Patent Publication Number: US-10788239-B2

Title: Generator set louver system

Description:
TECHNICAL FIELD 
     The disclosure relates to generator set enclosure ventilation. 
     BACKGROUND 
     A generator set enclosure protects a generator set from environmental elements, such as precipitation, temperature extremes, and foreign object damage. The generator set enclosure may include one or more openings to allow flow of air to and from the generator set. For example, a generator set enclosure may include an inlet opening to enable the generator set to draw supply air from an environment outside the generator set enclosure and an outlet opening to enable the generator set to discharge hot exhaust air to the environment outside the generator set enclosure. 
     SUMMARY 
     In some examples, the disclosure describes a system that includes a generator set enclosure, a gravity-operated louver, and an actuator. The generator set enclosure is configured to house the generator set. The gravity-operated louver is positioned in a wall of the generator set enclosure. The actuator is configured to exert an opening force on the louver in an operational state of the actuator. The louver is configured to open and close independent of the opening force from the actuator in a failed state of the actuator. 
     In other examples, the disclosure describes a method that includes receiving, by a controller, an operational indication from a generator set and sending, by the controller and in response to receiving the operational indication, a control signal to an actuator. The actuator is mechanically coupled to a gravity-operated louver through a mechanical link and configured to exert an opening force on the louver in an operational state of the actuator. The gravity-operated louver is positioned in a wall of the generator set enclosure and configured to open and close independent of the opening force from the actuator in a failed state of the actuator. The generator set enclosure is configured to house a generator set. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a conceptual diagram illustrating a side view of an example generator set enclosure. 
         FIG. 1B  is a conceptual diagram illustrating a side view of an example louver system for discharging exhaust from a generator set enclosure. 
         FIG. 1C  is a conceptual diagram illustrating a front view of an example louver system for discharging exhaust from a generator set enclosure. 
         FIG. 2A  is a conceptual diagram illustrating a side view of an example slat of a louver system and various forces acting on the slat. 
         FIG. 2B  is an example graph illustrating a louver position versus a position of a linear actuator. 
         FIG. 2C  is an example graph illustrating a louver position versus a force of exhaust air. 
         FIG. 3  is a flow diagram illustrating an example technique for operating an example louver system for discharging exhaust from a generator set enclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In some examples, the disclosure describes louver systems configured for both gravity- and actuator-operation to discharge exhaust air from a generator set enclosure. Example louver systems include a gravity-operated louver positioned in a wall of the generator set enclosure and an actuator mechanically coupled to the louver through a mechanical link. The gravity-operated louver may be positioned in an intended intake or discharge path of supply or exhaust air to or from a generator set, such that received supply air to the generator set or discharged exhaust air from the generator set may at least partially overcome a gravitational force on the louver to open the louver. The actuator and mechanical link are configured to exert an opening force on the louver in a single direction. For example, the actuator may be a linear actuator and the mechanical link may be a slacked cable or chain that transmits a force from the actuator through tension, but not compression. 
     When the generator is not operating, the louver may remain shut due to the gravitational force on the louver. During operation of the generator, the actuator may apply a force, such as tension, compression, or torque, to the mechanical link to control an open position of the louver. For example, the actuator may open the louver to an extent greater than a louver only opened by a force of exhaust air from the generator set, as the force of exhaust air from the generator set may only partially open the louver. In the event of failure, the actuator may fail closed to create slack in the mechanical link. However, the louver may continue to open and close due to the force of the supply air to or exhaust air from the generator set. 
     In this way, the louver system may protect the generator set from elements when not operating, improve supply intake to and/or exhaust discharge from the generator set enclosure during actuator operation (e.g., improve a rate of discharge of exhaust air from the generator set enclosure) by reducing restrictions and/or pressure drop across the louvers, and continue to allow intake of supply air to or discharge of exhaust air from the generator set enclosure during actuator failure. As a result, example louver systems discussed herein may safely and efficiently intake supply air and/or discharge exhaust air from the generator set enclosure. For example, a generator set enclosure located in a hot climate may utilize louver systems discussed herein to operate with a higher cooling air throughput than louver systems solely operated by gravity, which may allow a generator set in the generator set enclosure to operate with correspondingly higher power ratings. 
