Thermostat Duty Cycle Control for Switch Heat Compensation
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Solution Overview
Problem
Existing thermostats using solid-state switches for HVAC systems face inaccuracies in temperature control due to heat dissipation, leading to excessive ambient temperature swings, as the heat generated by the switching device affects the temperature sensor's ability to accurately sense the ambient temperature.
Innovation Solution
A thermostat with a temperature sensor and a heat sink to dissipate heat, coupled with a processor that calculates a duty cycle ratio based on temperature delta and heat dissipation offset, to control the switching device's activation time and minimize heat impact, ensuring precise temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid state switching devices are used to control line voltage to heating elements, then switching speed and reliability are improved, but heat dissipation increases causing temperature sensing inaccuracies
Solution Approach 1:
The patent extracts the harmful heat dissipation effect from the switching device by introducing a dedicated heat sink component. The heat sink is thermally coupled to the solid state switching device to absorb and dissipate the heat that would otherwise affect the temperature sensor, thereby separating the harmful thermal effect from the sensing environment.
Solution Approach 2:
The heat sink acts as an intermediary between the solid state switching device and the temperature sensor. It intercepts the heat generated by the switching device and dissipates it to the ambient environment, preventing the heat from directly affecting the temperature sensor and thus protecting the accuracy of temperature measurements.
2Loss of energy
If the thermostat switch opens early due to sensor heat differential, then power consumption is reduced, but temperature control accuracy deteriorates causing excessive ambient temperature swings
Solution Approach 1:
The patent implements a feedback mechanism where the temperature sensor continuously monitors the ambient temperature and feeds this information back to the control algorithm. The control algorithm processes this feedback along with heat dissipation offset values to dynamically adjust the duty cycle, ensuring that the heating element is controlled based on actual ambient temperature conditions rather than being prematurely affected by internal heat differential.
Solution Approach 2:
The patent changes the operational parameters of the switching device by using pulse width modulation (PWM) control instead of simple on/off switching. The duty cycle is dynamically adjusted based on temperature differential and heat dissipation offset, allowing precise control of power delivery to the heating element while compensating for internal heat effects.
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
The solution effectively maintains ambient temperature within 2 degrees Celsius of the set point, reducing overshooting and enhancing energy efficiency by optimizing the power application to the heating element.
Implementation Method 1
A heat sink associated with the switch is provided, which is configured to dissipate heat generated by the switching device
Data Source
AI summary
A thermostat is provided that includes a temperature sensor for sensing ambient temperature, and a switching device that is configured to apply electrical power to a heating element when the switching device is activated. The thermostat further includes a processor that is configured to periodically determine for a finite switching time period a temperature delta value indicative of the difference between the sensed temperature and a desired set point temperature. The processor is further configured to calculate a duty cycle ratio of the switch activation time relative to the total switching time period. The calculated duty cycle ratio for determining the switch activation time is determined as a function of the temperature delta value, a duty cycle offset and a heat dissipation offset. The duty cycle offset and the heat dissipation offset are based on an average of a predetermined number of prior duty cycle ratios.