Expansion Valve Subcooling Control for Multi-Zone Air Conditioning
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Solution Overview
Problem
Conventional multiple-chamber air-conditioning apparatuses experience deteriorated heat transfer performance in cooling operations due to refrigerant flowing near the outlet of indoor heat exchangers becoming superheated gas, which has a lower heat transfer coefficient.
Innovation Solution
Incorporating a third heat exchanger and a control system that adjusts the expansion device's opening degree based on detected temperature and pressure, ensuring the refrigerant remains in a gas-liquid two-phase state, thereby optimizing refrigerant flow for each indoor heat exchanger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the opening degree of each expansion valve is controlled such that the degree of superheat of the refrigerant flowing through each indoor heat exchanger falls within a prescribed range, then the refrigerant flow amount can be adjusted for each indoor heat exchanger, but the heat transfer performance of each indoor heat exchanger deteriorates because the refrigerant becomes superheated gas with a lower heat transfer coefficient
Solution Approach 1:
The invention changes the control parameter from degree of superheat to degree of subcooling. By controlling the expansion valve opening degree based on subcooling degree (temperature difference between refrigerant at condenser outlet and saturation temperature), the system maintains refrigerant in gas-liquid two-phase state at evaporator outlet, thereby improving heat transfer performance while still achieving proper refrigerant flow distribution
Solution Approach 2:
The invention utilizes phase transition control by maintaining the refrigerant in gas-liquid two-phase state at the evaporator outlet rather than allowing it to become superheated gas. This is achieved by controlling subcooling degree at the condenser, which ensures better heat transfer coefficients are maintained throughout the refrigeration cycle
2Adaptability or versatility
If a multiple-chamber air-conditioning apparatus with multiple indoor heat exchangers connected in parallel is used, then the system can serve multiple zones, but the refrigerant flow must be differentiated for each heat exchanger requiring individual expansion valve control
Solution Approach 1:
The invention simplifies the control system by changing from individual superheat control to centralized subcooling control. A single subcooling control strategy can be applied to all indoor heat exchangers connected in parallel, reducing the complexity of control algorithms while maintaining the ability to serve multiple zones effectively
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 configuration enhances heat transfer performance and energy efficiency by maintaining a suitable refrigerant state for improved cooling operations, reducing noise and pressure instability, and allowing for a more compact design without the need for additional components like accumulators.
Implementation Method 1
a third heat exchanger configured to cause the refrigerant flowing through a refrigerant pipe between the first heat exchanger and the expansion device to exchange heat with the refrigerant flowing through a refrigerant pipe between the expansion device and the second heat exchanger
Data Source
AI summary
An air-conditioning apparatus includes an internal heat exchanger in which refrigerant flowing through a refrigerant pipe between an outdoor heat exchanger and an expansion device and refrigerant flowing through a refrigerant pipe between the expansion device and an indoor heat exchanger exchange heat, a pressure sensor, a first temperature sensor that detects temperature of the refrigerant flowing into the expansion device in the cooling operation, and a control unit configured to control the opening degree of the expansion device based on results of detection by the pressure sensor and the first temperature sensor in the cooling operation.