Heat medium circulation type heating heat pump device

Abstract

To provide a heat medium circulation-type heating heat pump device which can maintain a compression ratio within a use range at a small pressure-difference operation of a compressor without detecting the pressure of a refrigerant.SOLUTION: A heat medium circulation-type heating heat pump device 1 comprises: a refrigeration cycle 5 having a compressor 11, a first heat exchanger 13, an expansion valve 15, and a second heat exchanger 16; a use-side apparatus 27; a heat medium flow passage 58 for connecting the first heat exchanger 13 of the refrigeration cycle 5 and the use-side apparatus 27 to each other, and making a heat medium circulate; a temperature sensor for detecting the temperature of any point of the refrigeration cycle 5; and a control part 29 for changing a lower limit value of the operation frequency of the compressor 11 on the basis of the temperature detected by the temperature sensor so that the compression ratio of the compressor 11 does not deviate from a use range when performing a small pressure-difference operation in which the difference between the suction pressure and the discharge pressure of the compressor 11 is small.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment according to the present invention relates to a heat medium circulation type heat pump device. [Background technology]

[0002] A conventional refrigeration system with a heat pump refrigeration cycle, for example, a medium-sized air conditioner, is equipped with a high-pressure sensor provided on the discharge side of the compressor and a low-pressure sensor provided on the suction side of the compressor. The air conditioner controls the operating frequency of the compressor based on the pressures detected by these pressure sensors so that the pressure on the discharge side of the compressor, the pressure on the suction side of the compressor, and the compression ratio are within appropriate ranges. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-185373 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional air conditioning systems require a high pressure sensor provided on the discharge side of the compressor and a low pressure sensor provided on the suction side of the compressor to control the operating frequency of the compressor so that the pressure on the discharge side of the compressor, the pressure on the suction side of the compressor, and the compression ratio fall within the operating ranges determined by the compressor specifications.

[0005] Incidentally, a heat medium circulation type heating heat pump device needs to maintain the target heat medium, such as hot water, at a set temperature. Therefore, under operating conditions where the outside air temperature is high and the set temperature on the user side is low, when the temperature of the heat medium circulating on the user side rises to near the set temperature, the heat medium circulation type heating heat pump device gradually lowers the operating frequency of the compressor so as to achieve low capacity, and finally lowers the rotation frequency of the compressor. The operating state of the compressor at this time is low differential pressure operation, in which the difference between the suction pressure and the discharge pressure is small. Here, in an extremely low differential pressure operation, there is a risk that the compression ratio will deviate from the operating range of the compressor.

[0006] In order to maintain the compression ratio within the usable range when the compressor is operating at low differential pressure, it is conceivable to provide two pressure sensors on the suction side and discharge side of the compressor to control the operating frequency of the compressor as in conventional air conditioners. However, in consideration of the reliability of the entire device, how to respond when the pressure sensors fail, the manufacturability of the device, the manufacturing costs of the device, and the like, it is desirable to maintain the compression ratio within the usable range when the compressor is operating at low differential pressure without using pressure sensors.

[0007] Therefore, an object of the present invention is to provide a heat medium circulation type heating heat pump device that can maintain the compression ratio within the usable range during low differential pressure operation of the compressor without detecting the pressure of the refrigerant. [Means for solving the problem]

