Carbon dioxide heat pump heating system with multiple bypass adaptive configurations and control method

Abstract

The present application relates to a kind of bypass adaptive configuration carbon dioxide heat pump heating system and control method, wherein the bypass adaptive configuration carbon dioxide heat pump heating system of multiple includes carbon dioxide sub-cycle, refrigerant sub-cycle and water supply flow path connected with each other heat exchange;Carbon dioxide sub-cycle includes main carbon dioxide loop and regenerator bypass;Main carbon dioxide loop includes sequentially connected carbon dioxide compressor, carbon dioxide-water heat exchanger I, carbon dioxide-water heat exchanger II, carbon dioxide-refrigerant heat exchanger, carbon dioxide throttling valve I, carbon dioxide evaporator;Water supply flow path is connected with the main carbon dioxide loop by carbon dioxide-water heat exchanger I and carbon dioxide-water heat exchanger II heat exchange connection.Compared with prior art, while realizing the efficient operation of system full heating season, the present application can adaptively match different end conditions, while having more efficient and stable defrosting effect and more reliable compressor safety guarantee.

Description

Technical Field

[0001] This invention relates to the field of heat pump heating systems, and more particularly to a carbon dioxide heat pump heating system based on multiple bypass adaptive configurations. Background Technology

[0002] Air source heat pumps have received widespread attention and promotion as a highly efficient energy utilization technology.

[0003] Patent CN 111336707 A proposes a topological homeomorphic carbon dioxide heat pump heating system. This invention can switch between a mechanically assisted subcooling cycle and a superheat recovery cascade cycle according to changes in ambient temperature, ensuring continuous and efficient heating throughout the heating season. Patent CN 111795423 A, building upon this, proposes an innovative water circuit structure that optimizes water-side heat exchange matching, further improving system energy efficiency. Based on the cycles proposed in these patents, carbon dioxide heat pumps exhibit good adaptability to the varied operating conditions in winter heating scenarios, theoretically guaranteeing optimal energy efficiency under all operating conditions, making it an important energy-saving technology. However, when this technology is applied to actual machines, it will still face the following challenges.

[0004] First, given the varying supply and return water temperature differences, it's difficult for the system design to simultaneously guarantee heat exchange performance and a reasonable water-side pressure drop. Currently, mainstream heat pump products are often designed specifically for particular supply and return water conditions. However, the diversity of terminal devices in heating scenarios means that the required supply and return water temperature difference can range from as low as 5K (fan coil units) to as high as 25K (radiators), representing a five-fold difference in supply flow rate. This indicates that the water resistance difference between the maximum and minimum flow rates can be as high as 25 times. Therefore, designing the heat exchanger for low flow rate conditions will result in significant water resistance under high flow rate conditions, leading to a substantial increase in pump power consumption. Conversely, designing for high flow rate conditions may result in insufficient heat exchange under low flow rate conditions, significantly reducing system energy efficiency.

[0005] Secondly, the defrosting problem at low temperatures in carbon dioxide heating heat pumps is also a key challenge affecting the stable heating supply of the unit. Common defrosting methods for air source heat pumps include electric heating defrosting, hot gas bypass defrosting, and reverse cycle defrosting. Among them, electric heating and hot gas bypass defrosting have low efficiency, high energy consumption, and poor safety and reliability. In comparison, reverse cycle defrosting is more efficient due to the heat exchange caused by the phase change of the refrigerant. However, for carbon dioxide cycles, reverse defrosting means that the evaporator coil will bear the heat exchange of high-pressure carbon dioxide fluid. Since the pressure resistance of the evaporator coil is limited, this method poses a significant safety hazard. Therefore, it is necessary to design an efficient and stable defrosting method for carbon dioxide heating heat pumps.

[0006] Finally, compressor safety is also a crucial factor to consider in practical applications. In a carbon dioxide cycle, the expansion valve is prioritized for controlling high-pressure circulation to ensure high energy efficiency, while the gas-liquid separator and regenerator are often used in combination to ensure the compressor's suction superheat and prevent compressor damage caused by liquid carryover during suction. The addition of a regenerator can also improve the performance of the carbon dioxide cycle. However, carbon dioxide heating heat pumps operate in low and extremely low temperature environments, where the compressor's operating pressure ratio is high and the refrigerant flow rate is low. The increase in suction superheat caused by the regenerator can lead to the compressor's discharge temperature exceeding limits, affecting the compressor's safe operation. Therefore, while the regenerator avoids liquid carryover during compressor suction, it also threatens the compressor's discharge temperature, requiring further rational consideration in its application in carbon dioxide heating heat pumps. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art by providing a carbon dioxide heat pump heating system and control method based on multiple bypass adaptive configurations. While achieving efficient operation of the system throughout the heating season, it can adaptively match different terminal operating conditions, and has a more efficient and stable defrosting effect and a more reliable compressor safety guarantee.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] The first aspect of the present invention provides a carbon dioxide heat pump heating system with multiple bypass adaptive configurations, including a carbon dioxide sub-cycle, a refrigerant sub-cycle, and a water supply path that are connected in a heat exchange manner.

