JP2018059666A - Control device, refrigerant circuit system, and control method - Google Patents

Abstract

A control device capable of performing an oil return operation commensurate with a load is provided. A control device for controlling a refrigerant circuit system includes a condenser so that a difference between a heating capacity of the refrigerant circuit system during oil return operation in a heating cycle and a heating capacity during normal operation is within a predetermined range. The enthalpy difference between the inlet side and the outlet side of the compressor and the frequency of the compressor are controlled. By setting the target temperature at the outlet of the condenser to be higher than that during normal operation, the enthalpy difference during oil return operation is controlled to be smaller than during normal operation. [Selection] Figure 6

Description

  The present invention relates to a control device, a refrigerant circuit system, and a control method.

  Conventionally, in a refrigerant circuit equipped with a multistage compressor, in order to improve cooling capacity and COP (Coefficient Of Performance), a part of the high-pressure refrigerant condensed in the condenser is branched, and the branched refrigerant is used as a compressor. A refrigerant circuit with an injection circuit that performs injection is known. For example, Patent Document 1 describes a technique for improving COP in a refrigerant circuit with an injection circuit by switching between injection operation and non-operation according to the load level and the ratio between the condensation pressure and the evaporation pressure.

  Conventionally, an oil return operation is performed to recover the refrigeration oil that has flowed into the refrigerant circuit to the compressor. For example, in Patent Document 2, an excessive increase in the refrigerant pressure is suppressed by increasing the capacity of the compressor during the heating operation to increase the circulation amount of the refrigerant and reducing the air volume of the heat source side fan. A technique that enables stable oil return operation even at times is described.

JP 2003-185286 A Japanese Patent No. 2760218

  In general, in oil return operation, control is performed to increase the frequency of the compressor and increase the amount of refrigerant circulation to maintain the flow rate of the refrigerant in the pipe at a constant speed or higher necessary for recovery of the refrigerating machine oil. However, if the frequency of the compressor is increased while the outlet side temperature of the condenser is maintained at a predetermined target temperature during the heating operation, there is a problem that the heating capacity becomes excessive.

  Then, this invention aims at providing the control apparatus, refrigerant circuit system, and control method which can solve the above-mentioned subject.

  1st aspect of this invention is a control apparatus which controls a refrigerant circuit system, Comprising: The heating capability of the said refrigerant circuit system at the time of the oil return operation | movement in a heating cycle, and the heating capability of the said refrigerant circuit system at the time of normal operation A control device that controls an enthalpy difference between an inlet side and an outlet side of a condenser included in the refrigerant circuit system and a circulation amount of the refrigerant flowing through the refrigerant circuit system so that the difference is within a predetermined range; is there.

  The control device according to the second aspect of the present invention maintains the enthalpy on the inlet side of the condenser at a predetermined target value, and sets the target temperature on the outlet side of the condenser during the oil return operation more than during normal operation. By setting the temperature high, the enthalpy on the outlet side of the condenser is set higher than that during normal operation.

  In the control device according to the third aspect of the present invention, the difference between the enthalpy of the condenser during the oil return operation is the product of the frequency of the compressor included in the refrigerant circuit system and the enthalpy difference between the normal operation and the oil return. It is calculated so as to coincide with the time of operation, and during the oil return operation, the temperature on the outlet side of the condenser based on the calculated enthalpy difference is set as a target temperature, and the temperature on the outlet side of the condenser is Control to achieve the target temperature.

  The control device according to the fourth aspect of the present invention controls the valve opening degree of the expansion valve provided on the outlet side of the condenser based on the target temperature on the outlet side of the condenser.

  The refrigerant circuit system according to the fifth aspect of the present invention includes a plurality of compressors that compress refrigerant, a condenser that condenses the compressed refrigerant, a first expansion valve that depressurizes the condensed refrigerant, A receiver storing a part of the refrigerant decompressed by the first expansion valve; a second expansion valve decompressing the refrigerant flowing out of the receiver; and the refrigerant decompressed by the second expansion valve. A mainstream circuit connected to an evaporator to be evaporated and a part of the refrigerant flowing out from the receiver are branched, and the branched refrigerant is supplied to a suction side of a predetermined compressor among the plurality of compressors. An intermediate heat exchange that is an injection circuit and performs heat exchange between the third expansion valve that decompresses the part of the branched refrigerant and the refrigerant that has passed through the third expansion valve and the refrigerant that has passed through the mainstream circuit. And A control circuit, wherein the control device sets the target temperature on the outlet side of the condenser to a temperature higher by a predetermined temperature than the temperature of the use side medium flowing into the condenser during normal operation, During oil return operation, the target temperature on the outlet side of the condenser is set to a temperature higher than the target temperature during normal operation.

