Abstract:
A refrigerant system is provided with a variable speed drive for at least one of its fluid-moving devices, wherein the variable speed drive is provided by an automated mechanical drive. In the disclosed embodiment, one of the pulleys for driving the fluid-moving device has a variable diameter to vary the speed at which the fluid-moving device is driven. The pulley may include two plates that are biased in one direction by a spring or permanent magnet force, and in an opposed direction by a hydraulic or electromagnetic force. A control adjusts the amount of hydraulic or electromagnetic force delivered to the plates to achieve a desired speed for the fluid-moving device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application relates to a variable speed drive provided for a fluid-moving device such as a fan operated within a refrigerant system, wherein the variable speed is achieved by an automated mechanical control for the fan drive.  
         [0002]     Refrigerant systems are utilized in many applications to condition an environment. In particular, air conditioners and heat pumps are employed to cool and/or heat a secondary fluid such as air entering an environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and as the temperature and/or humidity set points are adjusted by an occupant of the environment.  
         [0003]     It would be desirable to have a variable speed control for fluid-moving devices, such as the fans moving air over indoor and outdoor heat exchangers. As an example, a fan speed change may be desirable when there is a change in the compressor speed or mode of operation. As known, the compressor speed may need to be adjusted to accommodate internal and external thermal load demands. Further, to have an ability to operate in various modes, a refrigerant system may be provided with an economizer cycle, and a compressor may be equipped with an unloading function. When the compressor is run unloaded or economized, it may be desirable to change the fan speed accordingly to maintain operational parameters, such as temperature and humidity, within the environment to be conditioned. Additionally, the fan speed may be required to be adjusted with a change in occupancy level or to maintain desired sensible heat ratios to provide a certain level of comfort for an occupant of the environment. Also, it may be desirable to decrease the fan speed to improve the system efficiency by minimizing fan power draw.  
         [0004]     In another example, it may also be desirable to adjust the fan speed in response to changes of ambient conditions or variations in cooling requirements. For instance, to provide safe and reliable refrigerant system operation a condenser fan speed may be increased at high ambient temperatures to reduce discharge pressure (an opposite functionality may be required at low ambient temperatures), or an evaporator fan speed may need to be raised to prevent coil frosting.  
         [0005]     In the past, if variable speed fan operation was desired, a variable frequency drive needed to be provided. However, variable speed drives are expensive, and are challenging to integrate with conventional system controls. Also, variable speed drives carry additional efficiency losses and reliability issues for a refrigerant system.  
         [0006]     In the past, to vary the fan speed, mechanical drives for the fans have been adjusted manually. As an example, such fans are typically driven by a mechanical pulley, and a mechanic would manually adjust the setting on the pulley to set the fan speed. However, such technology does not change the fan speed on the fly, and has typically been performed only at initial set-up/installation. Thus, this option does not allow a fan speed change in response to constantly changing operating conditions and cooling demands.  
         [0007]     Thus, there is a need exists for automated mechanical variable speed drive for air moving devices provided within a refrigerant system.  
       SUMMARY OF THE INVENTION  
       [0008]     In a disclosed embodiment of this invention, a drive for a fan incorporates an automated variable diameter pulley system. In a disclosed embodiment, two plates of a conical shape (two adjustable pulley halves) driven by a belt (or to drive a belt) are movable toward and away from each other to vary the diameter of the contact surface between the belt and the plates. As this diameter varies, the speed at which the fan will be operated will also vary.  
         [0009]     In a disclosed embodiment, a hydraulic fluid may be injected into chambers associated with the pulley plates to drive these plates toward and away from each other. A spring biases the plates in opposition to the force exerted hydraulic fluid.  
         [0010]     In another embodiment, an electric current may be provided to the electric coil to create an electromagnetic force to drive the pulley plates toward and away from each other.  
         [0011]     In still another embodiment, a permanent magnet may be used to replace the spring.  
         [0012]     The present invention may also be utilized in refrigerant systems incorporating an unloader function, an economizer function, and other optional controls and features. The fan speed may be varied dependent upon whether these functions are actuated. Also, a desired fan speed may change based upon the thermal load or system operating conditions, such as the condenser or evaporator refrigerant pressures. A worker in this art would recognize when a fan speed should change. The present invention provides a simple way to change the fan speed.  
         [0013]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic view of a refrigerant system incorporating the present invention.  
         [0015]      FIG. 2  is a view of an adjustable pulley according to the present invention.  
         [0016]      FIG. 3A  shows another feature of the present invention.  
         [0017]      FIG. 3B  shows another optional embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     A refrigerant system  20  is illustrated in  FIG. 1  and incorporates a compressor  22  for compressing a refrigerant and delivering it to a downstream condenser or in this case an outdoor heat exchanger  24 . A fan  26  blows air over the heat exchanger  24  and is associated with a motor drive  28 . Also, an optional economizer circuit is illustrated in  FIG. 1 . Downstream of the outdoor heat exchanger  24  is an economizer heat exchanger  100 . As is known, the refrigerant is tapped through a tap line  102 , past an economizer expansion device  103 , and exchanges heat with the main flow of refrigerant in the economizer heat exchanger  100 . The tapped refrigerant is typically returned as a vapor through an economizer line  104  to an intermediate compression point in the compressor  22 .  
