Abstract:
Methods and apparatus for an energy efficient freezer or cooler defrost, which are particularly suited for an automated system, include procedures utilized for this purpose. The procedures are included in the firmware of an embedded controller and operate the cooler or freezer defrost cycle when required for increased energy efficiency.

Description:
CROSS-REFERENCED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/566,555, filed on Dec. 2, 2011, which is incorporated herein in its entirety by reference thereto. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Disclosure 
         [0003]    This disclosure generally relates to a refrigeration apparatus and method and, in particular, to a refrigeration apparatus and method for efficient defrost of an evaporator assembly. 
         [0004]    2. Discussion of the Background Art 
         [0005]    In the current economic climate and legislative arena there is a necessity to reduce the energy consumption of HVAC and refrigeration equipment. To reduce the overall energy consumption of this equipment, electronic controllers are being applied to optimize the energy consumption of such equipment. One function that requires optimization is evaporator defrost. 
         [0006]    Prior art defrost strategies have used a timer to initiate a defrost process based on a predetermined schedule, whether or not needed. For the case of not needed, there is an unnecessary consumption of energy. The process of defrosting introduces heat into the conditioned air space, making energy saving important (i) to reduce the amount of energy used to defrost, and (ii) to reduce the additional energy required to remove the defrost heat from the conditioned air space. 
         [0007]    Thus, there is a need for a refrigeration apparatus and method that initiates a defrost only when needed. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    A refrigeration apparatus according to the present disclosure comprises a fan that provides an airflow, an evaporator assembly that comprises an evaporator coil disposed in the airflow, and a refrigerant assembly disposed in fluid communication with the evaporator coil to supply refrigerant to the evaporator coil. A first sensor that senses a temperature of the airflow at an airflow input side of the evaporator coil and a second sensor that senses a temperature of the airflow at an airflow output side of the evaporator coil. A third sensor that senses the temperature on the suction line near the outlet of the evaporator coil. A fourth sensor that senses the temperature in a location that is representative of the evaporator coil surface temperature. A fifth sensor (pressure transducer) that senses the pressure of the refrigerant leaving the evaporator coil. A controller is connected to the first, second, third, fourth and fifth sensors to control the evaporator assembly and the refrigerant assembly in a cooling mode and in a defrost mode. The controller controls an initiation of the defrost mode based on comparison of a reference dynamic efficiency with a dynamic efficiency that is a function of current values of the input airflow temperature, the output airflow temperature and an output saturated refrigerant temperature of the refrigerant leaving the evaporator coil. The controller controls the termination of the defrost mode based on the temperature value sensed by the fourth sensor satisfying a temperature setting value within the defrost program or by time based on satisfying a time setting within the defrost program. The defrost mode terminates when the temperature setting or time setting has been satisfied (first achieved). 
         [0009]    A method for efficient defrosting of an evaporator assembly, the method comprising: (a) Initiating start up of a refrigeration assembly, fan motor and fan if Tair, in is greater than a temperature set point; (b) Cooling Tair, in to within a predetermined temperature setting relevant to a thermostat set point; (c) Initiating a defrost program if Tair, in is within a predetermined range of the thermostat set point; (d) Calculating reference dynamic efficiency (RE) and dynamic efficiency (DE) values; (e) Determining if RE minus DE divided by RE is equal to a predetermined threshold (DET) and if yes, then initiating an electric defrost by deactivating the refrigeration assembly, deactivating the fans and activating at least one defrost heater; (f) Determining if (a) a temperature sensed by a defrost termination sensor is equal to or greater than preset defrost termination temperature, (b) a defrost time is equal to or greater than a preset defrost termination time, or (c) a evaporator coil temperature is equal to or greater than a heater safety termination temperature; and (g) If any one of (a)-(c) in step (f) occur, deactivating the defrost heater, activating the refrigeration assembly and activating the fans. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Other and further objects, advantages and features of the present disclosure will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and: 
           [0011]      FIG. 1  is a block diagram of a refrigeration apparatus according to the present disclosure; 
           [0012]      FIG. 2  is a block diagram that depicts components of the refrigeration apparatus of  FIGS. 1 ; and 
           [0013]      FIG. 3  is a flow diagram of the programs of  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Referring to  FIG. 1 , a refrigeration apparatus  20  of the present disclosure comprises an evaporator assembly  22 , a refrigerant assembly  24  and a controller  26 . 
