Abstract:
A diagnostic method for testing a fan or pump assembly in a refrigerant system includes steps of operating a controller to periodically shut down, or reduce fan or pump speed for a short period of time, while continuing to operate the refrigerant system. Changes in an operating condition such as pressure, temperature, electric current or operating speed are monitored. If expected changes do not occur, a determination can be made that a fan or pump assembly is malfunctioning.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a method and control for identifying a malfunctioning fan or pump, or an associated malfunctioning drive for the fan or pump in a refrigerant system. 
         [0002]    Refrigerant systems are known, and are utilized in various air conditioning and refrigeration applications for heating, cooling, humidifying and dehumidifying a secondary fluid such as air. Typically, fans drive this air, over a pair of heat exchangers in an air-coupled refrigerant system. Analogously, pumps move water or brine through the water-to-refrigerant or brine-to-refrigerant heat exchangers in a water-coupled or brine-coupled refrigerant system. Hereafter, the references in the text will be made with respect to the fans of the refrigerant systems, with the understanding that similar conclusions can be devised regarding the pumps for secondary fluids. That is, a “fluid moving device” as used in this application refers to a fan or a pump. 
         [0003]    As known, a compressor typically compresses a refrigerant and delivers that refrigerant to a condenser. A fan drives a secondary fluid, which is typically air, over the condenser. Generally, in a conventional air conditioning system, the condenser is located outdoors. 
         [0004]    Refrigerant from the condenser is delivered to an expansion device, and then to an evaporator. Another fan drives the secondary fluid, which is once again typically air, over the evaporator. This air is usually directed into an environment to be conditioned. 
         [0005]    The refrigerant is returned from the evaporator to the compressor in a closed-loop manner. Other optional components and features are often included in the refrigerant system schematic but are not required for understanding the proposed concepts. 
         [0006]    If a fan or its associated motor or drive should malfunction, then the proper amount of the secondary fluid is not driven over the condenser or evaporator. If this occurs, there can be significant damage to other system components, and in particular, to the compressor. Also, the refrigerant system will no longer deliver the expected space conditioning performance. 
         [0007]    As an example, if a condenser fan fails and this failure is not detected, the compressor will begin to operate at substantially higher than design discharge pressures and temperatures. This can cause damage to the compressor. Similarly, an evaporator fan malfunctioning can cause undesirably low compressor suction pressures and refrigerant flow rates, which can also result in compressor damage. Additionally, an evaporator coil can freeze-up. Further, low refrigerant flow rates can adversely affect oil return to the compressor leading to efficiency degradation and potential compressor damage. Thus, it is desirable to obtain a simple means to detect a fan failure in a refrigerant system to prevent system or performance deterioration. 
       SUMMARY OF THE INVENTION 
       [0008]    A simple system test is provided by a method and control that is utilized to identify a fan assembly failure in a refrigerant system. This system test is preferably performed periodically, such as when the system is shut down (not operational), or with a certain frequency, such as once a day. 
         [0009]    In a disclosed embodiment, the fan motor associated with each of the condenser and the evaporator is shut off for a short time interval. The refrigerant system continues to run, and the control determines changes in system operating conditions. As an example, with the condenser shut down, the pressure or temperature at the discharge side of the compressor should increase. If such an increase is not seen, then a determination can be made that the condenser fan had already failed. 
         [0010]    In a similar manner, if the evaporator fan is shut down, the suction pressure of the refrigerant being delivered to the compressor should fall. Again, if no such reduction is observed, a determination can be made that the evaporator fan or the fan drive has already failed. 
         [0011]    By also looking at the current or power draw for the fan motors, similar diagnostics can be made. As an example, if the control sends a signal to shut down a fan, and the current draw by the fan does not change, a determination can be made that there is a malfunction within the fan system typically associated with the fan or fan drive. By combining the measurements of these electrical characteristics for the fan and refrigerant pressure and/or temperature observations, a determination can be made whether the malfunction is associated with the fan system or with the obstruction to the airflow within the heat exchanger or air filters. 
