Refrigerant cascade jet heat pump system based on external heat source and control method thereof

Abstract

The present invention discloses a refrigerant cascade jet heat pump system based on an external heat source and a control method thereof, wherein the system comprises a heat pump unit and an internal heat source heat exchange unit, wherein the internal heat source heat exchange unit is connected to the heat pump unit, and the refrigerant cascade jet heat pump system based on an external heat source also comprises an external heat source heat exchange unit, wherein the external heat source heat exchange unit is connected to the internal heat source heat exchange unit and the heat pump unit; in view of the problem that the internal heat source heat supplement is insufficient and the system capacity is seriously attenuated under ultra-low temperature conditions, the present invention increases the heating capacity of the unit by adding external heat source heat supplement on the basis of the internal heat source jet of the system, thereby achieving no attenuation of the system capacity under ultra-low temperature conditions and achieving the purpose of improving the reliability of the unit.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pump systems, and in particular to a refrigerant cascade jet heat pump system based on an external heat source and a control method thereof. Background Art

[0002] Air conditioning and heating equipment account for the largest share of building energy consumption, reaching more than 65%. On the other hand, people have higher requirements for the comfort and hygiene of their living environment. Conventional air conditioning and heating equipment have serious heating capacity and energy efficiency degradation in low-temperature environments, making it difficult to meet the needs of high-quality life and energy efficiency requirements. At present, heat pump system units have begun to enter ordinary households and are accepted by consumers.

[0003] However, the capacity and energy efficiency of the heat pump system also have the problem of attenuation in low temperature environment. Through the injection enthalpy increase technology, the subcooling degree of the heat pump liquid pipe can be increased to increase the heat exchange temperature difference between the refrigerant and the ambient temperature in the evaporator, increase the evaporation heat exchange, and increase the compression work of the compressor, thereby improving the total heating capacity and energy efficiency of the heat pump system. However, the injection heat of the injected refrigerant comes from the heat pump itself, and the enthalpy difference of the injection process cannot be converted into heating capacity. It is a passive injection, and the improvement of heat pump performance is limited.

[0004] Therefore, it is of great significance to study a heat pump injection system and use injection technology to convert external low-grade heat sources into heating capacity to maximize the heating capacity and energy efficiency of the heat pump. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a refrigerant cascade injection heat pump system based on an external heat source and a control method thereof, which aims to solve the problems of insufficient internal heat source heating and serious system capacity attenuation under ultra-low temperature conditions by adding external heat source heating on the basis of internal heat source injection in the system to increase the heating capacity of the unit, thereby achieving no system capacity attenuation under ultra-low temperature conditions and achieving the purpose of improving the reliability of the unit.

[0006] The refrigerant cascade jet heat pump system based on an external heat source of the present invention includes a heat pump unit and an internal heat source heat exchange unit, and the internal heat source heat exchange unit is connected to the heat pump unit. The refrigerant cascade jet heat pump system based on an external heat source also includes an external heat source heat exchange unit, and the external heat source heat exchange unit is connected to the internal heat source heat exchange unit and the heat pump unit.

[0007] The refrigerant cascade jet heat pump system based on an external heat source of the present invention, wherein the external heat source heat exchange unit is connected in series with the internal heat source heat exchange unit; the heat pump unit includes a DC variable frequency compressor, a high-pressure switch, a four-way reversing valve, a fin heat exchanger, a main electronic expansion valve, a gas-liquid separator and a low-pressure switch, the internal heat source heat exchange unit includes an internal heat source heat exchanger, an internal heat source jet electronic expansion valve, a main water side heat exchanger and a terminal water pump, and the external heat source heat exchange unit includes an external heat source jet electronic expansion valve, an external heat source heat exchanger, an external heat source side water pump and a one-way valve; the outlet end of the DC variable frequency compressor is connected to the first end of the four-way reversing valve, the second end of the four-way reversing valve is connected in series with the fin heat exchanger and the main electronic expansion valve in sequence, and then connected to the second end of the internal heat source heat exchanger, and the first end of the internal heat source heat exchanger is connected to the first end of the main water side heat exchanger The second end of the main water side heat exchanger is connected to the fourth end of the four-way reversing valve, the two ends of the internal heat source injection electronic expansion valve are respectively connected to the fourth end of the internal heat source heat exchanger and the first end of the main water side heat exchanger, the outlet end of the terminal water pump is connected to the third end of the main water side heat exchanger, the third end of the four-way reversing valve is connected in series with the gas-liquid separator and then connected to the inlet end of the DC variable frequency compressor, the high-pressure switch is installed on the pipeline between the DC variable frequency compressor and the four-way reversing valve, and the low-pressure switch is installed on the pipeline between the gas-liquid separator and the DC variable frequency compressor; the first end of the external heat source heat exchanger is connected in series with the external heat source injection electronic expansion valve and then connected to the third end of the internal heat source heat exchanger, the second end of the external heat source heat exchanger is connected in series with the one-way valve and then connected to the inlet end of the DC variable frequency compressor, and the outlet end of the external heat source side water pump is connected to the fourth end of the external heat source heat exchanger.

