Variable frequency heat recovery system and heat recovery unit

Abstract

The variable-frequency heat recovery system comprises a compressor unit, three heat exchangers, a variable-frequency driving module and a liquid storage device, the compressor unit can be connected with any two heat exchangers to form a refrigerant circulation loop, and an inlet pipe of the liquid storage device is connected to the outlet side of a condenser of the refrigerant circulation loop; the variable frequency driving module is provided with a heat dissipation pipeline, and the heat dissipation pipeline is connected with an inlet pipe of the liquid storage device in series so that refrigerants conveyed to the liquid storage device can pass through the heat dissipation pipeline. According to the heat recovery system, the pipeline connecting structure in the system is designed, the refrigerant before throttling is adopted to cool the variable frequency driving module, the cooling effect of the variable frequency driving module in different modes is ensured, and the reliability of the heat recovery system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pump systems, and particularly to a variable-frequency heat recovery system and a heat recovery unit. Background Art

[0002] Heat recovery air-conditioning units have been widely used in the field of heating, ventilation, and air conditioning due to their excellent energy utilization efficiency. Currently, the mainstream models usually have five operating modes: refrigeration, heating, refrigeration + hot water, hot water production, and heating + hot water production. Among them, the refrigeration + hot water mode recovers the condensation heat generated during the refrigeration process to produce domestic hot water, realizing the cascade utilization of energy. The comprehensive energy efficiency ratio of the unit in this mode is significantly higher than that of ordinary air-cooled chilled water units, showing significant economic benefits and environmental advantages.

[0003] With the rapid development of variable-frequency technology, heat recovery units with variable-frequency control have more prominent performances in terms of operating energy efficiency and temperature regulation accuracy. At the same time, the environmentally friendly refrigerant R32 is gradually replacing traditional refrigerants due to its low global warming potential value and excellent heat transfer performance, making variable-frequency heat recovery units using R32 refrigerant an important development direction in the future market.

[0004] However, in practical applications, such units still face technical problems that need to be solved urgently. When operating in heat recovery modes such as refrigeration + hot water or hot water production, since the air-side heat exchanger is in a non-operating state, the variable-frequency drive module of the compressor cannot be effectively cooled by the conventional air-cooled method. This problem is particularly prominent in variable-frequency units using R32 refrigerant, mainly because the higher working pressure of the R32 system leads to an increase in the heat generation of the variable-frequency drive module, and the heat dissipation demand increases due to continuous high-load operation in the heat recovery mode. Although various solutions including liquid-cooled heat dissipation systems and independent air-cooled channels have been proposed in the prior art, these solutions either significantly increase the system complexity and manufacturing cost, or affect the overall structure design of the unit, and it is difficult to achieve an economical and reliable heat dissipation effect while ensuring the system performance.

[0005] Therefore, designing a variable-frequency heat recovery system that can effectively solve the heat dissipation problem of the variable-frequency drive module is of great significance for promoting the development of heat recovery technology. Summary of the Invention

[0006] In order to solve the defect that the prior art cannot ensure the heat dissipation effect of the variable-frequency drive module, the present invention proposes a variable-frequency heat recovery system and a heat recovery unit. By designing the pipeline connection structure in the system and using the refrigerant before throttling to cool the variable-frequency drive module, the cooling effect of the variable-frequency drive module in different modes is ensured, and the reliability of the heat recovery system is improved.

[0007] The technical solution adopted by the present invention is to design a variable-frequency heat recovery system, including: a compressor unit, three heat exchangers, a variable-frequency drive module, and a liquid receiver. The compressor unit can be connected to any two heat exchangers to form a refrigerant circulation loop. The inlet pipe of the liquid receiver is connected to the condenser outlet side of the refrigerant circulation loop. The variable-frequency drive module is configured with a heat dissipation pipeline, and the heat dissipation pipeline is connected in series with the inlet pipe of the liquid receiver so that the refrigerant sent to the liquid receiver passes through the heat dissipation pipeline.

[0008] In some embodiments, the three heat exchangers are a first heat exchanger, a second heat exchanger, and a third heat exchanger respectively. The exhaust side of the compressor unit can be switched to connect to the first end of any one of the heat exchangers, and the second end of each heat exchanger is respectively connected to the inlet pipe of the liquid receiver through a valve member; the second end of the first heat exchanger is connected to the second end of the third heat exchanger through a throttling pipeline, and a first throttle valve and a second throttle valve are connected in series in the throttling pipeline. The outlet pipe of the liquid receiver is connected between the first throttle valve and the second throttle valve.

[0009] Furthermore, the second end of the second heat exchanger is connected to the section between the first throttle valve and the second throttle valve through a defrosting branch, and the defrosting branch is provided with a throttling element and a control valve for switching the on-off state.

[0010] Furthermore, the working modes of the variable-frequency heat recovery system include at least one of a hot water mode, a cooling mode, a heating mode, a cooling and heating water mode, and a heating and heating water mode;

[0011] When the variable-frequency heat recovery system operates in the hot water mode, the second heat exchanger serves as a condenser, the third heat exchanger serves as an evaporator, and the first heat exchanger does not participate in the refrigerant circulation;

[0012] And / or when the variable-frequency heat recovery system operates in the cooling mode, the first heat exchanger serves as an evaporator, the third heat exchanger serves as a condenser, and the second heat exchanger does not participate in the refrigerant circulation;

[0013] And / or when the variable-frequency heat recovery system operates in the heating mode, the first heat exchanger serves as a condenser, the third heat exchanger serves as an evaporator, and the second heat exchanger does not participate in the refrigerant circulation;

[0014] And / or when the variable-frequency heat recovery system operates in the cooling and heating water mode, the third heat exchanger serves as an evaporator, the second heat exchanger serves as a condenser, and the first heat exchanger does not participate in the refrigerant circulation;

[0015] And / or when the variable-frequency heat recovery system operates in the heating and heating water mode, the first heat exchanger or the second heat exchanger serves as a condenser, and the third heat exchanger serves as an evaporator.