       FIG. 1A  is a conceptual diagram illustrating a side view of system  10  that includes an example generator set enclosure and an exhaust louver system capable of both active operation from an actuator and passive operation from an exhaust system. While system  10  will be described with reference to a generator set enclosure, the principles of operation of system  10  may be used on a variety of systems in which a generator set is enclosed and requires adequate ventilation, such as an engine room. 
     System  10  includes a generator set enclosure  12  configured to house a generator set  16  in an enclosure space  14 . In some examples, enclosure  12  may be configured to shelter components of system  10  from exposure to external conditions. For example, enclosure  12  may include equipment or systems that protect components of system  10  from rain, low temperatures, and the like. In some examples, enclosure  12  may be configured to provide a controlled environment around components of system  10 . For example, enclosure  12  may provide enclosure space  14  around components of system  10  that may be controlled for ambient temperature, humidity, or other ambient conditions that may affect performance of an engine  20  and/or a generator  18  of a generator set  16 . Generator set enclosures that may be used include, but are not limited to, drop-over enclosures, power module enclosures, engine rooms, and the like. 
     System  10  includes generator set  16 . Generator set  16  may be configured to produce electrical power using a fuel source. Generator set  16  includes generator  18 , engine  20 , an exhaust system  22 , and a controller  32 . Generator set  16  may include other components not shown, such as a starter system, liquid cooling system, and other accessory systems. 
     Generator  18  may be mechanically coupled to engine  20 , such as through a mechanical shaft or any other mechanical link configured to transfer mechanical energy from engine  20  to generator  18 . Generator  18  may be configured to convert mechanical energy to electrical energy. Generator  18  may include any generator capable of converting the mechanical energy to electrical energy, such as an alternator. Generator  18  may be electrically coupled to an electrical distribution system (not shown in  FIG. 1A ) and configured to supply electrical power to the electrical distribution system. In some examples, the electrical distribution system may include one or more connections to an electrical grid, such that generator  18  may provide an alternative electrical power supply. In other examples, the electrical distribution system may be an islanded distribution system that may be isolated from any other electrical grid, such that generator  18  may be an on-demand power supply. 
     Engine  20  may be configured generate mechanical energy from a fuel source and transfer the mechanical energy to generator  18  for conversion into electrical power. Engine  20  may include any engine capable of generating mechanical energy from a fuel source, such as a diesel engine. Engine  20  may be fluidically coupled to the fuel source (not shown). For example, engine  20  may be fluidically coupled to a diesel fuel source, a gasoline fuel source, a biofuel fuel source, or any other fuel source that may provide fuel to engine  20 . 
     Exhaust system  22  may be configured to discharge exhaust air from enclosure space  14 . Exhaust system  22  may control flow of cooling air that removes radiant heat from components of generator set  16 , such as engine  20  and generator  18 , such as by controlling cooling or exhaust fans. For example, a temperature within enclosure space  14  may be limited to due to safety concerns, equipment temperature limits (e.g., reduced ratings for generator  18  above 40° C.), and the like. In some examples, exhaust system  22  may be part of a ventilation system for enclosure  12 , such as a system that provides both combustion air for engine  20  and cooling air for generator set  16 . In some examples, exhaust system  22  may be a stand-alone system for cooling engine  20  and/or generator  18 , such as an engine-mounted radiator or remote radiator. Exhaust system  22  may include a variety of types of equipment configured to discharge air from enclosure space  14  including, but not limited to, engine-mounted exhaust fans, free-standing exhaust fans, wall-mounted exhaust fans, engine cooling fans (e.g., engine fans that draw air across components of engine  20  and/or generator  18  for cooling), and the like. In some examples, exhaust system  22  may include components configured to remove heat from components of generator set  16  to enclosure space  14  prior to discharge of the air from enclosure space  14 , such as radiators or heat exchangers. 
