Heat pump with surge detection function based on motor shaft displacement

Abstract

A heat pump having a motor shaft displacement-based surge detection function according to the present invention comprises: a double-suction centrifugal compressor having a low-stage compression section and a high-stage compression section, respectively, for compressing refrigerant in two stages on both sides of a motor; a condenser for condensing the refrigerant compressed in the high-stage compression section; an expansion valve for expanding the refrigerant discharged from the condenser; an evaporator for evaporating the refrigerant that has passed through the expansion valve; an internal heat exchanger for heat exchange between the refrigerant supplied from the condenser to the expansion valve and the refrigerant supplied from the evaporator to the low-stage compression section; an accumulator installed between the evaporator and the internal heat exchanger as a fluid bed for the refrigerant to temporarily store and supply the refrigerant discharged from the evaporator before it flows into the internal heat exchanger; and a bypass path branched from a refrigerant discharge path connecting the outlet of the high-stage compression section and the condenser, and connected to the accumulator. The apparatus includes a control unit that opens a bypass valve installed in the bypass path so that, upon detection of a surge, a portion of the refrigerant discharged from the high-stage compression section is supplied to the accumulator through the bypass path and mixed with the refrigerant in the accumulator, wherein the control unit detects the surge based on sensing data associated with the positive suction centrifugal compressor, and the sensing data is provided in the positive suction centrifugal compressor.

Description

Technology Field

[0001] The present invention relates to a heat pump having a motor shaft displacement-based surge detection function. Background Technology

[0002] Since heat pumps for steam generation must be able to compress refrigerant to higher temperatures and pressures, the use of high-performance compressors is required. In this regard, double-suction centrifugal compressors capable of compressing refrigerant in two stages can be utilized for heat pumps for steam generation. Double-suction centrifugal compressors have the advantage of having a relatively simple structure and can be designed so that they do not require the use of lubricating oil, thereby preventing the problem of efficiency degradation caused by lubricating oil.

[0003] However, in the case of centrifugal compressors, including double-suction centrifugal compressors, surges may occur—a phenomenon in which fluid backflow repeatedly occurs because the compressor fails to produce a pressure greater than the system pressure. The occurrence of surges can lead to compressor damage, which can cause not only a reduction in the compressor's lifespan but also critical problems for the performance of the entire heat pump system.

[0004] Conventionally, when a surge was suspected, the refrigerant discharged from the centrifugal compressor was bypassed downstream of the evaporator. However, this configuration had a problem where thermal efficiency was reduced because the bypassed refrigerant entered the intercooler (internal heat exchanger) without being properly mixed during the process of merging with the refrigerant downstream of the evaporator. The problem to be solved

[0005] The objective of the present invention is to provide a heat pump equipped with a surge prevention function and a control method thereof, which can operate stably and efficiently by preventing surges while minimizing the reduction in thermal efficiency. means of solving the problem

[0006] To solve the problem described above, a heat pump having a surge protection function according to the present invention comprises: a double-suction centrifugal compressor having a low-stage compression section and a high-stage compression section, respectively, on both sides of a motor to compress refrigerant in two stages; a condenser for condensing the refrigerant compressed in the high-stage compression section; an expansion valve for expanding the refrigerant discharged from the condenser; an evaporator for evaporating the refrigerant that has passed through the expansion valve; an internal heat exchanger for heat exchange between the refrigerant supplied from the condenser to the expansion valve and the refrigerant supplied from the evaporator to the low-stage compression section; an accumulator installed between the evaporator and the internal heat exchanger as a fluid bed for the refrigerant to temporarily store and supply the refrigerant discharged from the evaporator before it flows into the internal heat exchanger; and a bypass path branched from a refrigerant discharge path connecting the outlet of the high-stage compression section and the condenser, and connected to the accumulator. and includes a control unit that opens a bypass valve installed in the bypass path so that, upon detection of a surge, a portion of the refrigerant discharged from the high-stage compression section is supplied to the accumulator through the bypass path and mixed with the refrigerant in the accumulator.

[0007] In one embodiment, the control unit can detect surge occurrence based on sensing data associated with the double-suction centrifugal compressor.

[0008] In one embodiment, the sensing data may be the pressure measured at the outlet of the high-stage compression section.

[0009] In one embodiment, the sensing data may be the shaft displacement of the motor equipped in the double-suction centrifugal compressor.

[0010] In one embodiment, the sensing data can be corrected by the outlet temperature of the high-stage compression section.

[0011] In one embodiment, the control unit can calculate the flow rate of the refrigerant discharged to the accumulator through the bypass path based on the corrected sensing data.

[0012] In one embodiment, a cooling path may be further included to bypass a portion of the refrigerant discharged from the internal heat exchanger and pass through the interior of the double-suction centrifugal compressor in order to cool the motor of the double-suction centrifugal compressor.

[0013] In one embodiment, the cooling path may include: a supply path branched between the internal heat exchanger and the expansion valve and connected to the positive suction centrifugal compressor so that a portion of the refrigerant is supplied to the interior of the positive suction centrifugal compressor; and a return path extending from the positive suction centrifugal compressor and connected to the accumulator so that the refrigerant that has cooled the motor of the positive suction centrifugal compressor is discharged and mixed with the refrigerant in the accumulator.

