Abstract:
A cooling system and related method of defrosting a refrigeration unit or a freezer unit involves the steps of (a) monitoring a compressor running time, (b) monitoring an evaporator coil temperature, (c) monitoring a first time period since a last cooled compartment door open alarm of the unit, (d) monitoring a second time period since a last defrost operation, (e) monitoring a third time period during which the cooled compartment door is closed, and (f) controlling initiation of a defrost operation as a function of the monitored compressor running time, the monitored evaporator coil temperature, the monitored first time period, the monitored second time period, and the monitored third time period. Various sets of conditions may be established for triggering initiation of the defrost operation. The system may also detect refrigerant leaks and a clogged condenser as a function of compressor running time and compressor discharge line temperature.

Description:
TECHNICAL FIELD 
     This invention pertains generally to refrigeration and freezer units, and more specifically to a control system for such units and related methods for controlling defrost, monitoring the status of a system condenser coil, and monitoring for refrigerant leaks. 
     BACKGROUND OF THE INVENTION 
     Cooling systems are utilized in many different types of refrigeration units and freezer units. For example, commercial refrigeration and freezer units used by those in the food industry such as restaurants generally include some variation of the standard cooling system which has existed for many years. Similarly, numerous control schemes for such cooling systems are known, including control schemes for defrost operations of the cooling systems in order to eliminate frost build up on the evaporator coils of such systems. However, improvements in such defrost control schemes are continually sought. 
     One problem associated with such cooling systems is that air is generally passed through a condenser to remove heat from the refrigerant. The intake air to the condenser passes through the condenser coil. As particulates build up on the condenser, air flow through the coil decreases and system efficiency may be reduced. Accordingly, it would be desirable to provide the ability to detect a clogged condenser in order to clean the condenser when needed. 
     Another problem associated with such cooling systems is the occurrence of refrigerant leaks in the system. Accordingly, it would be desirable to provide the ability to detect such refrigerant leaks. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a method of defrosting a refrigeration unit or a freezer unit involves the steps of (a) monitoring a compressor running time, (b) monitoring an evaporator coil temperature, (c) monitoring a first time period since a last cooled compartment door open alarm of the unit, (d) monitoring a second time period since a last defrost operation, (e) monitoring a third time period during which the cooled compartment door is closed, and (f) controlling initiation of a defrost operation as a function of the monitored compressor running time, the monitored evaporator coil temperature, the monitored first time period, the monitored second time period, and the monitored third time period. Various sets of conditions may be established for triggering initiation of the defrost operation. 
     In another aspect of the invention a method of monitoring a refrigeration system for refrigerant leaks involves (a) monitoring a running time of a compressor, (b) monitoring a temperature of a discharge line of the compressor, (c) controlling activation of a line leak alarm based at least in part upon: (i) the running time of the compressor exceeding a threshold running time; and (ii) comparison of the discharge line temperature to a threshold discharge line temperature. 
     Yet a further aspect of the invention provides a method of monitoring the condenser of a cooling system. The method involves (a) monitoring a running time of a compressor, (b) monitoring a temperature of a discharge line of the compressor, (c) controlling activation of a clogged condenser alarm based at least in part upon: (i) the running time of the compressor exceeding a threshold running time; and (ii) comparison of the discharge line temperature to a threshold discharge line temperature. 
     An electronic controller may be utilized to implement the foregoing methods in conjunction with various sensors associated with the system components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial schematic of a cooling system; 
     FIG. 2 is a high-level flow chart of system defrost control operation; 
     FIG. 3 is a high-level flow chart of clogged condenser detection operation; and 
     FIG. 4 is a high-level flow chart of refrigerant leak detection operation. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a high-level schematic of a refrigeration system  10  is shown. The refrigeration system  10  includes a compressor  12 , a condenser  14 , a refrigerant chamber  16  and an evaporator  18  which typically includes an evaporator coil. As a refrigerant fluid within the system  10  enters the evaporator  18 , the fluid is cooler than the surrounding area. This surrounding area is established by, or is in communication with a cooled compartment  20  in which items such as food products are kept cool or frozen. In the evaporator, refrigerant fluid in liquid form absorbs heat from the compartment  20  and vaporizes. The vaporized refrigerant is then forced into the compressor  12  where its temperature increases as a result of compression. The compressed coolant vapor passes to the condenser  14  where it cools down and liquifies as heat is transferred to the cooler air. In this regard, intake air  24  to the condenser  14  is typically passed through or over cooling coils of the condenser. The air flow may be generated by a fan unit (not shown). 
