US20240118003A1

US20240118003A1 - CO2 Heat Pump System or CO2 Refrigeration System Comprising an Ejector Assembly and Method for Controlling an Ejector Assembly of a CO2 Heat Pump System or a CO2 Refrigeration System

Info

Publication number: US20240118003A1
Application number: US18/376,936
Authority: US
Inventors: Kim Gardø Christensen; Mads Holst Nielsen; Jonas Lund Rasmussen; Jacob Skaarup Nielsen
Original assignee: Fenagy AS
Current assignee: Fenagy AS
Priority date: 2022-10-07
Filing date: 2023-10-05
Publication date: 2024-04-11
Also published as: EP4350248A1; DK202200912A1; CA3215349A1; DK181547B1

Abstract

A CO₂based system, such as a heat pump system or a refrigeration system, is disclosed. The system comprises a plurality of ejectors arranged in parallel. Each of the ejectors comprises a motive port and a suction port. Each of the ejectors has a fixed geometry. A first actuated ball valve is arranged in front of the motive port. A second actuated ball valve is arranged in front of the suction port. The system comprises a control unit arranged and configured to control the activity of the ball valves on the basis of one or more predefined criteria.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to Danish Application No. PA 2022 00912, filed Oct. 7, 2022, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

The present invention relates to a heat pump or a refrigeration system applying vapor compression and an ejector cycle. The system comprises an ejector assembly as a pumping means for circulating low pressure refrigerant through the ejector cycle.

BACKGROUND

Many prior CO₂based heat pumps and refrigeration systems comprise one or more ejectors. An ejector comprises a primary nozzle (also named a motive nozzle), a suction chamber, a mixing chamber and a diffuser. The primary nozzle can be a convergent type or a convergent—divergent type. When the high pressure fluid (known as primary fluid or motive fluid) expands and accelerates through the primary nozzle, it flows out with high speed and hereby creates a very low pressure region at the exit plane of the nozzle. Accordingly, a pressure difference is created between the streams at the nozzle exit plane and the secondary fluid inlet. Thus, the secondary fluid is drawn through the suction chamber by the entrainment effect. Therefore, both fluids are mixed in the mixing chamber and flow through the diffuser hereby converting the kinetic energies of the mixture to pressure energy.
Typical prior art CO₂based heat pumps and refrigeration systems comprise variable ejectors that are configured to change geometry in order to regulate the flow. In these systems, a check valve is arranged next to the suction port of each ejector. The use of check valves is associated with a risk of experiencing fluid leakage because check valves are not leak-tight.
US20190111764A1 discloses a refrigeration cycle device that includes a compressor, a first branch portion, a radiator, a second branch portion, a first decompressor, a first evaporator, a second decompressor, a second evaporator, and an ejector. The first branch portion divides a flow of a refrigerant discharged from the compressor into one flow and another flow. The radiator radiates heat from the refrigerant of the one flow. The second branch portion divides a flow of the refrigerant from the radiator into one flow and another flow. The first decompressor decompresses the refrigerant of the one flow divided in the second branch portion. The second decompressor decompresses the refrigerant of the other flow divided in the second branch portion. A nozzle of the ejector decompresses and injects the refrigerant of the other flow divided in the first branch portion. The refrigerant suction port draws the refrigerant from the second evaporator. This solution is, however, associated with a risk of experiencing fluid leakage in front of the ports of the ejector.
Accordingly, it would be desirable to be able to provide an alternative solution that reduces or even eliminates the above-mentioned disadvantages of the prior art.

BRIEF DESCRIPTION

It is an object of the disclosed systems and methods to reduce the risk of fluid leakage in front of the ports of the ejector. The object can be achieved by CO₂based systems and methods disclosed herein.
A system according to an embodiment is a CO₂based system that comprises one or more ejectors arranged in parallel, wherein each of the ejectors comprises a motive port and a suction port, wherein each of the ejectors has a fixed geometry and

- a first actuated ball valve is arranged in front of the motive port; and
- a second actuated ball valve is arranged in front of the suction port,
  wherein the system comprises a control unit arranged and configured to control the activity of the ball valves on the basis of one or more predefined criteria.

