CN110895061A

CN110895061A - Refrigerant circulation system and defrosting method thereof

Info

Publication number: CN110895061A
Application number: CN201811063397.3A
Authority: CN
Inventors: 杨春; 束宏飞; 王蒙
Original assignee: Emerson Climate Technologies Suzhou Co Ltd
Current assignee: Copeland Suzhou Co Ltd
Priority date: 2018-09-12
Filing date: 2018-09-12
Publication date: 2020-03-20

Abstract

A refrigerant cycle system and a defrosting method thereof are provided, the refrigerant cycle system comprises: a compressor; a first heat exchanger disposed at a low pressure side of the compressor; a second heat exchanger disposed at a high pressure side of the compressor; and a main expansion valve disposed between the second heat exchanger and the first heat exchanger. The refrigerant cycle system further includes an expansion device and a third heat exchanger which are arranged between the first heat exchanger and the compressor, and the expansion device is connected in series with the upstream side of the third heat exchanger. The refrigerant cycle system is switchable between at least a first mode of operation in which the second heat exchanger functions as a condenser, the first heat exchanger functions as an evaporator and the expansion device and the third heat exchanger are bypassed; in the second mode of operation, the first heat exchanger functions as a condenser and the third heat exchanger functions as an evaporator. The refrigerant circulating system does not need a four-way reversing valve, has high defrosting speed, and does not have the problems of noise and liquid return of the compressor.

Description

Refrigerant circulation system and defrosting method thereof

Technical Field

The present disclosure relates to a novel refrigerant circulation system and a method for defrosting using the same.

Background

This section provides background information related to the present disclosure, which is not necessarily prior art.

The heat pump system is a typical refrigerant circulation system which transfers heat energy of a low-temperature heat source to a high-temperature heat source by performing work through electric power. The working principle of the heat pump system is consistent with that of a compression type refrigerator. In the existing heat pump system, the evaporator and the condenser are exchanged to work by adopting a four-way reversing valve, so that the same set of device is used for realizing refrigeration and heating. The low temperature heat source commonly used in heat pump installations is water and the medium surrounding us, air. With the adjustment of energy structure and the proposal of sustainable development strategy in the global scope, people pay more and more attention to the development and utilization of clean, safe and efficient energy. The air source heat pump system takes electric energy as driving force, takes outdoor ambient air as a heat source, provides refrigeration and heat supply for an adjusted object, and is one of environment-friendly and efficient energy supply modes which are vigorously popularized by China.

The majority of northern winter heat pump heating systems are air-water heat pump systems, and the heating terminals are mainly radiators or floor heating. The heat pump system transfers heat absorbed in air and motor power of the compressor to circulating water, and the circulating water supplies heat to rooms through heating radiators or floor heating. When the air source heat pump supplies heat in winter, the outdoor heat exchanger is easy to frost. Therefore, to ensure proper operation of the system, the surfaces of the outdoor heat exchanger must be periodically defrosted. Reverse Cycle Defrost (RCD) and Hot Gas Bypass Defrost (HGBD) are the predominant defrost modes for existing air source heat pump systems. However, these two defrosting methods still have respective advantages and disadvantages, and there is a demand for further optimizing the defrosting performance of a refrigerant circulation system such as an air source heat pump system.

Disclosure of Invention

A general summary of the disclosure is provided in this section and is not a comprehensive disclosure of the full scope of the disclosure or all of the features of the disclosure.

It is an object of the present disclosure to provide a refrigerant circulation system with optimized defrost performance that overcomes or mitigates at least one of the many disadvantages of the prior art defrost modes.

Another object of the present disclosure is to provide a refrigerant circulation system with a simplified structure.

It is another object of the present disclosure to provide a refrigerant cycle system with improved energy efficiency and stability, thereby improving comfort of a use environment of the refrigerant cycle system.

According to an aspect of the present disclosure, there is provided a refrigerant circulation system including: a compressor; a first heat exchanger disposed at a low pressure side of the compressor; a second heat exchanger disposed on a high pressure side of the compressor; and a main expansion valve disposed between the second heat exchanger and the first heat exchanger. The refrigerant circulation system further includes an expansion device and a third heat exchanger which are disposed between the first heat exchanger and the compressor, and the expansion device is connected in series to an upstream side of the third heat exchanger. The refrigerant cycle system being switchable between at least a first mode of operation in which the second heat exchanger functions as a condenser, the first heat exchanger functions as an evaporator and the expansion device and the third heat exchanger are bypassed; in the second mode of operation, the first heat exchanger functions as a condenser and the third heat exchanger functions as an evaporator.

In some embodiments, the second heat exchanger may not exchange heat in the second mode of operation.

In some embodiments, the refrigerant circulation system may further include an electronic three-way valve disposed between the second heat exchanger and the third heat exchanger, the electronic three-way valve including a water inlet connected to a water pump and a water outlet selectively communicable with the second heat exchanger or the third heat exchanger, wherein the electronic three-way valve may be controlled to: in the first mode of operation, the water outlet is in communication with the second heat exchanger, and in the second mode of operation, the water outlet is in communication with the third heat exchanger.

In some embodiments, the refrigerant circulation system may further include: a first switching valve disposed in series with the second heat exchanger; a first bypass passage provided in parallel with the second heat exchanger; and a second on-off valve disposed in the first bypass passage, wherein in the first operating mode, the first on-off valve is open and the second on-off valve is closed to communicate with the second heat exchanger; in the second mode of operation, the first on-off valve is closed and the second on-off valve is open to bypass the second heat exchanger.

According to some embodiments, in the second mode of operation, the second heat exchanger may function as a primary condenser and the first heat exchanger may function as a secondary condenser.

In some embodiments, the refrigerant circulation system may further include an electronic three-way valve disposed between the second heat exchanger and the third heat exchanger, the electronic three-way valve including a water inlet in communication with the water outlet of the second heat exchanger and a water outlet selectively communicable with the water inlet or the water outlet of the third heat exchanger, wherein the electronic three-way valve may be controlled to: in the first mode of operation, an outlet of the electronic three-way valve is in communication with an outlet of the third heat exchanger, and in the second mode of operation, an outlet of the electronic three-way valve is in communication with an inlet of the third heat exchanger.