[0008] In order to solve the above problems, a heat medium circulation type heating heat pump device according to an embodiment of the present invention includes a refrigeration cycle having a compressor, a first heat exchanger, a throttling device, and a second heat exchanger; a user side device; a medium flow path that connects the first heat exchanger of the refrigeration cycle and the user side device to circulate a heat medium; a temperature sensor that detects a temperature at any point of the refrigeration cycle; and a control unit that changes a lower limit value of an operating frequency of the compressor based on a temperature detected by the temperature sensor when the compressor performs a low differential pressure operation in which the difference between the suction pressure and the discharge pressure is small so that the compression ratio of the compressor does not deviate from a usage range. an input unit capable of inputting a desired set temperature of the heat medium in the utilization side device; Equipped with The temperature sensor detects an ambient temperature of a place where the second heat exchanger is installed, and the control unit increases the lower limit value of the operation frequency as the ambient temperature increases and increases the lower limit value of the operation frequency as the set temperature decreases. do. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a heat medium circulation type heat pump device according to an embodiment of the present invention. [Diagram 2] 4 is a diagram illustrating a relationship between a suction pressure, a discharge pressure, and a usable range of a compression ratio of a compressor. FIG. [Diagram 3] 4 is a flowchart showing a lower limit value control of the operating frequency of a compressor executed by the heat medium circulation type heating heat pump device according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating a correction value used in a correction process for a lower limit value of an operation frequency of a compressor in the heat medium circulation type heating heat pump device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of a heat medium circulation type heating heat pump device according to the present invention will be described with reference to Fig. 1 to Fig. 4. Note that the same or corresponding components are denoted by the same reference numerals in the multiple drawings.

[0011] FIG. 1 is a block diagram of a heat medium circulation type heat pump device according to an embodiment of the present invention.

[0012] As shown in FIG. 1, a heat medium circulation type heating heat pump device 1 according to this embodiment includes a heat source unit 2 that exchanges heat between a circulating refrigerant and outside air and between the circulating refrigerant and the circulating heat medium, and a load unit 3 that circulates and utilizes the heat medium heated by the heat source unit 2.

[0013] In the following description, the heat medium circulation type heating heat pump device 1 will be simply referred to as the "heat pump device 1".

[0014] The heat source unit 2 includes a refrigeration cycle 5. The refrigeration cycle 5 includes a compressor 11, a four-way valve 12, a first heat exchanger 13, an expansion valve 15 as a throttling device, a second heat exchanger 16, and refrigerant piping 17 that sequentially connects these components. The compressor 11 circulates a refrigerant through these refrigeration cycle components. The refrigerant circulating through the refrigeration cycle 5 is, for example, R410A or R32.

[0015] The first heat exchanger 13, which is generally also called a water heat exchanger, is a heat exchanger that exchanges heat between the refrigerant and the heat medium circulating through the heat exchanger unit 3. When the heat medium is heated, the first heat exchanger 13 functions as a condenser, and the flow direction of the refrigerant flowing through the refrigerant piping 17 is set by the four-way valve 11 that controls the flow direction of the refrigerant so that the second heat exchanger 16 functions as an evaporator.

[0016] Compressor 11 includes a high-pressure container, a compression mechanism housed in the high-pressure container, and a DC brushless motor housed in the high-pressure container and driving the compression mechanism using inverter device 25 as a power source. Compressor 11 compresses and pressurizes the refrigerant using the compression mechanism, and discharges the refrigerant in a high-temperature, high-pressure state. The operation frequency of compressor 11 is changed by inverter device 25. By increasing the rotation speed of compressor 11, the amount of heat transferred to the high-temperature portion increases, and by decreasing the rotation speed, the amount of heat transferred to the high-temperature portion decreases.

[0017] The expansion valve 15 is, for example, an electronic expansion valve (Pulse Motor Valve: PMV). The opening degree of the expansion valve 15 is adjusted according to the state of the refrigeration cycle. The expansion valve 15 is provided in series in the refrigerant pipe 17 between the first heat exchanger 13 and the second heat exchanger 16. The expansion valve 15 reduces the pressure of the refrigerant to allow the refrigerant to flow out in a low-temperature and low-pressure state.

[0018] The second heat exchanger 16 is also called an air heat exchanger. The second heat exchanger 16 exchanges heat between the refrigerant in the refrigerant pipe 17 and the atmosphere of the second heat exchanger 16, which is usually the outside air.