[0008] The refrigerant cascade jet heat pump system based on an external heat source of the present invention, wherein the external heat source heat exchange unit is connected in parallel with the internal heat source heat exchange unit; the heat pump unit includes a DC variable frequency compressor, a high-pressure switch, a four-way reversing valve, a fin heat exchanger, a main electronic expansion valve, a gas-liquid separator and a low-pressure switch, the internal heat source heat exchange unit includes an internal heat source heat exchanger, an internal heat source jet electronic expansion valve, a main water side heat exchanger and a terminal water pump, and the external heat source heat exchange unit includes an external heat source jet electronic expansion valve, an external heat source heat exchanger, an external heat source side water pump and a one-way valve; the outlet end of the DC variable frequency compressor is connected to the first end of the four-way reversing valve, the second end of the four-way reversing valve is connected in series with the fin heat exchanger and the main electronic expansion valve in sequence, and then connected to the second end of the internal heat source heat exchanger, the first end of the internal heat source heat exchanger is connected to the first end of the main water side heat exchanger, and the second end of the main water side heat exchanger is connected to The fourth end of the four-way reversing valve is connected, the two ends of the internal heat source injection electronic expansion valve are respectively connected to the fourth end of the internal heat source heat exchanger and the first end of the main water side heat exchanger, the outlet end of the terminal water pump is connected to the third end of the main water side heat exchanger, the third end of the four-way reversing valve is connected in series with the gas-liquid separator and then connected to the inlet end of the DC variable frequency compressor, the high-pressure switch is installed on the pipeline between the DC variable frequency compressor and the four-way reversing valve, and the low-pressure switch is installed on the pipeline between the gas-liquid separator and the DC variable frequency compressor; the first end of the external heat source heat exchanger is connected in series with the external heat source injection electronic expansion valve and then connected to the second end of the internal heat source heat exchanger, the second end of the external heat source heat exchanger is connected in series with a one-way valve and then connected to the inlet end of the DC variable frequency compressor, the outlet end of the external heat source side water pump is connected to the fourth end of the external heat source heat exchanger, and the third end of the internal heat source heat exchanger is connected to the inlet end of the DC variable frequency compressor.

[0009] A control method for a refrigerant cascade jet heat pump system based on an external heat source, the control method is a series jet control method, in the heating mode, a part of the refrigerant after condensation and heat release in the main water side heat exchanger flows through the main path: passes through the internal heat source heat exchanger, the main electronic expansion valve, the fin heat exchanger and the four-way reversing valve, and then returns to the DC variable frequency compressor; the other part enters the jet auxiliary path, passes through the internal heat source jet electronic expansion valve for throttling, and then enters the internal heat source heat exchanger to exchange heat with the main refrigerant, the refrigerant evaporates and absorbs heat, and then passes through the external heat source jet electronic expansion valve for throttling, enters the external heat source heat exchanger, exchanges heat with the external heat source, and enters the medium-pressure chamber of the DC variable frequency compressor after further evaporation and heat absorption.

[0010] A control method for a refrigerant cascade jet heat pump system based on an external heat source, wherein an internal heat source jet electronic expansion valve is controlled according to a target subcooling degree, and subcooling degree is defined as the main inlet temperature T of the internal heat source heat exchanger. liq1 -Internal heat source heat exchanger main outlet temperature T liq2; When |actual subcooling - target subcooling|≤1℃, the internal heat source injection electronic expansion valve keeps the current opening unchanged; when the actual subcooling - target superheating > 1℃, the internal heat source injection electronic expansion valve performs valve closing control based on the current opening; when the actual subcooling - target subcooling <-1℃, the internal heat source injection electronic expansion valve performs valve opening control based on the current opening; at the same time, when the actual current exhaust temperature detected is > the target upper limit exhaust temperature T d When the set value is reached, the internal heat source injection electronic expansion valve will be set first according to the target upper limit exhaust temperature T d Perform valve opening control for control target;

[0011] When the exhaust gas superheat (T d -T liq1 ) is greater than the exhaust superheat setting value of the injection auxiliary circuit, the internal heat source injection electronic expansion valve is opened to the initial opening setting value, and then the valve opening is controlled according to the target subcooling degree;

