阅读说明：本技术 喷气增焓变频空气源热泵热水系统及运行控制方法 (Enhanced vapor injection variable-frequency air source heat pump hot water system and operation control method ) 是由 徐言生 张正国 徐涛 吴治将 孙婉纯 李锡宇 李东洺 于 2021-09-14 设计创作，主要内容包括：本发明涉及一种喷气增焓变频空气源热泵热水系统及运行控制方法,特点是喷气增焓变频空气源热泵热水系统包括压缩机、储热换热器、旁路电子膨胀阀、制冷剂-水换热器、三通比例调节阀、循环水回水温度传感器、循环水出水温度传感器、喷气电子膨胀阀、经济器、主电子膨胀阀、室外环境温度传感器、室外机风机、室外机换热器、室外机换热器管温传感器、三通阀及气液分离器。实现了喷气增焓热泵热水系统在化霜运行时仍按正向制热运行且能继续为用热端提供热量,供热稳定。(The invention relates to an enhanced vapor injection variable-frequency air source heat pump hot water system and an operation control method, and is characterized in that the enhanced vapor injection variable-frequency air source heat pump hot water system comprises a compressor, a heat storage heat exchanger, a bypass electronic expansion valve, a refrigerant-water heat exchanger, a three-way proportional regulating valve, a circulating water return water temperature sensor, a circulating water outlet water temperature sensor, an electronic expansion valve, an economizer, a main electronic expansion valve, an outdoor environment temperature sensor, an outdoor unit fan, an outdoor unit heat exchanger pipe temperature sensor, a three-way valve and a gas-liquid separator. The enhanced vapor injection heat pump hot water system can still operate according to the forward heating mode during defrosting operation, can continuously provide heat for the hot end, and is stable in heat supply.)

1. An enhanced vapor injection variable-frequency air source heat pump hot water system is characterized by comprising a compressor (1), a heat storage heat exchanger (2), a bypass electronic expansion valve (3), a refrigerant-water heat exchanger (4), a three-way proportional control valve (5), a circulating water return water temperature sensor (6), a circulating water outlet water temperature sensor (7), a jet electronic expansion valve (8), an economizer (9), a main electronic expansion valve (10), an outdoor environment temperature sensor (11), an outdoor unit fan (12), an outdoor unit heat exchanger (13), an outdoor unit heat exchanger pipe temperature sensor (14), a three-way valve (15) and a gas-liquid separator (16);

an exhaust outlet a of the compressor (1) is communicated with an inlet of a heat-releasing heat exchange tube of the heat storage heat exchanger (2), and an outlet of the heat-releasing heat exchange tube of the heat storage heat exchanger (2) is communicated with an inlet of a refrigerant pipeline of the refrigerant-water heat exchanger (4); the outlet of a refrigerant pipeline of the refrigerant-water heat exchanger (4) is divided into two paths, wherein one path of pipeline is communicated with the inlet of the electronic air injection expansion valve (8), and the other path of pipeline is communicated with the inlet of a refrigerant supercooling pipe of the economizer (9); the outlet of the jet electronic expansion valve (8) is communicated with the intermediate refrigerant inlet of the economizer (9), the intermediate refrigerant outlet of the economizer (9) is communicated with the jet suction port b of the compressor (1), the refrigerant supercooling pipe outlet of the economizer (9) is communicated with the inlet of the main electronic expansion valve (10), the outlet of the main electronic expansion valve (10) is communicated with the inlet of an outdoor heat exchanger (13), the outlet of the outdoor heat exchanger (13) is communicated with the pipe A of a three-way valve (15), the inlet of the gas-liquid separator (16) is respectively communicated with the pipe B of the three-way valve (15) and the outlet of the heat absorption heat exchange pipe of the heat storage heat exchanger (2), the outlet of the gas-liquid separator (16) is communicated with the air return port c of the compressor (1), the pipe C of the three-way valve (15) is communicated with the inlet of the bypass electronic expansion valve (3), and the outlet of the bypass electronic expansion valve (3) is communicated with the inlet of the heat absorption heat exchange pipe of the heat storage heat exchanger (2); the E pipe of the three-way proportional control valve (5) is communicated with a circulating water return pipe, the F pipe of the three-way proportional control valve (5) is communicated with the water pipeline inlet of the refrigerant-water heat exchanger (4), and the G pipe of the three-way proportional control valve (5) is respectively communicated with a circulating water outlet pipe and the water pipeline outlet of the refrigerant-water heat exchanger (4); the circulating water return temperature sensed by the circulating water return temperature sensor (6) is T1, the circulating water outlet temperature sensed by the circulating water outlet temperature sensor (7) is T2, the outdoor environment temperature sensed by the outdoor environment temperature sensor (11) is T3, and the outdoor heat exchanger tube temperature sensed by the outdoor heat exchanger tube temperature sensor (14) is T4.