     In some examples, exhaust system  22  may be positioned proximal to at least one of exhaust louver  26 A or intake louver  26 B (generically referred to as “louver  26 ” and collectively referred to as “louvers  26 ”), such as within five feet of one of louvers  26 . Exhaust system  22  may be configured to exert an opening force one or both of louvers  26 , as will be explained further in  FIG. 2A  below. For example, exhaust system  22  may be configured to supply a force of exhaust air (e.g., a flow rate of exhaust air, a pressure of exhaust air, etc.) that is sufficient to at least partially open one or both of louvers  26  upon failure of a respective one of exhaust actuator  28 A or intake actuator  28 B (generically referred to as “actuator  28 ” and collectively referred to as “actuators  28 ”) such that generator set  16  may continue operation. 
     Controller  32  may be communicatively coupled to and configured to control components of system  10 . For example, controller  32  may be configured to manage operation of components of system  10  based on operational inputs for system  10 . Operational inputs of system  10  may include, but are not limited to: temperature setpoints, such as for ambient air of enclosure  12 ; pressure setpoints, such as for pressure ambient air of enclosure  12 ; startup sequence and timing of engine  20  and generator  18 ; and the like. While not shown, system  10  may include a variety of sensors, such as pressure sensors (e.g., pressure differential sensors for maintaining a positive or negative pressure in enclosure  12 ), temperature sensors, carbon monoxide sensors, and the like. Controller  32  may include any one or more of a wide range of devices, including processors (e.g., one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), or the like), one or more servers, one or more desktop computers, one or more notebook (i.e., laptop) computers, one or more cloud computing clusters, or the like. 
     In some examples, controller  32  may be configured to control exhaust system  22 . For example, controller  32  may be configured to receive an ambient temperature of enclosure space  14  from a temperature sensor, a pressure of enclosure space  14  from a pressure sensor, a power level from generator set  16 , and other feedback related to cooling of components of generator set  16 . Controller  32  may be configured to control exhaust system  22  to adequately cool components of generator set  16 . For example, controller  32  may control a flow rate of exhaust system  22 , such as a power of exhaust fans of exhaust system  22 , to control the ambient temperature below a maximum temperature setpoint, a pressure above a minimum pressure setpoint, a flow rate of exhaust air above a flow rate setpoint, and the like, for a limit, rating, or power level of generator set  16 . For example, generator set  16  or enclosure  12  may have absolute temperature limits or conditional (e.g., power level of generator set  16 ) flow rate schedules or ratings for various power levels. 
     In addition to exhaust system  22 , system  10  includes structural components to enable air to be supplied to and discharged from enclosure space  14 . For example, while shown in  FIG. 1A  as a gravity-operated louvers, in some examples, one of louvers  26  may be a fixed damper. For example, intake louver  26 B may be configured as an intake damper to allow air into enclosure  12 , such as combustion air for engine  20  or cooling air for generator set  16 . Intake louver  26 B may be fixed so that combustion and/or cooling air is continuously and safely provided to enclosure space  14 . However, in other examples, unfixed (movable) dampers or louvers may be used. 
     System  10  includes at least one gravity-operated louver  26  positioned in a wall of generator set enclosure  12 . Gravity-operated louver  26  may be configured to receive a closing force due to gravity. For example, as will be explained further in  FIG. 1B  below, gravity-operated louver  26  may be configured to translate a vertical or substantially vertical gravitational force into a closing force and translate a horizontal or substantially horizontal force of supply or exhaust air into an opening force. As such, in the absence of other forces on louver  26 , louver  26  may operate (i.e., open and close) based on a change in a difference between a relatively constant gravitational force and a varying force from discharge of exhaust air from or intake of supply air to enclosure  12  by exhaust system  22 . 