[0010] The carbon dioxide sub-cycle includes a main carbon dioxide loop and a regenerator bypass;

[0011] The main carbon dioxide loop includes a carbon dioxide compressor, a carbon dioxide-water heat exchanger I, a carbon dioxide-water heat exchanger II, a carbon dioxide-refrigerant heat exchanger, a carbon dioxide expansion valve I, and a carbon dioxide evaporator connected in sequence.

[0012] The regenerator bypass is located between the outlet of the carbon dioxide-refrigerant heat exchanger and the inlet of the carbon dioxide evaporator.

[0013] The carbon dioxide cycle and the refrigerant sub-cycle are connected by a carbon dioxide-refrigerant heat exchanger.

[0014] The water supply path is connected to the main carbon dioxide loop through carbon dioxide-water heat exchanger I and carbon dioxide-water heat exchanger II.

[0015] Furthermore, the regenerator bypass includes a regenerator and a carbon dioxide throttling valve II connected in sequence, and the regenerator bypass is used to regulate the refrigerant flow rate through the regenerator.

[0016] Furthermore, the carbon dioxide-water heat exchanger I, carbon dioxide-water heat exchanger II, and refrigerant-water heat exchanger are provided with a refrigerant channel and a coolant channel. The carbon dioxide-refrigerant heat exchanger and the regenerator are provided with dual refrigerant channels. Common types include plate heat exchangers and shell-and-tube heat exchangers.

[0017] Furthermore, the refrigerant sub-cycle includes a first refrigerant loop and a second refrigerant bypass;

[0018] The first refrigerant loop includes a refrigerant compressor, a four-way reversing valve, a refrigerant passage of a refrigerant-water heat exchanger, a refrigerant throttle valve I, and a first refrigerant passage of a carbon dioxide-refrigerant heat exchanger connected in sequence.

[0019] The second refrigerant bypass is located between the outlet of the refrigerant compressor and the refrigerant passage of the refrigerant-water heat exchanger, and includes a refrigerant compressor, a shut-off valve, a defroster, a refrigerant expansion valve II, and the refrigerant passage of the refrigerant-water heat exchanger connected in sequence.

[0020] Furthermore, the carbon dioxide evaporator and the defroster share the same set of heat exchange fins, forming an integral finned tube heat exchanger with heat exchange pipelines distributed in a cross-row configuration.

[0021] Furthermore, the water supply path includes a water pump, a water channel for carbon dioxide-water heat exchanger II, a water channel for refrigerant-water heat exchanger, a water channel for carbon dioxide-water heat exchanger I, and an adaptive control water bypass connected in sequence.

[0022] Furthermore, the adaptive water bypass includes electric valve I and electric valve II;

[0023] Electric valve I and electric valve II are respectively installed between the inlet and outlet water channels of carbon dioxide-water heat exchanger I and carbon dioxide-water heat exchanger II, and are used to regulate the proportion of water flow through the heat exchangers.

[0024] Furthermore, the two ports of the four-way reversing valve are respectively connected to the suction port and the discharge port of the refrigerant compressor, and the other two ports of the four-way reversing valve are respectively connected to the refrigerant channels of the refrigerant-water heat exchanger and the carbon dioxide-refrigerant heat exchanger.

[0025] Furthermore, the carbon dioxide throttling valve I, carbon dioxide throttling valve II, refrigerant throttling valve I, and refrigerant throttling valve II can be common throttling devices used to adjust the refrigerant flow rate to achieve the control target;

[0026] The second aspect of the present invention provides a control method for a carbon dioxide heat pump heating system with various bypass adaptive configurations as described above. The carbon dioxide heat pump heating system includes a normal heating mode. During normal heating, depending on the ambient temperature, the system can select to operate in the state with higher energy efficiency between mechanically assisted subcooling cycle and superheat recovery cascade cycle.

