A heat pump energy storage and supply system

Abstract

The application relates to a heat pump energy storage and supply system, belonging to the field of heat pump energy saving and heat storage. The system comprises an evaporator, a compressor, a staged heat exchange gas cooler, a heat storage water tank, a throttling device, a shunt pipeline and a water tank partition plate and the like. The heat storage water tank is provided with multiple fixed partition plates. The cooling water in the gas cooler is shunted based on the fixed heat supply capacity. Low-temperature water is directly used for instant heating of users, high-efficiency direct supply is realized, high-temperature water enters the heat storage water tank and is used for energy storage, is released and used during a heat supply demand peak, the heat exchange mismatch in the gas cooler is solved, the supply and return water temperature difference is increased, the water tank heat storage density is improved, the heat stratification effect of the heat storage water tank is enhanced through the partition plates, and continuous and stable high-efficiency heat supply with a large temperature difference is realized.

Description

Technical Field

[0001] This invention relates to a heat pump energy storage and supply system, belonging to the field of heat pump energy saving and heat storage. Background Technology

[0002] Renewable energy generation can reduce building carbon emissions, but its inherent instability can easily lead to a mismatch between energy supply and demand, especially during peak heating seasons. Combining heat pumps with thermal storage technology is a key solution for achieving stable clean energy heating under large temperature difference conditions. Among these, transcritical CO2 heat pumps have attracted much attention due to their environmental friendliness and large temperature difference heating characteristics. However, the drastic change in CO2 specific heat capacity near the critical point causes temperature mismatch issues during heat exchange in gas coolers, resulting in significant irreversible heat losses. Furthermore, as a typical sensible heat storage medium, water tanks have good thermal conductivity, and water is inexpensive and environmentally friendly. However, its heat storage density per unit volume is low, and this value mainly depends on the temperature difference. Due to the temperature mismatch during heat exchange, traditional heat pump systems struggle to create a large supply and return water temperature difference, leading to a reduction in the water tank's heat storage capacity and a decline in system performance. Summary of the Invention

[0003] The purpose of this invention is to design a transcritical CO2 heat pump energy storage and supply system, which can reduce the temperature matching degree between CO2 and cooling water in the gas cooler, increase the supply and return water temperatures, increase the heat storage density of the water tank, strengthen the thermal stratification of the water tank, and achieve stable heating with a large temperature difference.

[0004] The present invention specifically adopts the following technical solution:

[0005] Figure 1 The flow chart of this heat pump heating and storage system includes an evaporator (1), a compressor (2), a gas cooler (3), a throttle valve (4), a branch point, a branch valve, a three-way valve, a heat user (7), a large temperature difference hot water storage tank (10), and a pump; one side (e.g., the left side) is a transcritical CO2 heat pump cycle, the outlet of the evaporator (1) is connected to the inlet of the compressor (2), the outlet of the compressor (2) is connected to the gas inlet of the gas cooler (3), the gas outlet of the gas cooler (3) is connected to the inlet of the throttle valve (4), and the outlet of the throttle valve (4) is connected to the outlet of the gas cooler (3). The inlet is connected to the inlet of the evaporator (1); in this transcritical CO2 heat pump cycle, the evaporator (1) exchanges heat with the air medium. The low-temperature and low-pressure superheated CO2 gas generated in the evaporator (1) is compressed into high-temperature and high-pressure supercritical CO2 by the compressor (2), and then enters the gas path of the gas cooler (3) to exchange heat with the liquid cooling water in the cooling water pipeline of the gas cooler (3) in a countercurrent manner. The generated low-temperature and high-pressure supercritical CO2 is depressurized by the throttle valve (4) and enters the evaporator (1) in a low-temperature and low-pressure two-phase state, thus completing the heat pump cycle.

[0006] On the other side (such as the right side), there is a cooling water circulation, which includes a heating circulation and a heat storage circulation;

[0007] The heating cycle involves multiple branch points (5a, 5b, 5c) at different locations on the side of the cooling water pipeline of the gas cooler (3), such as... Figure 1 As shown, each branch point is connected to the first interface of the general three-way valve (6) via a branch valve. The second interface of the general three-way valve (6) is connected to the inlet of the heat user (7). The outlet of the heat user (7) is connected to the first interface of the first three-way valve (8). The second interface of the first three-way valve (8) is connected to the cooling water inlet of the gas cooler (3) via the first pump (13). This is the heating cycle.

