Control system and method for controlling a cooling system of a vessel

Abstract

A control system (30) and method for controlling a cooling system (1) of a marine vessel are disclosed. The cooling system comprises a circulation circuit (10) wherein a cooling fluid is circulated by a pump (130), and a heat exchanger (110) for cooling a heat generating element. Temperature sensing means (1521) and flow monitoring means are provided downstream of the heat exchanger for monitoring an outlet temperature, Tout, and a flow, F, exiting the heat exchanger. A flow regulating valve (150) is arranged downstream of the heat exchanger. The control system compares a maximum allowable temperature Tmax and a minimum required flow, Freq, with Tout and F, respectively, and will increase the flow of cooling fluid through the heat exchanger if Tout > Tmax, and reduce the flow if Tout < Tmax, while at the same time keeping F ≥ Freq.

Description

[0001] CONTROL SYSTEM AND METHOD FOR CONTROLLING A COOLING SYSTEM OF A VESSEL

[0002] The invention relates to a control system for controlling a cooling system of a vessel, typically a marine vessel such as a ship. The ship may for instance be a supply ship for offshore industry. The invention further relates to a method for controlling the cooling system and for optimizing its functions. The method for controlling the cooling system may preferably be a computer-implemented method executed by a programmable control unit in the control system.

[0003] To illustrate the background for control systems for cooling systems, prior art cooling systems will be discussed first.

[0004] There are many prior art cooling systems for vessels. One common type of cooling system comprises an open seawater circuit and one or more closed freshwater circuits. The seawater circuit typically having a seawater inlet, a seawater pump which sucks in seawater from the ocean and circulates it through a main heat exchanger, and a seawater outlet. The main heat exchanger is typically called the central cooler of the cooling system. The central cooler is connected to the one or more closed freshwater circuits, for cooling the freshwater circulating therein.

[0005] In the vessel, there are normally multiple heat generating pieces of equipment which need cooling. The heat generating pieces of equipment include the vessel’s engine and any auxiliary engines, and can also include for example compressors, electric motors, frequency converters, hydraulic aggregates and more. The one or more freshwater circuits of the cooling system comprise(s) one or more heat exchangers, each one arranged to provide cooling for a heat generating piece of equipment. This means that freshwater cooled by the central cooler, circulates to the heat exchanger in connection with the heat generating equipment and takes up heat. The heated freshwater circulates back for being cooled down again by the central cooler. It is also known from prior art, that the central cooler, i.e. , the main heat exchanger, can be placed outside of the vessel, submerged in seawater, when the ship is in use, and thus not necessarily has to be part of an open seawater circuit.

[0006] In the one or more closed freshwater circuits, a circulation pump is provided for circulating cooling water in the circuits. While it is crucial to avoid overheating of equipment in the vessel, it has also become increasingly important, both for environmental and economic reasons, to reduce energy consumption, in particular fossil fuel consumption. However, also alternative marine fuels like methanol, ethanol, ammonia, hydrogen, and liquefied biogas come with a high cost, and reduction of energy consumption is useful regardless of the type of fuel.

[0007] There are some prior art solutions aiming at reducing the energy consumption for seawater pumps in cooling systems for vessels. Patent publication EP2986500B1 discloses a variable flowrate cooling system for large seafaring vessels. In particular, the publication concerns a cooling system which includes a seawater pump for drawing seawater into a seawater circuit. The problem addressed in EP2986500B1 is that the pumps that are typically employed to draw seawater into such systems, are operated at a constant speed regardless of the amount of seawater necessary to achieve sufficient cooling. A proposed solution to this problem is to adjust the rotational speed of the seawater pump upon detection of a temperature in the freshwater circuit which deviates from a desired temperature. The adjustments are performed by a controller arrangement operatively connected to a pump arrangement, for saving energy in a system having seawater pumps.

[0008] Patent publication KR101324949B1 discloses a cooling system for a ship, wherein the rotational speed of both a seawater pump and a freshwater pump are adjusted by changing the rotational speed of the pumps based on temperature measurements in the freshwater circuit of the cooling system.

[0009] Patent publication KR20190066353A discloses a cooling system for a ship, the system using freshwater flow control. In the cooling system, temperature values of classified equipment groups are measured, and an opening of a flow control valve is increased when the measured temperature values exceed a predetermined target temperature and is decreased when the measured temperature values does not exceed the predetermined target temperature. While the prior art solutions presented above, all save energy and make sure that the cooling water in the freshwater circuit will not be too hot or too cold, there are other challenges which, if addressed, can reduce the energy consumption even more.

[0010] The invention has for its object to provide a control system for cooling systems for marine vessels, such as ships, for example supply ships for the offshore industry, which further saves energy, and which also optimizes the cooling provided by the cooling system without reducing the total cooling capacity of the cooling system. Further, the invention has for its object to provide a method, preferably a computer-implemented method, for controlling a cooling system, wherein the method can readily be applied both to existing cooling systems to optimize and save energy in ships already in operation, and to new cooling systems.

[0011] The object is achieved by the features disclosed in the description below and in the claims that follow. The invention is defined by the independent patent claims. Advantageous embodiments of the invention are defined in the dependent claims and further elaborated on in the description below.

[0012] In a first aspect, the invention concerns a control system for controlling a cooling system of a marine vessel, the cooling system comprising:

[0013] - a central cooler for cooling a cooling fluid in the cooling system;

[0014] - a temperature regulating valve for regulating a temperature of the cooling fluid to a pre-set desired temperature;

[0015] - a circulation circuit;

[0016] - a pump for circulating a flow of the cooling fluid in the circulation circuit; and

[0017] - a first temperature sensing means for monitoring the temperature of the cooling fluid entering the circulation circuit from the temperature regulating valve; the circulation circuit comprising:

[0018] - tubing;

[0019] - at least one heat exchanger for cooling a heat generating element in the marine vessel, and wherein each of the at least one heat exchanger has a maximum allowable outlet temperature, Tmax;

[0020] - a second temperature sensing means for monitoring an outlet temperature, Tout, of cooling fluid exiting each of the at least one heat exchanger;

[0021] - a flow regulating valve arranged downstream of each of the at least one heat exchanger; and

[0022] - a flow monitoring means for monitoring the flow, F, through each of the at least one heat exchanger; the control system comprising a programmable control unit provided with information about Tmax, and about a minimum required flow, Freq, to be maintained through the at least one heat exchanger, the control system is operatively connectable to:

[0023] - the second temperature sensing means;

[0024] - the flow monitoring means; and

[0025] - the flow regulating valve; for increasing the flow of cooling fluid through the at least one heat exchanger if Tout > Tmax, and for reducing the flow of cooling fluid through the at least one heat exchanger if Tout < Tmax, while at the same time keeping F > Freq.