[0027] Furthermore, when in a mechanically assisted subcooling cycle:

[0028] The carbon dioxide sub-cycle serves as the main cycle, a transcritical carbon dioxide cycle, and is responsible for the main output of heat to the water-side circulation path; the refrigerant sub-cycle serves as an auxiliary cycle, a mechanical subcooling cycle, to achieve subcooling of the carbon dioxide temperature at the outlet of the carbon dioxide-refrigerant heat exchanger.

[0029] Furthermore, when in a superheated recovery cascade cycle state:

[0030] The carbon dioxide subcycle, as a low-temperature stage cycle, is a subcritical carbon dioxide cycle and serves as the low-temperature heat source for the refrigerant subcycle; the refrigerant subcycle, as a high-temperature stage cycle, is a heat pump cycle and undertakes the main output of heat to the water supply path.

[0031] In both of the above states, the carbon dioxide sub-cycle operates normally, the four-way reversing valves A and B of the auxiliary sub-cycle are connected, C and D are connected, and the shut-off valve and refrigerant throttling valve II are in the closed state.

[0032] Water supply flow path operation status: Based on the different temperature differences between the supply and return water (water supply flow rate), the adaptive control water bypass can dynamically adjust the ratio of water flow through carbon dioxide-water heat exchangers I and II to minimize the work of the compressor and pump.

[0033] When the temperature difference between the supply and return water sides is large (i.e., the water flow rate is small), the opening degree of electric valve I and electric valve II decreases. At this time, the return water is heated in three stages in series: carbon dioxide-water heat exchanger I, refrigerant-water heat exchanger, and carbon dioxide-water heat exchanger II. When the temperature difference between the supply and return water sides is small (i.e., the water flow rate is large), the opening degree of electric valve I and electric valve II increases. At this time, the hot water is mainly heated by the high-temperature stage condenser, some of the hot water is reheated by carbon dioxide-water heat exchangers I and II, and some of the hot water is bypassed.

[0034] Furthermore, the refrigerant's operating state in the carbon dioxide sub-cycle is as follows: Low-pressure, low-temperature carbon dioxide gas exiting the regenerator is compressed by the carbon dioxide compressor to form high-temperature, high-pressure gas. This gas undergoes cooling and heat exchange with the water-side flow path when passing through carbon dioxide-water heat exchangers I and II. It then passes through the carbon dioxide-refrigerant heat exchanger, where it exchanges heat with the low-temperature refrigerant fluid. The carbon dioxide fluid exiting the carbon dioxide-refrigerant heat exchanger splits into two parts. One part undergoes heat exchange in the regenerator and then is throttled by carbon dioxide expansion valve II, forming a low-temperature gas-liquid two-phase fluid. The other part directly enters carbon dioxide expansion valve I, forming another low-temperature gas-liquid two-phase fluid. These two two-phase fluids mix in the refrigerant pipeline and enter the carbon dioxide evaporator together, absorbing heat from the outside air to become low-temperature, low-pressure carbon dioxide gas. Finally, it passes through the regenerator and enters the carbon dioxide compressor for another compression cycle.

[0035] In the carbon dioxide subcycle, the function of carbon dioxide throttling valve I is to regulate the cycle high pressure to ensure high energy efficiency. When the cycle high pressure is lower than the set value, the opening of carbon dioxide throttling valve I decreases to reduce the refrigerant flow, increasing the refrigerant storage on the high-pressure side and thus raising the high pressure; conversely, the same applies. The function of carbon dioxide throttling valve II is to regulate the suction superheat of the carbon dioxide compressor to ensure the safe operation of the compressor. When the compressor suction superheat is lower than the set value, the opening of carbon dioxide throttling valve II increases to increase the flow of high-temperature carbon dioxide fluid through the regenerator, thereby increasing the suction superheat; conversely, the same applies.

[0036] By setting up a bypass for the carbon dioxide regenerator, the regeneration effect can be adjusted in real time according to the operating status, which can effectively ensure the safe operation of the compressor and achieve optimal performance of the carbon dioxide circuit.

[0037] The working state of the refrigerant in the refrigerant sub-cycle is as follows: The low-temperature refrigerant at the outlet of the carbon dioxide-refrigerant heat exchanger is compressed by the refrigerant compressor and becomes a high-temperature and high-pressure gas. It enters the refrigerant-water heat exchanger through the four-way reversing valve, where it undergoes condensation and heat exchange with the water circuit. Then, it is throttled into a gas-liquid two-phase state in the refrigerant throttling valve I. After that, it enters the carbon dioxide-refrigerant heat exchanger to exchange heat with the carbon dioxide fluid. After the refrigerant fluid evaporates and absorbs heat, it becomes a low-temperature and low-pressure gas. Finally, it re-enters the refrigerant compressor through the four-way reversing valve.

