Abstract:
A control apparatus and associated method for a refrigeration system are provided. The control apparatus includes sensors capable of detecting controlled refrigerator zone temperatures and superheat levels of refrigerant vapour exiting an evaporator. The control module receives input from the sensors, compares the input to a determined controlled refrigerator zone set point and a learned superheat level, and generates an output with respect thereto. In particular the output modulates an electronic evaporator pressure regulating (EEPR) valve between an open and a closed position in response to detecting abnormal operation of the thermostatic expansion valve or electronic expansion valve.

Description:
FIELD OF THE INVENTION 
     This invention relates to a refrigeration system. In particular, the invention provides a refrigeration system that includes a control system for controlling one or more components of the refrigeration system. 
     BACKGROUND OF THE INVENTION 
     Generally, a refrigeration system includes a compressor, a condenser, an expansion valve, and an evaporator. Refrigerant vapor is compressed to a high pressure by the compressor and is conducted through the condenser where it is cooled to form a liquid under high pressure. This high pressure liquid is then adiabatically expanded through the expansion valve into the evaporator. In the evaporator, the refrigerant absorbs heat from the surroundings of the evaporator, which transforms the low pressure liquid refrigerant into a vapor. In this process, the environment surrounding the evaporator, for example, a refrigerator case, is cooled. The refrigerant vapor is then returned to the compressor via a suction line. 
     Generally, it is desirable to control the amount of liquid refrigerant returning to the inlet of the compressor from the evaporator. In some cases, liquid refrigerant may dilute the lubricating oil in a typical hermetic compressor and thus cause damage to the compressor. Also, liquid refrigerant may damage certain of the compressor components, such as the compressor reed valves. 
     Another concern with many refrigeration systems is the presence of ice on the evaporator coils. During normal operation of many refrigeration systems, the evaporators may operate at temperatures low enough for water vapor to crystallize on the evaporator coils. This can produce a “frost” on the coils, which may reduce the efficiency of the refrigeration system and may result in liquid refrigerant flooding the compressor. As a result, the surfaces of the evaporator coils must periodically be defrosted. 
     Various techniques for defrosting refrigeration systems are known. For example, one method for defrosting refrigeration systems is to reverse the refrigeration cycle. When the refrigeration cycle is reversed, hot refrigerant vapor from the compressor is directed into the evaporator outlet, through the evaporator, into the condenser inlet, through the condenser, and back into the compressor. A problem with this method is that often the temperature of refrigerant entering the compressor is so low that some liquid is introduced into the compressor. As discussed above, the presence of liquid in the compressor may damage or destroy the compressor. In addition, the temperature of the refrigerant entering the evaporator may be too low for rapid or complete defrosting of the evaporator. Thus, the defrost cycle may be very time consuming or the evaporator may not be completely defrosted. 
     As such, there is a need for improved refrigeration systems, in particular, for refrigeration systems in which the amount of liquid refrigerant entering the compressor is controlled and/or in which the amount of ice build up on the evaporator coils is controlled. 
     SUMMARY 
     The refrigeration system described herein provides a method and system for controlling the amount of liquid refrigerant entering the compressor and/or icing of evaporator coils. In particular, the refrigeration control system includes one or more microprocessor based controls. 
     One embodiment of the refrigeration system includes a control apparatus for a refrigeration system having one or more evaporators, each having an inlet and an outlet; one or more controlled refrigerator zones operably associated with one or more evaporators; one or more controlled refrigeration zone sensors operably associated with one or more controlled refrigerator zones and capable of detecting one or more controlled refrigerator zone temperatures; one or more evaporator outlet temperature sensors; an electronic evaporator pressure regulating (EEPR) valve disposed along a suction line of the refrigeration system and having an open and a closed position and capable of modulating between said open and said closed position; one or more refrigerant pressure sensors capable of detecting pressure in the suction line of the refrigeration system; and a control module capable of receiving input from said sensors and operable to learn a baseline superheat during normal operation, compute an amount of superheat, and take control action on the EEPR valve when the superheat deviates from normal operation. 
