Improvements relating to cooling wind turbines

Abstract

A wind turbine cooling system comprising: a power converter enclosure having an first air cooling circuit being adapted to pass airflow over at least one power converter component, the blown-air cooling circuit comprising an air-to air heat exchanger and an air-to-liquid heat exchanger which are configured to cool air flowing in the blown-air cooling circuit; a second air cooling circuit configured to convey a flow of air between an air source and the air-to-air heat exchanger of the power converter enclosure to cool the air flowing in the first air cooling circuit; a liquid coolant circuit adapted to convey a flow of coolant between the air-to-liquid heat exchanger of the power converter enclosure, wherein the air-to-liquid heat exchanger is at is arranged to heat coolant flowing through the liquid coolant circuit; and, wherein the liquid coolant circuit further comprises a further heat exchanger configured to cool coolant flowing through the liquid coolant circuit. Beneficially, the cooling system of the invention provides cooling functionality for a power system of a wind turbine which is effective over a wider range of ambient conditions which means that the power generation systems of the wind turbine can maintain output power generation at extreme temperature ranges.

Description

[0001] IMPROVEMENTS RELATING TO COOLING WIND TURBINES

[0002] Technical Field

[0003] This disclosure relates to systems, apparatus and methods adapted to control the temperature of components of a wind turbine generator.

[0004] Background

[0005] The components housed in the nacelle of a wind turbine generator, such as the electrical generator and power converter, operate most effectively within respective optimal temperature bands. Accordingly, selective cooling and / or heating systems are required to regulate the temperatures of these components.

[0006] One of the main components in a wind turbine that requires cooling is an on-board power converter system which, as is known, has the function of converting the AC power produced by the generator into AC or DC power for export from the wind turbine.

[0007] Converter electronics generate heat during operation and so a provision for cooling the power converter system is required.

[0008] A known approach for cooling the converter electronics is to provide a recirculated air system to a sealed enclosure or cabinet within which the power converter system is housed. The sealed enclosure is adapted to define an airflow path along which air is blown by a cooling fan. The circulating air passes the power electronics components and then flows through an air-to-air heat exchanger of a known type. The air-to-air heat exchanger receives a cool air flow from the ambient environment surrounding the wind turbine which may also be a blown-air source. The external air flow absorbs thermal energy from the air-to-air heat exchanger by which mechanism the air flow in the system enclosure is cooled. Such a cooling system provides generally acceptable performance across a range of power dissipation conditions and ambient temperatures. However, such systems are challenged by the demand for siting wind turbines in hotter climates which may experience low wind conditions.

[0009] It is against this background that the invention has been devised. Summary of the Invention

[0010] According to a first aspect of the invention, there is provided a wind turbine cooling system comprising: a power converter enclosure having an first air cooling circuit being adapted to pass airflow over at least one power converter component, the blown-air cooling circuit comprising an air-to air heat exchanger and an air-to-liquid heat exchanger which are configured to cool air flowing in the blown-air cooling circuit; a second air cooling circuit configured to convey a flow of air between an air source and the air-to-air heat exchanger of the power converter enclosure to cool the air flowing in the first air cooling circuit; a liquid coolant circuit adapted to convey a flow of coolant between the air-to-liquid heat exchanger of the power converter enclosure, wherein the air-to-liquid heat exchanger is at is arranged to heat coolant flowing through the liquid coolant circuit; and, wherein the liquid coolant circuit further comprises a further heat exchanger configured to cool coolant flowing through the liquid coolant circuit.

[0011] Beneficially, the cooling system of the invention provides cooling functionality for a power system of a wind turbine which is effective over a wider range of ambient conditions which means that the power generation systems of the wind turbine can maintain output power generation at extreme temperature ranges.

[0012] The power converter enclosure may be a hermetically sealed environment which means that the air-cooling circuit is protected from outside contamination. Suitable fans / blowers and filtration devices may be provided to circulate air around the air-cooling circuit and maintain a clean environment that is suitable for power converter electronics and associated componentry.

[0013] The further heat exchanger may be of a type known as a ‘cooler top’ design that is located on an external surface of a nacelle of the wind turbine. For instance, the further heat exchanger may be located on the roof of a wind turbine thereby being exposed to air flowing across the nacelle.

[0014] The functionality of the cooling system may be further enhanced by the provision of a heater device and / or a chiller device arranged to transfer thermal energy to / from the liquid cooling circuit. Beneficially, a heater device provides improved functionality during low temperature conditions in which it may be desirable to bring the surrounding temperature of the power converters above a threshold temperature as quickly as possible.

