Abstract:
A control method and device for controlling the operation of various components of a refrigeration system provides more efficient operation of those components. Energization of the compressor is delayed upon power interruption, and high pressure is relieved through operation of a valve. The compressor runs is energized if the cabin temperature exceeds a specified temperature for a predetermined length of time, is is de-energized if the cabin temperature drops below a specified temperature. The condenser fan is energized based on the temperature of the condenser coil inlet and the ambient temperature. The evaporator fan is energized based on the cabin temperature and the temperature of the evaporator coil outlet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to a method and device for controlling the operation of a refrigeration system, and is particularly directed to a method and device for controlling the operation of the compressor, the condenser fan and the evaporator fan of a refrigeration system. The method and device will be disclosed in connection with a refrigeration system, such as that disclosed in my U.S. Pat. No. 5,809,789, issued Sep. 22, 1998, and incorporated herein by reference.  
         BRIEF SUMMARY OF THE INVENTION  
         [0002]    A refrigeration system is used to maintain the temperature within an area, referred to herein as the cabin. A mechanical vapor compression refrigeration system uses a liquid refrigerant as a working fluid in a closed loop cycle to produce heat transfer through evaporation of liquid refrigerant under reduced pressure and temperature, followed by compression of the liquid to elevate the saturation temperature of the vapor, allowing the vapor to be condensed by heat rejection. Examples of refrigeration systems include air conditioners and freezers. A refrigeration system can also act as a heat pump.  
           [0003]    The principal components of a mechanical vapor compression refrigeration system are a compressor, a condenser, a condenser fan, an evaporator and an evaporator fan. The condenser and evaporator are, of course, heat exchangers. The evaporator absorbs heat and the condenser rejects heat, whether the refrigeration system is used to cool a controlled space or to heat a controlled space.  
           [0004]    The present invention is a unique method and device for controlling the operation of the compressor, the condenser fan and the evaporator fan in a more efficient manner. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0005]    U.S. Pat. No. 5,809,789 describes an energy efficient refrigeration module with a set of temperature sensors connected to a programmed digital computer. The computer processes the temperature measurements using control logic configured to implement the operation described therein. Based on the control logic, as applied to the measured temperature, the computer actuates a heater valve for defrosting the evaporator coil of the system.  
         [0006]    Referring to FIG. 3 of U.S. Pat. No. 5,809,789, the disclosed refrigeration module includes compressor  18 , condenser fan  26 , and evaporator fan  24 , all of which are controlled by RISC processor  70 . Processor  70  controls operation of valve  28 , which functions, when actuated, to allow hot gas from the high pressure outlet of compressor  18  to flow to the inlet side of evaporator  22 , thereby melting any ice which may have formed on the evaporator coils.  
         [0007]    Actuation of valve  28  is controlled based on the process in U.S. Pat. No. 5,809,789 using temperature information collected by six temperature sensors. Sensor  90  measures the ambient air temperature; sensor  91  measures the temperature of the chilled cabin (cabin temperature), sensors  92  and  93  respectively measure the inlet and outlet temperatures of evaporator  22 , and sensors  94  and  95  respectively measure the inlet and outlet temperature of condenser  20 .  
         [0008]    Although U.S. Pat. No. 5,809,789 discloses, in part, a particular control and control method which includes control of compressor  18 , condenser fan  26  and evaporator fan  24 , the present invention of this patent is a different control and control method for these components. Although the present invention is disclosed in conjunction with the refrigeration system of U.S. Pat. No. 5,809,789 and its control, the various aspects of the present invention are capable of use on any refrigeration system, and independent of the specific control used thereon.  
         [0009]    In the present invention, the compressor, condenser fan and evaporator fan are controlled independent of each other. A controller, preferably comprising a computer processor, is used to actuate these components based on the following processes. If is of course possible to control these components without a computer processor, and the present invention and claims herein are not to be interpreted as being limited to a computer processor.  
