Heat Pump System

Abstract

The present invention provides a heat pump system, which includes: a first-stage circuit, on which a first-stage compressor, a condenser evaporator, a first-stage main expansion valve and a first-stage evaporator are arranged in sequence along the flow direction of the refrigerant; a second-stage circuit, on which a second-stage compressor, a second-stage condenser, a jet reheat heat exchanger, a second-stage main expansion valve and a condenser evaporator are arranged in sequence along the flow direction of the refrigerant, wherein the condenser evaporator is used as a condenser in the first-stage circuit and as an evaporator in the second-stage circuit; and a jet reheat branch, wherein the first-stage compressor has a first refrigerant replenishment port, and the jet reheat branch extends from a first branch point on the first-stage circuit downstream of the condenser evaporator, passes through the jet reheat heat exchanger, and is connected to the first refrigerant replenishment port.

Description

Technical Field

[0001] The present invention relates to the field of heat pump systems, and more particularly to a cascade system for industrial heat pump applications. Background Art

[0002] This section provides background information related to the present disclosure which does not necessarily constitute prior art.

[0003] There is a great demand for high-temperature heat sources above 100°C in industrial applications, such as the regeneration of rotary dehumidification, drying of lithium batteries, and drying of cement. At present, this high-temperature heat source is usually achieved by traditional methods such as electric heating, gas, and fuel oil, but there are problems such as serious energy consumption and high pollution. As an efficient and environmentally friendly new energy technology, the heat pump system can be used in many occasions to improve the problems existing in the traditional high-temperature heat source supply method. For example, the heat pump system is used in the coal-to-electricity project in the north. The heat pump system absorbs heat from the air and transfers it to hot water, which can achieve an efficiency of 3.0.

[0004] The condensation temperature of a typical heat pump system is about 65°C. However, in industrial heat pump applications, the condensation temperature is very high, usually exceeding 100°C, and can even reach 135°C. On the one hand, this means that the system pressure ratio is very high, so a cascade system is usually used to achieve this. On the other hand, the high condensation temperature also leads to high temperature resistance requirements for the expansion valve, and the maximum temperature resistance of a general expansion valve is 70°C. If a special expansion valve is used, it will lead to an increase in cost. Therefore, the temperature resistance of the expansion valve limits the large-scale promotion and application of high-temperature heat pump systems.

[0005] Therefore, it is necessary to provide an improved heat pump system, which can reduce the refrigerant temperature before the expansion valve to ensure the reliability of system operation on the one hand, and improve the system energy efficiency and controllability on the other hand. Summary of the invention

[0006] This section provides a general summary of the invention, and is not a comprehensive disclosure of its full scope or all of its features.

[0007] The object of the present invention is to provide a reliable and efficient heat pump system, which adopts a cascade system design. On the one hand, the heat pump system uses the refrigerant in the first-stage circuit to cool the refrigerant in front of the expansion valve in the second-stage circuit, thereby reducing the temperature in front of the valve in the second-stage circuit, solving the problem of temperature resistance requirements of the expansion valve in the existing heat pump system; on the other hand, the refrigerant in the first-stage circuit cools the refrigerant in front of the expansion valve in the second-stage circuit and then sprays it into the first-stage compressor as a jet enthalpy-increasing fluid, thereby improving the energy efficiency of the system; on the other hand, the heat pump system can also set a cooling branch in the second-stage circuit, so as to achieve the exhaust temperature control requirements of the high-temperature compressor with a small amount of spray liquid, thereby improving the controllability and efficiency of the system.

[0008] According to one aspect of the present invention, a heat pump system is provided, which includes: a first-stage circuit, on which a first-stage compressor, a condenser evaporator, a first-stage main expansion valve and a first-stage evaporator are arranged in sequence along the flow direction of the refrigerant; a second-stage circuit, on which a second-stage compressor, a second-stage condenser, a jet reheat heat exchanger, a second-stage main expansion valve and a condenser evaporator are arranged in sequence along the flow direction of the refrigerant, wherein the condenser evaporator is used as a condenser in the first-stage circuit and as an evaporator in the second-stage circuit; and a jet reheat branch, wherein the first-stage compressor has a first refrigerant replenishment port, and the jet reheat branch extends from a first branch point on the first-stage circuit downstream of the condenser evaporator, passes through the jet reheat heat exchanger, and is connected to the first refrigerant replenishment port.