[0008] Heat storage cycle: The cooling water outlet of the gas cooler (3) is connected to the first port of the second three-way valve (9), the second port of the second three-way valve (9) is connected to the upper inlet of the large temperature difference hot water storage tank (10), the lower outlet of the large temperature difference hot water storage tank (10) is connected to the first port of the third three-way valve (11), the second port of the third three-way valve (11) is connected to the third port of the first three-way valve (8), and the second port of the first three-way valve (8) is connected to the cooling water inlet of the gas cooler (3) via the first pump (13). This is the heat storage cycle.

[0009] In the cooling water circulation, the high-temperature CO2 in the gas cooler (3) exchanges heat with the cooling water in a countercurrent manner. Under certain pinch temperature difference (the minimum heat transfer temperature difference between CO2 and cooling water corresponding to the gas cooler (3)), the exhaust pressure of the compressor (2) and the water flow rate corresponding to the inlet of the gas cooler (3) are optimized based on the COP of the transcritical CO2 heat pump. The hot water in the gas cooler (3) is divided into two paths according to the target heat supply: the main path is the heating branch for heat users, and the heat supply / storage (the heat flowing into the heat user (7) from the branch point and the heat storage) are divided into two paths according to the target heat supply. After the flow point, the water enters the large temperature difference hot water storage tank (10) via the second three-way valve (9). The system uses one or more of the multiple flow points (5a, 5b, 5c) of the gas cooler (3) to divert water to the heat user at different temperatures or heat levels. This portion of the water that reaches the target heat does not need further heating and is directly transported to the heat user via the first and second interfaces of the diversion valve (6a, 6b, 6c) and the main three-way valve (6). For example, in the case of floor heating, fan coil units, etc., the low-temperature water flowing out from the heat user (7) returns to the gas cooler (3) through the first and second ports of the first three-way valve (8) and the first pump (13) to complete the heating cycle; the bypass is a heat storage branch. The remaining water flow that is not diverted after the diversion point continues to flow forward (towards the high-temperature CO2 inlet end) in the gas cooler (3) to absorb higher-grade heat and the temperature continues to rise. This part of the high-temperature hot water eventually flows out of the gas cooler (3). The water flows through the first and second ports of the second three-way valve (9) into the inlet of the large temperature difference hot water storage tank (10) for storage. It can be used for higher temperature needs (such as domestic hot water) or to supplement the system when the heating demand is large, so as to realize the storage and flexible scheduling of high-grade heat. The water flowing out of the bottom outlet of the large temperature difference hot water storage tank (10) returns to the cooling water inlet of the gas cooler (3) through the first and second ports of the third three-way valve (11), the third and second ports of the first three-way valve (8), and the first pump (13) to complete the heat storage cycle.

[0010] The large temperature difference hot water storage tank (10) also includes a hot water storage tank heating cycle: the upper inlet of the large temperature difference hot water storage tank (10) is connected to the second interface of the second three-way valve (9), the third interface of the second three-way valve (9) is connected to the first interface of the fourth three-way valve (12) via the second pump (14), the second interface of the fourth three-way valve (12) is connected to the third interface of the summing three-way valve (6), the second interface of the summing three-way valve (6) is connected to the inlet of the heat user (7), the outlet of the heat user (7) is connected to the first interface of the first three-way valve (8), the third interface of the first three-way valve (8) is connected to the second interface of the third three-way valve (11), and the first interface of the third three-way valve (11) is connected to the lower inlet of the large temperature difference hot water storage tank (10); at the same time, the third interface of the third three-way valve (11) is connected to the third interface of the fourth three-way valve (12) via the third pump (15);

[0011] Due to the instability and intermittency of renewable energy, when the transcritical CO2 heat pump (i.e., heat pump COP) cannot provide continuous heating, the system can activate the hot water storage tank heating cycle. In this cycle, hot water is supplied to the heat user (7) from the upper inlet of the large temperature difference hot water storage tank (10) through the second and third ports of the second three-way valve (9), the second pump (14), the first and second ports of the fourth three-way valve (12), and the third and second ports of the summing three-way valve (6). The return water from the outlet of the heat user (7) passes through the first three-way valve (9). The first and third interfaces of 8), the second and first interfaces of the third three-way valve (11) return to the outlet at the lower end of the large temperature difference hot water storage tank (10); sometimes, the water temperature at the upper part of the large temperature difference hot water storage tank (10) is unstable. In order to adjust the hot water supply temperature of the heating user (7) to keep it stable, the third interface in the third three-way valve (11) can be connected to the third interface of the fourth three-way valve (12) through the third pump (15) to transport the lower temperature water at the bottom of the large temperature difference hot water storage tank (10) to the upper part to adjust the temperature.