[0038] During defrosting, the carbon dioxide subcycle is not operating. The four-way reversing valves B and C of the refrigerant subcycle are connected, the shut-off valve is open, the refrigerant throttle valve II is operating, and the refrigerant throttle valve I is closed.

[0039] The working state of the refrigerant in the refrigerant sub-cycle is as follows: the high-temperature and high-pressure refrigerant gas at the compressor outlet enters the defrost unit. Since the defrost unit and the carbon dioxide evaporator share the same set of heat exchange fins, the condensation heat released by the refrigerant in the defrost unit can be directly used to defrost the carbon dioxide evaporator. The condensed high-temperature refrigerant is then throttled into a gas-liquid two-phase state by the refrigerant throttling valve II, and then enters the refrigerant-water heat exchanger. After absorbing heat from the heating return water, it becomes a low-temperature and low-pressure gas state, and finally re-enters the refrigerant compressor through the four-way reversing valve.

[0040] Operating status of the water supply path: Electric valves I and II remain fully open. The water-side fluid passes sequentially through electric valve II, the refrigerant-water heat exchanger, and electric valve I, releasing heat in the refrigerant-water heat exchanger. The released heat is used for defrosting the carbon dioxide evaporator in the high-temperature stage cycle.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0042] 1. This invention proposes multiple bypass adaptive configurations for carbon dioxide heat pump heating systems with theoretical energy efficiency advantages. While ensuring efficient operation throughout the heating season, these configurations can adaptively match different terminal operating conditions, and also provide more efficient and stable defrosting effects and more reliable compressor safety assurance.

[0043] 2. This invention proposes a variable temperature difference adaptive control water-side bypass configuration. A control bypass is set between the inlet and outlet water channels of CO2-water heat exchangers I and II. The bypass ratio is adjusted by an electric valve, enabling the system to maintain efficient operation under different supply and return water temperature differences (flow rates). The goal of water circuit control is to minimize the total energy consumption of the compressor and water pump. When the supply and return water temperature difference is large (i.e., the water flow rate is small), almost all the hot water undergoes three-stage series heating, matching the temperature shift on the CO2 side with the hot water temperature rise, thus improving heat exchange uniformity. When the supply and return water temperature difference is small (i.e., the water flow rate is large), the hot water is mainly heated by the high-temperature stage condenser, and part of the water in the CO2-water heat exchanger is bypassed to reduce water pump power consumption.

[0044] 3. This invention proposes a high-temperature stage defrosting bypass configuration suitable for cascade systems. Compared with ordinary cascade systems, this system incorporates a high-pressure defrosting branch integrated on the evaporator coil within the high-temperature stage circulation. During defrosting, the high-temperature stage circulation reverses, drawing heat from the heating return water for defrosting. Compared to electric heating and hot gas bypass, this technical solution offers advantages such as high defrosting efficiency and a stable defrosting process, ensuring rapid defrosting of the system under harsh winter conditions.

[0045] 4. This invention proposes an adjustable regenerator bypass configuration suitable for carbon dioxide cycles. By combining the carbon dioxide throttling valve II and the regenerator, different regeneration effects can be achieved under different operating conditions. Compared with the traditional single regenerator scheme, it not only utilizes the advantages of the regenerator in improving suction superheat and cycle performance, but also ensures the safe operation of the compressor through controllable adjustment. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the system in this invention;

[0047] Figure 2 This is a schematic diagram of the system in heating mode in this invention;

[0048] Figure 3 This is a schematic diagram of the system in defrosting mode in this invention;

[0049] Figure 4 Here is a schematic diagram of the integrated finned tube heat exchanger in this invention.