[0009] Optionally, the heat pump system is configured such that the first refrigerant supplied to the first refrigerant replenishing port via the injection enthalpy increase branch is in a pure gas state.

[0010] Optionally, on the jet enthalpy increase branch, a first branch expansion valve is arranged between the first branch point and the jet enthalpy increase heat exchanger.

[0011] Optionally, the second-stage compressor has a second refrigerant replenishment port, and the heat pump system also includes a cooling branch, which extends from a second branch point on the second-stage loop between the jet enthalpy heat exchanger and the second-stage main expansion valve and is connected to the second refrigerant replenishment port.

[0012] Optionally, the heat pump system is configured such that the second refrigerant supplied to the second refrigerant replenishing port via the cooling branch is in a pure liquid state.

[0013] Optionally, a throttle valve is provided on the cooling branch.

[0014] Optionally, the heat pump system is configured such that the condensing temperature of the second-stage condenser is higher than 100°C and the refrigerant temperature immediately upstream of the second-stage main expansion valve is lower than 70°C.

[0015] Optionally, the first refrigerant in the primary circuit is different from the second refrigerant in the secondary circuit.

[0016] In general, the heat pump system according to the present invention brings at least the following beneficial effects: the heat pump system according to the present invention can not only effectively reduce the refrigerant temperature before the main expansion valve in the second-stage circuit by setting the jet enthalpy increase branch between the first-stage circuit and the second-stage circuit, thereby ensuring that the system can still operate reliably when using a common expansion valve, expanding the application range of the heat pump system, but also spray the jet enthalpy increase fluid into the first-stage compressor through the jet enthalpy increase branch, thereby improving the energy efficiency of the system. In addition, the heat pump system according to the present invention can also achieve exhaust cooling of the high-temperature compressor with a small amount of liquid spray by setting a cooling branch in the second-stage circuit, thereby improving the controllability and efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and other features and characteristics of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings, which are provided as examples only and are not necessarily drawn to scale. In the accompanying drawings, the same reference numerals are used to indicate the same components, and in the drawings:

[0018] Figure 1 A schematic diagram showing a heat pump system according to a first embodiment of the present invention;

[0019] Figure 2 and Figure 3 Enthalpy-pressure diagrams of the first-stage loop and the second-stage loop of the heat pump system according to the first embodiment of the present invention are respectively shown;

[0020] Figure 4 A schematic diagram showing a heat pump system according to a second embodiment of the present invention;

[0021] Figure 5 shows an enthalpy-pressure diagram of a secondary loop of a heat pump system according to a second embodiment of the present invention;

[0022] Figure 6 shows a schematic diagram of a heat pump system according to a first comparative example;

[0023] Figure 7 and Figure 8 enthalpy-pressure diagrams of a primary loop and a secondary loop of a heat pump system according to a first comparative example are respectively shown;

[0024] Fig. 9 a schematic diagram showing a high temperature circuit of a heat pump system according to a second comparative example; and

[0025] Fig.10 An enthalpy-pressure diagram of a secondary loop of a heat pump system according to a second comparative example is shown. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings. The following description is exemplary in nature and is not intended to limit the present invention and its application or use. In each view, corresponding components or parts are marked with the same reference numerals.

[0027] Figure 1 A schematic diagram of a heat pump system S according to a first embodiment of the present invention is shown, and the heat pump system S is a cascade system, including a first-stage circuit (low-temperature circuit) and a second-stage circuit (high-temperature circuit). Preferably, the refrigerant in the first-stage circuit is different from the refrigerant in the second-stage circuit, so as to be suitable for different working conditions. For example, the first-stage circuit can use conventional HFC, HCFC refrigerants, such as R410A, R22, R134a, etc., and the second-stage circuit can use a refrigerant with a critical temperature above 100°C, such as HFO refrigerants such as R245fa or R1233zde.

