Heat Pump Expansion Valve Control for Injection Supercooling
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Solution Overview
Problem
Heat pump apparatuses face challenges in maintaining high coefficient of performance (COP) when liquid refrigerant is injected, as the optimal supercooling degree is affected by the increased refrigerant flow rate, leading to deteriorated COP and inability to continue high heating ability operations.
Innovation Solution
A heat pump apparatus with a refrigerant circuit, including a compressor, utilization-side heat exchanger, and outdoor heat exchanger, equipped with a solenoid switching valve and a second expansion valve, uses an objective supercooling degree table to control the first expansion valve based on condensing pressure and compressor rotation number, switching between injection ON and OFF modes to maintain optimal supercooling degrees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If liquid refrigerant is injected to the compressor to increase refrigerant flow rate in the utilization-side heat exchanger, then heating ability is improved, but the optimal supercooling degree is affected and COP deteriorates
Solution Approach 1:
The patent applies dynamics by making the expansion valve opening degree adjustable and variable based on operating conditions. The control unit dynamically changes the opening degree of the expansion valve according to the detected refrigerant flow rate (via supercooling degree) and injection status, allowing the system to adapt to different operating states and maintain optimal performance whether injection is ON or OFF.
Solution Approach 2:
The patent changes the parameter of expansion valve opening degree based on the injection status and measured supercooling degree. When liquid refrigerant injection is detected, the control unit modifies the opening degree parameter to compensate for the change in optimal supercooling degree, thereby maintaining high COP while allowing the refrigerant flow rate to be increased for high heating ability.
2Reliability
If the expansion valve is controlled to maintain a fixed objective supercooling degree, then optimal operation is achieved under particular conditions, but COP deteriorates when refrigerant injection status changes
Solution Approach 1:
The patent implements feedback control by using the supercooling degree detector to continuously monitor the refrigerant state and feed this information back to the control unit. The control unit compares the detected supercooling degree with the target value and adjusts the expansion valve opening degree accordingly, ensuring optimal operation is maintained regardless of injection status changes.
Solution Approach 2:
The system transitions from a static fixed opening degree control to a dynamic adaptive control where the expansion valve opening degree is continuously adjusted based on real-time detection of supercooling degree and injection status, allowing the system to maintain reliability and efficiency under varying operating conditions.
3Power
If refrigerant flow rate is increased through liquid injection to achieve high heating ability, then heating performance is improved, but the optimal supercooling degree varies and high COP operation cannot be continued
Solution Approach 1:
The patent makes the system adaptive by dynamically adjusting the expansion valve opening degree based on injection status and detected supercooling degree. This allows the system to maintain both high heating performance (through increased refrigerant flow rate during injection) and high COP (through appropriate supercooling degree control) continuously under varying operating conditions.
Solution Approach 2:
The control unit changes the expansion valve opening degree parameter in response to injection status changes, allowing the system to adapt to the varying optimal supercooling degree that occurs with different refrigerant flow rates, thereby maintaining both heating performance and efficiency continuously.
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 allows the heat pump apparatus to maintain high heating ability and COP irrespective of refrigerant injection, by adjusting the supercooling degree and refrigerant flow rate, ensuring continuous high-performance operation.
Implementation Method 1
a first expansion valve 4 for reducing the pressure of the liquid refrigerant; a supercooling degree detector 23 for detecting a supercooling degree of the liquid refrigerant
Implementation Method 2
a compressor 1 for compressing the refrigerant; a discharging temperature sensor 22 for detecting a discharging temperature of the compressor
Implementation Method 3
an utilization-side heat exchanger 3 for heating water by using the refrigerant
Implementation Method 4
an outdoor heat exchanger 5 for cooling the refrigerant by using outdoor air
Implementation Method 5
an injection pipe 14 having a solenoid switching valve 16 and a second expansion valve 15
Data Source
AI summary
A heat pump apparatus includes: a refrigerant circuit which includes a compressor, an utilization-side heat exchanger, a first expansion valve, and an outdoor heat exchanger; an injection pipe which includes a solenoid switching valve and a second expansion valve; and an objective supercooling degree table which stores objective supercooling degrees according to condensing pressure in the refrigerant circuit and rotation number of the compressor. In the heat pump apparatus, liquid refrigerant is injected to the compressor by way of the injection pipe. The heat pump apparatus switches between a first case where the liquid refrigerant is injected to the compressor and a second case where the liquid refrigerant is not injected, and a value of the objective supercooling degree is changed between the first case and the second case to control the first expansion valve based on the value of the objective supercooling degree.