2. The operation control method of the enhanced vapor injection variable-frequency air source heat pump hot water system according to claim 1, characterized in that the control method comprises the following procedures:

when the heat pump system normally heats, a pipe A of the three-way valve (15) is communicated with a pipe B, the pipe A of the three-way valve (15) is not communicated with a pipe C, the compressor (1) exhausts air to a heat-releasing heat exchange pipe of the heat-storing heat exchanger (2), the heat-releasing heat exchange pipe of the heat-storing heat exchanger (2) exchanges heat with a heat-storing material in the heat-storing heat exchanger (2) to release part of heat, then the heat is exchanged with circulating water backwater in the refrigerant-water heat exchanger (4) to release heat and is condensed into refrigerant liquid, and the liquid refrigerant is divided into two paths: one path of refrigerant is throttled by an electronic air injection expansion valve (8), exchanges heat with refrigerant in a refrigerant supercooling pipe of an economizer (9), absorbs heat and evaporates into gaseous refrigerant, and the gaseous refrigerant enters an air injection air suction port of the compressor (1); the other path of refrigerant is cooled into a supercooled liquid after being subjected to heat release by a refrigerant supercooling pipe of the economizer (9), then enters an outdoor unit heat exchanger (13) after being throttled by a main electronic expansion valve (10) to be evaporated and absorbs heat from the external environment, and a gaseous refrigerant flows into a pipe A of a three-way valve (15), returns to a gas-liquid separator (16) from a pipe B of the three-way valve (15) and then returns to the compressor (1);

(II) when the heat pump system operates in defrosting mode, the pipe A of the three-way valve (15) is communicated with the pipe C, at the moment, the pipe A of the three-way valve (15) is not communicated with the pipe B, the exhaust gas of the compressor (1) is discharged through the heat-releasing heat exchange pipe of the heat-storing heat exchanger (2) to release part of heat, and then the part of heat is released through the refrigerant-water heat exchanger (4) to be circulated water, the refrigerant becomes high-dryness saturated wet vapor, at the moment, the air-injecting electronic expansion valve (8) is fully closed, all the refrigerant flows to the main electronic expansion valve (10) through the economizer (9) to be subjected to primary pressure reduction and throttling, the pressure and the temperature of the refrigerant are reduced, then the refrigerant enters the outdoor unit heat exchanger (13) to continuously release heat, the high-dryness saturated wet vapor is all condensed into refrigerant liquid, the frost layer on the surface of the outdoor unit heat exchanger (13) absorbs heat to be defrosted, the refrigerant liquid flows into the bypass electronic expansion valve (3) from the pipe C of the pipe (15) to be subjected to secondary throttling, the throttled refrigerant enters a heat absorption heat exchange tube of the heat storage heat exchanger (2), absorbs heat from the heat storage material through the heat absorption heat exchange tube and becomes refrigerant vapor, and the gaseous refrigerant returns to the compressor (1) through the gas-liquid separator (16); in the defrosting process, the heat pump system still continues to provide certain heat for the circulating water system;