[0028] The first-stage circuit includes a low-temperature refrigerant circulation main path formed by connecting the first-stage compressor PL, the condenser evaporator EC, the first-stage main expansion valve VL and the first-stage evaporator EL in sequence through pipelines (the arrow in the attached figure indicates the flow direction of the refrigerant). That is, the first-stage compressor PL, the condenser evaporator EC, the first-stage main expansion valve VL and the first-stage evaporator EL are arranged in the first-stage circuit in sequence along the flow direction of the low-temperature refrigerant (the first refrigerant). The second-stage circuit includes a high-temperature refrigerant circulation main path formed by connecting the second-stage compressor PH, the condenser CH, the jet enthalpy heat exchanger EH, the second-stage main expansion valve VH and the condenser evaporator EC in sequence through pipelines (the arrow in the attached figure indicates the flow direction of the refrigerant). That is, the second-stage compressor PH, the condenser CH, the jet enthalpy heat exchanger EH, the second-stage main expansion valve VH and the condenser evaporator EC are arranged in the second-stage circuit in sequence along the flow direction of the high-temperature refrigerant (the second refrigerant).

[0029] The primary circuit and the secondary circuit are thermally connected through the condenser evaporator EC. That is, the condenser evaporator EC includes a refrigerant evaporation channel as a part of the secondary circuit and a refrigerant condensation channel as a part of the primary circuit, and the high-temperature refrigerant exchanges heat with the low-temperature refrigerant in the condenser evaporator EC, whereby the second refrigerant in the refrigerant evaporation channel is evaporated and the first refrigerant in the refrigerant condensation channel is condensed. In other words, the condenser evaporator EC serves as a condenser in the primary circuit and as an evaporator in the secondary circuit.

[0030] The heat pump system S also includes an injection enthalpy increase branch, in which a first branch expansion valve VX and an injection enthalpy increase heat exchanger EH may be arranged. The injection enthalpy increase heat exchanger EH is a refrigerant-refrigerant heat exchanger, which may be a plate heat exchanger, a shell and tube heat exchanger, etc. The injection enthalpy increase heat exchanger EH includes a second refrigerant channel as part of the second-stage loop and a first refrigerant channel as part of the injection enthalpy increase branch. In the heat pump system with the injection enthalpy increase branch, the first-stage compressor PL is constructed as an injection enthalpy increase compressor. Compared with ordinary compressors, the injection enthalpy increase compressor has a first refrigerant replenishment port PLI in addition to an air intake port and an air discharge port. The first-stage loop also includes a first branch point P located downstream of the condenser evaporator EC and on the path between the condenser evaporator EC and the first-stage main expansion valve VL. The jet enthalpy increase branch extends from the first branch point P, passes through the first refrigerant channel in the jet enthalpy increase heat exchanger EH and is finally connected to the first refrigerant replenishing port PLI of the first stage compression PL (the arrow in the accompanying drawing indicates the flow direction of the refrigerant), and the first branch expansion valve VX is arranged on the path between the first branch point P and the inlet of the first refrigerant channel (at point c).

[0031] Refer to the following Figures 2 to 3 The working process of the heat pump system S is described. In the first-stage circuit, the first refrigerant discharged from the first-stage compressor PL is in a high-temperature and high-pressure state (corresponding to Figure 2 The first refrigerant then enters the condenser evaporator EC through the pipeline, where it is condensed and converted into a liquid state (corresponding to Figure 2 The state of midpoint 3). In this embodiment, the condensation temperature of the first-stage circuit is about 80°C. The condensed first refrigerant is discharged from the condenser evaporator EC. Then, a part of the first refrigerant (hereinafter referred to as the first refrigerant first part) enters the first-stage main circuit expansion valve VL, and is converted into a low-temperature and low-pressure refrigerant (corresponding to Figure 2 Then, the first part of the first refrigerant enters the first-stage evaporator EL, where it is evaporated and transformed into a gaseous state (corresponding to Figure 2 The state of the midpoint 1). In this embodiment, the evaporation temperature of the first-stage circuit is about 30° C. The first part of the evaporated first refrigerant is discharged from the first-stage evaporator EL and then enters the air inlet of the first-stage compressor PL.