Hereby, it is possible to provide a CO₂based heat pump or CO₂based refrigeration system, in which the disadvantages of the prior art can be avoided. It is possible to reduce the risk of experiencing fluid leakage. Moreover, it is possible to achieve an improved efficiency because the resistance induced by check valves used in front of the ports of the ejectors in the prior art can be reduced.
In an embodiment, the system is a heat pump.
In an embodiment, the system is a refrigeration system.
In an embodiment, the system comprises a plurality of ejectors arranged in parallel. In an embodiment, the system comprises three or more ejectors arranged in parallel. In an embodiment, the system comprises four or more ejectors arranged in parallel.
A motive line is connected to the motive port. By the phrase “in front of the motive port” is meant “in the motive line”.
A suction line is connected to the suction port. By the phrase “in front of the suction port” is meant “in the suction line”.
In an embodiment, the ejectors are high-pressure ejectors designed for high lift applications. Such ejectors are used to achieve the highest possible pressure lift at a lower delivery rate. High-pressure ejectors are suitable for transporting superheated gas.
A system according to an embodiment is a CO₂based system that comprises one or more ejectors arranged in parallel. If the system comprises a single ejector only, this ejector is not arranged in parallel. However, if the system comprises several ejectors, the ejectors are arranged in parallel.
Each of the ejectors comprises a motive port and a suction port.
Each of the ejectors has a fixed geometry. Accordingly, the ejectors are not variable geometry ejectors.
A first actuated ball valve is arranged in front of the motive port and a second actuated ball valve is arranged in front of the suction port.
By the term “ball valve” is meant a shut-off valve. Accordingly, the “ball valve” may be a “butterfly valve”, a “ball valve”, or another valve that is capable of:

- a) in a first mode shutting-off a line; and
- b) in a second mode being brought into an open configuration.

In an embodiment, the ball valve is a flow control device comprising a hollow, perforated and pivoting ball to control liquid flowing through it, wherein the ball valve is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by a valve handle, blocking the flow.
The control unit is arranged and configured to control the activity of the ball valves on the basis of one or more predefined criteria. In an embodiment, the control unit is connected to the actuators of the ball valves via a wired connection. In an embodiment, the control unit is connected to the actuators of the ball valves via a wireless connection.
In an embodiment, the system comprises:

- a liquid-gas separator having an inlet port, a gas outlet port and a liquid outlet port;
- a gas cooler having an inlet port and an outlet port;
- a high pressure valve arranged between the outlet port of the gas cooler and the inlet port of the liquid-gas separator;
- a temperature sensor arranged to detect the temperature of the fluid leaving the gas cooler;
- a pressure sensor arranged to detect the pressure of the fluid leaving the gas cooler;
- an evaporator having an inlet port and an outlet port, wherein the suction ports of the ejectors are in fluid communication with the evaporator, wherein the inlet port of the evaporator is in fluid communication with the liquid outlet port of the liquid-gas separator;
- a gas-bypass valve arranged between the gas outlet port of the liquid-gas separator and the evaporator;
- an intermediate temperature compressor arranged between the gas outlet port of the liquid-gas separator and the inlet port of the gas cooler;
- a medium temperature compressor arranged between the gas outlet port of the liquid-gas separator and the inlet port of the gas cooler.

Accordingly, by applying a system disclosed herein, it is possible not to apply a check valve in front of the suction ports of the ejectors to prevent backflow. Therefore, the disclosed systems reduce or even eliminate the risk of experiencing fluid leakage associated to the use of check valves (that are not leak-tight).
In an embodiment, the control unit is configured to detect the opening degree of the high-pressure valve, wherein the control unit is configured to open one or more of the actuated ball valves arranged in front of the motive ports of the ejectors if:

- the control unit is in operation state; and
- the opening degree of the high pressure valve is equal to or higher than a predefined level of the opening degree of the high-pressure valve.