[0019] The heat source unit 2 also includes a blower fan 21 that blows out the outside air after heat exchange in the second heat exchanger 16, a plurality of temperature sensors that detect the temperature of each part of the refrigeration cycle 5, an inverter device 25 that is connected to a commercial AC power source E and drives the DC brushless motor of the compressor 11 at a variable speed, a controller 26 (input unit) that is an input device that accepts operations by a user, a display unit 28 that displays the settings and operating states as operating conditions of the heat source unit 2 and the user side equipment 27, and a control unit 29 that controls the operation of the heat source unit 2 and the user side equipment 27 based on the operation of the controller 26.

[0020] The multiple temperature sensors provided in various parts include a suction temperature sensor 41 provided in the refrigerant piping 17 on the suction side of the compressor 11 to detect the temperature TS of the refrigerant being sucked into the compressor 11, a discharge temperature sensor 42 attached to the refrigerant piping 17 on the discharge side of the compressor 11 as in the conventional manner to detect the temperature TD of the refrigerant discharged from the compressor 11, a refrigerant outlet side temperature sensor 43 provided in the refrigerant piping 17 to detect the temperature TC (condensation temperature) of the refrigerant after heat exchange flowing out of the first heat exchanger 13, a refrigerant temperature sensor 45 provided in the second heat exchanger 16 to detect the temperature TE (evaporation temperature) of the refrigerant flowing through the second heat exchanger 16, and an outside air temperature sensor 46 to detect the outside air temperature TO.

[0021] The outside air temperature sensor 46 is disposed upstream of the second heat exchanger 16 in the blowing direction of the blower fan 21 in order to accurately detect the outside air temperature.

[0022] It should be noted that the heat source unit 2 is not provided with a pressure sensor for detecting the pressure of the refrigerant circulating in the refrigeration cycle 5.

[0023] The load unit 3 includes a first heat exchanger 13 shared by the load unit 3 and the heat source unit 2, a user-side device such as a hot water tank 51, and a user-side heat exchanger 52 that performs heat exchange between the liquid (hot water) in the hot water tank 51 and the heat medium after heat exchange in the first heat exchanger 13.

[0024] The heat medium circuit is illustrated as a closed circuit, but does not have to be a closed circuit. The heat medium circuit includes a circulation pump 53 for circulating the heat medium, a constant flow rate valve 55 for keeping the circulating flow rate of the heat medium constant, a check valve 56 for preventing backflow of the heat medium, a hot water tank 51, a flow meter 57, and a heat medium flow path 58 for circulating water as a heat medium by connecting the first heat exchanger 13. The heat medium is generally water, but antifreeze may be used to prevent freezing.

[0025] A user of the heat pump device 1 inputs a desired set temperature for the load unit 3 from the controller 26. The heat pump device 1 is used to constantly maintain liquid such as hot water in the hot water tank 51 for external use in the load unit 3 at a high temperature. For this reason, the set temperature of the heat medium set in the controller 26 is determined by the needs of the hot water user. This set temperature is, for example, 30°C to 64°C, which is higher than the set temperature of an air conditioner for heating purposes.

[0026] The circulation pump 53 circulates the heat medium between the first heat exchanger 13 and the user-side device 27 when in operation. The circulation pump 53, the constant flow valve 55, the check valve 56, and the flow meter 57 may be provided in the heat medium flow path 58 on the load unit 3 side, or may be provided in the heat medium flow path 58 on the heat source unit 2 side. If the refrigerant circulating through the refrigerant pipe 17 is at a higher temperature than the heat medium circulating through the heat medium flow path 58, the heat medium is heated in the first heat exchanger 13, heats the liquid in the hot water tank 51 in the user-side heat exchanger 52 (radiator), radiates heat, and is returned to the first heat exchanger 13.

[0027] The heat medium flow path 58 includes pipe joints 59, 59. These pipe joints 59, 59 connect the heat source unit 2 and the load unit 3 in a detachable manner.