         [0012]    Further, if the fan is provided with a variable speed drive (or multi-speed motor), rather than completely shutting down the fan motor, the speed at which the fan is operating can be modified. Again, some change (similar to the changes described above) in the operating conditions would be expected. 
         [0013]    Also, if changes in pressures and/or temperatures at certain environmental conditions are observed over time, a prognosis can be made regarding component deterioration rate and expected time to failure, such that preventive maintenance can be performed prior to extensive damage throughout the refrigerant system. 
         [0014]    The present invention thus provides a simplified method of identifying a fan malfunction, fan drive malfunction or a malfunction in the controls for a fan. 
         [0015]    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 
         [0016]      FIG. 1A  is a schematic view of a refrigerant system incorporating the present invention. 
           [0017]      FIG. 1B  shows an optional feature. 
           [0018]      FIG. 2  is a chart showing a properly functioning condenser fan. 
           [0019]      FIG. 3  is a chart showing a properly functioning evaporator fan. 
           [0020]      FIG. 4  shows a properly functioning fan wherein fan current draw is reviewed. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    A refrigerant system  19  is illustrated in  FIG. 1A . A compressor  20  delivers refrigerant downstream to a condenser  24 . A discharge sensor  22  senses either the pressure or temperature on the discharge refrigerant line. Alternatively, the discharge sensor  22  can be located within the condenser  24  or between the condenser  24  and expansion device  26 . Downstream of the condenser  24  is an expansion device  26 . Downstream of the expansion device  26  is an evaporator  28 . A suction pressure or temperature sensor  30  monitors conditions of the refrigerant flowing from the evaporator  28  back to the compressor  20 . 
         [0022]    If the system is equipped with an economizer circuit (vapor injection line), then a pressure or temperature sensor can be located at any place on this intermediate pressure line. One of the economizer circuit schematics is shown incorporated into a refrigerant system  51  in  FIG. 1B . A compressor  20  delivers refrigerant to a condenser  24 , and receives refrigerant from an evaporator (not shown in this figure). However, downstream of the condenser, and upstream of the main expansion device  26 , a tap line  52  taps refrigerant from a liquid line  54 . The tapped refrigerant in the tap line  52  passes through an auxiliary expansion device  56 . That tapped refrigerant then flows through an economizer heat exchanger  50  in which it cools refrigerant in the liquid line  54  also passing through the economizer heat exchanger  50 . Such economizer circuits are utilized to provide capacity and/or efficiency boost in some refrigerant systems. While the tapped refrigerant in the tap line  52  is shown flowing in the same direction, as the refrigerant the liquid line  54 , through the economizer heat exchanger  50 , this is only for illustration simplicity. In practice, the flows are typically arranged in a counterflow configuration. The tapped refrigerant is returned through a vapor injection line  58  to the compressor  20 , and is injected into the compressor, typically at some intermediate pressure (between suction pressure and discharge pressure). A pressure or temperature sensor  60  may be located on this vapor injection line  58 , and this pressures or temperature can be utilized in a similar fashion to the other pressures or temperatures that will be described below. Alternatively, the pressure or temperature sensor  60  may be located with the economizer heat exchanger  50  or between the economizer heat exchanger  50  and the auxiliary expansion device  56 . 
         [0023]    Similarly, the suction sensor  30  can be located within the evaporator  28  or between the evaporator  28  and expansion device  26 . A fan assembly  45  consists of a fan  25  and a fan motor  27 . A fan assembly can additionally include a variable speed drive or a multi-speed drive  33 . A fan  25  is driven by a fan motor  27  to move a secondary fluid over the condenser  24 . Typically, this fluid is air. 
         [0024]    Analogously, another fan assembly  49  consists of a fan  29  and motor  31 . This fan assembly can also include an optional variable speed drive or a multi-speed drive. The fan  29  is driven by a motor  31  to move air over the evaporator  28 . A current, power or speed sensor  35  may be associated with both or one of the motors  27  and  31  or associated fans. Another current, power or speed sensor  37  may be associated with the compressor  20 . Signals from each of the sensors are sent back to a control  32  for the refrigerant system  19 . 