[0014] Meanwhile, a control method for a heat pump according to the present invention comprises: a double-suction centrifugal compressor having a low-stage compression section and a high-stage compression section each equipped on both sides of a motor to compress refrigerant in two stages; a condenser for condensing the refrigerant compressed in the high-stage compression section; an expansion valve for expanding the refrigerant discharged from the condenser; an evaporator for evaporating the refrigerant that has passed through the expansion valve; an internal heat exchanger for heat-exchanging the refrigerant supplied from the condenser to the expansion valve and the refrigerant supplied from the evaporator to the low-stage compression section; an accumulator installed between the evaporator and the internal heat exchanger as a fluid bed for the refrigerant to temporarily store and supply the refrigerant discharged from the evaporator before it flows into the internal heat exchanger; and a bypass path branched from a refrigerant discharge path connecting the outlet of the high-stage compression section and the condenser and connected to the accumulator, wherein the control method comprises the steps of: collecting sensing data associated with the double-suction centrifugal compressor; and determining whether a surge has occurred based on the sensing data. The method includes the step of opening a bypass valve installed in the bypass path so that, upon detection of a surge, a portion of the refrigerant from the high-stage compression section is supplied to the accumulator through the bypass path and mixed with the refrigerant in the accumulator, and the sensing data includes at least one of the outlet pressure of the high-stage compression section, the shaft displacement of the motor, and the rotational speed of the motor.

[0015] In one embodiment, the method may further include the step of detecting the degree of overheating of the motor based on the sensing data; and the step of controlling the flow rate of the refrigerant that bypasses between the internal heat exchanger and the expansion valve and passes through the interior of the positive suction centrifugal compressor based on the degree of overheating of the motor.

[0016] Meanwhile, a heat pump having a motor shaft displacement-based surge detection function according to the present invention comprises: a double-suction centrifugal compressor having a low-stage compression section and a high-stage compression section each provided on both sides of the motor to compress the refrigerant in two stages; a condenser that condenses the refrigerant compressed in the high-stage compression section; an expansion valve that expands the refrigerant discharged from the condenser; an evaporator that evaporates the refrigerant that has passed through the expansion valve; an internal heat exchanger that exchanges heat between the refrigerant supplied from the condenser to the expansion valve and the refrigerant supplied from the evaporator to the low-stage compression section; an accumulator installed between the evaporator and the internal heat exchanger as a fluid bed for the refrigerant to temporarily store and supply the refrigerant discharged from the evaporator before it flows into the internal heat exchanger; and a bypass path branched from a refrigerant discharge path connecting the outlet of the high-stage compression section and the condenser, and connected to the accumulator. The apparatus includes a control unit that opens a bypass valve installed in the bypass path so that, upon detection of a surge, a portion of the refrigerant discharged from the high-stage compression section is supplied to the accumulator through the bypass path and mixed with the refrigerant in the accumulator, and the control unit detects the surge based on sensing data associated with the double-suction centrifugal compressor, and the sensing data may include the shaft displacement of the motor equipped in the double-suction centrifugal compressor.

[0017] In one embodiment, the sensing data can be corrected by the outlet temperature of the high-stage compression section.

[0018] In one embodiment, the control unit can calculate the flow rate of the refrigerant discharged to the accumulator through the bypass path based on the corrected sensing data.

[0019] In one embodiment, the control unit may open the bypass valve temporarily or in stages based on the calculated flow rate of the refrigerant.

[0020] In one embodiment, the sensing data may further include the rotational speed of the motor.

[0021] In one embodiment, the control unit counts the sensing data as one occurrence if it meets a preset standard within a preset time, and determines that a surge has occurred if it is counted one or more times.

[0022] In one embodiment, the control unit may determine that a surge has occurred when both the change in the shaft displacement of the motor and the change in the outlet pressure of the high-stage compression unit satisfy a preset standard.

[0023] In one embodiment, the double-suction centrifugal compressor may have an axial support structure using magnetic bearings.

[0024] In one embodiment, an inlet guide vane controlled to regulate the flow rate of the refrigerant flowing into the low-stage compression unit may be provided on the inlet side of the low-stage compression unit.

[0025] In one embodiment, the system further includes a flow sensor installed around the positive suction centrifugal compressor or on the positive suction centrifugal compressor, and the sensing data may further include the flow rate of the refrigerant sucked into or discharged from the positive suction centrifugal compressor.

[0026] In one embodiment, the heat pump may further include a steam flash tank that generates steam through heat exchange with the condenser using circulating water.

[0027] In one embodiment, the heat pump may further include a first circulation path that guides the circulating water, which has absorbed heat from the condenser, to flow into the steam flash tank; and a second circulation path that guides the circulating water to flow from the steam flash tank to the condenser. Effects of the invention

[0028] The heat pump having a surge prevention function and the control method thereof according to the present invention can improve the stability of the heat pump by minimizing the occurrence of surges by bypassing a portion of the refrigerant discharged from the high-stage compression section of a double-suction centrifugal compressor to an accumulator. At the same time, the heat pump having a surge prevention function and the control method thereof according to the present invention can improve the heat exchange efficiency within the internal heat exchanger supplied with sufficiently mixed refrigerant by ensuring that the bypassed refrigerant, which has a temperature difference, and the refrigerant in the accumulator are sufficiently mixed with each other. This leads to an improvement in the compression efficiency of the double-suction centrifugal compressor, thereby having the effect of improving the performance of the heat pump.