[0028] In order to control the temperature of the heat medium, the heat source unit 2 is provided with a heat medium inlet temperature sensor 71 provided on the inlet side of the first heat exchanger 13 to detect a temperature TWI of the heat medium flowing into the first heat exchanger 13, and a heat medium outlet temperature sensor 72 provided on the outlet side of the first heat exchanger 13 to detect a temperature TWO of the heat medium flowing out from the first heat exchanger 13. The temperature TWI is the temperature of the heat medium before heat exchange with the refrigerant of the refrigeration cycle 5 in the first heat exchanger 13 (return temperature), and the temperature TWO is the temperature of the heat medium after heat exchange with the refrigerant of the refrigeration cycle 5 in the first heat exchanger 13 (outlet temperature).

[0029] The load unit 3 may include a flowmeter 57 that detects the flow rate of the heat medium circulating through the heat medium flow path 58. The circulating flow rate of the heat medium may be detected by the flowmeter 57, may be a flow rate that is stored in advance corresponding to the rotation speed of the circulating pump 53, or may be a flow rate that is set by manual input.

[0030] The control unit 29 includes hardware resources such as a processor, a memory, and peripheral circuits thereof, etc. The control unit 29 is configured as a computer in which the processor executes various programs to realize information processing by software using the hardware resources.

[0031] Furthermore, the control unit 29 controls the operation of the heat source unit 2 and the operation of the load unit 3 based on an input operation to the controller 26. That is, the control unit 29 controls the operations of the compressor 11, the inverter device 25, the four-way valve 12, the expansion valve 15, and the blower fan 21 based on an input operation by the user using the controller 26.

[0032] Furthermore, the control unit 29 controls the operation stop and rotation speed of the compressor 11, the direction of the four-way valve 12, the opening degree of the expansion valve 15, and the operation stop and rotation speed of the blower fan 21 based on one or more of the temperature detection values ​​of each part by the suction temperature sensor 41, the discharge temperature sensor 42, the refrigerant outlet side temperature sensor 43, the refrigerant temperature sensor 45, the outside air temperature sensor 46, the heat medium inlet temperature sensor 71, and the heat medium outlet temperature sensor 72, and the circulation flow rate of the heat medium detected or calculated. For example, the rotation speed of the compressor 11, i.e., the output frequency of the inverter device 25, is determined according to the difference between the detected temperature of the heat medium outlet temperature sensor 72 and the set temperature of the heat medium set by the controller 26. In addition, the condensation temperature, which is the detected temperature of the refrigerant outlet side temperature sensor 43, is used to prevent the refrigeration cycle components such as the first heat exchanger from becoming abnormally high pressure. That is, when the condensation temperature, which is the detected temperature of the refrigerant outlet side temperature sensor 43, exceeds a predetermined value, for example, 65°C, the rotation speed of the compressor 11 is reduced.

[0033] In addition, in order to remove frost formed in the second heat exchanger 16 during the operation of heating the heat medium in the first heat exchanger 13, the refrigeration cycle 5 performs a defrosting operation by switching the flow direction of the refrigerant flowing through the refrigerant pipe 17 by the four-way valve 12. When performing the defrosting operation, the heat pump device 1 reverses the four-way valve 12 to generate a refrigerant flow in the refrigeration cycle 5 in a direction opposite to the refrigerant flow that heats the heat medium. That is, the refrigeration cycle 5 causes the refrigerant to flow through the compressor 11, the four-way valve 12, the second heat exchanger 16, the expansion valve 15, the first heat exchanger 13, the four-way valve 12, and the compressor 11 in this order. During this defrosting operation, the second heat exchanger 16 functions as a condenser, and the first heat exchanger 13 functions as an evaporator. The second heat exchanger 16, which functions as a condenser, melts the frost attached to its surface.

[0034] In addition, for warm regions where defrosting operation is not required, the refrigeration cycle 5 may be dedicated to heating water without the four-way valve 12. In this case, the discharge side of the compressor 11 is connected to the first heat exchanger 13 via the refrigerant piping 17, and the suction side of the compressor 11 is connected to the second heat exchanger 16 via the refrigerant piping 17.