In some embodiments, the refrigerant circulation system may further include: a third on/off valve provided in series with the expansion device and the third heat exchanger; a second bypass passage provided in parallel with the expansion device and the third heat exchanger; and a fourth switching valve disposed in the bypass passage, wherein in the first operating mode, the third switching valve is closed and the fourth switching valve is opened to bypass the expansion device and the third heat exchanger; in the second operation mode, the third switching valve is opened and the fourth switching valve is closed to communicate the expansion device and the third heat exchanger.

In some embodiments, the refrigerant circulation system may further include a three-way reversing valve disposed between the expansion device, the first heat exchanger, and the low pressure side intake port of the compressor, the three-way reversing valve including a first heat exchanger interface and an expansion device interface and a compressor interface selectively communicable with the first heat exchanger interface, wherein in the first mode of operation, the three-way reversing valve is in a first position where the first heat exchanger interface is communicable with the compressor interface to bypass the expansion device and the third heat exchanger; in the second mode of operation, the three-way reversing valve is in a second position in which the first heat exchanger port is in communication with the expansion device port to communicate the expansion device and the third heat exchanger.

In some embodiments, the three-way reversing valve may further include an interface in communication with a high-side discharge of the compressor to urge a main spool valve of the three-way reversing valve to slide between the first position and the second position by a discharge pressure of the compressor.

In some embodiments, the second heat exchanger and the third heat exchanger may be integrated within one housing.

In some embodiments, the refrigerant cycle system may further include an economizer disposed between the second heat exchanger and the main expansion valve, wherein in the first mode of operation, the economizer is operable to subcool a working fluid and provide enhanced vapor injection to the compressor; in the second mode of operation, the economizer does not function as a heat exchanger.

In some embodiments, the refrigerant circulation system may further include a third bypass passage disposed in parallel with the main expansion valve and a fifth switching valve disposed in the third bypass passage, wherein in the first operation mode, the fifth switching valve is closed and the main expansion valve is opened at a predetermined opening degree; in the second operation mode, the fifth switching valve is opened and the main expansion valve is kept fully opened or closed.

In some embodiments, the refrigerant circulation system may further include a gas-liquid separator disposed between the evaporator and the compressor.

In some embodiments, the coolant circulation system may be a heat pump system.

According to another aspect of the present disclosure, a method for defrosting a refrigerant cycle system is provided, the refrigerant cycle system being any one of the refrigerant cycle systems described above, wherein the first heat exchanger of the refrigerant cycle system is defrosted by switching the refrigerant cycle system to the second operation mode.

The defrosting operation of the refrigerant circulating system has the advantages of reverse cycle defrosting and hot gas bypass defrosting, and the defects of the reverse cycle defrosting and the hot gas bypass defrosting are partially or completely eliminated, the compressor does not need to be stopped during defrosting, the pressure change of the system is gentle, defrosting noise does not exist, and the performance loss of the system, which needs to continuously reestablish pressure difference during reverse cycle defrosting, does not exist. In addition, as the defrosting heat source is the compressor power and the circulating water heat as in the reverse cycle defrosting, and the defrosting is not stopped in the middle, the defrosting speed is high, and the problem of liquid return of the compressor is solved. The energy efficiency and the applicability of the refrigerant circulating system are improved, and the refrigerant circulating system has a wide application prospect.

Drawings

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

FIG. 1 illustrates a schematic diagram of an exemplary heat pump system operating for reverse cycle defrosting;

FIG. 2 is a timing diagram illustrating control of the components of the heat pump system shown in FIG. 1 during a defrost operation;

FIG. 3 shows the basic construction of a four-way reversing valve;

FIG. 4 illustrates an operational schematic of an exemplary heat pump system for hot gas bypass defrost;

FIG. 5 is a timing diagram illustrating control of the components of the heat pump system shown in FIG. 4 during a defrost operation;

fig. 6 shows an operation principle diagram of a heat pump system according to a first modification example;

FIG. 7 is a timing diagram illustrating control of the components of the heat pump system shown in FIG. 6 during a defrost operation;

fig. 8 shows an operation principle diagram of a heat pump system according to a second modified example;

FIG. 9 is a timing diagram illustrating control of the components of the heat pump system shown in FIG. 8 during a defrost operation;

fig. 10 is an enlarged schematic configuration diagram of a three-way valve used in the heat pump system shown in fig. 8;

fig. 11 shows an operation principle diagram of a heat pump system according to a third modified example;

FIG. 12 is a timing diagram illustrating control of the components of the heat pump system shown in FIG. 11 during a defrost operation;

fig. 13 shows an operation principle diagram of a heat pump system according to a fourth modified example; and

fig. 14 is a control timing diagram of the components of the heat pump system shown in fig. 13 during a defrost operation.

Detailed Description

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

Example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope to those skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known methods, well-known device structures, and well-known technologies are not described in detail.

When an element or layer is referred to as being "on," "engaged to," "connected to" or "coupled to" another element or layer, it can be directly on, engaged, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," or "directly engaged with," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in the same manner (e.g., "between …" versus "directly between …", "adjacent" versus "directly adjacent", etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

The construction of the refrigerant cycle system and its defrosting operation will be described below with reference to the drawings, taking the heat pump system as an example, but the innovative concepts of the present disclosure are equally applicable to other suitable refrigerant cycle systems. Additionally, for purposes of example, these heat pump systems are shown as air-to-water heat pump systems. However, the present teachings are equally applicable to air-to-air heat pump systems and the like. In addition, in the operation schematic diagram of the heat pump system, solid arrows indicate a flow path of the working fluid when the heat pump system performs a heating operation during the heating mode, and dotted arrows indicate a flow path of the working fluid when the defrosting operation is performed during the heat pump system during the heating mode.

First, the defrosting operation of the exemplary heat pump system is explained with reference to fig. 1 to 5, in which fig. 1 schematically shows the construction of the heat pump system 10 and its operation principle of performing reverse cycle defrosting; FIG. 2 is a timing diagram of control of the components of the heat pump system 10 during defrost operation; FIG. 3 shows the basic configuration of a four-way reversing valve 4 used in the heat pump system 10; FIG. 4 schematically illustrates the construction of the heat pump system 20 and its operation for hot gas bypass defrost; and fig. 5 is a control timing diagram of the components of the heat pump system 20 shown in fig. 4 during a defrosting operation.

