Internal Heat Exchanger Control for Variable Refrigerant Superheat
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Solution Overview
Problem
Heat pumps employing vapor compression cycles face inefficiencies due to inadequate control over refrigerant superheat, leading to suboptimal heat transfer and potential compressor damage, especially when operating under varying conditions.
Innovation Solution
A heat pump system with an internal heat exchanger and a controller that dynamically adjusts the expansion valve to maintain a variable target superheat based on operating conditions, ensuring at least 90% of superheating occurs in the internal heat exchanger, thereby optimizing evaporative and sensible heating distribution between the evaporator and internal heat exchanger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed superheat control method is used, then the compressor is protected from damage, but the heat pump efficiency deteriorates under varying operating conditions
Solution Approach 1:
The patent implements dynamic superheat control by varying the target superheat value based on operating conditions such as evaporator temperature, condenser temperature, and refrigerant flow rate. The controller continuously adjusts the expansion valve position to maintain the optimal superheat level for current operating conditions, transforming the static control system into a dynamic one that adapts to changing conditions while protecting the compressor and maximizing efficiency.
Solution Approach 2:
The patent changes the superheat parameter from a fixed value to a variable value that depends on operating conditions. By establishing a relationship between superheat and parameters like evaporator temperature, condenser temperature, and refrigerant mass flow rate, the system optimizes heat transfer efficiency across different operating points while ensuring compressor protection through maintained minimum superheat levels.
2Reliability
If superheat is increased to protect the compressor, then reliability improves, but heat transfer efficiency deteriorates
Solution Approach 1:
The patent optimizes the superheat parameter by establishing it as a function of operating conditions rather than using a fixed high value. The controller calculates the optimal superheat level that provides sufficient compressor protection while minimizing excessive superheat that would reduce heat transfer efficiency. This dynamic parameter adjustment ensures the minimum necessary superheat is maintained without the energy loss associated with consistently high superheat levels.
3Reliability
If the expansion valve is controlled to maintain constant superheat, then compressor protection is ensured, but adaptability to varying operating conditions deteriorates
Solution Approach 1:
The patent transforms the static constant superheat control into a dynamic adaptive control system. The controller continuously monitors operating conditions including evaporator temperature, condenser temperature, and refrigerant flow rate, and adjusts the target superheat value accordingly. This dynamic control maintains compressor protection while adapting to varying operating conditions such as part-load operation, different ambient temperatures, and varying heat transfer demands.
Solution Approach 2:
The patent implements a feedback control mechanism where the actual superheat is measured or calculated and compared with the target superheat value. The controller uses this feedback information to adjust the expansion valve position and maintain the optimal superheat level for current operating conditions, enabling adaptive control that responds to real-time system state changes while ensuring compressor protection.
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 coefficient of performance (COP) of the heat pump by efficiently distributing heat transfer, maintaining a dry saturation location within the vaporization portion, and preventing compressor damage by optimizing refrigerant superheat levels.
Implementation Method 1
an internal heat exchanger configured to transfer heat from refrigerant in the liquid line pathway to refrigerant in the suction line pathway, to superheat the refrigerant upstream of the compressor
Data Source
Figure 1
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AI summary
There is disclosed heat pump 10, comprising: an internal heat exchanger 40 configured to transfer heat from refrigerant in a liquid line pathway to refrigerant in a suction line pathway, to superheat the refrigerant upstream of a compressor 12; and a controller 50 configured to: control an expansion valve 16 to maintain a target superheat of refrigerant at a control location. The target superheat is variable and is determined based on one or more operating conditions of the heat pump. There is also disclosed a method of operating a heat pump and a simulation method to determine a variable superheat.