[0012] For external heat source injection electronic expansion valve: a. If the temperature on the external heat source side is T h,in ≥External heat source injection inlet temperature T inj,in +2℃, the water pump on the external heat source side starts to run, and the electronic expansion valve on the external heat source side opens to the actual detected current △T (external heat source side temperature T hin - External heat source side injection inlet temperature T inj，in ) corresponding to the valve opening, and then perform valve opening control according to the control model; when the actual △T ≥ △ Ttarget At this time, the external heat source injection electronic expansion valve opens to the maximum; at the same time, if △T gradually decreases, the heat provided by the external heat source decreases, and the external heat source injection electronic expansion valve gradually closes accordingly, but the internal heat source injection still needs to be guaranteed. In order to ensure the smooth flow of the series injection auxiliary path, the minimum opening degree PMV of the external heat source injection electronic expansion valve is limited. min , b. If the temperature on the external heat source side is T h,in ≤External heat source injection inlet temperature T inj,in , the external heat source does not provide heat, the water pump on the external heat source side stops running, and the injection electronic expansion valve on the external heat source side opens to the maximum opening and maintains it.

[0013] A control method for a refrigerant cascade jet heat pump system based on an external heat source, the control method is a parallel jet control method, in the heating mode, after condensing and releasing heat in the main water side heat exchanger, a part of the refrigerant flows through the main path: after passing through the internal heat source heat exchanger, the main electronic expansion valve, the fin heat exchanger and the four-way reversing valve, it returns to the DC variable frequency compressor; a part of the refrigerant enters the internal heat source jet auxiliary path, is throttled by the internal heat source jet electronic expansion valve, enters the internal heat source heat exchanger to exchange heat with the main path refrigerant; another part of the refrigerant enters the external heat source jet auxiliary path, is throttled by the external heat source jet electronic expansion valve, enters the external heat source heat exchanger to exchange heat with the external heat source, evaporates and absorbs heat, merges with the refrigerant in the internal heat source jet auxiliary path, and enters the medium-pressure chamber of the DC variable frequency compressor.

[0014] A control method for a refrigerant cascade jet heat pump system based on an external heat source, wherein an internal heat source jet electronic expansion valve is controlled according to a target subcooling degree, and subcooling degree is defined as the main inlet temperature T of the internal heat source heat exchanger. liq1 -Internal heat source heat exchanger main outlet temperature T liq2 ; When |actual subcooling - target subcooling|≤1℃, the internal heat source injection electronic expansion valve keeps the current opening unchanged; when the actual subcooling - target superheating > 1℃, the internal heat source injection electronic expansion valve performs valve closing control based on the current opening; when the actual subcooling - target subcooling <-1℃, the internal heat source injection electronic expansion valve performs valve opening control based on the current opening; at the same time, when the actual current exhaust temperature detected is > the target upper limit exhaust temperature T d When the set value is reached, the internal heat source injection electronic expansion valve will be set first according to the target upper limit exhaust temperature T d Perform valve opening control for control target;

[0015] When the exhaust gas superheat (T d -T liq1 ) is greater than the exhaust superheat setting value of the injection auxiliary circuit, the internal heat source injection electronic expansion valve is opened to the initial opening setting value, and then the valve opening is controlled according to the target subcooling degree;

[0016] For external heat injection electronic expansion valve: a. If the temperature on the external heat source side is T h,in ≥External heat source injection inlet temperature T inj,in +2℃, the water pump on the external heat source side starts to run, and the electronic expansion valve on the external heat source side opens to the actual detected current △T (external heat source side temperature T hin - External heat source side injection inlet temperature T inj，in ) corresponding to the valve opening, and then control the valve opening according to the control model; b. If the temperature on the external heat source side T h,in ≤External heat source injection inlet temperature T inj,in, the external heat source does not provide heat, the water pump on the external heat source side stops running, and the injection electronic expansion valve on the external heat source side remains closed.

[0017] When the exhaust gas superheat (T d -T liq1 ) is less than the exhaust superheat setting value for closing the auxiliary injection line, the internal heat source injection electronic expansion valve and the external heat source injection electronic expansion valve are closed.

[0018] The present invention aims to solve the problem of insufficient internal heat source heating and serious system capacity attenuation under ultra-low temperature conditions. By adding external heat source heating on the basis of internal heat source injection in the system, the heating capacity of the unit is increased, thereby achieving no system capacity attenuation under ultra-low temperature conditions and achieving the purpose of improving the reliability of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 is the pressure-enthalpy diagram of the heat pump system without injection;

[0021] Figure 2 It is a principle diagram of double heat source series injection of a refrigerant cascade injection heat pump system based on an external heat source according to the present invention;

[0022] Figure 3 The present invention relates to a pressure-enthalpy diagram of a double heat source series injection of a refrigerant cascade injection heat pump system based on an external heat source;

[0023] Figure 4 It is a principle diagram of a dual heat source parallel injection of a refrigerant cascade injection heat pump system based on an external heat source according to the present invention;

[0024] Figure 5 The present invention relates to a pressure-enthalpy diagram of a refrigerant cascade injection heat pump system with dual heat sources injected in parallel based on an external heat source.

