Adaptive Thermostat Current Control for Safe HVAC Power Stealing
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Solution Overview
Problem
Thermostats face challenges in power harvesting from HVAC systems without a C-wire, as they must balance power draw to avoid false switching of HVAC functions, and existing solutions are not user-friendly or efficient in managing varying HVAC system configurations.
Innovation Solution
A method and thermostat design that includes a power stealing circuitry with voltage measurement and control mechanisms to adjust current draw based on measurements, ensuring a voltage drop of less than 8VRMS across the call switch, allowing for safe and efficient power harvesting during both active and inactive HVAC periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the thermostat draws more current during power stealing, then adequate power for thermostat operation is provided, but the likelihood of false switching of HVAC function increases
Solution Approach 1:
The thermostat dynamically adjusts its current draw during power stealing operations based on real-time measurements of voltage drop across the call switch. The system transitions from a static current draw approach to a dynamic one where the current is modulated to maintain voltage drop within safe thresholds, thereby preventing false HVAC switching while maximizing power harvesting.
Solution Approach 2:
The system implements a feedback mechanism by continuously measuring the voltage drop across the call switch during power stealing and using this measurement to control the amount of current drawn. This closed-loop control ensures that the thermostat harvests maximum power without exceeding the threshold that would cause the load coil to drop out and trigger false HVAC switching.
2Reliability
If the thermostat draws less current during power stealing, then false switching is reduced, but inadequate power is provided for thermostat operation
Solution Approach 1:
The system changes the operating parameters of power stealing by adjusting the current draw based on the measured voltage drop characteristics of the specific HVAC system. Rather than using a fixed conservative current limit, the system adapts the current parameter to match the actual electrical characteristics of the connected HVAC equipment, maximizing power availability while maintaining reliability.
Solution Approach 2:
The thermostat employs dynamic current adjustment during power stealing, transitioning from static to adaptive current draw. The system continuously monitors voltage drop and modulates current in real-time to optimize the balance between power harvesting and preventing false HVAC switching, ensuring adequate power for advanced functions without compromising system reliability.
3Adaptability or versatility
If the thermostat is designed to work with a wide variety of HVAC systems, then adaptability is improved, but determining safe current draw becomes more complicated
Solution Approach 1:
The thermostat performs self-characterization by automatically measuring the voltage drop across the call switch during installation and operation. This self-service approach eliminates the need for manual configuration or complex lookup tables for different HVAC systems. The system independently determines its safe operating parameters by testing and measuring the actual electrical characteristics of the connected equipment.
Solution Approach 2:
The system performs preliminary measurements during installation to characterize the HVAC system's electrical properties before normal operation begins. By conducting voltage drop measurements and determining safe current thresholds in advance, the thermostat prepares the optimal power stealing parameters specific to each installation, simplifying subsequent operation across diverse HVAC configurations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the likelihood of inadvertently switching the HVAC function on or off, enabling reliable and efficient power harvesting across different HVAC systems without the need for a C-wire, extending battery life and improving device reliability.
Implementation Method 1
making at least one measurement that is at least partially influenced by the amount of electrical current flowing through the call switch
Implementation Method 2
The thermostat 'steals,' 'shares' or 'harvests' its power during the 'OFF' or 'inactive' periods of the heating or cooling system by allowing a small amount of current to flow through it into the load coil below its response threshold
Data Source
AI summary
An electronic thermostat and associated methods are disclosed for power stealing from an HVAC triggering circuit. The methods include making voltage measurements while controlling the amount of current drawn by the power stealing circuitry so as to determine a relationship that can be used to select how much current to draw during power stealing. Through the use of the described methods, the likelihood of inadvertent switching of the HVAC function (on or off) can be significantly reduced.