  A sixth aspect of the present invention includes a plurality of compressors that compress the refrigerant, a condenser that condenses the compressed refrigerant, a first expansion valve that decompresses the condensed refrigerant, and the first expansion valve. A receiver for storing a part of the decompressed refrigerant, a second expansion valve for decompressing the refrigerant flowing out of the receiver, and an evaporator for evaporating the refrigerant decompressed by the second expansion valve; An injection circuit for branching a part of the refrigerant flowing out from the receiver, and supplying the branched refrigerant to a suction side of a predetermined compressor among the plurality of compressors; An injection circuit comprising: a third expansion valve that depressurizes a part of the branched refrigerant; and an intermediate heat exchanger that performs heat exchange between the refrigerant that has passed through the third expansion valve and the refrigerant that has passed through the mainstream circuit. And any one of the above A refrigerant circuit system and a control device according to.

  According to a seventh aspect of the present invention, there is provided a control device that controls the refrigerant circuit system, wherein a difference between a heating capacity of the refrigerant circuit system during an oil return operation in a heating cycle and a heating capacity of the refrigerant circuit system during a normal operation. And a control method for controlling an enthalpy difference between an inlet side and an outlet side of a condenser provided in the refrigerant circuit system and a circulation amount of the refrigerant flowing through the refrigerant circuit system so as to be within a predetermined range.

  According to the present invention, the oil return operation can be executed while maintaining the heating capacity commensurate with the load.

It is a figure which shows an example of the refrigerant circuit system in one Embodiment of this invention. It is a 1st Ph diagram of a refrigerant circuit system in one embodiment of the present invention. It is a 2nd Ph diagram of the refrigerant circuit system in one embodiment of the present invention. It is a 1st figure explaining the control method at the time of the oil return operation in one Embodiment of this invention. It is a 2nd figure explaining the control method at the time of the oil return operation in one Embodiment of this invention. It is a figure explaining the effect of the oil return driving | operation in one Embodiment of this invention. It is a flowchart of the control apparatus in one Embodiment of this invention.

<Embodiment>
Hereinafter, a refrigerant circuit system according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram illustrating an example of a refrigerant circuit system according to an embodiment of the present invention.
The refrigerant circuit system 1 is used in a water heater or the like, and constitutes a refrigerant circuit that operates in a heating cycle (heating cycle). The refrigerant circuit system 1 raises the water supply (use side medium) supplied from the outside to a predetermined set target temperature (for example, 80 ° C.), and supplies this hot water to the user. In the present embodiment, the set target temperature (tapping water temperature) of the water supplied to the user is constant. The set target temperature of the water supply is referred to as the use side outlet temperature. Moreover, the temperature of the feed water supplied from the outside is called a utilization side inlet temperature.

As shown in FIG. 1, the refrigerant circuit system 1 includes a high-stage compressor 10A, a low-stage compressor 10B, a use-side heat exchanger (condenser) 11, a first expansion valve 12, a receiver 13, A main flow circuit including a second expansion valve 14, a heat source side heat exchanger (evaporator) 15, an accumulator 16, and a main flow pipe 17 connecting them, an injection pipe 20, and a third expansion The valve 21, the injection circuit configured to include the intermediate heat exchanger 22, and the control device 100 are configured.
The specific configuration of the refrigerant circuit system 1 illustrated in FIG. 1 schematically illustrates the basic configuration of the refrigerant circuit system 1, and may further include other components.

The high-stage compressor 10A and the low-stage compressor 10B compress the refrigerant and discharge the high-pressure refrigerant. The low stage compressor 10B and the high stage compressor 10A are connected in series. The suction side of the low-stage compressor 10B is connected to the accumulator 16. The discharge side of the low stage compressor 10B is connected to the suction side of the high stage compressor 10A. The low-stage compressor 10B sucks the low-pressure refrigerant supplied from the accumulator 16, performs compression, and discharges the intermediate-pressure refrigerant to the high-stage compressor 10A side. An injection pipe 20 is connected to the suction side of the high-stage compressor 10A, and intermediate pressure refrigerant is supplied from the injection pipe 20 as will be described later.
The frequencies of the high-stage compressor 10A and the low-stage compressor 10B are controlled by the control device 100 by an inverter circuit. In the present embodiment, the frequency of the high-stage compressor 10A is set at a predetermined temperature (for example, 82) that matches the discharge pressure saturation temperature of the high-stage compressor 10A with a preset use-side outlet temperature (for example, 80 ° C.). The temperature is controlled by the control device 100. Thus, in this embodiment, the target high pressure is determined according to the use side outlet temperature, and the value is controlled to be constant regardless of the change in the use side inlet temperature. The high-temperature and high-pressure refrigerant discharged from the high stage side compressor 10 </ b> A is supplied to the use side heat exchanger 11.