[0035] The horizontal axis of Fig. 2 is the suction pressure of compressor 11, the vertical axis of Fig. 2 is the discharge pressure of compressor 11, and the left end of the horizontal axis is the minimum suction pressure value that can be used during stable operation of compressor 11 excluding a transitional period such as at the start-up of compressor 11. Line segment A in Fig. 2 is the lower limit of the usable range of the compression ratio of compressor 11.

[0036] 2, the lower limit of the usable range of the compression ratio of compressor 11 can be represented by line segment A sloping upward to the right, which is proportional to the suction pressure and discharge pressure of compressor 11. From the viewpoint of compressor reliability, steady operation of compressor 11 below line segment A is not permitted. In other words, the compression ratio of compressor 11 during steady operation is required to belong to region B above line segment A.

[0037] The state where the difference between the suction pressure and the discharge pressure is small and the compression ratio is low is located near line A.

[0038] The heat pump device 1 according to this embodiment does not include a pressure sensor in the refrigeration cycle 5. Therefore, the heat pump device 1 cannot control the operating frequency of the compressor 11 based on the pressure detected by the pressure sensor so that the compressor discharge pressure, compressor suction pressure, and compression ratio fall within the usable range (area B).

[0039] Here, in order to keep the compression ratio of the compressor 11 within the usage range, it is conceivable to set the output frequency of the inverter device 25, i.e., the lower limit of the operating frequency of the compressor 11, higher in advance so as not to enter area B above line segment A of the compressor 11. However, if the lower limit of the operating frequency is increased, the minimum capacity of the refrigeration cycle 5 increases, the range of the heating capacity of the heat pump device 1 narrows, and the efficiency decreases. Note that if the discharge pressure, suction pressure, and compression ratio of the compressor 11 deviate from the usage range, the risk of failure of the compressor 11 increases, which is not preferable.

[0040] Therefore, when the operating state of the compressor 11 is low differential pressure operation in which the difference between the suction pressure and the discharge pressure is small, the control unit 29 of the heat pump device 1 in this embodiment changes the lower limit value of the operating frequency of the compressor 11 based on the temperature detected by a temperature sensor that detects the temperature at any point in the refrigeration cycle 5, so that the compression ratio of the compressor 11 does not fall outside the operating range.

[0041] 3 is a flowchart of the lower limit value control of the operating frequency of the compressor executed by the heat medium circulation type heating heat pump device according to the embodiment of the present invention. In the following description, each step S* in the flowchart will be represented by S*.

[0042] 3, when the control unit 29 of the heat pump device 1 starts operation, it determines whether the outlet temperature TWO of the first heat exchanger 13 of the heat medium is larger than the set temperature TWOt of the heat medium set in the controller 26 (S1). Specifically, while the compressor 11 is stopped, it is determined whether the outlet temperature TWO is equal to or smaller than the set temperature TWOt (step S1). On the other hand, while the compressor 11 is operating, it is determined whether the outlet temperature TWO exceeds the value of (set temperature TWOt+α).

[0043] If the determination in step S1 is positive while the compressor 11 is operating, that is, if (temperature TWO)>(set temperature TWOt)+α, or if (temperature TWO)>(set temperature TWOt) while the compressor 11 is stopped (S1 Yes), the control unit 29 stops the compressor 11 or keeps the compressor 11 stopped (S2), and returns to S1. Here, the differential value α is, for example, 2°C.

[0044] When the determination in S1 is negative, that is, when (temperature TWO) ≤ (set temperature TWOt) + α during the operation of the compressor 11 and (temperature TWO) ≤ (set temperature TWOt) when the compressor 11 is stopped (S1 Yes), the compressor 11 is started or continued in operation in the subsequent steps. Specifically, the control unit 29 determines whether the compressor 11 is stopped (S3). When the compressor 11 is stopped (S3 Yes), the control unit 29 starts the compressor 11 (S4), substantially simultaneously starts the timing of the start timer of the compressor 11 (S5), and returns to S1.