         [0015]    Evaporator assembly  22  is located in an enclosed space  28  that requires refrigeration or air conditioning. Refrigerant assembly  24  and controller  26  are located outside enclosed space  28  with connections to one another and to evaporator assembly  22 . Enclosed space  28  may be a room that is being cooled for refrigeration or air conditioning. For example, in a preferred embodiment, enclosed space  28  is a walk in refrigeration room. 
         [0016]    Evaporator assembly  22  comprises a cabinet  29  that has openings  31  and  33  located in opposed sidewalls. Disposed within cabinet  29  are an evaporator coil  30 , one or more defrost heater(s)  32 , one or more fan(s)  34  and one or more fan motor(s)  36 . Refrigerant enters cabinet  29  via a liquid line  40  and leaves via a compressor suction line  42 . Lines  40  and  42  are connected to refrigerant assembly  24 . Air flows through cabinet  29  via openings  31  and  33  as indicated by arrows  44  and  46 . Defrost heater  32  comprises one or more heating elements (not shown). 
         [0017]    During a cooling mode, controller  26  operates refrigerant assembly  24  to flow refrigerant through liquid line  40 , refrigerant metering device  48  typically an electric expansion valve or mechanical expansion valve, evaporator coil  30  and suction line  42 . Controller  26  also operates fan motor  36  to rotate fan  34  to draw air from enclosed space  28  via opening  31  through evaporator coil  30  by fan  34 . As the air passes through evaporator coil  30 , heat is removed from the air and transferred to the colder refrigerant flowing through evaporator coil  30 . That is, air is cooled and moved by fan  34  into enclosed space  28  via opening  33 . The net effect is that the air in enclosed space  28  is cooled. 
         [0018]    Evaporator coil (heat exchanger)  30  is constructed such that the refrigerant and airflow pass through the evaporator coil without the two mediums coming physically into contact. For example, evaporator coil  30  is constructed with a tube through which the refrigerant flows, the tube being arranged as evaporator coil  30 . Evaporator coil  30  facilitates heat transfer from the air to the refrigerant. 
         [0019]    Enclosed space  28  generally requires access by a user that results in warm moist/humid air being introduced to enclosed space  28 . The moisture in the infiltrating air or from the product stored inside enclosed space  28  will be attracted to the cold surfaces within the enclosed space. Since the evaporator coil surfaces are the coldest surfaces in enclosed space  28  and exposed to a higher airflow rate than any other surfaces in enclosed space  28 , when the fan(s)  34  circulate the air through the evaporator coil  30 , the moisture in the air is deposited on the evaporator coil surfaces. 
         [0020]    The ice deposits on evaporator coil  30  impede the performance of evaporator assembly  22  in two ways. First, the ice on the fins (not shown) of evaporator coil  30  acts as an additional insulative barrier between the airflow and the refrigerant; thereby reducing heat transfer from the air to the refrigerant. Second, the ice constricts the airflow through evaporator coil  30 , thereby causing reduced airflow. To remove the ice deposits and maintain the design performance efficiency of evaporator assembly  22 , defrosting is required. A defrost mode may be activated by one of three methods:
       Demand Defrost Mode (primary active defrost mode)—a demand defrost automatically initiated based on operating efficiency status of evaporator.
           Safety Defrost Mode—a safety defrost automatically initiated (if actively programmed) if applicable preprogrammed parameters have been satisfied.   Manual Defrost Mode—a manual defrost can be manually initiated via the controller interface.   
               
 
         [0024]    During a defrost mode, controller  26  operates defrost heater  32  to melt the ice. Defrost heater  32  is embedded in, attached to or in close proximity to evaporator coil  30  and the air heat transfer surfaces of evaporator coil  30 . During defrost the surfaces of evaporator coil  30  are heated to above the freezing point of the ice. As a result the ice melts into a liquid that is removed from enclosed space  28  via an evaporator drain (not shown). 