The use side heat exchanger 11 functions as a condenser. The high-pressure refrigerant supplied to the use-side heat exchanger 11 exchanges heat with water supplied by the user to dissipate heat, and is condensed and liquefied. On the other hand, the feed water supplied to the use side heat exchanger 11 absorbs heat from the high-pressure refrigerant, is heated to a predetermined set target temperature (use side outlet temperature), and is provided to the user. In the figure, dotted arrows indicate the flow direction of the water supply, and solid arrows indicate the flow direction of the refrigerant (heating cycle).
The first expansion valve 12 is a flow control valve that depressurizes the refrigerant. The high-pressure refrigerant after heat exchange by the use side heat exchanger 11 is decompressed and expanded by the first expansion valve 12 and supplied to the receiver 13. The opening degree of the first expansion valve 12 is controlled by the control device 100. The control device 100 controls the opening degree of the first expansion valve 12 so that the outlet side temperature of the use side heat exchanger 11 becomes a predetermined value. For example, during normal operation, the control device 100 controls the outlet side temperature of the use side heat exchanger 11 to be higher than the use side inlet temperature by a predetermined value (for example, 2 ° C.). For example, if the use side inlet temperature is 5 ° C., the set target temperature of the outlet side temperature of the use side heat exchanger 11 is 7 ° C. Further, during the oil return operation, the control device 100 performs the first expansion with the temperature at which the outlet side temperature of the use side heat exchanger 11 is equal to the heating temperature of the refrigerant circuit system 1 as compared with that during the normal operation being the target temperature. The opening degree of the valve 12 is controlled.

The receiver 13 is a pressure vessel that temporarily stores a part of the supplied refrigerant. In the receiver 13, a two-phase refrigerant of gas and liquid is mixed and stored. The first expansion valve 12 is provided on the upstream side of the receiver 13, and the branch to the injection pipe 20, the intermediate heat exchanger 22, and the second expansion valve 14 are provided on the downstream side. A part of the refrigerant flowing out from the receiver 13 is branched to the injection pipe 20, and the remaining refrigerant flows through the mainstream circuit.
The second expansion valve 14 is a flow control valve that depressurizes the refrigerant. The liquid refrigerant flowing through the main flow circuit is cooled by heat exchange with a part of the refrigerant flowing (branched) through the injection pipe 20 in the intermediate heat exchanger 22, and is depressurized and expanded in the second expansion valve 14 to become low-pressure refrigerant. .

  The heat source side heat exchanger 15 functions as an evaporator. The heat source side heat exchanger 15 evaporates the low-pressure refrigerant flowing from the second expansion valve 14 by absorbing heat from a heat source such as outside air. The refrigerant that has passed through the heat source side heat exchanger 15 is supplied to the accumulator 16. The refrigerant is separated into gas and liquid by the accumulator 16, and only the gaseous refrigerant is sucked into the low-stage compressor 10B. The low stage compressor 10B compresses the refrigerant and discharges it to the high stage compressor 10A side.

On the other hand, the refrigerant branched on the downstream side of the receiver 13 is supplied to the suction side of the high stage compressor 10 </ b> A via the injection pipe 20. The injection pipe 20 is provided with a third expansion valve 21 and an intermediate heat exchanger 22.
The third expansion valve 21 is a flow control valve that decompresses a part of the branched refrigerant.
The intermediate heat exchanger 22 performs heat exchange between the refrigerant passing through the third expansion valve 21 and the refrigerant passing through the main flow pipe 17. The refrigerant decompressed by the third expansion valve 21 is heated by heat exchange in the intermediate heat exchanger 22 and returned to the high stage compressor 10A to be recompressed. This injection circuit can improve the COP of the refrigeration cycle as is well known.

  The control device 100 is a computer device such as a microcomputer. For example, as described above, the control device 100 controls the devices constituting the refrigerant circuit, such as the high-stage compressor 10A and the first expansion valve 12. In particular, in the present embodiment, the control device 100 determines that the ratio of the enthalpy difference during the oil return operation to the enthalpy difference during the normal operation with respect to the enthalpy difference during the oil return operation is the oil return from the normal operation. The outlet side temperature of the use side heat exchanger 11 is controlled so as to be the reciprocal of the increase rate of the refrigerant circulation amount due to the increase in the frequency of the high stage compressor 10A and the low stage compressor 10B when the operation is switched. Specifically, the control device 100 controls the opening degree of the first expansion valve 12 so that the outlet side temperature of the use side heat exchanger 11 becomes the target temperature.