[0029] In addition, the heat pump having a surge protection function and the control method thereof according to the present invention can cool the superheated motor of a double-suction centrifugal compressor by utilizing a portion of the refrigerant between the internal heat exchanger and the expansion valve, and by returning the refrigerant that cooled the motor to the accumulator, the refrigerant that cooled the motor, which has a temperature difference, and the refrigerant in the accumulator can be sufficiently mixed with each other. This also improves the compression efficiency of the double-suction centrifugal compressor, thereby improving the performance of the heat pump. Brief explanation of the drawing

[0030] FIG. 1 is a conceptual diagram schematically illustrating a heat pump according to one embodiment of the present invention. FIG. 2(a) is a block diagram illustrating the relationship between a control unit and components connected thereto according to one embodiment of the present invention, and FIG. 2(b) is a block diagram illustrating the relationship between a control unit and components connected thereto according to another embodiment of the present invention. FIG. 3 is a flowchart illustrating the operation for surge prevention according to the present invention. FIG. 4 is a conceptual diagram schematically illustrating a heat pump according to another embodiment of the present invention. FIG. 5 is a flowchart illustrating the operation for motor cooling according to the present invention. Specific details for implementing the invention

[0031] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings. In this specification, identical or similar configurations are assigned the same reference number even if they are different embodiments, and redundant descriptions thereof will be omitted. The suffixes "module," "unit," and "part" used for components in the following description are assigned or used interchangeably solely for the ease of drafting the specification and do not have distinct meanings or roles in themselves. Furthermore, the attached drawings are intended only to facilitate understanding of the embodiments disclosed in this specification, and the technical concept disclosed in this specification is not limited by the attached drawings; it should be understood that they include all modifications, equivalents, and substitutions that fall within the spirit and technical scope of the invention.

[0032] Terms including ordinal numbers, such as first, second, etc., may be used to describe various components, but said components are not limited by said terms. These terms are used solely for the purpose of distinguishing one component from another.

[0033] As used in this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0034] Where in this specification it is stated that a component is "connected" or "connected" to another component, it should be understood that it may be directly connected to or connected to the other component, or that there may be other components in between. On the other hand, where it is stated that a component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0035] In addition, terms such as “comprising” or “having” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0036] The present invention relates to a heat pump (10) having a surge prevention function and a method for controlling the same.

[0037] FIG. 1 is a conceptual diagram schematically illustrating a heat pump (10) according to one embodiment of the present invention.

[0038] Referring to FIG. 1, the heat pump (10) includes a double-suction centrifugal compressor (110), a condenser (120), an expansion valve (130), an evaporator (140), an internal heat exchanger (150), and an accumulator (160).

[0039] A double-suction centrifugal compressor (110) is equipped with a motor (111) configured to provide power for compressing refrigerant, and is equipped with a low-stage compression section (112) and a high-stage compression section (113) on each side of the motor (111) to compress the refrigerant in two stages. The low-stage compression section (112) and the high-stage compression section (113) are each connected to the motor (111) through a shaft to receive power generated by the motor (111) and to compress the refrigerant. Each of these low-stage compression section (112) and high-stage compression section (113) may be equipped with at least one of an impeller, a diffuser, and a volute. Additionally, an inlet guide vane (IGV) may be provided on the inlet side of the low-stage compression section (112) to control the flow rate of the refrigerant flowing into the low-stage compression section (112).

[0040] The double-suction centrifugal compressor (110) can be configured in a lubrication-free manner. For example, the double-suction centrifugal compressor (110) may have an axial support structure using magnetic bearings. To this end, radial magnetic bearings that support the shaft in the radial direction may be provided on each side of the motor (111), and, if necessary, a thrust magnetic bearing that supports the shaft in the axial direction may be provided on at least one side of the motor (111).

[0041] Since the double-suction centrifugal compressor (110) equipped with magnetic bearings does not require oil supply, a configuration for supplying oil to the double-suction centrifugal compressor (110) is not required. However, since the oil supplied to the double-suction centrifugal compressor (110) also served to cool the overheated motor (111), a configuration for cooling the motor (111) may be required in the double-suction centrifugal compressor (110) equipped with magnetic bearings. Accordingly, the heat pump (10) may be provided with a cooling path (173) to be described later so as to use a refrigerant to cool the motor (111) of the double-suction centrifugal compressor (110). The cooling path (173) will be explained in more detail later with reference to the drawings.