[0026] On board a vessel, the consequences of overheating of heat generating equipment can be detrimental, and in worst case life threatening. Therefore, as a safety measure for both machinery and crew, there has been a tendency towards over-dimensioning the cooling systems of marine vessels. Consequently, the pump(s) in a cooling system is / are typically run at a too high rotational speed, thus consuming more energy than necessary. Prior art solutions have been focused on reducing the rotational speed of the pump(s) for saving energy, for example when certain pieces of heat generating equipment are not in use. Adjusting the rotational speed of the one or more pumps in a cooling system will certainly save energy, and the need for fuels will be reduced, as prior art solutions indicate.

[0027] What prior art is not concerned with, and which is solved by the present invention, is to fully make use of an overcapacity present in the at least one heat exchanger, for further reduction of energy consumption. This will be explained in detail in the following.

[0028] The manufacturer of a heat exchanger will provide details of the heat exchanger. Amongst other parameters, such details will include the maximum outlet temperature, Tmax, and an optimal temperature difference, ATopt, between cooling fluid entering the heat exchanger and cooling fluid exiting the heat exchanger.

[0029] Prior art cooling systems seem to have been concerned only with the issue of avoiding overheating while reducing fuel consumption. However, avoiding overheating is not the same as making the cooling system more efficient.

[0030] The present invention is based on providing more efficient cooling for each of the at least one heat exchangers. This is done by monitoring the outlet temperature, Tout, from the at least one heat exchanger, comparing that temperature to the maximum outlet temperature, Tmax, for the same heat exchanger, and if Tout is lower than Tmax, reducing the flow through that heat exchanger.

[0031] The at least one heat exchanger provided in the circulation circuit for cooling a heat generating element of the marine vessel, is chosen according to a maximum heat load generated by the heat generating element. This is common knowledge: the heat exchanger needs to be dimensioned for being able to cool down a connected piece of equipment, like for instance an engine, when the engine runs on full capacity, and still avoid overheating. The heat exchanger is dimensioned so that it can handle a set maximum seawater temperature. The heat exchangers in a cooling system are dimensioned so as to handle all equipment on board the vessel running at the same time and at maximum capacity. This is very rarely the actual situation, and the heat exchangers in the system often have an unused extra capacity. In addition, when an actual seawater temperature is lower than the set maximum seawater temperature, the heat exchanger has an even larger extra capacity which is not utilized in prior art solutions.

[0032] The invention exploits the “extra” capacity and therefore utilizes the cooling system more efficiently, by regulating the flow so that the at least one heat exchanger always delivers Tout close to or similar to Tmax for that particular heat exchanger.

[0033] Aiming at a highest possible outlet temperature is counter-intuitive in this technical field, and prior art solutions are not operated that way.

[0034] The effect of maximizing the outlet temperature from each of the at least one heat exchanger, is that flow can be kept at a minimum while at the same time sufficient to take up the heat load from the heat generating equipment cooled by the respective heat exchanger. This way, the pump speed may be reduced much more than prior art suggests. An example is shown below in the description of Figures 5 and 6.

[0035] The present invention aims at saving more energy and optimising the efficiency of the cooling system, while at the same time maintaining the total cooling capacity of the cooling system. Where prior art solutions look at the pumps only, the present invention takes a different approach and starts with looking at the efficiency of the at least one heat exchanger and the heat load it is supposed to handle. The control system can then be pre-programmed with initial information about both the heat exchanger and the flow regulating valve, as well as with parameters such as seawater temperature, desired temperature of cooling fluid delivered by the temperature regulating valve, a maximum allowable temperature of the cooling fluid exiting the heat exchanger, and the expected heat load from the heat generating element.

[0036] Hereinbelow, some of the terms used in describing the first aspect of the invention will be explained in more detail.

[0037] In a marine vessel, for instance a ship such as a supply ship for offshore industry, a cooling system is required to provide cooling for multiple heat generating elements. One such heat generating element may be a combustion engine. Other heat generating elements may be thrusters for positioning of the ship, pumps, generators, compressors, motors, boilers, and auxiliary machinery.

[0038] Herein, the terms marine vessel and ship will be used interchangeably.

[0039] The central cooler is the main cooler in the cooling system, and it can be a heat exchanger of any type, for instance box, keel, plate, tube, or rack cooler, typically cooled down by seawater. The central cooler may be part of a seawater cooling circuit, hereinbelow called a seawater circuit, which also comprises an inlet, a seawater pump, piping, and an outlet on a discharge side of the central cooler, or the central cooler may be directly cooled down by seawater by being placed externally on the ship and in contact with the seawater when the ship is operated.

[0040] The pump may interchangeably be called a circulation pump herein. The circulation pump may be a centrifugal pump.

[0041] By a heat exchanger’s maximum outlet temperature is herein meant a maximum outlet temperature given by the manufacturer of the actual heat exchanger. The maximum outlet temperature will therefore be different depending on which heat exchanger is used.

[0042] To give an example, a desired cooling water temperature may be set to 32 °C. The manufacturer will, based on this temperature, set at maximum temperature, for example 40 °C, and a minimum flow for a given heat exchanger.

[0043] The at least one heat exchanger has a required flow, Freq, which is the minimum flow that needs to pass through the heat exchanger in order for it to cool sufficiently. This Freq may vary depending on an operational mode of the vessel. Examples of operational modes for marine vessels are mentioned below. In general, the operational mode of the vessel is referring to what kind of operation the vessel is performing, such as manoeuvring or standby mode. The flow monitoring means for monitoring the flow, F, of cooling fluid may typically be arranged downstream of each of the at least one heat exchanger. The control unit then compares said flow, F, to the required flow, Freq, so that if the flow, F, is lower than the required flow, Freq, the control unit may instruct the flow regulating valve to adjust the flow, F, so that F > Freq at all times.

[0044] Herein is also disclosed a control system for controlling a cooling system of a marine vessel, the cooling system comprising:

[0045] - a central cooler for cooling a cooling fluid in the cooling system;

[0046] - a temperature regulating valve for regulating a temperature of the cooling fluid to a pre-set desired temperature;

[0047] - a circulation circuit; and

[0048] - a pump for circulating a flow, F, of the cooling fluid in the circulation circuit; the circulation circuit comprising:

[0049] - at least one heat exchanger for cooling a heat generating element in the marine vessel, wherein the heat generating element has a heat load, and wherein the at least one heat exchanger has an optimal temperature difference, ATopt, for optimal cooling effect and an actual temperature difference, AT, when in use;

[0050] - temperature sensing means for monitoring the temperature of the cooling fluid upstream and downstream of the at least one heat exchanger; and

[0051] - a flow regulating valve arranged downstream of the at least one heat exchanger; the control system comprising a programmable control unit operatively connectable to:

[0052] - the temperature sensing means for deciding the actual temperature difference, AT, and comparing it to the optimal temperature difference, ATopt; and

[0053] - the flow regulating valve for adjusting the flow, F, of cooling fluid in the circulation circuit if the actual temperature difference, AT, deviates from the optimal temperature difference, ATopt

[0054] A heat exchanger works more efficiently the higher the temperature difference over the heat exchanger is. While aiming at an output temperature, Tout, of each of the at least one heat exchangers to be as close to the respective Tmax as possible, will increase the efficiency of the cooling system and save energy, another solution is to aim for increasing the temperature difference over the at least one heat exchanger as much as possible. The present control system may monitor the temperature difference over the at least one heat exchanger and adjust the flow by means of the flow regulating valve. Ultimately, this means that pump rotational speed can be held relatively low, and only adjusted if required, and at the same time achieving a more efficient cooling, due to the monitoring of temperature difference.