< reverse cycle defrost example >

The heat pump system 10 shown in fig. 1 generally includes a compressor 1, a gas-liquid separator 2, a first heat exchanger (outdoor heat exchanger) 3, a four-way selector valve 4, a second heat exchanger (indoor heat exchanger) 5, an economizer 6, an auxiliary expansion valve EXV1, and a main expansion valve EXV 2. Here, components such as the gas-liquid separator 2 and the economizer 6 may be omitted as appropriate.

The four-way selector valve 4 is a typical solenoid selector valve, which will be described in detail below. In the heating mode, the solenoid of the four-way selector valve 4 is in the deenergized state, i.e., the state shown in fig. 3. At this time, the D port of the four-way selector valve 4, which is connected to the compressor discharge port O1 (high pressure side), communicates with the C port, which is connected to the indoor heat exchanger, and the S port of the four-way selector valve 4, which is connected to the low pressure side of the compressor via the gas-liquid separator 2, communicates with the E port, which is connected to the outdoor heat exchanger, while the communication between the D port and the C port and the S port and the E port is interrupted. Referring to fig. 1 and 2, the high-temperature and high-pressure working fluid discharged from the compressor 1 enters the D port of the four-way reversing valve 4, is discharged from the C port, and enters the second heat exchanger 5 as a condenser to be heat-exchanged with water to be heated. The working fluid condenses in the second heat exchanger 5 and is converted into a liquid of medium temperature and high pressure. The water and the working fluid flow in the reverse direction, and the heat is absorbed to become hot water to be discharged. The working fluid exiting the second heat exchanger 5 enters the economizer 6. The economizer 6 is a heat exchanger and includes four ports P1, P2, P3 and P4. The high pressure liquid working fluid from the second heat exchanger 5 enters the economizer 6 from port P1 and is split into two portions after exiting port P2 of the economizer, one portion being throttled by the auxiliary expansion valve EXV1 and entering the economizer 6 via port P3 to evaporate absorbing heat, thereby reducing and subcooling the temperature of the working fluid entering the economizer 6 from port P1. The gaseous working fluid, which throttles the heat absorbed by evaporation, exits from port P4 of the economizer 6 and enters the compressor 1 via the enhanced vapor injection port O3 of the compressor 1 to participate in the recirculation. Another portion of the subcooled working fluid exiting port P2 then flows through main expansion valve EXV2 directly into first heat exchanger 3 acting as an evaporator where it absorbs heat. The working fluid from the first heat exchanger 3 flows in from the E port and flows out from the S port of the four-way selector valve 4, and is finally returned to the low-pressure side intake port O2 of the compressor 1, thereby forming a heating cycle. Before entering the low-pressure side intake port O2 of the compressor 1, the working fluid flows through the gas-liquid separator 2 to prevent excessive liquid refrigerant from entering the compressor 1 and causing liquid slugging, and the gas-liquid separator also has the functions of filtering, oil return, liquid storage and the like. Therefore, the gas-liquid separator 2 is always disposed upstream of the compressor intake. Additionally, the heat pump system may also include an outdoor fan (not shown) to force ambient air into faster contact with the evaporator to increase heat exchange.

When the defrosting operation is required, as shown in fig. 2, the compressor 1 is first stopped, and then the solenoid of the four-way selector valve 4 is energized. At this time, the D port of the four-way selector valve 4 connected to the compressor discharge port O1 (high pressure side) communicates with the E port connected to the outdoor heat exchanger, and the S port of the four-way selector valve 4 connected to the low pressure side of the compressor via the gas-liquid separator 2 communicates with the C port connected to the indoor heat exchanger, and the communication between the D and E ports and the S and C ports is interrupted. In addition, while the compressor 1 is stopped, the outdoor fan and the auxiliary expansion valve EXV1 may be closed and the opening degree of the main expansion valve EXV2 may be adjusted. The above operation corresponds to temporarily switching the heat pump system 10 shown in fig. 1 to the cooling mode through the four-way selector valve 4.

After the switching operation is completed, the heat pump system 10 is in a stable standby state, and the compressor 1 is operated. As shown by the dotted arrows in fig. 1, the high-temperature and high-pressure working fluid discharged from the discharge port O1 of the compressor 1 enters the D port of the four-way selector valve 4, is discharged from the E port, enters the first heat exchanger 3 serving as a condenser, and exchanges heat with outdoor air. The working fluid condenses in the first heat exchanger 3 to release heat for the purpose of defrosting the outdoor heat exchanger 3. After leaving the first heat exchanger 3, the working fluid flows through the main expansion valve EXV2, the economizer 6, and the second heat exchanger 5 as an evaporator in this order, evaporates in the second heat exchanger 5, and absorbs heat from the circulating water. Since the auxiliary expansion valve EXV1 is closed, the working fluid from the main expansion valve EXV2 is all admitted from port P2 of the economizer 6 and is discharged directly from port P1 of the economizer 6 without heat exchange. The working fluid from the second heat exchanger 5 (evaporator) flows in from the C port of the four-way selector valve 4 and flows out from the S port. Also, the working fluid flows through the gas-liquid separator 2 first and then enters the low pressure side intake port O2 of the compressor 1, thereby forming a refrigeration cycle.

As shown in fig. 2, after defrosting is completed, the compressor 1 still needs to be stopped first, and then the outdoor fan is turned on and the four-way reversing valve is switched. When all is ready, the compressor 1 is re-operated while the auxiliary expansion valve EXV1 is opened and the opening degree of the main expansion valve EXV2 is appropriately adjusted, so that the heat pump system 10 is re-operated in the heating mode.

The reverse cycle defrosting is essentially a process of converting a heating process into a cooling process by changing the direction of a working fluid using a four-way reversing valve, and is also called as a four-way reversing valve defrosting. The defrosting mode has the advantages of clean and thorough defrosting, simple and convenient defrosting operation, no need of additional equipment and small influence on the compressor. However, as noted above, a shutdown is required and defrosting requires heat extraction from circulating water or air to be heated when a switching operation is performed, which causes large fluctuations in the indoor ambient temperature, affecting comfort. This has less effect on the air-to-water heat pump system since the heat capacity of water is greater than that of air. Secondly, the compressor and the four-way reversing valve are frequently started and stopped and switched, so that the noise problem is generated, and the reliability is influenced. Moreover, because the system pressure fluctuation is large, pressure balance needs to be continuously established in the switching process, so the heating recovery is slow, and the system energy efficiency is influenced.

