Abstract:
Apparatus and methodologies are provided to improve the refrigeration system by precisely controlling refrigerator compartment and heat exchanger temperatures through continuous modulation of device speeds or positions to match capacity with instantaneous load. A controller in a refrigerator is configured to provide a plurality of control loops to control various operational aspects of selected components in the refrigerator. A first loop controls the operating speed of a compressor based on temperature of the evaporator or based on the desired speed of an evaporator fan. A second control loop controls speed of an evaporator fan to maintain a prescribed freezer compartment temperature. A third control loop maintains a prescribed temperature in a fresh food compartment. In certain embodiments selected of the control loops may be thermodynamically coupled by way of thermal interaction between the various cooled compartments rather than being electrically coupled. The control loops may be individually configured as one of a proportional, proportional-integral, or proportional-integral-derivative control loop.

Description:
FIELD OF THE INVENTION 
     The present subject matter relates to refrigerators. More particularly, the present subject matter relates to improved energy consumption and temperature control within refrigerator compartments. 
     BACKGROUND OF THE INVENTION 
     Currently available refrigeration systems employ banded temperature control schemes that operated as either ON/OFF or LOW, MED, HIGH and required operational deadbands within their temperature control systems. Such systems include certain inherent inefficiencies such as having to run at lower than optimal evaporation temperatures in order to allow the unit to cycle off for a reasonable amount of time, as well as start losses and reliability penalties associated with starting and stopping a sealed system. In addition, internal humidity control is made more difficult due to off cycle time. 
     In view of these concerns, it would be advantageous to provide a refrigeration system that could provide a continuously modulated compressor, fan(s) refrigerant control valve(s), and/or damper in order to improve the refrigeration cycle resulting in reductions in the standard deviation of heat exchanger temperatures and compartment temperatures while also maintaining a higher percent run time on the compressor to reduce start losses. A higher percentage of run time would also be advantageous to improve internal humidity control. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     The present subject matter relates to a method for use in a refrigerator having one or more components including a fresh food compartment, a freezer compartment, a damper between the fresh food compartment and the freezer compartment, a controller, a compressor, a condenser, an evaporator, an evaporator fan, a fresh food fan, and a plurality of condition responsive sensors. The method provides for improving cycle efficiency by configuring the controller to provide continuous modulation of one or more of the speed of the evaporator fan, the speed of the condenser fan, the speed of the fresh food fan, the operating speed of the compressor, and the position of the damper. The method also provides for configuring the controller to maintain prescribed compartment conditions based on at least one of feedback from one or more of the plurality of condition sensors and thermodynamic interaction between one or more of the refrigerator components. 
     In certain embodiments one of the plurality of condition responsive sensors is a temperature sensor located on one of the evaporator, a suction line of the compressor, or is mounted within the freezer compartment. In other embodiments the plurality of condition responsive sensors includes one or more of a pressure sensor and a flow sensor. In specific embodiments the controller is configured as one of a proportional controller, a proportional-integral controller, and a proportional-integral-derivative controller. In selected embodiments, the controller is configured to maintain prescribed compartment conditions based on thermodynamic interaction between the freezer compartment, the fresh food compartment and the evaporator temperature. 
     The present subject matter also relates to a method for providing refrigerator compartment temperature control. In selected embodiments, the method provides a refrigerator including a housing including a fresh food compartment and a freezer compartment. The method also provides other refrigerator components including a controller, a compressor, and a condenser. Further, the method positions an evaporator within the freezer compartment and provides an evaporator fan to provide air flow across the evaporator. The method also provides first, second, and third temperature sensor at selected locations within the housing. 
     In specific embodiments, the method provides for configuring the controller to provide a plurality of control loops, including a first control loop configured to monitor one of temperature from the first temperature sensor or speed of the evaporator fan and to continuously modulate the operating speed of the compressor to maintain a prescribed target evaporator temperature, or the target evaporator fan speed. In these embodiments, the method also provides for configuring the controller to provide a second control loop configured to monitor temperature from the second temperature sensor and to continuously modulate the operating speed of the evaporator fan to maintain a prescribed freezer compartment temperature. Further in these embodiments, the method provides for configuring the controller to provide a third control loop configured to monitor temperature from the third temperature sensor to maintain a prescribed temperature in the fresh food compartment. 
