Cascading heat pump
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Solution Overview
Problem
Conventional heat pumps struggle to produce water at high temperatures, such as 80°C, especially in cold external conditions, and existing solutions like vapor injection and CO2 cycles are either inefficient or costly, while cascade cycles face challenges in energy transmission and defrosting.
Innovation Solution
A cascade system of two heat pumps connected by an intermediate water circuit with a buffer tank or decoupling bottle, allowing energy storage and thermal inertia, enabling efficient high-temperature water production and defrosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single-stage vapor compression cycle is used to produce high-temperature water, then water temperature can reach 80°C, but the coefficient of performance decreases and discharge temperature becomes excessively high
Solution Approach 1:
The single-stage compression cycle is divided into two separate compression stages with an intermediate heat exchanger. The first compressor raises pressure to an intermediate level, the intermediate heat exchanger removes heat, and the second compressor completes the pressure rise. This segmentation allows each compressor to operate at lower discharge temperatures while achieving the same final high-temperature output, thereby maintaining higher coefficient of performance.
2Stress or pressure
If vapor injection cycle is used to cool compressed gases, then compressor can reach higher pressures, but water temperature is limited to around 65°C
Solution Approach 1:
An intermediate heat exchanger is introduced between two compression stages as a mediator. This heat exchanger removes heat from the refrigerant after the first compression stage and before the second stage, allowing the system to achieve both high pressure and high temperature output. The intermediate heat exchanger acts as the intermediary component that enables the system to overcome the temperature limitation of single-stage vapor injection cycles.
3Temperature
If CO2 transcritical cycle is used, then high-temperature water production is achieved, but system cost increases significantly
Solution Approach 1:
The system uses parameter changes by adjusting the refrigerant pressure and temperature through two staged compression with intermediate cooling. By controlling the intermediate pressure and temperature parameters in the heat exchanger, the system achieves high-temperature output using conventional refrigerants instead of expensive CO2, thereby reducing manufacturing costs while maintaining effective high-temperature water production capability.
4Power
If air-to-water heat pump is used, then heating capacity depends on outside temperature, but ability to produce high-temperature water is lost when outside temperature is cold
Solution Approach 1:
The two-stage compression system with intermediate heat exchanger enables continuous high-temperature water production regardless of outside temperature conditions. The first compressor and intermediate heat exchanger continuously remove heat at an intermediate stage, while the second compressor continuously completes the pressure rise, ensuring uninterrupted high-temperature output even when outside temperatures are low, thus maintaining continuous useful heating action.
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 solution ensures consistent calorific power, enabling heat pumps to substitute conventional boilers by producing water at 80°C even in severe cold, while maintaining component safety and efficiency.
Implementation Method 1
The invention consists primarily in that the two hydraulic circuits formed by the two cascaded heat pumps are connected by an intermediate water circuit including a buffer water volume.
Implementation Method 2
The first heat pump provides water at a maximum temperature of approximately 55°C, while the second, connected in cascade to the first, provides water at a temperature of at least 80°C.
Implementation Method 3
One possibility is the use of a vapor injection cycle, which involves cooling the gases during compression to allow the compressor to reach higher pressures without reaching the maximum discharge temperature.
Implementation Method 4
Gas cooling is achieved by a liquid-vapor mixture produced by expanding the liquid refrigerant at the condenser outlet to an intermediate pressure.
Implementation Method 5
The refrigerant is compressed, then cooled in a gas cooler into which it enters at a temperature of approximately 120°C and a pressure of around 110 bar. It is then expanded and evaporated to complete the cycle.
Implementation Method 6
The refrigerant is compressed, then cooled in a gas cooler into which it enters at a temperature of approximately 120°C and a pressure of around 110 bar. It is then expanded and evaporated to complete the cycle.
Data Source
Figure 1~2
AI summary
Heat pump intended to supply hot water to a heating network and comprising two heat pumps constituting two hydraulic circuits (P1, P2) coupled in cascade, a first hydraulic circuit for the lowest temperatures and a second hydraulic circuit for the highest temperatures, each comprising an evaporator (1, 5) and a condenser (2, 6) separated on the one hand by a compressor (3, 7) located between the outlet of the secondary of the evaporator (1, 5) and the inlet of the primary of the condenser (2, 6) and on the other hand by an expansion valve (4, 8) placed between the outlet of the primary of the condenser (2, 6) and the inlet of the secondary of the evaporator (1, 5).This pump is characterized in that the secondary of the condenser (2) of the first circuit (P1) is connected in parallel to the heating network and the primary of the evaporator (5) of the second circuit (P2) whose output is also connected to the heating network, a tank (9, 13) as well as means for selecting (11) the heating network or the second circuit (P2) being arranged between the two hydraulic circuits (P1, P2).