     A second embodiment includes method of operating a control module associated with a refrigeration system. The method includes calculating a superheat level and monitoring a controlled refrigeration zone temperature of the refrigeration system; comparing said superheat level with a learned superheat level and comparing said controlled refrigeration zone temperature with a controlled refrigeration zone temperature set point; determining whether said superheat level is below said learned superheat level; determining whether said controlled refrigeration zone temperature is within an activating range; and transmitting a signal to close an electronic evaporator pressure regulating (EEPR) valve an appropriate amount in response to a superheat level below said learned superheat level and a controlled refrigeration zone temperature within said activating range. 
     The above summary of the present invention is not intended to describe each discussed embodiment of the present invention. This is the purpose of the figures and the detailed description that follows. 
    
    
     
       DRAWINGS 
       The invention may be more completely understood in connection with the following drawings, in which: 
         FIG. 1  is a diagrammatic representation of a typical refrigeration system. 
         FIG. 2  is a diagrammatic representation of an embodiment of a refrigeration system described herein. 
         FIG. 3  is a schematic flow chart of controller operation of a refrigeration system as described herein. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. It should be understood, however, that the invention is not limited to the particular embodiments described. On the contrary, the intention is to cover modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION 
     The invention relates to a refrigeration system. In particular, the disclosure provides a refrigeration system that may include one or more controllers that can be used to control various components of the refrigeration system. In one embodiment, the refrigeration system can include a controller configured to regulate one or more EEPR (electronic evaporator pressure regulating) valves. For example, it may be desirable to control the one or more EEPR valves to regulate the amount of liquid refrigerant entering the compressor and/or to modulate icing of one or more evaporator coils. The term “refrigeration system” as used herein can refer to many different refrigeration systems, including commercial refrigeration systems, domestic refrigerators, air conditioners and heat pumps. 
     Overview of a Refrigeration System 
     A typical refrigeration system will first be described with reference to  FIG. 1 . The refrigeration system  100  generally includes one or more compressors  10 , one or more condensers  20 , and one or more evaporators  30 . Metering of refrigerant through the one or more evaporators  30  may be carried out by one or more expansion valves  25  and/or one or more electronic evaporator pressure regulating (EEPR) valves  75 . 
     In operation, refrigerant vapor is compressed to a high pressure by the compressor  10  and is conducted through the compressor outlet  12  to one or more condensers  20 . In the condenser  20 , the refrigerant vapor is condensed to a liquid refrigerant under high pressure. The high pressure liquid refrigerant exits the condenser outlet  22  and is expanded through one or more expansion valves  25  into an evaporator  30  that may include one or more evaporator coils (not shown). Some refrigeration systems include a plurality of parallel evaporators  30 . In some systems, each evaporator  30  is associated with an expansion valve  25 . In other systems, more than one evaporator  30  can be associated with one expansion valve  25 . The refrigerant in the one or more evaporators  30  absorbs heat from the surroundings, which cools the surroundings, referred to herein as a controlled refrigeration zone, and transforms the low pressure liquid refrigerant into a vapor. The refrigerant vapor exits the evaporator  30  through the evaporator outlet  32  and is returned to in inlet  11  of the compressor  10 , for example, through a suction line  50 . 
     The term “superheat” as used herein refers to the additional heat (in degrees) that is absorbed by the evaporator coil  30  above the boiling point of the refrigerant in the evaporator coil  30 . The boiling point of the refrigerant may vary depending upon the type of refrigerant used and/or the pressure of the refrigerant in the evaporator coil. In some instances, superheat is not directly measured, but rather is calculated as the difference between the saturated suction temperature of the evaporator and the evaporator outlet temperature. The term “saturated suction temperature” refers to the temperature of the vapor line at the suction pressure, for example, as measured by a pressure sensor. 