     The cooled compartment  20  includes a door  26  which provides access to the compartment. A switch  28  is situated to generate a signal indicative of the open/closed status of the door  26 . A temperature sensor  30  is provided for generating signals indicative of the evaporator coil temperature. A combination temperature/humidity sensor  32  may also be provided for generating a signal indicative of the temperature and relative humidity of the ambient air in or around the cooled compartment  20 . Separate sensors could also be utilized. A temperature sensor  34  is also provided at the discharge line of the compressor for generating signals indicative of the discharge line temperature. The temperature sensors may be of any suitable type known in the art. 
     An electronic controller  36  is provided for controlling the operations of the cooling system  10 . Controller  36  may have various configurations but will typically include some type of processor such as a micro-processor, micro-controller, or ASIC, along with associated memory such as RAM, ROM, and/or EEPROM, and one or more associated timers or clocks. The controller  36  also includes input/output circuitry for interfacing with the various system components via electrical connections therewith. For example, the controller receives and interprets signals from sensors  28 ,  30 ,  32 , and  34 . The controller also controls activation of the compressor  12  via connection thereto, or via connection between the compressor and a power source (not shown). The controller  36  may also be connected to output devices  38  and  40  which may be annunciators or alarms such as light emitting elements or sound emitting elements the energization of which is controlled by the controller  36 . The elements  38  and  40  may be separate from the controller or may be located in proximity to the controller  36  within the same housing. It is recognized that the cooling system  10  may include various other components and sensors which are unrelated to the various aspects of the invention. Given the foregoing system  10 , the various aspects of the present invention are explained below. 
     Reference is now made to the defrost control flow chart  50  of FIG.  2 . Preferably, the controller is configured to initiate regular defrost operations at standard intervals. The standard interval may be stored in memory of the controller, and various intervals may be stored in memory to be selected according to operating conditions of the system  10 . Operation according to the flow chart  50  enables an intermediate defrost operation to be initiated between the regular defrost operations if necessary. However, the control scheme of flow chart  50  could also be utilized in systems where defrost operations are not initiated at standard intervals. 
     In FIG. 2 the following nomenclature is utilized: 
     “LDTP” stands for “last defrost time period” and represents the length of time which has passed since the end of the last defrost operation; 
     “TLDTP” stands for “threshold last defrost time period”; 
     “CRT” stands for compressor running time and represents the length of time during which the compressor runs during a cooling cycle of the system; 
     “TRT” stands for “threshold running time”; 
     “LDATP” stands for door “last door alarm time period” and represents the length of time which has passed since end of the last cooled compartment door open alarm; 
     “TLDATP” stands for “threshold last door alarm time period”; 
     “DCTP” stands for “door closed time period” and represents the length of time which has passed since the cooled compartment door was last closed; 
     “TDCTP” stands for “threshold door closed time period”; 
     “ECTEMP” stands for “evaporator coil temperature” and represents the temperature of the evaporator coil as sensed by temperature sensor  30 ; and 
     “TCTEMP” stands for “threshold coil temperature.” 
     The routine of flow chart  50  may be executed periodically to determine whether or not to initiate a defrost operation. The routine will typically be initiated during a cooling cycle of the system  10 , that is, when the compressor  12  is running. When called upon the routine begins at block  52  and moves to block  54  where the last defrost time period is compared to a threshold last defrost time period. The threshold last defrost time period is preferably established as a time period which is long enough to assure that the average temperature within the cooled compartment  20  does not exceed a desired level if another defrost operation is performed. For example, it is possible that if two defrost operations are performed in quick succession the average temperature of the cooled compartment may raise above a desired level for an unacceptable length of time. Accordingly, if the last defrost time period is not greater than the threshold last defrost time period, the routine is exited at block  56  and no defrost operation is performed. 