< Hot gas bypass defrost example >

The heat pump system 20 shown in fig. 4 generally includes a compressor 1, a gas-liquid separator 2, a first heat exchanger (outdoor heat exchanger) 3, an on-off valve V, a second heat exchanger (indoor heat exchanger) 5, an economizer 6, a capillary tube 7, an auxiliary expansion valve EXV1, and a main expansion valve EXV 2.

As shown in fig. 5, in the heat pump system 20, the non-defrosting operation and the defrosting operation differ only in whether the electromagnetic opening/closing valve V is open, that is, only in whether the bypass passage provided with the opening/closing valve V is open.

In the heating mode, when the defrosting operation is not performed, the on-off valve V is closed. As indicated by the solid arrows in fig. 4, the high-temperature and high-pressure working fluid discharged from the discharge port O1 of the compressor 1 can flow into the second heat exchanger 5 only in the counterclockwise direction at the junction point T. The working fluid is condensed to release heat, and the circulating water absorbs the heat to become hot water to be discharged. As described above, the working fluid flowing out of the second heat exchanger 5 enters the economizer 6 via the port P1, is branched at the port P2 of the economizer 6, flows through the auxiliary expansion valve EXV1, and is returned to the economizer 6 via the port P3, and a portion of the working fluid is further cooled to a supercooled state. The portion of the working fluid returning to the economizer 6 evaporates and absorbs heat and becomes a gaseous working fluid exiting the economizer 6 at port P4 and entering the compressor 1 via the enhanced vapor injection port O3 of the compressor 1 to participate in the recirculation. Another portion of the subcooled working fluid tapped at port P2 of economizer 6 flows through main expansion valve EXV2 and into first heat exchanger 3. The first heat exchanger 3 acts as an evaporator, evaporating the working fluid and absorbing heat from the ambient air. The working fluid from the first heat exchanger 3 directly enters the gas-liquid separator 2, is subjected to filtration and gas-liquid separation in the gas-liquid separator 2, and then returns from the low-pressure side intake port O2 of the compressor 1 to the compressor 1 for recirculation.

When the defrosting operation is required, the compressor 1 is kept in normal operation, and only the on-off valve V needs to be opened. The working fluid will circulate along the solid arrows in fig. 4 for heating and simultaneously flow along the dashed arrows for defrosting as described above. The high-temperature and high-pressure working fluid discharged from the discharge port O1 of the compressor 1 is branched at the junction point T, and a part of the working fluid is heated while circulating as indicated by the solid arrow, and the other part of the working fluid flows through the on-off valve V as indicated by the broken arrow and then flows into the capillary 7. This other portion of the working fluid is throttled down by capillary tube 7 and then merged with the working fluid discharged from main expansion valve EXV2 during the heating cycle, and then flows into first heat exchanger 3 as an evaporator. Since the working fluid entering the outdoor heat exchanger through the capillary tube 7 does not undergo a condensation heat release process, the temperature is high, and thus the purpose of defrosting the outdoor heat exchanger is achieved.

It can be seen that hot gas bypass defrosting does not require a change in the heating cycle of the heat pump system, but rather defrosts the hot working fluid bypassing the heat exchanger that needs defrosting. Compared with reverse circulation defrosting, hot gas bypass defrosting is not changed by a four-way valve, a compressor does not need to be stopped, mechanical impact is small, noise is low, heating circulation is not changed by hot gas bypass defrosting, heat is not absorbed from an indoor environment, temperature fluctuation of the indoor environment is small, and comfort is good. However, the hot gas bypass defrosting requires a sacrifice of a part of the compressor power as a defrosting heat source and the heat exchanger requiring defrosting is still used as an evaporator, so that the defrosting time is long and the system efficiency is reduced, effective defrosting is difficult when frost is thick and the ambient temperature is low, and in addition, reliability problems such as easy generation of compressor liquid return due to incomplete evaporation and vaporization of the working fluid entering the evaporator are caused. The four-way reversing valve 4 shown in fig. 1 may be incorporated into the heat pump system 20 to allow for hot gas bypass when there is little or no frost formation and reverse circulation when frost formation is severe.

In addition, in order to eliminate the adverse effects of reverse cycle defrosting and hot gas bypass defrosting, the present invention proposes the following modified embodiments. These modified examples will now be described in detail with reference to fig. 6 to 14.

< first modified example >

Fig. 6 and 7 show a heat pump system 100 according to a first modified example, in which fig. 6 is a schematic diagram showing an operation principle of the heat pump system 100, and fig. 7 is a control timing chart of components of the heat pump system 100 during a defrosting operation.

As shown in fig. 6, the heat pump system 100 generally includes a compressor 101, a gas-liquid separator 102, a first heat exchanger (outdoor heat exchanger) 103, an electronic three-way valve 104, a second heat exchanger (indoor heat exchanger) 105, an economizer 106, a capillary tube 107 (corresponding to an expansion device according to the present invention), an auxiliary expansion valve EXV11 and a main expansion valve EXV12, a third heat exchanger (indoor heat exchanger) 108, and an on-off valve V11 (corresponding to a third on-off valve according to the present invention), V12 (corresponding to a fourth on-off valve according to the present invention), and V13 (corresponding to a fifth on-off valve according to the present invention). Wherein the on-off valves V11, V12, and V13 are electromagnetic on-off valves.

In the heating mode, the compressor 101 is turned on, the outdoor fan (not shown) is opened, the auxiliary expansion valve EXV11 and the main expansion valve EXV12 are both opened at a heating opening degree, the switching valve V11 is closed, the switching valve V12 is opened, the switching valve V13 is closed, the electronic three-way valve 104 is turned on the port a without turning on the port B, and the water pump 150 for circulating water is always in an open state as shown in fig. 7. The high-temperature and high-pressure working fluid discharged from the discharge port O1 of the compressor 101 directly enters the second heat exchanger 105 as indicated by the solid arrows in fig. 6. Meanwhile, the water pumped by the water pump 150 enters the electronic three-way valve 104, flows into the second heat exchanger 105 from the port a of the electronic three-way valve 104, and exchanges heat with the high-temperature and high-pressure working fluid from the compressor 101 in the second heat exchanger 105. The second heat exchanger 105 functions as a condenser, the working fluid condenses to release heat, and the circulating water absorbs the heat and becomes hot water to be discharged from the water outlet 160. Similar to the

heat pump systems

10 and 20, the working fluid flowing from the second heat exchanger 105 is further reduced in temperature to a subcooled state by the economizer 106, wherein a portion of the working fluid flows in sequence through the auxiliary expansion valve EXV11, the economizer 106 and back to the compressor 101 via the enhanced vapor injection port O3 for recirculation, for providing enhanced vapor injection to the compressor 101; another part of the working fluid in the supercooled state flows through the main expansion valve EXV12, the first heat exchanger 103, the on-off valve V12, the gas-liquid separator 102 in this order and returns to the compressor 101 via the air inlet O2 to start the recirculation. Here, the first heat exchanger 103 acts as an evaporator, evaporating the working fluid and absorbing heat from the ambient air.

