Thermal systems, ships including thermal systems, methods and apparatus for controlling thermal systems

Abstract

The present invention relates to a thermal system for a ship, comprising: a hot liquid circuit (10); a pump system (11) for circulating hot liquid in the hot liquid circuit (10); a plurality of heat consumers (20) arranged in parallel in the hot liquid circuit (10), and the heat consumers (20) arranged in series with corresponding pressure-independent control valves (PICVs) (30); and a control device (12) for controlling the pump system (11). A differential pressure sensor (13) is adapted to sense a differential pressure indicating the differential pressure on a critical pressure-independent control valve (30.1a) of the pressure-independent control valves, and the signal from the differential pressure sensor (13) is used by the control device (12) as the basis for controlling the pump system.

Description

[0001] This application is a divisional application of the invention patent application filed on January 6, 2023, with application number 202380016367.X, entitled "A thermal system for a ship, such a system installed in a ship, a ship including the thermal system, a method for controlling the thermal system, and a control device". Technical Field

[0002] This invention relates to a thermal system for a ship, comprising: a hot liquid circuit; a pump system for circulating the hot liquid in the hot liquid circuit; a plurality of heat consumers arranged in parallel in the hot liquid circuit, and the heat consumers arranged in series with corresponding pressure-independent control valves (PICVs); and a control device for controlling the pump system. The invention further relates to a ship including the thermal system, a method for controlling the thermal system, and a control device. Background Technology

[0003] In ships or vessels of a certain size, such as the cooling systems in the aforementioned fields, thermal systems are used to provide cooling for multiple cooling consumers.

[0004] It should be noted that although cooling is the primary objective of this invention, it can also be used in conjunction with centralized heating in ships or vessels.

[0005] Therefore, the term "heat" in this article can be understood as either "cooling" or "heating".

[0006] Given that in many cases approximately 20% of the electricity generated by a vessel is used to drive pumps, a reduction in pump energy demand can provide significant energy savings in the operation of the vessel or ship.

[0007] Thermal systems (especially cooling systems) use pumps to circulate hot liquids (especially coolant liquids) in a liquid loop that can branch extensively on a ship, for example, in places where cooling is required (i.e., where heat or cooling devices are present).

[0008] For ease of explanation, cooling will be mentioned below.

[0009] Cooling consumers may include engines and other machinery, air conditioners, etc.

[0010] However, in some cases, the cooling demand of different consuming components is relatively constant, while in other cases, the cooling demand may be lower than usual, for example, when the engine is only running under partial load.

[0011] In a heat or cooling system of the type mentioned in the introduction, the amount of heat or coolant circulating through a given consumer is controlled by a PICV (i.e., a pressure-independent control valve). Such valves are known in the art and typically include a pressure-absorbing section or mechanism, often referred to as a differential pressure regulator, which absorbs a portion of the differential pressure applied to the valve, thereby enabling another portion of the valve to provide at least approximately the desired flow rate through the valve based on the residual amount of the differential pressure, which is regulated by the pressure-absorbing section of the valve. Thus, the residual pressure can be kept constant by means of the pressure-absorbing section of the valve.

[0012] A certain pressure differential needs to be applied to the PICV in order to fully regulate the flow rate through it.

[0013] Therefore, in existing thermal or cooling systems, the pump system operates at a certain level to ensure that there is a sufficient pressure differential throughout the thermal or cooling system.

[0014] However, since in many cases most of the pressure differential provided is absorbed by the PIVC in the system, operating the pump system at the default high level to ensure sufficient pressure differential for the entire heat or cooling system results in a significant energy loss. Summary of the Invention

[0015] One objective of this invention is to reduce this energy loss.

[0016] In a first aspect, this objective is achieved in a thermal system of the type mentioned in the introduction, characterized by a differential pressure sensor adapted to sense a differential pressure indicating the differential pressure on a critical pressure-independent control valve in the pressure-independent control valve, thereby the signal from the differential pressure sensor is used by the control device as the basis for controlling the pump system.

[0017] The term “critical” in relation to pressure-independent control valves (PICVs) should be understood as referring to PICVs in thermal or cooling systems where the risk of a pressure differential becoming too low is anticipated if pump energy drops to an excessively low level.