[0015] Conversely, the inclusion of a chiller device provides the cooling system with enhanced cooling capabilities particularly in circumstances where the ambient temperature is high and the wind turbine is operating at high power loads. The inclusion of a chiller device may also be beneficial under noise restriction requirements because cooling can be provided to the power converter enclosure predominantly by the air-to-liquid heat exchanger, reducing the cooling requirement on the air-to-air heat exchanger which means that forced air blowers associated with the air-to-air heat exchanger can be set at a lower power level, thereby reducing noise output.

[0016] The cooling system may be adapted so that air flows along the air-cooling circuit through the air-to-liquid heat exchanger before flowing through air-to-air heat exchanger. In one example, the air-to-liquid heat exchanger and the air-to-air heat exchanger are integrated into a single package. Usefully this means that a single unit can be replaced in the case of a failure or other maintenance requirement.

[0017] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all examples and / or features of any example can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0018] Brief Description of the Drawings

[0019] The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0020] Figure 1 is a schematic view of a wind turbine including a cooling system;

[0021] Figure 2 is a schematic view which shows a more detailed example of the cooling system of Figure 1 ; Figure 3 is a schematic view of another example of a cooling system which is similar to that shown in Figure 2 but varies in certain respects;

[0022] Figure 4 is a schematic view of a further example of a cooling system.

[0023] Detailed Description

[0024] A specific embodiment of the invention will now be described in which numerous features will be discussed in detail to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the invention may be put into effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

[0025] In order to place the embodiments of the invention in a suitable context, reference will firstly be made to Figure 1 , which illustrates a typical Horizontal Axis Wind Turbine 1 (HAWT) comprising a tower 2, a nacelle 4 rotatably coupled to the top of the tower 2, a rotating hub or ‘rotor’ 6 mounted to the nacelle 4 and a plurality of wind turbine rotor blades 8 coupled to the rotor 6.

[0026] The rotor 6 is connected to a power generation system 10 housed within the nacelle 4. The power generation system 10 comprises components required to convert rotation of the rotor 6 into electricity, including a drive train, a generator and one or more transformer(s), converter(s), bearing(s) and brake(s), none of which are shown here for brevity. However, the skilled person would understand that these are conventional components of a wind turbine power generation system. A down conductor 12 is connected to the power generation system 10 to transport power to a distribution network (not shown). It should be noted that the wind turbine described here may be installed in an offshore or an onshore location and the specific type of wind turbine is not central to the invention.

[0027] The wind turbine also includes a cooling system 20 which is shown here as being housed at least partly within the nacelle 4. This is because most of the heat-generating components are housed within the nacelle 4. However, in principle some or all of the components of the cooling system 20 may be located in other areas of the wind turbine 1.

[0028] The cooling system 20 comprises a first heat exchanger arrangement 22 or ‘heating device’ that is coupled thermally to components of the power generation system 12, as will be further explained in the discussion that follows. The cooling system 20 further comprises a further heat exchanger arrangement or ‘cooling device’ 24 that is positioned so it is exposed to a cooling airflow. In this example, the second heat exchanger arrangement 24 is located on top of the nacelle 4 in a ‘cooler top’ configuration which is known in some wind turbine designs.

[0029] Whilst Figure 1 provides a general overview, Figure 2 shows the cooling system 20 in more detail.

[0030] In overview, the cooling system comprises a liquid cooling circuit or loop 28 that is configured to convey liquid coolant between the first heat exchanger arrangement 22 and the second heat exchanger arrangement 24. A liquid coolant pump 30 is provided to circulate coolant around the liquid cooling circuit 28.

[0031] As discussed above, the second heat exchanger arrangement 24 is in the form of a radiator that is positioned on an external surface of the nacelle 4 of the wind turbine, as is generally known.

[0032] The first heat exchanger arrangement 22 forms part of a power converter enclosure or cabinet 34. The power converter cabinet 34 is located inside the nacelle 4, although that is not shown in Figure 2.

[0033] The power converter cabinet 34 is a structure that is known generally in the art as a sealed enclosure that has suitable mounting arrangements for accommodating electronics boards for the purpose of electrical power conversion. For example, the electronics boards may comprise high frequency filters, reactive / inductive power compensating equipment, AC-DC power converters, DC-AC power converters, buses, chokes and so on. The precise makeup of the components is not central to the invention. However, in general such electronic cabinets would comprise at least one power converter. Although the power converter cabinet 34 may be hermetically sealed so as to establish a completely airtight seal for air to flow within it, in some examples a hermetic seal may not be required.