The refrigerant circuit system 1 is provided with detection means such as a temperature sensor and a pressure sensor. For example, the temperature sensor 31 is provided at the inlet through which the water supply (use side medium) of the use side heat exchanger 11 passes. The temperature sensor 31 measures the use side inlet temperature. A temperature sensor 33 is provided on the outlet side of the use side heat exchanger 11. The temperature sensor 33 measures the temperature of the refrigerant on the outlet side of the use side heat exchanger 11. The temperature sensor 31 and the temperature sensor 33 output the measured temperature information to the control device 100. A pressure sensor 32 is provided on the inlet side of the use side heat exchanger 11. The pressure sensor 32 measures the pressure of the refrigerant on the inlet side of the use side heat exchanger 11. The pressure sensor 32 outputs information on the measured pressure to the control device 100.
Next, changes in the heating capacity during normal operation and during oil return operation will be described using the refrigeration cycle in the refrigerant circuit system 1 illustrated in FIG.

FIG. 2 is a first Ph diagram of the refrigerant circuit system in one embodiment of the present invention.
FIG. 2 is a relationship diagram of pressure and enthalpy representing a refrigeration cycle when the refrigerant circuit system 1 is operated. In the Ph diagram of FIG. 2, each symbol indicates the following state. That is, A1 is the state of the refrigerant discharged from the high stage compressor 10A, A2 is the state of the refrigerant on the outlet side of the use side heat exchanger 11, A3 is the state of the refrigerant on the outlet side of the first expansion valve 12, A4 is the state of the refrigerant on the inlet side of the second expansion valve 14, A5 is the state of the refrigerant on the outlet side of the second expansion valve 14, A6 is the state of the refrigerant on the outlet side of the heat source side heat exchanger 15, A7 Indicates the state of the refrigerant discharged from the low-stage compressor 10B, A8 indicates the state of the refrigerant on the outlet side of the third expansion valve 21, and A9 indicates the state of the refrigerant on the suction side of the high-stage compressor 10A, respectively. ing.

  The high-temperature and high-pressure refrigerant (state A1) discharged from the high-stage compressor 10A dissipates heat and condenses and liquefies in the use-side heat exchanger 11, and becomes a high-pressure liquid refrigerant (state A2). In this embodiment, the enthalpy difference is earned by bringing the outlet side temperature of the use side heat exchanger 11 close to the use side outlet temperature, and the heating capacity is increased to increase the COP. The high-pressure liquid refrigerant is reduced in pressure and expanded by the first expansion valve 12 (state A3) and flows into the receiver 13. Of the refrigerant flowing out from the receiver 13, the refrigerant flowing through the main circuit is cooled by the intermediate heat exchanger 22 (state A <b> 4) and reaches the second expansion valve 14. The refrigerant is further depressurized by the second expansion valve 14 (state A5), flows into the heat source side heat exchanger 15 and evaporates, and becomes a low-pressure gas refrigerant (state A6). The low-pressure gas refrigerant is boosted to a predetermined intermediate pressure by the low-stage compressor 10B (state A7) and supplied to the suction side of the high-stage compressor 10A. On the other hand, the refrigerant branched into the injection circuit is depressurized to a predetermined intermediate pressure by the third expansion valve 21 (state A8), absorbs heat through the intermediate heat exchanger 22, and passes through the injection pipe 20 to the high stage compressor. 10A is supplied to the suction side. Here, the refrigerant supplied through the injection pipe 20 and the refrigerant compressed by the low-stage compressor 10B are mixed, and the intermediate-pressure refrigerant whose temperature is lowered (state A9) is the high-stage compressor 10A. To be supplied. The high-stage compressor 10A compresses the intermediate-pressure refrigerant and discharges the high-temperature and high-pressure refrigerant (state A1). Thereafter, the same cycle is repeated.

In FIG. 2, Δi in the drawing represents the enthalpy difference between the refrigerant inlet (state A 1) and the outlet (state A 2) that has passed through the use-side heat exchanger 11. The heating capacity Q by this refrigeration cycle is represented by the product of the enthalpy difference Δi and the refrigerant circulation amount Gr.
Q = Δi × Gr (1)
Here, if the refrigerant circulation amount Gr is the refrigerant circulation amount during normal operation, the heating capacity Q during normal operation can be calculated by the above equation (1).

Next, the heating capacity Q ′ when the oil return operation is performed by the conventional control method will be described. In general, during the oil return operation, the frequency of the compressor is increased so that the flow rate of the refrigerant becomes equal to or higher than a predetermined speed (for example, flooding speed, zero penetration speed, etc.). When the frequency of the compressor is increased, the refrigerant circulation amount Gr ′ also increases. Therefore, if the oil return operation is performed at the same operating point as the refrigeration cycle shown in FIG. 2, the heating capacity Qα in that case can be calculated by the following equation (2).
Qα = Δi × Gr ′ (2)
Here, the enthalpy difference Δi is equivalent to that during normal operation, and the refrigerant circulation amount Gr ′ increases as the frequency of the high stage compressor 10A and the low stage compressor 10B increases, so that the heating capacity Qα during oil return operation is increased. Is a larger value (Qα> Q) than the heating capacity Q during normal operation. As a result, problems such as an excessive heating capacity with respect to the load and a high pressure increase due to a frequency increase of the high stage compressor 10A and the low stage compressor 10B occur. Next, the control method of the oil return operation in this embodiment that avoids such a problem will be described.

