JP5144959B2 - Heat source machine and control method thereof - Google Patents

Description

  The present invention relates to a heat source machine having a two-stage economizer cycle and a control method thereof.

Generally, a two-stage economizer cycle is known as a cycle aimed at improving the efficiency of the refrigeration cycle. In this two-stage economizer cycle, the liquid refrigerant condensed in the condenser is partially branched before being throttled by the main expansion valve, and the branched liquid refrigerant is throttled by the sub-expansion valve, and after being throttled by the sub-expansion valve The liquid refrigerant before being led to the main expansion valve by the latent heat of evaporation when the liquid refrigerant evaporates is supercooled.
In the heat source machine that realizes such a two-stage economizer cycle, the main expansion valve and the sub expansion valve are connected in parallel to the condenser, so that the liquid refrigerant is distributed so as to securely seal the expansion valve. Control is required.
In addition, in a heat source device that includes a plurality of systems having a main expansion valve and a sub expansion valve in parallel with respect to a common compressor, it is further difficult to appropriately distribute the liquid refrigerant.
In addition to properly distributing the liquid refrigerant to each system, it is necessary to control the main expansion valve and the sub expansion valve of each system so that the heat source unit can operate at a target operating point.

  On the other hand, Patent Document 1 discloses a heat pump type air conditioner in which a plurality of indoor heat exchangers are connected in parallel to a common compressor. This document discloses a technique for controlling the opening degree of an expansion valve so as to reduce the subcool deviation of each indoor heat exchanger during operation during heating.

JP-A 61-195255

  However, Patent Document 1 does not employ a two-stage economizer cycle, and there is no suggestion for controlling the opening of the main expansion valve and the sub expansion valve. Moreover, although the subcool deviation of each indoor heat exchanger can be reduced, there is no suggestion as to how to control when the operating point of the entire apparatus is not the target state.

  The present invention has been made in view of such circumstances, and provides a heat source apparatus and a control method thereof that can appropriately distribute liquid refrigerant in each system while operating at an appropriate target point. The purpose is to provide.

In order to solve the above-described problems, the heat source machine and the control method thereof according to the present invention employ the following means.
That is, the heat source apparatus according to the present invention is provided between a condenser that condenses the refrigerant compressed by the compressor, an evaporator that evaporates the condensed refrigerant, and the condenser and the evaporator, A main expansion valve that expands the liquid refrigerant guided from the condenser and a liquid refrigerant that is provided between the condenser and the intermediate stage of the compressor and that is branched from between the condenser and the main expansion valve. A compressor in which a plurality of systems includes a sub-expansion valve that expands, and an economizer that exchanges heat between the refrigerant flowing from the condenser to the main expansion valve and the refrigerant expanded by the sub-expansion valve in parallel. In the control method of the heat source apparatus that controls the opening degree of the main expansion valve and the sub expansion valve of each of the systems, a target state that is a target value of the state amount of the refrigerant after heat exchange of the economizer the amount each Used as a common target value serial system calculates a target opening of the main expansion valve and the sub-expansion valve of each of the systems, is the state quantity of the refrigerant after the heat exchange of the current of the economizer in each said line A difference amount between the current value state quantity and the target state quantity is calculated for each of the systems, and for the system in which the difference quantity is less than a predetermined value, the target opening is set to the main expansion valve of the system and / or Or, instructing the sub-expansion valve, and for a system in which the difference amount is equal to or greater than a predetermined value, the main expansion valve and / or the sub The expansion valve is instructed.

By calculating the target opening using the target state quantity common to each system and instructing this opening to each main expansion valve and / or each sub expansion valve, each system is linked to the target value. Can lead.
Further, for a system in which the difference amount between the target state amount and the current value state amount is equal to or greater than a predetermined value, the opening based on the difference amount is given to the main expansion valve and / or the sub-expansion valve as a correction opening degree. Thus, only a specific system that is out of the target state quantity can be brought close to the target state quantity. Thereby, the state of each system | strain can be maintained substantially uniform. The correction opening is given based on the difference amount. For example, correction is performed so that the current value state amount approaches the target state amount by a predetermined ratio of the difference amount.
In addition, for the main expansion valve and / or sub-expansion valve of the system in which the difference between the target state quantity and the current value state quantity is less than the predetermined value, the target opening degree is instructed without giving the correction opening degree. It was decided. As a result, simple control can be realized and the stability of the control can be improved.
Here, the state quantity means, for example, pressure, temperature, and enthalpy.