     Thermostatic Expansion Valve 
     Many refrigeration systems  100  include one or more thermostatic expansion valves (TXV)  25 . Various configurations of expansion valves  25  are possible and are known to one skilled in the art. Typically, the TXV  25  is configured to maintain a sufficient supply of refrigerant to the evaporator  30  while controlling the amount of liquid refrigerant passing into the suction line  50  and/or compressor  10 . For example, the TXV  25  may be configured to meter the flow of liquid refrigerant into the evaporator  30  at a rate corresponding to the amount of refrigerant boiled off in the evaporator  30 . Alternately, the TXV  25  may be configured to control the flow of the refrigerant into the evaporator  30  to maintain the superheat of the refrigerant vapor leaving the evaporator  30  at a predetermined level. In some instances, it may be desirable to have the TXV  25  configured to maintain the superheat of the refrigerant exhausted from the evaporator  30  near a preferred or preset superheat setting. In general, a TXV  25  controls the flow rate of refrigerant to the evaporator  30  based on a temperature and/or pressure sensed at an outlet  32  of the evaporator  30  during a refrigeration cycle. Consequently, a TXV  25  typically includes a sensor capable of sensing the temperature and/or pressure of refrigerant exiting the evaporator  30 . 
     In general, opening the TXV  25  increases the amount of refrigerant entering the evaporator  30  and thereby reduces the superheat temperature (T SH ) of the vapor exhausted from the evaporator  30 . Conversely, closing the TXV  25  reduces the flow of refrigerant to the evaporator  30  and therefore typically increases the superheat temperature (T SH ) of the vapor exhausted from the evaporator  30 . 
     Electronic Evaporator Pressure Regulating Valve 
     Many refrigeration systems also include one or more electronic evaporator pressure regulating (EEPR) valves  75  interposed on a suction line  50  between one or more evaporators  30  and one or more compressors  10 . Generally, the EEPR valve  75  regulates the flow of refrigerant vapor from the evaporator  30  to the compressor  10 . Additionally, the EEPR valve  75  may help establish and maintain Suction pressure (P S ) relative to the compressor  10 , and/or help maintain the superheat temperature (T SH ) within the evaporator  30 . 
     In general, an EEPR valve  75  includes valve body operably connected to the suction line  50  and a valve element movable within the valve body between a fully closed position and a fully open position, and any position in between. Typically, the position of the valve element is controlled by a motor. Various configurations of EEPR valves  75  are possible and are known to those of skill in the art. 
     Operation of the EEPR valve  75  may be controlled by a controller  500  that is operably connected to the EEPR valve  75  and is capable of activating the valve motor to open, close or modulate the valve opening. In one embodiment, the controller  500  activates the valve motor in response to a reduction in superheat (T SH ) temperature of the refrigerant vapor exiting the one or more evaporators  30 , combined with an undesirably high temperature in the associated controlled refrigeration zone. In another embodiment, the controller  500  activates the valve motor in response to a reduction in superheat (T SH ) temperature of the refrigerant vapor exiting the one or more evaporators  30 , combined with an undesirably low temperature  35  in the associated controlled refrigeration zone  33 . The suction pressure (P S ) can be detected by a sensor (for example, at location “B” in  FIG. 2 ) in the refrigeration system  100 , and the superheat temperature can be calculated by converting the refrigerant pressure to its associated temperature, and comparing it to the temperature of the refrigerant line as it exists at the outlet of the evaporator  32 . Methods for converting a refrigerant pressure to a refrigerant temperature are known to those of skill in the art and include, for example, using calculations based on known equations or looking up the corresponding associated temperature in a table or chart. 
     Controlled Refrigerator Zone 
     The refrigeration system  100  may also include one or more controlled refrigerator zones  33  and one or more controlled refrigerator zone temperature sensors  35 , wherein each controlled refrigerator zone  33  is associated with at least one evaporator  30  and adapted to be cooled by the evaporator  30 . As used herein, the term controlled refrigerator zone  33  refers to the environment that is being cooled by the refrigeration system  100 , regardless of encapsulation. The controlled refrigerator zone  33  can take a variety of forms, including, but not limited to, a domestic or commercial refrigerator case, a walk-in freezer, a merchandizing case, or a room being cooled by an air conditioner. In many refrigeration systems  100 , the controlled refrigerator zone  33  includes more than one evaporator  30 . The controlled refrigerator zone  33  may also include one or more sensors  35  that are operably connected to the controller  500  and are capable of determining the temperature in the controlled refrigerator zone (T C ) and sending a signal to the controller  500  regarding the temperature in the controlled refrigerator zone  33 . The controller  500  can then compare the temperature in the controlled refrigerator zone (T C ) to the desired controlled refrigeration zone temperature setpoint (T CSET ). 