[0018] Expressions such as "pressure difference on a component (e.g., a valve)" or "pressure difference applied to a component (e.g., a valve)" should be understood as the difference between the pressure upstream (immediately adjacent) of the component and the pressure downstream (immediately adjacent) of the component.

[0019] It should be understood that the differential pressure requirement of a given PICV may differ from that of another PICV, and this should be taken into account when choosing which PICV to consider as the critical PICV in a given heating or cooling system.

[0020] The differential pressure sensed or measured by the differential pressure sensor can be a combination of the differential pressure of the heat consumer and the PICV attached to it. In this case, the measured differential pressure indicates the differential pressure on the PICV: when the flow resistance of the heat consumer is known at least by an estimate, the differential pressure on the PICV can be calculated or approximated as the indicated differential pressure based on the measured differential pressure and the known or estimated value of the flow resistance of the heat consumer.

[0021] Regarding the term "pump system," it should be noted that a pump system may include a single pump or a greater number of pumps operating in parallel or series, as is known in the art.

[0022] In one embodiment, the hot liquid is water, preferably fresh water. Here, "fresh water" should be understood as the opposite of the saltwater in which ships typically navigate. Therefore, the term "fresh water" should not be construed as excluding any additives such as corrosion inhibitors that are typically added to the circulating fluids of heating or cooling systems.

[0023] In one implementation, each heat consumer in the heat consumer is arranged in series with a pressure-independent control valve, thereby controlling and balancing the total amount of hot liquid flow. This allows for effective control of the hot or cooling liquid flow throughout the system.

[0024] In one embodiment, at least one first heat consumer is arranged in series with a controllable pressure-independent control valve, and preferably a pressure and / or temperature sensor is attached to the first heat consumer to provide a control signal to control the controllable pressure-independent control valve. The controllable pressure-independent control valve itself is known in the art and may, for example, include a valve body whose position is controlled by a control element, which itself may receive input from, for example, a temperature sensor, thereby adjusting the position of the valve body to regulate the flow through the PICV and thus through the heat or cooling consumer attached to the PICV, whereby the temperature sensed by the sensor can remain substantially constant or consistent with a given scenario. The control element may also receive input from a pressure sensor, or the PICV may be controlled by an external signal, such as an operating signal from, for example, a motor, or another external signal from the respective consumer requiring cooling or heating.

[0025] As an alternative to or supplement to a specified temperature, temperature-based control of a controllable PICV can be accomplished based on a temperature difference. Therefore, the temperature difference across, for example, the corresponding consumer can be measured to provide a temperature difference signal for controlling the controllable PICV. The temperature measurement used for control (whether a specified temperature or a temperature difference) can be obtained from the hot liquid in an appropriate manner, or the measurement can be obtained from the fluid on the second side of the heat exchanger, wherein the hot liquid in the hot liquid loop flows on the first side of the heat exchanger.

[0026] Temperature-based (whether a specified temperature or a temperature difference) PICV control can be combined with control based on, for example, an operating signal. In this case, when a device (e.g., an engine acting as a corresponding consumer) starts up and receives the operating signal before receiving the temperature signal, the PICV can be adjusted to be fully open. This avoids the device tripping due to insufficient cooling caused by slow temperature measurement response from the cooling / hot liquid relative to the rapid heating during device startup.

[0027] In one embodiment, the second heat consumer comprises a plurality of smaller heat consumers arranged in parallel and / or in series, such that the smaller heat consumers are typically arranged in series with a corresponding second pressure-independent control valve. Here, the number of PICVs in the thermal system can be reduced compared to a system in which each individual consumer is attached to its own PICV.

[0028] In one embodiment, a plurality of differential pressure sensors are provided, which are adapted to sense a corresponding differential pressure indicating a differential pressure on a corresponding pressure-independent control valve. Specifically, it is anticipated that each PICV includes or has a corresponding differential pressure sensor attached. This may be suitable, for example, for thermal systems where it is difficult or impossible to determine which PICV is the critical PICV. This may be the case, for example, in thermal systems where certain heat consumers are sometimes shut down and are effectively removed from the thermal system (of its functioning). In this embodiment, the control device for controlling the pump system may be adapted to use the indicated differential pressure closest to the required differential pressure of the corresponding pressure-independent control valve as the basis for controlling the pump system. Therefore, the control device should understand the differential pressure requirement of the PICV for which the differential pressure is measured, calculated, or indicated, and for each of these PICVs, compare the differential pressure requirement with the measured, calculated, or indicated differential pressure of the corresponding PICV to determine which PICV has the smallest difference between the measured, calculated, or indicated differential pressure and the differential pressure requirement, and then use the differential pressure on that PICV as the basis for controlling the pump system.