[0016] Further, the compressor unit is connected to three heat exchangers through two four-way valves; the D end of the first four-way valve is connected to the exhaust side of the compressor unit, the E end is connected to the first end of the first heat exchanger, the S end is connected to the suction side of the compressor unit, and the C end is connected to the D end of the second four-way valve; the C end of the second four-way valve is connected to the first end of the third heat exchanger, the E end is connected to the first end of the second heat exchanger, and the S end is connected to the suction side of the compressor unit.

[0017] In some other embodiments, the three heat exchangers are the first heat exchanger, the second heat exchanger, and the third heat exchanger respectively. The exhaust side of the compressor unit can be switched to connect to the first end of the second heat exchanger or the first end of the third heat exchanger, and the second ends of the second heat exchanger and the third heat exchanger are respectively connected to the inlet pipe of the liquid receiver through valve components; the first end of the first heat exchanger is connected to the suction side of the compressor unit, the second end of the first heat exchanger is connected to the second end of the third heat exchanger through a throttling pipeline, a first throttle valve and a second throttle valve are connected in series in the throttling pipeline, and the outlet pipe of the liquid receiver is connected between the first throttle valve and the second throttle valve.

[0018] Further, the compressor unit is connected to three heat exchangers through a third four-way valve; the D end of the third four-way valve is connected to the exhaust side of the compressor unit, the E end is connected to the first end of the second heat exchanger, the S end is connected to the suction side of the compressor unit, and the C end is connected to the first end of the third heat exchanger.

[0019] Further, the valve component is a check valve, and the check valve only allows the refrigerant to flow towards the liquid receiver.

[0020] Further, the first heat exchanger is an air-conditioning water heat exchanger, the second heat exchanger is a hot water heat exchanger, and the third heat exchanger is an outdoor heat exchanger.

[0021] Further, the compressor unit includes two compressors arranged in parallel. The suction side of the compressor unit is connected to a gas-liquid separator having two outlet pipes, and each compressor is correspondingly connected to one outlet pipe.

[0022] The present invention also proposes a heat recovery unit, and this heat recovery unit adopts the above-mentioned variable-frequency heat recovery system.

[0023] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0024] 1. By designing the pipeline connection structure in the system, the compressor unit can be connected to any two heat exchangers to form a refrigerant circulation loop, and the inlet pipe of the liquid receiver is always connected to the condenser outlet side of the refrigerant circulation loop, and the refrigerant before throttling is used to cool the variable-frequency drive module, ensuring the cooling effect of the variable-frequency drive module in different modes and improving the reliability of the heat recovery system;

[0025] 2. A defrosting branch is designed between the second heat exchanger and the third heat exchanger. The second end of the second heat exchanger is connected between the first throttle valve and the second throttle valve through the defrosting branch. When the third heat exchanger needs defrosting, it can be selectively connected to the second heat exchanger through the defrosting branch, and the first throttle valve and the second throttle valve are closed. While defrosting the third heat exchanger, the refrigerant flowing out of the third heat exchanger is sent to the liquid storage tank to cool down the variable frequency drive module.

[0026] 3. A parallel compressor unit is adopted to improve the operating performance and reliability of the heat recovery system. A double-tube gas-liquid separator is connected to the suction side of the compressor unit, and each compressor sucks air separately to avoid uneven exhaust temperatures of the two compressors. Brief Description of the Drawings

[0027] The present invention will be described in detail below in conjunction with embodiments and drawings, where:

[0028] Figure 1 is a schematic diagram of the system connection of the first type of feasible embodiment of the present invention;

[0029] Figure 2 is a schematic diagram of the refrigerant flow direction in the hot water mode of the first type of feasible embodiment;

[0030] Figure 3 is a schematic diagram of the refrigerant flow direction in the cooling mode of the first type of feasible embodiment;

[0031] Figure 4 is a schematic diagram of the refrigerant flow direction in the heating mode of the first type of feasible embodiment;

[0032] Figure 5 is a schematic diagram of the refrigerant flow direction in the cooling and hot water mode of the first type of feasible embodiment;

[0033] Figure 6 is a schematic diagram of the system connection of the second type of feasible embodiment of the present invention;

[0034] Figure 7 is a schematic diagram of the refrigerant flow direction in the hot water mode of the second type of feasible embodiment;

[0035] Figure 8 is a schematic diagram of the refrigerant flow direction in the cooling mode of the second type of feasible embodiment;

[0036] Figure 9 is a schematic diagram of the refrigerant flow direction in the cooling and hot water mode of the second type of feasible embodiment;

[0037] Description of the Drawings: 1. Compressor unit; 2. First heat exchanger; 3. Second heat exchanger; 4. Third heat exchanger; 5. Liquid receiver; 6. Control valve; 7. First check valve; 8. Second check valve; 9. Third check valve; 10. First throttle valve; 11. Second throttle valve; 12. Throttling element; 13. First four-way valve; 14. Second four-way valve; 15. Variable-frequency drive module; 16. Gas-liquid separator; 17. Third four-way valve; 18. Oil separator; 19. Oil return valve. Detailed Embodiment

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] The variable-frequency heat recovery system proposed by the present invention has variable-frequency power components (such as variable-frequency compressors, variable-frequency fans), etc. The variable-frequency power components are controlled by a variable-frequency drive module. The variable-frequency drive module includes power switching devices (such as IPM modules, etc.). During the operation of the heat recovery system, the variable-frequency drive module generates a significant heat load due to power loss and needs to maintain its working temperature within the allowable range through continuous heat dissipation to ensure the long-term operation stability of the system.

[0040] As Figure 1 、 6 shown, specifically, the variable-frequency heat recovery system includes: a compressor unit 1, three heat exchangers, a variable-frequency drive module 15, and a liquid receiver 5. The compressor unit 1 includes at least one compressor. By designing the pipeline connection structure in the system, the compressor unit 1 can be connected to any two heat exchangers to form a refrigerant circulation loop, and the inlet pipe of the liquid receiver 5 is always connected to the condenser outlet side of the refrigerant circulation loop. The variable-frequency drive module 15 is configured with a heat dissipation pipeline, and the heat dissipation pipeline is connected in series to the inlet pipe of the liquid receiver 5 so that the refrigerant sent to the liquid receiver 5 passes through the heat dissipation pipeline.

