HVAC Thermostat Duty-Cycle Signaling for Variable Speed Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional thermostats cannot effectively control variable speed compressors or blower motors in HVAC systems, leading to inefficiencies due to their simple ON/OFF control mechanisms, which do not maximize the performance of variable speed controlled compressors.
Innovation Solution
The system adjusts the duty cycle of a signal sent from a thermostat unit to a compressor or furnace controller unit based on the temperature difference between ambient and set temperatures, allowing the compressor or blower motor speed to be adjusted accordingly, using existing wiring and minimizing hardware changes, with a microprocessor-controlled PWM controller configuring an IGBT array to achieve desired compressor speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a simple ON/OFF control mechanism is used from the thermostat, then the device complexity is reduced and ease of operation is improved, but the compressor cannot function at maximum efficiency and energy usage is not optimized
Solution Approach 1:
The patent transforms the simple binary ON/OFF control signal into a variable duty cycle signal that encodes temperature difference information. By changing the parameter of the control signal from a binary state to a variable duty cycle (0-100%), the thermostat can communicate nuanced temperature information to the compressor controller, enabling efficient variable speed operation without complicating the thermostat hardware.
Solution Approach 2:
The patent introduces an intermediary encoding scheme where the thermostat modulates the AC control signal into a duty cycle waveform that represents temperature difference. This intermediary representation allows the simple thermostat to convey complex temperature information that the compressor controller then decodes and acts upon, bridging the gap between simple control and complex operation.
2Loss of energy
If variable speed control is implemented to optimize energy usage, then energy efficiency is improved, but the control system complexity and hardware requirements increase
Solution Approach 1:
The patent makes the existing AC control line serve multiple functions: it continues to provide power to the compressor while simultaneously encoding and transmitting temperature difference control information through duty cycle modulation. This multi-functionality eliminates the need for separate control wiring, reducing overall system complexity despite implementing variable speed control.
Solution Approach 2:
The system implements a feedback loop where the compressor controller receives duty cycle information representing temperature difference, decodes it, and adjusts compressor speed accordingly. The controller continuously monitors the duty cycle signal and dynamically adjusts speed to maintain optimal efficiency, creating a closed-loop control system that optimizes energy usage.
3Ease of manufacture
If existing wiring is used without modifications, then ease of manufacture and installation are improved, but the ability to transmit temperature difference information from thermostat to controller is limited
Solution Approach 1:
The patent uses periodic AC waveforms with varying duty cycles to encode temperature difference information. By switching the AC line on and off in specific duty cycle patterns (e.g., 0-100% duty cycle corresponding to temperature ranges), the system transmits continuous temperature information through periodic signal modulation, maximizing information transmission through existing two-wire AC control wiring.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Methods and apparatuses that support the transfer of data from a thermostat unit (100) to a ontroller unit to control a variable speed heating, ventilation, and air conditioning (HVAC) system are disclosed. The duty cycle of a signal that is sent from a thermostat unit (100) to a controller unit is adjusted in accordance with a temperature difference between the ambient temperature of an nvironmentally controlled space and a set temperature, and the controller unit (300) measures the duty ycle to determine the temperature difference and adjusts the speed of a blower motor or compressor in accordance with the temperature difference. The signal is switched on and off, in which the AC waveform is conducted and blocked by the thermostat unit (100) signal, determines the temperature from the duty cycle, and adjusts the speed from a predetermined relationship.