[0034] As such, the power converter cabinet 34 in Figure 2 is shown as housing two power converters 40,42 for the sake of convenient illustration, although in practice many more electrical components would be housed within the power converter cabinet 34.

[0035] The power converter cabinet 34 is configured to define an air-cooling circuit 44 that circulates around the interior of the power converter cabinet 34, as driven by a fan 46. It should be noted at this point that suitable power supplies and cabling for the fan 46 and the power converters 40, 42 is not shown in Figure 2 for the sake of clarity.

[0036] Preferably the power converter cabinet 34 provides a sealed environment for the power converters 40,42 so that the circulating air remains free of contaminants. Suitable filtration devices may be provided to ensure a clean flow of air although this has not been shown in Figure 1 as it is not central to the invention.

[0037] Since Figure 2 is schematic in form, it will be noted that the actual interior structure of the power converter cabinet 34 may differ significantly from what is shown here. However, the principle is that a flow of cooling air is blown from the fan 46 past the power converters 40,42, which heat up the flow of air. From there, the air flows through the first heat exchanger arrangement 22 which cools down the flow of air which then travels back to the fan 46 for recirculation. Suitable baffles, openings and flow diverters may be provided within the power converter cabinet 34

[0038] It will be noted that the first heat exchanger arrangement 22 has two ways of cooling the air flowing through it within the power converter cabinet 34. To this end, the first heat exchanger arrangement 22 comprises an air-to-liquid (A2L) heat exchanger 48 and an air-to-air (A2A) heat exchanger 50. Both the A2L heat exchanger 48 and the A2A heat exchanger 50 are configured within the power converter cabinet 34 to cool the flow of air through the internal cooling circuit 44.

[0039] The A2L heat exchanger 48 is provided with cooling by the liquid cooling circuit 28. As can be seen, liquid coolant within the liquid coolant circuit 28 is circulated by the liquid coolant pump 30. The liquid coolant circuit 28 divides into two branches at a position downstream from the liquid coolant pump 30. A first coolant branch 54 leads to the first and second power converters 40,42 and back to the second heat exchanger arrangement 24. By this means, the first coolant branch 54 carries liquid coolant to the power converters 40,42. The power converters 40,42 are adapted with suitable cooling passages, channels, ducts (not shown) and so on to enable components that heat up during use to be exposed to coolant from the first coolant branch 54 either directly, or indirectly using heat sinks, for example. Such cooling passages are not shown in Figure 2 but such arrangements would be understood by the skilled person so a detailed discussion will be omitted.

[0040] The first coolant branch 54 has a respective input 54a at each of the first and second power converters 40,42 and a respective output 54b from each of the respective first and second power converters 40,42.

[0041] A second coolant branch 56 leads to the A2L heat exchanger 48 of the power converter cabinet 34. The second coolant branch 56 includes an input 56a into the A2L heat exchanger 56 and an output 56b from the A2L heat exchanger 56. After the coolant has passed through the A2L heat exchanger 48, it flows back to the first coolant branch 54.

[0042] Liquid coolant flowing through the second coolant branch 56 therefore acts to cool the air flowing through the A2L heat exchanger 48.

[0043] The A2L heat exchanger 48 may be any suitable A2L heat exchanger that is known to the skilled person.

[0044] As mentioned above, the air-cooling circuit 44 also passes through the A2A heat exchanger 50. Cooling is provided for the A2A heat exchanger 50 by a second air cooling circuit 60. The second air cooling circuit 60 is shown in Figure 2 as extending between the A2A heat exchanger 50 and an external air source 62. The external air source 62 may be a suitable external vent opening to the ambient environment thereby to allow a flow of air through to the A2A heat exchanger 50. The second air cooling circuit 60 may include suitable fans 63 and filtration devices (not shown) as is required, and as are generally conventional. In this example, the air source 62 ducts cooling air to the A2A heat exchanger 50 from an external source, it should be noted that in other examples of the invention it is envisaged that the source of air may be from the interior of the nacelle 4. At this point it should be noted that the configuration of the A2A heat exchanger 50 may be any suitable A2A heat exchanger known in the art as would be apparent to the skilled person.