[0042] Meanwhile, the process of compressing the refrigerant by the double-suction centrifugal compressor (110) is carried out as follows. First, the refrigerant supplied (or introduced) to the low-stage compression section (112) is compressed in the low-stage compression section (112) and then sent to the high-stage compression section (113). To this end, the double-suction centrifugal compressor (110) may further be provided with a connecting passage (114) connecting the outlet of the low-stage compression section (112) and the inlet of the high-stage compression section (113). The connecting passage (114) guides the refrigerant compressed in the low-stage compression section (112) to flow (or move) to the high-stage compression section (113). The refrigerant supplied to the high-stage compression section (113) is compressed to a higher pressure in the high-stage compression section (113), and the refrigerant compressed in the high-stage compression section (113) is discharged (or released) from the high-stage compression section (113).

[0043] Here, being supplied to the low-stage compression section (112) is equivalent to being supplied to the double-suction centrifugal compressor (110), and being discharged from the high-stage compression section (113) should be considered equivalent to being discharged from the double-suction centrifugal compressor (110).

[0044] The refrigerant discharged from the high-stage compression section (113) can flow through the refrigerant discharge path (171) connecting the outlet of the high-stage compression section (113) and the condenser (120) and be introduced into the condenser (120).

[0046] *

[0047] The condenser (120) condenses the refrigerant compressed in the high-stage compression section (113). Specifically, the refrigerant compressed in the high-stage compression section (113) and in a high-temperature, high-pressure state is introduced into the condenser (120), and the introduced refrigerant is configured to release heat as it condenses within the condenser (120). The condenser (120) may also be referred to as a “cooler” or a “heat exchanger.” The refrigerant, whose temperature has been lowered by releasing heat in the condenser (120), is sent to the expansion valve (130).

[0048] At this time, as illustrated in FIG. 1, the refrigerant discharged from the condenser (120) may be configured to pass through an internal heat exchanger (150) before being sent to the expansion valve (130). That is, the refrigerant discharged from the condenser (120) may flow along the first path (181) and enter the internal heat exchanger (150), and the refrigerant discharged from the internal heat exchanger (150) may flow along the second path (182) and pass through the expansion valve (130). The internal heat exchanger (150) will be described in detail later.

[0049] The expansion valve (130) expands the refrigerant discharged from the condenser (120). Specifically, the expansion valve (130) can expand the refrigerant discharged from the condenser (120) and passing through the internal heat exchanger (150) so that the pressure of the refrigerant is lowered and it becomes a liquid state. It is also possible to control the flow rate of the refrigerant passing through this expansion valve (130). The refrigerant passing through the expansion valve (130) flows along the third path (183) and is sent to the evaporator (140).

[0050] The evaporator (140) evaporates the refrigerant that has passed through the expansion valve (130) using thermal energy transferred from the heat source. Accordingly, the liquid refrigerant absorbs the thermal energy from the heat source and becomes a gaseous state. The refrigerant discharged from the evaporator (140) is sent to the low-stage compression section (112).

[0051] At this time, as illustrated in FIG. 1, the refrigerant discharged from the evaporator (140) may be configured to pass through an internal heat exchanger (150) before being sent to the low-stage compression unit (112). Accordingly, the refrigerant discharged from the condenser (120) passes through the heat exchanger, and at the same time, the refrigerant discharged from the evaporator (140) passes through it. That is, the internal heat exchanger (150) can exchange heat between the refrigerant supplied from the condenser (120) to the expansion valve (130) and the refrigerant supplied from the evaporator (140) to the low-stage compression unit (112). The introduction of such a heat exchanger has the effect of increasing the temperature of the refrigerant supplied to the low-stage compression unit (112) and reducing the compression ratio.

[0052] Meanwhile, the refrigerant discharged from the evaporator (140) may be configured to pass through an accumulator (160) before flowing into the internal heat exchanger (150). The accumulator (160) is installed between the fluidized bed evaporator (140) and the internal heat exchanger (150) to temporarily store and supply the refrigerant discharged from the evaporator (140) before flowing into the internal heat exchanger (150).

[0053] Based on the flow of the refrigerant, the refrigerant discharged from the evaporator (140) flows along the fourth path (184) and is supplied to the accumulator (160), the refrigerant discharged from the accumulator (160) flows along the fifth path (185) and is supplied to the internal heat exchanger (150), and the refrigerant discharged from the internal heat exchanger (150) flows along the sixth path (186) and is supplied to the low-stage compression section (112).

[0054] In this way, the heat pump (10) circulates a refrigerant according to the above configuration and is configured to absorb heat from a low-temperature heat source and transport heat to a high-temperature heat source.

[0055] However, since the suction pressure of the refrigerant in the low-stage compression section (112) is always lower than the discharge pressure (or discharge pressure) of the refrigerant in the high-stage compression section (113), the refrigerant may flow back and cause a surge. To solve this, the heat pump (10) further includes a bypass path (172) used to lower the discharge pressure of the refrigerant in the high-stage compression section (113) when a surge is detected.

[0056] Referring to FIG. 1, the bypass path (172) branches off from the refrigerant discharge path (171) connecting the outlet of the high-stage compression section (113) and the condenser (120) and is connected to the accumulator (160). That is, the inlet (172a) of the bypass path is connected to the refrigerant discharge path (171), and the outlet (172b) of the bypass path is connected to the accumulator (160) that temporarily stores and supplies refrigerant.