[0032] Another part of the first refrigerant discharged from the condenser evaporator EC (hereinafter referred to as the second part of the first refrigerant) enters the jet enthalpy increase branch from the first branch point P on the first-stage circuit. After throttling through the first branch expansion valve VX, the pressure of the second part of the first refrigerant decreases, and it changes from a liquid refrigerant to a gas-liquid mixed refrigerant. At this time, the temperature of the second part of the first refrigerant is about 53°C. Subsequently, the second part of the first refrigerant enters the first refrigerant channel in the jet enthalpy increase heat exchanger EH, that is, at the inlet point c of the first refrigerant channel of the jet enthalpy increase heat exchanger EH, the temperature of the second part of the first refrigerant is about 53°C. The second part of the first refrigerant exchanges heat with the second refrigerant in the second refrigerant channel in the first refrigerant channel, absorbs the heat of the second refrigerant and reduces the temperature of the second refrigerant. Subsequently, the second part of the first refrigerant is discharged from the outlet point d of the first refrigerant channel of the jet enthalpy increase heat exchanger EH and is delivered to the first refrigerant replenishment port PLI of the first-stage compressor PL connected to the medium-pressure part. The second part of the first refrigerant delivered back to the first refrigerant replenishing port PLI of the first stage compressor PL is finally mixed with the first part of the first refrigerant entering from the air inlet of the first stage compressor PL in the first stage compressor PL, and is compressed again to the state of point 2 before being discharged from the first stage compressor PL. Preferably, the first refrigerant discharged from the outlet point d of the first refrigerant channel of the injection enthalpy heat exchanger EH and delivered to the first refrigerant replenishing port PLI of the first stage compressor PL is in a pure gas state, thereby further effectively reducing the refrigerant temperature immediately upstream of the main expansion valve in the second stage circuit and effectively improving the system efficiency.

[0033] In the second stage circuit, the second refrigerant discharged from the second stage compressor PH is in a high temperature and high pressure gas state (corresponding to Figure 3 The second refrigerant then enters the second-stage condenser CH through the pipeline, where it is condensed and converted into a liquid state (corresponding to Figure 3 The state of point 7 in the middle). In this embodiment, the condensing temperature of the second-stage circuit is about 135°C. The condensed second refrigerant is discharged from the condensing evaporator EC, and then enters the jet enthalpy heat exchanger EH from the inlet point a of the second refrigerant channel of the jet enthalpy heat exchanger EH. In the jet enthalpy heat exchanger EH, the heat of the second refrigerant in the second refrigerant channel is absorbed by the second part of the first refrigerant in the first refrigerant channel, thereby further reducing the temperature of the second refrigerant, and then is discharged from the jet enthalpy heat exchanger EH from the outlet point b of the second refrigerant channel. Then, the second refrigerant enters the second-stage main expansion valve VH, and is converted into a temperature corresponding to the pressure drop of the second-stage main expansion valve VH. Figure 3The state of midpoint 8. Subsequently, the second refrigerant enters the refrigerant evaporation channel of the condenser evaporator EC. In the condenser evaporator EC, the second refrigerant in the refrigerant evaporation channel exchanges heat with the first refrigerant in the refrigerant condensation channel, and the second refrigerant is evaporated and converted into a gaseous state (corresponding to Figure 3 The state of the midpoint 5). In this embodiment, the evaporation temperature of the second-stage circuit is 75° C. The evaporated second refrigerant is discharged from the condenser evaporator EC and enters the air inlet of the second-stage compressor PH.

[0034] The following is combined with Figures 6 to 8 The heat pump system of the first comparative example is shown to illustrate the advantageous effects of the heat pump system according to the first embodiment of the present invention.