[0045] It will be appreciated from the above discussion that power converter cabinet 34 and the first heat exchanger arrangement 22 are configured so that air flow in the air-cooling circuit 44 flows through the A2L heat exchanger 48 and also the A2A heat exchanger 50. As shown in Figure 2, air flows in a predefined flow direction through the two heat exchangers 48,50 in series. Although not essential, in the illustrated example the A2L heat exchanger 48 and the A2A heat exchanger 50 are arranged in an adjacent or ‘back- to-back’ configuration so that air flows out of the A2L heat exchanger 48 and then directly into the A2A heat exchanger 50. In this way, air flows through the A2L heat exchanger 48 before flowing through the A2A heat exchanger 50. The two heat exchangers 48,50 may be an integrated structural package in one example, which is a particularly convenient arrangement for the purposes of maintenance.

[0046] It is envisaged that it is beneficial to position the A2L heat exchanger 48 upstream relative to the A2A heat exchanger 50 such that the position of the A2L heat exchanger 48 makes most use of the high efficiency of that heat exchanger. Conversely, the position of the A2A heat exchanger 50 makes use of the low air temperature, as it is placed after the A2L heat exchanger 48.

[0047] This configuration of cooling system 20 provides cooling functionality that is flexible and effective across a wider range of operating scenarios than is currently the case. In particular, it will be noted that the airflow in the first air-cooling circuit 44 is cooled by both the A2L heat exchanger 48 and the A2A heat exchanger 50 which means that increased cooling capacity can be brought to bear on the first air-cooling circuit 44 for cooling the power converters 40,42 when they are operating at a high current capacity. This is especially beneficial for hot weather conditions where cooling capacity from the A2A heat exchanger 50 alone may be compromised. Notably, the use of both A2L and A2A heat exchangers means that the system is less dependent on liquid coolant. So, in a low wind scenario where the cooling system generally would be functioning less efficiently, the converter would still be able to carry full load. The flow of liquid coolant around the liquid coolant circuit 28 may be controlled by valve means to enhance the functionality of the cooling system 20. In this respect, the valve means includes a first flow control valve 64.

[0048] The first flow control valve 64 in the illustrated example is shown as located at the start of the second coolant branch 56. The first flow control valve 64 is operable to control the flow of liquid coolant along the second coolant branch 56 to the A2L heat exchanger 48. The first flow control valve 64 may operate between fully open and fully closed position to or may be a proportional valve, as appropriate. The operation of the first flow control valve 64 may be controlled by a suitable computer controller 66.

[0049] The computer controller 66 may take various input signals 68 and implement a suitable control algorithm to provide a series of output signals 70. The output signals 70 may control the first flow control valve 64 to provide the required functionality, but also may control the operation of the liquid coolant pump 52 and the fans 46,63.

[0050] A second flow control valve 72 is provided in the illustrated example. The second flow control valve 72 is located in the liquid coolant circuit 28 in a position upstream from the second heat exchanger arrangement 24. The second flow control valve 72 therefore controls the bulk flow of coolant through the liquid coolant circuit 28 and can therefore be considered to control the cooling ‘power’ provided by the liquid cooling circuit 28, together with speed regulation of the coolant pump 30. The second flow control valve 72 controlled by appropriate control output signals 70 provided by the computer controller 66.

[0051] The functionality of the cooling system 20 can be appreciated by considering the following use cases.

[0052] High wind speeds combined with high ambient temperature.

[0053] It is becoming more common for wind turbines to be required to be installed in areas of higher average temperatures which means extreme temperatures are encountered more frequently. This can be challenging for conventional wind turbine cooling systems which generally rely on blown-air cooling for the internal electronic subsystems. In this scenario, power converter electronics are required to operate at a high load due to the high wind speeds, both in terms of active power and also potentially reactive power, and this generates higher levels of waste heat. In the respect of the cooling system in the examples of the invention, the A2A heat exchanger 50 has a reduced capability to reduce the temperature of the recirculating air within the air-cooling circuit 44 because of the higher ambient temperatures, even when operating at a high internal air flow.

[0054] The cooling system 20 is able to mitigate this situation as the first flow control valve 64 may be controlled by the computer controller 66 to enable a high flow rate of coolant through the first coolant branch 56 so that the A2L heat exchanger 48 provides additional cooling capability for the air-cooling circuit 44.

[0055] Moderate wind speeds combined with high temperature and noise restriction

[0056] In this scenario, the cooling requirement is complicated due to the need to observe noise restrictions, which may be the case where wind turbine installations are nearby to residential area such that noise restrictions may be put in place at certain times, such as overnight.