FIG. 3 is a second Ph diagram of the refrigerant circuit system in one embodiment of the present invention.
The state indicated by each symbol in the Ph diagram of FIG. 3 is the same as that described in FIG. That is, B1 is the state of the refrigerant discharged from the high stage compressor 10A, B2 is the state of the refrigerant on the outlet side of the use side heat exchanger 11, B3 is the state of the refrigerant on the outlet side of the first expansion valve 12, B4 is the state of the refrigerant on the inlet side of the second expansion valve 14, B5 is the state of the refrigerant on the outlet side of the second expansion valve 14, B6 is the state of the refrigerant on the outlet side of the heat source side heat exchanger 15, B7 Indicates the state of the refrigerant discharged from the low stage compressor 10B, B8 indicates the state of the refrigerant on the outlet side of the third expansion valve 21, and B9 indicates the state of the refrigerant on the suction side of the high stage compressor 10A, respectively. ing. The correspondence between the refrigerant flow in the refrigerant circuit and the states B1 to B9 is the same as that described with reference to FIG.

  Next, the control method of the oil return operation according to the present embodiment will be described with reference to FIG. Also in the oil return operation of the present embodiment, the pressure and temperature on the discharge side of the high stage compressor 10A are controlled to the same pressure and temperature as during normal operation (state B1). Therefore, the enthalpy equivalent to that during normal operation is maintained on the inlet side of the use side heat exchanger 11. However, the target temperature on the outlet side of the use side heat exchanger 11 is set to be higher than the target temperature during normal operation (state B2). Therefore, the enthalpy difference Δi ′ between the inlet side and the outlet side of the use side heat exchanger 11 during the oil return operation is smaller than the enthalpy difference Δi during the normal operation (Δi ′ <Δi). In addition, since the pressure difference between the upstream side (state B3) and the downstream side (state B8) of the third expansion valve 21 provided in the injection circuit is large, the refrigerant circulation amount flowing into the injection circuit increases compared to that during normal operation. Accordingly, the amount of refrigerant circulating in the mainstream circuit decreases.

Here, the heating capability Q ′ in the oil return operation of the present embodiment can be calculated by the following equation (3).
Q ′ = Δi ′ × Gr ′ (3)
As described above, the enthalpy difference Δi ′ is smaller than that during normal operation (Δi), and the refrigerant circulation amount Gr ′ increases as the frequency of the high-stage compressor 10A and the low-stage compressor 10B increases. Therefore, the heating capacity Q ′ during the oil return operation is smaller than the above Qα, and the increase amount from the heating capacity Q during the normal operation is small. Thereby, the excessive heating capability at the time of oil return operation can be suppressed. Moreover, since the supercooling area | region of the utilization side heat exchanger 11 decreases, a high voltage | pressure rise can be suppressed.
Next, a control method for maintaining the heating capacity Q ′ during the oil return operation in the present embodiment at the same level as the heating capacity Q during the normal operation will be described.

FIG. 4 is a first diagram illustrating a control method during an oil return operation in one embodiment of the present invention.
The vertical axis of the graph shown in FIG. 4 indicates the enthalpy difference, and the horizontal axis indicates the refrigerant circulation amount. The graph shown in FIG. 4 shows the relationship between the circulation amount of the refrigerant flowing through the refrigerant circuit system 1 realized by the control device 100 of the present embodiment and the enthalpy difference between the inlet side and the outlet side in the use side heat exchanger 11. Is shown. The graph shown in FIG. 4 shows that the product of the refrigerant circulation amount and the enthalpy difference is always a constant value (the refrigerant circulation amount and the enthalpy difference are inversely proportional). That is, the ratio of the enthalpy difference during normal operation to the enthalpy difference during oil return operation is the reciprocal of the ratio of the refrigerant circulation amount during normal operation to the refrigerant circulation amount during oil return operation. For example, if the refrigerant circulation amount during oil return operation is 1.2 times that during normal operation, the enthalpy difference during oil return operation is 1 / 1.2 times that during normal operation.