         [0025]    Evaporator assembly  22  further comprises an input air temperature sensor  50 , an output air temperature sensor  52 , an evaporator output refrigerant temperature sensor  82 , a defrost termination sensor  84 ,  92 , a heater safety termination (HSTS) switch  68  and a refrigerant suction pressure transducer (sensor)  86 . Input air temperature sensor  50  is disposed in the airflow at or near an input port of evaporator assembly  22  or of evaporator coil  30 . Output air temperature sensor  52  is disposed in the airflow at or near an output port of evaporator coil  30  or of evaporator assembly  22 . The output signals of input air and output air temperature sensors  50  and  52  are labeled, respectively, Tair, in ( 50 ,  56 ) and Tair, out ( 52 ,  58 ) and are proportional to the input airflow and output airflow temperatures, respectively. Refrigerant suction pressure transducer (sensor)  86  is located to measure the pressure of the refrigerant that exits evaporator coil  30 . The output signal of refrigerant suction pressure transducer (sensor)  86 ,  88  is labeled Tref, out and can be used to determine the output saturated refrigerant temperature in evaporator coil  30 . 
         [0026]    Evaporator output temperature sensor  82  is located adjacent to and in contact with suction line  42  at or near its connection to the output side of evaporator coil  30 . Defrost termination sensor  84  is located on the evaporator coil  30 . HSTS sensor  68  is a safety switch which opens or closes based on coil temperature and is located on evaporator coil  30 . 
         [0027]    Referring to  FIG. 2 , controller  26  comprises a processor  70 , a memory  74  and an input/output (I/O) interface  72  that are interconnected by a bus  76 . Memory  74  comprises programs that are executed by processor  70  to operate refrigeration apparatus  20 . Germane to the present disclosure are a cooling program  78  and a defrost program  80 . Although shown as separate programs, defrost program  80  in some embodiments may be incorporated within cooling program  78 . 
         [0028]    Processor  70  may be any suitable processor that executes or runs the programs stored in memory  74 . For example, processor  70  may be a microprocessor. 
         [0029]    Memory  74  may be any suitable memory that stores the parameters and data required for operation and maintenance of refrigeration apparatus  20 . For example, memory  74  may comprise one or more of a random access memory, a read only memory, an EPROM, a plug in memory such as a flash memory or a data key, and the like. 
         [0030]    I/O (input/output) interface  72  is further connected to input air temperature sensor  50 , output air temperature sensor  52 , fan motor  36 , defrost heater  32 , refrigerant assembly  24 , a refrigerant pressure transducer  86 , an output refrigerant temperature sensor  82 , a defrost termination sensor  84 , and an HSTS switch  68  via connections  56 ,  58 ,  62 ,  64 ,  66 ,  88 ,  90 ,  92  and  96 , respectively. 
         [0031]    Processor  70  executes cooling program  78  in a cooling mode to cause refrigerant assembly  24  to flow refrigerant through liquid line  40 , a refrigerant metering device  48  (such as an electric expansion valve or mechanical expansion valve), evaporator coil  30  and suction line  42 . Processor  70  also operates fan motor  36  to rotate fan  34  to draw air via opening  31  from enclosed space  28  through evaporator coil  30  by fan  34  as indicated by arrow  44 . As the air passes through evaporator coil  30 , heat is removed from the air and transferred to the colder refrigerant flowing through evaporator coil  30 . That is, air is cooled and moved by fan  34  via opening  33  into enclosed space  28  as indicated by arrow  46 . The net effect is that the air in enclosed space  28  is cooled. 
         [0032]    As noted above, warm moist/humid air introduced to enclosed space  28  causes a deposit of ice on cold surfaces in the enclosed space  28 . These ice deposits will be most prominent at the surfaces of evaporator coil  30 , which are the coldest surfaces in enclosed space  28  and exposed to a higher airflow rate than any other surfaces in enclosed space  28 . 
         [0033]    While cooling program  78  is being executed, processor  70  frequently checks the temperature values of Tair, in, Tair, out and Tref, out for a predetermined temperature condition based on at least one and, preferably more of these temperatures, that requires an initiation of a defrost mode. For example, the checking operation is an initial step of defrost program  80 . If the temperature condition does not require defrost, processor  70  continues to execute cooling program  78 . 
