Ejector Heat Pump Control to Avoid Parallel Expansion Valve Complexity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Ejector operation in heat pumps deviates from the design or optimum operating point in various applications, leading to diminished performance, particularly in mild winter conditions where the potential work recovery from the high-pressure motive flow is low, resulting in increased system complexity and cost when a parallel expansion valve is utilized.
Innovation Solution
A method and system for operating a heat pump that switches between cooling and heating modes, using an ejector with a controller to adjust fan speed and potentially a needle, based on refrigerant pressure or temperature measurements, to optimize ejector performance without the need for a parallel expansion device, thereby maintaining efficient operation across different conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a parallel expansion valve is utilized to bypass the ejector in mild winter conditions, then the system can operate in low potential work recovery conditions, but the system complexity and cost increase
Solution Approach 1:
The ejector is designed to function as both an expansion device and a work recovery device across different operating conditions. By optimizing the ejector geometry and control strategy, the system eliminates the need for a separate parallel expansion valve, achieving multi-functionality with a single component.
Solution Approach 2:
The ejector operation is dynamically controlled by adjusting the motive flow rate through the ejector based on operating conditions. This dynamic control allows the ejector to adapt to varying potential work recovery conditions, maintaining effectiveness across a wide operational range without requiring additional hardware.
2Adaptability or versatility
If the ejector operates away from the design or optimum operating point, then the system can handle wide range of applications, but the cycle performance improvement diminishes
Solution Approach 1:
The system incorporates feedback control by monitoring operating conditions and adjusting the ejector motive flow rate accordingly. This feedback mechanism ensures the ejector operates near its optimal performance point across varying conditions, maintaining high cycle performance while handling diverse applications.
Solution Approach 2:
The ejector performance is optimized by changing operational parameters, specifically the motive flow rate, based on operating conditions. This parameter adjustment allows the ejector to maintain high entrainment ratio and pressure lift ratio across a wide range of applications, preventing performance degradation.
3Use of energy by moving object
If the ejector is used to improve COP in conventional cycles, then the coefficient of performance increases, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The ejector system is designed to self-regulate by utilizing the natural pressure differential and flow characteristics to control the motive flow rate. This self-service approach maintains high COP improvement while minimizing the need for complex external control mechanisms, reducing overall system 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
This approach enhances the efficiency and reduces complexity and cost by maintaining optimal ejector performance across varying conditions without requiring a parallel expansion device, improving the coefficient of performance and operational range of heat pumps.
Implementation Method 1
A primary or motive flow of high pressure refrigerant from the condenser enters the primary or motive port (inlet) and passes through the motive nozzle of the ejector where it accelerates. It exits the motive nozzle with a high velocity and generates low pressure area around the exit.
Implementation Method 2
A secondary or suction flow of refrigerant vapor from the evaporator is entrained (i.e., sucked) into the secondary or suction port (inlet) of the ejector and is thereby accelerated.
Implementation Method 3
High velocity motive flow refrigerant decelerates and mixes with accelerating suction flow refrigerant in the mixing section (mixer) of the ejector.
Implementation Method 4
After mixing, the two phase refrigerant mixture enters the diffuser of the ejector, decelerates thereby recovering pressure.
Implementation Method 5
The resulting two-phase refrigerant stream enters the separator where the vapor and liquid phases are separated.
Implementation Method 6
Vapor is sucked into the compressor where it is compressed and discharged to the condenser or gas cooler.
Implementation Method 7
In the condenser, the compressed high pressure, high temperature vapor is cooled and condensed.
Implementation Method 8
Liquid from the separator enters the evaporator after passing through an expansion valve, evaporates and vapor flows to the suction port of the ejector.
Implementation Method 9
Liquid from the separator enters the evaporator after passing through an expansion valve, evaporates and vapor flows to the suction port of the ejector.
Data Source
AI summary
A method for operating a heat pump (20; 300) includes operating in a cooling mode wherein heat is absorbed by refrigerant in the indoor heat exchanger (26) and rejected by refrigerant in the outdoor heat exchanger (24). The heat pump switches to operation in a heating mode wherein heat is rejected by refrigerant in the indoor heat exchanger, heat is absorbed by refrigerant in the outdoor heat exchanger, and there is an ejector (60) motive flow and ejector secondary flow. In the heating mode a refrigerant pressure (PH) or temperature (TL) is measured and, responsive to the measured refrigerant pressure or temperature, at least one of a fan speed is changed and a needle (132) of the ejector is actuated.