[0055] Then, during use, the control system collects information from the temperature sensing means, calculates the actual temperature difference over the heat exchanger and compares it to the optimal temperature difference. The control system then adjusts the flow in the circulation circuit accordingly, by regulating the flow regulating valve. The effect is that the heat exchanger continuously operates as efficiently as possible, which in turn allows for more flexible regulation of the flow of cooling fluid, i.e. , according to the actual cooling need. This approach allows for more efficient use of the circulation pump, and thus saves more fuel which again may lead to reduced emission of greenhouse gases, and / or financial savings. Another advantage of the more efficient use of the circulation pump, i.e., longer periods with lower rotational speed, is reduced need for maintenance of the pump.

[0056] The optimal temperature difference, ATopt, for optimal cooling effect referred to herein, is an optimal temperature difference given by the manufacturer of the actual heat exchanger.

[0057] By “an actual temperature difference, AT” is herein meant the difference calculated by monitoring a first temperature upstream of the heat exchanger in use, and a second temperature which is the outlet temperature downstream of the heat exchanger.

[0058] The word “deviate” as used herein in the feature “if the actual temperature difference, AT, deviates from the optimal temperature difference, ATopt, and / or if the outlet temperature deviates from the maximum outlet temperature” may require a further explanation. Typically, temperature measurements have a resolution of 0.1 °C and regulation normally takes place as soon as such a difference is sensed. However, such regulation could cause the system to oscillate due to very frequent adjustments. Therefore, a configurable parameter may be set which gives a dead band for temperatures below the optimal values of outlet temperature and / or optimal temperature difference over the heat exchanger. Should instead the outlet temperature exceed the maximum outlet temperature, there is no dead band, and the flow will be adjusted instantly.

[0059] The pre-set desired temperature of the cooling fluid leaving the temperature regulating valve may preferably be set to 28-35 °C. The circulation circuit may comprise more than one heat exchanger, each arranged for providing cooling of a heat generating element. In one embodiment, the at least one heat exchanger may comprise one or more further heat exchangers arranged in parallel. As already mentioned above, in connection with each of the heat exchangers, a second temperature sensing means, a flow regulating valve and a flow monitoring means may be provided and operatively connected to the programmable control unit for individual monitoring and adjusting the flow through each of the heat exchangers. The effect of this is that outlet temperature, Tout, or alternatively, the temperature difference for each of the heat exchangers may be monitored independently, and regulation of the flow by means of the flow regulating valve downstream of any one of the heat exchangers, may be done independently of the other flow regulating valves, for making the best possible use of each heat exchanger’s capacity and improving the overall cooling efficiency in the cooling system.

[0060] When the flow through each of the heat exchangers is regulated individually according to their actual heat load, the pressure in the circulation circuit will change. The pressure will naturally try to balance out across all the flow regulating valves. The flow regulating valves will then again regulate to the correct flow. The result is a dynamic cooling system which selfregulates for optimising the flow over each of the heat exchangers.

[0061] In order to avoid any oscillation or resonance in the cooling system due to the continuous self-regulation, parameters concerning for example minimum opening angle for the flow regulating valves, may be included as part of the pre-programmed information of the control system.

[0062] Start-up routine and balancing of the cooling system, is not part of the present invention. All cooling systems, including prior art, static, cooling systems require a startup procedure with adjustments of valves, etc. In a dynamic system as presented herein, the startup procedure will include programming of the relevant parameters for the actual system (i.e. for the heat exchangers, the maximum heat load of the system, the minimum opening angle of the flow regulating valves, and so on, as mentioned hereinabove). The skilled person understands that this will differ from cooling system to cooling system, and that the principle for the control system for controlling the cooling system will be the same regardless of the differing parameters.

[0063] It is advantageous to make sure that there is a minimum flow, Fmin, of cooling fluid circulating in the circulation circuit of the cooling system in order to prevent potential water condensation in cold equipment as well as to maintain preheating of the equipment. If the cooling system also comprises a seawater circuit as mentioned hereinabove, there is also a minimum flow for the seawater circuit. This minimum flow in the seawater circuit is to reduce fouling, i.e. to keep fouling at an acceptable level. In addition, the minimum flow maintains an air ejector functionality of the seawater pump.

[0064] As described above, a high temperature difference over the heat exchanger, improves the cooling efficiency of the heat exchanger. A lower flow will improve, i.e., increase, the temperature difference over the heat exchanger and further add to the energy saving of the present invention by adapting the flow over each of the at least one heat exchanger in the cooling system, to the actual cooling need. The flow is optimised by monitoring the flow and adapting it to the required flow of the heat exchanger. The required flow of the heat exchanger is based on the heat load produced by the associated heat generating equipment.

[0065] By reducing or restricting the flow, aiming at the required flow, the temperature difference over the heat exchanger is optimised, and the cooling system is overall more efficient and requires less energy. This means that when a heat generating equipment is turned off, there is no need for cooling, and the required flow is limited to the minimum flow, Fmin, to prevent condensation and to maintain preheating of the equipment.

[0066] By “flow monitoring” is meant to monitor the necessary parameters for being able to calculate volume and speed of the flow of the cooling fluid through the at least one heat exchanger.

[0067] Such monitoring in combination with a flow regulating valve, will allow for keeping the flow as low as possible for efficient cooling and reduced energy consumption of the cooling system.

[0068] The flow monitoring means may comprise a flow meter, for example an ultrasonic flow meter, a mechanical turbine flow meter, a differential pressure flow meter, or a magnetic flow meter.

[0069] When arranged in connection with the at least one heat exchanger, the flow meter will monitor the flow through the heat exchanger so that the flow can be adjusted if it deviates from the required flow. In operation, the control unit of the control system may receive information from the flow meter and in turn instruct the flow regulating valve to adjust its opening if required.

[0070] An ultrasonic flow meter uses ultrasound to measure the speed and volume of the fluid flowing through a section of the circulation circuit.