  As described above, the control device 100 calculates the enthalpy difference during the oil return operation so that the product of the refrigerant circulation amount and the enthalpy difference during the normal operation matches the product of the refrigerant circulation amount and the enthalpy difference during the oil return operation. Control. In order to collect the refrigerating machine oil, it is necessary to set the flow rate of the refrigerant to a certain level or higher. Therefore, also in the present embodiment, the control device 100 uses the high-stage compressor 10A and the low-stage compressor during the oil return operation. Control is performed to increase the frequency of the side compressor 10B as usual. Since the refrigerant circulation amount increases substantially in proportion to the increase in the frequency of the compressor, the refrigerant circulation amount is controlled by the frequency control of the high stage compressor 10A and the low stage compressor 10B as in the conventional oil return operation. To increase. Therefore, the control device 100 performs control to reduce the enthalpy difference in order to maintain the relationship shown in the graph of FIG. In this embodiment, since the enthalpy on the inlet side of the use side heat exchanger 11 is constant, the enthalpy difference between the inlet side and the outlet side of the use side heat exchanger 11 is reduced by increasing the enthalpy on the outlet side. Specifically, the control device 100 raises the target temperature on the outlet side of the use side heat exchanger 11 and controls the opening degree of the first expansion valve 12 toward the target temperature.

FIG. 5 is a second diagram illustrating the control method during the oil return operation according to the embodiment of the present invention.
The vertical axis of the graph shown in FIG. 5 indicates the refrigerant circulation amount, and the horizontal axis indicates the condenser outlet temperature. The graph shown in FIG. 5 shows the relationship between the outlet side temperature of the use side heat exchanger 11 and the refrigerant circulation amount for realizing the relationship between the product of the enthalpy difference and the refrigerant circulation amount described in FIG. In addition, since the circulation amount of the refrigerant discharged from the high stage side compressor 10A increases almost in proportion to the increase in the frequency of the high stage side compressor 10A, the frequency of the high stage side compressor 10A and the use side The relationship with the outlet side temperature of the heat exchanger 11 can also be expressed as a graph similar to the graph of FIG.

  The control device 100 has a built-in storage unit (not shown) that converts the refrigerant circulation rate illustrated in FIG. 5 and the outlet side temperature of the use side heat exchanger 11 or the frequency of the high stage compressor 10A, etc. And a conversion table of the outlet side temperature of the use side heat exchanger 11 is stored. These conversion tables are created in advance and recorded in the storage unit by calculations or experiments based on a function indicating the relationship between enthalpy, refrigerant temperature, and refrigerant pressure in the use-side heat exchanger 11. When the oil return operation is started, the control device 100 calculates the refrigerant circulation amount Gr ′ in the oil return operation by a known method, and refers to the conversion table illustrated in FIG. 5 to refer to the refrigerant circulation amount Gr ′. The outlet side temperature T ′ of the use side heat exchanger 11 corresponding to is calculated. The calculated outlet side temperature T ′ is the target temperature on the outlet side of the use side heat exchanger 11 during the oil return operation. The control device 100 controls the opening degree of the first expansion valve 12 so that the outlet side temperature of the use side heat exchanger 11 becomes T ′. Then, the product (heating capacity Q ′) of the refrigerant circulation amount Gr ′ and the enthalpy difference Δi ′ at that time has the same value as the product (heating capacity Q) of the refrigerant circulation amount Gr and the enthalpy difference Δi during normal operation. Become. By controlling in this way, the oil return operation can be performed while maintaining the heating capability during the normal operation.

FIG. 6 is a diagram for explaining the effect of the oil return operation in the embodiment of the present invention.
The lower diagram of FIG. 6 shows the refrigerant circulation amount during normal operation and during oil return operation. The refrigerant circulation amount during normal operation is represented by square marks, the refrigerant circulation amount during oil return operation by the conventional control method is represented by a triangle mark, and the refrigerant circulation amount during oil return operation by the control method of the present embodiment is represented by a circle mark. Yes. In the drawings described below, it is assumed that the operation state of the refrigerant circuit system 1 corresponding to the square mark, the triangle mark, and the circle mark is the same. As shown in the lower diagram of FIG. 6, in both the conventional oil return operation and the oil return operation of the present embodiment, the refrigerant is circulated at a flow rate necessary for collecting the refrigeration oil. To rise.
The middle diagram of FIG. 6 shows the enthalpy difference during normal operation and during oil return operation. As shown in the middle diagram of FIG. 6, the enthalpy difference during normal operation and the enthalpy difference during oil return operation according to the conventional control method are the same. Decrease.
The upper diagram in FIG. 6 shows the heating capacity during normal operation and during oil return operation. As shown in the upper diagram of FIG. 6, there is no change in the heating capacity between the heating capacity during normal operation and the oil return operation according to the control method of the present embodiment. On the other hand, in the oil return operation by the conventional control method, the heating capacity increases as compared with them.