after defrosting is finished, the pipe A of the three-way valve (15) is communicated with the pipe B, at the moment, the pipe A of the three-way valve (15) is not communicated with the pipe C, and the heat pump system is switched to normal heating operation; the compressor (1) is not stopped in the defrosting-heating conversion process;

in the defrosting operation process of the heat pump system, the frequency of the compressor (1), the proportion of the three-way proportional regulating valve (5), the opening degree of the main electronic expansion valve (10) and the opening degree of the bypass electronic expansion valve (3) need to be controlled, and the control mode is as follows:

(1) the running frequency of the compressor (1) is increased to increase the heating capacity of the heat pump system, the defrosting running frequency range is 80-120 Hz, and if the running frequency of the compressor (1) before defrosting is greater than 100 Hz, the original running frequency is kept;

(2) according to the defrosting operation frequency of the compressor (1) and the circulating water return temperature T1, the proportion of the three-way proportional control valve (5) and the preset numerical values of the opening degrees of the main electronic expansion valve (10) and the bypass electronic expansion valve (3) are obtained through an experimental method;

(3) the opening degree of the main electronic expansion valve (10) is adjusted for the second time according to the difference between the inlet and outlet water temperatures of hot water delta T = T2-T1; when delta T is more than or equal to 3 ℃ and less than or equal to 7 ℃, the opening degree of the main electronic expansion valve (10) is unchanged; when the delta T is less than 3 ℃, the opening degree of the main electronic expansion valve (10) is reduced to increase the heat supply to the circulating water system; when the delta T is more than 7 ℃, the opening degree of the main electronic expansion valve (10) is increased to increase defrosting heat supply to the outdoor heat exchanger (13).

3. The operation control method of the enhanced vapor injection variable-frequency air source heat pump hot water system according to claim 2, characterized in that the defrosting operation of the compressor (1) is particularly preferably performed at a frequency of 100 Hz.

Technical Field

The invention relates to an enhanced vapor injection variable-frequency air source heat pump hot water system and an operation control method.

Background

The enhanced vapor injection heat pump system can better solve the problems that the heat pump system is in low-temperature operation and the heating capacity and the energy efficiency are rapidly reduced, but the surface of a heat exchanger of an outdoor unit of the heat pump system is more seriously frosted along with the reduction of the outdoor environment temperature, so that the defrosting of the heat pump system is more frequent.

Currently, the most common defrosting method is the reverse operation of the heat pump system, i.e. the refrigeration operation, which requires heat from the original hot end. The main problem of the defrosting mode is that the defrosting process can not provide heat for the hot end, but needs to extract heat from the hot end. For a building heating system, the comfort of a human body can be influenced. In addition, after defrosting is finished, the compressor of the heat pump system needs to be stopped for a while to be switched into heating operation, and then the compressor is started again, so that the reliable operation of the heat pump system can be ensured. In the switching process of defrosting operation and heating operation, the operation stability of the heat pump system is influenced, and the performances of system energy consumption, heating capacity and the like are also influenced. The problem to be solved is firstly to solve the problem of heat source during defrosting and secondly to solve the problem of how to always perform forward heating operation of the heat pump system.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides an enhanced vapor injection variable-frequency air source heat pump hot water system and an operation control method thereof, so that the enhanced vapor injection heat pump hot water system can still operate according to forward heating during defrosting operation, can continuously provide heat for a hot end, and can stably supply heat.