[0041] Based on the heat recovery system, the present invention designs a liquid receiver that is always involved in the refrigerant circulation. The liquid receiver 5 is arranged on the condenser outlet side of the refrigerant circulation loop, and the heat dissipation pipeline of the variable-frequency drive module 15 is arranged on the inlet pipe of the liquid receiver 5, so that the refrigerant cooled by the condenser always passes through the heat dissipation pipeline, ensuring the heat dissipation effect of the variable-frequency drive module in different modes and improving the reliability of the heat recovery system. In addition, since the inlet pipe of the liquid receiver 5 is on the condenser outlet side, it is equivalent to using the refrigerant before throttling to dissipate heat from the variable-frequency drive module 15, avoiding the risk of condensation on the variable-frequency drive module 15 due to too low refrigerant temperature and improving the electrical safety and operation reliability of the system.

[0042] For ease of understanding, the three heat exchangers are respectively referred to as the first heat exchanger 2, the second heat exchanger 3, and the third heat exchanger 4. The first end and the second end of each heat exchanger have been marked on the connection schematic diagram of the heat recovery system. The first end is "①" and the second end is "②".

[0043] As Figure 1 shown, in the first type of feasible embodiments of the present invention, the exhaust side of the compressor unit 1 can be switched to connect to the first end ① of any one of the heat exchangers, and the second end ② of each heat exchanger is respectively connected to the inlet pipe of the accumulator 5 through a valve member. When the compressor unit 1 is connected to the first end ① of a certain heat exchanger, this heat exchanger serves as a condenser, and the second end ② of the heat exchanger is the condenser outlet side. The refrigerant flowing out of the second end ② can enter the accumulator 5 through the valve member.

[0044] The second end ② of the first heat exchanger 2 is connected to the second end ② of the third heat exchanger 4 through a throttling pipeline. A first throttle valve 10 and a second throttle valve 11 are connected in series in the throttling pipeline. The first throttle valve 10 is close to the first heat exchanger 2, and the second throttle valve 11 is close to the third heat exchanger 4. The outlet pipe of the accumulator 5 is connected between the first throttle valve 10 and the second throttle valve 11. The refrigerant flowing out of the accumulator 5 can enter the first heat exchanger 2 through the first throttle valve 10, and the refrigerant flowing out of the main pipeline can also enter the third heat exchanger 4 through the second throttle valve 11. The specific flow direction depends on the working mode of the heat recovery system.

[0045] This design can flexibly switch the connection relationship of the three heat exchangers to meet different user needs. By controlling the refrigerant distribution state of the three heat exchangers through the first throttle valve 10 and the second throttle valve 11, while maintaining the simplicity of the pipeline, high-precision adjustment of the refrigerant flow rate and flow direction is achieved, which is especially suitable for heat recovery systems with diverse working modes.

[0046] In addition, the valve member in the above text can be a control valve with a switchable state, or a check valve. The check valve of the first heat exchanger 2 is the second check valve 8, the check valve of the second heat exchanger 3 is the first check valve 7, and the check valve of the third heat exchanger 4 is the third check valve 9. Utilizing the one-way conduction characteristic of the check valve to ensure that the refrigerant can only flow from the heat exchanger to the accumulator 5, avoiding the reverse flow of the refrigerant during different mode switches, which may cause system pressure disorder or efficiency decline, without additional electric control signals, reducing the complexity of valve adjustment.

[0047] On this basis, in order to further optimize the heat recovery system, a defrosting branch is designed between the second heat exchanger 3 and the third heat exchanger 4. The specific connection method is that one end of the defrosting branch is connected to the second end of the second heat exchanger 3, and the other end is connected between the first throttle valve 10 and the second throttle valve 11. The defrosting branch is provided with a throttling element 12 and a control valve 6, and the on-off state of the defrosting branch is switched through the control valve 6. The control valve 6 is opened when the third heat exchanger 4 serves as a condenser and the second heat exchanger 3 serves as an evaporator (that is, during the defrosting process of the third heat exchanger 4, the second heat exchanger 3 participates in the refrigerant cycle). The first throttle valve 10 and the second throttle valve 11 are both closed when the control valve 6 is opened.

[0048] The function of this design is that when the third heat exchanger 4 has a defrosting requirement, it is possible to choose to connect the second heat exchanger 3 and the third heat exchanger 4 through the defrosting branch. While defrosting the third heat exchanger 4, the refrigerant flowing out of the third heat exchanger 4 is sent to the liquid storage tank 5 to cool the variable frequency drive module 15, making the heat recovery system more flexible and better adaptable to the environment. For example, in the hot water mode (the second heat exchanger 3 serves as a condenser and the third heat exchanger 4 serves as an evaporator), if the third heat exchanger 4 has a defrosting requirement during the preparation of hot water, the refrigerant flow direction can be adjusted, the defrosting branch can be connected, and the high-temperature refrigerant discharged from the compressor unit 1 is sent into the third heat exchanger 4 for defrosting. The refrigerant flowing out of the third heat exchanger 4 sequentially passes through the heat dissipation pipeline of the variable frequency drive module 15, the liquid storage tank 5, the defrosting branch, and the second heat exchanger 3, and finally returns to the compressor unit 1.

[0049] Based on the system structure of the first type of feasible embodiments, the working modes of the heat recovery system include at least one of a hot water mode, a cooling mode, a heating mode, a cooling plus heating mode, and a heating plus hot water mode. The operating states of the three heat exchangers in different working modes are introduced in detail below.

[0050] As Figure 2 shown, when the heat recovery system operates in the hot water mode, the second heat exchanger 3 serves as a condenser, the third heat exchanger 4 serves as an evaporator, the first heat exchanger 2 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the second heat exchanger 3, and the refrigerant circulation loop flow direction is compressor unit 1 → second heat exchanger 3 → liquid storage tank 5 → second throttle valve 11 → third heat exchanger 4 → return to compressor unit 1.

