Patent Publication Number: US-7712320-B2

Title: Compressor operation following sensor failure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. patent application Ser. No. 10/420,754, filed Apr. 23, 2003, entitled COMPRESSOR OPERATION FOLLOWING SENSOR FAILURE, the disclosure of which both applications are incorporated herein by reference in their entirety. 
   FIELD OF INVENTION 
   The present invention relates generally to refrigeration systems. More particularly, the present invention relates to a compressor operation in response to sensor failure in a refrigeration system. 
   BACKGROUND OF THE INVENTION 
   In refrigeration systems, a refrigerant gas is compressed in a compressor unit. Heat generated by the compression is then removed generally by passing the compressed gas through a water or air cooled condenser coil. The cooled, condensed gas is then allowed to rapidly expand into an evaporator coil where the gas becomes much colder, thus cooling the coil and the inside of the refrigeration system box around which the coil is placed. 
   Life Science researchers have a need for ultra low temperature (“ULT”) storage chambers to store products such as living organisms, biologically active reagents, and the like. As these products may die or become biologically inactive when improperly warmed, these researchers also need to minimize any product warm-up. In this regard, generally, sensors are utilized to determine whether the inside of the refrigeration system box or cabinet is within a predetermined temperature range. In response to sensed temperatures being outside this predetermined temperature range, a controller typically modulates the compressor to effect an appropriate temperature change. For example, if the temperature rises above the predetermined temperature range, the controller may modulate the compressor to turn on or increase speed. 
   A problem, which has arisen with such ULT freezers, is that when the sensor fails, the controller may improperly modulate the compressor and the temperature may deviate outside the predetermined temperature range. Known ULT freezers typically include an alert system designed to notify a user of potential problems. Often, these freezers also include a default operation. This default operation is generally only appropriate for a relatively narrow range of operating conditions. As these ULT freezers are commonly located in remote areas, the alert system may go un-noticed for an extended period of time. Thus, if the operational conditions are outside the relatively narrow range for which the default operation is optimized, the temperature may deviate outside the predetermined temperature range and the contents of the ULT freezer may be destroyed. 
   In addition, temperature deviations outside the predetermined temperature range are not only undesirable for the contents, but lowering the temperature below the predetermined temperature range places increased loads on the refrigeration unit as it must operate on a more continuous basis than it was designed. This increased load may decrease compressor life or cause compressor failure. 
   The present invention overcomes the above mentioned disadvantages to a great extent, and provides many additional advantages which shall become apparent as described below. 
   SUMMARY OF THE INVENTION 
   It is therefore a feature of the present invention to provide method of controlling a compressor. In this method, a compressor operation log is generated and stored. In addition, a compressor operation is selected from the compressor operation log in response to a sensor failure. Furthermore, the compressor is modulated according to the selected compressor operation in response to the sensor failure. 
   Another feature of the present invention pertains to an apparatus for controlling a compressor. This apparatus includes a refrigerant compressor and a memory configured to store compressor data associated with controlling the compressor. In addition, the apparatus includes a first sensor configured to transmit measurements associated with environmental conditions within a cabinet and a controller operatively connected to the compressor, the memory, and the first sensor. Furthermore, in response to a failure of the first sensor, the controller is configured to modulate the compressor according to the compressor data. 
   Yet another feature of the present invention relates to an apparatus for controlling a compressor. This apparatus includes a means for generating and storing a compressor operation log. In addition, the apparatus includes a means for selecting a compressor operation in response to a sensor failure. This compressor operation is selected from the compressor operation log. The apparatus further includes a means for modulating the compressor according to the selected compressor operation in response to the sensor failure. 
   There has been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
   In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purposes of description and should not be regarded as limiting. 
   As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent construction insofar as they do not depart from the spirit and scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a system architecture according to an embodiment of the present invention. 
       FIG. 2  is a flow diagram according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
   Referring now to the Figures, in  FIG. 1  there is shown a system architecture of a freezer unit  10  according to an embodiment of the invention. The freezer unit  10  includes a freezer sub-unit  12  and a control system  14 . The freezer sub-unit  12  includes a cabinet  16  configured to provide a refrigerated storage volume. In this regard, the cabinet  16  is cooled by the action of refrigerant evaporating in an evaporator  18 . This evaporator  18  may be located with the cabinet  16  or, more preferably, thermally attached to the cabinet  16 . For example, the evaporator  18  may be attached to the cabinet  16  via a thermally conductive material such as metal. In a preferred embodiment, the refrigerant is compressed by a compressor  20  and condensed in a condenser  22 . 
   The freezer sub-unit  12  further includes at least one cabinet sensor  24 . The cabinet sensor  24  senses environmental conditions within the cabinet  16 . For example, the cabinet sensor  24  may sense at least one of temperature, humidity, frost buildup, and the like. The freezer sub-unit  12  may, optionally, also include another cabinet sensor  26 . This cabinet sensor  26  may be utilized in conjunction with the cabinet sensor  24 , for example, to determine an average environmental condition and/or confirm measurements of the cabinet sensor  24 . In addition, the cabinet sensor  26  may serve as a backup sensor in the event of primary sensor failure, for example, failure of the cabinet sensor  24 . 
