Learning Thermostat Power Scaling for Battery Depletion Prevention
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Solution Overview
Problem
Thermostats with rechargeable batteries face challenges in managing power usage efficiently, especially when power harvesting is interrupted or insufficient, leading to potential battery depletion and reduced functionality.
Innovation Solution
A multi-sensing, wirelessly communicating thermostat that uses power harvesting from HVAC systems to charge a rechargeable battery, with automated adjustments in functionality based on battery voltage and capacity to reduce power consumption through progressive stages of power saving, including reducing display backlighting, curtailing communications, and disabling non-essential features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If power harvesting is used to charge the battery, then the thermostat can maintain advanced functionalities (wireless communication, multi-sensing, display), but the battery may become depleted when power harvesting is interrupted or insufficient
Solution Approach 1:
The thermostat dynamically adjusts its operational characteristics based on battery charge status. When power harvesting provides sufficient energy, the system operates with full functionality including wireless communication, multi-sensing, and display. When battery charge drops below thresholds, the system automatically reduces functionality to essential operations only, ensuring continuous basic operation while preserving battery life
Solution Approach 2:
The system changes operational parameters based on power availability. It monitors battery voltage and charge status, then adjusts communication frequency, display refresh rates, and sensor polling intervals accordingly. This parameter adaptation allows the thermostat to maintain reliability across varying power conditions
2Adaptability or versatility
If processor intensive functions and wireless communications are enabled, then the thermostat provides enhanced functionality, but power consumption increases beyond what battery power or power stealing can sustain
Solution Approach 1:
The thermostat implements periodic operation for processor-intensive functions and wireless communications. Instead of continuous operation, these functions are activated at scheduled intervals when power is available, reducing average power consumption while maintaining essential functionality. Communication bursts are timed to coincide with power availability from harvesting or stealing
Solution Approach 2:
The power management system integrates multiple power sources (power harvesting from HVAC system, power stealing from control wires, and rechargeable battery) into a universal power supply architecture. The system can draw from any available source and automatically switches between them, allowing processor-intensive functions to operate when any power source provides sufficient energy
3Ease of operation
If the LCD display continuously shows temperature, then user convenience is improved, but battery power is depleted faster
Solution Approach 1:
The LCD display operates periodically rather than continuously. It refreshes at intervals based on battery charge status, showing temperature updates only when necessary. In low-power mode, the display may show information less frequently or only upon user interaction, significantly reducing power consumption while maintaining usability
4Reliability
If wireless communication frequency is increased, then data transfer reliability is improved, but battery power is consumed faster
Solution Approach 1:
The wireless communication system dynamically adjusts its transmission frequency and data rate based on available power. When battery charge is high or power harvesting is active, communication occurs more frequently with higher reliability. When battery charge drops, the system reduces communication frequency to essential updates only, balancing reliability with power conservation
Data Source
AI summary
In a multi-sensing, wirelessly communicating learning thermostat that uses power-harvesting to charge an internal battery, methods are disclosed for ensuring that the battery does not become depleted or damaged while at the same time ensuring selected levels of thermostat functionality. Battery charge status is monitored to determine whether the present rate of power usage needs to be stemmed. If the present rate of power usage needs to be stemmed, then a progression of performance levels and/or functionalities are scaled back according to a predetermined progressive power conservation algorithm. In a less preferred embodiment, there is a simple progressive shutdown of functionalities turned off in sequence until the desired amount of discharge stemming is reached. Battery charge preservation measures are also described for cases when an interruption of external supply power used to recharge the battery is detected.