[0051] As Figure 3 shown, when the heat recovery system operates in the cooling mode, the first heat exchanger 2 serves as an evaporator, the third heat exchanger 4 serves as a condenser, the second heat exchanger 3 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the third heat exchanger 4, and the refrigerant circulation loop flow direction is compressor unit 1 → third heat exchanger 4 → liquid storage tank 5 → first throttle valve 10 → first heat exchanger 2 → return to compressor unit 1.

[0052] As Figure 4 shown, when the heat recovery system operates in the heating mode, the first heat exchanger 2 acts as a condenser, the third heat exchanger 4 acts as an evaporator, the second heat exchanger 3 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the first heat exchanger 2, and the refrigerant circulation loop flow direction is compressor unit 1 → first heat exchanger 2 → liquid storage tank 5 → second throttle valve 11 → third heat exchanger 4 → return to compressor unit 1.

[0053] As Figure 5 shown, when the heat recovery system operates in the cooling and heating water mode, the first heat exchanger 2 acts as an evaporator, the second heat exchanger 3 acts as a condenser, the third heat exchanger 4 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the first heat exchanger 2, and the refrigerant circulation loop flow direction is compressor unit 1 → second heat exchanger 3 → liquid storage tank 5 → first throttle valve 10 → first heat exchanger 2 → return to compressor unit 1.

[0054] When the heat recovery system operates in the heating and heating water mode, both the first heat exchanger 2 and the second heat exchanger 3 act as condensers, and the third heat exchanger 4 acts as an evaporator. The heat recovery system usually defaults to giving priority to domestic hot water, and users can also independently set the priority of air conditioning heating and domestic hot water. Taking domestic hot water priority as an example, it first operates according to the hot water mode, the second heat exchanger 3 acts as a condenser, the third heat exchanger 4 acts as an evaporator, and the first heat exchanger 2 does not participate in the refrigerant cycle; after the hot water has met the customer's needs, it operates according to the heating mode, the first heat exchanger 2 acts as a condenser, the third heat exchanger 4 acts as an evaporator, and the second heat exchanger 3 does not participate in the refrigeration cycle. In the heating and heating water mode, after the current function reaches the shutdown condition, it is judged whether the other function meets the startup condition. If so, the function is started and operated. For example, by default, domestic hot water is prioritized. After the hot water function reaches the shutdown condition, it is judged whether the heating function meets the startup condition. If so, the heating function is started and operated until the shutdown condition of the heating function is reached.

[0055] The heat recovery system can flexibly switch operating modes under different working conditions through the coordinated operation of three heat exchangers to maximize the recovery of waste heat. For example, in the cooling mode, the refrigerant absorbs heat in the first heat exchanger to achieve refrigeration; in the heating mode, the high-temperature refrigerant discharged from the compressor unit 1 releases heat in the first heat exchanger to achieve heating; in the hot water mode, the high-temperature refrigerant discharged from the compressor unit 1 is used to heat domestic water in the second heat exchanger to improve the hot water supply efficiency; in the composite working mode (cooling + hot water / heating + hot water), the heat of the refrigerant is recovered to heat domestic hot water / for heating, realizing cascaded utilization of energy and improving the energy efficiency of the heat recovery system.

[0056] As Figure 1As shown, in the preferred solution, the operating modes of the heat recovery system include the five operating modes mentioned above. To achieve a more accurate and reliable switch to different operating modes, the compressor unit 1 is connected to three heat exchangers through two four-way valves. Specifically, the D end of the first four-way valve 13 is connected to the exhaust side of the compressor unit 1, the E end is connected to the first end of the first heat exchanger 2, the S end is connected to the suction side of the compressor unit 1, and the C end is connected to the D end of the second four-way valve 14; the C end of the second four-way valve 14 is connected to the first end of the third heat exchanger 4, the E end is connected to the first end of the second heat exchanger 3, and the S end is connected to the suction side of the compressor unit 1.

[0057] Specifically, the switching states of the four-way valves under different operating modes are as follows:

[0058] When the variable-frequency heat recovery system operates in the hot water mode, the D end of the first four-way valve 13 is connected to the C end, the E end is connected to the S end, the D end of the second four-way valve 14 is connected to the E end, and the C end is connected to the S end;

[0059] When the variable-frequency heat recovery system operates in the cooling mode, the D end of the first four-way valve 13 is connected to the C end, the E end is connected to the S end, the D end of the second four-way valve 14 is connected to the C end, and the E end is connected to the S end;

[0060] When the variable-frequency heat recovery system operates in the heating mode, the D end of the first four-way valve 13 is connected to the E end, the C end is connected to the S end, the D end of the second four-way valve 14 is connected to the E end, and the C end is connected to the S end;

[0061] When the variable-frequency heat recovery system operates in the cooling and heating hot water mode, the D end of the first four-way valve 13 is connected to the C end, the E end is connected to the S end, the D end of the second four-way valve 14 is connected to the E end, and the C end is connected to the S end.

[0062] When the variable-frequency heat recovery system operates in the heating and heating hot water mode, the heat pump system usually defaults to giving priority to domestic hot water, and users can also independently set the priority of air-conditioning heating and domestic hot water. If domestic hot water is prioritized, the state of the four-way valve and the refrigerant flow direction are the same as those in the hot water mode. If air-conditioning heating is prioritized, the state of the four-way valve and the refrigerant flow direction are the same as those in the heating mode.

[0063] For ease of understanding, the operating states under different operating modes are described using application examples of the present invention.

[0064] Hot water mode

[0065] As Figure 2 shown, when the variable-frequency heat recovery system is turned on and enters the hot water mode, the first four-way valve 13 is de-energized (the D end is connected to the C end, the E end is connected to the S end), the second four-way valve 14 is energized (the D end is connected to the E end, the C end is connected to the S end), the second throttle valve 11 enters the operating mode, the compressor unit 1 is turned on, and the first throttle valve 10 and the control valve 6 remain closed.

