VAPOR INJECTION HEAT PUMP SYSTEM AND METHOD FOR OPERATING SAME

Description

TECHNICAL FIELD

An embodiment relates to a vapor injection heat pump system and an operation method thereof.

BACKGROUND ART

Under the trend of development of eco-friendly industries and development of energy sources that replace fossil fuels, the most attractive fields in the automobile industry in recent years are electric and hybrid vehicle fields. Batteries are mounted in electric and hybrid vehicles, provide driving power to the electric and hybrid vehicles, and are used not only for traveling but also for heating and cooling.

In vehicles in which driving power is provided using batteries, the use of batteries as a heat source during cooling or heating means that a traveling distance thereof is reduced as much, and a method of applying a heat pump system that is conventionally widely used as a home cooling and heating system to vehicles has been proposed to overcome the above problem.

A heat pump is an apparatus that absorbs low-temperature heat and changes the absorbed heat to high-temperature heat. As one example, the heat pump has a cycle in which a liquid refrigerant becomes gas by evaporating in an evaporator, absorbing heat from surroundings, and then is liquefied while emitting heat to the surroundings by a condenser. When the heat pump is applied to an electric vehicle or hybrid vehicle, there is an advantage of securing a heat source that is insufficient in a conventional general air conditioner case.

Such a heat pump system may operate in a first heating mode and a second heating mode according to a heating load. In this case, noise due to switching of a refrigerant valve may occur, and vibrations increase while a refrigerant in an abnormal state of a high flow speed hits a wall surface of a gas-liquid separator, circulates downward along an inner wall, and is separated into a gas phase refrigerant and a liquid phase refrigerant.

Technical Problem

The present invention is directed to providing a vapor injection heat pump system and an operation method thereof.

Technical Solution

One aspect of the present invention provides an operation method of a vapor injection heat pump system which includes a compressor, an indoor heat exchanger, a vapor injection module, an outdoor heat exchanger, and an evaporator and in which the vapor injection module includes a first expansion unit, a gas-liquid separator, and a second expansion unit, the operation method including an operation of performing control in a first heating mode which is a non-vapor injection heating mode or a second heating mode which is a vapor injection heating mode, wherein, in the operation of performing control, a refrigerant introduced into the vapor injection module is controlled to expand in the first expansion unit, not expand after passing through the gas-liquid separator, and pass through the second expansion unit in the first heating mode, and the refrigerant introduced into the vapor injection module is controlled to expand primarily in the first expansion unit, pass through the gas-liquid separator, and then expand secondarily in the second expansion unit in the second heating mode.

In the operation of performing control, when the first heating mode is performed for a predetermined time and then switched to the second heating mode, an end time of the first heating mode and a start time of the second heating mode may be set to be the same, or the end time of the first heating mode may be set to be later than the start time of the second heating mode.

In the operation of performing control, the second heating mode may be performed for a predetermined time and then switched to the first heating mode, and an end time of the first heating mode and a start time of the second heating mode may be set to be the same, or the end time of the second heating mode may be set to be later than the start time of the first heating mode.

The operation of performing control may perform control in the first heating mode for a predetermined time and then control in the second heating mode or perform direct control in the second heating mode according to a pressure difference between an inlet side pressure and an outlet side pressure of the compressor.

The operation of performing control may perform control in the second heating mode when a pressure difference between the inlet side pressure and the outlet side pressure of the compressor is greater than a predetermined reference pressure and perform control in the first heating mode when the pressure difference is smaller than or equal to the predetermined reference pressure.

