HVAC Thermostat Control With CPH Cycling and Deadband Staging
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Solution Overview
Problem
Existing HVAC control systems, such as those using cycle per hour (CPH) control or deadband control, often result in temperature overshooting and shifting away from the set point, failing to maintain a stable temperature within 1° F (0.5° C) of the user-set temperature.
Innovation Solution
A thermostat system that defines a temperature set point, temperature differential, and cycles per hour, using a cycling control algorithm to determine a duty cycle for temperature control sources within the differential, and a deadband algorithm to turn on/off sources based on temperature extremes, ensuring precise temperature regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If CPH control is used to maintain average temperature near set point, then temperature stability is improved, but temperature overshooting beyond 1°F occurs
Solution Approach 1:
The control range is segmented into multiple zones: a hysteresis band for deadband control and a narrower differential band for CPH control. This segmentation allows the system to use appropriate control strategies for different temperature conditions, preventing overshoot while maintaining stability.
Solution Approach 2:
The system dynamically switches between deadband control and CPH control based on temperature conditions. When temperature is within the hysteresis band, deadband control applies; when within the differential band, CPH control applies. This dynamic adaptation resolves the contradiction between stability and precision.
2Manufacturing precision
If deadband control is used to prevent overshooting, then temperature precision is improved, but set point shifting occurs
Solution Approach 1:
The control strategy is segmented into two temperature zones defined by different thresholds: hysteresis band for deadband control and differential band for CPH control. This ensures precision through deadband while maintaining set point stability through CPH in the critical range.
Solution Approach 2:
The system continuously monitors temperature and provides feedback to adjust control strategy. When temperature approaches the set point within the differential band, CPH control with feedback ensures the average temperature remains near the set point, preventing set point shifting.
3Speed
If multi-stage HVAC system uses deadband control, then response time is improved, but temperature distribution uniformity deteriorates
Solution Approach 1:
The temperature control range is segmented into multiple zones with different control strategies. The hysteresis band uses deadband control for rapid response, while the differential band uses CPH control for uniform temperature distribution, resolving the contradiction between response time and uniformity.
Solution Approach 2:
Different control qualities are applied to different temperature conditions. Deadband control provides aggressive response when needed, while CPH control provides gentle, uniform temperature maintenance when near the set point, achieving both rapid response and uniformity.
Data Source
AI summary
A method of controlling an HVAC system including programming a thermostat of the HVAC system to define a temperature set point, a temperature differential around the temperature set point, and a number of cycles per hour for a temperature control source of the HVAC system. The method also includes sensing a temperature, executing a cycling control algorithm that includes the temperature, the temperature set point, and the number of cycles per hour as inputs to determine a duty cycle, and running the temperature control source according to the duty cycle when the temperature is within the temperature differential. The method further includes executing a deadband algorithm to turn on the temperature control source when the temperature is outside of the temperature differential at one extreme and to turn off the temperature control source when the temperature is outside the temperature differential at the opposite extreme.