   The freezer unit  10  is configured to substantially maintain the temperature of the interior of the cabinet  16  within a predetermined range of a set temperature (“T set ”). In this regard, the control system  14  includes a controller  28  configured to control the compressor  20  via a relay  30 . This controller  28  is further configured to receive measurements or signals from the cabinet sensors  24  and/or  26  and modulate the operation of the compressor  20  in response to the received measurements. In this manner, the temperature of the interior of the cabinet  16  may be substantially maintained within a predetermined range of the T set . 
   Additionally, the control system  14  includes a memory  32  operable to store and retrieve data for the controller  28 . In a preferred embodiment of the invention, compressor operations such as duty cycles, time on, time off, speed, pressures, and the like are stored to the memory  32  in the form of a compressor log (“log”)  34 . This log  34  preferably includes a chronologically ordered list of compressor operations. In the event of a sensor failure, the controller  28  is configured to access the memory  32  and retrieve a relatively recently stored compressor operation (“logged operation”) from the log  34 . Generally, conditions such as payload within the cabinet  16  and ambient temperature are likely to be similar to those conditions experienced recently. Thus, a compressor operation utilized to control the compressor  20  during recently experienced conditions may more closely approximate actual conditions than a default operation. 
   The controller  28  may further be configured to evaluate the logged operation. For example, the logged operation may be compared to a predetermined range of compressor operations and if the logged operation is outside of this predetermined range, another compressor operation may be utilized. This predetermined range of compressor operations preferably includes compressor operations for essentially all reasonable conditions. In a specific example, a duty cycle having an on:off ratio between 2:1 and 7:1 may reasonably be expected to maintain the cabinet  16  at the T set . Thus, if the logged operation falls outside this predetermined range, a default duty cycle of 20 minutes on, 8 minutes off (2.5:1) is employed in this example. The default duty cycle is only used after a determination that data in the log is deemed inappropriate or in error and provides a second level of redundancy. The default mode of operation may be determined via targeting a specific cabinet temperature operating in relatively severe ambient conditions. In an embodiment of the invention, the controller  28  is configured to access the log  34  in reverse chronological order and evaluate each logged operation until a logged operation within the predetermined range of compressor operations is identified. The controller  28  is further configured to utilize a default compressor operation if a logged operation within the predetermined range of compressor operations is not identified. Moreover, the memory  32  may store and retrieve a variety data types such as default compressor operations, predetermined range of compressor operations, ambient environmental conditions, set temperatures, door events, and the like. 
   In a preferred embodiment of the invention, control system  14  further includes a plurality of counters  36  and  38  that are configured to initiate a plurality of respective compressor operations. This plurality of counters includes a short cycle counter  36  and a delog/defrost counter  38 . Each time the compressor  20  is turned on or off, the short cycle counter  36  is configured to initiate counting down from a predetermined value (“short count ”). This short count  has been empirically determined to provide sufficient time for excessive head pressure to dissipate from the compressor  20 . The controller  28  is configured to reference the short cycle counter  36  to determine if sufficient time has elapsed to modulate the compressor  20 . 
   The delog/defrost counter  38  may be configured to initiate a delog/defrost operation in response to a predetermined elapsed period (“delog/defrost count ”) since a previous delog/defrost period having been executed. This delog/defrost count  is reset at the end of the current delog/defrost cycle. If the compressor  20  remains on and/or within a duty cycle for a period exceeding a predetermined delog/defrost period, the delog/defrost counter  38  is configured to initiate a delog/defrost cycle for the compressor  20 . At an operational minimum, the delog/defrost counter  38  will call for a delog/defrost cycle. For example, an attempt to initiate a delog/defrost cycle at the minimum point of a temperature cycle. In addition or alternatively, if the compressor  20  remains on for a period exceeding a predetermined delog period, the delog/defrost counter  38  is configured to initiate a delog or rest period for the compressor  20 . This rest period following the delog/defrost count  has been empirically determined to provide an opportunity for oil within the compressor  28  to liquefy and thereby extend the useful life of the oil. In some instances, particularly defrost scenarios, control of ice formation may be the objective of the compressor rest period. In a specific example, the delog/defrost counter  38  may initiate a  10  minute “off” period in response to the compressor  20  being on and/or in a duty cycle for 8 hours. In this way, a rest period of a duration long enough to protect the system oil is essentially assured. 
   In this and/or various other embodiments of the invention, the freezer sub-unit  12  may include an ambient sensor  42 , a door sensor  44 , and a control panel  46  having an alarm  48 . The controller  28  is configured to receive signals from the ambient sensor  42  and the door sensor  44 . The controller  28  is further configured to associate signals received from the ambient sensor  42  and the door sensor  44  with compressor operations and store these signals to the log  34 . In this manner, ambient environmental conditions and door open and/or close events may serve to initiate compressor operations. This data may also be appended to the log  34  in order to aid in determination of a compressor duty cycle to employ in the event no temperature feedback is provided due to one or more failed sensor(s). 