[0066] After the system runs stably, the refrigerant vapor at high temperature and high pressure is discharged from the compressor unit 1, successively flows through the D-C passage of the first four-way valve 13 and the D-E passage of the second four-way valve 14, enters the second heat exchanger 3 for heat exchange, transfers the heat to the water side, is subcooled to high-pressure liquid refrigerant and then flows out of the second heat exchanger 3, passes through the first check valve 7 to cool the variable-frequency drive module 15 and then enters the liquid receiver 5, and is then sent to the upstream of the second throttle valve 11 through the outlet pipe of the liquid receiver 5. After throttling at the second throttle valve 11, it enters the third heat exchanger 4 as low-temperature and low-pressure two-phase refrigerant to absorb the heat in the air, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, enters the gas-liquid separator 16 through the C-S passage of the second four-way valve 14, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0067] Cooling mode

[0068] As Figure 3 shown, when the variable-frequency heat recovery system is powered on and enters the cooling mode, the first four-way valve 13 is de-energized (the D end is connected to the C end, and the E end is connected to the S end), the second four-way valve 14 is de-energized (the D end is connected to the C end, and the E end is connected to the S end), the first throttle valve 10 enters the working mode, the compressor unit 1 is powered on, and the second throttle valve 11 and the control valve 6 remain closed.

[0069] After the system runs stably, the refrigerant vapor at high temperature and high pressure is discharged from the compressor unit 1, successively flows through the D-C passage of the first four-way valve 13 and the D-C passage of the second four-way valve 14, enters the third heat exchanger 4 for heat exchange, is subcooled to high-pressure liquid refrigerant and then flows out, passes through the third check valve 9 to cool the variable-frequency drive module 15, and is then sent out through the outlet pipe of the liquid receiver 5 to the upstream of the first throttle valve 10. After throttling at the first throttle valve 10, it enters the first heat exchanger 2 as low-temperature and low-pressure two-phase refrigerant to absorb the heat in the air-conditioning water side, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, enters the gas-liquid separator 16 through the E-S passage of the first four-way valve 13, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0070] The water pump on the water side of the first heat exchanger 2 starts, driving the cold water in the first heat exchanger 2 to the end for users to use for refrigeration.

[0071] Heating mode

[0072] As Figure 4 shown, when the heat recovery system is powered on and enters the heating mode, the first four-way valve 13 is powered on (the D end is connected to the E end, and the C end is connected to the S end), the second four-way valve 14 is powered on (the D end is connected to the E end, and the C end is connected to the S end), the second throttle valve 11 enters the working mode, the compressor unit 1 is powered on, and the first throttle valve 10 and the control valve 6 remain closed.

[0073] After the system runs stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, flows through the D-E passage of the first four-way valve 13, enters the first heat exchanger 2 for heat exchange, transfers heat to the water side, and exits as a subcooled high-pressure liquid refrigerant. After dissipating heat from the variable-frequency drive module 15 through the second check valve 8, it is sent out from the outlet pipe of the accumulator 5 to the upstream of the second throttle valve 11. After throttling at the second throttle valve 11, it enters the third heat exchanger 4 as a low-temperature and low-pressure two-phase refrigerant to absorb heat from the air, vaporizes into a low-temperature and low-pressure refrigerant vapor and then exits, enters the gas-liquid separator 16 through the C-S passage of the second four-way valve 14, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0074] The water pump on the water side of the first heat exchanger 2 starts, driving the hot water in the first heat exchanger 2 to the end for users to use for heating.

[0075] Cooling and heating water mode

[0076] As Figure 5 As shown, when the heat recovery system is turned on and enters the cooling and heating water mode, the first four-way valve 13 is de-energized (the D end is connected to the C end, and the E end is connected to the S end), the second four-way valve 14 is energized (the D end is connected to the E end, and the C end is connected to the S end), the first throttle valve 10 enters the working mode, the compressor unit 1 is turned on, and the second throttle valve 11 and the control valve 6 remain closed.

[0077] After the heat recovery system runs stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, successively flows through the D-C passage of the first four-way valve 13 and the D-E passage of the second four-way valve 14, enters the second heat exchanger 3 for heat exchange, transfers heat to the water side, and exits as a subcooled high-pressure liquid refrigerant from the second heat exchanger 3. After dissipating heat from the variable-frequency drive module 15 through the first check valve 7, it is sent out from the outlet pipe of the accumulator 5 to the upstream of the first throttle valve 10. After throttling at the first throttle valve 10, it enters the first heat exchanger 2 as a low-temperature and low-pressure two-phase refrigerant to absorb heat from the air-conditioning water side, vaporizes into a low-temperature and low-pressure refrigerant vapor and then exits, enters the gas-liquid separator through the E-S passage of the first four-way valve 13, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0078] The water pump on the water side of the first heat exchanger 2 starts, driving the cold water in the first heat exchanger 2 to the end for users to use for cooling.

[0079] Heating and heating water mode

[0080] Taking the example of prioritizing hot water production and then heating, first operate in the hot water mode. The variable frequency heat recovery system starts up and enters the hot water mode. The first four-way valve 13 is de-energized (the D end is connected to the C end, and the E end is connected to the S end), the second four-way valve 14 is energized (the D end is connected to the E end, and the C end is connected to the S end), the second throttle valve 11 enters the working mode, the compressor unit 1 starts up, and the first throttle valve 10 and the control valve 6 remain closed.

[0081] After the system operates stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, successively flows through the D-C passage of the first four-way valve 13 and the D-E passage of the second four-way valve 14, enters the second heat exchanger 3 for heat exchange, transfers the heat to the water side, is subcooled into high-pressure liquid refrigerant and then flows out of the second heat exchanger 3, passes through the first check valve 7 to dissipate heat from the variable frequency drive module 15 and then enters the accumulator 5, and then is sent to the upstream of the second throttle valve 11 through the outlet pipe of the accumulator 5. After throttling at the second throttle valve 11, it enters the third heat exchanger 4 as low-temperature and low-pressure two-phase refrigerant to absorb heat from the air, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, enters the gas-liquid separator 16 through the C-S passage of the second four-way valve 14, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0082] After the hot water has met the user's needs, the heat recovery system starts up and enters the heating mode. The first four-way valve 13 is energized (the D end is connected to the E end, and the C end is connected to the S end), the second four-way valve 14 is energized (the D end is connected to the E end, and the C end is connected to the S end), the second throttle valve 11 enters the working mode, the compressor unit 1 starts up, and the first throttle valve 10 and the control valve 6 remain closed.