Another aspect of the present invention provides a vapor injection heat pump system including a compressor, an indoor heat exchanger, a vapor injection module, an outdoor heat exchanger, an evaporator, and a controller, wherein the vapor injection module includes a first expansion unit which blocks a flow of a condensed refrigerant or expands and transfers the condensed refrigerant according to a first heating mode which is a non-vapor injection heating mode or a second heating mode which is a vapor injection heating mode, a gas-liquid separator which separates the refrigerant received from the first expansion unit into a gas phase refrigerant and a liquid phase refrigerant, and a second expansion unit which allows the condensed refrigerant to pass therethrough or expand or allows the liquid phase refrigerant separated in the gas-liquid separator to expand according to the first heating mode or the second heating mode, and the controller controls the refrigerant introduced into the vapor injection module to expand in the first expansion units, not expand after passing through the gas-liquid separator, and pass through the second expansion unit in the first heating mode and controls the refrigerant introduced into the vapor injection module to expand primarily in the first expansion unit and expand secondarily in the second expansion unit after passing through the gas-liquid separator in the second heating mode.

The controller may set a control time for the first expansion unit and a control time for the second expansion unit to be the same or set the control time for the first expansion unit to be later than the control time for the second expansion unit when the first heating mode is performed for a predetermined time and then switched to the second heating mode.

The controller may set a control time for the first expansion unit and a control time for the second expansion unit to be the same or set the control time for the second expansion unit to be later than the control time for the first expansion unit when the second heating mode is performed for a predetermined time and then switched to the first heating mode.

The controller may perform control in the first heating mode for a predetermined time or perform direct control in the second heating mode according to a pressure difference between an entrance side pressure and an exit side pressure of the compressor.

The controller may perform control in the second heating mode when a pressure difference between the inlet side pressure and the outlet side pressure of the compressor is greater than a predetermined reference pressure and control in the first heating mode when the pressure difference is smaller than or equal to the predetermined reference pressure.

Advantageous Effects

According to an embodiment, a refrigerant transferred to a compressor can be minimized by adjusting an opening extent of a first expansion unit to meet a target control value and fully opening a second expansion unit in a non-vapor injection heating mode, and system stability can be improved because the first expansion unit is not closed.

According to an embodiment, the occurrence of instantaneous high pressure can be suppressed by simultaneously opening a first expansion unit and a second expansion unit or sequentially opening the first expansion unit and the second expansion unit in a vapor injection module when a first heating mode is switched to a second heating mode, thereby reducing noise and vibration due to the mode switching.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a vapor injection heat pump system according to an embodiment of the present invention.

FIG. 2 is a view illustrating a detailed configuration of a vapor injection module illustrated in FIG. 1.

FIG. 3 is a view illustrating an operation method of a cooling mode according to the embodiment of the present invention.

FIG. 4 is a view illustrating an operation method of a heating mode according to the embodiment of the present invention.

FIGS. 5A and 5B are views for describing a principle of operating in the heating mode.

FIG. 6 is a view illustrating an operation method of a first heating mode illustrated in FIG. 4.

FIG. 7 is a view illustrating an operation method of a second heating mode illustrated in FIG. 4.

MODES OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, the technical spirit of the present invention is not limited to some embodiments which will be described and may be implemented in a variety of different forms, and one or more components of the embodiments may be selectively combined, substituted, and used within the range of the technical spirit of the present invention.

In addition, unless clearly and specifically defined otherwise by the context, all terms (including technical and scientific terms) used herein can be interpreted as having meanings customarily understood by those skilled in the art, and the meanings of generally used terms, such as those defined in commonly used dictionaries, will be interpreted in consideration of contextual meanings of the related art.

In addition, the terms used in the embodiments of the present invention are considered in a descriptive sense only and not to limit the present invention.

In the present specification, unless specifically indicated otherwise by the context, singular forms include plural forms, and in a case in which “at least one (or one or more) among A, B, and C” is described, this may include at least one combination among all possible combinations of A, B, and C.

In addition, in descriptions of components of the present invention, terms such as “first,” “second,” “A,” “B,” “(a),” and “(b)” may be used.

The terms are only to distinguish one component from another component, and the essence, order, and the like of the components are not limited by the terms.

In addition, it should be understood that, when a first component is referred to as being “connected,” “coupled,” or “linked” to a second component, such a description may include both a case in which the first component is directly connected, coupled, or linked to the second component, and a case in which the first component is connected or coupled to the second component with a third component disposed therebetween.