  Further, in the heat source device of the present invention, the state quantity of the refrigerant after the heat exchange of the economizer used as the target state quantity and the current value state quantity is the value of the high-pressure liquid refrigerant flowing from the condenser to the main expansion valve. It is characterized by the temperature at the exit of the economizer.

As the state quantity of the economizer outlet used as the target state quantity and the current value state quantity, the temperature of the high-pressure liquid refrigerant flowing from the condenser to the main expansion valve, that is, the supercooling temperature (subcool temperature) is used. As described above, since the temperature of the supercooled liquid is measured, a larger heat capacity is measured as compared with the case of measuring the gas refrigerant that has passed through the economizer from the sub expansion valve, and the measurement accuracy can be improved. .
In addition, when using gas refrigerant that has passed through the economizer from the sub expansion valve, the refrigerant does not flow when the sub expansion valve is closed, so it is difficult to take control starting points, but the main expansion valve is always in operation of the heat source machine. Since it is open, there is an advantage that there is no such inconvenience.

  Furthermore, the heat source machine of the present invention is characterized in that an upper limit is set for the correction amount of the correction opening.

  The upper limit is set to the correction amount of the correction opening, that is, the difference between the target opening and the correction opening. As a result, a significant change in the opening degree is prohibited, and the stability of the entire system can be achieved.

Further, the control method of the heat source apparatus of the present invention is provided between the condenser that condenses the refrigerant compressed by the compressor, the evaporator that evaporates the condensed refrigerant, and the condenser and the evaporator. A liquid which is provided between a main expansion valve for expanding the liquid refrigerant guided from the condenser and an intermediate stage of the condenser and the compressor, and is branched from between the condenser and the main expansion valve. A plurality of systems having a sub-expansion valve that expands the refrigerant, and an economizer that exchanges heat between the refrigerant flowing from the condenser to the main expansion valve and the refrigerant expanded by the sub-expansion valve are shared in parallel. In the control method of the heat source device connected to the compressor and controlling the opening degree of the main expansion valve and the sub expansion valve of each of the systems, it is a target value of the state quantity of the refrigerant after heat exchange of the economizer the target state amount each Used as a common target value serial system calculates a target opening of the main expansion valve and the sub-expansion valve of each of the systems, the current value state quantity is a state quantity of the refrigerant after the heat exchange of the current of the economizer And the target opening is instructed to the main expansion valve and / or the sub expansion valve of the system for a system in which the difference is less than a predetermined value. In addition, for the system in which the difference amount is equal to or greater than a predetermined value, the opening based on the difference amount is instructed to the main expansion valve and / or the sub expansion valve of the system as a correction opening. And

By calculating the target opening using the target state quantity common to each system and instructing this opening to each main expansion valve and / or each sub expansion valve, each system is linked to the target value. Can lead.
Further, for a system in which the difference amount between the target state amount and the current value state amount is equal to or greater than a predetermined value, the opening based on the difference amount is given to the main expansion valve and / or the sub-expansion valve as a correction opening degree. Thus, only a specific system that is out of the target state quantity can be brought close to the target state quantity. Thereby, the state of each system | strain can be maintained substantially uniform. The correction opening is given based on the difference amount. For example, correction is performed so that the current value state amount approaches the target state amount by a predetermined ratio of the difference amount.
In addition, for the main expansion valve and / or sub expansion valve of the system in which the difference between the target state quantity and the current value state quantity is less than the predetermined value, the target opening degree is instructed without giving a correction opening degree. It was decided to. As a result, simple control can be realized and the stability of the control can be improved.
Here, the state quantity means, for example, pressure, temperature, and enthalpy.

  According to the present invention, it is possible to appropriately distribute liquid refrigerant in each system while operating at an appropriate target point.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration diagram of a turbo refrigerator (heat source machine) 1 using a turbo compressor. As will be described later, the turbo refrigerator 1 constitutes a two-stage economizer cycle. Further, the turbo refrigerator performs not only a cooling operation in which cold water is cooled by an evaporator, but also a heat pump heating operation in which hot water is heated by a condenser. FIG. 1 shows a configuration during cooling operation.

  The turbo refrigerator 1 includes a turbo compressor 3 that compresses refrigerant, a high-pressure header 5 that is connected to the discharge side of the turbo compressor 3, a low-pressure header 7 that is connected to the suction side of the compressor 3, and the compressor 3. And an intermediate pressure header 9 connected to the intermediate stage.

