HVAC Signaling Over Two-Wire Circuit Using Ripple Voltage Modulation
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Solution Overview
Problem
Legacy HVAC systems with two-wire circuits face challenges when upgrading to advanced thermostats, as parasitic power methods can cause false activations due to varying current sensitivities, and existing solutions like wiring extenders generate heat and are costly.
Innovation Solution
A system using a sender unit at the thermostat to alter the ripple voltage of the two-wire connection and a detector unit at the HVAC equipment to normalize this voltage, allowing for reliable power and signaling without heat generation or additional wiring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If parasitic power method is used to power the advanced thermostat, then the thermostat can operate without external wiring, but false activations occur due to varying current sensitivities of different HVAC equipment
Solution Approach 1:
The patent introduces a current isolation circuit as an intermediary between the two-wire circuit and the HVAC equipment control input. This isolation circuit blocks the parasitic current from reaching the HVAC equipment while still allowing the thermostat to be powered, thereby eliminating false activations. The isolation circuit acts as a mediator that separates the power function from the control signal function.
Solution Approach 2:
The patent segments the two-wire circuit into separate functional paths: one path for power delivery to the thermostat and another path for control signals to the HVAC equipment. This segmentation is achieved through the use of isolation circuits and rectification components that direct current flow differently for power and signaling, preventing the parasitic current from causing false activations.
2Reliability
If wiring extenders are used to isolate the two-wire circuit from HVAC control input, then false activations are eliminated, but significant heat is generated affecting thermostat temperature detection
Solution Approach 1:
The patent replaces the mechanical/thermal isolation method of wiring extenders (which use resistive loads that generate heat) with an electrical isolation method using isolation circuits and rectification. This substitution eliminates the heat generation problem while maintaining the isolation function. The electrical components isolate circuits without converting electrical energy to thermal energy like resistive loads do.
3Reliability
If wiring extenders are used to provide isolation, then the two-wire circuit can be used safely, but the transmitter unit is bulky and requires significant mounting space
Solution Approach 1:
The patent merges the isolation circuit, rectification circuit, and thermostat into a single integrated unit. The sender unit incorporates both the isolation functionality and the thermostat controls, eliminating the need for a separate bulky transmitter unit. This integration significantly reduces the mounting space required while maintaining all necessary functions.
4Reliability
If wiring extenders are used to enable power and signaling over two-wire connection, then false activations are prevented, but the system becomes expensive representing significant portion of upgrade cost
Solution Approach 1:
The patent creates a universal thermostat design that can be used with both traditional four-wire systems and legacy two-wire systems. The same thermostat unit incorporates adaptive circuitry that automatically detects the wiring type and configures itself accordingly. This universality eliminates the need for expensive specialized wiring extender systems, as the thermostat itself provides the necessary isolation and adaptation functionality.
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
Enables efficient power and signaling over two-wire connections with reduced heat impact on thermostat temperature monitoring and lower costs compared to existing solutions.
Implementation Method 1
a sender associated with the thermostat and electrically connected across the two wire connection, the sender responsive to a signal from the thermostat to alter a ripple voltage of the power supplied through the two wire connection
Implementation Method 2
a detector associated with the HVAC equipment and operable to detect the ripple voltage and provide a signal to activate the HVAC equipment if the ripple voltage has been altered by the sender
Data Source
AI summary
A method and system for providing HVAC signaling over a two-wire circuit is disclosed which also provides operating power for a thermostat. The system is relatively inexpensive to implement and produces only low levels of heat at the sender unit to avoid adversely affecting the ability of the thermostat to monitor the temperature of its surroundings.