[0071] The cooling system may further comprise a pressure sensor, and the programmable control unit may be operatively connectable to said pressure sensor. The pressure in the circulation circuit may be selected to be constant or variable, depending on the operational mode of the vessel. Monitoring of pressure may be done for safety purposes. In case of pressure drop in the cooling system, an alarm may sound. The control system may regulate the pressure to allow the cooling system to work on a required minimum pressure to secure the volume of cooling fluid flowing through the entire circulation circuit.

[0072] The circulation pump of the cooling system may have adjustable rotational speed, and the control unit may further be operatively connectable to the pump for adjusting said rotational speed for further regulating the flow and / or pressure of cooling fluid in the circulation circuit.

[0073] The cooling fluid circulating in the circulation circuit may comprise freshwater. The cooling fluid may be freshwater alone, or in some embodiments, the freshwater may be mixed with coolants such as glycol or other coolant additives such as anti-rust additives.

[0074] The control system may be adapted to control a cooling system comprising one or more further circulation circuits. The circulation circuits may be arranged in parallel. The one or more further circulation circuits may comprise similar elements to the circulation circuit, i.e. , at least one heat exchanger, temperature sensing means, a flow regulating valve, and advantageously also flow monitoring means.

[0075] The cooling fluid circulating in the circulation circuits may be circulated by the same circulation pump, by one circulation pump per circulation circuit, or by a plurality of circulation pumps.

[0076] In one embodiment, the cooling system may comprise two or more pumps, and the control system according to the invention may allow for individually adjusting the two or more pumps by the control unit being operatively connectable to each of the pumps.

[0077] The control unit may be operatively connectable to the temperature regulating valve. One advantage of this is that if, over time, a circuit temperature deviates from a desired temperature, the temperature regulating valve can be controlled by the control unit and given new instructions. One example of this is that if the ship operates in colder waters over time, the temperature regulating valve can be given new instructions in order to make better use of the capacity of the heat exchangers, by adjusting the flow of cooling fluid to increase the Tout towards Tmax. This way the temperature difference AT over the at least one heat exchanger is increased by reducing the flow through the at least one heat exchanger.

[0078] A variable frequency drive, VFD, may be provided for driving the pump. A marine vessel typically has an integrated automation system, IAS, and the present control system may optionally be connected to the IAS to receive useful information about for instance the vessel’s operational mode. A marine vessel typically has a variety of operational modes, and these may be different for different kinds of vessels. The main operational modes for cargo and passenger ships for instance, are transit, manoeuvre and hotelling. For supply ships for offshore industry, there are other operational modes to be considered as well, for example dynamic positioning mode (DP mode), port, shore power, standby, non- eco, and transit mode.

[0079] The cooling system may be adapted to different operational modes and run at a set of parameters applicable to the actual mode. However, there is a challenge when it comes to for example the so-called dynamic positioning mode (DP mode). Some vessels, for example supply ships for the petroleum industry and other offshore industry, need to be operated at DP mode where it is crucial that the ship maintains its position while work operations are performed on for instance an offshore installation. DP mode is a special mode in that there are certain redundancy requirements regarding machinery. To make sure that one error in the system does not cause further errors, there is provided extra equipment. For instance, if a thruster for some reason does not get proper cooling, an extra thruster is available to maintain the thruster function.

[0080] In DP mode, different pieces of heat generating equipment, such as the thrusters, may be turned on and off or run at different speeds, during the operation. In this mode, the flow regulating valves are automatically set in a position that ensures maximum cooling regardless of the actual need for cooling. However, since the control system according to the present invention allows for increasing the temperature difference AT when the seawater temperature is lower, as mentioned hereinabove, the flow in the cooling circuit will be lower, and consequently the energy consumption will be lower than for a prior art cooling system.

[0081] To give an example: the temperature regulating valve can for instance be set to deliver cooling water of a desired temperature of 29-30 °C to the circulation circuit instead of the common temperature of 37-38 °C. This way, the control system according to the present invention can cause a cooling system to provide the same cooling capacity but at half the flow.

[0082] The programmable control unit of the control system may be operatively connectable to the ship’s integrated automation system, IAS, or the programmable control unit may form an integral part of the IAS, so that the IAS may constitute the control system. The control system may further comprise a second control unit. It is also conceivable that the control system may comprise a plurality of control units in a network, for controlling separate parts of a cooling system or for controlling separate cooling systems on board the vessel.

[0083] The control system may in a preferred embodiment be operatively connectable to the variable frequency drive, VFD, for regulating the rotational speed of the pump for adjusting the flow of cooling fluid in the circulation circuit. It must be understood that in a cooling system comprising more than one pump, each pump may be connected to a variable frequency drive. The control system may be operatively connectable to a plurality of VFDs.

[0084] The variable frequency drive is typically connected to a programmable logic controller, which in the present control system is the programmable control unit, and which, as described above is arranged for controlling components of the cooling system. The variable frequency drive is arranged to receive instructions, i.e. , parameters, from the programmable control unit. In a preferred embodiment the control unit is programmed so that, if the variable frequency drive is replaced by another VFD, the control unit will feed the replacement VFD with the same parameters as the removed VFD, thus allowing fast replacement and minimum downtime of the cooling system of the marine vessel.

[0085] It must be understood that the control system according to the first aspect of the invention may be operatively connectable to a variety of components in a cooling system, and that the cooling system may be different from vessel to vessel. For instance, one cooling system may have flow regulating valves, temperature sensors and one or more pumps in communication with the control system, another cooling system may have flow meters, flow regulating valves and pump in communication with the control system, whereas even another one may have a variety of sensors for flow, pressure and temperature as well as flow regulating valves, pumps and a temperature regulating valve in communication with the control system. The skilled person is familiar with a variety of cooling systems for marine vessels. What is important, is that according to the present invention the outlet temperature of the at least one heat exchanger is compared to the maximum allowed temperature of the same heat exchanger, and the flow through the heat exchanger is reduced if the outlet temperature is lower than the maximum allowed temperature. This way the overcapacity of the at least one heat exchanger is utilized. Further, temperature difference over the at least one heat exchanger, and / or the required flow over the at least one heat exchanger may be monitored for achieving both efficient cooling and optimised energy consumption, i.e., saving energy without jeopardizing the efficiency of the cooling. As mentioned above, the cooling system may comprise a seawater circuit including a seawater pump, a seawater inlet, the central cooler which is a heat exchanger, and a seawater outlet. In a cooling system of this kind, the seawater circuit may be provided with temperature sensors as well as a pressure sensor. The control system according to the invention may be in communication with the temperature sensors and the seawater pump, with the same purpose as described hereinabove for the circulation circuit, i.e. , the freshwater circuit, namely to optimize a temperature difference, delta T over the central cooler. The purpose of the pressure sensor is to make sure that in case of low cooling need, the pressure is kept high enough to ensure circulation of water in the circuit. Pressure in the seawater circuit may be increased by throttling a seawater flow regulating valve provided downstream of the central cooler.