     On the other hand, if the last defrost time period is greater than the threshold last defrost time period the routine moves to block  58  where the compressor running time is compared to a threshold running time. The compressor running time may be maintained by a timer associated with the controller  36 . The threshold running time is established as a time which indicates that the compressor has run longer than it should have to in order to cool, representing a build up of frost on the evaporator coil. Preferably, the threshold running time is established by the electronic controller based upon a running average of compressor running times over a preceding time period such as thirty-six hours. The running average may be incremented by some predetermined amount such as twenty-five percent. However, this percent is merely representative and it is recognized that the exact percent could be established for a given unit or system  10  based upon testing. If the compressor running time exceeds the threshold running time the routine moves to block  60  and a defrost operation is initiated. If the compressor running time does not exceed the threshold running time, the routine moves to block  62 . 
     At block  62  the last door alarm time period is compared to a threshold last door alarm time period. The threshold last door alarm time period is established to account for increases in evaporator coil temperature which might result from the door remaining open for an excessive period of time, and again may be established by testing. If the last door alarm time period is not less than the threshold last door alarm time period, the routine moves to block  64  where the evaporator coil temperature is evaluated. If the current evaporator coil temperature is greater than a threshold coil temperature then the routine moves to block  60  and a defrost operation is initiated. The threshold coil temperature is established as a temperature indicative of frost build up on the evaporator coil and is preferably set at a value which is dependent upon the lowest evaporator coil temperature since the end of the last defrost operation. For example, the threshold coil temperature may be established automatically by the controller as the lowest evaporator coil temperature since the last defrost operation incremented by a certain amount. If the current evaporator coil temperature at block  64  is not greater than the threshold coil temperature, the routine is exited at block  56  and no defrost operation is performed. 
     Returning to block  62 , if the last door alarm time period is less than the threshold last door alarm time period the routine moves to block  66  where the open/closed status of the door  26  is checked. If the door  26  is not closed the routine is exited at block  56  and no defrost operation is performed because it is undesirable to perform a defrost operation when the door is open. If the door  26  is closed the routine moves to block  68  and the door closed time period is compared with a threshold door closed time period. The threshold door closed time period is preferably established as a time period of sufficient length to allow the evaporator coil temperature to cool down and stabilize after the door has been open for an excessive period of time and may be determined by testing of the particular unit and system  10 . If the door closed time period does not exceed the threshold door closed time period the routine moves to block  56  and no defrost operation is performed. However, if the door closed time period exceeds the threshold door closed time period the routine moves to block  64  and a determination of whether or not to initiated a defrost operation is made as described above. 
     The routine described in flow chart  50  therefore provides a defrost control system and method in which the compressor running time, evaporator coil temperature, last door alarm time period, last defrost time period, and door closed time period are monitored and in which initiation of a defrost operation is controlled as a function of the compressor running time, evaporator coil temperature, last door alarm time period, last defrost time period, and door closed time period. Preferably, a defrost operation is initiated when one or more of three sets of conditions exist. Namely, condition set  1  in which the compressor running time exceeds the threshold running time and the last defrost time period exceeds the threshold last defrost time period; condition set  2  in which the evaporator coil temperature exceeds the threshold coil temperature, the last defrost time period exceeds the threshold last defrost time period, and the last door alarm time period exceeds the threshold last door alarm time period; and condition set  3  in which the evaporator coil temperature exceeds the threshold coil temperature, the last defrost time period exceeds the threshold last defrost time period, the last door alarm time period is less than the threshold last door alarm time period, and the door closed time period exceeds the threshold door closed time period. 
     The electronic controller is programmed or otherwise configured to control defrost according to the flow chart  50 . The electronic controller  36  may initiate a defrost operation by inhibiting operation of the compressor  12 . The length of a given defrost operation may be predetermined or may vary upon other monitored parameters of the system  10 . As described herein initiation of a defrost operation may include starting the defrost operation immediately when block  60  of flow chart  50  is reached, but may also include setting a flag which will cause the defrost operation to start after the compressor  12  stops running during a cooling sequence. 
     Referring now to FIG. 3, an additional feature of the system  10  is described and provides the ability to determine when the condenser  14  of the system becomes clogged. The following nomenclature is utilized in FIG.  3 : 
     “CRT” stands for compressor running time and represents the length of time during which the compressor runs during a cooling cycle of the system; 
     “TRT CF ” stands for “threshold running time” indicative of a clogged condenser; 
     “DLT” stands for “discharge line temperature” of the compressor; and 
     “TDLT CF ” stands for “threshold discharge line temperature” indicative of a clogged condenser. 