[0057] During high ambient temperatures and moderate wind speeds, the power converter electronics are expected to operate at a high load, both in terms of active power and reactive power, which generates significant waste heat. However, the high ambient temperatures compromise the ability of the A2A heat exchanger 50 to reduce the temperature of the air-cooling circuit 44, which is particularly the case where noise restrictions require the second air-cooling circuit 60 to run at a lower flow level i.e. the fan 63 of the second air-cooling circuit 60 must operate at a lower speed in order to reduce noise output.

[0058] In such a situation, the cooling system 20 may be configured to operate the first flow control valve 64 to enable a high flow rate of coolant through the first coolant branch 56 so that the A2L heat exchanger 48 provides additional cooling capability for the air- cooling circuit 44. This means that a lower performance of the A2A heat exchanger 50 is acceptable. A further example configuration of the cooling system 20 is shown in Figure 3. Note that the cooling system 20 shown in Figure 3 is generally the same as the cooling system 20 shown in Figure 2, so the following discussion will focus only on the differentiating features of this illustrated example.

[0059] The cooling system 20 in the example of Figure 3 further includes a heating device 80, which is positioned in this example so that it heats coolant in the liquid coolant circuit 28. In this example, the heating device 80 is located in the liquid coolant circuit 28 downstream from the liquid coolant pump 30 but upstream from the first flow control valve 64. The heating device 80 may be embodied in various ways which may be conceived by the skilled person. In the illustrated example, however, the heating device 80 is located in a third coolant branch 82. The third coolant branch 82 may include a heater flow control valve 84 to control the extent to which coolant flows along the third coolant branch 82.

[0060] The heating device 80 may take any suitable form. For example, the heating device 80 may be an electrically heated body through which the liquid coolant is passed to heat the coolant. Other arrangements of heating devices would be acceptable and would be able to be conceived by the skilled person.

[0061] The operation of the heating device 80 may be governed by the computer controller 66 by outputting suitable output control signals 70 to the heater device 80. The heater device 80 may be controlled to be simply on or off thereby providing a single level of thermal energy output or its heating power may be varied in a suitable manner.

[0062] Beneficially, the heating device 80 and the heater flow control valve 84 may be operated in circumstances where it is detected that the ambient temperature is cold such that the temperatures of the power converter enclosure should be warmed before operation. Such a scenario may occur in cold conditions prior to starting up the wind turbine. Therefore, the cooling system 20 may be run in a warming mode, through operation of the heating device to transfer thermal energy into the A2L heat exchanger 48 and into the air-cooling circuit 44 thereby increasing the temperature of the first and second power converters 40,42.

[0063] A further example of the cooling system 20 is shown in Figure 4. Note that the cooling system 20 shown in Figure 4 is generally the same as the cooling system 20 shown in Figure 2, so the following discussion will focus only on the differentiating features of this illustrated example.

[0064] The cooling system 20 in the example of Figure 4 further includes a chiller device 90, which is positioned in this example so that it chills coolant in the liquid coolant circuit 28. More specifically, in this example the chiller device 90 is positioned in the second coolant branch 56. The chiller device 90 may be positioned in an upstream position or a downstream position relative to the first flow control valve 64. In Figure 4, the chiller device 90 is positioned upstream of the first flow control valve 64. Furthermore, the chiller device 90 is positioned upstream of the A2L heat exchanger 48.

[0065] The chiller device 90 may be embodied in various ways which may be conceived by the skilled person. In the illustrated example, however, the chiller device 90 is located in a fourth coolant branch 92. The fourth coolant branch 92 may include a chiller flow control valve 94 to control the extent to which coolant flows along the fourth coolant branch 82, thereby controlling the functionality of the chiller device 90.

[0066] The chiller device 90 may take any suitable form. For example, the chiller device 90 may incorporate a refrigeration cycle and comprise an evaporator, a condenser, a compressor, and an expansion unit. Since these components are well known in the art, a full discussion is not provided here so as not to obscure the invention. A skilled person would conceive an appropriate chiller device capable of providing a required cooling effect to the fourth cooling branch 92.

[0067] Although in this example the chiller device 90 is shown in a parallel arrangement with respect to the first coolant branch 56, it should be noted that the chiller device 90 could be configured ‘in line’ with the first coolant branch 56.