Next, the flow of processing during the oil return operation will be described with reference to FIG.
FIG. 7 is a flowchart of the control device according to the embodiment of the present invention.
As a premise, the control device 100 acquires the temperature information measured by the temperature sensor 31 and the temperature sensor 33 and the pressure information measured by the pressure sensor 32 at predetermined time intervals, and incorporates the acquired temperature and pressure information. To be recorded in a storage unit (not shown). In addition, the storage unit (not shown) of the control device 100 includes a conversion table of the refrigerant circulation amount and the condenser outlet temperature exemplified in FIG. 5 (or the frequency of the high stage compressor 10A and the like and the condenser outlet temperature). Conversion table) is recorded. Further, the control device 100 sets the pressure on the discharge side of the high stage compressor 10A (measured value by the pressure sensor 32) based on the pressure on the use side outlet temperature (for example, a temperature 2 ° C. higher than the use side outlet temperature as the saturation temperature) The respective frequencies are controlled so that the high pressure side compressor 10A and the low pressure side compressor 10B have an equal pressure ratio. Further, the control device 100 determines that the temperature on the outlet side of the use side heat exchanger 11 (measured value of the temperature sensor 33) is a predetermined temperature (for example, 2 ° C.) from the use side inlet temperature (measured value of the temperature sensor 31). The opening degree of the first expansion valve 12 is controlled so that the target temperature becomes as high as possible. In addition, for example, the control device 100 starts the oil return operation based on the fact that a predetermined condition such as the accumulation of the execution time of the normal operation since the previous oil return operation is equal to or greater than a threshold is satisfied. Suppose it is a scene.

First, the control device 100 increases the frequencies of the two compressors (the high-stage compressor 10A and the low-stage compressor 10B) (step S11). For example, a frequency at which the flow rate of the refrigerant flowing through the pipe becomes a flow rate necessary for collecting the refrigerating machine oil is predetermined for each compressor and recorded in the storage unit, and the control device 100 is based on this information. Thus, the frequencies of the high-stage compressor 10A and the low-stage compressor 10B are increased. Next, the control device 100 calculates the condenser outlet temperature (step S12). The condenser outlet temperature is obtained by calculating the product of the enthalpy difference Δi during normal operation and the refrigerant circulation amount Gr (or the frequency of the high-stage compressor 10A or the like) as the enthalpy difference Δi ′ during oil return operation. This is the target temperature on the outlet side of the use side heat exchanger 11 calculated so as to be equal to the product of the refrigerant circulation amount Gr ′. The control device 100 calculates the condenser outlet temperature with reference to the conversion table illustrated in FIG. 5 using the frequency of each compressor or the refrigerant circulation amount calculated in step S11.
Next, the control device 100 controls the opening degree of the first expansion valve 12 so that the outlet side temperature of the use side heat exchanger 11 becomes the condenser outlet temperature calculated in step S12 (step S13). For example, for each target temperature, a data table or the like in which a valve opening degree corresponding to the difference between the temperature measured by the temperature sensor 33 and the target temperature is set is recorded in the storage unit, and the control device 100 stores the data table in this data table. Based on this, the opening degree of the first expansion valve 12 is adjusted. Thereby, the enthalpy difference between the inlet side and the outlet side of the use-side heat exchanger 11 can be set as a target enthalpy difference, and the heating capability during the oil return operation can be made equal to that during the normal operation.
In addition, the calculation method of the condenser outlet temperature in step S12 is not limited to the calculation method based on the conversion table illustrated in FIG. For example, even if the product of the refrigerant circulation amount and the enthalpy difference during normal operation does not match the product of the refrigerant circulation amount and the enthalpy difference during the oil return operation, the control device 100 keeps the difference between the two within a predetermined range. Control may be performed using an arbitrary temperature that falls within the range as the condenser outlet temperature. Thereby, it is possible to mitigate excessive capacity during the oil return operation.

  According to the present embodiment, the control device 100 uses the use side heat exchange so that the difference between the heating capability during the oil return operation in the heating cycle and the heating capability during the normal operation is within a predetermined range or equivalent. The enthalpy difference between the inlet side and the outlet side of the vessel 11 and the frequencies of the high stage compressor 10A and the low stage compressor 10B are controlled. More specifically, the control device 100 maintains the enthalpy on the inlet side of the use side heat exchanger 11 at a predetermined target value, and sets the target temperature on the outlet side of the use side heat exchanger 11 to the high temperature side during the oil return operation. Set enthalpy high by setting to. As a result, the enthalpy difference becomes smaller than that during normal operation, and the increased amount of refrigerant circulation due to an increase in the frequency of the high stage compressor 10A and the like is offset. Preferably, the enthalpy difference during the oil return operation is calculated such that the product of the frequency and the enthalpy difference of the high-stage compressor 10A, etc. matches between the normal operation and the oil return operation, and the calculated enthalpy difference The temperature on the outlet side of the use side heat exchanger 11 based on the above is set to the target temperature. Then, even during the oil return operation, the heating capacity commensurate with the load can be maintained without changing from the normal operation. As a result, there is a problem that the capacity that has been apt to occur during the oil return operation in the heating cycle is excessive, the compressor is temporarily stopped due to the operation of the high pressure protection control against the high pressure rise, the temperature fluctuation accompanying it, the feeling of feeling Deterioration can be prevented.