[0086] The control unit may preferably be a programmable data processing device, which is able to execute a method for controlling the cooling system. Said method will be described in the following.

[0087] In a further embodiment, the control unit of the control system may be programmed to provide periodic flushing of the seawater circuit of the cooling system to remove any fouling.

[0088] Herein is also described a cooling system for a marine vessel, the cooling system comprising:

[0089] - a central cooler for cooling a cooling fluid in the cooling system;

[0090] - a temperature regulating valve for regulating a temperature of the cooling fluid to a pre-set desired temperature;

[0091] - a circulation circuit;

[0092] - a pump for circulating a flow, F, of the cooling fluid in the circulation circuit; and

[0093] - a first temperature sensing means for monitoring the temperature of the cooling fluid entering the circulation circuit from the temperature regulating valve; the circulation circuit comprising:

[0094] - tubing;

[0095] - at least one heat exchanger for cooling a heat generating element in the marine vessel, wherein the heat exchanger has a maximum allowable outlet temperature, Tmax;

[0096] - a second temperature sensing means for monitoring an outlet temperature, Tout, of cooling fluid exiting each of the at least one heat exchanger;

[0097] - a flow regulating valve arranged downstream of each of the at least one heat exchanger; and

[0098] - a flow monitoring means for monitoring the flow through each of the at least one heat exchanger; wherein the cooling system is adapted to be controlled by a control system according to the first aspect of the invention.

[0099] In a second aspect, the invention concerns a method for controlling a cooling system of a marine vessel by means of the control system according to the first aspect of the invention, the method comprising the following steps:

[0100] - feeding the control unit with information about Tmax for each of the at least one heat exchanger;

[0101] - feeding the control unit with information about the minimum required flow, Freq, to be maintained in the circulation circuit;

[0102] - reading the outlet temperature, Tout, of the cooling fluid downstream of each of the at least one heat exchanger detected by the second temperature sensing means;

[0103] - reading the flow, F, as detected by the flow monitoring means;

[0104] - increasing the flow of cooling fluid through the at least one heat exchanger if Tout > Tmax, or reducing the flow, F, of cooling fluid through the at least one heat exchanger by means of the flow regulating valve if Tout < Tmax, while at the same time keeping F > Freq.

[0105] The effect of the method as set out above, is that the outlet temperature of each of the at least one heat exchanger, is “pushed” towards the maximum temperature of the respective heat exchanger. This provides the most energy efficient cooling. The capacity of the at least one heat exchanger is better utilized, and the energy consumption of the vessel is reduced, since the cooling system is adapted to the actual need for cooling.

[0106] An alternative way of obtaining a similar effect, is to base the method on monitoring and optimising the temperature difference over each of the at least one heat exchanger. Such method of controlling a cooling system of a marine vessel by means of the control system according to the first aspect of the invention, may comprise the following steps:

[0107] - detecting a temperature of the cooling fluid upstream and downstream of the at least one heat exchanger by means of the temperature sensing means;

[0108] - calculating the actual temperature difference, AT, based on the detected temperatures;

[0109] - comparing the actual temperature difference, AT, to the optimal temperature difference, ATopt; and

[0110] - adjusting the flow, F, of cooling fluid in the circulation circuit by means of the flow regulating valve if the actual temperature difference, AT, deviates from the optimal temperature difference, ATopt.

[0111] The present control method for a cooling system offers significant energy savings, i.e. , reduced fuel consumption, by dynamically adjusting the flow of cooling fluid through each of the at least one heat exchangers either based on minimizing the flow and maximizing the output temperature of each of the at least one heat exchanger or based on comparison of optimal temperature difference with actual temperature difference over the heat exchanger. This way, cooling for the various thrusters, and other heat generating equipment, will be adjusted based on the actual need and not only on pre-set parameters based on the selected ship operational mode.

[0112] The method may further comprise the following steps:

[0113] - before starting to use the control system, performing a startup calibration of the control unit for deciding a minimum required pressure in the circulation circuit at a minimum flow and for deciding a maximum pressure in the circulation circuit at a maximum flow; and

[0114] - regulating the rotational speed of the pump to maintain the minimum required pressure, wherein said minimum required pressure is set for maintaining the minimum required flow, Freq-

[0115] The method may comprise adjusting the flow for keeping an optimal temperature difference, ATopt, over the at least one heat exchanger when the heat load from the heat generating equipment is at a maximum.

[0116] The method may further comprise the steps:

[0117] - detecting an operational mode from the vessel’s IAS or manually selecting an operational mode; and

[0118] - selecting the required flow, Freq, for the at least one heat exchanger based on the operational mode.

[0119] Other parameters may also be selected based on detected operational mode, for example minimum pump pressure.

[0120] When the cooling system comprises a variable frequency drive fed with parameters for driving the pump, the method may further comprise the step of:

[0121] - if, the variable frequency drive (VFD) is replaced by a replacement VFD, feeding the replacement VFD with the same parameters, such as pressure and rotational speed for driving the pump.

[0122] The VFD may for instance be replaced if it fails.

[0123] The method according to the second aspect of the invention may be a computer- implemented method.

[0124] Further, in a third aspect, the invention concerns a data processing device comprising means for carrying out the method according to the second aspect of the invention, wherein the data processing device comprises the control unit of the control system according to the first aspect of the invention.

[0125] It must be understood that the computer-implemented method may be written as a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the second aspect of the invention.

[0126] The instructions may be stored on a computer-readable medium.

[0127] In the following, the invention will be illustrated and explained by way of examples.

[0128] The accompanying drawings are described in detail below, where:

[0129] Fig. 1 shows a prior art cooling system for a vessel, this kind of cooling system is considered the starting point for the invention;

[0130] Fig. 2 shows another prior art cooling system for a vessel, the cooling system is modified compared to that in Figure 1;

[0131] Fig. 3 shows an embodiment of a control system for a cooling system of a vessel, according to the invention;

[0132] Fig. 4 shows a preferred embodiment of the control system for a cooling system, according to the invention;

[0133] Fig. 5 shows four graphs illustrating examples of some effects of the present control system for cooling systems of a marine vessel; and

[0134] Fig. 6 shows the fourth diagram from Fig. 5, for further illustrating energy savings in a particular example.

[0135] Any position indications refer to the position shown in the Figures. In the Figures, same or corresponding elements are indicated with the same reference number. Some places only one of a plurality of similar / same features is provided with a reference number. This is to increase legibility of the Figures. It must be understood that the Figures are principle sketches only. Relative proportions between elements in the Figures may be distorted.

[0136] In Figures 1—4, flow direction is indicated by arrows, and signal lines for communication are shown as dash-dotted lines.