[0083] After the system operates stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, flows through the D-E passage of the first four-way valve 13, enters the first heat exchanger 2 for heat exchange, transfers the heat to the water side, is subcooled into high-pressure liquid refrigerant and then flows out, passes through the second check valve 8 to dissipate heat from the variable frequency drive module 15, and then is sent out through the outlet pipe of the accumulator 5 to the upstream of the second throttle valve 11. After throttling at the second throttle valve 11, it enters the third heat exchanger 4 as low-temperature and low-pressure two-phase refrigerant to absorb heat from the air, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, enters the gas-liquid separator 16 through the C-S passage of the second four-way valve 14, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0084] The water pump on the water side of the first heat exchanger 2 starts, driving the hot water in the first heat exchanger 2 to the end for the user to use for heating.

[0085] Such as Figure 6As shown in the figure, in the second type of feasible embodiments of the present invention, the exhaust side of the compressor unit 1 can be switched to connect to the first end ① of the second heat exchanger 3 or the first end ① of the third heat exchanger 4, and the second end ② of the second heat exchanger 3 and the second end ② of the third heat exchanger 4 are respectively connected to the inlet pipe of the liquid receiver 5 through valve components. When the compressor unit 1 is connected to the first end ① of a certain heat exchanger, this heat exchanger serves as a condenser, and the second end ② of the heat exchanger is the condenser outlet side. The refrigerant flowing out from the second end ② can enter the liquid receiver 5 through the valve component.

[0086] The first end ① of the first heat exchanger 2 is connected to the suction side of the compressor unit 1. The second end ② of the first heat exchanger 2 is connected to the second end ② of the third heat exchanger 4 through a throttling pipeline. A first throttle valve 10 and a second throttle valve 11 are connected in series in the throttling pipeline. The outlet pipe of the liquid receiver 5 is connected between the first throttle valve 10 and the second throttle valve 11. The refrigerant flowing out from the liquid receiver 5 can enter the first heat exchanger 2 through the first throttle valve 10, and the refrigerant flowing out from the main pipeline can also enter the third heat exchanger 4 through the second throttle valve 11. The specific flow direction depends on the working mode of the heat recovery system.

[0087] This design simplifies the connection pipeline of the heat recovery system. The high-temperature refrigerant discharged from the compressor can enter the second heat exchanger or the third heat exchanger. The refrigerant distribution state of the three heat exchangers is controlled by the first throttle valve 10 and the second throttle valve 11, realizing high-precision adjustment of the refrigerant flow rate and flow direction. It is applicable to heat recovery systems with fewer working modes, especially in application scenarios where users have no demand for air-conditioning heating.

[0088] In addition, the valve components in the above text can be control valves that can switch the on-off state, or check valves. The check valve of the second heat exchanger 3 is the first check valve 7, and the check valve of the third heat exchanger 4 is the third check valve 9. Utilizing the one-way conduction characteristic of the check valve to ensure that the refrigerant can only flow from the heat exchanger to the liquid receiver 5, avoiding the reverse flow of the refrigerant during different mode switches, which may cause system pressure disorder or efficiency decline, without additional electric control signals, reducing the complexity of valve adjustment.

[0089] It should be understood that in actual applications, if it is necessary for the second heat exchanger to participate in the defrosting process of the third heat exchanger as an evaporator, a defrosting branch can be designed between the second heat exchanger and the third heat exchanger, that is, a defrosting branch can also be designed in the second type of feasible embodiments. The specific connection method of the defrosting branch has been described in detail in the first type of feasible embodiments and will not be elaborated here.

[0090] Based on the system structure of the second type of feasible embodiments, the working modes of the heat recovery system include at least one of the hot water mode, the cooling mode, and the cooling plus heating mode. The operating states of the three heat exchangers in different working modes will be introduced in detail below.

[0091] As Figure 7As shown, when the heat recovery system operates in the hot water mode, the second heat exchanger 3 serves as a condenser, the third heat exchanger 4 serves as an evaporator, the first heat exchanger 2 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the second heat exchanger 3, and the refrigerant circulation loop flows as compressor unit 1 → second heat exchanger 3 → liquid receiver 5 → second throttle valve 11 → third heat exchanger 4 → back to compressor unit 1.

[0092] As Figure 8 shown, when the heat recovery system operates in the cooling mode, the first heat exchanger 2 serves as an evaporator, the third heat exchanger 4 serves as a condenser, the second heat exchanger 3 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the third heat exchanger 4, and the refrigerant circulation loop flows as compressor unit 1 → third heat exchanger 4 → liquid receiver 5 → first throttle valve 10 → first heat exchanger 2 → back to compressor unit 1.

[0093] As Figure 9 shown, when the heat recovery system operates in the cooling and heating water mode, the first heat exchanger 2 serves as an evaporator, the second heat exchanger 3 serves as a condenser, the third heat exchanger 4 does not participate in the refrigerant cycle, the exhaust side of the compressor unit 1 is connected to the first end of the first heat exchanger 2, and the refrigerant circulation loop flows as compressor unit 1 → second heat exchanger 3 → liquid receiver 5 → first throttle valve 10 → first heat exchanger 2 → back to compressor unit 1.

[0094] As Figure 6 shown, in the preferred embodiment, the operating modes of the heat recovery system include the three operating modes mentioned above. To achieve a more accurate and reliable switch to different operating modes, the compressor unit 1 is connected to the second heat exchanger and the third heat exchanger through a four-way valve. Specifically, the compressor unit 1 is connected to the second heat exchanger 3 and the third heat exchanger 4 through the third four-way valve 17; the D end of the third four-way valve 17 is connected to the exhaust side of the compressor unit 1, the E end is connected to the first end of the second heat exchanger 3, the S end is connected to the suction side of the compressor unit 1, and the C end is connected to the first end of the third heat exchanger 4.