         [0034]    If the temperature condition requires defrost, processor  70  initiates defrost program  80 . Processor  70  then, if refrigeration apparatus  20  is configured in an electric defrost mode, causes fan motor  36  to be turned off, defrost heater  32  to be turned on and refrigerant assembly  24  to discontinue supplying refrigerant to evaporator coil  30 . If refrigeration apparatus  20  is configured in an air defrost mode, processor  70  causes refrigerant assembly  24  to discontinue supplying refrigerant to evaporator coil  30  for a predetermined period of time and also causes the fan(s)  34  to continue operating and circulating air through the evaporator coil surfaces. 
         [0035]    Defrost program  80  in a preferred embodiment determines the temperature condition based on a dynamic effectiveness (DE) of the performance of a heat exchanger (evaporator coil  30 ). DE is defined as the actual heat transfer of a heat exchanger divided by the maximum amount of heat that could be transferred for the same inlet temperature and flow rates in both cases. For the evaporator where the refrigerant flow has a greater “heat capacity” than the air flow the effectiveness (E) can be expressed as the ratio: 
         [0000]        E =(Tair,in−Tair,out)/(Tair,in−Tref,out),   (1)
 
         [0000]    where Tair, in is the temperature of the air entering evaporator coil  30 , Tair, out is the temperature of the air exiting evaporator coil  30 , and Tref, out is the saturated refrigerant temperature exiting evaporator coil  30 . 
         [0036]    Processor  70  executes defrost program  80  to monitor Tair, in, Tair, out and Tref, out to determine dynamic effectiveness DE. Tref, out is determined by looking up the saturation temperature that corresponds to a measured refrigerant pressure. A pressure transducer  86  measures the refrigerant pressure. 
         [0037]    Each time processor  80  monitors Tair, in, Tair, out and Tref, out during execution of defrost program  80 , the value of E is calculated by processor  70 . 
         [0038]    In the following description of defrost program  80  and  FIG. 3 , the following acronyms are used:
       DE Dynamic Effectiveness   RE Reference Effectiveness   DET Defrost Effectiveness Threshold   DTT Defrost Termination Temperature   DTS Defrost Termination Sensor Temperature   DT Defrost Time   DETT Defrost Termination Time   HSTS Heater Safety Termination Switch   HSTT Heater Safety Termination Temperature       
 
         [0048]    DET is a temperature value determined by design and user requirements. In one embodiment, DET is 35%. DTT is the predetermined defrost termination temperature that is found through testing, for example, typically 40-55° F. DETT is the amount of time that the defrost cycle operates if the defrost cycle is terminated by time.—HSTT is the coil temperature that cannot be exceeded, for example, 70° F. in one embodiment. 
         [0049]    Referring to  FIG. 3 , processor  70  executes instructions of cooling program  78  to control start up of refrigeration apparatus  20  at box  100  by determining if Tair, in is greater than a temperature set point. If not, refrigerant assembly  24  is not started. 
         [0050]    If yes, processor  70  initiates start up of refrigerant assembly  24 , fan motor  36  and fan  34 . Once start up begins, there is a delay at box  102  while processor  70  waits until Tair, in is cooled to within a predetermined programmed temperature setting (in one embodiment 15° F.) relevant to the thermostat set point before initiating defrost program  80 . The temperature set point and thermostat set point are identical and are determined by the end user for the product that is being placed in enclosed space  28 . 
         [0051]    Once Tair, in is within 15° F. of the thermostat set point, processor  70  executes instructions of defrost program  80 . At box  104  processor  70  executes instructions to start collecting data and calculations are initiated to establish RE and DE values. In one embodiment, the RE and DE values are initially both set to equal 0. Initially, DE will equal RE and DE will continue to equal RE until a peak RE value has been established. The peak RE value may change based on system operation as the system continues to operate and DE will also change accordingly. Once the final peak RE value is established (DE will equal RE) then the efficiency of the evaporator coil starts to deteriorate, the DE value will start to drop below the RE value. 
         [0052]    At box  106  processor  70  executes instructions using equation (1) to calculate RE and DE in real time during operation of refrigeration apparatus  20 . This calculation uses the current values of Tair, in, Tair out and Tref, out provided by input air temperature sensor  50 , output air temperature sensor  52  and pressure transducer (sensor)  86 . The processor  70  processes the collected real time data calculations and then per defrost program  80  instructions, generates RE and DE values. At box  108  processor  70  determines if the current processed value of DE is equal to RE. If yes, in box  110  DE is set equal to the current value of RE, which is used for the next comparison in box  108 . Processor  70  then returns to box  104 . 