         [0019]     Downstream of the economizer heat exchanger  100  is a main expansion device  30 , and downstream of the main expansion device  30  is an evaporator or in this case an indoor heat exchanger  32 . A fan  34  is provided with a motor drive  36  and blows air over the evaporator  32 . A system control  38  controls the speed of the fan motor drive  36 , as will be explained below. Similar control  38  may also be associated with the fan motor drive  28  (not shown) but in reality it would be used less frequently than the control  38 . The controls  38  may communicate to, or be integrated with, a refrigerant system control  18 . The system control  38  can also control other components within the refrigerant system  20 .  
         [0020]     A suction line  110  returns refrigerant to the compressor  22  from the evaporator  32 . A bypass line  106  allows at least a portion of partially compressed refrigerant to be selectively bypassed from the compressor  22  back to the suction line  110 . An unloader valve  108  opens or closes this bypass line. Of course, the single compressor  22  can be replaced with two compressor stages and the unloader function can bypass refrigerant from a point intermediate the two stages.  
         [0021]     As shown in  FIG. 2A , the drive  36  may include an automated adjustable pulley  39  having two opposed plates  40 , typically of a conical shape. As shown, plates  40  have internal conical surfaces  41  that together provide a contact surface for a pulley belt  42 . The pulley belt  42  is driven by another pulley connected to a motor, as explained below, and in turn drives the plates  40  to rotate fan  26  or  34 . Analogously, an adjustable pulley can be located on drive side connected to a motor.  
         [0022]     A center core  46  carries springs  48  that bias the plates  40  away from each other. Chambers  50  selectively receive hydraulic fluid from a pump and reservoir  52  to force the plates  40  back toward each other. A control  38  controls the flow of hydraulic fluid to the cambers  50  that in turn controls the position of the plates. By adjusting the position of the plates toward and away from each other, and as is clearly shown between  FIGS. 2A and 2B , the pulley belt may move between an outer position  142  ( FIG. 2A ), and toward an inner position  44  ( FIG. 2B ). At the inner position  44 , the fan will be operated at a lower speed than when the pulley belt is at its outer position  142 . Thus, by controlling the position of the plates  40 , the control  38  can achieve variable fan speeds. Obviously enough, the spring force and the hydraulic force acting on the pulley plates  40  may reverse directions (and still oppose each other), such that the hydraulic force is pushing pulley plates  40  away from each other and the spring force pulls them together. Further, as shown in  FIG. 2C , the mechanical spring  48  can be replaced by a permanent magnet  48 M and hydraulic system  50 - 52  can be replaced by an electro-magnetic system  150 , providing identical operational functionality. As an example, electromagnetic coils  150  can be energized or de-energized to move the plates  40  closer or away from each other. Moreover, if the adjustable pulley were located on a drive (motor) end then the inner position  44  would be associated with a higher fan speed than the outer position  142 .  
         [0023]      FIGS. 3A and 3B  show that an electric motor drives a first pulley  60 , which drives the second pulley  39  through the belt  42 . An adjustable tension member  62  includes a wheel  64  that is adjustable to ensure that tension remains adequate for proper operation of the belt  42  as the belt moves between the positions  142  and  44 . It should be understood that an infinite number of positions can be achieved for the belt  42 , and thus an infinite number of speeds can be provided. The adjustable tension member may be also driven by the pump and reservoir  52 . Obviously, other known belt tension mechanisms (such as an adjustable screw type mechanism, for instance) can be utilized as well.  
         [0024]     The adjustment for the pulley  39  is shown schematically in this application. However, automated pulley drive systems are well known. A worker of ordinary skill in the art, given the teachings of this application, would be able to provide a suitable drive system.  
         [0025]     Also, while  FIG. 1  shows the flow of refrigerant from compressor  22  to the outdoor heat exchanger  24  operating as a condenser, this application would also extend to flow in the opposite direction, at which the indoor heat exchanger  32  is operating as a condenser to heat air delivered by fan  34  into an environment to be conditioned.  
         [0026]     A control  18  for the refrigerant system  20  determines a desired fan speed, and adjusts the position of the plates to achieve that desired fan speed. A worker of ordinary skill in the art would recognize when and how a desired fan speed change would be determined.  
         [0027]     As shown in  FIG. 1 , appropriately positioned pressure transducers P or temperature sensors T can provide feedback on the conditions in the indoor and outdoor environment and operating parameters within the refrigerant system  20 . Any of these characteristics or a combination of them can be utilized to determine a desired fan speed. Again, a worker of ordinary skill in the art would recognize what a desired fan speed would be. The present invention is directed to provide a cost-effective way for a variable speed fan functionality to satisfy a wide spectrum of applications and operating conditions as well as ensure safe and reliable refrigerant system operation.  
         [0028]     It is understood that the present invention may equally benefit belt-driven applications outside of the air conditioning, heating, ventilation and refrigeration field. Also, it is understood that although the present invention was explained in relation to the fans blowing air across the heat exchangers, it can be equally applied to belt-driven pumps utilized in chiller applications for pumping secondary loop liquid through these heat exchangers. Further, the present invention can be used with an open drive belt-driven compressors.  
         [0029]     A worker of ordinary skill in the art would understand that various modifications of the disclosed embodiment would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.