     Louver  26  may be designed for a variety of safety and operational conditions of enclosure  12  and/or generator set  16  including, but not limited to, a static restriction, a flow rate, a minimum operating position, an operating position schedule, and other conditions related to exhaust air discharge from and/or supply air intake to enclosure  12 . In some examples, louver  26  may be configured to open less than about 75% at full exhaust from generator set  16  without an opening force from actuator  28 . For example, louver  26  may be designed (e.g., by selecting weight, pivot position, etc.) to remain closed during strong winds. As a result of these design factors, louver  26  may only partially open from discharge of exhaust air or intake of supply air without an opening force from actuator  28 . In some examples, louver  26  may be configured to open greater than about 25% at full exhaust from generator set  16  without an opening force from actuator  28 . For example, louver  26  may be designed for a minimum amount of discharge air or discharge pressure from enclosure  12  that corresponds to, for example, 25% position. Exhaust fans from exhaust system  22  may experience a static pressure due to restriction caused by louver  26 , so that more closed positions may create additional restrictions on the exhaust fans. As such, louver  26  may be designed such that louver  26  has a position greater than, for example, 25% so as to reduce a restriction on the exhaust fans while operating. A position of louver  26  may be represented by, for example, an angle of slats of louver  26  from a wall of enclosure  12 , an open area of louver  26  as a percentage of total area, a static restriction pressure measurement of louver  26 , or any other measure related to a state of louver  26  that correlates to a rate of discharge of exhaust air or intake of supply air for a particular force from exhaust air. 
     System  10  includes an actuator  28  mechanically coupled to each louver  26  through a respective mechanical link  30 A or  30 B (generically referred to as “mechanical link  30 ” and collectively referred to as “mechanical links  30 ”). When in an operational state, actuator  28  may be configured to exert an opening force on louver  26 . When in a failed state, actuator  28  may not exert an opening force on louver  26 , such that louver  26  may be configured to open and close independent of the opening force from the actuator in a failed state of the actuator. For example, each of actuators  28  is configured to open a respective louver  26  by exerting an opening force on louver  26  in a first direction and fail closed in a second direction, opposite the first direction. For example, actuator  28  may be configured to exert an opening force on louver  26  in the first direction that substantially opposes a gravitational force on louver  26 . If actuator  28  fails to a failed state (i.e., loses power, loses a control signal, malfunctions, mechanically fails, etc.), actuator  28  may fail closed in a direction opposite the first direction of the opening force. For example, actuator  28  may include various components, such as solenoid valves, springs, pressure relief valves, and the like, that are configured to place actuator  28 , upon failure, in a position that corresponds to a closed, or more closed, position of louver  26 . 
     In some examples, actuator  28  includes a linear actuator. For example, a linear actuator may include a contracted piston position that corresponds to an open position of the linear actuator, and thus an open position of louver  26  or vice versa, an expanded piston position that corresponds to a closed position of the linear actuator, and thus a closed position of louver  26  or vice versa, and various gradations between the contracted and expanded piston positions that correspond to partially open positions of the linear actuator, and thus various partially open positions of louver  26 . A spring or pressure bladder within a piston of the linear actuator may provide a closing force such that, if power is lost to the linear actuator, the piston fails to the closed position of the linear actuator, and thus the closed position of louver  26 . 
     In some examples, actuator  28  includes an electromechanical actuator. For example, an electromechanical actuator may be powered by an electrical source and configured to translate electrical power into mechanical energy to operate louver  26 . In some examples, the electromechanical actuator may be configured to receive electrical power from electrical energy produced by generator  18 , such as direct current (DC) power. For example, once generator set  16  is producing electrical power, actuator  28  may receive a portion of the electrical power. In some examples, actuator  28  may be configured to automatically actuate in response to receiving electrical power from generator set  16 . For example, to ensure intake of supply air and/or discharge of exhaust air while generator set  16  is operating, one or both of actuators  28  may be configured to automatically open louvers  28  upon start-up of generator set  16 , with minimal or no control from controller  32 . In this way, control of louvers  26  may be simplified compared to systems that use control logic to operate louvers. 