Referring to fig. 7, when a defrosting operation is required, the compressor 101 does not need to be stopped, the outdoor fan is turned off, the auxiliary expansion valve EXV11 is closed, the main expansion valve EXV12 is kept fully open and the on-off valve V13 is opened with a delay or the on-off valve V13 is directly opened and the main expansion valve EXV12 is closed, the on-off valve V11 is opened and the on-off valve V12 is closed, the electronic three-way valve 104 is switched to connect the port B without connecting the port a, and the water pump 150 is always in an open state. The working fluid then follows the heating cycle along the path indicated by the dashed arrow in fig. 6. Specifically, the high-temperature and high-pressure working fluid discharged from the discharge port O1 of the compressor 101 still directly enters the second heat exchanger 105. However, since the port a is not turned on, water does not pass through the second heat exchanger 105, and the working fluid passes through the second heat exchanger 105 without heat exchange. That is, the second heat exchanger 105 is not operated, and only functions for communication. Water pumped by the water pump 150 will flow through the electronic three-way valve 104 from port B to the third heat exchanger 108 and exchange heat with the working fluid flowing through the third heat exchanger 108, as will be further described below. The high-temperature, high-pressure working fluid flowing out of the second heat exchanger 105 enters the economizer 106. As described above, since the auxiliary expansion valve EXV11 is closed in the defrost mode, the economizer 106 does not operate as the second heat exchanger 105, but only functions as a communication; and the full opening of the main expansion valve EXV12 means that the main expansion valve EXV12 does not play a role in throttling and depressurizing, but only plays a role in communication. Then, the working fluid discharged from the discharge port O1 of the compressor 101 thus flows through the second heat exchanger 105, through the economizer 106, through the main expansion valve EXV12, and simultaneously through the on-off valve V13 with the on-off valve V13 open, and thereafter enters the first heat exchanger 103 to be heat-exchanged with the ambient air while being maintained in a high-temperature and high-pressure state. The line of the switching valve V13 is connected in parallel to the line of the main expansion valve EXV12 to increase the flow rate of the working fluid. Normally, when the switching is performed, the opening of the switching valve V13 is delayed, that is, V13 is opened after the EXV12 is fully opened. This can alleviate the flow squeal caused by the high and low pressure flows being conducted due to the sudden opening of the switching valve V13. At this time, the first heat exchanger 103 serves as a condenser, and the working fluid condenses to release heat, so that the surface temperature of the first heat exchanger 103 is raised for the purpose of defrosting. The condensed and cooled liquid working fluid flows through the capillary 107 to be depressurized, and then is changed into a low-temperature and low-pressure liquid working fluid, and then enters the third heat exchanger 108 to exchange heat with water introduced into the third heat exchanger 108. Thus, where the third heat exchanger 108 acts as an evaporator, the working fluid evaporates and extracts heat from the circulating water, becoming a low pressure gaseous working fluid. The circulating water provides heat and the temperature is reduced and exits the third heat exchanger 108 and exits the outlet 160. The working fluid from the third heat exchanger 108 flows through the on-off valve V11, enters the gas-liquid separator 102, is filtered and gas-liquid separated in the gas-liquid separator 102, and then returns from the low-pressure side intake O2 of the compressor 101 to the compressor 101 for recirculation.

In the heat pump system 100, when the control unit (not shown in the figure) judges that defrosting is required, the electronic three-way valve 104 controlling the water path is switched from communication with the port a to communication with the port B, the auxiliary expansion valve EXV11 is closed, the main expansion valve EXV12 is kept fully open, and the on-off valve V13 is opened, which corresponds to discarding the second heat exchanger 105 previously used as a condenser and allowing the high-temperature and high-pressure working fluid to directly enter the first heat exchanger 103 previously used as an evaporator for defrosting, and the outflowing liquid working fluid is throttled to flow through the third heat exchanger 108 and evaporated to absorb heat to become a low-pressure gaseous working fluid, thereby forming a complete refrigeration cycle. However, this switching is different from the reverse cycle switching of the four-way selector valve and does not have any direct influence on the compressor, except that the heat exchanger forming the heating cycle or the refrigeration cycle in combination with the first heat exchanger (the outdoor heat exchanger to be defrosted) is switched between the second heat exchanger and the third heat exchanger. Therefore, the heat pump system and method using the backup heat exchanger for defrosting according to the first modified example do not require a four-way reversing valve, do not require a stop of the compressor during defrosting, have smooth pressure change of the system, do not have defrosting noise, and do not have system performance loss caused by the need to constantly reestablish a pressure difference during reverse cycle defrosting, as compared to reverse cycle defrosting. In addition, since the defrosting heat source is the compressor power and the circulating water heat as in the reverse cycle defrosting without stopping in between, the method of the first modification example has the advantage of faster defrosting speed and no compressor return. Although this method requires heat absorption from the circulating water during defrosting to cause fluctuation in the indoor temperature, the influence on the air-water heat pump system is very small due to the above-described advantages.

< second modified example >

Fig. 8 and 9 show a heat pump system 200 according to a second modified example, in which fig. 8 is a schematic diagram showing an operation principle of the heat pump system 200, and fig. 9 is a control timing chart of components of the heat pump system 200 during a defrosting operation.