[0050] In the diagram: 1-Carbon dioxide compressor; 2-Carbon dioxide-water heat exchanger I; 3-Carbon dioxide-water heat exchanger II; 4-Carbon dioxide-refrigerant heat exchanger; 5-Regenerator; 6-Carbon dioxide expansion valve II; 7-Carbon dioxide evaporator; 8-Carbon dioxide expansion valve I; 9-Refrigerant compressor; 10-Four-way reversing valve; 11-Refrigerant-water heat exchanger; 12-Refrigerant expansion valve I; 13-Stop valve; 14-Defrost device; 15-Refrigerant expansion valve II; 16-Water pump; 17-40 Refrigerant piping; 41-52 Water-side piping; 53-Electric valve II; 54-Electric valve I; 55-Heat exchange tube; 56-57 Carbon dioxide refrigerant inlet; 58-High-temperature refrigerant inlet; 59-Heat exchange tube connecting pipe; 60-61 High-temperature refrigerant outlet; 62-Carbon dioxide refrigerant outlet; 63-Heat exchange fins. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0052] Example 1

[0053] This embodiment presents a carbon dioxide heat pump heating system based on multiple bypass adaptive configurations, the structure of which is as follows: Figure 1 As shown, it mainly includes a carbon dioxide sub-cycle, a refrigerant sub-cycle, and a water supply path that are connected by mutual heat exchange.

[0054] The carbon dioxide sub-cycle includes a main carbon dioxide loop and a regenerator bypass. The main carbon dioxide loop consists of a carbon dioxide compressor 1, connecting pipe 17, carbon dioxide-water heat exchanger I 2, connecting pipe 18, carbon dioxide-water heat exchanger II 3, connecting pipe 19, carbon dioxide-refrigerant heat exchanger 4, connecting pipes 20 and 27, carbon dioxide throttling valve I 8, connecting pipes 28 and 24, carbon dioxide evaporator 7, and connecting pipes 25 and 26 connected in sequence. The regenerator bypass is located between the outlet of carbon dioxide-refrigerant heat exchanger 4 and the inlet of carbon dioxide evaporator 7. This bypass includes a connecting pipe 21, regenerator 5, connecting pipe 22, carbon dioxide throttling valve II 6, and connecting pipe 23 connected in sequence. Connecting pipe 21 is connected to the outlet pipe 20 of carbon dioxide-refrigerant heat exchanger 4, and connecting pipe 23 is connected to the inlet pipe 24 of carbon dioxide evaporator 7. One side of regenerator 5 is connected to connecting pipe 22 by connecting pipe 21, and the other side is connected to connecting pipe 26 by connecting pipe 25.

[0055] The carbon dioxide cycle and the refrigerant sub-cycle are connected by a carbon dioxide-refrigerant heat exchanger 4.

[0056] The refrigerant sub-cycle includes a first refrigerant loop and a second refrigerant bypass. The first refrigerant loop consists of a refrigerant compressor 9, connecting pipes 29-30, a four-way reversing valve 10, connecting pipe 31, a refrigerant-water heat exchanger 11, connecting pipes 32-33, a refrigerant throttling valve I 12, connecting pipe 34, a carbon dioxide-refrigerant heat exchanger 4, connecting pipe 35, a four-way reversing valve 10, and connecting pipe 36, connected in sequence. The second refrigerant bypass is located between the outlet of the refrigerant compressor 9 and the refrigerant passage of the refrigerant-water heat exchanger 11, and consists of a refrigerant compressor 9, connecting pipes 29 and 37, a shut-off valve 13, connecting pipe 38, a defroster 14, connecting pipe 39, a refrigerant throttling valve II 15, connecting pipes 40 and 32, and the refrigerant-water heat exchanger 11, connected in sequence.

[0057] The water-side flow path consists of a water pump 16, water pipes 41-42, carbon dioxide-water heat exchanger II3, water pipes 43-44, refrigerant-water heat exchanger 11, water pipes 45-46, carbon dioxide-water heat exchanger I2, water pipes 47-48 connected in sequence, and an adaptive control water bypass. The adaptive control water bypass includes electric valve I54, electric valve II53, and water pipes 49-52. One end of electric valve I54 is connected to the inlet water pipe 46 of carbon dioxide-water heat exchanger I2 via water pipe 51, and the other end is connected to the outlet water pipe 47 of carbon dioxide-water heat exchanger I2 via water pipe 52. One end of electric valve II53 is connected to the inlet water pipe 42 of carbon dioxide-water heat exchanger II3 via water pipe 49, and the other end is connected to the outlet water pipe 43 of carbon dioxide-water heat exchanger II3 via water pipe 50.

[0058] The carbon dioxide evaporator 7 and the defroster 14 share the same set of heat exchange fins, making it an integral finned tube heat exchanger. Figure 4 This paper presents a pipe-connected embodiment of an integral finned tube heat exchanger consisting of a carbon dioxide evaporator 7 and a defroster 14. The carbon dioxide circulation path and the high-temperature refrigerant circulation path are arranged in a cross-row configuration to improve defrosting efficiency. Carbon dioxide refrigerant flows in from inlets 60 and 61 and flows out from outlets 56 and 57; high-temperature refrigerant flows in from inlet 58 and flows out from outlet 62. The heat exchange tubes of both circulations share the same set of heat exchange fins 63, thus forming an integral finned tube heat exchanger. It should be noted that, in this embodiment, the pipe-connected configuration of the integral finned tube heat exchanger includes, but is not limited to, the above-described configuration.