     In some examples, actuator  28  includes a hydraulic actuator. For example, a hydraulic actuator may be powered by a pressure source and configured to translate the pressure source into mechanical energy to operate louver  26 . In some examples, the hydraulic actuator is coupled to a hydraulic circuit of generator set  16  and configured to receive hydraulic power (i.e., hydraulic fluid at pressure) from the hydraulic circuit. For example, once engine  20  has started up, actuator  28  may receive a portion of the hydraulic power. In some examples, actuator  28  may be configured to automatically actuate in response to receiving hydraulic power from generator set  16 . For example, to ensure intake of supply air and/or discharge of exhaust air while generator set  16  is operating, one or both of actuators  28  may be configured to automatically open louvers  28  upon startup of engine  20 , with minimal or no control from controller  32 . In this way, control of louvers  26  may be simplified compared to systems that use control logic to operate louvers. 
     In some examples, mechanical link  30  is a slacked, or flexible, mechanical link configured to transmit an opening force from actuator  28  in the first direction through tension. For example, a solid mechanical link, such as a rod, may enable actuator  28  to transmit an opening force from actuator  28  in the first direction, but may continue to exert a closing force from actuator  28  in the second direction, opposite the first direction, through compression. As a result, such solid mechanical links may not enable louver  26  to continue to operate in the event of failure of actuator  28 . By using a slacked or flexible mechanical link for mechanical link  30 , system  10  may allow gravity-operated louver  26  to continue to operate in response to gravitational forces and/or forces from exhaust air or supply air in the event of actuator  28  failing open in the second direction (and the louvers failing closed but still responsive to gravity and air pressure). In some examples, mechanical link  30  includes at least one of a wire, string, ribbon, belt, cable, a chain, or the like. 
     In some examples, actuator  28  is positioned away from louver  26 . For example, exhaust system  22  may be located close to louver  26 A, such that exhaust air discharged from exhaust system  22  may discharge more directly through louver  26 A and/or create a greater force on louver  26 A. However, such close placement limit access to components near louver  26 A may interfere with access to louver  26 A for servicing. To enable easier access to actuator  28  for servicing and/or remove actuator  28  from interfering with passage through enclosure  12 , actuator  28  may be located away from louver  26 . In some examples, actuator  28  may be positioned greater than about one foot from louver  26 . For example, louver  26  may be positioned between about one foot and about five feet from the floor of enclosure  12 , such that placement of actuator  28  greater than about one foot from louver  26  may remove actuator  28  from interfering with working space within enclosure space  14 , reduce an exposure of actuator  28  to heated exhaust air, allow closer placement of exhaust system  22  to louver  26  while maintaining access to louver  26  for servicing, and/or allow a lower profile for louver  26 . In some examples, actuator  28  may be positioned on at least one of a ceiling or a wall of generator set enclosure  12 . For example, an upper volume of enclosure space  14  that may not be used for components of generator set  16  may be used to house actuator  28 , thereby more efficiently utilizing enclosure space  14 , allowing electronics (e.g., controller  34  and/or actuator  28 ) of system  10  to be in enclosure  12 , and/or allowing easier access to actuator  28 , such as for maintenance. 