[0012] The large temperature difference hot water storage tank (10) includes a tank shell (10-1), an upper inlet (10-2), and a lower outlet (10-3). Multiple fixed partitions (10-4a, 10-4b, 10-4c, 10-4d, etc.) are installed inside the tank shell to divide the interior of the tank shell (10-1) into multiple independent spaces from top to bottom. Each fixed partition is equipped with small holes to allow water to flow from top to bottom. The upper inlet (10-2) is located above the first fixed partition, and the lower outlet (10-3) is located below the last fixed partition. The high-temperature hot water from the transcritical CO2 heat pump (i.e., the heat pump COP) enters the tank through the second three-way valve (9) from the inlet (10-2). The fixed partitions (4a, 4b, 4c, 4d) divide the interior of the tank into five sections along the height. Each chamber is an independent chamber, and the water is completely mixed inside each chamber. The water flows through the small holes on the fixed partition (4a, 4b, 4c, 4d) and flows down layer by layer to reduce the speed of water mixing. The heat transfer between adjacent chambers is carried out by the heat conduction of the fixed partition (4a, 4b, 4c, 4d) and the heat carried by the water flow. Finally, the water flows out from the bottom outlet (3) as the water source for the heat pump inlet. Figure 2 This is a schematic diagram of the layered partition water tank. Attached Figure Description

[0013] Appendix Figure 1 Flowchart of a heat pump heating and heat storage system;

[0014] Includes an evaporator (1), a compressor (2), a gas cooler (3), a throttle valve (4), multiple branch points (5a, 5b, 5c), multiple branch valves (6a, 6b, 6c), a central three-way valve (6), a heat user (7), a first three-way valve (8), a second three-way valve (9), a large temperature difference hot water storage tank (10), a third three-way valve (11), a fourth three-way valve (12), a first pump (13), a second pump (14), and a third pump (15).

[0015] Appendix Figure 2 Schematic diagram of a multi-tiered partition water tank;

[0016] Water tank shell (10-1), water inlet (10-2), water outlet (10-3), and multiple fixed baffles (10-4a, 10-4b, 10-4c, 10-4d). Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0018] Example 1:

[0019] like Figure 1 , Figure 2The transcritical CO2 heat pump staged supply and storage system with a fixed partition water tank and coupling 4 shown includes an evaporator (1), a compressor (2), a gas cooler (3), a throttling valve (4), a branch point, a branch valve, a three-way valve, a heat user (7), a large temperature difference hot water storage tank (10), and a pump. The relevant parameters of the heat pump system and water tank are shown in Table 1.

[0020] Table 1. Relevant parameters of heat pump system and baffled water tank

[0021] Parameter name unit numerical values Water tank height m 2.0 cross-sectional area of ​​water tank m 1.495 Thermal conductivity of water tank baffle W / (m·℃) 0.5 Water tank baffle thickness m 0.01 initial temperature ℃ 30 heat pump evaporation temperature ℃ -20 Gas cooler pinch temperature ℃ 5 compressor isentropic efficiency - 0.7

[0022] In the transcritical CO2 heat pump cycle, the evaporator (1) exchanges heat with the air medium, and the generated low-temperature and low-pressure superheated CO2 gas enters the compressor (2) and is compressed into high-temperature and high-pressure supercritical CO2. Then it enters the gas cooler (3) and exchanges heat with the cooling water at the inlet in a countercurrent manner. The generated low-temperature and high-pressure supercritical CO2 is depressurized through the throttle valve (4) and becomes a low-temperature and low-pressure two-phase state, thus completing the heat pump cycle.

[0023] The right side is the cooling water circulation, which includes a heating circulation and a heat storage circulation. In the cooling water circulation, the high-temperature CO2 in the air cooler (3) exchanges heat with the cooling water in a countercurrent manner. Under certain pinch temperature difference conditions, the exhaust pressure and water flow rate are optimized based on the heat pump COP. The hot water produced is divided into two routes according to the target heat supply: the main route is the heating branch. The system diverts a portion of the water at the branch point (5a) in the cooling water pipeline of the air cooler (3), and delivers it to the heat user (7) via the three-way valve (6) or directly. The low-temperature return water flowing out from the heat user (7) passes through the first three-way valve (8) and the first pump (1). 3) Return to the air cooler (3) to complete the heating cycle; the bypass is the heat storage branch. The remaining water flow that is not diverted at the diversion point (5a) continues to flow forward (towards the high temperature CO2 inlet) in the air cooler (3), and the temperature continues to rise. This part of the high temperature hot water eventually flows out of the air cooler (3) and enters the large temperature difference hot water storage tank (10) through the second three-way valve (9) for storage. The low temperature water flowing out of the hot water storage tank (10) returns to the air cooler (3) through the three-way valve (11, 8) and the first pump (13) to complete the heat storage cycle.