[0057] A bypass valve (172c) may be installed in the bypass path (172). When a surge is detected, the bypass valve (172c) may be opened, and accordingly, a portion of the refrigerant discharged from the high-stage compression section (113) may be supplied to the accumulator (160) through the bypass path (172) and mixed with the refrigerant in the accumulator (160).

[0058] For the detection of surge occurrence and control of the bypass valve (172c), the heat pump (10) further includes a control unit (100). The control unit (100) and the components connected to the control unit (100) will be described with reference to FIG. 2. FIG. 2(a) is a block diagram illustrating the relationship between the components connected to the control unit (100) according to one embodiment of the present invention, and FIG. 2(b) is a block diagram illustrating the relationship between the components connected to the control unit (100) according to another embodiment of the present invention.

[0059] The control unit (100) can detect surge occurrence based on sensing data associated with the double-suction centrifugal compressor (110).

[0060] The sensing data may include values ​​measured (or sensed) by various sensors provided in the heat pump (10).

[0061] Referring to FIG. 2(a), the heat pump (10) may further include at least one pressure sensor (101). If only one pressure sensor is provided, the pressure sensor may be installed on the outlet side of the high-stage compression unit (113), and accordingly, the sensing data may include the outlet pressure of the high-stage compression unit (113). If two pressure sensors are provided, one of them may be installed on the outlet side of the high-stage compression unit (113), and the other may be installed on the inlet side of the low-stage compression unit (112) or on the double-suction centrifugal compressor (110) itself. Accordingly, the sensing data may also include data measured by both pressure sensors.

[0062] Additionally, the heat pump (10) may further include at least one temperature sensor (102). If the temperature sensor is installed on the outlet side of the high-stage compression unit (113), the sensing data may further include the outlet temperature of the high-stage compression unit (113).

[0063] Referring to FIG. 2(b), the heat pump (10) may further include a motor shaft displacement sensor (103) that senses the shaft displacement of a motor (111) provided in a double-suction centrifugal compressor (110), and accordingly, the sensing data may further include the shaft displacement of the motor (111).

[0064] Although not shown in FIG. 2, the heat pump (10) may further include a flow sensor installed around the positive suction centrifugal compressor (110) or on the positive suction centrifugal compressor (110) itself, and accordingly, the sensing data may further include the flow rate of the refrigerant sucked into or discharged from the positive suction centrifugal compressor (110).

[0065] In addition, the sensing data may include the rotational speed of the motor (111), the temperature of the motor (111), the current of the motor (111), etc., and the heat pump (10) may further include a configuration capable of sensing such data.

[0066] Any value of the sensing data may be corrected by another value of the sensing data. For example, the sensing data may be corrected by the outlet temperature of the high-stage compression unit (113). Specifically, the outlet pressure of the high-stage compression unit (113) may be corrected by the outlet temperature of the high-stage compression unit (113).

[0067] The control unit (100) detects the occurrence of a surge based on the sensing data, and when the occurrence of a surge is detected, opens the bypass valve (172c) installed in the bypass path (172) so that a portion of the refrigerant discharged from the high-stage compression unit (113) is supplied to the accumulator (160) through the bypass path (172) and mixed with the refrigerant in the accumulator (160).

[0068] The operation for surge prevention performed by the control unit (100) will be explained in detail with reference to FIG. 3. FIG. 3 is a flowchart illustrating the operation for surge prevention according to the present invention.

[0069] First, according to the control method of the heat pump (10) according to the present invention, a process of collecting sensing data is carried out (S310).

[0070] As previously explained, the sensing data may include at least one of the outlet pressure of the high-stage compression unit (113), the outlet temperature of the high-stage compression unit (113), the flow rate of refrigerant flowing into the low-stage compression unit (112) or discharged from the high-stage compression unit (113), the shaft displacement of the motor (111), and the rotational speed of the motor (111).

[0071] The control unit (100) can collect such sensing data from each sensor. To do this, the control unit (100) may be configured to communicate with each sensor via wired or wireless connection. At least some of the sensing data may be temporarily stored in the control unit (100).

[0072] The heat pump (10) may further include a storage unit. The storage unit may be equipped with a storage facility or a cloud (or server) configured to store sensing data, and such storage unit may be connected to the control unit (100) via a wired or wireless connection to transmit and receive sensing data. The storage unit may also exist in a form integrated with the control unit (100).

[0073] Next, according to the control method of the heat pump (10) according to the present invention, a process of determining whether a surge occurs based on sensing data is carried out (S320).

[0074] “Surge occurrence detection” may include cases where it is determined (or predicted) that a surge has occurred based on sensing data, or cases where a surge has not yet occurred but is determined (or predicted) that a surge will occur soon based on sensing data.

[0075] The control unit (100) can determine whether a surge has occurred based on an indicator based on sensing data. For example, the control unit (100) can determine that a “surge has occurred” if the outlet pressure of the high-stage compression unit (113) has changed rapidly, the outlet temperature of the high-stage compression unit (113) has risen abnormally, the shaft displacement of the motor (111) has changed rapidly, the rotational speed of the motor (111) is not constant, the current of the motor (111) has changed rapidly, or the flow rate of the refrigerant flowing into the low-stage compression unit (112) has decreased rapidly.