[0029] Pressure measurement can be integrated into the PICV via a built-in PT connector or similar means, using a permanently installed pressure (differential pressure) sensor. The output signal from this pressure sensor can be relayed to the control unit independently, or it can be integrated into the PICV's actuator for relay to the control unit. In this regard, a communication network (MODBUS, etc.) can be used. Therefore, the PICV and / or its corresponding actuator can form a network for controlling the pump rate.

[0030] In one embodiment, the thermal system further includes: a central thermal unit; a branch of the hot liquid circuit passing through the central thermal unit; a bypass of the hot liquid circuit bypassing the central thermal unit; a three-way valve controlling the flow rate through the branch and the flow rate through the bypass; a temperature sensor measuring the flow temperature downstream of the branch and the bypass; and a controller for controlling the three-way valve in response to a signal from the temperature sensor. The central thermal unit can provide a colder or hotter hot liquid depending on whether the thermal system is a cooling or heating system, and the three-way valve allows liquid from the central thermal unit to be mixed with the hot liquid flowing in the hot liquid circuit to achieve a desired flow temperature in the hot liquid circuit.

[0031] In another embodiment, the thermal system further includes: a central thermal unit; the central thermal unit including a heat exchanger having a primary side and a secondary side, the primary side being part of the hot liquid loop of the thermal system, the secondary side of the central thermal unit being supplied with a second hot liquid by a heat exchanger pump system; a branch of the hot liquid loop passing through the central thermal unit; a bypass of the hot liquid loop bypassing the central thermal unit; a three-way valve controlling the flow rate through the branch and the flow rate through the bypass; a temperature sensor measuring the flow temperature downstream of the branch and the bypass; and a controller for controlling the heat exchanger pump system in response to a signal from the temperature sensor. In this embodiment, the central thermal unit can provide a colder or hotter hot liquid depending on whether the thermal system is a cooling system or a heating system, and the operating level of the heat exchanger pump system can be adjusted by regulating the energy supplied to the heat exchanger pump system, thereby regulating the heat transferred in the heat exchanger to adjust the flow temperature in the hot liquid loop to approximately the desired flow temperature in the hot liquid loop.

[0032] In another embodiment, the controller is also adapted to control the three-way valve in response to a signal from at least a temperature sensor. Here, the amount of cooling or heating introduced into the hot liquid circuit can be reduced, for example, relative to the minimum amount that the central heating unit can deliver.

[0033] In a second aspect, this objective is achieved by a vessel that includes a thermal system according to the invention.

[0034] In a third aspect, the invention is achieved by a method for controlling the thermal system according to the invention as described above, the method comprising: circulating a hot liquid in the hot liquid circuit by means of a pump system; obtaining from the differential pressure sensor a signal indicating the differential pressure on a key pressure-independent control valve in the pressure-independent control valve; and adjusting the power of the pump system to obtain a signal from the differential pressure sensor within a desired range. This can reduce energy loss.

[0035] In one embodiment, the thermal system includes a plurality of differential pressure sensors adapted to sense a corresponding differential pressure indicating a pressure difference across a respective pressure-independent control valve. The method then includes determining a required minimum value for the signal provided by each of these differential pressure sensors, and adjusting the power of the pump system based on the signal from the differential pressure sensor that provides the lowest value relative to the required minimum value. In this embodiment, the control device for controlling the pump system may be adapted to use the indicated differential pressure closest to the required differential pressure of the respective pressure-independent control valve as the basis for controlling the pump system. Therefore, the control device should understand the differential pressure requirement of the PICV (Pressure Independent Valve Vehicle) being measured, calculated, or indicated, and for each of these PICVs, compare the differential pressure requirement with the measured, calculated, or indicated differential pressure of the corresponding PICV to determine which PICV has the smallest difference between its measured, calculated, or indicated differential pressure and the differential pressure requirement, and then use the differential pressure on that PICV as the basis for controlling the pump system.