     In selected embodiments, the method provides for locating the first temperature sensor on one of the evaporator or a suction line of the compressor. In other selected embodiments, the method provides for locating the second temperature sensor within the freezer compartment. In particular embodiments, the method comprises configuring the first controller to monitor speed of the evaporator fan to maintain a target evaporator fan speed. 
     In further embodiments, the method provides a fresh food fan within the fresh food compartment and provides for configuring the third controller to continuously modulate the operational speed of the fresh food fan to maintain a prescribed temperature in the fresh food compartment. In selected particular embodiments, the method provides a fresh food damper between the fresh food compartment and the freezer compartment causes the third controller to continuously modulate the position of the fresh food damper to maintain a prescribed temperature in the fresh food compartment. 
     In certain particular embodiments of the method, the method provides for configuring each of the first, second, and third control loops individually as one of a proportional controller, a proportional-integral controller, or a proportional-integral-derivative controller. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  provides an illustration of an exemplary embodiment of a refrigerator as may be used with the present subject matter; 
         FIG. 2  is a schematic illustration providing an example of a refrigeration cycle as may be used with the present subject matter; 
         FIG. 3  is a schematic illustration providing an example of a proportional-integral-derivative (PID) controlled refrigerator in accordance with the present technology; and 
         FIG. 4  is a graphical illustration of the state points showing a time averaged baseline cycling control versus a PID modulated cycle in accordance with present technology. 
     
    
    
     Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As noted in the Summary section, the present subject matter is directed toward methods of improved energy consumption through precise temperature control for a refrigerator applying the fundamentals of proportional-integral-differential (PID) feedback control systems to maintain constant compartment and heat exchanger core temperatures. 
       FIG. 1  provides a front view of a representative refrigerator  10  incorporating an exemplary embodiment of the present invention. For illustrative purposes, the present invention is described with a refrigerator  10  having a construction as shown and described further below. As used herein, a refrigerator includes appliances such as a freezer, refrigerator/freezer combination, compact, and any other style or model of a refrigerator. Accordingly, other configurations including multiple and different styled compartments could be used with refrigerator  10 , it being understood that the configuration shown in  FIG. 1  is by way of example only. 
     Refrigerator  10  includes a fresh food storage compartment  12  and a freezer storage compartment  14 . Freezer compartment  14  and fresh food compartment  12  are arranged side-by-side within an outer case  16 . Breaker strip  22  and mullion  24  form a front face, and extend completely around inner peripheral edges of case  16 . In addition, refrigerator  10  includes shelves  28  and slide-out storage drawers  30  which normally are provided in fresh food compartment  12  to support items being stored therein. 
     Refrigerator  10  is controlled by a processing device or other controller, such as a microprocessor (not shown in  FIG. 1 ), according to user preference via manipulation of a control interface  32  mounted in an upper region of fresh food storage compartment  12  and coupled to the microprocessor. A shelf  34  and wire baskets  36  are provided in freezer compartment  14 . In addition, an ice maker  38  may be provided in freezer compartment  14 . 
     A freezer door  42  and a fresh food door  44  close access openings to fresh food and freezer compartments  12 ,  14 , respectively. Each door  42 ,  44  is mounted to rotate about its outer vertical edge between an open position, as shown in  FIG. 1 , and a closed position (not shown) closing the associated storage compartment. Freezer door  42  includes a plurality of storage shelves  46 , and fresh food door  44  includes a plurality of storage shelves  48 . 
       FIG. 2  is a schematic view of refrigerator  10  ( FIG. 1 ) including an exemplary sealed cooling system  60 . In accordance with known refrigerators, refrigerator  10  includes a machinery compartment  62  that at least partially contains components for executing a known vapor compression cycle for cooling air. The components include a compressor  64 , a heat exchanger or condenser  66 , an expansion device  68 , and an evaporator  70  connected in series and charged with a refrigerant. Evaporator  70  is also a type of heat exchanger that transfers heat from air passing over the evaporator to a refrigerant flowing through evaporator  70  thereby causing the refrigerant to vaporize. As such, cooled air is produced and configured to refrigerate compartments  12 ,  14  of refrigerator  10 . 