In order to achieve the purpose, the technical scheme of the enhanced vapor injection variable-frequency air source heat pump hot water system is realized by the following steps that the system is characterized by comprising a compressor, a heat storage heat exchanger, a bypass electronic expansion valve, a refrigerant-water heat exchanger, a three-way proportional control valve, a circulating water return water temperature sensor, a circulating water outlet water temperature sensor, an electronic expansion valve, an economizer, a main electronic expansion valve, an outdoor environment temperature sensor, an outdoor unit fan, an outdoor unit heat exchanger pipe temperature sensor, a three-way valve and a gas-liquid separator;

an exhaust outlet a of the compressor is communicated with an inlet of a heat-releasing heat exchange tube of the heat storage heat exchanger, and an outlet of the heat-releasing heat exchange tube of the heat storage heat exchanger is communicated with an inlet of a refrigerant pipeline of the refrigerant-water heat exchanger; the outlet of the refrigerant pipeline of the refrigerant-water heat exchanger is divided into two paths, wherein one path of pipeline is communicated with the inlet of the electronic air injection expansion valve, and the other path of pipeline is communicated with the inlet of a refrigerant supercooling pipe of the economizer; the outlet of the electronic air injection expansion valve is communicated with the intermediate refrigerant inlet of the economizer, the intermediate refrigerant outlet of the economizer is communicated with the air injection and suction port B of the compressor, the outlet of a refrigerant supercooling pipe of the economizer is communicated with the inlet of the main electronic expansion valve, the outlet of the main electronic expansion valve is communicated with the inlet of an outdoor unit heat exchanger, the outlet of the outdoor unit heat exchanger is communicated with the pipe A of a three-way valve, the inlet of a gas-liquid separator is respectively communicated with the pipe B of the three-way valve and the outlet of a heat absorption and heat exchange pipe of the heat storage heat exchanger, the outlet of the gas-liquid separator is communicated with the air return port C of the compressor, the pipe C of the three-way valve is communicated with the inlet of a bypass electronic expansion valve, and the outlet of the bypass electronic expansion valve is communicated with the inlet of the heat absorption and heat exchange pipe of the heat storage heat exchanger; the E pipe of the three-way proportional regulating valve is communicated with a circulating water return pipe, the F pipe of the three-way proportional regulating valve is communicated with a water pipeline inlet of the refrigerant-water heat exchanger, and the G pipe of the three-way proportional regulating valve is respectively communicated with a circulating water outlet pipe and a water pipeline outlet of the refrigerant-water heat exchanger; the circulating water return temperature sensed by the circulating water return temperature sensor is T1, the circulating water outlet temperature sensed by the circulating water outlet temperature sensor is T2, the outdoor environment temperature sensed by the outdoor environment temperature sensor is T3, and the outdoor heat exchanger tube temperature sensed by the outdoor heat exchanger tube temperature sensor is T4.

In order to achieve the purpose, the technical scheme of the operation control method of the enhanced vapor injection variable-frequency air source heat pump hot water system is realized as follows, and the method is characterized by comprising the following steps:

when the heat pump system normally heats, the pipe A of the three-way valve is communicated with the pipe B, the pipe A of the three-way valve is not communicated with the pipe C, the compressor exhausts air to the heat-releasing heat exchange pipe of the heat-storing heat exchanger, the heat-releasing heat exchange pipe of the heat-storing heat exchanger exchanges heat with the heat-storing material in the heat-storing heat exchanger to release part of heat, then the heat is exchanged with circulating water return water in the refrigerant-water heat exchanger to release heat and be condensed into refrigerant liquid, and the liquid refrigerant is divided into two paths: one path of refrigerant is throttled by the electronic air injection expansion valve, exchanges heat with the refrigerant in a refrigerant supercooling pipe of the economizer, absorbs heat and evaporates into gaseous refrigerant, and the gaseous refrigerant enters an air injection air suction port of the compressor; the other path of refrigerant is cooled into supercooled liquid through a refrigerant supercooling pipe of the economizer, then enters an outdoor unit heat exchanger for evaporation after being throttled by a main electronic expansion valve and absorbs heat from the external environment, and gaseous refrigerant flows into a pipe A of a three-way valve and returns to a gas-liquid separator from a pipe B of the three-way valve and then returns to a compressor;