[0076] The control unit (100) may determine whether a surge has occurred based on a single indicator, but may also determine whether a surge has occurred based on two or more indicators. For example, the control unit (100) may determine that a “surge has occurred” when both the case where the outlet pressure of the high-stage compression unit (113) changes rapidly and the case where the shaft displacement of the motor (111) changes rapidly are satisfied.

[0077] Furthermore, the control unit (100) counts the case as one time when the set criteria are met within a set time, and can determine that it is a “surge occurrence detection” when it is counted at least once.

[0078] For example, the control unit (100) can count the increase or decrease in the outlet pressure of the high-stage compression unit (113) as one occurrence if it is significantly increased or decreased within 5 seconds, and can determine that it is a “surge occurrence detection” if it is counted three times.

[0079] When a surge is not detected (NO), a process (S320) of determining whether a surge has occurred based on the sensing data is performed again, and when a surge is detected (YES), a process of opening the bypass valve (172c) installed in the bypass path (172) is performed (S330).

[0080] When the bypass valve (172c) is opened by the control unit (100), a portion of the refrigerant from the high-stage compression unit (113) is supplied to the accumulator (160) through the bypass path (172) and mixed with the refrigerant in the accumulator (160).

[0081] There is a temperature difference between the bypassed refrigerant and the refrigerant in the accumulator (160). If a portion of the refrigerant discharged from the high-stage compression section (113) is bypassed to the accumulator (160), the bypassed refrigerant and the refrigerant in the accumulator (160) can be sufficiently mixed with each other. Accordingly, the heat exchange efficiency increases in the internal heat exchanger (150) supplied with the mixed refrigerant, which leads to an improvement in the compression efficiency of the double-suction centrifugal compressor (110), thereby improving the performance of the heat pump (10).

[0082] In contrast, if the flow path is bypassed to the front of the internal heat exchanger (150) rather than the accumulator (160), the refrigerant is supplied to the internal heat exchanger (150) without being sufficiently mixed with the refrigerant at the front of the internal heat exchanger (150), so the thermal efficiency may decrease.

[0083] Meanwhile, the control unit (100) can calculate the flow rate of the refrigerant discharged to the accumulator (160) through the bypass path (172) based on the sensing data. Here, the sensing data may be corrected sensing data. When using corrected sensing data, the flow rate of the refrigerant bypassed through the bypass path (172) can be calculated more accurately.

[0084] For example, if the state changes from “surge not detected” to “surge detected” based on sensing data, the control unit (100) can set the flow rate of the refrigerant bypassed through the bypass path (172) to 50% of the maximum flow rate. And if the “surge detected” state continues based on sensing data, the control unit (100) can increase the flow rate of the refrigerant bypassed through the bypass path (172) to 75% of the maximum flow rate. Conversely, if the state changes from “surge detected” to “surge not detected” based on sensing data, the control unit (100) can set the flow rate of the refrigerant bypassed through the bypass path (172) to 0% of the maximum flow rate.

[0085] Additionally, the control unit (100) can open the bypass valve (172c) temporarily or in stages based on the calculated flow rate of the refrigerant.

[0086] For example, the control unit (100) may partially open or fully open the bypass valve (172c) to increase the flow rate of the refrigerant bypassed through the bypass path (172). Here, partial opening means that the valve opening rate increases from before and changes to a value between 0% and 100%. Partial opening does not necessarily mean that the valve is opened when the valve opening rate is 0%; for example, the valve opening rate going from 10% to 20% can also be considered partial opening. Fully open means that the valve opening rate becomes 100%. Fully open also does not necessarily mean that the valve is opened when the valve opening rate is 0%; for example, the valve opening rate going from 50% to 100% can also be considered full opening.

[0087] Conversely, the control unit (100) may partially or completely close the bypass valve (172c) to reduce the flow rate of the refrigerant bypassed to the bypass path (172). Here, partial closure means that the valve opening rate decreases from the previous value and changes to a value between 0% and 100%, and complete closure means that the valve opening rate decreases to a state of 0%.

[0088] As such, the heat pump (10) according to the present invention is equipped with a surge prevention function, so that it can improve operational stability while preventing a decrease in thermal efficiency.

[0089] Meanwhile, the heat pump (10) according to the present invention may further be provided with a motor cooling function. To this end, the heat pump (10) may further include a cooling path (173). This will be explained with reference to FIG. 4. FIG. 4 is a conceptual diagram schematically illustrating a heat pump (10) according to another embodiment of the present invention.

[0090] Referring to FIG. 4, the cooling path (173) is formed to bypass a portion of the refrigerant discharged from the internal heat exchanger (150) and pass through the interior of the positive suction centrifugal compressor (110). This cooling path (173) may include a supply path (173a) and a return path (173b).

[0091] Referring to FIG. 4, the supply path (173a) may be branched between the internal heat exchanger (150) and the expansion valve (130) of the refrigerant fluid bed and connected to the positive suction centrifugal compressor (110). Specifically, the inlet of the supply path (173a) may be connected to a second path (182) connecting the internal heat exchanger (150) and the expansion valve (130), and the outlet of the supply path (173a) may be connected to the positive suction centrifugal compressor (110). Accordingly, a portion of the refrigerant flowing along the second path (182) may be supplied to the interior of the positive suction centrifugal compressor (110).