     In some examples, controller  32  may be communicatively coupled to actuator  28  and generator set  16 . For example, controller  32  may be configured to receive an operational indication from generator set  16  and send, in response to receiving the operational indication, a control signal to actuator  28 . For example, the operational indication may include at least one of a start-up of the generator set or exceeding a power threshold of the generator set. In some examples, controller  32  may send a control signal to actuator  28  prior to start-up of generator set  16 . For example, controller  32  may be configured to send a control signal to actuator  28  as part of a start-up sequence. In other examples, controller  32  may send a control signal to actuator  28  after start-up of generator set  16 . For example, actuator  28  may be configured to receive power from generator  18  once generator  18  is producing power. Further operation of controller  32  will be described in  FIG. 3  below. In some examples, as explained above, actuators  28  may automatically actuate upon receiving power from generator set  16 , such as electrical power or hydraulic power, such that controller  32  may not control actuators  28 . 
       FIG. 1B  is a conceptual diagram illustrating a side view of louver  26  for discharging exhaust air from or receiving supply air to generator set enclosure  12 , while  FIG. 1C  is a conceptual diagram illustrating a front view of louver  26  for discharging exhaust from or receiving supply air to generator set enclosure  12 . 
     Louver  26  includes a plurality of moveable slats  36 . The plurality of moveable slats  36  may be configured to receive an opening force from either of actuator  28  or an exhaust from or supply to generator set  16 , such as exhaust system  22 . For example, while actuator  28  is in an operational state and generator set  16  is in an operational state, both actuator  28  and exhaust from or supply to generator set  16  may exert opening forces on louver  26 . The plurality of moveable slats  36  may also be configured to receive a closing force from gravity. For example, while actuator  28  is in a failed state and generator set  16  is in an operation state, exhaust from or supply to generator  16  may exert an opening force on louver  26  and gravity may exert a closing force on louver  26 . As such, the plurality of moveable slats  36  may be configured to open and close based on a change in opening and closing forces on the plurality of moveable slats  36  due to gravity, exhaust/supply flow, and/or actuator  28 . 
     Louver  26  includes a frame  34 . In some examples, frame  34  is part of a wall of enclosure  12 , while in other examples, frame  34  is a stand-alone structure fitted into a wall of enclosure  12 . Each moveable slat of the plurality of moveable slats  36  includes one or more pivots  38  for enabling each respective moveable slat to move relative to frame  34 . In the example of  FIG. 1B , each pivot  38  may include an extension that fits into a pocket or other recess of frame  34 ; however, in other examples, other mechanisms and configurations may be used. Each pivot  38  may be positioned relative to a center of mass such that the respective moveable slat may open in response to a horizontal exhaust air force and close in response to a vertical gravitational force, as will be explained further in  FIGS. 2A-2C  below. 
     The plurality of moveable slats  36  may be configured to operate across a range of louver positions. In some examples, each slat of the plurality of moveable slats  36  is configured to be fully open at an angle greater than about 80 degrees from the wall of generator set enclosure  12  and fully closed at an angle less than about 10 degrees from the wall of generator set enclosure  12 , and positioned at an intermediate angle in response to the balance of opening and closing forces described above. 
     Louver  26  includes an operating member  40  coupled to the plurality of moveable slats  36  and mechanical link  30 . Operating member  40  may be configured to exert the opening force from actuator  28  on the plurality of moveable slats  36 . For example, operating member  40  may be configured to rotate the plurality of moveable slats  36  around the respective pivots  38  to open louver  26 . While operating member  40  is illustrated as a rod, in other examples, operating member  40  may include any mechanical mechanism that is capable of rotating the plurality of slats  36  to open louver  26  in response to an opening force exerted on operating member  40  by mechanical link  30 . 
     As explained above, louver systems described herein may operate using opening forces provided by an actuator and an exhaust/supply flow and closing forces provided by gravity.  FIG. 2A  is a conceptual diagram illustrating a side view of an example slat  36  of a louver system and various forces acting on the slat. For example, the louver system may include louver  26 , actuator  28 , and mechanical link  30  of  FIGS. 1A-C . Slat  36  includes a center of mass  42  and is configured to rotate around pivot  38  in response to a change in a difference of opening and closing forces. Slat  36  may be configured to open through a range of louver positions from 0% (i.e., substantially closed) to 100% (i.e., substantially open). 