     The routine of flow chart  70  begins at block  72  and moves to block  74  where operation of the compressor  12  is started. At block  76  a timer for monitoring the compressor running time is started. At block  78  the compressor running time is compared to a threshold running time which is indicative of a clogged condenser. The threshold running time may be established by testing of the unit and system, by tracking prior compressor running times, or a combination of the two. If the compressor running time exceeds the threshold running time the routine moves to block  80  where the discharge line temperature is compared to a threshold discharge line temperature indicative of a clogged condenser. The threshold discharge line temperature may be established by testing of the unit and system, by tracking prior discharge line temperatures, or a combination of the two. If the discharge line temperature exceeds the threshold discharge line temperature then an alarm is initiated at block  82 . The discharge line temperature check is provided to verify that the excessive compressor running time is not due to a compressor malfunction such as a refrigerant leak or otherwise caused low refrigerant level as discussed in more detail below. The alarm may be activation of one of the sound element or light element  38  or  40 , or may merely be a flag which is set in memory for later retrieval. If the compressor discharge line temperature does not exceed the threshold discharge line temperature, the routine moves to block  84  where other processing may continue. Referring again to block  78 , if the compressor running time does not exceed the threshold running time the routine moves to block  86  where other control operations and tasks may be performed before the routine again moves to block  78 . The routine of flow chart  70  may be continuously or periodically run during a cooling cycle of the system  10 . 
     In FIG. 4 a flow chart  100  depicts a routine for determining when a refrigerant leak exists in the system  10 . The following nomenclature is utilized in FIG.  4 : 
     “CRT” stands for compressor running time and represents the length of time during which the compressor runs during a cooling cycle of the system; 
     “TRT LL ” stands for “threshold running time” indicative of a line leak in the system; 
     “DLT” stands for “discharge line temperature” of the compressor; and 
     “TDLT LL ” stands for “threshold discharge line temperature” indicative of a refrigerant line leak. 
     The routine of flow chart  100  begins at block  102  and moves to block  104  where operation of the compressor  12  is started. At block  106  a timer for monitoring the compressor running time is started. At block  108  the initial discharge line temperature (IDLT) is checked and recorded or stored in memory. At block  110  the compressor running time is compared to a threshold running time which is indicative of a refrigerant line leak. The threshold running time may be established by testing of the unit and system, by tracking prior compressor running times, or a combination of the two. If the compressor running time exceeds the threshold running time the routine moves to block  112  where the discharge line temperature is compared to a threshold discharge line temperature indicative of a refrigerant line leak. Preferably, the threshold discharge line temperature is based upon the initial discharge line temperature incremented by a predetermined amount established by testing. If the discharge line temperature does not exceed the threshold discharge line temperature then an alarm is initiated at block  114 . This scenario is indicative of a refrigerant leak because the discharge line temperature should rise after compressor start up due to an increase in system pressure. If the refrigerant level is low—or if there is a leak in the system, the pressure cannot build and therefore the discharge line temperature will not increase as it should. The alarm may be activation of one of the sound element or light element  38  or  40 , or may merely be a flag which is set in memory for later retrieval. If the compressor discharge line temperature does exceed the threshold discharge line temperature, the routine moves to block  116  where other processing may continue. Referring again to block  110 , if the compressor running time does not exceed the threshold running time the routine moves to block  118  where other control operations and tasks may be performed before the routine again moves to block  110 . The routine of flow chart  100  may be continuously or periodically run during a cooling cycle of the system  10 . 
     Regarding the routines of flow charts  70  and  100 , it is recognized that an excessive compressor running time could be indicative of a need for a defrost operation instead of a clogged condenser or refrigerant line leak. Therefore, in each routine a back-up check of the discharge line temperature is provided. Based upon known system performance under various circumstances, and the combination these two system checks, both clogged condensers and refrigerant leaks can be effectively monitored and detected. Given the similarity between the two routines, it is recognized that a single routine which simultaneously checks for the clogged condenser and the refrigerant leak could be provided. 
     While the forms of the apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and changes may be made therein without departing from the scope of the invention.