In an embodiment, the actuated ball valves are fully opened when they are opened.
In an embodiment, the actuated ball valves are fully closed when they are closed.
The predefined level may be a user defined input. The predefined level would typically be in the range 30-50%, or 30-40%. The user will typically provide an input directly to the control unit or indirectly to the control unit via an intermediate device (e.g. a smartphone, tablet or computer).
The control unit will typically be configured to determine the opening degree of the high-pressure valve. In an embodiment, the control unit is communicatively (via a wired connection or wirelessly) connected to a detection unit that is arranged and configured to detect the opening degree of the high-pressure valve.
In an embodiment, the control unit is configured to close one or more of the actuated ball valves arranged in front of the motive ports of the ejectors if:

- the opening degree of the high pressure valve is equal to or less than a predefined level;
- the pressure at an outlet port of gas-cooler is equal to or less than a predefined setpoint pressure at the outlet port of the gas-cooler; and
- the suction ports for the respective ejectors are closed.

In an embodiment, the predefined level is a user defined input. In an embodiment, the predefined level is in the range 7-12%. In an embodiment, the predefined level is in the range 8-10%. In an embodiment, the predefined level is 8 bars. In an embodiment, the predefined level is 10 bars.
In an embodiment, the control unit is configured to determine the opening degree of the gas-bypass valve and to open the actuated ball valves arranged in front of the suction ports of one or more of the ejectors if:

- the motive ports of the one or more of the ejectors are open;
- the temperature of the fluid at the outlet port of the gas cooler is within a predefined temperature range;
- the suction pressure at the intermediate temperature compressor is within a predefined range;
- the opening degree of the gas-bypass valve is below a predefined level; and
- the number of actively operated ejectors corresponds to a predefined number based on the number of actively operated medium temperature compressors.

It is important to emphasize that the control unit is configured to open the actuated ball valves arranged in front of the suction ports of one or more of the ejectors only if the capacity of the intermediate temperature compressors is below 100%. Hereby, it is ensured that suction ports of one or more additional ejectors are only opened if the intermediate temperature compressors have additional capacity.
The capacity of the intermediate temperature compressors is below 100% when the intermediate temperature compressors can provide a higher capacity. The capacity of the intermediate temperature compressors can be increased by activating an additional intermediate temperature compressor. If three out of four intermediate temperature compressors are active, the capacity is 75%. Accordingly, the capacity of the intermediate temperature compressors can be increased by activating the last intermediate temperature compressor so that all four intermediate temperature compressors are active.
In an embodiment, the control unit is configured to determine the opening degree of the gas-bypass valve and to open the actuated ball valves arranged in front of the suction ports of one or more of the ejectors if the capacity of the intermediate temperature compressors is below 100%.
In an embodiment, the predefined level is a user defined input.
In an embodiment, the system comprises a temperature sensor arranged to detect the temperature of the fluid at the outlet port of the gas cooler.
By ensuring that the number of actively operated ejectors corresponds to a predefined number based on the number of actively operated medium temperature compressors, it is possible to ensure that the number of actively operated ejectors is selected in dependency of the compressor capacity.
In an embodiment, the control unit is configured to delay execution of opening and closing of the stop valves for a predefined delay time period within a predefined range. In an embodiment, the predefined delay time period is within the range of 10-120 seconds. In an embodiment, the predefined delay time period is within the range of 15-90 seconds. In an embodiment, the predefined delay time period is within the range of 20-60 seconds. In an embodiment, the predefined delay time period is within the range of 25-45 seconds. In an embodiment, the predefined delay time period is within the range of 25-35 seconds.
In an embodiment, the control unit is configured to close the actuated ball valves arranged in front of the suction ports of one or more of the ejectors if either of the following constraints are met:

- the temperature of the fluid leaving the gas cooler is not within a predefined temperature range limit;
- the opening degree of the gas-bypass valve exceeds a predefined level; and
- the number of actively operated ejectors exceeds a predefined number, wherein the predefined number is based on the number of actively operated medium temperature compressors.

A method for controlling a CO₂based system, such as, a heat pump system or a refrigeration system, comprising a plurality of ejectors arranged in parallel, wherein each of the ejectors comprises a motive port and a suction port, comprises:

- applying ejectors having a fixed geometry, wherein a first actuated ball valve is arranged in front of the motive port and a second actuated ball valve is arranged in front of the suction port; and
- controlling the activity of the ball valves on the basis of one or more predefined criteria.