[0025] Figure 6 It is a control model diagram of an external heat source injection electronic expansion valve when dual heat sources are injected in series in a refrigerant cascade injection heat pump system based on an external heat source of the present invention;

[0026] Figure 7 It is a control model diagram of an external heat source injection electronic expansion valve when dual heat sources are injected in parallel in a refrigerant cascade injection heat pump system based on an external heat source of the present invention.

[0027] As shown in the figure, among them: 1-DC variable frequency compressor; 2-main water side heat exchanger; 3-main electronic expansion valve; 4-fin heat exchanger; 5-four-way reversing valve; 6-gas-liquid separator; 7-internal heat source heat exchanger; 8-internal heat source injection electronic expansion valve; 9-external heat source injection electronic expansion valve; 10-external heat source heat exchanger; 11-terminal water pump; 12-external heat source side water pump; 13-check valve; 14-high pressure switch; 15-low pressure switch. DETAILED DESCRIPTION

[0028] The following will disclose multiple embodiments of the present invention with drawings. For the purpose of clear description, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present invention. That is, in some embodiments of the present invention, these practical details are not necessary. In addition, for the purpose of simplifying the drawings, some conventional structures and components will be depicted in a simple schematic manner in the drawings.

[0029] In addition, in the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes, and do not specifically refer to the order or sequence, nor are they used to limit the present invention. They are only used to distinguish components or operations described with the same technical terms, and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0030] Implementation Method 1

[0031] The refrigerant cascade jet heat pump system based on an external heat source of the present invention includes a heat pump unit and an internal heat source heat exchange unit, and the internal heat source heat exchange unit is connected to the heat pump unit. The refrigerant cascade jet heat pump system based on an external heat source also includes an external heat source heat exchange unit, and the external heat source heat exchange unit is connected to the internal heat source heat exchange unit and the heat pump unit.

[0032] The external heat source heat exchange unit is connected in series with the internal heat source heat exchange unit; the heat pump unit includes a DC variable frequency compressor 1, a high-pressure switch 14, a four-way reversing valve 5, a fin heat exchanger 4, a main electronic expansion valve 3, a gas-liquid separator 6 and a low-pressure switch 15, the internal heat source heat exchange unit includes an internal heat source heat exchanger 7, an internal heat source injection electronic expansion valve 8, a main water side heat exchanger 2 and a terminal water pump 11, and the external heat source heat exchange unit includes an external heat source injection electronic expansion valve 9, an external heat source heat exchanger 10, an external heat source side water pump 12 and a one-way valve 13; the outlet end of the DC variable frequency compressor 1 is connected to the first end of the four-way reversing valve 5, the second end of the four-way reversing valve 5 is connected in series with the fin heat exchanger 4 and the main electronic expansion valve 3 in sequence, and then connected to the second end of the internal heat source heat exchanger 7, the first end of the internal heat source heat exchanger 7 is connected to the first end of the main water side heat exchanger 2, and the second end of the main water side heat exchanger 2 is connected to the four The fourth end of the four-way reversing valve 5 is connected, the two ends of the internal heat source injection electronic expansion valve 8 are respectively connected to the fourth end of the internal heat source heat exchanger 7 and the first end of the main water side heat exchanger 2, the outlet end of the terminal water pump 11 is connected to the third end of the main water side heat exchanger 2, the third end of the four-way reversing valve 5 is connected in series with the gas-liquid separator 6 and then connected to the inlet end of the DC variable frequency compressor 1, the high-pressure switch 14 is installed on the pipeline between the DC variable frequency compressor 1 and the four-way reversing valve 5, and the low-pressure switch 15 is installed on the pipeline between the gas-liquid separator 6 and the DC variable frequency compressor 1; the first end of the external heat source heat exchanger 10 is connected in series with the external heat source injection electronic expansion valve 9 and then connected to the third end of the internal heat source heat exchanger 7, the second end of the external heat source heat exchanger 10 is connected in series with the one-way valve 13 and then connected to the inlet end of the DC variable frequency compressor 1, and the outlet end of the external heat source side water pump 12 is connected to the fourth end of the external heat source heat exchanger 10.