[0059] This embodiment presents a carbon dioxide heat pump heating system based on multiple bypass adaptive configurations, which has both normal heating and defrosting functions:

[0060] During normal heating, see Figure 2 Depending on the operating conditions, the system can be selected to operate in the more energy-efficient state between mechanically assisted subcooling cycle and superheat recovery cascade cycle.

[0061] Furthermore, when in a mechanically assisted subcooling cycle:

[0062] The carbon dioxide sub-cycle serves as the main cycle, a transcritical carbon dioxide cycle, and is responsible for the main output of heat to the water-side circulation path; the refrigerant sub-cycle serves as an auxiliary cycle, a mechanical subcooling cycle, to achieve subcooling of the carbon dioxide temperature at the outlet of the carbon dioxide-refrigerant heat exchanger 4.

[0063] Furthermore, when in a superheated recovery cascade cycle state:

[0064] The carbon dioxide subcycle, as a low-temperature stage cycle, is a subcritical carbon dioxide cycle and serves as the low-temperature heat source for the refrigerant subcycle; the refrigerant subcycle, as a high-temperature stage cycle, is a heat pump cycle and undertakes the main output of heat to the water supply path.

[0065] In both of the above states, the carbon dioxide sub-cycle operates normally, the four-way reversing valve 10A of the auxiliary sub-cycle is connected to B, and C is connected to D, while the shut-off valve 13 and the refrigerant throttling valve II 15 are in the closed state.

[0066] Water supply flow path operation status: Based on the different temperature differences between the supply and return water (water supply flow rate), the adaptive control water bypass can dynamically adjust the ratio of water flow through carbon dioxide-water heat exchangers I2 and II3 to minimize the work of the compressor and pump.

[0067] When the temperature difference between the supply and return water sides is large (i.e., the water flow rate is small), the opening degree of electric valve I54 and electric valve II53 decreases. At this time, the return water passes through three stages of series heating: carbon dioxide-water heat exchanger II3, refrigerant-water heat exchanger 11, and carbon dioxide-water heat exchanger I2. When the temperature difference between the supply and return water sides is small (i.e., the water flow rate is large), the opening degree of electric valve I54 and electric valve II53 increases. At this time, the hot water is mainly heated by the high-temperature stage condenser, and some of the water in the carbon dioxide-water heat exchanger is bypassed.

[0068] Furthermore, the refrigerant's operating state in the carbon dioxide sub-cycle is as follows: Low-pressure, low-temperature carbon dioxide gas exiting the regenerator 5 is compressed by the carbon dioxide compressor 1 to form a high-temperature, high-pressure gas. This gas undergoes cooling and heat exchange with the water-side flow path when passing through carbon dioxide-water heat exchangers I2 and II3. It then passes through the carbon dioxide-refrigerant heat exchanger 4, where it exchanges heat with the low-temperature refrigerant fluid. The carbon dioxide fluid exiting the carbon dioxide-refrigerant heat exchanger 4 is divided into two parts. One part passes through the regenerator 5 for heat exchange and then is throttled by the carbon dioxide expansion valve II6, forming a low-temperature gas-liquid two-phase fluid. The other part directly enters the carbon dioxide expansion valve I8 for throttling, forming another low-temperature gas-liquid two-phase fluid. The two two-phase fluids mix in the refrigerant pipeline and enter the carbon dioxide evaporator 7, where they absorb heat from the outside air to become low-temperature, low-pressure carbon dioxide gas. Finally, they pass through the regenerator 5 and enter the carbon dioxide compressor 1 for another compression cycle.

[0069] In the carbon dioxide sub-cycle, the function of carbon dioxide throttling valve I8 is to regulate the cycle high pressure to ensure high energy efficiency. When the cycle high pressure is lower than the set value, the opening of carbon dioxide throttling valve I8 decreases to reduce the refrigerant flow, increasing the refrigerant storage on the high-pressure side and thus raising the high pressure; conversely, the same applies. The function of carbon dioxide throttling valve II6 is to regulate the suction superheat of carbon dioxide compressor 1 to ensure the safe operation of the compressor. When the compressor suction superheat is lower than the set value, the opening of carbon dioxide throttling valve II6 increases to increase the flow of high-temperature carbon dioxide fluid through the regenerator, thereby increasing the suction superheat; conversely, the same applies.