[0035] Figure 6 A schematic diagram of a heat pump system S' according to a first comparative example is shown. Similar to the first embodiment of the present invention, the heat pump system S' is also a cascade system including a first-stage circuit and a second-stage circuit. The main components, arrangement, connection mode, and selection of refrigerants of the first-stage circuit and the second-stage circuit are the same as those of the first embodiment of the present invention. For example, the first-stage circuit is formed by connecting the first-stage compressor PL, the condenser evaporator EC, the first-stage main expansion valve VL, and the first-stage evaporator EL in sequence along the flow direction of the low-temperature refrigerant (the first refrigerant). The second-stage circuit is formed by connecting the second-stage compressor PH, the second-stage condenser CH, the jet enthalpy heat exchanger EH, the second-stage main expansion valve VH, and the condenser evaporator EC in sequence along the flow direction of the high-temperature refrigerant (the second refrigerant), and the first-stage circuit and the second-stage circuit are thermally connected through the condenser evaporator EC.

[0036] Different from the first embodiment, in the heat pump system S', the second-stage compressor PH is constructed as an injection reheating compressor with an air supply port, and the injection reheating branch extends from the downstream of the injection reheating heat exchanger EH in the second-stage loop, and from the branch point Q between the injection reheating heat exchanger EH and the second-stage main expansion valve VH, and is connected to the air supply port of the second-stage compressor PH after passing through the second branch expansion valve VX and the injection reheating heat exchanger EH. Figure 7 and Figure 8 A portion of the second refrigerant discharged from the outlet b of the second refrigerant passage of the jet enthalpy heat exchanger EH (hereinafter referred to as the first portion of the second refrigerant) enters the second-stage main expansion valve VH, and is converted into a refrigerant having a pressure drop of 1.1 V and a pressure drop of 1.1 V. Figure 8 Then, the first part of the second refrigerant enters the condenser evaporator EC, where it is evaporated and transformed into a gaseous state (corresponding to point 8 in FIG. Figure 8The state of the midpoint 5), and then discharged from the condenser evaporator EC and enter the air inlet of the second stage compressor PL. Another part of the second refrigerant discharged from the outlet point b of the second refrigerant channel of the jet enthalpy heat exchanger EH (hereinafter referred to as the second part of the second refrigerant) enters the jet enthalpy branch from the branch point Q on the second stage circuit, and after throttling through the second branch expansion valve VX', the pressure of the second part of the second refrigerant is reduced. At this time, the temperature of the second part of the second refrigerant is the saturation temperature corresponding to the injection pressure, that is, about 103°C. Subsequently, the second part of the second refrigerant enters the first refrigerant channel in the jet enthalpy heat exchanger EH, that is, at the inlet point c of the first refrigerant channel of the jet enthalpy heat exchanger EH, the temperature of the second part of the second refrigerant is about 103°C. The second part of the second refrigerant exchanges heat with the second refrigerant in the second refrigerant channel in the first refrigerant channel, absorbs the heat of the second refrigerant and reduces the temperature of the second refrigerant, thereby reducing the temperature of the second refrigerant before the second stage main expansion valve VH. Then, the second part of the second refrigerant is discharged from the outlet point d of the first refrigerant channel of the jet enthalpy heat exchanger EH, and is delivered to the air supply port of the second-stage compressor PH which is connected to its medium-pressure part. The second part of the second refrigerant delivered back to the air supply port of the second-stage compressor PH is finally mixed with the first part of the second refrigerant which enters the second-stage compressor PH from the air inlet of the second-stage compressor PH, and is compressed again to a high-temperature and high-pressure gas (corresponding to the state of point 6) and then discharged from the second-stage compressor PH. Figure 8 It can be seen that the condensing temperature of the second-stage circuit is about 135°C, and the temperature of the second refrigerant after throttling by the second branch expansion valve VX' (i.e., point c) is about 103°C. Assuming the heat exchange temperature difference is 5°C, the temperature before the second-stage main expansion valve VH (corresponding to the temperature at point b) is about 108°C. This temperature far exceeds the long-term use tolerance temperature (about 70°C) of most electronic expansion valves, so it is difficult to find suitable electronic expansion valve products on the market, affecting the reliability of valve components and even the system.