[0033] A control method for a refrigerant cascade jet heat pump system based on an external heat source, which is a series jet control method. In the heating mode, a part of the refrigerant after condensation and heat release in the main water side heat exchanger flows through the main circuit: after passing through the internal heat source heat exchanger, the main electronic expansion valve, the fin heat exchanger and the four-way reversing valve, it returns to the DC variable frequency compressor; the other part enters the jet auxiliary circuit, passes through the internal heat source jet electronic expansion valve for throttling, and then enters the internal heat source heat exchanger for heat exchange with the main circuit refrigerant. The refrigerant evaporates and absorbs heat, and then passes through the external heat source jet electronic expansion valve for throttling, enters the external heat source heat exchanger, exchanges heat with the external heat source, and enters the medium-pressure chamber of the DC variable frequency compressor after further evaporation and heat absorption.

[0034] like Figure 3 The pressure-enthalpy diagram of the dual heat source series injection of the refrigerant cascade injection heat pump system based on the external heat source is shown. The state points of the refrigerant are as follows: V1 is the state point of the compressor suction port, V2 is the state point of the compressor exhaust port, V3 is the state point before the main electronic expansion valve throttling, V4 is the state point after the main electronic expansion valve throttling, V5 is the state point after the condenser releases heat, V'6-i is the state point after the internal heat source electronic expansion valve is throttled, V 6-i is the state point after heat exchange in the internal heat source heat exchanger, V' 7-o is the state point after the external heat source electronic expansion valve is throttled, V 7-o It is the state point after heat exchange in the external heat source heat exchanger, V8 is the state point when the compressor reaches the medium pressure chamber after one compression, and V9 is the state point after the series injection auxiliary refrigerant and the one-compressed refrigerant are mixed in the compressor medium pressure chamber. The heating capacity of the heat pump system during series injection is:

[0035] Q k =Q e +W+Q inj,out

[0036] Among them, Q k Q is the heat exchange capacity of the condenser, i.e. the heating capacity; e is the heat exchange of the evaporator; W is the power consumption of the compressor; Q inj,out It is the heat absorbed by the refrigerant in the external heat source heat exchanger.

[0037]

[0038] Q inj,out =m inj ×(V 7-o -V' 7-o ).

[0039] The control method of the refrigerant cascade injection heat pump system based on the external heat source, the internal heat source injection electronic expansion valve is controlled according to the target subcooling degree, and the definition of subcooling degree = the main inlet temperature T of the internal heat source heat exchanger liq1 -Internal heat source heat exchanger main outlet temperature T liq2 ; When |actual subcooling - target subcooling|≤1℃, the internal heat source injection electronic expansion valve keeps the current opening unchanged; when the actual subcooling - target superheating > 1℃, the internal heat source injection electronic expansion valve performs valve closing control based on the current opening; when the actual subcooling - target subcooling <-1℃, the internal heat source injection electronic expansion valve performs valve opening control based on the current opening; at the same time, when the actual current exhaust temperature detected is > the target upper limit exhaust temperature T d When the set value is reached, the internal heat source injection electronic expansion valve will be set first according to the target upper limit exhaust temperature T d Perform valve opening control for control target;

[0040] When the exhaust gas superheat (T d -T liq1 ) is greater than the exhaust superheat setting value of the injection auxiliary circuit, the internal heat source injection electronic expansion valve is opened to the initial opening setting value, and then the valve opening is controlled according to the target subcooling degree;

[0041] For external heat source injection electronic expansion valve: a. If the temperature on the external heat source side is T h,in ≥External heat source injection inlet temperature T inj,in +2℃, the water pump on the external heat source side starts to run, and the electronic expansion valve on the external heat source side opens to the actual detected current △T (external heat source side temperature T hin - External heat source side injection inlet temperature T inj，in ) corresponding to the valve opening, and then perform valve opening control according to the control model; when the actual △T ≥ △ Ttarget At this time, the external heat source injection electronic expansion valve opens to the maximum; at the same time, if △T gradually decreases, the heat provided by the external heat source decreases, and the external heat source injection electronic expansion valve gradually closes accordingly, but the internal heat source injection still needs to be guaranteed. In order to ensure the smooth flow of the series injection auxiliary path, the minimum opening degree PMV of the external heat source injection electronic expansion valve is limited. min , b. If the temperature on the external heat source side is T h,in ≤External heat source injection inlet temperature T inj,in , the external heat source does not provide heat, the water pump on the external heat source side stops running, and the injection electronic expansion valve on the external heat source side opens to the maximum opening and maintains it.

[0042] Implementation Method 2

[0043] The refrigerant cascade jet heat pump system based on an external heat source of the present invention includes a heat pump unit and an internal heat source heat exchange unit, and the internal heat source heat exchange unit is connected to the heat pump unit. The refrigerant cascade jet heat pump system based on an external heat source also includes an external heat source heat exchange unit, and the external heat source heat exchange unit is connected to the internal heat source heat exchange unit and the heat pump unit.

