Bi-directional cascade heat pump system
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Solution Overview
Problem
Current geothermal heat pump systems face limitations in operating modes, require reversible refrigerant circuits, and often mix high and low temperature fluids unnecessarily, necessitating a more versatile and efficient heat pump system for geothermal and conventional water source applications.
Innovation Solution
A cascade heat pump system with multiple pumps and a fluid circulation loop that allows sequential flow through condensers and evaporators, enabling variable speed control and multiple operating modes without reversing refrigerant flow or switching heat exchanger operations, and utilizing a secondary fluid source to manage temperature and heat transfer efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If reversible refrigerant circuits are used to provide multiple operating modes, then the system can achieve heating and cooling functions, but the system complexity increases and reliability decreases
Solution Approach 1:
The refrigerant system is divided into separate circuits: a first refrigerant circuit with a first compressor and first heat exchanger, and a second refrigerant circuit with a second compressor and second heat exchanger. This segmentation allows each circuit to operate independently in fixed configurations, eliminating the need for reversible connections while providing multiple operating modes through coordinated control of the separate circuits.
Solution Approach 2:
The fluid circulation loop serves multiple functions by sequentially connecting to different heat exchangers in different operating modes. The loop can connect to the first heat exchanger for geothermal cooling, then to the second heat exchanger for process cooling, and vice versa, allowing a single circulation system to support multiple cooling applications without requiring reversible refrigerant circuits.
2Adaptability or versatility
If heat exchangers are switched between condensing and evaporating operations to achieve different modes, then heating and cooling functions are provided, but the operational complexity and potential failure points increase
Solution Approach 1:
The system uses separate refrigerant circuits with dedicated heat exchangers for different functions. The first heat exchanger is dedicated to geothermal heat exchange operations, while the second heat exchanger is dedicated to process fluid heat exchange operations. This segmentation eliminates the need to switch each heat exchanger between condensing and evaporating modes, as each operates in its optimized mode continuously.
Solution Approach 2:
Instead of switching the function of individual heat exchangers between condensing and evaporating, the system inverts the approach by using multiple dedicated heat exchangers and switching which ones are active in the fluid circulation loop. This allows the system to achieve mode changes without requiring any heat exchanger to operate outside its designed function.
3Device complexity
If high and low temperature fluids are mixed to simplify system design, then the system structure is simplified, but energy efficiency decreases due to unnecessary heat transfer
Solution Approach 1:
The fluid circulation system is segmented into temperature-appropriate zones and connections. The fluid loop selectively connects to heat exchangers based on temperature requirements, ensuring that high-temperature and low-temperature fluid streams remain separate until appropriate heat exchange occurs. This prevents unnecessary mixing while maintaining system simplicity through controlled selective connectivity.
Solution Approach 2:
Different portions of the fluid circulation loop are configured with different connection configurations appropriate to local temperature requirements. The loop can be configured to connect to the first heat exchanger when geothermal temperature differences are available, or to the second heat exchanger when process fluid temperature differences are available, optimizing heat transfer efficiency at each operational stage.
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 provides a wide range of heating and cooling modes with reduced fluid mixing, optimized flow rates, and flexible operation, enhancing efficiency and adaptability for geothermal and conventional water source systems.
Implementation Method 1
a condenser receiving the refrigerant from the compressor and transferring heat from the refrigerant to a fluid
Implementation Method 2
an evaporator receiving the refrigerant from the flow restriction and transferring heat from a fluid to the refrigerant
Implementation Method 3
a geothermal fluid source, a first chiller with a condenser, a second chiller with an evaporator, and a fluid circulation loop coupling the geothermal fluid source in heat transfer relationship with the first chiller and the second chiller
Data Source
AI summary
A multi-mode, bi-directional cascade heat pump system, according to some examples, includes at least two chillers each being part of a unidirectional refrigerant circuit. The system includes heat exchangers each of which are dedicated to operate as just a condenser or as just an evaporator, regardless of the system's operating mode. In some modes, a secondary fluid transfers heat between the condenser of one chiller and the evaporator of another chiller before the fluid returns to a secondary fluid source such as, for example, a geothermal borefield or a conventional water source. In some embodiments, fluid is withdrawn from a borefield by way of a pump having a speed that varies to maintain a desired fluid temperature and/or a desired heat transfer rate at the borefield. The heat pump system includes means for minimizing flow through the borefield and for minimizing unnecessary mixing of relatively high and low temperature fluid.