[0037] In contrast, in the first embodiment of the present invention, the condensing temperature of the second-stage circuit can be higher than 100°C, for example, about 135°C, and the temperature of the first refrigerant after throttling by the first branch expansion valve VX in the jet enthalpy increase branch is about 53°C (i.e., the first refrigerant temperature at point c), so the first refrigerant in the jet enthalpy increase heat exchanger can fully cool the second refrigerant, so that the second refrigerant reaches a sufficiently low valve pre-temperature (i.e., the second refrigerant temperature at point b), i.e., lower than 70°C. For example, assuming that the heat exchange temperature difference is 5°C, the valve pre-temperature of the second-stage main expansion valve VH (i.e., the second refrigerant temperature at point b) is 58°C, and an ordinary electronic expansion valve can meet the temperature resistance requirements, thereby reducing the cost of the system and ensuring the reliable operation of the system.

[0038] Therefore, in the heat pump system according to the first embodiment of the present invention, on the one hand, by introducing a part of the first refrigerant in the first-stage loop that has been condensed by the condensing evaporator EC into the jet reheat increase branch, after being throttled by the first branch expansion valve VX, the condensed second refrigerant in the second-stage loop is fully cooled in the jet reheat increase heat exchanger EH using the first refrigerant with a lower temperature, the temperature before the second-stage main expansion valve VH in the second-stage loop can be significantly reduced, so that the system can adopt an ordinary electronic expansion valve, thereby reducing the cost of the system and ensuring the reliable operation of the system.

[0039] On the other hand, the first refrigerant discharged from the jet enthalpy increase heat exchanger EH (point d) is delivered to the first refrigerant replenishing port PLI of the first-stage compressor PL at a suitable medium temperature and medium pressure. Compared with the related scheme of delivering the medium-temperature and medium-pressure first refrigerant back to the inlet of the first-stage compressor PL or on the path before the inlet, the system efficiency is improved because the medium-temperature and medium-pressure first refrigerant is directly provided to the medium-pressure chamber of the first-stage compressor PL for further compression.

[0040] The second embodiment of the present invention is a modification made on the basis of the first embodiment of the present invention. Figure 4 and Figure 5 A second embodiment of the present invention will be described.

[0041] Similar to the first embodiment of the present invention, the heat pump system S according to the second embodiment of the present invention is also a cascade system including a first-stage circuit and a second-stage circuit. Among them, the main components, layout, connection method, selection of refrigerant, etc. of the first-stage circuit, the second-stage circuit and the injection enthalpy increase branch are the same as those of the first embodiment of the present invention, and will not be repeated here.

[0042] Different from the first embodiment of the present invention, the second embodiment of the present invention is further provided with a cooling branch circuit based on the heat pump system shown in the first embodiment of the present invention. The cooling branch circuit extends from the downstream of the jet enthalpy heat exchanger EH of the second-stage loop, passes through the throttle valve VY, and is finally connected to the second refrigerant replenishing port PHI of the second-stage compressor PH that is connected to the medium pressure chamber. Preferably, the cooling branch circuit extends from the second branch point R between the jet enthalpy heat exchanger EH and the second-stage main circuit expansion valve VH, so that the refrigerant supplied to the second refrigerant replenishing port PHI has a suitable temperature and pressure. See Figure 4 A portion of the second refrigerant discharged from the outlet b of the second refrigerant passage of the injection enthalpy heat exchanger EH (hereinafter referred to as the second refrigerant first portion) enters the second-stage main expansion valve VH, and is converted into a second refrigerant having a pressure drop effect of the second-stage main expansion valve VH. Figure 5Subsequently, the first part of the second refrigerant enters the condenser evaporator EC, where it is evaporated and transformed into a gaseous state (corresponding to Figure 5 The state of point 5 in the middle), and then discharged from the condensing evaporator EC into the air inlet of the second-stage compressor PL. Another part of the second refrigerant discharged from the outlet point b of the second refrigerant channel of the injection enthalpy increase heat exchanger EH (hereinafter referred to as the second part of the second refrigerant) enters the cooling branch from the second branch point R on the second-stage circuit. After throttling by the throttle valve VY, the pressure of the second part of the second refrigerant is reduced. Subsequently, the second part of the second refrigerant is injected into the medium-pressure chamber of the second-stage compressor PH at a lower temperature and a suitable pressure, and is in contact with the high-temperature gas in the medium-pressure chamber (the high-temperature gas is the part of the second refrigerant sucked from the air inlet of the second-stage compressor PH and compressed into the medium-pressure chamber, which is in contact with the high-temperature gas in the medium-pressure chamber). Figure 5 The state corresponding to point g in Figure 5 The state corresponding to point e in is compressed together to Figure 5 The gas is discharged from the second stage compressor PH after reaching the state corresponding to point 6 in the figure.