The turbo compressor 3 is a centrifugal compressor capable of obtaining a high pressure ratio.
The turbo compressor 3 includes two impellers (not shown) provided coaxially in the housing and an inlet vane (not shown) for adjusting the suction refrigerant flow rate.
Each impeller is rotated by a drive motor (not shown). The two impellers are connected in series with the refrigerant flow path. The refrigerant flowing into the turbo compressor 3 is compressed by the upstream impeller and then further compressed by the downstream impeller. The gas refrigerant guided from the intermediate pressure header 7 is introduced between the two impellers (intermediate stage).

A plurality of main flow paths 11 are provided in parallel between the high-pressure header 5 and the low-pressure header 7.
In each main channel 11, a condenser 15 located on the downstream side of the high-pressure header 5, an evaporator 16 located on the upstream side of the low-pressure header, and a main provided between the condenser 15 and the evaporator 16. An expansion valve 18 is provided.
A cooling water pipe 20 is connected to the condenser 15 so that the latent heat of condensation of the refrigerant is taken away by the cooling water flowing through the cooling water pipe 20. The condenser 15 may be an air heat exchanger that exchanges heat with external air without connecting the cooling water pipe 20.
The evaporator 16 is connected to a chilled water pipe 22 that supplies chilled water to an external heat load, and takes away the latent heat of evaporation of the refrigerant from the chilled water flowing through the chilled water pipe 22.
The main expansion valve 18 is an electronic expansion valve, and the liquid refrigerant is expanded by controlling the opening degree by a control unit (not shown).

A sub flow path 25 branches from each main flow path 11.
The sub flow path 25 branches from between the condenser 15 of the main flow path 11 and the main expansion valve 18 and is connected to the intermediate pressure header 7. The sub flow path 25 is provided with a sub expansion valve 27 for expanding the liquid refrigerant.
The sub expansion valve 27 is an electronic expansion valve whose opening is controlled by a control unit (not shown).
An economizer 29 that exchanges heat with the liquid refrigerant in the main flow path 11 before flowing into the main expansion valve 18 is provided on the downstream side of the sub expansion valve 27. In this economizer 29, the liquid refrigerant in the main flow path 11 is cooled and supercooled by the latent heat of evaporation of the refrigerant that is expanded by the sub expansion valve 27 and evaporates.
As described above, the turbo chiller 1 of the present embodiment has a configuration in which a plurality of systems including the main flow path 11 and the sub flow path 25 are provided in parallel (four systems in the present embodiment).

A control unit (not shown) of the turbo refrigerator 1 is provided on a control board in the control panel of the turbo refrigerator 1 and includes a CPU and a memory. The control unit calculates each control amount by digital calculation for each control cycle based on the outside air temperature, the refrigerant pressure, the cold water inlet / outlet temperature, and the like.
Further, as will be described later, the control unit controls the opening degrees of the main expansion valve 18 and the sub expansion valve 27 based on each calculation amount.

Next, the operation of the turbo refrigerator 1 having the above configuration will be described.
The turbo compressor 3 is rotated at a predetermined frequency by a control unit (not shown).

  The low-pressure gas refrigerant sucked from the evaporator 9 (state A in FIG. 2) is compressed by the turbo compressor 3 and compressed to an intermediate pressure (state B in FIG. 2). The gas refrigerant compressed to the intermediate pressure is cooled by joining with the intermediate pressure gas refrigerant flowing in from the intermediate pressure header 7 (state C in FIG. 2). The gas refrigerant cooled by the intermediate-pressure gas refrigerant is further compressed by the turbo compressor 3 to become a high-pressure gas refrigerant (state D in FIG. 2).

The high-pressure gas refrigerant discharged from the turbo compressor 3 passes through the high-pressure header 5 and is led to the condenser 15 of each system.
In the condenser 15, the high-pressure gas refrigerant is cooled at substantially equal pressure by the cooling water flowing in the cooling water pipe 20, and becomes high-pressure liquid refrigerant (state E in FIG. 2). The high-pressure liquid refrigerant is branched into the main flow path 11 and the sub flow path 25.
The high-pressure liquid refrigerant flowing through the main flow path 11 is cooled by the refrigerant flowing through the sub flow path 25 in the economizer 29 (state F in FIG. 2) and is guided to the main expansion valve 18. On the other hand, the high-pressure liquid refrigerant flowing through the sub-flow path 25 is isoenthalpy-expanded to the intermediate pressure by the sub-expansion valve 27 (state G in FIG. 2), and is guided to the economizer 29. Then, when evaporating in the economizer 29, heat is taken from the high-pressure liquid refrigerant flowing through the main flow path 11, and supercooling is applied to the high-pressure liquid refrigerant flowing through the main flow path 11. The refrigerant flowing through the sub flow path 25 passes through the economizer 29, is then guided to the intermediate pressure header 7, and flows into the intermediate stage of the turbo compressor 3.