[0044] The external heat source heat exchange unit is connected in parallel with the internal heat source heat exchange unit; the heat pump unit includes a DC variable frequency compressor 1, a high-pressure switch 14, a four-way reversing valve 5, a fin heat exchanger 4, a main electronic expansion valve 3, a gas-liquid separator 6 and a low-pressure switch 15, the internal heat source heat exchange unit includes an internal heat source heat exchanger 7, an internal heat source injection electronic expansion valve 8, a main water side heat exchanger 2 and a terminal water pump 11, and the external heat source heat exchange unit includes an external heat source injection electronic expansion valve 9, an external heat source heat exchanger 10, an external heat source side water pump 12 and a one-way valve 13; the outlet end of the DC variable frequency compressor 1 is connected to the first end of the four-way reversing valve 5, the second end of the four-way reversing valve 5 is connected in series with the fin heat exchanger 4 and the main electronic expansion valve 3 in sequence, and then connected to the second end of the internal heat source heat exchanger 7, the first end of the internal heat source heat exchanger 7 is connected to the first end of the main water side heat exchanger 2, the second end of the main water side heat exchanger 2 is connected to the fourth end of the four-way reversing valve 5, and the internal The two ends of the heat source injection electronic expansion valve 8 are respectively connected to the fourth end of the internal heat source heat exchanger 7 and the first end of the main water side heat exchanger 2, the outlet end of the terminal water pump 11 is connected to the third end of the main water side heat exchanger 2, the third end of the four-way reversing valve 5 is connected in series with the gas-liquid separator 6 and then connected to the inlet end of the DC variable frequency compressor 1, the high-pressure switch 14 is installed on the pipeline between the DC variable frequency compressor 1 and the four-way reversing valve 5, and the low-pressure switch 15 is installed on the pipeline between the gas-liquid separator 6 and the DC variable frequency compressor 1; the first end of the external heat source heat exchanger 10 is connected in series with the external heat source injection electronic expansion valve 9 and then connected to the second end of the internal heat source heat exchanger 7, the second end of the external heat source heat exchanger 10 is connected in series with the one-way valve 13 and then connected to the inlet end of the DC variable frequency compressor 1, the outlet end of the external heat source side water pump 12 is connected to the fourth end of the external heat source heat exchanger 10, and the third end of the internal heat source heat exchanger 7 is connected to the inlet end of the DC variable frequency compressor 1.

[0045] A control method for a refrigerant cascade jet heat pump system based on an external heat source, the control method is a parallel jet control method, in the heating mode, a part of the refrigerant after condensing and releasing heat in the main water side heat exchanger flows through the main path: after passing through the internal heat source heat exchanger, the main electronic expansion valve, the fin heat exchanger and the four-way reversing valve, it returns to the DC variable frequency compressor; a part of the refrigerant enters the internal heat source jet auxiliary path, is throttled by the internal heat source jet electronic expansion valve, enters the internal heat source heat exchanger to exchange heat with the main refrigerant; another part of the refrigerant enters the external heat source jet auxiliary path, is throttled by the external heat source jet electronic expansion valve, enters the external heat source heat exchanger to exchange heat with the external heat source, evaporates and absorbs heat, merges with the refrigerant in the internal heat source jet auxiliary path, and enters the medium-pressure chamber of the DC variable frequency compressor.

[0046] like Figure 5The pressure-enthalpy diagram of the dual heat source parallel injection of the refrigerant cascade injection heat pump system based on the external heat source is shown. The state points of the refrigerant are as follows: V1 is the state point of the compressor suction port, V2 is the state point of the compressor exhaust port, V3 is the state point before the main electronic expansion valve throttling, V4 is the state point after the main electronic expansion valve throttling, V5 is the state point after the condenser releases heat, V' 6-i is the state point after the internal heat source electronic expansion valve is throttled, V 6-i is the state point after heat exchange in the internal heat source heat exchanger, V' 7-o is the state point after the external heat source electronic expansion valve is throttled, V 7-o is the state point after heat exchange in the external heat source heat exchanger, V8 is the state point where the compressor reaches the medium pressure chamber after one compression, V9 is the state point where the parallel injection auxiliary refrigerant and the one-compressed refrigerant are mixed in the compressor medium pressure chamber, V 10 It is the refrigerant mixing state point after heat exchange between the internal heat source heat exchanger and the external heat source heat exchanger. The heating capacity of the heat pump system during parallel injection is:

[0047] Q k =Q e +W+Q inj,out

[0048] Among them, Q k Q is the heat exchange capacity of the condenser, i.e. the heating capacity; e is the heat exchange of the evaporator; W is the power consumption of the compressor; Q inj,out It is the heat absorbed by the refrigerant in the external heat source heat exchanger.