     From evaporator  70 , vaporized refrigerant flows to compressor  64 , which operates to increase the pressure of the refrigerant. This compression of the refrigerant raises its temperature, which is lowered by passing the gaseous refrigerant through condenser  66  where heat exchange with ambient air takes place so as to cool the refrigerant. A fan  72  is used to pull air across condenser  66 , as illustrated by arrows A, so as to provide forced convection for a more rapid and efficient heat exchange between the refrigerant and the ambient air. 
     Expansion device  68  further reduces the pressure of refrigerant leaving condenser  66  before being fed as a liquid to evaporator  70 . Collectively, the vapor compression cycle components in a refrigeration circuit, associated fans, and associated compartments are sometimes referred to as a sealed refrigeration system operable to force cold air through refrigeration compartments  12 ,  14 . The refrigeration system depicted in  FIG. 2  is provided by way of example only. It is within the scope of the present invention for other configurations of the refrigeration system to be used as well. For example, fan  74  may be repositioned so as to push air across evaporator  70 , dual evaporators may be used with one or more fans, and numerous other configurations may be applied as well. 
     With reference to  FIG. 3 , there is illustrated a schematic representation of an example of a proportional-integral-derivative (PID) controlled refrigerator  300  in accordance with the present technology. A refrigerator  300  constructed in accordance with present technology operates by continuously modulating speed and/or position of sealed system components including, but not limited to, compressor  364 , evaporator fan  374 , condenser fan  372 , fresh food fan  376 , damper  378 , or other devices, to match heat loads in real-time thereby delivering constant compartment and heat exchanger temperatures. 
     In accordance with a significant aspect of the present technology, by limiting the approach temperature of the evaporator and condenser, that is, in the case of the evaporator, the difference between the core evaporator temperature and the desired compartment temperature being cooled, while in the case of the condenser, the difference between the condenser core temperature and the ambient available to reject the heat. 
     In particular, by employing a controller to continuously modulate the speed of the compressor, the compressor speed can be reduced, resulting in less mass flow of refrigerant to the evaporator so that the evaporator and condenser may be held at desired core temperatures and pressures. In so doing, the extremely low evaporator temperatures that are a natural side effect of cycling systems are able to be substantially eliminated thereby shrinking the size of the refrigeration cycle and minimizing cycling losses to provide a higher compressor EER and system Coefficient of Performance (COP). 
     In exemplary configurations, such a controller may include, but is not limited to, a proportional (P) controller, a proportional-integral (PI) controller, a proportional-integral-derivative (PID) controller, a Fuzzy Logic based controller, a Neural Network, or a look up table based controller. 
     With reference to  FIG. 4 , there is illustrated a graphical representation  400  demonstrating the energy saving potential between a time averaged baseline cycling control  402  and a PID modulated cycle  404  in accordance with present technology. As can be seen with relation to saturation phase line  406 , the average PID modulated cycle  404  transitions from points  1 - 2 - 3 - 4  while baseline cycle  402  transitions from points a-b-c-d. In accordance with present technology, however, this modulated cycle  404  removes the same amount of latent heat over time as the baseline cycle  402  but with fewer start losses and with more stable resulting temperatures. From this it will be appreciated that the latent heat extracted by evaporator Δh a-b =Δh 1-2  however the energy of compression is less, i.e., Δh b-c &lt;Δh 2-3 . 