     Defrost Cycle 
     The refrigeration cycle may include a defrost cycle to reduce the presence of ice on the evaporator coils. The frequency with which a particular evaporator must be defrosted can depend on the rate at which ice builds up, the cooling load on the evaporator and the rate at which it can be defrosted. In general, the length of the defrost period is determined by the degree of ice accumulation on the evaporator and by the rate at which heat can be applied to melt off the ice. Ice accumulation can vary with the type of installation, the conditions inside the fixture and the frequency of defrosting. 
     Initiation of a defrost cycle can be controlled by a timer within the controller or by detection of some parameter other than time. Determining a suitable signal for initiating a defrost cycle is within the skill of one in the art. In any event, when the controller is informed that it is time for defrost, it enters the defrost mode. 
     Refrigeration Control System 
     Various embodiments of a refrigeration system  100  will now be described with reference to  FIG. 2 . As discussed previously, a refrigeration system  100  can include one or more compressors  10 , one or more condensers  20 , one or more expansion valves  25 , one or more evaporators  30 , one or more controlled refrigeration zones  33  and/or one or more EEPR valves  75 . The refrigeration system  100  may also include a system controller  500  operable to control one or more aspects of the refrigeration system. 
     Metering of refrigerant through the evaporators  30  can be accomplished by one or more expansion valves  25  and/or one or more EEPR valves  75 . In one embodiment, for example that shown in  FIG. 2 , the refrigeration system  100  includes more than one evaporator  30 . In many refrigeration systems  100  having more than one evaporator  30 , the evaporators are located in parallel and are positioned on one or more branches  41  stemming from a branch point  40  located downstream of a condenser outlet  22 . See for example,  FIG. 2 . If desired, each evaporator  30  can have an expansion valve  25  associated therewith, wherein the expansion valves  25  are located on the branches  41  downstream of the branch point  40 . If desired, each expansion valve  25  can be operated independently or the expansion valves  25  can be operated in concert. In an alternate embodiment (not shown), a single expansion valve  25  can be associated with more than one evaporator  30 . In this embodiment, the expansion valve  25  is generally located upstream of the branch point  40  (but downstream of the condenser outlet  22 ). In other embodiments, a combination in which one or more evaporators  30  is associated with one expansion valve  25  and in which one or more evaporators  30  is associated with its own expansion valve  25  may be desirable. 
     In the embodiment shown in  FIG. 2 , one EEPR valve  75  is associated with more than one evaporator  30 . In this embodiment, the EEPR valve  75  is located downstream of a junction  45  of the evaporator  30  branches  41 . In an alternate embodiment (not shown), at least one EEPR valve  75  can be employed for each evaporator  30 . Alternately, a combination in which one or more evaporators  30  is associated with one EEPR valve  75  and one or more evaporators  30  is associated with its own EEPR valve  75  may be desirable. If more than one EEPR valve  75  is included in the refrigeration system  100 , each EEPR valve  75  can be controlled separately by a separate controller  500 . Alternately, one or more EEPR valves  75  can be controlled with a single controller  500 . 
     Sensors 
     The refrigeration system  100  may include one or more sensors located between one or more evaporators  30  and one or more EEPR valves  75 , wherein the sensor is capable of detecting the superheat temperature (T SH ) of the refrigerant vapor exiting one or more evaporators  30 . In one embodiment, a sensor is associated with each evaporator  30  in the refrigeration system  100  (shown as “A” in  FIG. 2 ). In this embodiment, each sensor “A” is located proximate an outlet of its associated evaporator  30 . For example, each sensor “A” can be located on the same branch  41  as its associated evaporator  30  upstream of junction  45 . 
     Because the EEPR valve  75  may also help establish and maintain suction pressure (P S ) relative to the compressor  10 , it may be desirable to include a pressure sensor (shown as “B” in  FIG. 2 ) between the evaporator coil  30  and the EEPR valve  75 . The amount of superheat can be determined by reading the pressure sensor B, converting the pressure to the saturated suction temperature for the associated refrigerant (using a calculation or looking up in a table), and subtracting it from the temperature as read at location A. 