[0095] Specifically, the switching states of the third four-way valve in different operating modes are as follows:

[0096] When the variable frequency heat recovery system operates in the hot water mode, the D end of the third four-way valve is connected to the E end, and the C end is connected to the S end;

[0097] When the variable frequency heat recovery system operates in the cooling mode, the D end of the third four-way valve is connected to the C end, and the E end is connected to the S end;

[0098] When the variable frequency heat recovery system operates in the cooling and heating water mode, the D end of the third four-way valve is connected to the E end, and the C end is connected to the S end.

[0099] For easy understanding, the operating states in different operating modes are described by taking the application example of the present invention.

[0100] Hot water mode

[0101] As Figure 7 shown, when the variable frequency heat recovery system is powered on and enters the hot water mode, the third four-way valve 17 is powered on (the D end is connected to the E end, and the C end is connected to the S end), the second throttle valve 11 enters the working mode, the compressor unit 1 is powered on, and the first throttle valve 10 remains closed.

[0102] After the system runs stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, flows through the D-E channel of the third four-way valve 17, enters the second heat exchanger 3 for heat exchange, transfers the heat to the water side, is subcooled into high-pressure liquid refrigerant and then flows out of the second heat exchanger 3, enters the frequency conversion drive module 15 for heat dissipation through the first check valve 7 and then enters the liquid storage tank 5, and then is sent to the upstream of the second throttle valve 11 through the outlet pipe of the liquid storage tank 5. After throttling at the second throttle valve 11, it enters the third heat exchanger 4 as low-temperature and low-pressure two-phase refrigerant to absorb the heat in the air, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, enters the gas-liquid separator 16 through the C-S channel of the third four-way valve, and then returns to the compressor unit 1 from the gas-liquid separator 16.

[0103] Cooling mode

[0104] As Figure 8 shown, when the variable frequency heat recovery system is powered on and enters the cooling mode, the third four-way valve 17 is powered off (the D end is connected to the C end, and the E end is connected to the S end), the first throttle valve 10 enters the working mode, the compressor unit 1 is powered on, and the second throttle valve 11 remains closed.

[0105] After the system runs stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, flows through the D-C channel of the third four-way valve, enters the third heat exchanger 4 for heat exchange, is subcooled into high-pressure liquid refrigerant and then flows out, is sent to the upstream of the first throttle valve 10 through the outlet pipe of the liquid storage tank 5 after heat dissipation through the third check valve 9, and after throttling at the first throttle valve 10, it enters the first heat exchanger 2 as low-temperature and low-pressure two-phase refrigerant to absorb the heat in the air-conditioning water side, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, and returns to the compressor unit 1 from the gas-liquid separator 16.

[0106] The water pump on the water side of the first heat exchanger 2 starts, driving the cold water in the first heat exchanger 2 to the end for users to use for refrigeration.

[0107] Cooling and heating water mode

[0108] As Figure 9 shown, when the heat recovery system is powered on and enters the cooling and heating water mode, the third four-way valve is powered on (the D end is connected to the E end, and the C end is connected to the S end), the first throttle valve 10 enters the working mode, the compressor unit 1 is powered on, and the second throttle valve 11 remains closed.

[0109] After the heat recovery system operates stably, the high-temperature and high-pressure refrigerant vapor is discharged from the compressor unit 1, flows through the D-E passage of the third four-way valve successively, enters the second heat exchanger 3 for heat exchange, transfers the heat to the water side, is subcooled into high-pressure liquid refrigerant and then flows out of the second heat exchanger 3, after dissipating heat to the variable frequency drive module 15 through the first one-way valve 7, it is sent out from the outlet pipe of the liquid receiver 5 to the upstream of the first throttle valve 10, throttles at the first throttle valve 10, enters the first heat exchanger 2 as low-temperature and low-pressure two-phase refrigerant to absorb the heat in the air-conditioning water side, vaporizes into low-temperature and low-pressure refrigerant vapor and then flows out, and returns to the compressor unit 1 through the gas-liquid separator 16.

[0110] The water pump on the water side of the first heat exchanger 2 starts, driving the cold water in the first heat exchanger 2 to the end for users to use for refrigeration.

[0111] As Figure 1 、 6 shown, in common application scenarios, the first heat exchanger 2 is an air-conditioning water heat exchanger, and plate heat exchangers are commonly used for air-conditioning water heat exchangers; the second heat exchanger 3 is a hot water heat exchanger, and shell-and-tube heat exchangers are commonly used for hot water heat exchangers; the third heat exchanger 4 is an outdoor heat exchanger, and finned heat exchangers equipped with fans are commonly used for outdoor heat exchangers. When the finned heat exchanger participates in the refrigerant cycle, the fan of the finned heat exchanger is turned on. This design can concentrate cooling, heating, hot water and other modes in the heat recovery system by configuring the air-conditioning water heat exchanger, hot water heat exchanger and outdoor heat exchanger, with more efficient waste heat recovery and more stable low-temperature operation.

[0112] As Figure 1 、 6 shown, in the preferred embodiment of the present invention, the compressor unit 1 includes two compressors arranged in parallel. The parallel connection of the two compressors can control the operating state of the compressors according to the load, greatly improving the capacity and energy efficiency of the heat recovery system. The suction side of the compressor unit 1 is connected to a gas-liquid separator 16 with two outlet pipes (for the structure of the double-tube gas-liquid separator, see CN2597049Y), each compressor is correspondingly connected to an outlet pipe, and each compressor sucks air separately to avoid uneven exhaust temperatures of the two compressors.

[0113] An oil separator 18 is provided on the exhaust side of the compressor unit 1. The outlet pipe of the oil separator 18 is connected to the suction side of each compressor in series through an oil return valve 19, and the oil return valve 19 is opened when the compressor unit 1 is started. The oil separator 18 efficiently captures the refrigeration oil in the exhaust gas to avoid lubricating oil entering the circulation system and causing the compressor to lack oil and seize the cylinder. Each compressor returns oil separately to avoid uneven oil return of the two compressors.