     As is understood by those of ordinary skill in the art, a proportional-integral-derivative (PID) control system may be generally defined using the well recognized generic formula: 
               u   ⁡     (   t   )       =       K   C     ⁡     (     e   +       1     T   i       ⁢       ∫   0   t     ⁢     e   ⁢     ⅆ   i           ⁢           +       T   d     ⁢       ⅆ   e       ⅆ   t           )             
where the three summed terms represent proportional, integral, and derivative terms that, together with a multiplication constant, represent the control function u(t). Such PID control systems may be implemented in numerous manners including through hardware, software, or combinations thereof. It should be appreciated that while the presently illustrated exemplary embodiment describes a PID control system, other systems, as also previously noted, may be used to provide continuous modulation of the various controllable components within a refrigeration system to achieve improved cycle efficiency in accordance with present technology
 
     In accordance with an exemplary embodiment of the present subject matter, a control system, including controller  302 , provides a plurality of independent or cascaded/embedded proportional-integral-derivative (PID) control loops which drive component speed or position based on system feedback. Controller  302  may correspond to the previously noted microprocessor mentioned with respect to  FIG. 1 , or could correspond to other known control devices. System feedback to controller  302  could include, but is not limited to, signals from various temperature sensing devices  392 ,  394 ,  396 ,  398  or other devices including pressure and flow sensors not separately illustrated. As illustrated in exemplary form herein, the plurality of controlled loops may be thermodynamically coupled by way of thermal interaction between the cooled compartments  312 ,  314  rather than electrically coupled to derive cooling for fresh food compartment  312  and freezer compartment  314  of household refrigerator  300 . 
     In a first exemplary embodiment of the present subject matter, three independent PID control loops may be provided. The first PID control loop uses a temperature sensing device as feedback to the PID control loop to modulate compressor  364  speed by way of control line  340  from controller  302  to maintain a prescribed target temperature through varied refrigerant mass flow. In a first configuration of the first PID control loop, temperature sensing device  398  maybe located on evaporator  370  to provide temperature feedback to controller  302 . In an alternate configuration of the first PID control loop, the temperature-sensing device may correspond to temperature sensing device  396  that may be located on compressor  364 &#39;s suction line  386 . 
     Further in accordance with present technology, a second PID control loop uses a temperature-sensing device as feedback to the second PID control loop to modulate the evaporator/freezer fan  374  speed via control lines  332 ,  338  from controller  302  in order to maintain a prescribed freezer compartment  314  temperature. In this instance, temperature-sensing device  392  is mounted such that it obtains and transmits to controller  302  a representative freezer compartment  314  temperature. 
     A third PID control loop uses temperature sensing device  394  as feedback to the third PID control loop to modulate the fresh food fan  376  speed via control lines  332 ,  334  from controller  302  or fresh food damper  378  position via control lines  332 ,  336  from controller  302  in order to maintain a prescribed fresh food compartment  312  temperature. Temperature-sensing device  394  is mounted such that it obtains and transmits to controller  302  a representative fresh food compartment  312  temperature. 
     In a second embodiment of the present subject matter, two independent PID control loops with a cascaded/embedded third PID control loop may be provided. In accordance with this second embodiment of the present subject matter, the first PID control loop controlling the operating speed of compressor  364  uses a signal based on the evaporator/freezer fan  374  speed as its feedback instead of the previously employed temperature measuring device to maintain a prescribed target evaporator/freezer fan speed. The two independent control loops, that is, the previously noted second and third PID control loops, operate as previously described with respect to the first embodiment. 
     In accordance with the present technology, multiple control functions, rather than being electrically connected directly, may be thermodynamically connected. For example, when the fresh food door  44  ( FIG. 1 ) of refrigerator  10  is opened, the compressor senses the door opening by a thermodynamic connection as follows. The door opening results in heat entering the fresh food compartment  12  so that the fresh food compartment temperature increases. A damper  378  ( FIG. 3 ) opens which places more load on evaporator  370  in the freezer compartment  314 . As evaporator  370  warms due to the heat load, the controller system controlling the compressor senses the higher evaporator temperature and increases the speed of the compressor  364 . In an exemplary configuration this controlled increase in speed may be by way of continuous modulation of speed via a PID controller. 
     The increase in speed of the compressor  364  increases mass flow of refrigerant through evaporator  370  and brings the evaporator temperature back down to a desired target temperature. As heat is rejected, damper  378  begins to close back to its original state and the evaporator cools so that the compressor may then slow back down. In such a configuration, the coupling between the fresh food controller and the freezer controller is by way of the thermodynamic coupling controlled by operation of the damper and not an electrical connection as may be used in other embodiments. 
     An embodiment of the present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. The technical effect of the executable code is to facilitate prediction and optimization of modeled devices and systems. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.