Reversible heat pump
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Solution Overview
Problem
Chiller systems face challenges in efficiently heating and cooling process fluids while minimizing the risk of freezing and optimizing mass flow rates, particularly in reversible heat pump systems where counter-current flow in cooling modes can limit cooling capacity and increase freezing risks.
Innovation Solution
A reversible heat pump system with a suction line economizer heat exchanger (SLEHX) and a controller that manages the expansion device and modulation device to maintain target superheats and temperature changes, allowing for co-current flow in cooling and counter-current flow in heating modes, thereby optimizing heat transfer and reducing freezing risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If counter-current flow is used in cooling mode, then heat transfer efficiency is improved, but cooling capacity is limited and freezing risk increases
Solution Approach 1:
The system dynamically switches between counter-current and co-current flow configurations based on operational mode (cooling or heating). The flow direction is made variable through reversible heat pump design, allowing optimization for each specific operational requirement rather than being fixed in one configuration.
Solution Approach 2:
The invention changes the flow configuration parameter (from counter-current to co-current) specifically for the cooling mode to resolve the contradiction. By adjusting this operational parameter, the system achieves both adequate cooling capacity and reduced freezing risk while maintaining acceptable heat transfer efficiency.
2Temperature
If approach temperature is reduced to cool process fluid to target temperature, then cooling performance is improved, but freezing risk at evaporator increases
Solution Approach 1:
The suction line economizer heat exchanger acts as an intermediary component that heats the working fluid after evaporation. This mediator component allows the evaporator to operate at lower temperatures for better cooling performance while the economizer subsequently raises the temperature to eliminate freezing risk before the fluid returns to the compressor.
Solution Approach 2:
The system performs preliminary cooling at the evaporator to achieve target temperature, then applies a subsequent heating action through the suction line economizer. This two-stage approach allows aggressive cooling followed by protective heating to prevent freezing in subsequent operations.
3Productivity
If mass flow rate is increased to improve cooling capacity, then productivity is improved, but freezing risk and efficiency are worsened
Solution Approach 1:
The system segments the heat transfer process into two distinct stages: evaporation in the main evaporator and subsequent heating in the suction line economizer. This segmentation allows the first stage to focus on maximum cooling capacity while the second stage addresses freezing risk, enabling high mass flow rates without compromising reliability.
4Reliability
If saturation temperature is increased to reduce freezing risk, then reliability is improved, but cooling capacity and efficiency are reduced
Solution Approach 1:
The system adds another dimension to the temperature control by introducing the suction line economizer as a separate thermal management stage. This allows the evaporator to operate at lower saturation temperatures for high cooling capacity while the economizer provides the necessary temperature elevation, effectively adding a temporal/spatial dimension to temperature management.
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
The system enhances heating and cooling capacities, reduces freezing risks, and increases efficiency by allowing higher saturation temperatures and increased mass flow rates, while maintaining safe superheat conditions for the compressor, thus extending the operating map of the heat pump.
Implementation Method 1
condensed working fluid upstream of the expansion device transfers heat to superheated working fluid upstream of the compressor, at the suction line economiser heat exchanger
Implementation Method 2
compressed working fluid from the compressor rejects heat at the first heat exchanger to provide condensed working fluid to a liquid line
Implementation Method 3
a second heat exchanger for heat exchange with the process fluid of the chiller system
Implementation Method 4
expanded working fluid from the expansion device receives heat from the process fluid at the second heat exchanger to provide superheated working fluid along a suction line to the compressor
Data Source
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AI summary
There is disclosed a reversible heat pump system 100 and a method of operating a reversible heat pump system to control the temperature of a process fluid of a chiller system 500. In a cooling mode, a working fluid is circulated for co-current flow with a process fluid at a heat exchanger 104 functioning as an evaporator heat exchanger, whereas in a heating mode, the working fluid is circulated for counter-current flow with the process fluid at the same heat exchanger 104 functioning as a condenser heat exchanger.