[0137] Reference is first made to Fig. 1 which shows a prior art cooling system 1 comprising a circulation circuit 10, typically a freshwater circuit 10, and a seawater circuit 20.

[0138] The seawater circuit 20, shown on the right on the Figures, includes a central cooler 100, also denoted main cooler or main heat exchanger. The seawater circuit 20 further includes an inlet (not shown) which in use is in contact with a sea 201 , and two seawater pumps 202 which suck seawater in through the inlet via tubing / piping to the central cooler 100, and subsequently out past a flow regulating valve 205 to an outlet (not shown) for discharging the seawater back into the sea 201. The two seawater pumps 202 may be set to run alternately, or as one main seawater pump 202 and one back-up seawater pump 202. Each seawater pump 202 is connected to an electric motor 203 for driving the seawater pump 202. Each of the electric motors 203 is connected to a variable frequency drive (VFD) 204 via a power line. A seawater flow in the seawater circuit 20 can be regulated by adjusting the flow regulating valve 205 and / or by adjusting the rotational speed of the currently operating seawater pump 202, via the connected VFD 204. The electric motor 203 of one or both of the seawater pumps 202 may be connected to a DOL (Direct On Line) starter instead of the VFD 204. When connected to a DOL starter, the rotational speed of the electric motor 203 cannot be adjusted, as will be known to the skilled person.

[0139] The central cooler 100 may alternatively be arranged directly in contact with seawater, and that way the system can work without the seawater circuit 20.

[0140] The circulation circuit 10, shown on the left on the Figures, is a closed circuit comprising a tubing / piping system 120 for circulating a cooling fluid which is typically freshwater. In the following, the cooling fluid will be called freshwater or just water for simplicity, although it must be understood that the cooling fluid may comprise other fluids in addition to or instead of freshwater. The freshwater circulating in the circulation circuit 10 is cooled by the central cooler 100. A 3-way temperature regulating valve 140 is provided downstream of the central cooler 100. This valve 140 has two inlets, whereof a cold-water inlet and a hot water inlet, and one outlet where the mixed water leaves the valve 140. The cold-water inlet receives water which has just been cooled down by the central cooler 100, whereas the hot water inlet receives water via a bypass channel 123 which will be further described below.

[0141] The temperature regulating valve 140 is set to a desired circuit temperature and mixes cold and hot water accordingly. The water which leaves the valve 140 through the outlet holds the desired temperature and is circulated in the freshwater circuit 10 by means of a circulation pump 130, typically a centrifugal pump. The illustrated cooling system 1 is also provided with a back-up circulation pump 130, and both circulation pumps 130 are provided with electric motors 131 which in turn are in communication with a direct-on-line (DOL) motor starter 132 which starts the associated motor 131 at full load. The DOL starters 132 may be connected to the ship’s automation system AIS for remote start and stop. Each of the starters 132 is provided with a power connection 133.

[0142] In the following, when referring to “the circulation pump 130”, this means the main circulation pump and / or the back-up pump. The skilled person knows that a cooling system 1 of this kind, normally would have two circulation pumps 130 in parallel either to work alternately or to have a back-up if the main pump needs repair or somehow malfunctions. The back-up pump may start automatically if a pressure sensor is provided in the pipeline 120 and indicates a pressure which is too low.

[0143] The system 1 illustrated in Figure 1 , shows two heat exchangers 110 coupled in parallel. Each heat exchanger 110 is arranged to provide cooling for a heat generating equipment (not shown) of a vessel (not shown). It is indicated by arrows 121 , 122 that the system 1 can be expanded to further heat exchangers (not shown) arranged in parallel with the present heat exchangers 110. A flow regulating valve 150 is arranged downstream of each of the heat exchangers 110. When the cooling water leaves the heat exchanger 110 it has absorbed heat generated by the heat generating equipment. The heated water is circulated onwards in direction of the central cooler 100. Upstream of the central cooler 100 the bypass line 123 is arranged to bypass a portion of the hot water to the temperature regulating valve 140 if required for providing cooling fluid of the desired temperature.

[0144] According to classification societies rules, a ship’s machinery, and therefore also the cooling system, must be able to operate at a seawater temperature of 32 °C. In order to obtain a temperature difference between the seawater circuit 20 and the freshwater circuit 10, which is necessary for driving the cooling effect, the temperature in the freshwater circuit 10 is set higher than 32 °C. This way the freshwater circuit is dimensioned based on the maximum heat load which can be expected to occur. When the freshwater returns to the central cooler 100 for being cooled again, the seawater in the seawater circuit 20 downstream of the central cooler 100, will be heated. It is important that this seawater does not get too hot, as this will cause corrosion in the pipe system and also entails a risk of crystallization.

[0145] Reference is now made to Figure 2 wherein, in the circulation circuit 10 of the cooling system 1 , at least one temperature sensor 1521 is provided downstream of each of the heat exchangers 110.

[0146] Each temperature sensor 1521 is arranged to communicate with the respective flow regulating valve 150, so that if the temperature sensor 1521 detects a temperature exceeding a maximum acceptable temperature, the flow is regulated by means of the flow regulating valve 150.

[0147] Figure 3 illustrates a first embodiment of the present invention, namely a control system 30 for controlling the cooling system 1. The cooling system 1 as shown in Figure 3, will be described mainly in terms of the differences it shows compared to the prior art systems shown in Figures 1 and 2.

[0148] The cooling system 1 in Figure 3 is shown without a seawater circuit 20. On the seawater side of the cooling system in this embodiment, only the central cooler 100 is shown. This is to illustrate that such a solution is possible, and it must be understood that the seawater circuit 20 for example as shown in Figures 1 and 2, could have been part of the cooling system 1 of Figure 3 as well. In this version of the cooling system 1, the central cooler 100 is arranged to be put directly in contact with seawater during use. Apart from that, the cooling system 1 is provided with a further temperature sensor 1402. This temperature sensor 1402 is for sensing the temperature in the circulation circuit 10, and may for instance, as shown, be positioned immediately downstream of the 3-way temperature regulating valve 140. Thus, the temperature sensor 1402 will detect if the temperature regulating valve 140 does not provide cooling water of the desired temperature, i.e., if the valve 140 is malfunctioning.

[0149] The flow regulating valves 150 in this embodiment are preferably dynamic valves each provided with an actuator 1551 for adjusting an opening of the valve 150. The control system 30 in this embodiment comprises a control unit 3001, at least one power source connection 3011 , preferably at least two power source connections 3011 , as shown in the Figure, where the two power source connections 3011 are to be connected to two independent power sources (not shown), and an interface 3021 to an automation system of the vessel (not shown). The control unit 3001 is set up to receive information from the temperature sensors 1402, 1521. According to the invention, the control unit 3001 is set up with initial data about the desired circuit temperature, the heat load of the heat generating equipment which the heat exchangers 110 are to cool down, as well as an optimal temperature difference, ATopt, of each heat exchanger 110. Generally, a heat exchanger provides the most efficient cooling when the temperature difference is high. The closer the outlet temperature, Tout, is to the maximum outlet temperature, Tmax, the more efficient the cooling is.