[0045] Also, when the determination in S3 is negative, that is, when the compressor 11 is in operation (S3 No), the operation of the compressor 11 is continued and the process moves to S6, and then enters the control for determining the operating frequency of the compressor 11 hereafter. Subsequently, the control unit 29 determines whether the temperature TWO of the heat medium flowing out from the first heat exchanger 13 is lower than the set temperature TWOt (S6). When the temperature TWO of the heat medium flowing out from the first heat exchanger 13 is lower than the set temperature TWOt, that is, when (temperature TWO) < (set temperature TWOt) (S6 Yes), the set value of the operating frequency of the compressor 11 is increased every predetermined time (S7). When the temperature TWO of the heat medium flowing out from the first heat exchanger 13 is equal to or higher than the set temperature TWOt, that is, when (temperature TWO) ≥ (set temperature TWOt), the set value of the operating frequency of the compressor 11 is decreased every predetermined time (S8). Note that the increase in the operating frequency in S7 is, for example, 5 Hz / 30 seconds, and the decrease in the operating frequency in S8 is, for example, 5 Hz / 60 seconds. The increase rate and decrease rate of the operating frequency may be the same or different. Also, in order to prevent extreme overshoot, a differential of the determination condition in S6 may be provided such that TWO < TWOt - β, where, for example, β is 2°C.

[0046] In this embodiment, the operating frequency of the compressor 11 is determined by integral (I) control as described above, but it may also be determined by proportional integral (PI) control based on the temperature difference between (temperature TWO) and (set temperature TWOt), or further, differential control may be incorporated as PID control to determine an appropriate operating frequency.

[0047] Next, the control unit 29 determines whether or not a predetermined standby time has elapsed since the compressor 11 was started (S9). The predetermined time is set to avoid execution of the correction process (S12 to S15 described below) of the lower limit value of the operating frequency during the startup transition of the compressor 11. The predetermined time is set to, for example, 600 seconds.

[0048] If the determination in S9 is negative, that is, if the predetermined standby time has not elapsed since the compressor 11 was started (S9 No), the control unit 29 drives the compressor 11 at the set frequency determined in the above-mentioned S7 and S8 via the inverter device 25 (S10), and returns to S1. Note that, after the predetermined standby time has elapsed since the compressor 11 was started, the set frequency in S10 is also changed by a correction process for the lower limit of the operating frequency, which will be described below, in addition to S7 and S8.

[0049] If the judgment in S9 is positive, that is, after a predetermined waiting time (600 seconds) has elapsed since the compressor 11 was started (S9 Yes), the control unit 29 initializes (sets to zero) the timing of the start timer (S11), and executes a correction process for the lower limit value of the operating frequency, which will be described later.

[0050] The process of correcting the lower limit of the operating frequency of the compressor 11 will be described with reference to FIG.

[0051] 4, the control unit 29 of the heat pump device 1 calculates a correction value ΔLHz from the set temperature TWOt and the outside air temperature TO, which is the ambient temperature of the location where the second heat exchanger 16 is installed. This correction value ΔLHz is a correction value for increasing the lower limit of the operation frequency of the compressor 11, and is a positive value.

[0052] The correction value ΔLHz is larger as the outside air temperature TO increases and as the set temperature TWOt decreases. In other words, the correction value ΔLHz is smaller as the outside air temperature TO decreases and as the set temperature TWOt increases. The correction value ΔLHz is a negative value in a right-angled triangular area C having a right angle at the upper right side in FIG. 4. In this area C, the correction value ΔLHz is set to zero. That is, in area C, (correction value ΔLHz)=0.

[0053] Furthermore, in the region where the correction value ΔLHz is a positive value, unless control is performed to raise the lower limit of the operating frequency in this embodiment, there is a risk that the compression ratio of the compressor 11 will deviate from the usage range (plotted in the region below line A in Figure 2).