[0092] The refrigerant supplied to the inside of the double-suction centrifugal compressor (110) through the supply path (173a) can cool the motor (111) provided inside the double-suction centrifugal compressor (110).

[0093] The return path (173b) can be extended from the double-suction centrifugal compressor (110) and connected to the accumulator (160). Specifically, the inlet of the return path (173b) can be connected to the double-suction centrifugal compressor (110), and the outlet of the return path (173b) can be connected to the accumulator (160). Accordingly, the refrigerant that cooled the motor (111) of the double-suction centrifugal compressor (110) can be discharged and mixed with the refrigerant in the accumulator (160).

[0094] When the refrigerant that cooled the motor (111) is returned to the accumulator (160), the refrigerant that cooled the motor (111) at different temperatures and the refrigerant in the accumulator (160) can be sufficiently mixed. Accordingly, the heat exchange efficiency in the internal heat exchanger (150) supplied with the mixed refrigerant increases, which leads to an improvement in the compression efficiency of the double-suction centrifugal compressor (110), thereby improving the performance of the heat pump (10).

[0095] In this way, the accumulator (160) may receive refrigerant that is bypassed through the bypass path (172) and may also receive refrigerant that has cooled the motor (111). The accumulator (160) is configured to mix refrigerants of different temperatures and then discharge them to the internal heat exchanger (150).

[0096] FIG. 5 is a flowchart illustrating the operation for motor cooling according to the present invention.

[0097] According to the control method of the heat pump (10) according to the present invention, a process of collecting sensing data is carried out (S510).

[0098] The sensing data may include the temperature of the motor (111) in addition to the data described above. Accordingly, the heat pump (10) may further include a motor temperature sensor capable of sensing the temperature of the motor (111). The motor temperature sensor may measure the temperature of the motor (111) by direct contact or by non-contact. Here, the temperature of the motor (111) may refer to the temperature around the motor (111).

[0099] Next, according to the control method of the heat pump (10) according to the present invention, a process of detecting the degree of overheating of the motor (111) based on sensing data is performed (S520).

[0100] At this time, the control unit (100) can determine the degree of overheating of the motor (111) based on the sensing data. Specifically, if the temperature of the motor (111) included in the sensing data is higher than a preset temperature, the control unit (100) can determine that the motor (111) has overheated and that cooling of the motor (111) is required.

[0101] When motor (111) overheating is not detected (NO), a process (S520) of determining the degree of overheating of the motor (111) based on the sensing data is performed, and when motor (111) overheating is detected (YES), a process of controlling the cooling valve (173c) installed in the supply path (173a) is performed (S530).

[0102] The control unit (100) can control the opening of the cooling valve (173c) according to the degree of overheating of the motor (111).

[0103] For example, the control unit (100) can control the opening rate of the cooling valve (173c) to decrease when the temperature of the motor (111) is lower than the first reference temperature. The first reference temperature is a temperature at which the motor (111) is judged to be sufficiently cooled, and can be derived through experiment.

[0104] On the other hand, if the temperature of the motor (111) is higher than the first reference temperature, the control unit (100) can additionally determine whether the temperature of the motor (111) is higher than the second reference temperature. At this time, if the temperature of the motor (111) is higher than the second reference temperature, the control unit (100) can control the opening rate of the cooling valve (173c) to increase. The second reference temperature is the temperature at which the motor (111) is judged to be overheated, and this can also be derived through experiment.

[0105] On the other hand, if the temperature of the motor (111) is higher than the first reference temperature and lower than the second reference temperature, the control unit (100) can maintain the opening rate of the cooling valve (173c) at the same level as the previous state.

[0106] In this way, the control unit (100) can control the flow rate of the refrigerant passing through the interior of the double-suction centrifugal compressor (110) by bypassing between the internal heat exchanger (150) and the expansion valve (130) by controlling the cooling valve (173c) based on the degree of overheating of the motor (111).

[0107] Meanwhile, referring again to FIGS. 1 and FIGS. 4, the heat pump (10) may further include a configuration for storing heat and supplying it to an evaporator (140), and a configuration for generating steam using heat released from a condenser (120).

[0108] Specifically, the heat pump (10) may further include a heat source tank (190) and a steam flash tank (195).

[0109] A heat source tank (190) is a tank configured to store heat or thermal energy, and a hot water flow path (192) for supplying hot water, a water supply flow path (193) for supplying water, and a discharge flow path (194) for discharging water within the heat source tank (190) may be connected to the heat source tank (190). Furthermore, the heat source tank (190) supplies water that has stored heat from the heat source to an evaporator (140) through an evaporator supply flow path (191a), and after the refrigerant is evaporated in the evaporator (140), the water whose temperature has been lowered may be discharged through an evaporator discharge flow path (191b).

[0110] The steam flash tank (195) can generate steam through heat exchange with the condenser (120) using circulating water as a medium. Specifically, the steam flash tank (195) can generate steam by depressurizing the circulating water heated while passing through the condenser (120).

