This application claims the benefit of European Patent Application EP 12 382 088.8 filed March 13, 2012 and U.S. Provisional Patent Application Ser. No. 61/646,756 filed May 14, 2012.

The present disclosure relates to air conditioning systems for wind turbines and further relates to methods for ventilating and pressurizing a wind turbine.

BACKGROUND

In modern wind turbines, HVAC (Heating Ventilation & Air Conditioning) systems may be arranged to protect the internal components from external environmental hazards. The aim of these systems may be to control the temperature and humidity inside the turbine, and/or the prevention of water droplets, salt or dust inside the turbine. This may be particularly important when wind turbines are used in harsh environments, such as e.g. in an offshore wind park. In some implementations, such as e.g. in the desert, the humidity control may not be needed.

HVAC systems may be able to operate at different environmental and turbine power production conditions. At these different conditions, the system may have to fulfill different requirements, e.g. while overheating prevention requires a high rate ventilation flow, humidity control and dust intake prevention can only be done, in a cost-effective manner, with a lower air renewal rate. In order to control parameters such as the pressurization level within the wind turbine and/or the ventilation flow rate, control strategies may take into account factors such as the type of control or prevention that is required and the type of housing used in the wind turbine (e.g. substantially sealed or permeable). It is important to take this kind of factors into account in order to obtain a HVAC system with optimized power consumption, which is able to provide a suitable pressurization level within the wind turbine and which minimizes damages in the housing of the wind turbine.

In conventional HVAC systems, a minimum pressurization level within the wind turbine may be required in order to avoid uncontrolled inward air flow through the housing joints of the wind turbine. Thanks to continuous pressurization, water droplets, salt and/or dust intake may be prevented. Additionally, when the turbine is operating and cooling is needed, the system may be able to guarantee a minimum flow rate that is required in order to avoid excessive high temperatures in the wind turbine. In this respect, achieving this minimum flow rate may considerably increase the pressurization level within the wind turbine. This fact may lead to damage at housing joints and it may also require high energy consumption. It may also lead to premature wear of the ventilation system involved.

SUMMARY

In a first aspect, an air conditioning system for a wind turbine comprising at least one adjustable air intake, one adjustable air exhaust and a variable air flow generator is provided, wherein the adjustable air exhaust may be adapted to maintain the pressurization level in the wind turbine within a predetermined range.

An adjustable air exhaust within the wind turbine may be used to maintain the pressurization level within the wind turbine within a predetermined range of pressurization values. The variable flow generator may adapt the flow of (cooling) air within the wind turbine in accordance with circumstances: a minimum flow rate may be provided at all times to make sure dust, and water droplets, etc. do not enter the wind turbine. When overheating can become a problem, a higher flow rate may be provided than when overheating is not a potential problem. At the same time, the adjustable air exhaust can ensure that the pressure within the wind turbine stays under control. Advantages of using this adjustable air exhaust in air conditioning systems for wind turbines may be the reduction of energy consumption and keeping the pressurization level in an acceptable range so that damage at the housing joints may be substantially reduced or avoided.

In some embodiments, the variable air flow generator may comprise a low rate fan and a high rate fan. The low rate fan may be used for obtaining a pressurization level within the wind turbine above the minimum pressurization level required for water droplets, salt and/or dust intake prevention and may be active at all times. The high rate fan may be used for obtaining a high rate ventilation flow above the minimum flow rate required for avoiding excessively high temperatures within the wind turbine and may thus be activated only when cooling is needed.

In some embodiments, the variable air flow generator may comprise an adjustable rate fan adapted to work at least at two predetermined speeds, e.g. a two-speed fan. The adjustable rate fan may work at a first speed that may be used for obtaining a pressurization level within the wind turbine above the minimum pressurization level required, and at a second speed that may be used for obtaining a high rate ventilation flow above the minimum flow rate required for avoiding excessively high temperatures within the wind turbine. In some embodiments, an adjustable rate fan may be used that is connected to a variable frequency drive. The variable rate fan may thus be adapted to work at many different speeds.