[0024] Due to the instability and intermittency of renewable energy, when the heat pump cannot provide continuous heating, the system can start the heating cycle of the hot water storage tank. Hot water is supplied to the heat user (7) from the top of the hot water storage tank through the second three-way valve (9), the second pump (14), the fourth three-way valve (12) and the summing three-way valve (6). The return water returns to the water tank (10) through the first three-way valve (8) and the third three-way valve (11). In order to adjust the temperature of the hot water supply to keep it stable, some low-temperature return water can be directly transported to the high-temperature hot water supply pipeline through the three-way valves (11, 12) and the third pump (15) to complete the internal circulation of the hot water storage tank heating.

[0025] Simulation results show that the tiered supply and storage system can ensure the stability of user-side heating. The cumulative heat supply within one cycle (5h) is stable at around 243.7kWh. It effectively increases the temperature difference between the heat pump supply and return water, improves the heat storage density of the water tank, and the top water temperature can reach around 110℃. The vertical temperature difference can reach around 54.38℃, which improves the temperature matching degree between CO2 and cooling water in the air cooler. The average COP of the system reaches 3.234, and the gap with the ideal system has been reduced to within 8% (7.48%). It can achieve a good balance between the tiered supply and storage effect and system performance.

Claims

1. A heat pump heating and heat storage system, characterized in that, Includes evaporator (1), compressor (2), gas cooler (3), throttle valve (4), flow divider, flow divider valve, three-way valve, heat user (7), large temperature difference hot water storage tank (10), and pump; One side is a transcritical CO2 heat pump cycle. The outlet of the evaporator (1) is connected to the inlet of the compressor (2). The outlet of the compressor (2) is connected to the gas inlet of the gas cooler (3). The gas outlet of the gas cooler (3) is connected to the inlet of the throttle valve (4). The outlet of the throttle valve (4) is connected to the inlet of the evaporator (1). On the other side is the cooling water circulation, which includes a heating circulation and a heat storage circulation; The heating cycle is as follows: multiple branch points (5a, 5b, 5c) are led out from different positions on the side of the cooling water pipeline of the gas cooler (3) as shown in Figure 1. Each branch point is connected to the first interface of the general three-way valve (6) via a branch valve. The second interface of the general three-way valve (6) is connected to the inlet of the heat user (7). The outlet of the heat user (7) is connected to the first interface of the first three-way valve (8). The second interface of the first three-way valve (8) is connected to the cooling water inlet of the gas cooler (3) via the first pump (13). This is the heating cycle. Heat storage cycle: The cooling water outlet of the gas cooler (3) is connected to the first port of the second three-way valve (9), the second port of the second three-way valve (9) is connected to the upper inlet of the large temperature difference hot water storage tank (10), the lower outlet of the large temperature difference hot water storage tank (10) is connected to the first port of the third three-way valve (11), the second port of the third three-way valve (11) is connected to the third port of the first three-way valve (8), and the second port of the first three-way valve (8) is connected to the cooling water inlet of the gas cooler (3) via the first pump (13). This is the heat storage cycle. The large temperature difference hot water storage tank (10) also includes a hot water storage tank heating cycle: the upper inlet of the large temperature difference hot water storage tank (10) is connected to the second interface of the second three-way valve (9), the third interface of the second three-way valve (9) is connected to the first interface of the fourth three-way valve (12) via the second pump (14), the second interface of the fourth three-way valve (12) is connected to the third interface of the summing three-way valve (6), the second interface of the summing three-way valve (6) is connected to the inlet of the heat user (7), the outlet of the heat user (7) is connected to the first interface of the first three-way valve (8), the third interface of the first three-way valve (8) is connected to the second interface of the third three-way valve (11), and the first interface of the third three-way valve (11) is connected to the lower inlet of the large temperature difference hot water storage tank (10); at the same time, the third interface of the third three-way valve (11) and the third interface of the fourth three-way valve (12) are connected via the third pump (15).