[0070] By setting up a bypass for the carbon dioxide regenerator, the regeneration effect can be adjusted in real time according to the operating status, which can effectively ensure the safe operation of the compressor and achieve optimal performance of the carbon dioxide circuit.

[0071] The working state of the refrigerant in the refrigerant sub-cycle is as follows: The low-temperature refrigerant at the outlet of the carbon dioxide-refrigerant heat exchanger 4 is compressed by the refrigerant compressor 9 and becomes a high-temperature and high-pressure gas. It enters the refrigerant-water heat exchanger 11 through the four-way reversing valve 10, and after condensing and exchanging heat with the water, it is throttled into a gas-liquid two-phase state in the refrigerant throttling valve I 12. Then it enters the carbon dioxide-refrigerant heat exchanger 4 and exchanges heat with the carbon dioxide fluid. After the refrigerant fluid evaporates and absorbs heat, it becomes a low-temperature and low-pressure gas. Finally, it re-enters the refrigerant compressor 9 through the four-way reversing valve 10.

[0072] When defrosting, see Figure 3 The carbon dioxide subcycle is not working. The four-way reversing valve 10B of the refrigerant subcycle is connected to C, the shut-off valve 13 is open, the refrigerant throttling valve II 15 is working, and the refrigerant throttling valve I 12 is closed.

[0073] The working state of the refrigerant in the refrigerant sub-cycle is as follows: the high-temperature and high-pressure refrigerant gas at the outlet of compressor 9 enters the defrost 14. Since the defrost 14 and the carbon dioxide evaporator 7 share the same set of heat exchange fins, the condensation heat released by the refrigerant in the defrost 14 can be directly used to defrost the carbon dioxide evaporator 7. The condensed high-temperature refrigerant is then throttled into a gas-liquid two-phase state by the refrigerant throttling valve II 15, and then enters the refrigerant-water heat exchanger 11. After absorbing heat from the heating return water, it becomes a low-temperature and low-pressure gas state, and finally re-enters the refrigerant compressor 9 through the four-way reversing valve 10.

[0074] Operating status of the water supply path: Electric valve I 54 and electric valve II 53 remain fully open. The water-side fluid passes sequentially through electric valve II 53, refrigerant-water heat exchanger 11, and electric valve I 54, and releases heat in the refrigerant-water heat exchanger 11. The released heat is used for defrosting the carbon dioxide evaporator 7 in the high-temperature stage cycle.

[0075] It should be stated that other arrangements based on the principles of this invention are also within the scope of protection of this invention.

[0076] The terms "first" and "second" are used in this document to define components. Those skilled in the art should understand that the use of these terms is solely for the purpose of distinguishing components in description. Unless otherwise stated, these terms have no special meaning.

[0077] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A carbon dioxide heat pump heating system with multiple bypass adaptive configurations, characterized in that, This includes a carbon dioxide sub-cycle, a refrigerant sub-cycle, and a water supply path that are connected by mutual heat exchange. The carbon dioxide sub-cycle includes a main carbon dioxide loop and a regenerator bypass; The main carbon dioxide loop includes a carbon dioxide compressor (1), a carbon dioxide-water heat exchanger I (2), a carbon dioxide-water heat exchanger II (3), a carbon dioxide-refrigerant heat exchanger (4), a carbon dioxide throttle valve I (8), and a carbon dioxide evaporator (7) connected in sequence. The regenerator bypass is located between the outlet of the carbon dioxide-refrigerant heat exchanger (4) and the inlet of the carbon dioxide evaporator (7); the regenerator bypass includes a regenerator (5) and a carbon dioxide throttling valve II (6) connected in sequence, and the regenerator bypass is used to regulate the refrigerant flow through the regenerator (5). The carbon dioxide sub-cycle and the refrigerant sub-cycle are connected by a carbon dioxide-refrigerant heat exchanger (4); The refrigerant sub-cycle includes a first refrigerant loop and a second refrigerant bypass; The first refrigerant loop includes a refrigerant compressor (9), a four-way reversing valve (10), a refrigerant-water heat exchanger (11) connected in sequence, a refrigerant throttle valve I (12), and a first refrigerant channel of a carbon dioxide-refrigerant heat exchanger (4); The second refrigerant bypass is located between the outlet of the refrigerant compressor (9) and the refrigerant passage of the refrigerant-water heat exchanger, including the refrigerant compressor (9), shut-off valve (13), defrost device (14), refrigerant throttle valve II (15), and refrigerant passage of the refrigerant-water heat exchanger (11) connected in sequence; The carbon dioxide evaporator (7) and the defroster (14) share the same set of heat exchange fins; The water supply path is connected to the main carbon dioxide loop through carbon dioxide-water heat exchanger I (2) and carbon dioxide-water heat exchanger II (3); The water supply path includes a water pump (16), a water channel of carbon dioxide-water heat exchanger II (3), a water channel of refrigerant-water heat exchanger (11), a water channel of carbon dioxide-water heat exchanger I (2), and an adaptive control water bypass connected in sequence. The adaptive water bypass includes electric valve I (54) and electric valve II (53); The electric valve I (54) and electric valve II (53) are respectively installed between the inlet and outlet water channels of carbon dioxide-water heat exchanger I (2) and carbon dioxide-water heat exchanger II (3) for adjusting the proportion of water flow through the heat exchanger. When the temperature difference between the supply and return water sides is large, the opening of electric valve I (54) and electric valve II (53) decreases. At this time, the return water is heated in three stages in series: carbon dioxide-water heat exchanger II (3), refrigerant-water heat exchanger (11) and carbon dioxide-water heat exchanger I (2). When the temperature difference between the supply and return water is small, the opening of electric valve I (54) and electric valve II (53) increases. At this time, the hot water is mainly heated by the high-temperature condenser, and some of the water in the carbon dioxide-water heat exchanger is bypassed.

