At the beginning of the window, the system records both external and internal temperatures as reference values. Continuously throughout the window, the system compares current temperatures to these reference values. When external temperature has dropped by at least five degrees Celsius AND internal shed temperature has dropped by at least two degrees Celsius, both measured from the window start, the system concludes that the fire is genuinely retreating rather than experiencing a temporary lull, and transitions to cooldown phase.
The five-degree external drop threshold ensures that the temperature change represents a significant trend rather than normal atmospheric fluctuation. The additional requirement of a two-degree internal drop prevents false cooldown detection if external temperature drops due to a temporary wind shift while radiant heat continues warming the shed—internal temperature should also decline if the fire is truly retreating. The asymmetric thresholds (five degrees external, two degrees internal) reflect the fact that external temperature responds more quickly to fire movement while internal temperature changes more slowly due to thermal mass.
Once the system enters cooldown phase, it never returns to warmup phase during the current power-on session. This represents the recognition that bushfire events typically consist of a single fire front passage, and that conditions improving enough to trigger cooldown are unlikely to reverse. The system's strategy shifts from anticipating intensification to managing wind-down.
In cooldown phase, the temperature thresholds and sprinkler cycles change to more conservative values that recognize the fire's retreat. External temperature between 70 and 80 degrees Celsius triggers a cycle of three minutes on, five minutes off—more conservative than warmup's five minutes on, three minutes off at the same temperature band. Between 60 and 70 degrees Celsius, the cycle becomes three minutes on, eight minutes off—again more conservative than warmup behavior. Below 60 degrees Celsius in cooldown phase, sprinkler operation ceases entirely. The fire threat has diminished to the point where water conservation becomes paramount, and the system enters a passive monitoring state, ready to log final temperatures but no longer actively defending.
This dual-phase approach prevents the system from oscillating between aggressive and conservative modes if temperature fluctuates around threshold values, and recognizes that identical temperature readings have different strategic meanings depending on fire trajectory. A temperature of 75 degrees during warmup suggests fire is approaching and might intensify further, calling for aggressive defence. The same 75 degrees during cooldown suggests fire is departing and will continue cooling, calling for conservative water use.
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