In addition, when a first component is described as being formed or disposed “on (above)” or “under (below)” a second component, such a description includes both a case in which the two components are formed or disposed in direct contact with each other and a case in which one or more other components are interposed between the two components. In addition, when the first component is described as being formed “on (above) or under (below)” the second component, such a description may include a case in which the first component is formed at an upper side or a lower side with respect to the second component.

FIG. 1 is a view illustrating a vapor injection heat pump system according to an embodiment of the present invention, and FIG. 2 is a view illustrating a detailed configuration of a vapor injection module illustrated in FIG. 1.

Referring to FIGS. 1 and 2, the vapor injection heat pump system according to the embodiment of the present invention may include a vapor injection module 1, a compressor 10, an indoor heat exchanger 20, a condenser 30, an outdoor heat exchanger 40, a third expansion unit 50, an evaporator 60, a fourth expansion unit 70, a chiller 80, an accumulator 90, and a controller 2.

The compressor 10 is driven by power received from an engine (internal combustion engine), motor, or the like, suctions and compresses a refrigerant, and discharges the refrigerant in a high-temperature and high-pressure gas state toward the condenser 30.

The condenser 30 serves as a condenser 30 in both cooling and heating modes. The condenser 30 may condense the compressed refrigerant. The refrigerant condensed in the condenser 30 flows along a first line 100 and is supplied to the vapor injection module 1.

The vapor injection module 1 may include the first line 100, a second line 200, a third line 300, a gas-liquid separator 400, a first expansion unit 500, and a second expansion unit 600.

The first line 100 may be connected to an inlet 110, through which the refrigerant is introduced, to provide a passage through which the refrigerant is introduced into the vapor injection module 1. As an example, the first line 100 may have a circular pipe structure, and any of various pipe structures may be used for the first line 100.

The gas-liquid separator 400 may receive the refrigerant from the first expansion unit 500 and separate the refrigerant into a gas phase refrigerant and a liquid phase refrigerant. The gas-liquid separator 400 may move the separated gas phase refrigerant to the compressor 10 and move the separated liquid phase refrigerant to the third line 300.

The gas-liquid separator 400 may include a housing 410, an outlet passage 420, and a flow passage 430.

The housing 410 provides an inner space in which the refrigerant flows. The housing 410 may be provided to have a cylindrical structure, and an inner wall of the housing 410 may be inclined. Due to such an inclination, a radius decreases toward a lower portion, and thus, there is a flow speed compensation effect. An outlet may be disposed in an upper portion of the housing 410, and the flow passage 430 may be formed in a lower portion of the housing 410.

The outlet passage 420 may be connected to the outlet, and the gas phase refrigerant may flow to the outlet through the outlet passage 420.

The second line 200 may be connected to one upper region of the housing 410 and disposed such that the refrigerant is discharged toward a sidewall of the housing 410 to form a circulating flow. The refrigerant discharged from the second line 200 descends while whirling along a sidewall of the outlet passage 420.

The flow passage 430 provides a passage through which the refrigerant liquefied in the housing 410 flows toward the second expansion unit 600 disposed in the third line 300. A partition wall 440 for preventing scattering of the refrigerant may be disposed at one side of the flow passage 430.

The partition wall 440 may be disposed in a central portion of the flow passage 430, that is, under the outlet passage 420, and prevent the refrigerant flowing in the flow passage from being scattered and introduced into the outlet passage 420. As an example, the partition wall 440 may have a circular plate structure and a diameter greater than a diameter of the outlet passage 420. A shape of the partition wall 440 may not be limited, may be formed to be greater than a cross section of the outlet passage 420, and may be variously changed according to a cross-sectional shape of the outlet passage 420.

In addition, a fixed portion may be connected to the partition wall 440 and fixed to the housing 410. As an example, the fixed portion may have a rod structure and be fixed as a structure in which one side is connected to the partition wall 440 and the other side is fixed to the housing 410.