2. A heat pump heating and heat storage system according to claim 1, characterized in that, The large temperature difference hot water storage tank (10) includes a tank shell (10-1), an upper water inlet (10-2), and a lower water outlet (10-3). The tank shell is provided with multiple fixed partitions that divide the interior of the tank shell (10-1) into multiple independent spaces from top to bottom. At the same time, each fixed partition is provided with small holes to supply water so that heat can flow from top to bottom. The upper water inlet (10-2) is located above the first fixed partition, and the lower water outlet (10-3) is located below the last fixed partition.

3. A heat pump heating and heat storage system according to claim 2, characterized in that, There are 4 fixed partitions, which divide the interior of the water tank shell (10-1) into 5 independent spaces from top to bottom.

4. The operating method of a heat pump heating and heat storage system according to any one of claims 1-3, characterized in that, Including the following: In the transcritical CO2 heat pump cycle, the evaporator (1) exchanges heat with the air medium. The low-temperature and low-pressure superheated CO2 gas generated in the evaporator (1) is compressed into high-temperature and high-pressure supercritical CO2 by the compressor (2), and then enters the gas path of the gas cooler (3) to exchange heat with the liquid cooling water in the cooling water pipeline of the gas cooler (3) in a countercurrent flow. The generated low-temperature and high-pressure supercritical CO2 is depressurized by the throttle valve (4) and enters the evaporator (1) in a low-temperature and low-pressure two-phase state, thus completing the heat pump cycle. In the cooling water circulation, the high-temperature CO2 in the gas cooler (3) exchanges heat with the cooling water in a countercurrent manner. Under certain pinch temperature difference (the minimum heat transfer temperature difference between CO2 and cooling water corresponding to the gas cooler (3)), the exhaust pressure of the compressor (2) and the water flow corresponding to the inlet of the gas cooler (3) are optimized based on the COP of the transcritical CO2 heat pump. The hot water in the gas cooler (3) is divided into two paths according to the target heat supply: the main path is the heating branch for heat users. According to the heat supply / heat storage ratio, the system uses one or more of the multiple branch points of the gas cooler (3) to draw out a part of the water flow. This part of the water that reaches the target heat does not need to be further heated. It is directly transported to the heat user (7) through the first and second interfaces of the branch valve and the general three-way valve (6) for use such as floor heating, fan coil units, etc., to realize the instantaneous and efficient utilization of medium-grade heat. The low-temperature water returns to the gas cooler (3) through the first and second ports of the first three-way valve (8) and the first pump (13) to complete the heating cycle; the bypass is the heat storage branch. The remaining water flow that is not diverted after the diversion point continues to flow forward in the gas cooler (3) to absorb higher-grade heat and the temperature continues to rise. This part of the high-temperature hot water eventually flows out of the gas cooler (3) and enters the inlet of the large temperature difference hot water storage tank (10) through the first and second ports of the second three-way valve (9) for storage. It can be used for higher temperature demand or to supplement the system when the heating demand is large, so as to realize the storage and flexible scheduling of high-grade heat. The water flowing out of the bottom outlet of the large temperature difference hot water storage tank (10) returns to the cooling water inlet of the gas cooler (3) through the first and second ports of the third three-way valve (11), the third and second ports of the first three-way valve (8) and the first pump (13) to complete the heat storage cycle. Due to the instability and intermittency of renewable energy, when the transcritical CO2 heat pump (i.e., heat pump COP) cannot provide continuous heating, the system can activate the hot water storage tank heating cycle. In this cycle, hot water is supplied to the heat user (7) from the upper inlet of the large temperature difference hot water storage tank (10) through the second and third ports of the second three-way valve (9), the second pump (14), the first and second ports of the fourth three-way valve (12), and the third and second ports of the summing three-way valve (6). The return water from the outlet of the heat user (7) passes through the first three-way valve (9). The first and third interfaces of 8), the second and first interfaces of the third three-way valve (11) return to the outlet at the lower end of the large temperature difference hot water storage tank (10); sometimes, the water temperature at the upper part of the large temperature difference hot water storage tank (10) is unstable. In order to adjust the hot water supply temperature of the heating user (7) to keep it stable, the third interface in the third three-way valve (11) can be connected to the third interface of the fourth three-way valve (12) through the third pump (15) to transport the lower temperature water at the bottom of the large temperature difference hot water storage tank (10) to the upper part to adjust the temperature.

5. The method according to claim 4, characterized in that, Different locations can be used to distribute water at different temperatures or heat levels to heat users as needed.

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