[0054] Here, the correction value ΔLHz is calculated as follows, using the outside air reference value a, the outside air correction value b, and the set reference value c. Note that the outside air reference value a, the outside air correction value b, and the set reference value c are fixed values ​​experimentally determined in advance. [Number 1] (Correction value ΔLHz) = (Correction amount X) + (Correction amount Y) (Correction amount X) = (Outdoor temperature TO) + ((Outdoor temperature TO) - (Outdoor reference value a)) x (Outdoor correction value b) - (Set temperature TWOt) (Correction amount Y) = (Set reference value c) - (Set temperature TWOt)

[0055] 4, the correction value ΔLHz is set to a value equal to or greater than zero. In other words, if the calculation result of the correction value ΔLHz is a negative value, it is changed to zero.

[0056] The initial lower limit value LHz of the operating frequency of the compressor 11 and the corrected lower limit value LHz' of the operating frequency of the compressor 11 are corrected as follows. [Number 2] (Lower limit value after correction LHz') = (Initial lower limit value LHz) + (Correction value ΔLHz)

[0057] The initial lower limit LHz of the operating frequency of the compressor 11 is set to the lowest operating frequency value at which the compressor 11 can be operated without any malfunction within the normal operating range. For a typical rotary compressor, this initial lower limit LHz is, for example, 12 to 30 Hertz (Hz).

[0058] The outdoor air reference value a, the outdoor air correction value b, and the set reference value c differ depending on the capacity of the refrigeration cycle 5 and the load of the load unit 3. The outdoor air reference value a and the set reference value c are experimentally determined based on the specifications of the heat pump device 1 and the compressor 11. The outdoor air correction value b is experimentally set so that the compression ratio of the compressor 11 belongs to region B equal to or greater than line segment A in FIG. 2 by correction of [Equation 2].

[0059] 3, the control unit 29 calculates a correction value ΔLHz having the relationship shown in Fig. 4, which is calculated by [Equation 1] (S12), and calculates a corrected lower limit value LHz', which is calculated by [Equation 2] (S13). Note that the corrected lower limit value LHz' is set to a value larger than the initial lower limit value LHz only when (correction value ΔLHz)>0.

[0060] Next, the control unit 29 judges whether or not the set value of the operation frequency of the compressor 11 determined in steps S7 and S8 is smaller than the corrected lower limit value LHz' (S14). If the set value of the operation frequency of the compressor 11 is smaller than the corrected lower limit value LHz' (S14 Yes), the control unit 29 changes the set value of the operation frequency of the compressor 11 to the lower limit value LHz' (S15), drives the compressor 11 at the set value of the operation frequency via the inverter device 25 (S10), and then returns to S1.

[0061] On the other hand, if the set value of the operation frequency of the compressor 11 is equal to or higher than the corrected lower limit value LHz' (No in S14), the control unit 29 drives the compressor 11 at the set value of the operation frequency determined in steps S7 and S8 via the inverter device 25 (S10), and returns to S1.

[0062] As described above, in the heat pump device 1 according to the present embodiment, when the compressor 11 is operating at a low differential pressure, the lower limit of the operating frequency of the compressor 11 is changed based on the temperature detected by the temperature sensor so that the compression ratio of the compressor 11 does not deviate from the operating range. Therefore, the heat pump device 1 can reduce the risk of failure of the compressor 11 by operating while maintaining the compression ratio of the compressor 11 within the operating range without providing a pressure sensor in the refrigeration cycle 5. In addition, the heat pump device 1 according to the present embodiment changes the lower limit of the operating frequency of the compressor 11 depending on the level of the outdoor air temperature TO and the level of the set temperature TWOt of the load unit 3. In other words, the heat pump device 1 changes the lower limit of the operating frequency of the compressor 11 based on the outdoor air temperature sensor 46 that is provided in a general heat pump device 1 and is not exposed to abrupt temperature changes, and the set temperature TWOt of the load unit 3 that is generally desired by a user. Therefore, the heat pump device 1 does not require dedicated temperature sensors or pressure sensors to control the operating frequency of the compressor 11 so that the compression ratio of the compressor 11 does not deviate from the usage range, and the risk of failure of the compressor 11 can be reduced at extremely low cost.