One side of the second line 200 may be connected to the first line 100, and the other side thereof may be connected to one upper region of the gas-liquid separator 400. The second line 200 may provide a passage through which the refrigerant flows, and the first expansion unit 500 may be disposed in one region of the second line 200.

The first expansion unit 500 may block a flow of the condensed refrigerant or expand the condensed refrigerant and transfer the condensed refrigerant to the gas-liquid separator 400 according to an air conditioning mode. The first expansion unit 500 may include a first ball valve 510 disposed and rotated in a center of the second line 200. The first ball valve 510 may include a first inlet hole 511 and a first expansion groove 513 connected to the first inlet hole 511.

The refrigerant introduced into the first expansion unit 500 may flow through the first inlet hole 511 formed in the first ball valve 510, expand while passing through the first expansion groove 513, and be introduced into the gas-liquid separator 400.

A 2-way expansion valve may be used as the first expansion unit 500.

The first ball valve 510 may be connected to a driving part and rotated, and the refrigerant flowing to the second line 200 may be moved or blocked by the rotation of the first ball valve 510.

The third line 300 may be connected to the first line 100 and one region of a lower side of the gas-liquid separator 400 to provide a passage through which the refrigerant may flow. One side of the third line 300 may be connected to the first line 100, and the other side thereof may be connected to the flow passage 430 of the gas-liquid separator 400 so that the refrigerant may flow.

The second expansion unit 600 may allow the condensed refrigerant to pass therethrough or expand or allow the liquid phase refrigerant separated in the gas-liquid separator 400 to expand according to an air conditioning mode.

The second expansion unit 600 may be disposed on the third line 300 and control a flow direction or expansion of the liquid phase refrigerant introduced through the first line 100 or separated in and introduced from the gas-liquid separator 400. The second expansion unit 600 may allow the condensed refrigerant to pass therethrough or expand when the first expansion unit 500 blocks a flow of the condensed refrigerant.

A 3/2-way expansion valve may be used as the second expansion unit 600. The 3/2-way expansion valve may serve flow direction, expansion, and flow rate control functions for the introduced refrigerant.

The second expansion unit 600 may include a second inlet hole 611, a second outlet hole 613 connected to the second inlet hole 611, and a second ball valve 610 including a second expansion groove 613a formed in one side of the second outlet hole 613.

The second ball valve 610 may be formed in a spherical shape, connected to a driving part (not shown), and rotated. The second ball valve 610 may be disposed in the second expansion unit 600.

The second ball valve 610 may be connected to the second inlet hole 611 and the second outlet hole 613 to form a passage through which the refrigerant flows. As an example, the second inlet hole 611 and the second outlet hole 613 may be connected at 90 degrees. However, an angle between the second inlet hole 611 and the second outlet hole 613 is not limited and may be variously changed.

The second expansion groove 613a may be connected to an end portion of the second outlet hole 613, expand the refrigerant flowing through the second outlet hole 613, and allow the refrigerant to flow. As an example, the second expansion groove 613a may be formed in a slander shape to expand the refrigerant using a change in pressure of the flowing refrigerant.

The second ball valve 610 operates such that the refrigerant flows or expands. The second ball valve 610 may operate such that the refrigerant flows or expands by changing positions of the second inlet hole 611, the second outlet hole 613, and the second expansion groove 613a.

The first expansion unit 500 and the second expansion unit 600 may be electronic expansion valves, although not illustrated with reference numerals, include actuators (motors) for rotating the ball valves, and control expansion amounts and flow rates of the refrigerant according to rotation angles of the actuators.

The indoor heat exchanger 20 may heat indoors by exchanging heat of a refrigerant introduced from the compressor 10 with air conditioning wind. The indoor heat exchanger 20 may be disposed in an air conditioner case C of a vehicle with the evaporator 60, which will be described below, to heat the vehicle indoors.