[0036] In one embodiment, at least one first heat dissipator is arranged in series with a controllable pressure-independent control valve, and a pressure and / or temperature sensor is attached to the first heat dissipator. The method then includes obtaining a control signal from the pressure and / or temperature sensor and adjusting the controllable pressure-independent control valve based on the control signal from the pressure and / or temperature sensor. In this embodiment, the temperature sensed by the sensor can remain substantially constant or consistent with a given scheme.

[0037] In one embodiment, the thermal system includes: a central thermal unit; a branch of a hot liquid circuit passing through the central thermal unit; a bypass of the hot liquid circuit bypassing the central thermal unit; a three-way valve controlling the flow rate through the branch and the flow rate through the bypass; and a temperature sensor measuring the flow temperature downstream of the branch and the bypass. The method thus includes obtaining a temperature signal from the temperature sensor and controlling the three-way valve in response to the temperature signal from the temperature sensor. The central thermal unit can provide a colder or hotter hot liquid depending on whether the thermal system is a cooling or heating system, and the three-way valve allows liquid from the central thermal unit to be mixed with the hot liquid flowing in the hot liquid circuit to achieve a desired flow temperature in the hot liquid circuit.

[0038] In one embodiment, the thermal system includes: a central thermal unit; the central thermal unit including a heat exchanger having a primary side and a secondary side, the primary side being part of a hot liquid loop of the thermal system, the secondary side of the central thermal unit being supplied with a second hot liquid by a heat exchanger pump system; a branch of the hot liquid loop passing through the central thermal unit; a bypass of the hot liquid loop bypassing the central thermal unit; a three-way valve controlling the flow rate through the branch and the flow rate through the bypass; and a temperature sensor measuring the flow temperature downstream of the branch and the bypass, thereby the method includes obtaining a temperature signal from the temperature sensor and controlling the heat exchanger pump system in response to the signal from the temperature sensor. In this embodiment, the central thermal unit can provide a colder or hotter hot liquid depending on whether the thermal system is a cooling system or a heating system, and the operating level of the heat exchanger pump system can be adjusted by regulating the energy supplied to the heat exchanger pump system, thereby regulating the heat transferred in the heat exchanger to adjust the flow temperature in the hot liquid loop to approximately the desired flow temperature in the hot liquid loop.

[0039] In another aspect, the present invention includes a control device for a thermal system, the control device being adapted to perform the above-described method.

[0040] Unless otherwise stated, the embodiments and advantages described with reference to one aspect of the invention also apply to other aspects. Attached Figure Description

[0041] In the following, the invention will be explained in further detail with reference to the illustrative drawings and examples of embodiments, wherein...

[0042] Figure 1 A diagram of a cooling system according to the present invention is shown;

[0043] Figure 1a A diagram showing an alternative embodiment of the cooling system according to the invention; and

[0044] Figure 2 The diagram illustrates the characteristics of PICV under pressure / flow conditions. Detailed Implementation

[0045] Figure 1 The illustration shows the thermal systems, particularly the cooling systems, installed in ships.

[0046] The system includes a cooling liquid circuit 10; a pump system 11, indicated in this example by a single pump symbol, for circulating cooling liquid in the cooling liquid circuit 10; a plurality of cooling consumers 20 arranged in parallel in the cooling liquid circuit 10, and the cooling consumers 20 arranged in series with corresponding pressure-independent control valves (PICVs) 30; and a control device 12 for controlling the pump system 11.

[0047] The system further includes a differential pressure sensor 13 adapted to sense a differential pressure indicating the differential pressure on the critical pressure-independent control valve 30.1a in the pressure-independent control valve 30.

[0048] In this embodiment, the cooling liquid circulating in the cooling liquid circuit 10 is fresh water containing common additives for corrosion protection.

[0049] In this embodiment, each cooling consumer in the cooling consumer 20 is arranged in series with a pressure-independent control valve 30, thereby the total amount of cooling liquid flow is controlled and balanced by the pressure-independent control valve 30.

[0050] A set of first cooling consumers 20.1 are arranged in series with controllable first pressure-independent control valves 30.1. Pressure and / or temperature sensors 20.11 are attached to each first cooling consumer 20.1 to provide control signals to control the controllable first pressure-independent control valves 30.1.

