Two-Stage Refrigeration Cycle With Gas Injection Superheat Control
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Solution Overview
Problem
In refrigeration apparatuses, the injection of intermediate-pressure gas refrigerant into the compressor is reduced when a liquid-gas heat exchanger is used, leading to a decrease in the coefficient of performance (COP) and energy efficient heating operation, especially in cold climates where space heating capacity is required.
Innovation Solution
The refrigeration apparatus includes a gas injection pipe for intermediate-pressure gas refrigerant into the compressor and a liquid-gas heat exchanger to ensure a sufficient degree of superheat, with the intermediate pressure set to maximize the gas injection amount and COP, while adjusting the expansion valves to maintain the required temperature difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a liquid-gas heat exchanger is used to increase the degree of superheat of refrigerant sucked into the compressor, then the temperature of refrigerant discharged from the compressor increases and space heating capacity increases, but the amount of intermediate-pressure gas refrigerant injected into the compressor decreases leading to reduced coefficient of performance (COP)
Solution Approach 1:
The patent optimizes the degree of superheat as a controllable parameter to balance two competing objectives: increasing discharge temperature for heating capacity while maintaining sufficient gas injection amount for high COP. The controller adjusts the degree of superheat within a specific range (5-15K) to achieve the optimal trade-off between heating performance and energy efficiency.
Solution Approach 2:
The patent implements a feedback control system that monitors the actual degree of superheat and adjusts the expansion valve opening accordingly. The controller receives temperature signals from sensors and dynamically controls the first expansion valve to maintain the superheat degree within the optimal range, ensuring both heating capacity and COP requirements are met under varying operating conditions.
2Power
If the degree of superheat of refrigerant sucked into the compressor is increased, then space heating capacity increases, but the amount of gas refrigerant injected into the compressor decreases
Solution Approach 1:
The patent establishes an optimal range for the degree of superheat (5-15K) that simultaneously satisfies both heating capacity requirements and gas injection quantity requirements. By controlling the superheat degree within this specific range rather than maximizing it, the system achieves balanced performance for both power output and refrigerant circulation.
Solution Approach 2:
The patent employs dynamic control of the first expansion valve to adjust the degree of superheat according to operating conditions. The controller continuously modifies the valve opening to maintain superheat within the optimal range, allowing the system to adaptively balance heating capacity and gas injection amount under different load conditions and outdoor temperatures.
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 ensures a sufficient amount of gas refrigerant is injected into the compressor, adequately increasing both the COP and space heating capacity, enabling energy efficient heating operations that meet the required space heating capacity.
Implementation Method 1
a liquid-gas heat exchanger configured to exchange heat between low-pressure gas refrigerant obtained by evaporating refrigerant in the heat-source-side heat exchanger and travelling toward the compression mechanism and intermediate-pressure liquid refrigerant travelling from the gas-liquid separator toward the second expansion valve
Implementation Method 2
the low-pressure gas refrigerant exchanges heat with the intermediate-pressure liquid refrigerant in the liquid-gas heat exchanger, and is superheated
Implementation Method 3
the gas-liquid separator separates the intermediate-pressure refrigerant into an intermediate-pressure liquid refrigerant component and an intermediate-pressure gas refrigerant component
Implementation Method 4
the high-pressure liquid refrigerant obtained by condensing the refrigerant in the utilization-side heat exchanger is depressurized through the first expansion valve to form intermediate-pressure refrigerant
Implementation Method 5
the compression mechanism compresses the refrigerant
Implementation Method 6
high-pressure liquid refrigerant obtained by condensing the refrigerant in the utilization-side heat exchanger
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An air conditioning system (10) includes a refrigerant circuit (20) including a compressor (21), an indoor heat exchanger (22), a first expansion valve (23), a gas-liquid separator (24), a second expansion valve (26), and an outdoor heat exchanger (27) which are sequentially connected together to perform a two-stage expansion refrigeration cycle. The refrigerant circuit (20) further includes: a gas injection pipe (2c) through which intermediate-pressure gas refrigerant in the gas-liquid separator (24) flows into an intermediate port of the compressor (21), and a liquid-gas heat exchanger (25) configured to exchange heat between low-pressure gas refrigerant obtained by evaporating refrigerant in the outdoor heat exchanger (27) and travelling toward the compressor (21) and intermediate-pressure liquid refrigerant travelling from the gas-liquid separator (24) toward the second expansion valve (26).