         [0010]    In one aspect of the present invention, the control includes control logic configured to control operation of the compressor so that the compressor does not restart immediately in the event of a power interruption. Instead, once a power interruption of any detectable duration has occurred, actuation or reactuation of the compressor is delayed for a predetermined period of time. If there is any loss of power for any detectable duration of time, the compressor shuts down for the predetermined period of time. In one embodiment, the delay is a three minute delay. In addition, in one embodiment which includes a valve such as valve  28 , the control includes control logic which is configured to energize the valve following the restoration of power following a power interruption, equalizing the pressure of the coolant in the system by connecting the high pressure outlet side of the compressor with the lower pressure inlet side of the compressor, such as through the evaporator coil, as is achieved by actuation of valve  28  in U.S. Pat. No. 5,809,789. Of course, an appropriate valve may be located at any location in the coolant circuit which functions, directly or indirectly, to equalize the pressure across the compressor.  
         [0011]    The delayed restart and equalized pressure reduces stress on the compressor by eliminating high pressure load during restarts. It also stabilizes power flow to the compressor, avoiding the possibility of a power surge occurring immediately following power interruption.  
         [0012]    In another aspect of the present invention, the control includes control logic configured to energize the compressor when the temperature of the cabin being cooled exceeds a predetermined high temperature for at least a predetermined length of time, and to de-energize the compressor when the temperature of the cabin is less than a predetermined low temperature. In one embodiment, the predetermined high temperature is 48 degrees Fahrenheit, the predetermined length of time is one minute, and the predetermined low temperature is 38 degrees Fahrenheit.  
         [0013]    In another aspect of the present invention, the control includes control logic which is configured to control operation of the condenser fan based on the temperature of the condenser coil inlet and the ambient temperature. The condenser fan is energized if the condenser inlet temperature is greater than the ambient temperature plus a predetermined temperature difference. In one embodiment, the predetermined temperature is ten degrees Fahrenheit. The condenser fan remains energized until the condenser inlet temperature is less than the ambient temperature plus a predetermined temperature difference. In one embodiment, the predetermined difference is ten degrees Fahrenheit. Although in this embodiment the predetermined temperature differences for the fan energized and the fan de-energized conditions are equal, they do not necessarily have to be.  
         [0014]    In another aspect of the present invention, the control includes control logic configured to de-energize the compressor if the temperature of the condenser coil inlet reaches or exceeds a predetermined temperature. Such a condition occurs if, for example, there is inadequate air flow across the condenser coil, as would occur if the condenser fan failed or was blocked. In one embodiment, the predetermined temperature is 165 degrees Fahrenheit. The compressor remains de-energized until the temperature of the condenser coil inlet reaches or drops below a predetermined temperature. In one embodiment, the predetermined temperature is 120 degrees Fahrenheit. This control logic allows intermittent operation of the condenser even with inadequate air flow thereacross, providing some heat rejection from the condenser, and therefore some cooling by the evaporator. If the condenser inlet temperature exceeds the predetermined temperature and the compressor is de-energized as described, the control logic is configured to run the condenser fan constantly, without regard to the temperature difference between the temperature of the condenser inlet and the ambient temperature. If adequate air flow across the condenser is restored, then once the compressor is restarted, the operation of the condenser fan will return to being controlled based on the temperature difference between the temperature of the condenser inlet and the ambient temperature, as described above.  
         [0015]    In another aspect of the present invention, the control includes control logic which is configured to control operation of the evaporator fan based on the cabin temperature and the temperature of the evaporator coil outlet. The evaporator fan is energized if the cabin temperature is equal to or exceeds the evaporator coil outlet temperature plus a predetermined temperature difference. The evaporator fan is de-energized if the cabin temperature is not equal to or does not exceed the evaporator coil outlet temperature plus a predetermined temperature difference. In one embodiment, the predetermined temperature difference for energizing and de-energizing is the same, set at two degrees Fahrenheit. However, it is noted that the predetermined temperature difference could be different for energizing and de-energizing the evaporator fan.  
         [0016]    In another aspect of the present invention, the control includes control logic which is configured to shut down the compressor, the condenser fan and the evaporator fan if any of the temperature sensors fail. Although the temperatures may be sensed by any suitable sensor, as depicted in U.S. Pat. No. 5,809,789, the temperature sensors of one embodiment of the present invention are thermocouples whose resistance varies with temperature. The control logic checks to see if the resistance exceeds a high limit, indicating an open circuit, or is under a low limit, indicating a probable shorted circuit. The control logic will re-start the module (assuming all other components are functional) if a failed sensor resumes operation.  