  The high-pressure liquid refrigerant in the main flow path 11 that has been supercooled by the economizer 29 is expanded by equal enthalpy to the low pressure by the main expansion valve 18 (state H in FIG. 2), and is evaporated in the evaporator 16 (in FIG. 2). Heat is taken from the cold water pipe 22 from the state H to the state A). Thereby, for example, the cold water flowing in at 12 ° C. is returned to the load side at 7 ° C. The low-pressure gas refrigerant evaporated in the evaporator 16 is guided to the low-pressure header 9 and then flows into the suction port of the turbo compressor 3 and is compressed again.

Next, opening control of the main expansion valve 18 and the sub expansion valve 27 performed by the control unit will be described.
A refrigerant flow rate g1 (see FIG. 2) flowing through the main flow path 11 is obtained by the following equation.
g1 = Q / (heg-hcs) (1)
Here, Q is the cooling capacity, heg is the enthalpy in state A in FIG. 2, and hcs is the enthalpy in state F in FIG. The cooling capacity Q is obtained from the product of the temperature difference of the cold water flowing through the cold water pipe 22 cooled by the evaporator 16, the cold water flow rate, and the cold water density.
Moreover, the refrigerant | coolant flow volume gm (refer FIG. 2) which flows through the subchannel 25 is calculated | required by following Formula.
gm = (hcc-hcs) · g1 / (hmg-hcc) (2)
Here, hcc is the enthalpy in state E in FIG. 2, and hmg is the enthalpy in state C in FIG.

The Cv value of the main expansion valve 18 is calculated by the following formula using g1 of the formula (1).
Cv1 = A1 · g1 / (2 · ρ1 (Pc−Pe)) ^1/2 (3)
Here, A1 is the valve area, ρ1 is the refrigerant density, Pc is the condensation pressure (see FIG. 2), and Pe is the evaporation pressure (see FIG. 2).
The Cv value of the sub expansion valve 27 is calculated by the following equation using equation (2) gm.
Cvm = Am · gm / (2 · ρm (Pc−Pm)) ^1/2 (4)
Here, Am is the valve area, ρm is the refrigerant density, and Pm is the intermediate pressure (see FIG. 2).

The opening V1 (%) of the main expansion valve 18 is calculated by the following equation using Cv1 obtained by the equation (3).
V1 = f1 (Cv1) (5)
Here, f1 (Cv1) is a function determined by actually measuring the characteristics of the main expansion valve 18.
The opening degree Vm (%) of the sub expansion valve 27 is calculated by the following formula using Cvm obtained by the formula (4).
Vm = fm (Cvm) (6)
Here, fm (Cvm) is a function determined by actually measuring the characteristics of the sub expansion valve 27.

In order to provide appropriate supercooling in the state F of FIG. 2, the temperature Ts in the state F is set as follows.
Ts _set = Tm + Δt (7)
Here, Ts _set is a set value, and Tm is a temperature in the state G. Δt is arbitrarily given in consideration that the refrigerant temperature flowing through the main flow path 11 cooled by the economizer 29 cannot be lower than the refrigerant temperature Tm flowing through the sub flow path 25 to be cooled due to heat loss. It is a temperature difference.
In addition, (DELTA) t is good also as a function of the refrigerating capacity Q like following Formula.
Δt = f (Q) (8)
The function f (Q) increases as the refrigeration capacity Q increases, so that the refrigerant flow rate increases and heat transfer in the economizer 29 improves. Therefore, Δt is small when the refrigeration capacity Q is large, and Δt when the refrigeration capacity is small. Is a function that increases.