The outdoor heat exchanger 40 is installed in front of a vehicle engine room with a radiator as an air-cooled heat exchanger and disposed on a straight line in a flowing direction of air blown from a blower fan. In addition, the outdoor heat exchanger 40 may exchange heat with a low-temperature cooling water discharged from the radiator.

In addition, the outdoor heat exchanger 40 may serve to perform a different function according to an air conditioning mode. The outdoor heat exchanger 40 serves as a condenser 30 which is the same as a water-cooled condenser 30 in the cooling mode and serves as an evaporator 60 which is different from the water-cooled condenser 30 in the heating mode.

The third expansion unit 50 is disposed at an entrance of the evaporator 60 and may serve expansion and flow rate control functions for the refrigerant and opening and closing functions.

The evaporator 60 is installed in the air conditioner case C and disposed in a refrigerant circulation line, a low-temperature and low-pressure refrigerant discharged from the third expansion unit 50 is supplied to the evaporator 60, and air flowing in the air conditioner case C using a blower exchanges heat with the low-temperature and low-pressure refrigerant in the evaporator 60 and changes to cold wind while passing through the evaporator 60 and is discharged into the vehicle indoors to cool the vehicle indoors. That is, the evaporator 60 serves as an evaporator 60 in the refrigerant circulation line.

The fourth expansion unit 70 is connected to the third expansion unit 50 in parallel and may serve expansion and flow rate control functions for the circulating refrigerant and opening and closing functions.

In the chiller 80, a low-temperature and low-pressure refrigerant discharged from the fourth expansion unit 70 may be provided and exchange heat with cooling water flowing in a cooling water circulation line. Meanwhile, the cold cooling water of which heat is exchanged in the chiller 80 may circulate the cooling water circulation line and exchange heat with a high-temperature battery.

The accumulator 90 may be installed on a refrigerant circulation line at an inlet of the compressor 10, a refrigerant passing through the evaporator 60 and/or the chiller 80 may be joined to the accumulator 90, the accumulator 90 may separate the refrigerant into a liquid phase refrigerant and a gas phase refrigerant, supply only the gas phase refrigerant to the compressor 10, and store the remaining refrigerant.

A suction port of the compressor 10 may be connected to a gas phase refrigerant outlet of the accumulator 90 and prevent the liquid phase refrigerant from being suctioned to the compressor 10.

The controller 2 may control the vapor injection module 1 to control the cooling mode and the heating mode. The heating mode may include a first heating mode which is a non-vapor injection heating mode and a second heating mode which is a vapor injection heating mode.

In the cooling mode, the controller 2 may close the first expansion unit 500 of the vapor injection module to block a flow of a condensed refrigerant and fully open the second expansion unit 600 to allow the condensed refrigerant to pass therethrough.

The controller 2 may perform driving in the first heating mode or the second heating mode on the basis of a pressure difference between a first pressure which is a pressure at an inlet of the compressor and a second pressure which is a pressure at an outlet thereof.

As an example thereof, the controller 2 may drive the first heating mode when a pressure difference between a first pressure and a second pressure is greater than a predetermined reference pressure.

In the first heating mode, the controller 2 may expand the condensed refrigerant by opening the first expansion unit 500, that is, adjusting an opening extent to meet a target control value and expand the condensed refrigerant by fully opening the second expansion unit 600.

In this case, when the second expansion unit 600 is fully opened, the refrigerant transferred to the compressor can be minimized to an extremely small amount thereof.

In addition, the first heating mode may be switched to the second heating mode after performed for a predetermined time. In this case, an end time of the first heating mode may be set to be the same as a start time of the second heating mode, or the end time of the first heating mode may be set to be later than the start time of the second heating mode.

As another example, the controller 2 may drive the second heating mode when a pressure difference between a first pressure and a second pressure is smaller than or equal to the predetermined reference pressure.