[0043] Compared with the first embodiment, the cooling branch added in the second embodiment can provide a refrigerant with a lower temperature to the replenishing port PHI of the second-stage compressor PH, thereby achieving the purpose of preventing the exhaust gas of the second-stage compressor from being overheated, thereby improving the controllability and efficiency of the system. Preferably, the second part of the second refrigerant supplied to the second refrigerant replenishing port PHI after being throttled by the throttle valve VY is in a pure liquid state, thereby providing a sufficient cooling effect with as little refrigerant as possible, and also facilitating the reduction of the refrigerant temperature immediately upstream of the main expansion valve in the second-stage circuit.

[0044] On the other hand, from Figure 5 It can be seen that the condensing temperature of the second-stage circuit is about 135°C. Since the first refrigerant in the jet enthalpy heat exchanger can fully cool the second refrigerant, the temperature at the outlet point b of the second refrigerant channel of the jet enthalpy heat exchanger is as low as 58°C. Therefore, the temperature of the second part of the second refrigerant entering the cooling branch is also low enough, and only a small amount of liquid injection is needed to meet the requirements for the exhaust temperature control of the second-stage compressor. Fig. 9 and Fig.10 In the second comparative example shown, since there is no injection enthalpy increase branch introduced from the first-stage circuit, it is impossible to provide sufficient cooling for the second refrigerant in the second-stage circuit. The temperature of the second refrigerant is relatively high, resulting in a large amount of liquid injection being required to meet the requirement of controlling the exhaust temperature of the second-stage compressor.

[0045] Fig. 9The schematic diagram of the second stage circuit of the second comparative example is shown. In the second comparative example, the cooling branch extends from the second branch point R between the second stage condenser CH and the second stage main circuit expansion valve VH, downstream of the second stage condenser CH of the second stage circuit, passes through the throttle valve VY, and is finally connected to the second refrigerant replenishing port PHI' of the second stage compressor PH which is connected to the mid-pressure chamber. Fig.10 A portion of the second refrigerant in the state corresponding to point 7 in FIG. 1 (hereinafter referred to as the second refrigerant first portion) enters the second-stage main circuit expansion valve VH and is converted into the second-stage main circuit expansion valve VH through the pressure reduction effect of the second-stage main circuit expansion valve VH. Fig.10 Subsequently, the first part of the second refrigerant enters the condenser evaporator EC, where it is evaporated and transformed into a gaseous state (corresponding to Fig.10 The second refrigerant is discharged from the condenser evaporator EC and then enters the air inlet of the second compressor PL. The other part of the second refrigerant discharged from the condenser CH (hereinafter referred to as the second part of the second refrigerant) enters the cooling branch from the second branch point R on the second circuit. After being throttled by the throttle valve VY, the pressure of the second part of the second refrigerant is reduced and converted into Fig.10 The state corresponding to point f' in the figure is then obtained, and the second part of the second refrigerant is then injected into the medium-pressure chamber of the second-stage compressor PH through the second refrigerant replenishing port PHI', and is in contact with the high-temperature gas in the medium-pressure chamber (the high-temperature gas is the part of the second refrigerant sucked from the air inlet of the second-stage compressor PH and compressed into the medium-pressure chamber, which is in contact with the high-temperature gas in the medium-pressure chamber). Fig.10 The state corresponding to the point g' in Fig.10 The state corresponding to point e in is compressed together to Fig.10 The gas is discharged from the second stage compressor PH after reaching the state corresponding to point 6 in the figure.