   The control panel  46  is configured to provide a user the capability to enter information such as the T set  and the like. In this regard, the control panel  46  and the controller  28  are operable to intercommunicate. Additionally, the controller  28  is configured to initiate an alarm state in response to a detected failure. For example, if the cabinet sensor  24  and/or  26  fail, the controller  28  may initiate the alarm state and the alarm  48  may emit a visual and/or auditory warning. Furthermore, this alarm state may include transmitting a signal to a network connection. 
   Referring now to  FIG. 2 , there is illustrated a method  50  of controlling the freezer unit  10  according to an embodiment of the invention. As shown in  FIG. 2 , the method  50  may be initiated in response to the freezer unit  10  being turned on at step  52 . At step  54 , the log  34  may be generated and stored to the memory  32 . 
   At step  56 , it is determined if sufficient time has elapsed to facilitate a sufficient drop in head pressure within the compressor  20 . For example, the short cycle counter  36  may be referenced and if sufficient time has not elapsed, the controller  28  may wait at step  58  until sufficient time has elapsed. If sufficient time has elapsed, it is determined if it is time to perform a delog/defrost cycle at step  64 . For example, the controller  28  may refer to the delog/defrost counter  38  and if the delog/defrost count  has been exceeded, the delog/defrost cycle may be initiated at step  66 . In a manner similar to known delog/defrost cycles, the delog/defrost cycle initiated at step  66  is configured to warm the components of the freezer unit  10 , such as the evaporator  18 , to facilitate melting of ice which may have formed on the components and/or to protect system oil conditions. This delog/defrost cycle may further include a step to determine if sufficient time has elapsed to facilitate a sufficient drop in head pressure within the compressor  20 . 
   At step  68 , it is determined if sensor measurements associated with the environment within the cabinet  16  are being received. For example if a voltage reading across the cabinet sensor  24  is less than 1 millivolt (“mV”) or greater than 130 mV, it may be determined that the sensor  24  has failed and thus, no reasonable temperature may be correlated with measurements from sensor  24 . If the cabinet sensor  26  has also failed, it may thus be determined that the controller  28  is not receiving measurements associated with the environment within the cabinet  16 . If sensor measurements associated with the environment within the cabinet  16  are being received and correlate to reasonable temperatures, the compressor  20  may be modulated by the controller  28  in normal operating mode at step  70 . If, at step  68 , it is determined that sensor measurements associated with the environment within the cabinet  16  are not being received or in error, the log  34  may be accessed at step  72 . 
   At step  74 , it is determined if logged operations within the log  34  are within the predetermined range of compressor operations. In other words, the logged operations are evaluated against the predetermined range of compressor operation. If the logged operations are within the predetermined range of compressor operations, the compressor  20  may be modulated by the controller  28  based on the logged operations at step  76 . If the logged operations are outside of the predetermined range of compressor operations, the compressor  20  may be modulated by the controller  28  based on the default operations at step  78 . Following the modulation of the compressor  20  at steps  76  or  78 , it may be determined if sufficient time has elapsed to facilitate a sufficient drop in head pressure within the compressor  20  at step  56 . 
   At step  70 , the controller  28  may modulate the compressor  20  according to a normal mode. This normal mode is generally configured to facilitate maintaining the temperature in the cabinet  16  within a predetermined range of the T set . In this regard, the controller  28  modulates the compressor  20  based on measurements transmitted or forwarded by the cabinet sensors  24  and/or  26 . These compressor modulations are also stored to the log  34 . In this manner, the log  34  is updated and maintained with current compressor operations. 
   At step  80 , it is determined if an event has occurred. For example, if the door sensor  44  transmits a door open and/or close event to the controller  28 , it may be determined that an event has occurred. If it is determined that an event has not occurred, it may be determined if sufficient time has elapsed to facilitate a sufficient drop in head pressure within the compressor  20  at step  56 . 
   If, at step  80 , it is determined that an event has occurred, an event mode of operation may be initiated at step  82 . In this event mode, compressor operations utilized to substantially maintain or return the temperature within the cabinet  16  at the T set  are associated with the event and stored to the log. For example, if controlling the compressor  20  to remain on for 1 hour is sufficient to return the cabinet to the T set  following a door open/close event, the controller  28  may associate this duty cycle with the door open/close event and save it to the log  34 . In this manner, should the door be opened and closed during a cabinet sensor  24  and  26  failure, a response based upon previous compressor operations may be utilized to control the compressor at step  76 . In another example, if a duty cycle of 19 minutes on and 8 minutes off is utilized to maintain the T set  when the ambient temperature is 26° C., this duty cycle may be stored to the log  34  with the associated ambient temperature of 26° C. 
   The above description and drawings are only illustrative of preferred embodiments which achieve the objects, features, and advantages of the present invention, and it is not intended that the present invention be limited thereto. Any modification of the present invention which comes within the spirit and scope of the following claims is considered to be part of the present invention.