In the second heating mode, the controller 2 may expand the condensed refrigerant by opening the first expansion unit 500 and expand the condensed refrigerant by opening the second expansion unit 600, that is, reducing an opening extent thereof. The second heating mode may be switched to the first heating mode after performed for a predetermined time.

Then, the second heating mode may be switched to the first heating mode after performed for a predetermined time. In this case, an end time of the first heating mode may be set to be the same as a start time of the second heating mode, or the end time of the second heating mode may be set to be later than the start time of the first heating mode.

FIG. 3 is a view illustrating an operation method of the cooling mode according to the embodiment of the present invention.

Referring to FIG. 3, in the cooling mode, a first expansion valve of the vapor injection module may be closed to block a flow of a condensed refrigerant (S310), and a second expansion valve may be fully opened to allow the condensed refrigerant to pass therethrough (S320). That is, when a refrigerant is introduced through the inlet 110, the flow of the refrigerant is blocked by the first expansion unit 500 in the second line 200 connected to the first line 100.

The refrigerant blocked from flowing to the second line 200 by the first expansion unit 500 may flow to the third line 300, and the second expansion unit 600 may allow the refrigerant introduced through the third line 300 to bypass and flow to a refrigerant outlet.

FIG. 4 is a view illustrating an operation method of the heating mode according to the embodiment of the present invention, and FIGS. 5A and 5B are views for describing a principle of operating in the heating mode. FIG. 6 is a view illustrating an operation method of the first heating mode illustrated in FIG. 4, and FIG. 7 is a view illustrating an operation method of the second heating mode illustrated in FIG. 4.

Referring to FIGS. 4 to 7, the vapor injection heat pump system (hereinafter, heat pump system) according to the embodiment of the present invention may measure a first pressure which is an inlet side pressure of the compressor and a second pressure which is an outlet side pressure thereof when the heating mode is performed according to a manipulation of a user (S410).

The heat pump system may calculate a pressure difference between the first pressure and the second pressure (S420) and compare the calculated pressure difference with a predetermined reference pressure (S430). For example, the reference pressure may be set to 2 bar but is not necessarily limited thereto.

The heat pump system may operate in the first heating mode when the calculated pressure difference is greater than the predetermined reference pressure (S440).

When the first heating mode is performed as in FIGS. 5A and 6, the heat pump system may expand the condensed refrigerant by adjusting an opening extent of the first expansion unit 500 to meet a target control value and allow the condensed refrigerant to pass through the second expansion unit 600 by fully opening the second expansion unit 600.

In the first heating mode, when the refrigerant is introduced through the inlet 110, the refrigerant is expanded by the first expansion unit 500 in the second line 200 connected to the first line 100.

The second ball valve 610 of the second expansion unit 600 may operate to block the refrigerant from being introduced into the third line 300 from the first line 100 and allow the refrigerant to be introduced into the third line 300 connected to the first line 100.

The heat pump system may operate in the first heating mode for a predetermined time, then switch the first heating mode to the second heating mode, and operate in the second heating mode (S450). For example, the predetermined time may be set to 60 seconds but is not necessarily limited thereto

When the heating mode is performed as described above, the reason why the first heating mode is performed for the predetermined time and then switched to the second heating mode and the second heating mode is performed is for preventing a liquid phase refrigerant from being introduced into the suction port of the compressor at an initial state.

As in FIGS. 5B and 6, when the first heating mode is switched to the second heating mode, the first expansion unit 500 may expand the condensed refrigerant by adjusting an opening extent to meet the target control value, the gas-liquid separator 400 may separate the expanded refrigerant into a gas phase refrigerant and a liquid phase refrigerant, transfer the gas phase refrigerant to the compressor, and transfer the liquid phase refrigerant to the second expansion unit 600, and the second expansion unit 600 may expand the condensed refrigerant by reducing the opening extent to meet the target control value.