In an embodiment, the method utilizes a system comprising:

- a liquid-gas separator having an inlet port, a gas outlet port and a liquid outlet port;
- a gas cooler having an inlet port and an outlet port;
- a high pressure valve arranged between the outlet port of the gas cooler and the inlet port of the liquid-gas separator;
- a temperature sensor arranged to detect the temperature of the fluid leaving the gas cooler; and
- a pressure sensor arranged to detect the pressure of the fluid leaving the gas cooler.

In an embodiment, a method comprises the following steps:

- detecting the opening degree of the high-pressure valve;
- opening one or more of the actuated ball valves arranged in front of the motive ports of the ejectors if:
  - a) the control unit is in operation state; and
  - b) the opening degree of the high pressure valve is equal to or higher than a predefined level.

The predefined level may be a user defined input. In an embodiment, the predefined level is within the range 30-50%. In an embodiment, the predefined level is within the range 30-40%.
In an embodiment, one or more of the actuated ball valves arranged in front of the motive ports of the ejectors are closed if:

- the opening degree of the high pressure valve is equal to or less than a predefined level;
- the pressure at an outlet port of the gas-cooler is equal to or less than a predefined setpoint pressure at the outlet port of the gas-cooler; and
- the suction ports for the respective ejectors are closed.

The predefined level may be a user defined input. In an embodiment, the predefined level is within the range 8-12%. In an embodiment, the predefined level is within the range 8-10%.
In an embodiment, the method comprises the step of detecting the opening degree of the gas-bypass valve, wherein the actuated ball valves arranged in front of the suction ports of one or more of the ejectors are being opened if:

- the motive ports of one or more of the ejectors are open;
- the temperature of the fluid at the outlet port of the gas cooler is within a predefined temperature range;
- the suction pressure at the intermediate temperature compressor is within a predefined range;
- the opening degree of the gas-bypass valve is below a predefined level; and
- the number of actively operated ejectors corresponds to a predefined number based on the number of actively operated medium temperature compressors.

In an embodiment, the method comprises the step of closing the actuated ball valves arranged in front of the suction ports of one or more of the ejectors if any of the following constraints are met:

- the temperature of the fluid leaving the gas cooler is no longer within a predefined temperature range limit;
- the opening degree of the gas-bypass valve exceeds a predefined level; or
- the number of actively operated ejectors exceeds a predefined number, wherein the predefined number is based on the number of actively operated medium temperature compressors.

In an embodiment, the temperature range limit is a user defined input.
In an embodiment, the predefined level (the opening degree of the gas-bypass valve) is a user defined input. In an embodiment, the predefined level (the opening degree of the gas-bypass valve) is within the range 20-35%. In an embodiment, the predefined level (the opening degree of the gas-bypass valve) is within the range 25-35%. In an embodiment, the predefined level (the opening degree of the gas-bypass valve) is 30%.

BRIEF DESCRIPTION OF THE DRAWINGS

The systems and methods will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative. In the accompanying drawings:

FIG. 1 shows a schematic diagram of a CO₂based system (heat pump) according to an embodiment;

FIG. 2 shows a schematic diagram of an ejector according to an embodiment; and

FIG. 3 shows a cross-sectional view of an ejector according to an embodiment.