[0046] from Fig.10 As can be seen from the figure, the condensing temperature of the second-stage circuit is about 135°C. Assuming that the subcooling degree of the condenser CH is 5°C, the temperature of the second refrigerant discharged from the condenser CH in the state corresponding to point 7 is about 130°C, which is significantly higher than Figure 5 The temperature of the second refrigerant at point b is shown (58°C). Assuming that the refrigerant is R245fa, the saturation temperature corresponding to the injection pressure is about 103°C, and assuming that the pressure of the cooling refrigerant injected into the medium-pressure chamber remains unchanged after mixing with the refrigerant in the state g / g' in the medium-pressure chamber, other parameters of the refrigerant in the state f / f' and the state g / g' are shown in the following table (Table 1).

[0047] Table 1

[0048]

[0049] According to the above parameters, assuming that the mass of the refrigerant in the medium pressure chamber of the second-stage compressor PH (i.e., the refrigerant in the state corresponding to point g or point g') is 0.1kg, and the target temperature of the mixed state e is 110°C, it can be calculated that the mass of the refrigerant for cooling required to be injected according to the second embodiment of the present invention is about 0.015kg, while the mass of the refrigerant for cooling required to be injected according to the second comparative example is about 0.033kg. Therefore, the heat pump system according to the second embodiment of the present invention can achieve the purpose of controlling the exhaust temperature of the second-stage compressor with a small amount of liquid injection, further improving the system efficiency.

[0050] The above describes a high temperature heat pump system according to a preferred embodiment of the present invention in conjunction with a specific embodiment. It is understood that the above description is only exemplary and not restrictive, and those skilled in the art can conceive of various variations and modifications with reference to the above description without departing from the scope of the present invention. These variations and modifications are also included in the protection scope of the present invention.

Claims

1. A heat pump system (S), comprising: A first-stage circuit, on which a first-stage compressor (PL), a condenser evaporator (EC), a first-stage main circuit expansion valve (VL) and a first-stage evaporator (EL) are sequentially arranged along the refrigerant flow direction; a second-stage circuit, on which a second-stage compressor (PH), a second-stage condenser (CH), an injection enthalpy heat exchanger (EH), a second-stage main expansion valve (VH) and the condenser evaporator (EC) are sequentially arranged along the refrigerant flow direction, wherein the condenser evaporator (EC) is used as a condenser in the first-stage circuit and as an evaporator in the second-stage circuit; and Injection enthalpy increase branch, It is characterized in that the first-stage compressor has a first refrigerant replenishment port (PLI), and the jet enthalpy increase branch extends from a first branch point (P) on the first-stage circuit located downstream of the condenser evaporator (EC), passes through the jet enthalpy increase heat exchanger (EH), and is connected to the first refrigerant replenishment port (PLI).

2. The heat pump system (S) according to claim 1, characterized in that: The heat pump system is configured such that the first refrigerant supplied to the first refrigerant supply inlet (PLI) via the injection enthalpy increase branch is in a pure gas state.

3. The heat pump system (S) according to claim 1, characterized in that: On the injection enthalpy increase branch, a first branch expansion valve (VX) is provided between the first branch point (P) and the injection enthalpy increase heat exchanger (EH).

4. The heat pump system (S) according to any one of claims 1 to 3, characterized in that: The second-stage compressor (PH) has a second refrigerant replenishing port (PHI), and the heat pump system also includes a cooling branch, which extends from a second branch point (R) on the second-stage circuit between the injection enthalpy heat exchanger (EH) and the second-stage main expansion valve (VH) and is connected to the second refrigerant replenishing port (PHI).

5. The heat pump system (S) according to claim 4, characterized in that: The heat pump system is configured such that the second refrigerant supplied to the second refrigerant replenishing inlet (PHI) via the cooling branch is in a pure liquid state.

6. The heat pump system (S) according to claim 4, characterized in that: A throttle valve (VY) is arranged on the cooling branch.

7. The heat pump system (S) according to any one of claims 1 to 3, characterized in that: The heat pump system is configured such that the condensing temperature of the second-stage condenser (CH) is higher than 100°C and the refrigerant temperature immediately upstream of the second-stage main expansion valve (VH) is lower than 70°C.

8. The heat pump system (S) according to any one of claims 1 to 3, characterized in that: The first refrigerant in the primary circuit is different from the second refrigerant in the secondary circuit.

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