As shown in fig. 8, the heat pump system 200 generally includes a compressor 201, a gas-liquid separator 202, a first heat exchanger (outdoor heat exchanger) 203, an electronic three-way valve 204, a second heat exchanger (indoor heat exchanger) 205, an economizer 206, a capillary tube 207, an auxiliary expansion valve EXV21, and a main expansion valve EXV22, a third heat exchanger (indoor heat exchanger) 208, and a three-way selector valve 210. In addition, similarly, a bypass passage is provided in parallel with the main expansion valve EXV22, and an open-close valve V23 (corresponding to a fifth open-close valve according to the present invention) is provided in the bypass passage. The heat pump system 200 in the second modified example is the same as the heat pump system 100 in the first modified example, except that one three-way reversing valve 210 is used instead of the electromagnetic switch valve V11 and the electromagnetic switch valve V12 in fig. 6 for reversing. The above different points will be described in detail below.

The three-way selector valve 210 in the second modified example shown in fig. 10 can be obtained by modifying the four-way selector valve 4 shown in fig. 3.

Referring to fig. 3, in the four-way reversing valve 4, when the solenoid 46 is in a power-off state, the pilot spool 47 moves to the right under the driving of the left compression spring 45, the high-pressure gas introduced from the port D enters the left piston chamber 42 through the capillary tube, the piston 44 and the main spool 41 move to the right due to the pressure difference between the two ends of the double-headed piston 44, the gas in the right piston chamber 43 is discharged, the port D (the discharge port connection pipe of the compressor) communicates with the port C (the indoor unit connection pipe) through the orifice 48 of the main spool 41, and the port S (the suction port connection pipe of the compressor) communicates with the port E (the outdoor unit connection pipe), thereby forming a. When the solenoid 46 is in the energized state, the pilot spool 47 moves left against the tension of the compression spring 45 under the magnetic force generated by the solenoid 46, the high pressure gas introduced from the port D enters the right piston chamber 43 through the capillary tube, the piston 44 and the main spool 41 move left due to the pressure difference existing at both ends of the piston 44, the gas in the left piston chamber 42 is discharged, the port D (discharge port connection pipe of the compressor) is communicated with the port E (outdoor connection pipe) through the orifice 49 on the main spool 41, and the port S (suction port connection pipe of the compressor) is communicated with the port C (indoor connection pipe), thereby forming the refrigeration cycle.

In the modified three-way directional valve 210 of fig. 10, the port D, which is a discharge port connection pipe of the compressor, is moved to the pilot spool chamber and thus a capillary tube, which communicates the port D with the pilot spool chamber, is removed, and the port D, which is the port D in the four-way directional valve 4, which communicates with the main spool chamber is modified to a port E, which is a first heat exchanger (outdoor unit) connection pipe, and the other side leaves only the port C (indoor unit connection pipe) and the port S (suction port connection pipe of the compressor). Two switching modes of the heat pump system 200 and the three-way reversing valve 210 will now be described with reference to fig. 8 and 10. When the heat pump system 200 performs a heating cycle in the non-defrost mode, the solenoid 46 of the three-way selector valve 210 is in a power-off state, the pilot spool 47 is driven by the left compression spring 45 to move to the right, the high-pressure gas introduced from the port D enters the left piston chamber 42 through the capillary tube, the piston 44 and the main spool 41 move to the right, and the port E (first heat exchanger connection) communicating with the main spool chamber communicates with the port S (suction connection of the compressor) through the orifice 48 of the main spool 41. At this time, the working fluid flowing out of the first heat exchanger 203 enters from the port E of the three-way selector valve 210, flows out from the port S, flows directly into the gas-liquid separator 202 along the solid arrow, and then enters the inlet O2 of the compressor 201. When the heat pump system 200 performs a refrigeration cycle in the defrosting mode, as shown in fig. 10, the solenoid 46 of the three-way selector valve 210 is in an energized state, the pilot spool 47 is moved leftward against the tension of the compression spring 45 by the magnetic force generated by the solenoid 46, the high-pressure gas introduced from the port D enters the right-end piston chamber 43 via a capillary tube, the piston 44 and the main spool 41 are moved leftward, and the port E (first heat exchanger connection pipe) communicating with the main spool chamber communicates with the port C (indoor unit, i.e., third heat exchanger connection pipe) via the orifice 49 of the main spool 41. At this time, the working fluid flowing out of the first heat exchanger 203 enters from the port E of the three-way reversing valve 210, flows out of the port C, sequentially flows through the capillary tube 207 and the third heat exchanger 208 along the dotted arrow to throttle evaporation and absorb heat, and then returns to the compressor 201 via the gas-liquid separator 202.

Since the heat pump system 200 in the second modified example is the same as the heat pump system 100 in the first modified example except that the three-way selector valve 210 is used for switching instead of the electromagnetic switch valves V11 and V12 as described above, the same advantageous effects as in the first modified example can be obtained. In addition, compared with the electromagnetic switch valve, the cost can be reduced.

< third modified example >

Fig. 11 and 12 show a heat pump system 300 according to a third modified example, in which fig. 11 is a schematic diagram showing an operation principle of the heat pump system 300, and fig. 12 is a control timing chart of components of the heat pump system 300 during a defrosting operation.

As shown in fig. 11, the constituent components of the heat pump system 300 are the same as those of the heat pump system 100 of the first modified example, and generally include a compressor 301, a gas-liquid separator 302, a first heat exchanger (outdoor heat exchanger) 303, an electronic three-way valve 304, a second heat exchanger (indoor heat exchanger) 305, an economizer 306, a capillary tube 307, an auxiliary expansion valve EXV31, and a main expansion valve EXV32, a third heat exchanger (indoor heat exchanger) 308, and an on-off valve V31 (corresponding to a third on-off valve according to the present invention), a V32 (corresponding to a fourth on-off valve according to the present invention), and a V33 (corresponding to a fifth on-off valve according to the present invention). In the heat pump system 100, the second heat exchanger 105 and the third heat exchanger 108 are connected in parallel on the water path side, and the water flow through the second heat exchanger 105 or the water flow through the third heat exchanger 108 is switched by an electronic three-way valve; in the heat pump system 300, the second heat exchanger 305 and the third heat exchanger 308 are connected in series on the water path side, and the electronic three-way valve 304 is used to control whether the third heat exchanger 308 is supplied with water. Specifically, the electronic three-way valve 304 includes one water inlet port that communicates with the water outlet port of the second heat exchanger 305 and a water outlet port that can selectively communicate with the water inlet port (B port) or the water outlet port (a port) of the third heat exchanger 308.

