HVAC Controller Failsafe Modes for Irregularity Hold and Back-Off
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Solution Overview
Problem
Building control systems, such as HVAC controllers, often experience operational irregularities that can lead to unintended changes in environmental conditions, and existing systems lack effective mechanisms to maintain stability during these issues or revert to safe states when irregularities persist.
Innovation Solution
The implementation of a method where HVAC controllers enter a hold mode to maintain current control values until irregularities are corrected or a predetermined time expires, and if issues persist, transition to a back off mode to set control values to configurable backup settings, ensuring stability and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the HVAC controller continues operating in normal mode during irregularities, then operational continuity is maintained, but system stability deteriorates due to unintended environmental changes
Solution Approach 1:
The controller enters a hold mode that preserves current control values as a preliminary protective action before irreversible damage can occur. This preliminary state maintenance allows the system to stabilize while preventing the propagation of irregularities into environmental changes, thus resolving the contradiction between operational continuity and system stability.
2Reliability
If the HVAC controller immediately reverts to backup settings when irregularities are detected, then system safety is improved, but operational efficiency deteriorates due to unnecessary interruptions
Solution Approach 1:
The controller dynamically adapts its response based on the persistence and severity of irregularities. It transitions through staged modes (hold mode for temporary irregularities, back off mode for persistent issues), allowing the system to maintain high reliability only when necessary while preserving operational efficiency during transient disturbances.
Solution Approach 2:
The controller changes operational parameters (control values) based on the state of irregularities. During hold mode, it maintains current parameters to preserve efficiency. When irregularities persist beyond a threshold, it changes parameters to backup values, ensuring safety only when the situation warrants such intervention.
3Reliability
If the HVAC controller implements multiple failsafe modes with monitoring, then system reliability is improved, but device complexity increases
Solution Approach 1:
The failsafe mechanism is segmented into distinct operational modes (hold mode, back off mode) with clear transition criteria. This segmentation organizes the complexity into manageable, well-defined states rather than a monolithic complex system, making the controller's behavior more predictable and easier to implement reliably.
Data Source
AI summary
An HVAC controller provides control values to or more output ports of the HVAC controller. Operation of the HVAC controller is monitored for one or more irregularities. When one or more irregularities in the operation are identified, a hold mode is entered. The hold mode includes holding the one or more current control values on the one or more output ports of the HVAC controller until the one or more irregularities in the operation of the HVAC controller are corrected or a predetermined hold time expires, whichever occurs first. When the one or more irregularities in the operation of the HVAC controller are not corrected before the predetermined hold time expires, a back off mode is entered. The back off mode includes setting each of one or more control values on one or more output ports of the HVAC controller to a corresponding configurable back off value.