[0111] To enable the circulating water to circulate through the steam flash tank (195) and the condenser (120), the heat pump (10) may further include a first circulation path (196a) and a second circulation path (196b). The first circulation path (196a) may guide the circulating water, which has absorbed heat from the condenser (120), to flow into the steam flash tank (195). The second circulation path (196b) may guide the circulating water to flow from the steam flash tank (195) to the condenser (120). A pump (196c) that creates the flow of circulating water may be installed in the second circulation path (196b).

[0112] The circulating water, which repeatedly absorbs and releases heat while circulating through the steam flash tank (195) and the condenser (120), may gradually become contaminated over time and cause fouling or scaling in the condenser (120). Since fouling or scaling can degrade the heat exchange performance of the condenser (120), a purification process may be performed to prevent this by releasing a portion of the circulating water and replenishing it with clean water.

[0113] To this end, the heat pump (10) may further include a circulating water discharge path (198) for discharging a portion of the circulating water and a circulating water supply path (199) for supplying clean water.

[0114] Each of the circulating water discharge path (198) and the circulating water supply path (199) can be connected to any one of the first circulation path (196a), the second circulation path (196b), and the steam flash tank (195).

[0115] Steam generated in the steam flash tank (195) can be discharged to the outside through the steam flow path (197) connected to the steam flash tank (195).

[0116] Meanwhile, the above detailed description should not be interpreted restrictively in all respects but should be considered exemplary. The scope of the invention shall be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the invention are included within the scope of the invention.

Claims

Claim 1 A double-suction centrifugal compressor having a low-stage compression section and a high-stage compression section, respectively, on both sides of a motor to compress refrigerant in two stages; a condenser that condenses the refrigerant compressed in the high-stage compression section; an expansion valve that expands the refrigerant discharged from the condenser; an evaporator that evaporates the refrigerant passing through the expansion valve; an internal heat exchanger that exchanges heat between the refrigerant supplied from the condenser to the expansion valve and the refrigerant supplied from the evaporator to the low-stage compression section; an accumulator installed between the evaporator and the internal heat exchanger as a refrigerant fluid bed to temporarily store and supply the refrigerant discharged from the evaporator before it flows into the internal heat exchanger; and a bypass path branched from a refrigerant discharge path connecting the outlet of the high-stage compression section and the condenser, and connected to the accumulator. A heat pump having a motor shaft displacement-based surge detection function, comprising a control unit that opens a bypass valve installed in the bypass path so that when a surge is detected, a portion of the refrigerant discharged from the high-stage compression section is supplied to the accumulator through the bypass path and mixed with the refrigerant in the accumulator, wherein the control unit detects the occurrence of a surge based on sensing data associated with the positive suction centrifugal compressor, and the sensing data includes the shaft displacement of the motor equipped in the positive suction centrifugal compressor. Claim 2 A heat pump having a motor shaft displacement-based surge detection function, characterized in that, in claim 1, the sensing data is corrected by the outlet temperature of the high-stage compression section. Claim 3 A heat pump having a motor shaft displacement-based surge detection function, wherein, in paragraph 2, the control unit calculates the flow rate of the refrigerant discharged to the accumulator through the bypass path based on the corrected sensing data. Claim 4 A heat pump having a motor shaft displacement-based surge detection function, wherein, in paragraph 3, the control unit temporarily or stepwise opens the bypass valve based on the calculated refrigerant flow rate. Claim 5 A heat pump having a motor shaft displacement-based surge detection function, characterized in that, in claim 1, the sensing data further includes the rotational speed of the motor. Claim 6 A heat pump having a motor shaft displacement-based surge detection function, wherein, in claim 1, the control unit counts the sensing data as one occurrence when it meets a preset standard within a preset time, and determines that a surge is detected when it is counted one or more times. Claim 7 A heat pump having a motor shaft displacement-based surge detection function, wherein, in claim 1, the control unit determines that a surge has occurred when both the change in shaft displacement of the motor and the change in outlet pressure of the high-stage compression unit satisfy a preset standard. Claim 8 A heat pump having a motor shaft displacement-based surge detection function, characterized in that, in claim 1, the above-mentioned double-suction centrifugal compressor has a shaft support structure using magnetic bearings. Claim 9 A heat pump having a motor shaft displacement-based surge detection function, characterized in that, in the first aspect, an inlet guide vane is provided on the inlet side of the low-stage compression section to control the flow rate of the refrigerant flowing into the low-stage compression section. Claim 10 A heat pump having a motor shaft displacement-based surge detection function, characterized in that, in claim 1, it further includes a flow sensor installed around the positive suction centrifugal compressor or on the positive suction centrifugal compressor, and the sensing data further includes the flow rate of refrigerant sucked into or discharged from the positive suction centrifugal compressor. Claim 11 A heat pump having a motor shaft displacement-based surge detection function, further comprising a steam flash tank that generates steam through heat exchange with the condenser via circulating water in the first paragraph. Claim 12 A heat pump having a motor shaft displacement-based surge detection function, further comprising: a first circulation path that guides the circulating water, which has absorbed heat in the condenser, to flow into the steam flash tank; and a second circulation path that guides the circulating water to flow from the steam flash tank to the condenser.

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