In the case of the second heating mode, when a refrigerant is introduced through the inlet 110, the first expansion unit 500 is opened so that the refrigerant is introduced, and the introduced refrigerant is expanded as a middle-pressure refrigerant in the first expansion unit 500 and introduced into the gas-liquid separator 400. The first expansion unit 500 may expand the introduced refrigerant into the middle-pressure refrigerant to reduce a load applied to the compressor and improve heat exchange efficiency in the evaporator.

The refrigerant introduced into the gas-liquid separator 400 may circulate downward along the sidewall of the housing 410 of the gas-liquid separator 400, and the liquid phase refrigerant separated in the gas-liquid separator 400 may flow to the third line 300 through a connected passage, and the separated gas phase refrigerant may be discharged through the outlet passage 420.

The second ball valve 610 of the second expansion unit 600 may operate to block the refrigerant from being introduced into the third line 300 from the first line 100 and to allow the refrigerant to be introduced into the third line 300 connected to the gas-liquid separator 400. The refrigerant introduced into the second ball valve 610 may be expanded as a low-pressure refrigerant and discharged through the second expansion groove 613a.

As described above, in the second heating mode, an expansion pressure of the refrigerant may be adjusted while the refrigerant sequentially passes through the first expansion unit 500 and the second expansion unit 600, thereby improving efficiency.

In this case, when the first heating mode is switched to the second heating mode, since the second expansion unit 600 may be open prior to the first expansion unit 500, a blocked section may be generated instantaneously, and in this case, there is a concern that a high-pressure rapidly increases.

Therefore, in order to solve the problem in the embodiment, the control times for the first expansion unit 500 and the second expansion unit 600 may be set to be the same to open the first expansion unit 500 and the second expansion unit 600 at the same time, or the control time for the second expansion unit 600 may be set to be later than the control time for the first expansion unit 500 to open the first expansion unit 500 and the second expansion unit 600 sequentially. In this manner, the second expansion unit 600 is not opened prior to the first expansion unit 500. That is, even when the second expansion unit 600 is rotated and closed, since a passage is connected toward the compressor, a case at which the system is completely blocked does not happen.

However, the heat pump system may directly operate in the second heating mode when a calculated pressure difference is smaller than the predetermined reference pressure as in FIG. 7 (S450).

In the second heating mode, the first expansion unit 500 and the second expansion unit 600 may be opened at the same time, or the first expansion unit 500 and the second expansion unit 600 may be opened sequentially.

Meanwhile, here, an example of a case in which the first heating mode is switched to the second heating mode has been described, but the present invention is not necessarily limited thereto, and the second heating mode may be switched to the first heating mode.

When the second heating mode is switched to the first heating mode, since the first expansion unit is closed and the second expansion unit is opened in the first heating mode, a case, in which the first expansion unit is closed first and then a refrigerant does not flow, may happen.

Therefore, in order to solve the problem in the embodiment, the control times for the first expansion unit 500 and the second expansion unit 600 are set to be the same to open the first expansion unit 500 and the second expansion unit 600 simultaneously, or the control time for the first expansion unit 500 is set to be later than the control time for the second expansion unit 600 to open the first expansion unit 500 and the second expansion unit 600 sequentially. In this manner, the first expansion unit 500 is closed after the second expansion unit 600 is opened.

Terms such as “unit” used in the present embodiment refer to software or a hardware component such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), and objects termed “unit” perform certain roles. However, the term “unit” is not limited to software or hardware. A “unit” may reside on an addressable storage medium or operate one or more processors. Thus, in an example, the term “unit” includes components such as software components, object-oriented software components, class components, task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, micro-code, circuits, data, data bases, data structures, tables, arrays, and variables. Functions provided by these components and “units” may be combined into a smaller number of components and “units” or may be subdivided into additional components and “units.” Furthermore, the components and “units” may also be implemented to operate one or more central processing units (CPUs) within a device or a security multimedia card.

While the present invention has been described above with reference to exemplary embodiments, it may be understood by those skilled in the art that various modifications and changes of the present invention may be made within a range not departing from the spirit and scope of the present invention defined by the appended claims.