[0114] The present invention also provides a heat recovery unit. This heat recovery unit adopts the above-mentioned variable-frequency heat recovery system. By designing the pipeline connection structure within the system, the compressor unit can be connected to any two heat exchangers to form a refrigerant circulation loop, and the inlet pipe of the liquid receiver is always connected to the condenser outlet side of the refrigerant circulation loop. The variable-frequency drive module is cooled by the refrigerant before throttling to ensure the cooling effect of the variable-frequency drive module in different modes and improve the reliability of the heat recovery unit.

[0115] It should be noted that the terms used above are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. When the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The execution order of actions, steps, etc. in the devices and methods shown in the specification and drawings can be implemented in any order as long as there is no specific limitation on the order and the output of the previous process is not used in the subsequent process. The similar sequential terms used for convenience of description do not mean that they must be implemented in such an order.

[0116] Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0117] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Variable frequency heat recovery system, comprising: A compressor unit, three heat exchangers, and a variable-frequency drive module. The compressor unit can be connected to any two of the heat exchangers to form a refrigerant circulation loop. It is characterized in that it further includes: a liquid receiver, the inlet pipe of the liquid receiver is connected to the condenser outlet side of the refrigerant circulation loop, and the variable-frequency drive module is configured with a heat dissipation pipeline, and the heat dissipation pipeline is connected in series with the inlet pipe of the liquid receiver so that the refrigerant sent to the liquid receiver all passes through the heat dissipation pipeline.

2. The variable frequency heat recovery system according to claim 1, characterized in that, The three heat exchangers are respectively a first heat exchanger, a second heat exchanger, and a third heat exchanger. The exhaust side of the compressor unit can be switched to connect to the first end of any one of the heat exchangers, and the second end of each heat exchanger is respectively connected to the inlet pipe of the liquid receiver through a valve member; The second end of the first heat exchanger is connected to the second end of the third heat exchanger through a throttling pipeline, and a first throttle valve and a second throttle valve are connected in series in the throttling pipeline. The outlet pipe of the liquid receiver is connected between the first throttle valve and the second throttle valve.

3. The variable-frequency heat recovery system according to claim 2, wherein The second end of the second heat exchanger is connected between the first throttle valve and the second throttle valve through a defrosting branch, and the defrosting branch is provided with a throttling element and a control valve for switching the on-off state.

4. The variable-frequency heat recovery system according to claim 2, characterized in that The working modes of the variable-frequency heat recovery system include at least one of a hot water mode, a cooling mode, a heating mode, a cooling and heating water mode, and a heating and heating water mode; When the variable-frequency heat recovery system operates in the hot water mode, the second heat exchanger serves as a condenser, the third heat exchanger serves as an evaporator, and the first heat exchanger does not participate in the refrigerant circulation; And / or when the variable-frequency heat recovery system operates in the cooling mode, the first heat exchanger serves as an evaporator, the third heat exchanger serves as a condenser, and the second heat exchanger does not participate in the refrigerant circulation; And / or when the variable-frequency heat recovery system operates in the heating mode, the first heat exchanger serves as a condenser, the third heat exchanger serves as an evaporator, and the second heat exchanger does not participate in the refrigerant circulation; And / or when the variable-frequency heat recovery system operates in the cooling and heating water mode, the third heat exchanger serves as an evaporator, the second heat exchanger serves as a condenser, and the first heat exchanger does not participate in the refrigerant circulation; And / or when the variable-frequency heat recovery system operates in the heating and heating water mode, the first heat exchanger or the second heat exchanger serves as a condenser, and the third heat exchanger serves as an evaporator.

5. The variable-frequency heat recovery system according to claim 4, wherein The compressor unit is connected to the three heat exchangers through two four-way valves; The D end of the first four-way valve is connected to the exhaust side of the compressor unit, the E end is connected to the first end of the first heat exchanger, the S end is connected to the suction side of the compressor unit, and the C end is connected to the D end of the second four-way valve; The C end of the second four-way valve is connected to the first end of the third heat exchanger, the E end is connected to the first end of the second heat exchanger, and the S end is connected to the suction side of the compressor unit.

6. The variable frequency heat recovery system according to claim 1, characterized in that, The three heat exchangers are respectively a first heat exchanger, a second heat exchanger and a third heat exchanger. The exhaust side of the compressor unit can be switched to connect to the first end of the second heat exchanger or the first end of the third heat exchanger, and the second ends of the second heat exchanger and the third heat exchanger are respectively connected to the inlet pipe of the liquid storage tank through valve components; The first end of the first heat exchanger is connected to the suction side of the compressor unit. The second end of the first heat exchanger is connected to the second end of the third heat exchanger through a throttling pipeline. A first throttle valve and a second throttle valve are connected in series in the throttling pipeline. The outlet pipe of the liquid storage tank is connected between the first throttle valve and the second throttle valve.

7. The variable-frequency heat recovery system according to claim 6, characterized in that The compressor unit is connected to the three heat exchangers through a third four-way valve; The D end of the third four-way valve is connected to the exhaust side of the compressor unit, the E end is connected to the first end of the second heat exchanger, the S end is connected to the suction side of the compressor unit, and the C end is connected to the first end of the third heat exchanger.

8. The variable-frequency heat recovery system according to claim 2 or 6, characterized in that, The valve component is a check valve, and the check valve only allows the refrigerant to flow towards the liquid storage tank.

9. The variable frequency heat recovery system according to claim 2 or 6, characterized in that The first heat exchanger is an air-conditioning water heat exchanger, the second heat exchanger is a hot water heat exchanger, and the third heat exchanger is an outdoor heat exchanger.

10. The variable-frequency heat recovery system according to claim 1, wherein The compressor unit includes two compressors arranged in parallel. The suction side of the compressor unit is connected to a gas-liquid separator having two outlet pipes, and each compressor is correspondingly connected to one of the outlet pipes.

11. Heat recovery unit, characterized in that, The heat recovery unit adopts the variable-frequency heat recovery system according to any one of claims 1 to 10.

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