Heat Pump Reverse Start-Up Control for Flooded Start Prevention

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Solution Overview

Problem

Heat pumps experience 'flooded starts' due to refrigerant accumulation in the evaporator after shutdown, leading to potential compressor damage, contamination, and noise during start-up, which existing solutions like accumulators only partially address and are costly.

Innovation Solution

Operating the heat pump in reverse mode for a short period at start-up, switching from the previous mode to either heating or cooling mode, ensures that liquid refrigerant is diverted to the outdoor coil, where it flashes into vapor, preventing ingestion by the compressor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an accumulator is installed to prevent flooded starts, then compressor protection is improved, but system cost and complexity increase

Engineering Contradiction:

Improvecompressor protectionVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention extracts the harmful liquid refrigerant from the system by temporarily reversing the refrigerant flow, directing it away from the compressor and through the outdoor coil where it evaporates. This eliminates the need for an accumulator while still protecting the compressor from flooded starts.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention temporarily reverses the normal refrigerant flow direction by switching the four-way valve to heating mode. This inversion causes liquid refrigerant to be pushed through the outdoor coil instead of toward the compressor, preventing flooded starts without requiring additional components.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If an accumulator is installed to prevent flooded starts, then compressor protection is improved, but system cost increases

Engineering Contradiction:

Improvecompressor protectionVSAvoidsystem cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of using an expensive accumulator component, the invention uses the existing four-way valve and refrigerant cycle to temporarily redirect flow. The solution uses already-present system components rather than adding costly new hardware.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If the heat pump operates in reverse mode at start-up, then flooded starts are eliminated, but operating time is increased

Engineering Contradiction:

Improvecompressor protectionVSAvoidstart-up time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The invention applies partial action by using only a brief reverse mode operation at start-up, just long enough to clear liquid refrigerant from the indoor coil. This limited application of reverse mode eliminates flooded starts while minimizing the time penalty compared to continuous reverse operation.

Inventive Principle:

Principle #16Partial or excessive action

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

Effectively eliminates flooded starts by ensuring no liquid refrigerant is ingested by the compressor at start-up, reducing downtime and noise, and avoiding the additional costs and leak risks associated with accumulators.

Implementation Method 1

the liquid refrigerant in the indoor heat exchanger would have to pass downstream to the expansion device and then flash in the outdoor heat exchanger partially turning into vapor

Methodology Applied

Scientific EffectFlash evaporation: Flash Evaporation

Implementation Method 2

In the condenser, heat is exchanged between outside ambient air and the refrigerant. In the evaporator heat is exchanged between the refrigerant and the indoor air

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Data Source

PatentUS7540163B2Prevention of flooded starts in heat pumps

Publication Date: 2009.06.02 CARRIER CORP

AI summary

A heat pump is provided with a method and control for eliminating flooded starts. In particular, the heat pump at start-up is operated for a short period of time in the opposite mode to that in which it had been operated before the previous shutdown. In this way, the compressor ingestion of liquid refrigerant is limited or completely eliminated. After a short period of time, the heat pump is moved back to the intended mode of operation. Additional features can be added to the control scheme to limit this type of operation at start-up only to certain ambient conditions or only to a prolonged period between shutdown and start-up.