In the heating mode, as shown in fig. 12, the compressor 301 is turned on, the outdoor fan (not shown in the drawing) is opened, both the auxiliary expansion valve EXV31 and the main expansion valve EXV32 are opened and adjusted to an appropriate heating opening degree, the switching valve V31 is closed, the switching valve V32 is opened, the switching valve V33 is closed, the electronic three-way valve 304 turns on the port a without turning on the port B, and the water pump 350 for circulating water is always in an open state. That is, the second heat exchanger 305 is charged with water and performs a heat exchange function, while the third heat exchanger 308 is bypassed without being charged with water. At this time, the configuration and the communication path of the heat pump system 300 are identical to those of the heat pump system 100, and thus the operation process is identical, and will not be described again.

Referring next to fig. 12, when a defrosting operation is required, the compressor 301 does not need to be stopped, the outdoor fan is turned off, the auxiliary expansion valve EXV11 is turned off, the main expansion valve EXV12 is kept fully open, the on-off valve V31 is opened, the on-off valve V32 is closed, the on-off valve V33 is delayed to be opened, the electronic three-way valve 304 is switched to connect the port B without connecting the port a, and the water pump 350 is always in an open state. That is, the second heat exchanger 305 passes water and performs a heat exchange function, and the third heat exchanger 308 also passes water and performs a heat exchange function. This means that three heat exchangers are in series throughout the heat pump cycle. The working fluid will then circulate along the route indicated by the dashed arrow in fig. 11. Specifically, the high-temperature and high-pressure working fluid discharged from the discharge port O1 of the compressor 301 directly enters the second heat exchanger 305, and exchanges heat with the circulating water in the second heat exchanger 305. The working fluid condenses to release heat and the circulating water absorbs heat for heating, and the second heat exchanger 305 acts as a condenser. The working fluid then flows through the economizer 306, the main expansion valve EXV32, and the on-off valve V33 to the first heat exchanger 303. Because the auxiliary expansion valve EXV31 is closed and the main expansion valve EXV32 remains fully open, the working fluid does not experience overcooling at the economizer 306 and does not experience a throttling depressurization at the main expansion valve EXV 32. The working fluid coming to the first heat exchanger 303 is still in a medium-temperature and high-pressure state of mixing a gas state and a liquid state, so that when the working fluid exchanges heat with low-temperature ambient air in the first heat exchanger 303, the working fluid is continuously cooled and released heat, and the ambient air absorbs heat and is heated, so that the defrosting purpose is achieved. The first heat exchanger 303 corresponds to a two-stage condenser. Then, the working fluid cooled by the secondary condensation flows through the capillary tube 307 and is throttled and depressurized, and enters the third heat exchanger 308 to exchange heat with the circulating water in the third heat exchanger 308 and evaporate. Thus, where the third heat exchanger 308 acts as an evaporator, the working fluid evaporates and extracts heat from the circulating water, becoming a low pressure gaseous working fluid. The circulating water provides heat and the temperature is reduced and exits the outlet after leaving the third heat exchanger 308.

As in the first modified example, since the defrosting heat source is the compressor power and the circulating water heat amount without shutdown in the middle, the third modified example can obtain the same advantageous effects as the first modified example. In contrast, in the third modified example, since the first heat exchanger 303 requiring defrosting condenses the working fluid as the secondary condenser to release heat, the heat exchange defrosting efficiency is not as high as that of the first modified example. However, on the other hand, since the second heat exchanger 305 in the third modified example supplies heat to the circulating water as the first-stage condenser and the circulating water heated by the second heat exchanger 305 is supplied to the third heat exchanger 308 as the evaporator, the indoor temperature fluctuation is smaller, the comfort of the heat pump system is better, and the heat exchange efficiency of the third heat exchanger 308 is higher, as compared with the first modified example.

< fourth modified example >

Fig. 13 and 14 show a heat pump system 400 according to a fourth modified example, in which fig. 13 is a schematic diagram showing an operation principle of the heat pump system 400, and fig. 14 is a control timing chart of components of the heat pump system 400 during a defrosting operation.

As can be seen from comparison between fig. 13 and 6, in the heat pump system 400, the second heat exchanger 405 and the third heat exchanger 408 are integrated together to share a water path and the electronic three-way valve is removed, so that whether the second heat exchanger 405 and the third heat exchanger 408 are activated is no longer controlled in conjunction with the water path, but the on-off control of the working fluid is completely controlled by the electromagnetic switching valves V44 (corresponding to the first switching valve according to the present invention), V45 (corresponding to the second switching valve according to the present invention), V41 (corresponding to the third switching valve according to the present invention), V42 (corresponding to the fourth switching valve according to the present invention).

In the non-defrost mode, the switching valves V45 and V41 are closed, and the switching valves V44 and V42 are opened, thus activating the second heat exchanger 405 and deactivating the third heat exchanger 408. The control of the other components is similar to that in the first modified example. The high-temperature and high-pressure working fluid flowing out of the exhaust port O1 of the compressor 401 sequentially flows through the on-off valve V44, enters the second heat exchanger 405 to condense and release heat, flows through the economizer 406 to be subcooled, flows through the main expansion valve EXV42 to be depressurized, flows through the first heat exchanger 403 to evaporate and absorb heat, finally becomes low-pressure gaseous working fluid, enters the gas-liquid separator 402 to be filtered and separated from gas and liquid, and finally returns to the compressor 401 from the low-pressure side intake port O2 of the compressor 401, thereby completing the heating cycle. The second heat exchanger 405 functions as a condenser, and the first heat exchanger 403 functions as an evaporator.

In the defrost mode, the switching valves V44 and V42 are closed, and the switching valves V45 and V41 are opened, thus deactivating the second heat exchanger 405 and activating the third heat exchanger 408. The control of the other components is similar to that in the first modified example. The high-temperature and high-pressure working fluid flowing out of the discharge port O1 of the compressor 401 sequentially flows through the on-off valve V45, flows through the economizer 406 without heat exchange and supercooling, flows through the main expansion valve EXV42 and the on-off valve V43 (corresponding to the fifth on-off valve according to the present invention) without depressurization, flows through the first heat exchanger 403 to condense heat release, flows through the on-off valve V41, flows through the capillary tube 407 to throttle depressurization, flows through the third heat exchanger 408 to evaporate heat absorption into a low-pressure gaseous working fluid, enters the gas-liquid separator 402 to perform filtration and gas-liquid separation, and finally returns to the compressor 401 from the low-pressure side intake port O2 of the compressor 401, completing the refrigeration cycle. The first heat exchanger 403 functions as a condenser, and the third heat exchanger 408 functions as an evaporator.