DETAILED DESCRIPTION

Referring now in detail to the drawings for the purpose of illustrating embodiments of the present invention, a CO₂based system 20 of the present invention is illustrated in FIG. 1 .
FIG. 1 is a schematic diagram of a CO₂based system 20 constituting a heat pump 20. The heat pump 20 comprises a gas cooler 24 in fluid communication with an ejector assembly 52 comprising four ejectors 2, 2′, 2″, 2″. The gas cooler 24 has an inlet port 66 and an outlet port 68.
The ejectors 2, 2′, 2″, 2′″ are arranged in parallel. An outlet line 34 connects the gas cooler 24 and the motive ports of the ejectors 2, 2′, 2″, 2″. An actuated ball valve 4, 4′, 4″, 4′″ is, however, arranged in front of each of the motive ports. It is important to emphasize that the number of ejectors 2, 2′, 2″, 2′″ may be selected differently. The number of ejectors 2, 2′, 2″, 2′″ can be any desired number equal to or larger than one.
The system 20 comprises a temperature sensor 74 arranged and configured to detect the temperature of the fluid leaving the gas cooler 24. In an embodiment, the temperature sensor 74 is also configured to detect the pressure of the fluid leaving the gas cooler 24. In an embodiment, the system 20 comprises a separate pressure sensor 76 configured to detect the pressure of the fluid leaving the gas cooler 24. The pressure sensor 76 may be arranged close to the temperature sensor 74. The pressure sensor may be arranged at the outlet port 68 of gas cooler 24.
The ball valves 4, 4′, 4″, 4′″ are communicatively connected to a control unit 12. Accordingly, the control unit 12 can control the activity of the ball valves 4, 4′, 4″, 4′″ and thus connect and disconnect the connection between the gas cooler 24 and each of the ejectors 2, 2′, 2″, 2′″ independently. The control unit 12 is communicatively connected to the temperature sensor 74 and the pressure sensor 76. Accordingly, the control unit 12 receives the temperature measurements made by the temperature sensor 74 and pressure measurements made by the pressure sensor 76.
The suction ports of the ejectors 2, 2′, 2″, 2′″ are connected to a line 36 that is in fluid communication with an evaporator 22 that receives fluid from a liquid-gas separator 14. The liquid-gas separator 14 comprises an inlet port 60, a gas outlet port 62 and a liquid outlet port 64. The evaporator has an inlet port 70 and an outlet port 72.
An expansion valve 30 is arranged in the line 38 extending between the evaporator 22 and the liquid-gas separator 14. The outlet port of each of the ejectors 2, 2′, 2″, 2′″ is connected to the liquid-gas separator 14.
An actuated ball valve 6, 6′, 6″, 6′″ is arranged in front of each of the suction ports of the ejectors 2, 2′, 2″, 2″. The ball valves 6, 6′, 6″, 6′″ are communicatively connected to a control unit 12. Therefore, the control unit 12 is configured to control the activity of the ball valves 6, 6′, 6″, 6′″ and thus connect and disconnect the connection to the line 36.
The liquid-gas separator 14 has a liquid outlet port that is connected to the line 38. The liquid-gas separator 14 has a gas outlet port that is connected to a line 46. The line 46 is connected to a pressure point 32 via a line 40, in which a gas-bypass valve 28 is provided. The gas-bypass valve 28 is an activated valve. The suction ports of the ejectors 2, 2′, 2″, 2′″ are in fluid communication with the pressure point 32. Accordingly, the ejectors 2, 2′, 2″, 2′″ have access to gas from the line 40 as well as the outlet port of the evaporator 22.
The heat pump 20 comprises an intermediate temperature compressor 16 that is arranged between the gas outlet of the liquid-gas separator 14 and the inlet port of the gas cooler 24. A line 48 extends between the line 46 and the intermediate temperature compressor 16. A line 50 extends between the intermediate temperature compressor 16 and the inlet port of the gas cooler 24.
The heat pump 20 comprises a medium temperature compressor 18 that is arranged between the intermediate temperature compressor 16 and the pressure point 32. A line 42 extends between the medium temperature compressor 18 and the line 50.
A high-pressure valve 26 is arranged between the outlet port 68 of the gas cooler 24 and the inlet port 60 of the liquid-gas separator 14.
It is possible to apply several intermediate temperature compressors 16 and/or several medium temperature compressors 18 if a higher capacity is needed.
FIG. 2 illustrates a schematic diagram of an ejector 2 according to an embodiment. The ejector 2 has a fixed geometry and comprises a motive port 8 and a suction port 10. A first actuated ball valve 4 is arranged in front of the motive port 8. A second actuated ball valve 6 is arranged in front of the suction port 10. The CO₂based system, in an embodiment, comprises a control unit 12 arranged and configured to control the activity of the ball valves 4, 6 on the basis of one or more predefined criteria.
FIG. 3 illustrates a cross-sectional view of an ejector 2 according to an embodiment. The ejector 2 is a high-pressure ejector 2. The ejector 2 comprises a motive port 8 and a suction port 10. The ejector 2 comprises a nozzle 54, a mixing chamber 56 and a diffuser 58. The nozzle 54 converts the pressure energy of high pressure CO₂to the velocity energy in such a manner that the CO₂is depressurized and is expanded by the nozzle 54 in the mixing chamber 56. High velocity CO₂flow discharged from the nozzle 54 draws the vapor phase CO₂, which has been vaporized in the evaporator (see FIG. 1 ), into the mixing chamber 56 where it is mixed with the vapor phase CO₂. In the diffuser 58, the CO₂discharged from the nozzle 54 and the CO₂drawn from the evaporator are mixed in such a manner that the velocity energy of the CO₂is converted to the pressure energy to increase the pressure of the CO₂.
In an embodiment, the nozzle 54 has a throttled portion in its passage. The throttled portion increases the velocity of the CO₂, which is discharged from the nozzle 54. In the mixing chamber 56, the CO₂is mixed in such a manner that the sum of the kinetic momentum of the CO₂discharged from the nozzle 54 and the kinetic momentum of the CO₂drawn into the ejector 2 from the evaporator (see FIG. 1 ) is conserved. Accordingly, in the mixing chamber 56, the static pressure of the CO₂is increased.