     Control Sequence 
     In general, the controller  500  maintains the controlled refrigeration zone temperature  35  within a predetermined or desired temperature range (T SET ) by modulation of one or more EEPR valves  75 . Throughout the refrigeration cycle, the controller  500  receives signals from one or more temperature sensors associated with one or more evaporators  30 , one or more controlled refrigerator zones, and/or one or more pressure sensors “B”. Based on these inputs, the controller  500  modulates the opening of one or more EEPR valves  75 . 
     One control sequence  300  of the operation of the controller  500  is shown schematically in the flow chart of  FIG. 3 . At the onset of the refrigeration cycle, the controller  500  is programmed with a preferred or “learned” superheat (T SET ) level  310 . The “learned” superheat (T SET ) is determined by monitoring the superheat value on a regular basis when the EEPR is in normal operation and weighing it over a period of time into a baseline profile or an average value. The controller  500  is also programmed with a normal temperature “set point” for one or more controlled refrigerator zones (T CSET )  315 . The temperature set point is product and/or application specific and can be determined by the user. Factors that may be considered in determining a suitable set point include, for example, food type, case type, and case manufacturer. If desired, the set point can be different for different controlled refrigerator zones  33  within a refrigeration system  100 . Throughout the refrigeration cycle, the controller  500  receives signals from the one or more temperature sensors  35  associated with the controlled refrigerator zones  33  to determine the actual superheat (T SH ) level of the system  325 . During the refrigeration cycle, the actual superheat (T SH ) level is compared to the learned superheat (T SET )  350 . 
     Throughout the refrigeration cycle, the controller  500  also receives signals from the one or more temperature sensors  35  associated with one or more controlled refrigerator zones  33  to determine the actual controlled refrigerator zone temperature (T C )  340 . The actual controlled refrigerator zone temperature (T C ) is compared to a controlled refrigeration zone temperature set point (T CSET )  345 . 
     If the actual superheat (T SH ) drops a determined amount below the learned level (T SET )  335 , and if one or more sensed controlled refrigeration zone temperatures (T C ) are below a set point  345  (also referred to herein as a “normal” temperature) by a user specified amount (which may be application specific), the controller  500  transmits a signal to close the respective EEPR valve  75  an appropriate amount  355  to a modified EEPR position. The “determined amount below the learned level” can be defined by the user in the software, and may vary depending on the desired sensitivity of this function. The amount that the valve is closed is application specific and is a user specified parameter in the software for the controller. In this scenario, it is assumed that one or more of the expansion valves  25  are not closing sufficiently. Consequently, closing the EEPR valve  75  helps prevent liquid refrigerant from returning to the one or more compressors  10 . This modified EEPR position will remain in effect until the next defrost cycle occurs  360 . Upon detecting a defrost cycle, the controller will re-start the control sequence. At the end of a defrost cycle, the EEPR will be in the closed position, and it will begin to modulate open as far as it needs to go to bring the controlled refrigeration zone temperature  35  down to the associated setpoint (T CSET ). 
     An alternate control sequence  300  of the operation of the controller  500  is also shown schematically in the flow chart of  FIG. 3 . Many of the steps in the sequence are the same as described above. However, in this control sequence, if the actual superheat (T SH ) drops a determined amount below the learned level (T SET )  335 , and if one or more sensed controlled refrigeration zone temperatures (T C ) are a determined amount above a set point  345 , the controller  500  transmits a signal to close the EEPR valve  75  by an appropriate amount to a modified EEPR position  355 . As discussed above, the determined amount is user and/or application specific. In this scenario, closing the EEPR valve  75  results in an increase in the evaporator coil pressure and thereby helps reduce additional ice build-up on the evaporator coils. The modified EEPR position will be in effect until the next defrost cycle is detected  360 . Upon detecting a defrost cycle, the controller will re-start the control sequence. Starting from a closed position, the valve will begin to modulate open as far as it needs to go in order to bring the controlled refrigeration zone temperature down to the setpoint. 
     It will be understood that the foregoing is only illustrative of the principles of the invention and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. Accordingly, such embodiments will be recognized as within the scope of the present invention. Persons skilled in the art will also appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation and that the present invention is limited only by the claims that follow.