[0049]

[0050] Q inj,out =m inj,out ×(V 7-o -V' 7-o )

[0051] Comparison Figure 5 As shown in the pressure-enthalpy diagram of the heat pump system without injection, the heating capacity is:

[0052] Q k =Q e +W

[0053]

[0054] The increased heating capacity of the heat pump system with series and parallel injection compared to the one without injection is as follows: 1) the subcooling degree of the internal heat source heat exchanger is increased (V5→V3), which increases the heat exchange temperature difference between the refrigerant and the ambient temperature in the fin heat exchanger, thereby increasing the evaporation heat exchange; 2) the external heat source injection provides heat, which increases the heating capacity; 3) the compressor power consumption is increased. At the same time, the increase in system heating capacity is higher than the increase in compressor power consumption, and the overall energy efficiency of the unit is also improved.

[0055] The control method of the refrigerant cascade injection heat pump system based on the external heat source, the internal heat source injection electronic expansion valve is controlled according to the target subcooling degree, and the definition of subcooling degree = the main inlet temperature T of the internal heat source heat exchanger liq1 -Internal heat source heat exchanger main outlet temperature T liq2 ; When |actual subcooling - target subcooling|≤1℃, the internal heat source injection electronic expansion valve keeps the current opening unchanged; when the actual subcooling - target superheating > 1℃, the internal heat source injection electronic expansion valve performs valve closing control based on the current opening; when the actual subcooling - target subcooling <-1℃, the internal heat source injection electronic expansion valve performs valve opening control based on the current opening; at the same time, when the actual current exhaust temperature detected is > the target upper limit exhaust temperature T d When the set value is reached, the internal heat source injection electronic expansion valve will be set first according to the target upper limit exhaust temperature T d Perform valve opening control for control target;

[0056] When the exhaust gas superheat (T d -T liq1 ) is greater than the exhaust superheat setting value of the injection auxiliary circuit, the internal heat source injection electronic expansion valve is opened to the initial opening setting value, and then the valve opening is controlled according to the target subcooling degree;

[0057] For external heat injection electronic expansion valve: a. If the temperature on the external heat source side is T h,in ≥External heat source injection inlet temperature T inj,in +2℃, the water pump on the external heat source side starts to run, and the electronic expansion valve on the external heat source side opens to the actual detected current △T (external heat source side temperature T hin - External heat source side injection inlet temperature T inj，in ) corresponding to the valve opening, and then control the valve opening according to the control model; b. If the temperature on the external heat source side T h,in ≤External heat source injection inlet temperature T inj,in , the external heat source does not provide heat, the water pump on the external heat source side stops running, and the injection electronic expansion valve on the external heat source side remains closed.

[0058] When the exhaust gas superheat (T d -T liq1) is less than the exhaust superheat setting value for closing the auxiliary injection line, the internal heat source injection electronic expansion valve and the external heat source injection electronic expansion valve are closed.

[0059] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A control method for a refrigerant cascade jet heat pump system based on an external heat source, characterized in that: The refrigerant cascade jet heat pump system based on an external heat source comprises a heat pump unit and an internal heat source heat exchange unit, wherein the internal heat source heat exchange unit is connected to the heat pump unit; the refrigerant cascade jet heat pump system based on an external heat source also comprises an external heat source heat exchange unit, wherein the external heat source heat exchange unit is connected to the internal heat source heat exchange unit and the heat pump unit; the external heat source heat exchange unit is connected in series with the internal heat source heat exchange unit; the heat pump unit comprises a DC variable frequency compressor (1), a high-pressure switch (14), a four-way reversing valve (5), a fin heat exchanger (4), a main circuit electronic expansion valve (3), a gas-liquid separator (6) and a low-pressure The switch (15) is configured such that the internal heat source heat exchange unit comprises an internal heat source heat exchanger (7), an internal heat source injection electronic expansion valve (8), a main water side heat exchanger (2) and a terminal water pump (11); the external heat source heat exchange unit comprises an external heat source injection electronic expansion valve (9), an external heat source heat exchanger (10), an external heat source side water pump (12) and a one-way valve (13); the outlet end of the DC variable frequency compressor (1) is connected to the first end of the four-way reversing valve (5); the second end of the four-way reversing valve (5) is connected in series with the fin heat exchanger (4) and the main electronic expansion valve (3) in sequence, and then connected to the outlet end of the internal heat source heat exchanger (7). The first end of the internal heat source heat exchanger (7) is connected to the first end of the main water side heat exchanger (2), the second end of the main water side heat exchanger (2) is connected to the fourth end of the four-way reversing valve (5), the two ends of the internal heat source injection electronic expansion valve (8) are respectively connected to the fourth end of the internal heat source heat exchanger (7) and the first end of the main water side heat exchanger (2), the outlet end of the terminal water pump (11) is connected to the third end of the main water side heat exchanger (2), the third end of the four-way reversing valve (5) is connected in series with the gas-liquid separator (6) and then connected to the inlet end of the DC variable frequency compressor (1), and the high pressure switch The switch (14) is installed on the pipeline between the DC variable frequency compressor (1) and the four-way reversing valve (5), and the low-pressure switch (15) is installed on the pipeline between the gas-liquid separator (6) and the DC variable frequency compressor (1); the first end of the external heat source heat exchanger (10) is connected in series with the external heat source injection electronic expansion valve (9) and then connected to the third end of the internal heat source heat exchanger (7), the second end of the external heat source heat exchanger (10) is connected in series with the check valve (13) and then connected to the inlet end of the DC variable frequency compressor (1), and the outlet end of the external heat source side water pump (12) is connected to the fourth end of the external heat source heat exchanger (10); This control method is a series injection control method. In the heating mode, a part of the refrigerant after condensation and heat release in the main water side heat exchanger flows through the main circuit: after passing through the internal heat source heat exchanger, the main electronic expansion valve, the fin heat exchanger and the four-way reversing valve, it returns to the DC variable frequency compressor; the other part enters the injection auxiliary circuit, passes through the internal heat source injection electronic expansion valve for throttling, and then enters the internal heat source heat exchanger to exchange heat with the main circuit refrigerant. The refrigerant evaporates and absorbs heat, and then passes through the external heat source injection electronic expansion valve for throttling, enters the external heat source heat exchanger, exchanges heat with the external heat source, and enters the medium-pressure chamber of the DC variable frequency compressor after further evaporation and heat absorption.

