HVAC Controller Relay Failure Detection for Continuous Operation

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Solution Overview

Problem

HVAC system controllers face failures in relays, including shorted, open-circuited, or half-wave outputs from solid state relays, leading to equipment damage and system shutdowns, as existing solutions fail to detect these failures effectively.

Innovation Solution

An HVAC system controller with a processing device that monitors output terminals and switches between primary and secondary solid state relays or uses power control relays to maintain system operation, sending error messages when failures occur, ensuring continued functionality by altering the state of output terminals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a relay is used to control HVAC equipment output, then the system can switch between on and off states, but the relay may fail shorted or open circuited causing system shutdown

Engineering Contradiction:

Improverelay reliabilityVSAvoidsystem operational continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs preliminary detection of relay status by monitoring the output signal before critical failure occurs. The processor continuously checks whether the output terminal is in a high impedance state (open circuit) or shorted state, enabling early intervention before the relay failure completely shuts down the HVAC system.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the operational parameters of the second relay based on the detected failure state of the first relay. When a relay failure is detected, the controller adjusts the state (on/off) of alternative relays to compensate for the failure and maintain system functionality.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a solid state relay is used to control HVAC equipment, then switching is faster and more reliable, but it may fail in an intermediate way outputting half waves which can damage equipment

Engineering Contradiction:

Improvesolid state relay reliabilityVSAvoidequipment damage from half wave output

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The system implements feedback monitoring of the solid state relay output signal to detect abnormal half-wave conditions. The processor continuously analyzes the output signal characteristics and identifies when the solid state relay is failing to provide complete AC cycles, enabling detection of the harmful intermediate failure mode.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system takes preliminary anti-action by detecting the half-wave failure condition and immediately responding to prevent equipment damage. When abnormal output is detected, the controller takes corrective action by switching to alternative relays or shutting down the affected circuit before the half-wave condition can cause damage to connected HVAC equipment.

Inventive Principle:

Principle #9Preliminary anti-action

3Object-affected harmful factors

If the HVAC system controller ceases functioning when a relay fails, then system safety is maintained, but the entire system shuts down including non-affected components

Engineering Contradiction:

Improvesystem safetyVSAvoidsystem operational continuity

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The system segments the control functions by implementing independent monitoring and control paths for different relays and equipment. When one relay fails, only the specific function controlled by that relay is affected, while other functions continue to operate normally through their dedicated relays and control circuits.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The processor acts as an intermediary that detects relay failures and coordinates the switching between primary and backup relays. This intermediary function enables the system to maintain operation by routing control signals through alternative paths when a relay failure is detected, preventing complete system shutdown.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Device complexity

If no detection mechanism is implemented for relay failure, then the system structure remains simple, but undetected failures can damage connected valves and relays

Engineering Contradiction:

Improvedetection mechanism complexityVSAvoidequipment damage from undetected relay failure

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The system implements self-service monitoring where the controller's existing processing resources are used to detect relay failures without requiring separate dedicated detection hardware. The processor utilizes its existing capability to read output terminal states to simultaneously perform both control and failure detection functions.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS11841152B2System and method for operating an HVAC system controller

Publication Date: 2023.12.12 CARRIER CORP

AI summary

An HVAC system controller is provided having a first output terminal electrically coupled to at least one component, and a second output terminal electrically coupled to the at least one component. A processing device controls the first output terminal and the second output terminal. If the first output terminal fails, the processing device changes a state of at least one of the first output terminal and the second output terminal.