Outdoor Heat Exchanger Defrosting With Subcooling Feedback
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Solution Overview
Problem
Existing heat pump air-conditioning systems face inefficiencies in defrosting processes, particularly with medium-pressure defrosting, where energy and time are wasted due to incomplete frost melting, and it is challenging to determine defrosting completion accurately, affecting heating capability post-defrosting.
Innovation Solution
A heat source side unit with a compressor, heat exchangers, defrosting pipes, expansion devices, and a controller that controls refrigerant pressure and subcooling to efficiently defrost heat exchangers while maintaining heating, allowing for accurate defrosting completion determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If medium-pressure defrosting is performed by controlling refrigerant pressure in the outdoor heat exchanger to be within a predetermined range, then defrosting efficiency is improved and heating capability is maintained, but it becomes difficult to accurately determine defrosting completion
Solution Approach 1:
The patent uses subcooling degree as a feedback parameter to accurately determine defrosting completion. The controller calculates the subcooling degree based on refrigerant temperature and saturation temperature at the outlet of the outdoor heat exchanger, and uses this feedback to judge when defrosting is complete, solving the measurement accuracy problem while maintaining medium-pressure defrosting efficiency
Solution Approach 2:
The patent changes the determination parameter from temperature-based criteria to subcooling degree-based criteria. By calculating subcooling degree (difference between refrigerant temperature and saturation temperature at the same pressure), the system can accurately detect defrosting completion even under medium-pressure conditions where temperature changes are insufficient
2Power
If defrosting is performed by reversing refrigerant flow to supply high-temperature refrigerant to the outdoor heat exchanger, then defrosting capability is improved, but heating in the room must be stopped which impairs comfortability
Solution Approach 1:
The patent divides the outdoor heat exchanger into multiple independent heat exchange units, each with its own expansion valve and refrigerant flow path. This segmentation allows one unit to perform defrosting while other units continue heating, maintaining both defrosting capability and heating continuity simultaneously
Solution Approach 2:
The patent applies different operational states to different parts of the outdoor heat exchanger. One heat exchange unit is in defrosting mode (receiving high-temperature refrigerant) while other units remain in heating mode (exchanging heat with outdoor air), allowing local defrosting without global heating interruption
3Device complexity
If defrosting is performed for a certain period of time or based on temperature sensor thresholds, then defrosting process is simplified, but energy and time are wasted due to incomplete frost melting or premature termination
Solution Approach 1:
The patent implements real-time feedback control by continuously calculating the subcooling degree and comparing it against a predetermined threshold. When the subcooling degree reaches or exceeds the threshold, defrosting is automatically terminated, ensuring complete frost melting without energy waste from prolonged operation
Solution Approach 2:
The patent replaces simple time-based or temperature-threshold control with a calculated subcooling degree parameter. This substitution provides more precise control by considering both temperature and pressure conditions, reducing both energy waste and control complexity
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
Enables efficient defrosting of heat exchangers while maintaining continuous heating, ensuring accurate completion determination and quick restoration of the outdoor heat exchanger as an evaporator.
Implementation Method 1
a compressor (1) configured to compress and discharge refrigerant
Implementation Method 2
a plurality of heat source side heat exchangers (5) configured to allow heat exchange between the air and the refrigerant
Implementation Method 3
a first expansion device (10) configured to decompress the refrigerant passing through the first defrosting pipe (15)
Data Source
AI summary
An outdoor unit, connected with indoor units by pipes to constitute a refrigerant circuit, includes a compressor configured to compress and discharge refrigerant, a plurality of parallel heat exchangers configured to allow heat exchange between air and the refrigerant, a first defrosting pipe serving as a flow path for branching a part of the refrigerant discharged by the compressor and allowing the refrigerant to flow into the parallel heat exchanger to be defrosted for defrosting, a first expansion device configured to decompress the refrigerant passing through the first defrosting pipe, a second expansion device configured to adjust the pressure of the refrigerant that passed through the parallel heat exchanger to be defrosted, and a controller configured to control the second expansion device such that the pressure of the refrigerant that passed through the parallel heat exchanger to be defrosted falls within a predetermined range.