The heat pump system 400 of the fourth modified example can obtain the same advantageous effects as the heat pump system 100 of the first modified example.

Although not shown here, it is understood that the heat pump system 400 of the fourth modified example can also be implemented as a heat pump system that defrosts by two-stage condensation similarly to the heat pump system 300, with the electromagnetic opening and closing valves V44 and V45 removed.

Although various embodiments and modifications of the present disclosure have been specifically described above, it will be understood by those skilled in the art that the present disclosure is not limited to the specific embodiments and modifications described above but may include other various possible combinations and combinations. Other modifications and variations may be effected by one skilled in the art without departing from the spirit and scope of the disclosure. All such variations and modifications are intended to fall within the scope of the present disclosure. Moreover, all the components described herein may be replaced by other technically equivalent components.

Claims

1. A refrigerant cycle system, comprising:

a compressor;

a first heat exchanger disposed at a low pressure side of the compressor;

a second heat exchanger disposed on a high pressure side of the compressor; and

a main expansion valve disposed between the second heat exchanger and the first heat exchanger,

it is characterized in that the preparation method is characterized in that,

the refrigerant circulating system further includes an expansion device and a third heat exchanger disposed between the first heat exchanger and the compressor, the expansion device being connected in series to an upstream side of the third heat exchanger,

wherein the refrigerant cycle system is switchable between at least a first mode of operation in which the second heat exchanger functions as a condenser, the first heat exchanger functions as an evaporator and the expansion device and the third heat exchanger are bypassed; in the second mode of operation, the first heat exchanger functions as a condenser and the third heat exchanger functions as an evaporator.

2. The refrigerant cycle system as claimed in claim 1, wherein the second heat exchanger does not exchange heat in the second operation mode.

3. The refrigerant cycle system as set forth in claim 2, further comprising an electronic three-way valve disposed between said second heat exchanger and said third heat exchanger, said electronic three-way valve including a water inlet connected to a water pump and a water outlet selectively communicable with said second heat exchanger or said third heat exchanger, wherein said electronic three-way valve is controllable to:

in the first mode of operation, the water outlet is in communication with the second heat exchanger, and

in the second mode of operation, the water outlet is in communication with the third heat exchanger.

4. The refrigerant circulation system as claimed in claim 2, further comprising:

a first switching valve disposed in series with the second heat exchanger;

a first bypass passage provided in parallel with the second heat exchanger; and

a second switching valve provided in the first bypass passage,

wherein in the first mode of operation, the first on-off valve is open and the second on-off valve is closed to communicate with the second heat exchanger; in the second mode of operation, the first on-off valve is closed and the second on-off valve is open to bypass the second heat exchanger.

5. The refrigerant cycle system as set forth in claim 1, wherein in said second mode of operation, said second heat exchanger functions as a primary condenser and said first heat exchanger functions as a secondary condenser.

6. The refrigerant cycle system as set forth in claim 5, further comprising an electronic three-way valve disposed between said second heat exchanger and said third heat exchanger, said electronic three-way valve including a water inlet in communication with a water outlet of said second heat exchanger and a water outlet selectively communicable with a water inlet or a water outlet of said third heat exchanger, wherein said electronic three-way valve is controllable to:

in the first operation mode, a water outlet of the electronic three-way valve communicates with a water outlet of the third heat exchanger, and

in the second operation mode, a water outlet of the electronic three-way valve is communicated with a water inlet of the third heat exchanger.

7. The coolant circulation system according to any one of claims 1 to 6, further comprising:

a third on/off valve provided in series with the expansion device and the third heat exchanger;

a second bypass passage provided in parallel with the expansion device and the third heat exchanger; and

a fourth switching valve provided in the bypass passage,

wherein, in the first mode of operation, the third on-off valve is closed and the fourth on-off valve is open to bypass the expansion device and the third heat exchanger; in the second operation mode, the third switching valve is opened and the fourth switching valve is closed to communicate the expansion device and the third heat exchanger.

8. The refrigerant cycle system as recited in any one of claims 1 to 6 further comprising a three-way reversing valve disposed between the expansion device, the first heat exchanger, and the low pressure side intake of the compressor, the three-way reversing valve including a first heat exchanger interface and an expansion device interface and a compressor interface selectively communicable with the first heat exchanger interface,

wherein in the first mode of operation, the three-way reversing valve is in a first position in which the first heat exchanger port is in communication with the compressor port to bypass the expansion device and the third heat exchanger; in the second mode of operation, the three-way reversing valve is in a second position in which the first heat exchanger port is in communication with the expansion device port to communicate the expansion device and the third heat exchanger.

9. The refrigerant cycle system as recited in claim 8, wherein the three-way reversing valve further comprises an interface communicating with a high pressure side discharge port of the compressor to urge a main spool valve of the three-way reversing valve to slide between the first position and the second position by a discharge pressure of the compressor.

10. The refrigerant cycle system as claimed in any one of claims 1, 2, 4, and 5, wherein the second heat exchanger and the third heat exchanger are integrated in a single housing.

11. The refrigerant cycle system as set forth in any one of claims 1 to 6, further comprising an economizer disposed between said second heat exchanger and said main expansion valve, wherein in said first mode of operation, said economizer is for subcooling a working fluid and providing vapor injection enthalpy to said compressor; in the second mode of operation, the economizer does not function as a heat exchanger.

12. The refrigerant cycle system according to any one of claims 1 to 6, further comprising a third bypass passage provided in parallel with the main expansion valve and a fifth switching valve provided in the third bypass passage, wherein, in the first operation mode, the fifth switching valve is closed and the main expansion valve is opened at a predetermined opening degree; in the second operation mode, the fifth switching valve is opened and the main expansion valve is kept fully opened or closed.

13. The refrigerant cycle system as claimed in any one of claims 1 to 6, further comprising a gas-liquid separator disposed between the evaporator and the compressor.

14. The refrigerant cycle system according to any one of claims 1 to 6, wherein the refrigerant cycle system is a heat pump system.

15. A method of defrosting a refrigerant cycle system, wherein the refrigerant cycle system is as claimed in any one of claims 1 to 14, wherein the first heat exchanger of the refrigerant cycle system is defrosted by switching the refrigerant cycle system to the second mode of operation.