[0051] In this embodiment, the second cooling consumer 20.2 includes a plurality of (two indicated in the example) miniature cooling consumers 20.2a arranged in parallel, such that the miniature cooling consumers are typically arranged in series with a corresponding second pressure-independent control valve 30.2.

[0052] In this embodiment, a set of third cooling consumers 20.3, each connected in series with a third pressure-independent control valve 30.3, is typically arranged in series with a fourth cooling consumer 20.3a, which has a lower requirement for low cooling water temperature. Therefore, the flow rate through the fourth cooling consumer 20.3a is the sum of the combined flow rates through the third cooling consumers 20.3.

[0053] The cooling system further includes a central cooling unit 40.

[0054] A branch 10.1 of the cooling fluid circuit passes through the central cooling unit 40, and a bypass 10.2 of the cooling fluid circuit 10 bypasses the central cooling unit 40. A three-way valve 10.3 controls the flow rate through branch 10.1 and through bypass 10.2. A temperature sensor 10.4 measures the flow temperature downstream of branch 10.1 and bypass 10.2. A controller 10.5 is provided to control the three-way valve 10.3 in response to a signal from the temperature sensor 10.4.

[0055] The central cooling unit 40 provides a cooler liquid than the coolant circulating in the coolant circuit 10, and in particular than the coolant entering the three-way valve 10.3. The cooler liquid from the central cooling unit 40 can be mixed with the coolant flowing in the coolant circuit 10 by means of the three-way valve 10.3 to achieve the desired flow temperature in the coolant circuit 10 as measured by the temperature sensor 10.4.

[0056] The central cooling unit 40 includes a heat exchanger 40.1 having a primary side 40.1a and a secondary side 40.1b. The primary side 40.1a is part of the cooling liquid circuit 10 of the cooling system. The secondary side 40.1b of the central cooling unit 40 is supplied with a second hot liquid by a heat exchanger pump system 40.2. In the illustrated embodiment, the second hot liquid is seawater drawn from the surrounding seawater through the ship's navigation via a seawater inlet 40.3, circulated through the secondary side 40.1b of the heat exchanger 40.1 by the heat exchanger pump system 40.2, and discharged back into the surrounding seawater through a seawater outlet 40.4.

[0057] In one embodiment, the controller (e.g., control device 12) is adapted to control the heat exchanger pump system 40.2 in response to a signal from the temperature sensor 10.4.

[0058] In this implementation, the central cooling unit 40 can be configured to cool the entire volume of water circulating in the cooling liquid loop by adjusting the three-way valve 10.3 to allow all water to flow through the heat exchanger 40.1 and shutting off the bypass 10.2. By adjusting the energy supplied to the heat exchanger pump system 40.2, thereby regulating the operating level of the heat exchanger pump system 40.2, the heat transferred in the heat exchanger can be regulated, thereby adjusting the flow temperature in the hot liquid loop to approximately the expected flow temperature as indicated by the temperature sensor 10.4.

[0059] Furthermore, in this embodiment, the control device 12 may also be adapted to control the three-way valve 10.3 or activate the controller 10.5 in response to a signal from at least the temperature sensor 10.4. Here, the amount of cooling introduced into the hot liquid circuit 10 can be reduced, for example, relative to the minimum amount that the central heating unit 40 can deliver.

[0060] As described above, the cooling consumer 20 is connected in series with the pressure-independent control valve 30, thereby the cooling liquid flow in the cooling liquid circuit 10 is controlled and balanced by the pressure-independent control valve 30.

[0061] Each pressure-independent control valve 30 requires a certain minimum pressure differential in order to control the flow rate as expected by the respective pressure-independent control valve 30. This pressure differential is provided by the pump system 11 throughout the cooling liquid circuit 10.

[0062] To minimize the power supplied to pump system 11 and thus ensure sufficient pressure differential throughout the cooling fluid circuit 10, the indication of the pressure differential applied to the critical pressure-independent control valve 30.1a is obtained by means of a differential pressure sensor 13, and control device 12 adjusts pump system 11 based on the indicated pressure differential applied to critical pressure-independent control valve 30.1a. Here, considerable energy savings are achieved compared to a system in which the pump system continuously operates at default power.