LIST OF REFERENCE NUMERALS

- 2, 2′, 2″, 2′″ Ejector
- 4, 4′, 4″, 4′″ Actuated ball valve
- 6, 6′, 6″, 6′″ Actuated ball valve
- 8 Motive port
- 10 Suction port
- 12 Control unit
- 14 Liquid-gas separator
- 16 Intermediate temperature compressor
- 18 Medium temperature compressor
- 20 CO₂based system (heat pump system or a refrigeration system)
- 22 Evaporator (refrigerant-air heat exchanger)
- 24 Gas cooler
- 26 High-pressure valve
- 28 Gas-bypass valve
- 30 Valve
- 32 Pressure point
- 34, 36, 38 Line
- 40, 42, 44 Line
- 46, 48, 50 Line
- 52 Ejector assembly
- 54 Motive nozzle
- 56 Mixing chamber
- 58 Diffuser
- 60 Inlet port (of liquid-gas separator)
- 62 Gas outlet port (the liquid-gas separator)
- 64 Liquid outlet port (of liquid-gas separator)
- 66 Inlet port (of gas cooler)
- 68 Outlet port (of gas cooler)
- 70 Inlet port (of evaporator)
- 72 Outlet port (of evaporator)
- 74 Temperature sensor
- 76 Pressure sensor

Claims

What is claimed is:

1. A CO₂based system comprising:

one or more ejectors each having a motive port, a suction port, and a fixed geometry wherein a first actuated ball valve is arranged in front of the motive port and a second actuated ball valve is arranged in front of the suction port; and

a control unit arranged and configured to control the activity of the first actuated ball valve and the second actuated ball valve on the basis of one or more predefined criteria.

2. The system according to claim 1, further comprising two or more ejectors arranged in parallel.

3. The system according to claim 1, wherein the CO₂based system is a heat pump system or a refrigeration system.

4. The system according to claim 1, further comprising:

a liquid-gas separator having an inlet port, a gas outlet port and a liquid outlet port;

a gas cooler having an inlet port and an outlet port;

a high pressure valve arranged between the outlet port of the gas cooler and the inlet port of the liquid-gas separator;

a temperature sensor arranged to detect a temperature of fluid leaving the gas cooler;

a pressure sensor arranged to detect a pressure of the fluid leaving the gas cooler;

an evaporator having an inlet port and an outlet port, wherein the suction ports of the ejectors are in fluid communication with the evaporator, wherein the inlet port of the evaporator is in fluid communication with the liquid outlet port of the liquid-gas separator;

a gas-bypass valve arranged between the gas outlet port of the liquid-gas separator and the evaporator;

an intermediate temperature compressor arranged between the gas outlet port of the liquid-gas separator and the inlet port of the gas cooler; and

a medium temperature compressor arranged between the gas outlet port of the liquid-gas separator and the inlet port of the gas cooler.

