Two-Stage HVAC Recovery Mode Algorithm for Adaptive Staging Control
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Solution Overview
Problem
Traditional HVAC systems, particularly two-stage furnaces, face inefficiencies in determining when to initiate second-stage operation, leading to prolonged conditioning times and compatibility issues with thermostats, resulting in suboptimal temperature control.
Innovation Solution
A recovery mode algorithm is implemented in the HVAC system's controller to determine the elapsed time since the last cycle and compare it to a threshold, adjusting the operation mode based on this data, using weighted sums and percentage ranges to decide between first and second stage operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional control methods are used to determine second stage operation timing, then device complexity is reduced, but heat exchange efficiency deteriorates and conditioning time increases
Solution Approach 1:
The recovery mode algorithm pre-calculates and stores optimal stage up times based on elapsed time thresholds before actual operation. When a thermostat call is received, the controller simply retrieves the pre-determined stage up time corresponding to the measured elapsed time, avoiding complex real-time calculations and enabling fast response while maintaining controlled complexity.
Solution Approach 2:
The patent replaces traditional mechanical or simple on-off control mechanisms with an algorithmic control system that uses elapsed time measurements and predefined functions to determine staging decisions. This substitution enables more sophisticated control logic without proportionally increasing hardware complexity.
2Productivity
If second stage operation is initiated quickly to reduce conditioning time, then productivity improves, but energy efficiency deteriorates due to premature high-stage operation
Solution Approach 1:
The stage up time is dynamically determined based on the elapsed time since the last cycle using different functions (first function for shorter elapsed times, second function for longer elapsed times). This dynamic adjustment allows the system to optimize between speed and efficiency for each specific operating condition rather than using a fixed timing rule.
Solution Approach 2:
The controller changes the stage up time parameter based on the elapsed time parameter. By measuring how long it has been since the last cycle and comparing it to threshold values, the system adjusts the stage up time to achieve optimal balance between rapid conditioning and energy efficiency for each specific scenario.
3Adaptability or versatility
If fixed stage up time is used to simplify control logic, then device complexity is reduced, but adaptability to different operating conditions deteriorates
Solution Approach 1:
Multiple stage up time functions are pre-calculated and stored in the controller memory before operation. The first function applies when elapsed time is below a threshold, and the second function applies when elapsed time meets or exceeds the threshold. This preliminary preparation allows the system to adapt to different operating conditions without requiring complex real-time decision logic.
Solution Approach 2:
The elapsed time measurement acts as an intermediary parameter that mediates between the thermostat call and the staging decision. By comparing elapsed time to a threshold value, the system selects which function to use for determining stage up time, providing adaptability through a simple intermediary comparison rather than complex multi-variable logic.
Data Source
AI summary
A system includes two stage HVAC equipment and processing circuitry configured to receive a call for conditioning and, in response to the call for conditioning, execute a recovery mode algorithm. The recovery mode algorithm is configured to determine an elapsed time between the call for conditioning and an ending of a recent cycle and compare the elapsed time to a threshold time period. The recovery mode algorithm is also configured to, in response to the elapsed time being below the threshold time period, determine a first stage up time based on a first function corresponding to the elapsed time being below the threshold time period. The recovery mode algorithm is also configured to, in response to the elapsed time meeting or exceeding the threshold time period, determine a second stage up time based on a second function corresponding to the elapsed time meeting or exceeding the threshold time period.