2. The control method of the refrigerant cascade jet heat pump system based on an external heat source according to claim 1, characterized in that: The control method is a parallel injection control method. In the heating mode, part of the refrigerant after condensing and releasing heat in the main water side heat exchanger flows through the main circuit: after passing through the internal heat source heat exchanger, the main electronic expansion valve, the fin heat exchanger and the four-way reversing valve, it returns to the DC variable frequency compressor; A part of the refrigerant enters the internal heat source injection auxiliary circuit, is throttled by the internal heat source injection electronic expansion valve, and enters the internal heat source heat exchanger to exchange heat with the main circuit refrigerant; another part of the refrigerant enters the external heat source injection auxiliary circuit, is throttled by the external heat source injection electronic expansion valve, enters the external heat source heat exchanger to exchange heat with the external heat source, evaporates and absorbs heat, merges with the refrigerant in the internal heat source injection auxiliary circuit, and enters the medium-pressure chamber of the DC variable frequency compressor.

3. The control method of the refrigerant cascade jet heat pump system based on an external heat source according to claim 2, characterized in that: The internal heat source injection electronic expansion valve is controlled according to the target subcooling degree, which is defined as the main inlet temperature T of the internal heat source heat exchanger. liq1 -Internal heat source heat exchanger main outlet temperature T liq2 ; When |actual subcooling degree - target subcooling degree|≤1℃, the internal heat source injection electronic expansion valve maintains the current opening unchanged; When the actual subcooling degree - target superheating degree > 1°C, the internal heat source injection electronic expansion valve performs valve closing control based on the current opening degree; when the actual subcooling degree - target subcooling degree < -1°C, the internal heat source injection electronic expansion valve performs valve opening control based on the current opening degree; at the same time, when the actual current exhaust temperature detected is > the target upper limit exhaust temperature T d When the set value is reached, the internal heat source injection electronic expansion valve will be set first according to the target upper limit exhaust temperature T d Perform valve opening control for control target; When the exhaust gas superheat (T d -T liq1 ) is greater than the exhaust superheat setting value of the injection auxiliary circuit, the internal heat source injection electronic expansion valve is opened to the initial opening setting value, and then the valve opening is controlled according to the target subcooling degree; For external heat injection electronic expansion valve: a. If the temperature on the external heat source side is T h,in ≥External heat source injection inlet temperature T inj,in +2℃, the water pump on the external heat source side starts running, and the electronic expansion valve on the external heat source side opens to the valve opening corresponding to the current △T actually detected, where △T is the temperature T on the external heat source side. hin - External heat source side injection inlet temperature T inj，in , and then perform valve opening control according to the control model; b. If the temperature on the external heat source side is T h,in ≤External heat source injection inlet temperature T inj,in , the external heat source does not provide heat, the water pump on the external heat source side stops running, and the injection electronic expansion valve on the external heat source side remains closed; When the exhaust gas superheat (T d -T liq1 ) is less than the exhaust superheat setting value for closing the auxiliary injection line, the internal heat source injection electronic expansion valve and the external heat source injection electronic expansion valve are closed.

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