[0150] In use, when the control unit 3001 receives information from the temperature sensors 1402, 1521 in the circulation circuit 10, an actual temperature difference AT, can be calculated. If the calculated AT deviates from ATopt, the control unit 3001 can remotely control the flow regulating valves 150 individually, as required.

[0151] Referring now to Figure 4 which illustrates a preferred embodiment of the control system 30 in operation with the cooling system 1 further modified and improved.

[0152] In this embodiment, the cooling system 1 is again shown with both the seawater circuit 20 and the circulation circuit 10.

[0153] The cooling system 1 may comprise means for maintaining an actual temperature difference over the central cooler 100, on the Figure shown as a temperature sensor 2071 arranged downstream of the central cooler 100 in the freshwater cooling circuit.

[0154] In addition to the temperature sensor 2071 , there may also be a pressure sensor 2081 downstream of the central cooler 100, this one placed in the seawater circuit 20, for monitoring pressure. Further, the temperature sensor 2071 , the pressure sensor 2081 , and an actuator 2061 of the flow regulating valve 205 are arranged to communicate with the control unit 3001 . Also, the variable frequency drive 204 for the electric motor 203 of each of the seawater pumps 202 receives communication from the control system 30 via signal lines.

[0155] The circulation circuit 10 of this preferred embodiment of the cooling system 1 , also has some additional features compared to the first embodiment described above for Figure 3. First, the 3-way temperature regulating valve 140 is provided with an actuator 1401 which communicates with the control unit 3001 of the control system 30. Second, one of the DOL (direct-on-line) starters for the electric motors 131 of the circulation pumps 130 has been replaced by a VFD (variable frequency drive) 1321 for allowing change of rotational speed of the circulation pumps 130. A change-over switch 1341 may be provided for changing between the remaining DOL 132 and the VFD 1321 , as preferred. The change-over switch 1341 can replace the need of two VFDs 1321 , but at the same time use the VFD 1321 on either of the circulation pumps 130. One effect of this is to equalize running time of the circulation pumps 130 in an easy manner. Both the DOL starter 132 and the VFD 1321 are provided with power connections 133.

[0156] One pressure sensor 1322 is shown on either side of the circulation pump 130, to monitor the pressure in the circulation circuit 10. Both pressure sensors 1322 are in communication with the control unit 3001.

[0157] In this embodiment, downstream of each of the heat exchangers 110, preferably quite close to the heat exchanger 110, there is provided a flow monitoring means 1531. The flow monitoring means 1531 will typically monitor the volume and speed of the cooling fluid as it exits the heat exchanger 110 and can for instance be a flow meter.

[0158] In Figure 4, the temperature sensors 1521 and flow monitoring means 1531 are illustrated as separate means, however, it must be understood that their functions for instance could be integrated in the valves 150.

[0159] Also the control system 30 is shown in a bit more advanced version in this Figure than on Figure 3, however, the main concept is the same: the control unit 3001 sends and receives information via signal lines 1541 to and from the temperature sensors 1521, 1402, 2071 , the flow monitoring means 1531, the VFDs 204, 1321, the pressure sensors 1322, 2081, and the valve actuators 1401 , 1551, 2061, to monitor and control the cooling system 1 for the most efficient cooling with least possible energy consumption as explained in the general part of the present application.

[0160] In addition to the features shown in Figure 3, the control system 30 is in Figure 4 shown comprising a second control unit 3051 for controlling a further cooling circuit (not shown) illustrated by an outgoing connection line marked 3061 going to a further heat exchanger (not shown). The possibility of connecting the control unit 3001 to other remote cooling systems (not shown) is illustrated by the signal line marked 3031. There is also an internet connection 3041. The internet connection 3041 may for instance be used for remote surveillance of energy consumption, in particular energy saving, of the cooling system 1. Calculations of consumed energy can be performed by use of information from the various sensors in the cooling system which are sent to the control system 30.

[0161] It must be understood that there are a lot of possibilities for variation of the cooling system 1 and the control system 30, and that the embodiments shown in Figures 3 and 4 are examples of such variations.

[0162] Figure 5 illustrates some of the effects of the control system 30 for cooling systems 1 as described herein. The figure shows four diagrams or graphs, named Diagram 1 , Diagram 2, Diagram 3 and Diagram 4. The X-axis of all the diagrams shows Heat Exchange Load on the at least one heat exchanger 110, given in percentage from 0 to 100. The purpose of the graphs is to show how the claimed invention saves energy and optimises cooling by utilizing an extra capacity present in the at least one heat exchanger 110. The Y-axis of the graphs shows different parameters, namely system temperature (°C), system flow (m3 / h), system pressure (bar) and pump power (kW), respectively. Note that the values in the diagrams are given as examples only.

[0163] In Diagram 1 , the unbroken line denoted 5400 represents a seawater temperature of 32 °C, which is the standard seawater temperature which cooling systems for marine vessels are calibrated to handle, according to rules and regulations. The unbroken line denoted 5100 shows the corresponding freshwater circuit design temperature of 38 °C, as given by standard regulation. In a prior art solution, when the heat exchange load is increased from zero towards 100 %, the freshwater circuit temperature will increase linearly 5101 towards a maximum allowed temperature 5102, here shown as 42 °C.

[0164] Flow, pump pressure and pump power for the above-mentioned prior art solution, are illustrated by the unbroken lines 6100, 7100, 8100 in Diagrams 2, 3 and 4, respectively. The flow is kept constant, in this example at 94 m3 / h (Diagram 2), the pump pressure is kept constant, in this example at 3.5 bar (Diagram 3), and the pump power is also constant, in this example 17kW, regardless of the percentage of heat exchange load.

[0165] If, instead, the control system 30 claimed herein, is used, the flow through the at least one heat exchanger 110 is reduced if an output temperature, Tout, is below the maximum allowed temperature, Tmax, which in the example in the Diagrams is 42 °C. The effect of such flow reduction is that the freshwater circuit temperature is pushed towards the maximum temperature as illustrated by the dotted line denoted 5201 in Diagram 1. The flow, shown in Diagram 2, in this example is as low as 9 m3 / h (horizontal line denoted 6200) when the heat exchange load is low, and at a point, approximately at 15-20%, starts linearly increasing towards full flow at maximum load (following the line denoted 6201).