         [0053]    If no, at box  112  processor  70  determines if RE—DE divided by RE is equal to the predetermined threshold DET. If no, defrost program  80  returns to box  106 . 
         [0054]    If yes, control program  80  proceeds to either an electric defrost mode or an air defrost mode dependent on the system requirements or application, wherein refrigeration assembly is deactivated  116 , evaporator fans are deactivated  116 A and defrost heaters are activated  118  for electric defrost mode or refrigeration assembly is deactivated  136  and evaporator fans continue to operate  138  for air defrost mode. 
         [0055]    If refrigeration apparatus  20  is configured for an electric defrost mode, at box  116  refrigerant assembly  24  is disabled. That is, refrigerant is not supplied to evaporator coil  30 . At box  116 A controller  26  deactivates or turns off fan motor  36  and fan  34 . At box  118  controller  26  activates or turns on defrost heater  32 . 
         [0056]    At box  120  processor  70  uses the temperature sensed by DTS sensor  84  to determine if it is equal to or greater than the defrost termination temperature DTT. If no, at box  122  processor  70  determines if the defrost time DT is equal to or greater than the defrost termination time DETT. If no, at box  124  processor  70  determines if the evaporator coil temperature is equal to or greater than the heater safety termination temperature HSTT. If no, cooling program  80  returns to box  120 . If the determination at any of boxes  120 ,  122  or  124  is yes, at box  126  processor  70  causes controller  26  to deactivate defrost heater  32 . At box  128  processor initiates a time delay to allow a “drip time” for the evaporator coil  30 . When the delay has ended, refrigerant assembly  24  is activated, box  130 . At box  132  a time delay is then initiated. When the time delay has ended, at box  134  processor  70  causes controller  26  to turn fan motor  36  and fan  34  on. Processor  70  then resumes execution of defrost program  80  at box  104 . 
         [0057]    If refrigeration apparatus  20  is configured for an air defrost mode, at box  136  refrigerant assembly  24  is deactivated. At box  138  processor  70  allows continued operation of fan motor  36  and fan  34 . At box  140  processor  70  determines if DT is equal to or greater than DTT. If no, processor  70  continues to execute the instructions of box  140  until DT is equal to or greater than DTT. When this happens, at box  142  processor  70  causes controller  26  to activate refrigerant assembly  24  in box  142  to provide refrigerant flow to evaporator assembly  22 . Processor  70  then resumes execution of defrost program  80  at box  104 . 
         [0058]    If refrigeration apparatus  20  is configured for a manual defrost mode  114 , the method determined in  114 A if a manual defrost has been requested. If no, then no defrost is initiated  114 B. If yes, then defrost is initiated  115  and electric defrost procedures are followed in steps  116 - 142  as discussed above or air defrost procedures are followed in steps  136 - 142  as discussed above. 
         [0059]    The method also provides for a safety defrost mode  113 , wherein the system monitors various safety defrost parameters  113 A to determine if the maximum safety defrost parameters are exceeded  113 B. If parameters are not exceeded, then the system returns to  113 A. If the parameters are exceeded, then the system initiates defrost  115  and electric defrost procedures are followed in steps  116 - 142  as discussed above or air defrost procedures are followed in steps  136 - 142  as discussed above. 
         [0060]    There are several advantages to the electronic controller of the present disclosure. There is a cost saving, as energy costs increase the additional cost of the electronic controller becomes more justifiable. In a “smart kitchen concept” where all of the operating parameters are centralized in one microprocessor, the electronic controller of the present disclosure in refrigeration equipment is essential to communicate with a central microprocessor. There is also a legislative advantage as the electronic controller is able to collect and store temperature data, allowing a storeowner to prove correct storage temperature and conditions of food produce. The refrigeration apparatus of the present disclosure also has the advantage of initiating defrost when the conditions at the evaporator coil require defrost. 
         [0061]    The present disclosure having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present disclosure as defined in the appended claims.