         [0017]    It is also noted that the invention described herein is applicable to any process utilizing a working fluid undergoing compression and expansion to absorb heat from one area and to reject heat to another. In particular, the present invention my be used to control a refrigeration system used as a heat pump, with corresponding changes in the control logic to correspond to the fact that the cabin is being maintained at a temperature above its surrounding (i.e., being heated) in contrast to the use of a refrigeration system as an air conditioner or freezer when the cabin is being maintained at a temperature below its surrounding (i.e., being cooled). When used as a heat pump to heat a cabin, the condenser rejects heat to the cabin and the evaporator absorbs heat from the heat sources such as the air or geothermal sources.  
         [0018]    When the present invention is used with a refrigeration system being used as a heat pump, the control includes control logic configured to energize the compressor when the cabin temperature is less than a predetermined low temperature for at least a predetermined length of time, and to de-energize the compressor when the cabin temperature is greater than a predetermined high temperature.  
         [0019]    When the present invention is used with a refrigeration system being used as a heat pump, the control includes control logic configured to energize the condenser fan based on the cabin temperature and the condenser coil outlet temperature. The condenser fan is energized if the cabin temperature is equal to or less than the condenser coil outlet minus a predetermined temperature difference. The condenser fan is de-energized if the cabin temperature is not equal to or not less than the condenser coil outlet temperature minus a predetermined temperature difference. It is noted that the predetermined temperature difference could be different for energizing and de-energizing the condenser fan.  
         [0020]    When the present invention is used with a refrigeration system being used as a heat pump, the control includes control logic configured to control operation of the evaporator fan based on the temperature of the evaporator coil inlet and the ambient temperature. The evaporator fan is energized if the evaporator inlet temperature is less than the ambient temperature minus a predetermined temperature difference. The evaporator fan remains energized until the evaporator inlet temperature is greater than the ambient temperature minus a predetermined temperature difference. The predetermined temperature differences for the fan energized and the fan de-energized conditions do not have to be equal.  
         [0021]    When the present invention is used with a refrigeration system being used as a heat pump, the control includes control logic configured to de-energize the compressor if the temperature of the evaporator coil inlet drops below a predetermined temperature. Such a condition occurs if, for example, there is inadequate air flow across the evaporator coil, as would occur if the evaporator fan failed or was blocked. The compressor remains de-energized until the temperature of the evaporator coil inlet reaches or exceeds a predetermined temperature. This control logic allows intermittent operation of the evaporator even with inadequate air flow thereacross, providing some heat absorption by the evaporation, and therefore some heating by the condenser. If the evaporator inlet temperature drops below the predetermined temperature and the compressor is de-energized as described, the control logic is configured to run the evaporator fan constantly, without regard to the temperature difference between the temperature of the evaporator inlet and the ambient temperature. If adequate air flow across the evaporator is restored, then once the compressor is restarted, the operation of the evaporator fan will return to being controlled based on the temperature difference between the temperature of the evaporator inlet and the ambient temperature, as described above.  
         [0022]    It is noted that the reference to the evaporator fan in regard to operation as a heat pump is pertinent to an air to air heat exchanger. In the case of other heat sources, such as geothermal, the functional equivalent to the evaporator fan is the mover that places the heat source into heat transfer relationship with the evaporator. In the case of geothermal, where an liquid to liquid heat exchanger is used, the pump circulating the fluid across the evaporator coil is functionally equivalent to the evaporator fan. It is noted that for constant temperature heat sources, such as geothermal, the ambient temperature is constant and the heat pump should be designed and sized for constant operation of the pump.  
         [0023]    As described above, any of the various aspects of the present invention may be incorporated in a refrigeration system separately or together, in any combinations. The aspects may be implemented through a computer processor configured with the specified control logic, or may be implemented through non-programmable controls, or even be completely hardwired.  
         [0024]    As will also be appreciated, although specific inlet and outlet coil temperatures are described, the present invention may be practiced based on either the inlet or outlet coil temperature, or some other measure of the coil temperature, such as the average of the inlet and outlet temperatures.  
         [0025]    The control may be configured to communication with other devices through an acceptable protocol, such as the Multi-Drop Bus/Internal Communication Protocol (MDB/ICP).  
         [0026]    In summary, numerous benefits have been described which result from employing the concepts of the invention. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.