[0063] exist Figure 1a The diagram illustrates an alternative embodiment in which, as illustrated by differential pressure sensor 13a, a plurality of differential pressure sensors are provided, adapted to sense corresponding differential pressures indicating the differential pressure on a respective pressure-independent control valve 30, and the control device 12 for controlling the pump system 11 is adapted to use the indicated differential pressure closest to the required differential pressure of the respective pressure-independent control valve as the basis for controlling the pump system. Specifically, it is anticipated that each pressure-independent control valve 30 includes or is attached to a corresponding differential pressure sensor.

[0064] Figure 2 The diagram illustrates how the corresponding pressure-independent control valve 30 in the cooling fluid circuit 10 provides a substantially constant flow rate (assuming all pressure-independent control valves 30 are designed to provide the same flow rate). min This indicates the minimum differential pressure required for the critical pressure-independent control valve 30.1a. The pump system 11 is regulated to provide the pressure P indicated by the differential pressure sensor 13 at the critical pressure-independent control valve 30.1a. c The system operates at a certain speed. Due to the general pressure loss in the coolant circuit 10, the minimum differential pressure will be near the critical pressure-independent control valve 30.1a, and a higher differential pressure will be observed in the rest of the coolant circuit 10, such as... Figure 2 China P syst As indicated. The differential pressure regulator of the corresponding pressure-independent control valve 30 will absorb excess pressure at the corresponding pressure-independent control valve 30, so that the valve provides as indicated. Figure 2 The indicated expected traffic volume is as is well known to those skilled in the art.

Claims

1. A thermal system for a ship, comprising: Hot liquid circuit (10); A pump system (11) is used to circulate hot liquid in the hot liquid circuit (10); Multiple heat consumers (20) are arranged in parallel in the hot liquid circuit (10), and each heat consumer (20) is arranged in series with a corresponding pressure-independent control valve (PICV) (30); and Control device (12), which is used to control the pump system (11), is characterized in that, A differential pressure sensor (13) is adapted to sense a differential pressure that indicates the differential pressure on the critical pressure-independent control valve (30.1a) in the pressure-independent control valve, thereby the signal from the differential pressure sensor (13) is used by the control device (12) as the basis for controlling the pump system.

2. The thermal system of claim 1, wherein, The hot liquid is water, preferably fresh water.

3. The thermal system of claim 1 or 2, wherein, Each of these heat consuming devices (20.1, 20.2, 20.3, 20.3a) is arranged in series with pressure-independent control valves (30.1, 30.1a, 30.2, 30.3), thereby controlling and balancing the total amount of hot liquid flow.

4. The thermal system of any one of claims 1 to 3, wherein, At least one first heat consuming device (20.1) is arranged in series with a controllable pressure-independent control valve (30.1, 30.1a), and preferably a pressure and / or temperature sensor (20.11) is attached to the first heat consuming device (20.1) to provide a control signal to control the controllable pressure-independent control valve (30.1, 30.1a).

5. The thermal system according to any one of claims 1 to 4, wherein, The second heat consuming device (20.2) includes a plurality of smaller heat consuming devices (20.2a, 20.2b) arranged in parallel and / or in series, such that the smaller heat consuming devices (20.2a, 20.2b) are typically arranged in series with a corresponding second pressure-independent control valve (30.2).

6. The thermal system according to any one of claims 1 to 5, wherein, Multiple differential pressure sensors (13, 13a) are provided, which are adapted to sense corresponding differential pressures indicating the differential pressure on the corresponding pressure-independent control valve, and wherein preferably, the control device for controlling the pump system is adapted to use the indicated differential pressure closest to the required differential pressure of the corresponding pressure-independent control valve as the basis for controlling the pump system.

7. The thermal system according to any one of claims 1 to 6, further comprising: Central heating unit (40); The branch (10.1) of the hot liquid circuit (10) passes through the central hot unit (40). The bypass (10.2) of the hot liquid circuit (10) bypasses the central hot unit (40). A three-way valve (10.3) controls the flow rate through the branch (10.1) and the flow rate through the bypass (10.2); A temperature sensor (10.4) measures the flow temperature downstream of the branch (10.1) and the bypass (10.2); and A controller (10.5) is used to control the three-way valve (10.3) in response to a signal from the temperature sensor (10.4).

