode engages when AR3 determines that manual control is unavailable or when explicitly requested. That request is sent from AR1 via the HA_AUTO flag. Once engaged autonomous mode implements a comprehensive fire defence strategy based on environmental conditions. The algorithm is formally codified as the Fire Defence System specification, with all numeric thresholds collected in a single section of the AR3 source code to facilitate review and tuning. The algorithm balances multiple competing objectives: providing adequate protection against fire threat, conserving limited water resources for maximum defence duration, protecting equipment from heat damage, and adapting strategy as fire conditions evolve through different phases.
The algorithm operates hierarchically, with water level providing the highest-priority constraints that override temperature-based decisions. At the most basic level, if water depth falls to or below 0.05 meters (50 millimeters), the system enters dry cutoff mode, forcing all outputs off to prevent pump cavitation and mechanical damage. This threshold represents the minimum water column height necessary for reliable pump intake operation—below this level, the pump would draw air, causing the diesel engine to overheat and potentially destroying the pump impeller through dry running.
Between 0.05 and 0.30 meters water depth, the system enters gel priority mode. In this band, expected to occur only during extended fire events when water consumption has been severe, the system activates the main pump continuously at low flow (high flow valve P3 forced off) with the gel injection valve P4 activated. This mode maximizes the effectiveness of remaining water by enhancing it with fire retardant gel, which adheres to surfaces and provides prolonged protection even after water has evaporated. Critically, gel priority mode does not disable shed cooling—peripheral P2 can still activate based on internal temperature, recognizing that equipment protection remains important even when sprinkler water conservation is paramount. Fire defence continues, but in a form optimized for the minimal water remaining.
Between 0.30 and 0.50 meters depth, the recirculation band activates. In this mode, the system runs a fixed intermittent cycle of three minutes sprinklers on, eight minutes off, using the recirculation valve (P1) rather than pump cycling to achieve the intermittent pattern. The pump runs continuously while P1 cycles between pass-through (water to sprinklers) and recirculation (water returns to tank). This conserves water while maintaining some defensive capability, and importantly, this mode overrides any temperature-based requests for continuous sprinkler operation. Even if external temperature exceeds 80 degrees Celsius indicating fire front arrival, water conservation takes absolute priority in this band. The system will cycle sprinklers on for three minutes every 11 minutes regardless of external conditions, preventing complete water exhaustion while providing periodic cooling.
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