2. A carbon dioxide heat pump heating system with multiple bypass adaptive configurations according to claim 1, characterized in that, The two ports of the four-way reversing valve (10) are connected to the suction port and the exhaust port of the refrigerant compressor (9), respectively. The other two ports of the four-way reversing valve (10) are connected to the refrigerant channels of the refrigerant-water heat exchanger (11) and the carbon dioxide-refrigerant heat exchanger (4), respectively.

3. A control method for a carbon dioxide heat pump heating system with multiple bypass adaptive configurations as described in any one of claims 1 to 2, characterized in that, The carbon dioxide heat pump heating system includes a normal heating mode, which can be further selected to operate in a state with higher energy efficiency between mechanically assisted subcooling cycle and superheat recovery cascade cycle. When in mechanically assisted subcooling cycle mode: The carbon dioxide sub-cycle serves as the main cycle and is a transcritical carbon dioxide cycle, undertaking the main output of heat to the water-side circulation path; The refrigerant sub-cycle serves as an auxiliary cycle and is a mechanical subcooling cycle, thereby achieving subcooling of the carbon dioxide temperature at the outlet of the carbon dioxide-refrigerant heat exchanger (4). When selecting the state of superheated recovery cascade cycle: The carbon dioxide subcycle serves as a low-temperature stage cycle and is a subcritical carbon dioxide cycle, acting as a low-temperature heat source for the refrigerant subcycle. The refrigerant sub-cycle is a high-temperature stage cycle and a heat pump cycle, which undertakes the main output of heat to the water supply path.

4. The control method for a carbon dioxide heat pump heating system with multiple bypass adaptive configurations according to claim 3, characterized in that, Under the cascaded cycle of mechanically assisted subcooling and superheat recovery: When the carbon dioxide subcycle is working normally, the A and B ports of the four-way reversing valve (10) of the refrigerant subcycle are connected, the C and D ports are connected, and the shut-off valve (13) and the refrigerant throttle valve II (15) are in the closed state. The water supply flow path can dynamically adjust the ratio of water flow through carbon dioxide-water heat exchangers I (2) and II (3) according to the temperature difference between the supply and return water, so as to minimize the work of the compressor and pump.

5. The control method for a carbon dioxide heat pump heating system with multiple bypass adaptive configurations according to claim 4, characterized in that, The carbon dioxide heat pump heating system also includes a defrosting mode; In the defrost mode: The B and C ports of the four-way reversing valve (10) of the refrigerant sub-circuit are connected, the shut-off valve (13) is in the open state, the refrigerant throttle valve II (15) is working, and the refrigerant throttle valve I (12) is in the closed state. Electric valve I (54) and electric valve II (53) in the water supply path are kept fully open; The water-side fluid passes through electric valve II (53), refrigerant-water heat exchanger (11) and electric valve I (54) in sequence, and releases heat in refrigerant-water heat exchanger (11). The released heat is used to defrost the carbon dioxide evaporator (7) in the high-temperature stage cycle.

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