[0068] The operation of the chiller device 90 may be governed by the computer controller 66 by outputting suitable output signals 70 to the chiller device 90. The chiller device 90 may be controlled to be simply on or off thereby providing a single level of cooling or its cooling power may be varied in a suitable manner by a proportional control strategy.

[0069] Usefully, the inclusion of the chiller device 90 means that in high temperature environments an enhanced cooling functionality is provided to reduce the temperature of the coolant flowing through the first coolant branch 56 to the A2L heat exchanger 48, albeit at a modest increase in cost and control complexity.

[0070] It would be appreciated by the skilled person that the cooling system 20 described above may be implemented with a heating device 80 as shown in the example of Figure 3, and also the chiller device 90 as shown in the example of Figure 4. In such a configuration, the computer controller 66 may control each of the heating device 80 and the chiller device 90 independently for enhanced functionality.

[0071] Various modifications may be made to the specific embodiments that have been discussed above with reference to the accompanying figures. Some variants have already been discussed but others would be apparent to the skilled person. Therefore, the scope of the invention should be determined from the appended claims rather than with reference to the specific examples discussed in this text.

[0072] For example, in the above discussion the A2L heat exchanger 48 and the A2A heat exchanger 50 have been described as being located adjacent to one another, optionally in an integrated unit or module, such that air flow in series along the first air-cooling circuit 44 firstly through the A2L heat exchanger 48 and then through the A2A heat exchanger. However, it should be noted that in other examples (not shown), the two heat exchangers may be split and arranged along parallel airflow paths such that air flows along the first air-cooling circuit 44 and through the A2L heat exchanger 48 and the A2A heat exchanger 50 in parallel.

Claims

CLAIMS1. A wind turbine cooling system (20) comprising: a power converter enclosure (34) having a first air-cooling circuit (44) being adapted to pass airflow over at least one power converter component (40,42), the first air-cooling circuit (44) comprising an air-to-air heat exchanger (50) and an air-to-liquid heat exchanger (48) which are configured to cool air flowing in the first air-cooling circuit; a second air-cooling circuit (60) configured to convey a flow of air between an air source (62) and the air-to-air heat exchanger (50) of the power converter enclosure (32) to cool the air flowing in the first air cooling circuit (44); a liquid coolant circuit (28) adapted to convey a flow of liquid coolant between the air-to- liquid heat exchanger (48) of the power converter enclosure (32), wherein the air-to-liquid heat exchanger (48) is arranged to heat coolant flowing through the liquid coolant circuit (28); and, wherein the liquid coolant circuit (28) further comprises a further heat exchanger (24) configured to cool coolant flowing through the liquid coolant circuit (28).

2. The wind turbine cooling system of Claim 1 , wherein the power converter enclosure (34) is hermetically sealed.

3. The wind turbine cooling system of Claims 1 or 2, wherein the further heat exchanger (24) is a radiator adapted to be arranged on an external surface of a nacelle (4) of the wind turbine.

4. The wind turbine cooling system of any one of the preceding claims, further comprising a chiller device (90) located in the liquid coolant circuit (28) in a position upstream of the air-to-liquid heat exchanger (48).

5. The wind turbine cooling system of any one of the preceding claims, further comprising a heater device (80) located in the liquid coolant circuit (28) in a position upstream of the air-to-liquid heat exchanger (48).

6. The wind turbine cooling system of Claim 4, further comprising chiller flow control device (92) adapted to control the flow of liquid coolant through the chiller device (90).

7. The wind turbine cooling system of Claim 5, further comprising a heater flow control device (82) adapted to control the flow of coolant liquid through the heater device (80).

8. The wind turbine cooling system of any one of the preceding claims, further comprising a first heat exchanger flow control device (64) adapted to control the flow of liquid through the air-to-liquid heat exchanger (48).

9. The wind turbine cooling system of any one of the preceding claims, wherein air flows along the first air cooling circuit (44) through the air-to-liquid heat exchanger (48) before flowing through air-to-air heat exchanger (50).

10. The wind turbine cooling system of Claim 9, wherein the air-to-liquid heat exchanger (48) and the air-to-air heat exchanger (50) are configured relative to one another so that the air exits the air-to-liquid heat exchange (48) and flows directly through the air-to-air heat exchanger (50).

11. The wind turbine cooling system of any one of the preceding claims, wherein the air source (62) associated with the first air cooling circuit (44) is an external air source.

12. A wind turbine comprising a nacelle mounted on a tower and a cooling system according to any one of Claims 1 to 11.

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