when the heat pump system is in defrosting operation, the pipe A of the three-way valve is communicated with the pipe C, the pipe A of the three-way valve is not communicated with the pipe B, the exhaust gas of the compressor passes through the heat release heat exchange pipe of the heat storage heat exchanger to release part of heat, and then passes through the refrigerant-water heat exchanger to release part of the heat to the circulating water, the refrigerant is changed into high-dryness saturated wet vapor, at the moment, the air injection electronic expansion valve is fully closed, all the refrigerant passes through the economizer to the main electronic expansion valve to be subjected to primary pressure reduction and throttling, the pressure and the temperature of the refrigerant are reduced, then the refrigerant enters the outdoor unit heat exchanger to continuously release heat, the high-dryness saturated wet vapor is fully condensed into refrigerant liquid, the frost on the surface frost layer of the outdoor unit heat exchanger absorbs heat and is melted, the refrigerant liquid flows from the pipe A of the three-way valve to the bypass electronic expansion valve to be subjected to secondary throttling, and the throttled refrigerant enters the heat absorption heat exchange pipe of the heat storage heat exchanger, absorbing heat from the heat storage material through the heat absorbing heat exchange tube and changing the heat into refrigerant vapor, and returning the gaseous refrigerant to the compressor through the gas-liquid separator; in the defrosting process, the heat pump system still continues to provide certain heat for the circulating water system;

after defrosting is finished, the pipe A of the three-way valve is communicated with the pipe B, at the moment, the pipe A of the three-way valve is not communicated with the pipe C, and the heat pump system is switched to normal heating operation; the compressor (1) is not stopped in the defrosting-heating conversion process;

and (IV) controlling the frequency of the compressor, the proportion of the three-way proportional regulating valve, the opening of the main electronic expansion valve and the opening of the bypass electronic expansion valve in the defrosting operation process of the heat pump system in the following control mode:

(1) the running frequency of the compressor is increased to increase the heating capacity of the heat pump system, the defrosting running frequency range is 80-120 Hz, and if the running frequency of the compressor before defrosting is greater than 100 Hz, the original running frequency is kept;

(2) obtaining the proportion of a three-way proportional control valve and preset numerical values of the opening degrees of a main electronic expansion valve and a bypass electronic expansion valve through an experimental method according to the defrosting operation frequency of a compressor and the circulating water return temperature T1;

(3) the opening degree of the main electronic expansion valve is adjusted for the second time according to the difference between the temperature of the hot water inlet and outlet water delta T = T2-T1; when delta T is more than or equal to 3 ℃ and less than or equal to 7 ℃, the opening degree of the main electronic expansion valve 10 is unchanged; when the delta T is less than 3 ℃, the opening degree of the main electronic expansion valve is reduced to increase heat supply to the circulating water system; when the delta T is more than 7 ℃, the opening of the main electronic expansion valve is increased to increase defrosting heat supply to the outdoor heat exchanger.

In the technical scheme, the defrosting operation of the compressor is particularly preferably performed at the frequency of 100 Hz.

Compared with the prior art, the invention has the following advantages:

(1) when in defrosting operation, partial heat can be continuously provided for the circulating water system, the fluctuation of the water temperature of the circulating water system is reduced, the defect caused by heat extraction from the circulating water system is avoided, and particularly when the heat pump system is used in a heating system, the discomfort caused by the reduction of the room temperature when the traditional heat pump system is defrosted is reduced;

(2) during defrosting operation, the refrigerant of the heat pump system still flows in the forward direction, and in the switching process of heating, defrosting and heating, the compressor is started without stopping, so that the energy consumption of the compressor is reduced, the operation condition of the compressor is improved, and the total heat production of the heat pump system is improved.