         [0025]    A diagnostic method of the present invention will now be described. At some periodic time, for example late in the day when an air conditioning system may be shut down or is not in high demand, the control  32  will turn off the fan motors  27  and  31  in series for a short period of time. When this occurs, the refrigerant system  19  continues to operate, and a system conditions are monitored. 
         [0026]    When the motor  27  is shut down for a short period of time, then an increase in the pressure or temperature above the selected tolerance threshold, sensed by the sensor  22 , should be observed. As shown in  FIG. 2 , the discharge pressure increases with a sharp spike at the time the motor  27  is shut down. On the other hand, if the signal is relatively unchanged, such as shown at X in  FIG. 2 , this is an indication that the fan assembly  45  was already malfunctioning. The control  32  may then take corrective action. 
         [0027]    The similar logic can be applied by monitoring the current or power draw of the fan motor  27 . As an example, when the motor is shut down, if there is no change in the current or power draw, a determination can be made that the fan motor had already failed. 
         [0028]    The fan  29  for the evaporator  28  can be controlled in a similar manner by shutting off the motor  31  for a short period of time. As shown in  FIG. 3 , with such a shut down, the suction pressure (or temperature) would be expected to fall. If, as shown at Y, the pressure is not reduced below the predetermined tolerance threshold, a determination can be made that there is a failure in the evaporator fan system  49 . It should also be pointed out that the shutdown of the motor  27  would also cause a change in the reading of the sensor  30 . In a similar fashion, the shutdown of the motor  31  will cause a change in the reading of the sensor  22 . Therefore, a single sensor located either on the high pressure, low pressure or intermediate pressure (if economizer circuit is utilized) side of the refrigerant system  19  can be used to detect a malfunction of either condenser or evaporator fan. 
         [0029]      FIG. 4  shows an expected change of the fan current draw. By combining the measurements of the fan electrical characteristics and refrigerant pressure or temperature observations, the determination can be made whether the malfunction is associated with the fan system or with the obstruction to the airflow within the heat exchanger or air filters. At that point, the appropriate diagnostic code can be issued and action taken. 
         [0030]    For instance, when the control  32  monitors current drawn by the evaporator fan motor  31  along with the pressure sensor  30  feedback signal, an identification of a clogged filter associated with the evaporator  28  can be made. This would occur when the current downspike is detected by the sensor  35 , but the suction pressure monitored by sensor  30  remains relatively unchanged. The motor or fan speed can also be monitored to detect a malfunctioning component. For example, if the control  32  is programmed to issue a command to shut down the fan and there is no detected change in the fan or fan motor speed or current, then the fan or the associated motor is malfunctioning. 
         [0031]    It has to be noted that instead of pressure or temperature sensors  22  and  30 , the compressor current, power draw or speed sensor  37  can be used, since the correlations exist between suction/discharge pressures and compressor current, power draw and compressor speed. 
         [0032]    In addition, an optional variable frequency drive  33  is shown associated with the motor  27  (similarly a variable frequency drive can be associated with the motor  31 ). Such controls are known, and are operable to drive the motor  27  at any one of a number of speeds. By varying the speed, the method as described above, can also be performed. That is, the method can be performed without fully shutting the motor on and off, but rather simply varying the speed, observing a resultant change and comparing it to the tolerance threshold. 
         [0033]    Also, if the changes in pressures and/or temperatures at certain environmental conditions are observed over time, a prognosis can be made regarding component deterioration rate and expected time to failure, such that preventive maintenance can be performed prior to extensive damage throughout the refrigerant system. For instance, observing pressure spike change over time may provide an indication when the air filters are due to be replaced. The present invention thus provides a simple way to monitor the operation of a fan assembly and to quickly identify if it has malfunctioned, prior to any consequent extensive damage to the refrigerant system components. 
         [0034]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications 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.