Next, the procedure for controlling the opening of the main expansion valve 18 and the sub expansion valve 27 performed in the control unit will be described with reference to FIG.
When the start of the turbo chiller 1 is started (S0), the start sequence is executed (S1). In the startup sequence, the main expansion valve 18 is gradually opened with the sub expansion valve 27 fully closed, and then the sub expansion valve 27 is gradually opened. When the other startup sequence is completed (S2), the control unit determines a target supercooling temperature (subcooling temperature) Ts _set using Equation (7) (S3). Tm in Expression (7) is obtained as a saturation temperature from the pressure Pm of the intermediate pressure header 7 or the like. Therefore, Tm is a common value in each system.
In step S4, the base opening (target opening) V1 of the main expansion valve 18 is determined by equations (1), (3), and (5). The enthalpy heg in the state A (see FIG. 2) of the equation (1) is obtained from the evaporation pressure Pe at the low-pressure header 9 and the saturation temperature at the evaporation pressure Pe. Therefore, the enthalpy heg is a common value in each system. Further, the enthalpy hcs in the state F (see FIG. 2) of the equation (1) is obtained from the target supercooling temperature Ts _set and the condensation pressure Pc of the high-pressure header 5 and the like. Therefore, the enthalpy hcs is a common value in each system.

  Next, in step S5, the base opening (target opening) Vm of the sub expansion valve 27 is determined by equations (2), (4), and (6). The enthalpy hcc in the state E (see FIG. 2) of the equation (2) is obtained from the condensation pressure Pc of the high-pressure header 5 and the saturation temperature at the condensation pressure Pc. Therefore, the enthalpy hcc is a common value in each system. Further, the enthalpy hmg in the state C (see FIG. 2) of the equation (2) is obtained from the intermediate pressure Pm of the intermediate pressure header 7 and the saturation temperature at the intermediate pressure Pm. Therefore, enthalpy hmg is a common value in each system.

As described above, the base opening degree V1 of the main expansion valve 18 and the base opening degree Vm of the sub expansion valve 27 corresponding to the target subcooling temperature Ts _set are obtained for each system.

Next, in step S6, the absolute value of the difference between the target supercooling temperature _{Ts The set} and supercooling temperature of each line in the current (current value state _{quantity) Tsi (ABS (Ts set -Tsi} )) is calculated. That is, the difference is calculated for each system. When the absolute value of this difference exceeds 3 ° C., the process proceeds to step S7 and the opening degree is corrected. In step S7, the target supercooling temperature Ts _set is corrected by the following equation for each system.
Ts _setj = Ts _set + K * (Ts _set −Tsi) (9)
Here, Ts _setj is the corrected _subcooling temperature for each system, and K is a constant less than 1.

In step S8, the corrected opening (V1 + dV1) of the main expansion valve 18 and the corrected opening (Vm + dV1) of the sub expansion valve 27 are obtained. The method for calculating the corrected opening is performed in the same manner as the method for calculating the opening in steps S4 and S5. That is, although the target _subcooling temperature Ts _set is used in step S4 and step S5, it may be calculated similarly using the corrected _subcooling temperature Ts _setj for each system instead.
The correction opening dV1 and dVm calculated as described above have an upper limit of 3%. As a result, a significant change in the opening degree is prohibited, and the stability of the entire system is achieved.

If the absolute value of the difference between the target subcooling temperature Ts _set and the subcooling temperature Tsi of each system is 3 ° C. or less in step S6, the process proceeds to step S9, and the base opening calculated in step S4 and step S5 is performed. The degrees V1 and Vm are not changed (that is, dV1 and dVm are set to 0).

  When the opening degree is determined as described above, the corrected opening (or no correction) opening degree V1 ′ = V1 + dV1 is instructed to the main expansion valve 18 of each system, and the sub expansion valve 27 of each system is instructed. An opening degree Vm ′ = Vm + dVm after correction (or no correction) is instructed.

The above-described steps S3 to S10 are repeatedly performed at a predetermined control cycle when the turbo chiller 1 is in operation (S11). Therefore, in steps S3 to S5, the base opening degrees V1 and Vm are repeatedly corrected using the common target subcooling temperature Ts _set . In steps S7 and S8, the corrected subcooling temperature for each system is corrected. The correction _{amounts dV1} and _dVm of the correction opening are repeatedly corrected using Ts _setj .

  When the turbo chiller 1 stops, a stop sequence is executed (S12) and waits until the next start-up is performed (S0).

According to the turbo refrigerator 1 of this embodiment mentioned above, there exist the following effects.
By calculating the base opening V1, Vm using the target subcooling temperature Ts _set common to each system, and instructing the opening to each main expansion valve 18 and / or each sub expansion valve 27, The system can be linked to the target value.
Further, in a system in which the difference between the target supercooling temperature Ts _set and the current value of each system's subcooling temperature Tsi is equal to or greater than a predetermined value, the target subcooling temperature Ts _set and the current value of each system's subcooling Since the opening based on the difference from the temperature Tsi is given to the main expansion valve 18 and / or the sub expansion valve 27 as the corrected opening V1 ′, Vm ′, a specific system deviating from the target supercooling temperature Ts _set Only can be brought close to the target supercooling temperature Ts _set . Thereby, the state of each system | strain can be maintained substantially uniform.