8. The thermal system according to any one of claims 1 to 6, further comprising: Central heating unit (40); The central thermal unit (40) includes a heat exchanger (40.1) having a primary side (40.1a) and a secondary side (40.1b), the primary side (40.1a) being part of the hot liquid loop (10) of the thermal system, and the secondary side (40.1b) of the central thermal unit (40) being supplied with a second hot liquid by a heat exchanger pump system (40.2); The branch (10.1) of the hot liquid circuit (10) passes through the central hot unit (40). The bypass (10.2) of the hot liquid circuit (10) bypasses the central hot unit (40). A three-way valve (10.3) controls the flow rate through the branch (10.1) and the flow rate through the bypass (10.2); A temperature sensor (10.4) measures the flow temperature downstream of the branch (10.1) and the bypass (10.2); and A controller (12) is used to control the heat exchanger pump system (40.2) in response to a signal from the temperature sensor (10.4).

9. The thermal system according to claim 8, wherein, The controller (12) is also adapted to control the three-way valve (10.3) in response to a signal from at least the temperature sensor (10.4).

10. The thermal system according to any one of claims 1 to 9, wherein, This thermal system is a cooling system.

11. The thermal system according to any one of claims 1 to 10, wherein, The thermal system is installed in the ship.

12. A ship comprising a thermal system according to any one of claims 1 to 11.

13. A method for controlling a thermal system according to any one of claims 1 to 11, comprising: The hot liquid is circulated in the hot liquid circuit (10) by means of the pump system (11); The differential pressure sensor (13) provides a signal indicating the differential pressure across the critical pressure-independent control valve (30.1a) in the pressure-independent control valve system. Adjust the power of the pump system (11) to obtain a signal from the differential pressure sensor (13) within the expected range.

14. The method according to claim 13, wherein, The thermal system includes a plurality of differential pressure sensors (13, 13a) adapted to sense a corresponding differential pressure indicating a pressure difference on a corresponding pressure-independent control valve (30). The method includes determining a required minimum value of a signal provided by the corresponding differential pressure sensor for each of these differential pressure sensors, and adjusting the power of the pump system based on the signal of the differential pressure sensor that provides the lowest value relative to the corresponding required minimum value.

15. The method according to claim 13 or 14, wherein, At least one first heat consumer (20.1) is arranged in series with a controllable pressure-independent control valve (30.1, 30.1a), and a pressure and / or temperature sensor (20.11) is attached to the first heat consumer (201). The method includes obtaining a control signal from the pressure and / or temperature sensor (20.11) and adjusting the controllable pressure-independent control valve (30.1, 30.1a) according to the control signal from the pressure and / or temperature sensor (20.11).

16. The method according to any one of claims 13 to 15, wherein, The thermal system includes: Central heating unit (40); The branch (10.1) of the hot liquid circuit (10) passes through the central hot unit (40). The bypass (10.2) of the hot liquid circuit (10) bypasses the central hot unit (40). A three-way valve (10.3) controls the flow rate through the branch (10.1) and the flow rate through the bypass (10.2); and A temperature sensor (10.4) measures the flow temperature downstream of the branch (10.1) and the bypass (10.2). The method includes obtaining a temperature signal from the temperature sensor (10.4) and controlling the three-way valve (10.3) in response to the temperature signal from the temperature sensor (10.4).

17. The method according to any one of claims 13 to 16, wherein, The thermal system includes: Central heating unit (40); The central thermal unit (40) includes a heat exchanger (40.1) having a primary side (40.1a) and a secondary side (40.1b), the primary side (40.1a) being part of the hot liquid loop (10) of the thermal system, and the secondary side (40.1b) of the central thermal unit (40) being supplied with a second hot liquid by a heat exchanger pump system (40.2); The branch (10.1) of the hot liquid circuit (10) passes through the central hot unit (40). The bypass (10.2) of the hot liquid circuit (10) bypasses the central hot unit (40). A three-way valve (10.3) controls the flow rate through the branch (10.1) and the flow rate through the bypass (10.2); and A temperature sensor (10.4) measures the flow temperature downstream of the branch (10.1) and the bypass (10.2). The method includes obtaining a temperature signal from the temperature sensor (10.4) and controlling the heat exchanger pump system (40.2) in response to the signal from the temperature sensor (10.4).

18. A control device (10.5, 12) for a thermal system according to any one of claims 1 to 11, said control device being adapted to perform the method according to any one of claims 13 to 17.

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