[0063] Furthermore, the heat pump device 1 according to this embodiment increases the lower limit value of the operating frequency of the compressor 11 as the outdoor air temperature YO increases, and increases the lower limit value of the operating frequency of the compressor 11 as the set temperature TWOt of the load unit 3 decreases. Therefore, the heat pump device 1 can reduce the risk of failure of the compressor 11 by operating at a low differential pressure while maintaining the compression ratio of the compressor 11 within the usage range in response to a wide range of outdoor air temperatures TO and a wide range of set temperatures TWOt.

[0064] Therefore, the heat pump device 1 according to this embodiment can maintain the compression ratio within the usable range during low differential pressure operation of the compressor 11 without detecting the pressure of the refrigerant.

[0065] The compressor 11 is in the low differential pressure operation when the temperature of the heat medium approaches the set temperature TWOt. That is, in such a state, the temperature TWI of the heat medium flowing into the first heat exchanger 13 detected by the heat medium inlet temperature sensor 71 and the temperature TWO of the heat medium flowing out from the first heat exchanger 13 detected by the heat medium outlet temperature sensor 72 indicate values ​​close to the set temperature TWOt. Therefore, the set temperature TWOt in [Equation 2] used in the calculation of the correction value ΔLHz may be replaced with the temperature TWI of the heat medium flowing into the first heat exchanger 13 detected by the heat medium inlet temperature sensor 71 or the temperature TWO of the heat medium flowing out from the first heat exchanger 13 detected by the heat medium outlet temperature sensor 72. In this case, when the temperature of the heat medium is far from the set temperature TWOt on the low side, the correction value ΔLHz becomes large, but since the operating frequency of the compressor 11 is originally controlled to be high in such a situation, even if the correction value ΔLHz becomes large and the lower limit value LHz' of the operating frequency of the compressor 11 is set high, there is almost no adverse effect on the actual temperature control of the heat medium. In this case, the coefficients in [Equation 2], that is, the outside air reference value a and the outside air correction value b, can be used as they are, and it is desirable to slightly change the set reference value c.

[0066] In addition, the heat source unit 2 constituting the heat medium circulation type heating heat pump device 1 may be housed in an integrated housing, or may be configured as a two-housing structure in which the first heat exchanger 13 and other refrigeration cycle components are housed in separate housings.

[0067] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0068] 1...heat medium circulation type heating heat pump device, 2...heat source unit, 3...load unit, 5...refrigeration cycle, 11...compressor, 13...first heat exchanger, 16...second heat exchanger, 25...inverter device, 26...controller (input section), 27...user side equipment, 28...display section, 29...control section, 41...suction temperature sensor, 42...discharge temperature sensor, 43...refrigerant outlet side temperature sensor, 45...refrigerant temperature sensor, 46...outdoor air temperature sensor, 51...hot water tank, 52...user side heat exchanger, 71...heat medium inlet temperature sensor, 72...heat medium outlet temperature sensor.

Claims

[Claim 1] a refrigeration cycle having a compressor, a first heat exchanger, a throttling device, and a second heat exchanger; A user device; a medium flow path that connects the first heat exchanger of the refrigeration cycle and the utilization side device to circulate a heat medium; a temperature sensor for detecting a temperature at any point of the refrigeration cycle; a control unit that changes a lower limit value of an operating frequency of the compressor based on a temperature detected by the temperature sensor so that a compression ratio of the compressor does not deviate from a usage range when the compressor performs a low differential pressure operation in which a difference between a suction pressure and a discharge pressure is small; an input unit capable of inputting a desired set temperature of the heat medium in the utilization side device, The temperature sensor detects an ambient temperature of a location where the second heat exchanger is installed, The control unit increases the lower limit value of the operation frequency as the ambient temperature increases and increases the lower limit value of the operation frequency as the set temperature decreases.

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