In the present embodiment, the cooling operation of the turbo chiller 1 has been described. However, the present invention can be similarly applied to a heat pump heating operation and a cooling operation / heating operation of an air heat source heat pump.
Further, an upper limit value may be provided for the flow rate of the refrigerant flow rate g1 flowing through the main flow path 11, and the opening of the main expansion valve 18 may be limited so as not to exceed this refrigerant flow rate. Thereby, it is possible to prevent a decrease in efficiency due to an excessive flow of refrigerant and an increase in useless compression work.

It is the schematic which showed one Embodiment of the turbo refrigerator of this invention. It is a pressure (P) -enthalpy (h) diagram which showed operation | movement of the turbo refrigerator of FIG. 2 is a flowchart showing opening control of a main expansion valve and a sub expansion valve of the turbo chiller in FIG. 1.

Explanation of symbols

1 Turbo refrigerator (heat source machine)
3 Turbo compressor (compressor)
11 Main flow path 15 Condenser 16 Evaporator 18 Main expansion valve 25 Sub flow path 27 Sub expansion valve 29 Economizer

Claims (4)

A condenser for condensing the refrigerant compressed by the compressor;
An evaporator for evaporating the condensed refrigerant;
A main expansion valve that is provided between the condenser and the evaporator and expands the liquid refrigerant led from the condenser;
A sub-expansion valve that is provided between the condenser and the intermediate stage of the compressor and expands the liquid refrigerant branched from between the condenser and the main expansion valve;
An economizer for exchanging heat between the refrigerant flowing from the condenser to the main expansion valve and the refrigerant expanded by the sub expansion valve;
A plurality of lines with a connected against parallel common compressor,
In a heat source machine including a control unit that controls the opening degree of the main expansion valve and the sub expansion valve of each of the systems,
The control unit uses a target state quantity that is a target value of a refrigerant state quantity after heat exchange of the economizer as a target value common to each of the systems, and controls the main expansion valve and the sub expansion valve of each system. Calculate the target opening,
Calculate the difference amount between the current state value and the target state amount, which is the state amount of the refrigerant after heat exchange of the current economizer in each of the systems, for each system,
For the system in which the difference amount is less than a predetermined value, the target opening is instructed to the main expansion valve and / or the sub expansion valve of the system,
For the system in which the difference amount is equal to or greater than a predetermined value, the opening based on the difference amount is instructed to the main expansion valve and / or the sub expansion valve of the system as a correction opening. Heat source machine.   The state quantity of the refrigerant after the heat exchange of the economizer used as the target state quantity and the current value state quantity is the temperature of the economizer outlet of the high-pressure liquid refrigerant flowing from the condenser to the main expansion valve. The heat source machine according to claim 1.   The heat source device according to claim 1, wherein an upper limit is set for the correction amount of the correction opening. A condenser for condensing the refrigerant compressed by the compressor;
An evaporator for evaporating the condensed refrigerant;
A main expansion valve that is provided between the condenser and the evaporator and expands the liquid refrigerant led from the condenser;
A sub-expansion valve that is provided between the condenser and the intermediate stage of the compressor and expands the liquid refrigerant branched from between the condenser and the main expansion valve;
An economizer for exchanging heat between the refrigerant flowing from the condenser to the main expansion valve and the refrigerant expanded by the sub expansion valve;
A plurality of lines with a connected against parallel common compressor,
In the control method of the heat source machine that controls the opening degree of the main expansion valve and the sub expansion valve of each system,
The target opening of the main expansion valve and the sub expansion valve of each system is calculated using a target state quantity that is a target value of the state quantity of the refrigerant after heat exchange of the economizer as a common target value for each system. And
Calculating the amount of difference between the current state quantity and the target state quantity, which is the state quantity of the refrigerant after heat exchange of the current economizer,
For the system in which the difference amount is less than a predetermined value, the target opening is instructed to the main expansion valve and / or the sub expansion valve of the system,
For the system in which the difference amount is equal to or greater than a predetermined value, the opening based on the difference amount is instructed to the main expansion valve and / or the sub expansion valve of the system as a correction opening. Control method of heat source machine.

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