     Each slat  26  experiences a closing force from gravity (Fgravity). For example, the closing force from gravity may exert a downward force on center of mass  42 , causing slat  36  to rotate around pivot  38  counter-clockwise from the perspective of  FIG. 2A . This gravitational force may be dependent on a variety of factors including, but not limited to, a weight of slat  36  or other components coupled to slat  36 , a position of pivot  38 , and the like. As slat  36  rotates around pivot  38 , slat  36  may change a position of slat  36 . In the example of  FIG. 2A , a position of slat  36  is represented as an angle  48  of slat  36  between a plane  46  of slat  36  and a plane  44  of a wall of frame  34 , enclosure  12 , or any other structure in which louver  26  is positioned. However, in other examples, a position of slat  36  may be represented by another measure of a degree of openness of slat  36  within louver  26 . As slat  36  rotates around pivot  38  to increase an open position of slat  36  (e.g., increase angle  48 ), a distance between center of mass  42  and pivot  38  may increase, thereby increasing the gravitational force on slat  36 . 
     Each slat  26  may be configured to receive an opening force from an actuator  28  (F actuator ). This opening force may be in a direction substantially opposite the direction of the gravitational force. For example, the opening force from the actuator  28  may exert an upward force on center of mass  42 , causing slat  36  to rotate around pivot  38  clockwise from the perspective of  FIG. 2A . The opening force from actuator  28  may correspond to a desired position of louver  26 . For example, actuator  28  may be a liner actuator that exerts an amount of force required to move actuator  28  to a predetermined position that corresponds to the desired position of slat  36 . 
     Each slat  36  may be configured to receive an opening force from exhaust or supply air F exhaust/supply  from or to a generator set. The opening force from exhaust or supply air may correspond to a flow rate of exhaust air from exhaust system  22  out of or into enclosure  12 . For example, as a power level of generator set  16  increases or an ambient temperature of enclosure  12  increases, controller  32  may control exhaust system  22  to increase a flow rate of exhaust air from enclosure  12 . 
       FIG. 2B  is an example graph illustrating a louver position versus a position of a linear actuator as actuator  28 . In the example of  FIG. 2B , exhaust system  22  is not providing any opening force on slat  36  due to exhaust/supply flow, such that a louver position is linearly proportional to an actuator position through a range of the louver positions. During an operational state of actuator  28 , at least a portion of a range of the louver position may be controlled by actuator  28 , such that louver  26  may operate with less restriction than a louver that is not operated by an actuator. 
       FIG. 2C  is an example graph illustrating a louver position versus a force of exhaust/supply air from exhaust system  22 . In the example of  FIG. 2C , actuator  28  is not providing any operating force, such that a force of exhaust air from exhaust system  22  on louver  26  is equal to a gravitational force on louver  26 . As shown in  FIG. 2B , as louver position increases, a greater amount of force of exhaust air is required to open the louver due to a greater amount of gravitational force from a change in position of center of mass  42  of slat  36  relative to pivot  38 . As such, a range of louver positions may be restricted. 
     During an operational state of the linear actuator, at least a range of the louver position (opening and closing) may be controlled using the linear actuator. For example, if a low louver position (e.g., less than about 25% open) is desired, a force of exhaust air from an exhaust system may be capable of achieving the low louver position, as shown in  FIG. 2C , such that the linear actuator may not be operated. However, if a high louver position (e.g., greater than about 50% open) is desired, a force of exhaust air from exhaust system  22  may not be capable of achieving the high louver position due to the higher amount of force required to counteract gravity. As such, actuator  28  may be operated such that a position of actuator  28  corresponds to the high louver position. As a result, a higher louver position may be achieved than with a louver that is solely gravity and exhaust flow operated. Such higher louver position may reduce a restriction to a cooling or exhaust fan by mechanically holding the louvers open, enabling exhaust system  22  to discharge a higher rate of exhaust or supply air than a louver system with a lower maximum louver position, thereby increasing airflow for better cooling package performance. 
