Variable-Speed Compressor Control to Prevent HVAC Coil Freeze

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

HVAC systems face issues with coil freeze due to refrigerant loss or insufficient airflow, leading to system shutdown and extended downtime, as conventional systems lack effective methods to prevent or delay freezing while maintaining cooling operation.

Innovation Solution

The implementation of a variable-speed compressor controlled by a sensor that monitors saturated suction temperature or pressure, operating in a freeze-prevention mode to maintain the refrigerant above a setpoint value, thereby preventing or delaying evaporator freezing and allowing continued cooling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the HVAC system operates with a loss of charge or insufficient airflow, then cooling operation continues, but the evaporator temperature drops to freezing or near-freezing temperatures causing damage

Engineering Contradiction:

Improvecooling operation continuityVSAvoidevaporator damage risk

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system uses a sensor to continuously monitor evaporator temperature or pressure and feeds this information back to the controller. When the temperature approaches the freezing point or pressure indicates a fault condition, the controller adjusts the compressor speed to maintain safe operating parameters, preventing evaporator freezing while allowing continued cooling operation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent employs a variable-speed compressor that can dynamically adjust its operating speed based on real-time system conditions. During fault conditions such as loss of charge or insufficient airflow, the compressor speed is modulated to maintain evaporator temperature above freezing while still providing cooling capacity, rather than operating at fixed high speed that would cause freezing.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the HVAC system shuts down when refrigerant reaches freezing temperatures, then evaporator damage is prevented, but cooling operation stops and downtime extends

Engineering Contradiction:

Improveevaporator protectionVSAvoidsystem downtime

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system takes preliminary protective action by monitoring evaporator temperature and pressure before freezing actually occurs. When sensors detect that temperature is approaching the freezing point or pressure indicates a fault condition, the controller proactively adjusts compressor speed to prevent freezing, allowing the system to continue operating without shutdown and avoiding extended downtime.

Inventive Principle:

Principle #10Preliminary action

3Object-affected harmful factors

If a freeze-stat monitors refrigerant temperature and shuts down the system at freezing temperatures, then evaporator freezing is prevented, but the system cannot provide cooling during the shutdown period

Engineering Contradiction:

Improveevaporator freezing preventionVSAvoidcooling capacity availability

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

Instead of using a binary on/off control approach with a freeze-stat, the system changes the operating parameter of compressor speed to a variable continuous range. This allows the evaporator temperature to be maintained above freezing through gradual speed adjustment while still providing cooling capacity, rather than completely shutting down the system when temperature approaches the freezing point.

Inventive Principle:

Principle #35Parameter changes

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

This solution enables extended operation of HVAC systems during faults by preventing or delaying evaporator freezing, reducing downtime and maintaining cooling capacity, while also preventing damage to system components.

Implementation Method 1

an evaporator configured to receive a refrigerant and transfer heat from a flow of air to the refrigerant

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

a variable-speed compressor configured to receive the refrigerant and compress the received refrigerant

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentUS11703242B2Avoiding coil freeze in HVAC systems

Publication Date: 2023.07.18 LENNOX IND INC

AI summary

An HVAC system includes an evaporator. The evaporator includes a sensor configured to measure a property value (i.e., a saturated suction temperature or a saturated suction pressure) associated with saturated refrigerant flowing through the evaporator. The system includes a variable-speed compressor configured to receive the refrigerant and compress the received refrigerant. The system includes a controller communicatively coupled to the sensor and the variable-speed compressor. The controller monitors the property value measured by the sensor and detects a system fault, based on the monitored property value. In response to detecting the system fault, the controller operates the compressor in a freeze-prevention mode, which is configured to maintain the property value above a setpoint value by adjusting a speed of the variable-speed compressor. This prevents or delays freezing of the evaporator during operation of the system during the detected system fault.