[0166] Correspondingly, Diagram 3 and Diagram 4 show that starting from the standard temperature and utilizing the control system 30 claimed herein, pump pressure and therefore also pump power will follow a first flat curve, shown as 7200 and 8200 respectively, thereafter linearly increasing, following the lines 7201 and 8201 respectively, and only reaches a maximum when the heat exchange load is at 100 %. This means that a lot of energy is saved. Even more energy is saved, and the cooling system 1 is better utilized, by additionally changing the set seawater temperature and the set freshwater temperature. Even if the cooling system 1 is dimensioned to deal with seawater temperatures of 32 °C as a standard, the control system 30 may be arranged to adapt to the actual seawater temperatures, so that if the marine vessel over time is surrounded by seawater of lower temperatures, the seawater temperature of the cooling system 1 may be set to for example 26 °C (dash-dotted line denoted 5500 in Diagram 1) instead of the normal 32 °C. The freshwater circuit temperature is correspondingly set to a lower temperature than usual, for example 30 °C, see the dash-dotted line denoted 5300. Due to the lower initial temperature, the flow (Diagram 2), the pump pressure (Diagram 3) and eventually the pump power (Diagram 4) will be kept even lower, also at maximum heat exchange load. This is illustrated by the dash- dotted lines 6300 in Diagram 2, 7300 in Diagram 3, and 8300 in Diagram 4, respectively.

[0167] The control system 30 disclosed herein, therefore shows two options for saving considerable amounts of energy: reducing the set circuit temperatures in the control system 30 setting and reducing the flow through the at least one heat exchanger 110 in the freshwater circuit, i.e. the circulation circuit 10, for pushing the output temperature, Tout, towards the maximum allowable temperature, Tmax.

[0168] The two options may be used together or separately.

[0169] In a test project carried out by the Applicant, continuous logging of a marine vessel’s heat exchange load shows an average of 30 % heat exchange load over a year. At a 30 % heat exchange load, the diagram 4 shows that the control system according to the present invention may result in an average pump power of 4-6 kW as compared to 17 kW without the present control system. This means energy savings of approximately 65-75 %. This is better illustrated in Figure 6 which shows Diagram 4 with a vertical line 9 at a 30 % heat exchange load.

[0170] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0171] Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

C l a i m s1. A control system (30) for controlling a cooling system (1) of a marine vessel, the cooling system (1) comprising:- a central cooler (100) for cooling a cooling fluid in the cooling system (1);- a temperature regulating valve (140) for regulating a temperature of the cooling fluid to a pre-set desired temperature;- a circulation circuit (10);- a pump (130) for circulating a flow of the cooling fluid in the circulation circuit (10); and- a first temperature sensing means (1402) for monitoring the temperature of the cooling fluid entering the circulation circuit (10) from the temperature regulating valve (140); the circulation circuit (10) comprising:- tubing (120);- at least one heat exchanger (110) for cooling a heat generating element in the marine vessel, wherein each of the at least one heat exchanger (110) has a maximum allowable outlet temperature, Tmax;- a second temperature sensing means (1521) for monitoring an outlet temperature, Tout, of cooling fluid exiting each of the at least one heat exchanger (110);- a flow regulating valve (150) arranged downstream of each of the at least one heat exchanger (110); and- a flow monitoring means (1531) for monitoring the flow, F, through each of the at least one heat exchanger (110); the control system (30) comprising a programmable control unit (3001) provided with information about Tmax, and about a minimum required flow, Freq, to be maintained through the at least one heat exchanger (110), the control system (30) is operatively connectable to:- the second temperature sensing means (1521);- the flow monitoring means (1531); and- the flow regulating valve (150); for increasing the flow of cooling fluid through the at least one heat exchanger (110) if Tout > T max, and for reducing the flow of cooling fluid through the at least one heat exchanger (110) if Tout < Tmax, while at the same time keeping F > Freq.

2. The control system (30) according to claim 1, wherein the at least one heat exchanger (110) comprises one or more further heat exchangers (110) arranged in parallel.

3. The control system (30) according to claim 1 or claim 2, wherein the flow monitoring means (1531) comprises a flow meter.

4. The control system (30) according to any one of the preceding claims, wherein the cooling system (1) further comprises a pressure sensor (1322), and wherein the programmable control unit (3001) is operatively connectable to the pressure sensor (1322).

5. The control system (30) according to any one of the preceding claims, the pump (130) having an adjustable rotational speed, wherein the control unit (3001) is further operatively connectable to the pump (130) for adjusting the rotational speed of the pump (130) for further regulating the flow and pressure of cooling fluid in the circulation circuit (10).

6. The control system (30) according to any one of the preceding claims, the control unit (3001) further being operatively connectable to the temperature regulating valve (140).

7. The control system (30) according to any one of the preceding claims, wherein a variable frequency drive (1321), VFD, is arranged for driving the pump (130).

8. The control system (30) according to any one of the preceding claims, the marine vessel having an integrated automation system, IAS, wherein the programmable control unit (3001) is operatively connectable to the IAS or wherein the programmable control unit (3001) forms an integral part of the IAS.

9. A method for controlling a cooling system (1) of a marine vessel by means of the control system (30) according to any one of claims 1-8, the method comprising the following steps:- feeding the control unit (3001) with information about T max for each of the at least one heat exchanger (110);- feeding the control unit (3001) with information about the minimum required flow, Freq, to be maintained in the circulation circuit (10);- reading the outlet temperature, Tout, of the cooling fluid downstream of each of the at least one heat exchanger (110) detected by the second temperature sensing means (1521);- reading the flow, F, as detected by the flow monitoring means (1531);- increasing the flow of cooling fluid through the at least one heat exchanger (110) if Tout > Tmax, or reducing the flow, F, of cooling fluid through the at least one heat exchanger (110) by means of the flow regulating valve (150) if Tout < Tmax, while at the same time keeping F > Freq.

10. The method according to claim 9, further comprising the following steps:- before starting to use the control system (30), performing a startup calibration of the control unit (3001) for deciding a minimum required pressure in the circulation circuit (10) at the minimum required flow, Freq, and for deciding a maximum pressure in the circulation circuit (10) at a maximum flow; and- regulating the rotational speed of the pump (130) to maintain the minimum required pressure, wherein said minimum required pressure is set for maintaining the minimum required flow, Freq.11 . The method according to any one of claims 9-10, further comprising the steps of:- detecting an operational mode from the vessel’s IAS or manually selecting an operational mode; and- selecting the required flow, Freq, for the at least one heat exchanger (110), based on the detected operational mode.

12. The method according to any one of claims 9-11 , wherein, when the cooling system (1) comprises a variable frequency drive (1321), VFD, for driving the pump (130), the method further comprises the step of:- if, the VFD (1321) is replaced by a replacement VFD, feeding the replacement VFD with the same parameters for driving the pump (130).

13. The method according to any one of claims 9-12, wherein the method is a computer-implemented method.

14. A data processing device comprising means for carrying out the method according to any one of claims 9-12, wherein the data processing device comprises the control unit (3001) of the control system (30) according to any one of claims 1-8.

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