  In addition, it is possible to appropriately replace the components in the above-described embodiments with known components without departing from the spirit of the present invention. The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Refrigerant circuit system 10A ... High stage side compressor 10B ... Low stage side compressor 11 ... Usage side heat exchanger 12 ... 1st expansion valve 13 ... Receiver 14 ... -2nd expansion valve 15 ... Heat source side heat exchanger 16 ... Accumulator 17 ... Mainstream piping 20 ... Injection piping 21 ... 3rd expansion valve 22 ... Intermediate heat exchanger 31, 33 ... Temperature sensor 32 ... Pressure sensor 100 ... Control device

Claims (7)

A control device for controlling a refrigerant circuit system, wherein a difference between a heating capacity of the refrigerant circuit system during oil return operation in a heating cycle and a heating capacity of the refrigerant circuit system during normal operation is within a predetermined range. As described above, the enthalpy difference between the inlet side and the outlet side of the condenser provided in the refrigerant circuit system and the circulation amount of the refrigerant flowing through the refrigerant circuit system are controlled.
Control device. By maintaining the enthalpy on the inlet side of the condenser at a predetermined target value and setting the target temperature on the outlet side of the condenser to a higher temperature than in normal operation during the oil return operation, the outlet side of the condenser Set the enthalpy of higher than normal operation,
The control device according to claim 1. The difference in enthalpy of the condenser during oil return operation is calculated so that the product of the frequency of the compressor provided in the refrigerant circuit system and the difference in enthalpy matches between normal operation and oil return operation, The temperature at the outlet side of the condenser based on the calculated enthalpy difference is set as a target temperature during the return operation, and control is performed so that the temperature at the outlet side of the condenser becomes the target temperature. Item 3. The control device according to Item 2. Based on the target temperature on the outlet side of the condenser, the opening degree of the expansion valve provided on the outlet side of the condenser is controlled.
The control device according to claim 3. The refrigerant circuit system includes:
A plurality of compressors for compressing the refrigerant; a condenser for condensing the compressed refrigerant; a first expansion valve for depressurizing the condensed refrigerant; and one of the refrigerant decompressed by the first expansion valve. A main circuit that connects a receiver that stores a part, a second expansion valve that decompresses the refrigerant flowing out of the receiver, and an evaporator that evaporates the refrigerant decompressed by the second expansion valve;
An injection circuit for branching a part of the refrigerant flowing out from the receiver and supplying the branched refrigerant to a suction side of a predetermined compressor among the plurality of compressors, wherein the part of the branched refrigerant An injection circuit comprising: a third expansion valve for reducing pressure; and an intermediate heat exchanger for performing heat exchange between the refrigerant that has passed through the third expansion valve and the refrigerant that has passed through the mainstream circuit,
During normal operation, the target temperature on the outlet side of the condenser is set to a temperature that is higher than the temperature of the use-side medium flowing into the condenser by a predetermined temperature,
During oil return operation, the target temperature on the outlet side of the condenser is set to a temperature higher than the target temperature during normal operation.
The control device according to any one of claims 1 to 4. A plurality of compressors for compressing the refrigerant; a condenser for condensing the compressed refrigerant; a first expansion valve for depressurizing the condensed refrigerant; and one of the refrigerant decompressed by the first expansion valve. A main circuit that connects a receiver that stores a part, a second expansion valve that decompresses the refrigerant flowing out of the receiver, and an evaporator that evaporates the refrigerant decompressed by the second expansion valve;
An injection circuit for branching a part of the refrigerant flowing out from the receiver and supplying the branched refrigerant to a suction side of a predetermined compressor among the plurality of compressors, wherein the part of the branched refrigerant An injection circuit comprising: a third expansion valve that reduces pressure; and an intermediate heat exchanger that performs heat exchange between the refrigerant that has passed through the third expansion valve and the refrigerant that has passed through the mainstream circuit;
A control device according to any one of claims 1 to 5,
A refrigerant circuit system comprising: A control device for controlling the refrigerant circuit system
In the condenser provided in the refrigerant circuit system, the difference between the heating capacity of the refrigerant circuit system during the oil return operation in the heating cycle and the heating capacity of the refrigerant circuit system during the normal operation is within a predetermined range. A control method for controlling an enthalpy difference between an inlet side and an outlet side and a circulation amount of the refrigerant flowing through the refrigerant circuit system.

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