In another aspect, a method for controlling the ventilation and pressurization within a wind turbine is provided. The method comprises generating an air flow which maintains a minimum pressurization level within the wind turbine generator, and when cooling is needed, increasing the air flow in order to protect the wind turbine generator against overheating and maintaining the pressurization level within a predetermined range of pressurization values. Additional objects, advantages and features of embodiments of the invention will become apparent to those skilled in the art upon examination of the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments of the present invention will be described in the following by way of non-limiting examples, with reference to the appended drawings, in which:

Figure 1 shows an air conditioning system for a wind turbine according to an embodiment of the present invention.

Figure 2 shows a chart of the air conditioning system according to an embodiment of the present invention representing pressurization level versus ventilation flow rate.

DETAILED DESCRIPTION

Figure 1 shows an air conditioning system for a wind turbine 100 according to an embodiment of the present invention. The wind turbine 100 of Figure 1 may comprise blades 1 1 , a hub 10, a nacelle 13 and a tower 17. The air conditioning system that may be arranged in the wind turbine 100 of Figure 1 may comprise an adjustable air intake 12 and an adjustable air exhaust 14. The adjustable air intake 12 may comprise a variable air flow generator which may comprise a low rate fan 19 and a high rate fan 101 . In other embodiments, the variable air flow generator may comprise an adjustable rate fan that may work at least at two different predetermined speeds. In yet further embodiments, the adjustable rate fan may be connected to a variable frequency drive.

Furthermore, the adjustable air intake 12 may comprise an air treatment unit 102. The air treatment unit may comprise suitable filters and a dehumidifier 18. The dehumidifier 18 may dehumidify the air flow which may be ducted to pass through the low rate fan 19, avoiding excessive humidity levels that could potentially damage wind turbine components. The low rate fan may be used at all times to maintain a minimum pressurization level in the wind turbine (e.g. an overpressure of 100 Pa).

When extra cooling is needed, the high rate fan may be activated and may supplement (or substitute the air flow of the low rate fan). The air flow generated by the high rate fan 101 may not necessarily be ducted to pass through the dehumidifier because humidity may not be a problem during overheating conditions. Also, it may be beneficial that the dehumidifier is not used in combination with the high rate fan, since a fan of lower performance may be used. In some embodiments, the dehumidifier 18 may not be comprised within the adjustable air intake 12. In some embodiments, the wind turbine may not comprise a dehumidifier, e.g. in implementations in dry environments.

The adjustable air intake in this case is depicted arranged within the tower. In some implementation, the air intake may be located elsewhere. In other implementations, a plurality of air intakes may be provided, e.g. one in the tower, and one in the nacelle.

The adjustable air exhaust 14 that may be arranged e.g. in the nacelle 13 of the wind turbine may comprise an overpressure damper which may open when a specific pressurization level is achieved.

The variable air flow generator that may be comprised within the air intake 12 may generate a variable air flow 16. Reference 15a represents the air exhaust through the adjustable air exhaust 14. Reference 15b represents the air exhaust through the housing joints of the wind turbine. Air exhaust through the housing joints may exist particularly at the joint of the tower with the nacelle (i.e. at the yaw system) and at the joint of the rotor (shaft) with the nacelle. The low rate fan 19 may provide an air flow 16 that is sufficient to maintain the pressurization level within the wind turbine above the minimum pressurization level required. The variable air flow 16 may be increased to protect the wind turbine 100 against overheating when cooling is needed by activating the high rate fan 101 . The adjustable air exhaust 14 may maintain the pressurization level within a reduced range of pressurization values. The overpressure damper that may be comprised in the adjustable air exhaust 14 may act as a "relief valve" that may remain closed until a certain pressure level is achieved. Once this certain pressure level is reached, the overpressure damper may open and thus prevent the housing pressure increase and so, maintain the pressurization level within a reduced range of pressurization values.

In some embodiments, the overpressure damper may be a non-return damper comprising a number of blades hingedly mounted in a frame. The opening of the damper may be automatic when a certain pressure is reached. The blades of the damper may be closed e.g. with a mechanism based on magnets. Once the pressure is sufficient to overcome the magnetic force keeping the blades closed, the damper may be opened.