Drawings

Fig. 1 is a schematic diagram of an implementation of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

As shown in fig. 1, the enhanced vapor injection variable-frequency air source heat pump hot water system comprises a compressor 1, a heat storage heat exchanger 2, a bypass electronic expansion valve 3, a refrigerant-water heat exchanger 4, a three-way proportional control valve 5, a circulating water return temperature sensor 6, a circulating water outlet temperature sensor 7, a jet electronic expansion valve 8, an economizer 9, a main electronic expansion valve 10, an outdoor environment temperature sensor 11, an outdoor unit fan 12, an outdoor unit heat exchanger 13, an outdoor unit heat exchanger tube temperature sensor 14, a three-way valve 15 and a gas-liquid separator 16;

an exhaust outlet a of the compressor 1 is communicated with an inlet of a heat-releasing heat exchange tube in the heat storage heat exchanger 2, and an outlet of the heat-releasing heat exchange tube in the heat storage heat exchanger 2 is communicated with an inlet of a refrigerant pipeline in the refrigerant-water heat exchanger 4; the outlet of a refrigerant pipeline in the refrigerant-water heat exchanger 4 is divided into two paths, wherein one path of the pipeline is communicated with the inlet of the electronic air injection expansion valve 8, and the other path of the pipeline is communicated with the inlet of a refrigerant supercooling pipe of the economizer 9; an outlet of the jet electronic expansion valve 8 is communicated with an intermediate refrigerant inlet of the economizer 9, an intermediate refrigerant outlet of the economizer 9 is communicated with a jet suction port B of the compressor 1, an outlet of a refrigerant supercooling pipe of the economizer 9 is communicated with an inlet of the main electronic expansion valve 10, an outlet of the main electronic expansion valve 10 is communicated with an inlet of an outdoor heat exchanger 13, an outlet of the outdoor heat exchanger 13 is communicated with a pipe A of a three-way valve 15, an inlet of a gas-liquid separator 16 is respectively communicated with a pipe B of the three-way valve 15 and an outlet of a heat absorption heat exchange pipe in the heat storage heat exchanger 2, an outlet of the gas-liquid separator 16 is communicated with a return port C of the compressor 1, a pipe C of the three-way valve 15 is communicated with an inlet of a bypass electronic expansion valve 3, and an outlet of the bypass electronic expansion valve 3 is communicated with an inlet of the heat absorption heat exchange pipe in the heat storage heat exchanger 2; the E pipe of the three-way proportional regulating valve 5 is communicated with a circulating water return pipe, the F pipe of the three-way proportional regulating valve 5 is communicated with a water pipeline inlet of the refrigerant-water heat exchanger 4, and the G pipe of the three-way proportional regulating valve 5 is respectively communicated with a circulating water outlet pipe and a water pipeline outlet of the refrigerant-water heat exchanger 4;

the circulating water return temperature sensed by the circulating water return temperature sensor 6 is T1, the circulating water outlet temperature sensed by the circulating water outlet temperature sensor 7 is T2, the outdoor environment temperature sensed by the outdoor environment temperature sensor 11 is T3, and the outdoor heat exchanger tube temperature sensed by the outdoor heat exchanger tube temperature sensor 14 is T4.

In this embodiment, the operation control flow of the enhanced vapor injection variable frequency air source heat pump hot water system is as follows:

when the heat pump system normally heats, the pipe A of the three-way valve 15 is communicated with the pipe B, the pipe A of the three-way valve 15 is not communicated with the pipe C, the compressor 1 exhausts air to the heat-releasing heat exchange pipe of the heat-storing heat exchanger 2, the heat-releasing heat exchange pipe exchanges heat with the heat-storing material in the heat-storing heat exchanger 2 to release part of heat, then the heat is exchanged with circulating water return water in the refrigerant-water heat exchanger 4 to release heat and be condensed into refrigerant liquid, and the liquid refrigerant is divided into two paths: one path of refrigerant is throttled by the electronic air injection expansion valve 8, exchanges heat with refrigerant in a refrigerant supercooling pipe of the economizer 9, absorbs heat and evaporates into gaseous refrigerant, and the gaseous refrigerant enters an air injection air suction port of the compressor 1; the other path of refrigerant is cooled by heat released from a refrigerant supercooling pipe of the economizer 9 to form supercooled liquid, then enters an outdoor unit heat exchanger 13 after being throttled by a main electronic expansion valve 10 to be evaporated and absorb heat from the external environment, and gaseous refrigerant flows into a pipe A of a three-way valve 15 and returns to a gas-liquid separator 16 from a pipe B of the three-way valve 15 and then returns to the compressor 1;