     Upon failure of actuator  28  to a failed state, actuator  28  may fail closed, such the louver fails closed but slats  36  are free to move under the force of the exhaust or supply air from exhaust system  22  and gravity without assistance from the linear actuator, as shown in  FIG. 2C . While the range of louver position may be reduced compared to operation using the linear actuator, louver  26  may continue to operate, such that generator set  16  may maintain continuity of operation even in the event that actuator  28  fails. 
     While the louver systems have been described with respect to  FIGS. 1A-1C  and  FIGS. 2A-2C , other joint gravity- and actuator-operated louver systems operating within the principles of the disclosure may be used. For example, a rotary actuator may be used instead of a linear actuator, such that the actuator position with respect to louver position may not be linear, as shown in  FIG. 2B . 
     In some examples, louver systems discussed herein may have be capable of selecting active and passive operation based on operating conditions of generator set  16 .  FIG. 3  is a flow diagram illustrating an example technique for operating an example louver system for discharging exhaust from a generator set enclosure based on a power level of the generator set. The example technique of  FIG. 3  will be described with respect to system  10  of  FIGS. 1A-1C . However, the techniques of  FIG. 3  may be used with other systems and components. Additionally, the techniques of  FIG. 3  are described with respect to a power level of generator set  16 , but other variables related to cooling air, such as ambient temperature within enclosure  12  or pressure within enclosure  12 , and their corresponding setpoints, may be used as control variables for switching between active and passive operation of louver systems. 
     Controller  32  may receive a power level from generator set  16  ( 50 ). For example, controller  32  may receive a shaft speed of engine  20  corresponding to a power level of generator set  16 . As another example, controller  32  may receive the power level from generator set  16  by determining the power level of generator set  16 , such as from a control signal selected by an operator of generator set  16 . 
     Controller  32  may evaluate whether the power level is above a threshold ( 52 ). In some examples, the power level may be a power level indicating a start-up of generator set  16 . For example, controller  32  may be configured to control one or both of actuators  28  to at least partially open when generator set  16  is operating. In some examples, controller  32  may be configured to operate actuator  28  such that louver  26  is fully open when generator set  16  is operating. In some examples, the power level may be a power level that corresponds to increased cooling from exhaust system  22 . For example, as explained previously with respect to  FIGS. 2B and 2C , for low power levels, system  10  may be capable of adequately discharging exhaust air using only gravity-operation of louver  26 . As such, the threshold may correspond to a power level at which controller  32  may begin actuator-operation of louver  26 . Alternatively, rather than using a power level, controller  32  may use another threshold, such as a temperature threshold or pressure threshold, for a different operational indication. 
     Controller  32  may send, in response to determining that the power level exceeds the threshold, a control signal to actuator  28  ( 54 ). In some examples, the control signal is directly proportional to a power level of generator set  16 . 
     The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit including hardware may also perform one or more of the techniques of this disclosure. 
     Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various techniques described in this disclosure. In addition, any of the described units, modules or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware, firmware, or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware, firmware, or software components, or integrated within common or separate hardware, firmware, or software components. 
     The techniques described in this disclosure may also be embodied or encoded in an article of manufacture including a computer-readable storage medium encoded with instructions. Instructions embedded or encoded in an article of manufacture including a computer-readable storage medium, may cause one or more programmable processors, or other processors, to implement one or more of the techniques described herein, such as when instructions included or encoded in the computer-readable storage medium are executed by the one or more processors. Computer readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a compact disc ROM (CD-ROM), a floppy disk, a cassette, magnetic media, optical media, or other computer readable media. In some examples, an article of manufacture may include one or more computer-readable storage media. 
     In some examples, a computer-readable storage medium may include a non-transitory medium. The term “non-transitory” may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in RAM or cache). 
     Various examples have been described. These and other examples are within the scope of the following claims.