In alternative embodiments, the mechanism keeping the blades closed until a certain minimum pressure may be based on the weight of the blades. Alternatively, the blades may be kept shut using springs. Also in these cases, whenever the pressure inside the turbine rises to a certain predetermined level, the air exhaust may automatically open. In these passive systems, no sensors and motor are needed. In general, this kind of passive system may be reliable.

In further embodiments, it may be possible to use sensors to measure the pressure within the wind turbine, in combination with a motor that opens the air exhaust when needed.

In yet further embodiments, a motor that is coupled to e.g. the high rate fan may be used. Whenever, cooling is needed, and the high rate fan is therefore activated, the motor may open the air exhaust to reduce the pressure level.

Figure 2, shows a chart 20 related to the air conditioning system for the wind turbine 100 according to an embodiment of the present invention described in Figure 1 . The chart 20 may represent pressurization level versus ventilation flow rate. The pressurization level values are shown along the vertical axis 21 and the ventilation flow rate values are shown along the horizontal axis 22.

A minimum pressurization level that may be required within a conventional wind turbine may be represented by the limit 28. This pressurization level should be regarded as the pressurization level needed to avoid excessive inward flow of dust etc. The required pressurization level may e.g be an overpressure of approximately 100 Pa. A minimum flow rate that may be required during potential heating conditions within the wind turbine may be represented by the limit 29.

The air conditioning system according to an embodiment of the present invention may comprise a low rate fan 19 and a high rate fan 101 which may provide a characteristic curve 24 and 23, respectively. In this case, the curve 23 represents the combination of both the low and the high rate fan. The low rate fan 19 may generate a low rate ventilation flow working at low speed. The high rate fan 101 may generate an additional high rate ventilation flow working at high speed.

This air conditioning system may comprise an air exhaust 14 which may comprise an overpressure damper in which an opening pressure may be adjusted. The overpressure damper may remain closed until a specific pressurization level 210 may be achieved. If and when this level 210 is surpassed, the overpressure damper may open in order to avoid the further rising of the pressurization level within the wind turbine 100. The characteristic curve 27 of a housing with adjustable air exhaust is shown in Figure 2. In the air conditioning system according to an embodiment of the present invention, the low rate fan 19 may be always activated maintaining a pressunzation level within the wind turbine above the minimum pressurization level required 28, i.e. the working point 25 which may be the intersection between the housing with adjustable exhaust characteristic curve 27 and the characteristic curve 24 of the low rate fan 19 working at reduced speed.

The high rate fan 101 may be only activated when cooling may be needed (heating conditions). Once the high rate fan 101 is activated, the overpressure damper of the adjustable air exhaust may be opened at specific pressurization level 210 due to the pressure generated by the fan working at high speed. In preferred embodiments, the adjustable air exhaust may open automatically when a certain pressurization level is reached.

In consequence, , the minimum flow rate 29 for cooling may be reached without a significant increase of the pressurization level, i.e. the working point 26 which may be the intersection between the housing with adjustable exhaust characteristic curve 27 and the characteristic curve 23 of the high rate fan 101 working at high speed.

In some embodiments, an adjustable rate fan may be used. The adjustable rate fan may work at reduced speed in order to generate a low rate ventilation flow which may increase the pressurization level within the wind turbine 100 above the minimum pressurization level required 28. When heating up of components is a potential problem, the adjustable rate fan may work at maximum speed in order to generate a high rate ventilation flow which may increase the ventilation flow rate within the wind turbine 100 above the minimum flow rate limit 29 required for avoiding overheating in the wind turbine 100.

Although only a number of particular embodiments and examples of the invention have been disclosed herein, it will be understood by those skilled in the art that other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof are possible. Furthermore, the present invention covers all possible combinations of the particular embodiments described. Thus, the scope of the present invention should not be limited by particular embodiments, but should be determined only by a fair reading of the claims that follow.