(II) when the heat pump system operates in defrosting mode, the pipe A of the three-way valve 15 is communicated with the pipe C, at the moment, the pipe A of the three-way valve 15 is not communicated with the pipe B, the exhaust gas of the compressor 1 discharges part of heat through the heat-releasing heat exchange pipe of the heat-storage heat exchanger 2, and then discharges part of heat through the refrigerant-water heat exchanger 4 to circulating water, the refrigerant becomes high-dryness saturated wet vapor, at the moment, the air-injection electronic expansion valve 8 is fully closed, all the refrigerant flows through the economizer 9 to the main electronic expansion valve 10 to be subjected to primary pressure reduction and throttling, the pressure and the temperature of the refrigerant are reduced, then the refrigerant enters the outdoor unit heat exchanger 13 to continue to release heat, all the high-dryness saturated wet vapor is condensed into refrigerant liquid, frost on the surface of the outdoor unit heat exchanger 13 is absorbed by a frost, the refrigerant liquid flows into the pipe A of the three-way valve 15 from the pipe C to the bypass electronic expansion valve 3 to be subjected to secondary throttling, and the throttled refrigerant enters the heat-absorbing heat exchange pipe of the heat-storage heat exchanger 2, the heat is absorbed from the heat storage material through the heat absorbing heat exchanging pipe and changed into refrigerant vapor, and the gaseous refrigerant is returned to the compressor 1 through the gas-liquid separator 16. In the defrosting process, the heat pump system still continues to provide certain heat for the circulating water system;

and (III) after defrosting is finished, the pipe A of the three-way valve 15 is communicated with the pipe B, the pipe A of the three-way valve 15 is not communicated with the pipe C at the moment, and the heat pump system is switched to normal heating operation. The compressor 1 is not stopped in the defrosting-heating conversion process;

in the defrosting operation process of the heat pump system, the frequency of the compressor 1, the proportion of the three-way proportional regulating valve 5, the opening degree of the main electronic expansion valve 10 and the opening degree of the bypass electronic expansion valve 3 need to be controlled, and the following control mode is adopted:

(1) the running frequency of the compressor 1 is increased to increase the heating capacity of the heat pump system, the defrosting running frequency range is 80-120 Hz, the defrosting running frequency can be 80 Hz, 90 Hz, 100 Hz, 110 Hz and 120 Hz, the running frequency is particularly preferably 100 Hz, and if the running frequency of the compressor 1 before defrosting is greater than 100 Hz, the original running frequency is kept;

(2) obtaining the proportion of the three-way proportional control valve 5 and preset numerical values of the opening degrees of the main electronic expansion valve 10 and the bypass electronic expansion valve 3 through an experimental method according to the defrosting operation frequency of the compressor 1 and the circulating water return water temperature T1;

(3) the opening degree of the main electronic expansion valve 10 is secondarily adjusted according to the hot water inlet and outlet temperature difference delta T = T2-T1; when delta T is more than or equal to 3 ℃ and less than or equal to 7 ℃, the opening degree of the main electronic expansion valve 10 is unchanged; when the delta T is less than 3 ℃, the opening degree of the main electronic expansion valve 10 is reduced to increase the heat supply to the circulating water system; when the delta T is more than 7 ℃, the opening degree of the main electronic expansion valve 10 is increased to increase defrosting heat supply to the outdoor heat exchanger 13.

While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.