5. The system according to claim 4, wherein the control unit is configured to detect an opening degree of the high-pressure valve and to open one or more of the first actuated ball valves arranged in front of the motive ports of the ejectors if:

the control unit is in operation state; and

the opening degree of the high pressure valve is equal to or higher than a predefined level.

6. The system according to claim 5, wherein the control unit is configured to determine an opening degree of the gas-bypass valve and to open the second actuated ball valves arranged in front of the suction ports of one or more of the ejectors if:

the motive ports of the one or more of the ejectors are open;

the temperature of the fluid at the outlet port of the gas cooler is within a predefined temperature range;

the suction pressure at the intermediate temperature compressor is within a predefined range;

the opening degree of the gas-bypass valve is below a predefined level;

a number of actively operated ejectors corresponds to a predefined number based on a number of actively operated medium temperature compressors; and

a capacity of the intermediate temperature compressors is below 100%.

7. The system according to claim 5, wherein the control unit is configured to close one or more of the first actuated ball valves arranged in front of the motive ports of the ejectors if:

the opening degree of the high pressure valve is equal to or less than a predefined level;

the pressure at the outlet port of the gas-cooler is equal to or less than a predefined setpoint pressure; and

the suction ports for the respective ejectors are closed.

8. The system according to claim 7, wherein the control unit is configured to determine an opening degree of the gas-bypass valve and to open the second actuated ball valves arranged in front of the suction ports of one or more of the ejectors if:

the motive ports of the one or more of the ejectors are open;

the opening degree of the gas-bypass valve is below a predefined level;

a capacity of the intermediate temperature compressors is below 100%.

9. The system according to claim 8, wherein the control unit is configured to close the second actuated ball valves arranged in front of the suction ports of one or more of the ejectors if any of following constraints is met:

a temperature of the fluid leaving the gas cooler is outside the predefined temperature range;

the opening degree of the gas-bypass valve exceeds the predefined level;

the number of actively operated ejectors exceeds the predefined number that is based on the number of actively operated medium temperature compressors.

10. A method for controlling a CO₂based system having one or more ejectors having a motive port, a suction port, and a fixed geometry wherein a first actuated ball valve is arranged in front of the motive port and a second actuated ball valve is arranged in front of the suction port, the method comprising:

controlling the activity of the first actuated ball valve and the second actuated ball valve on the basis of one or more predefined criteria.

11. The method according to claim 10, further comprising two or more ejectors arranged in parallel.

12. The method according to claim 10, wherein the CO₂based system is a heat pump system or a refrigeration system.

13. The method according to claim 10, wherein the CO₂based system comprises:

a gas cooler having an inlet port and an outlet port;

14. The method according to claim 13, further comprising:

detecting an opening degree of the high-pressure valve;

opening one or more of the first actuated ball valves arranged in front of the motive ports of the ejectors if:

a) the control unit is in operation state; and

b) the opening degree of the high pressure valve is equal to or higher than a predefined level.

15. The method according to claim 14, wherein one or more of the first actuated ball valves arranged in front of the motive ports of the ejectors are closed if:

the suction ports for the respective ejectors are closed.

16. The method according to claim 14, further comprising:

detecting an opening degree of the gas-bypass valve, wherein the second actuated ball valves arranged in front of the suction ports of one or more of the ejectors are opened if:

the motive ports of the one or more of the ejectors are open;

the opening degree of the gas-bypass valve is below a predefined level;

a capacity of the intermediate temperature compressors is below 100%.

17. The method according to claim 16, further comprising:

closing the second actuated ball valves arranged in front of the suction ports of one or more of the ejectors if any of following constraints is met:

the temperature of the fluid leaving the gas cooler is outside the predefined temperature range;

the opening degree of the gas-bypass valve exceeds the predefined level;