Abstract:
A system for controlling a defrost cycle of an evaporator having a sensor module and a control module. The sensor module includes a light source configured to emit light toward the evaporator when activated and to deactivate in response to a lockout signal. The sensor module also includes a light sensor configured to determine an amount of the emitted light reflected by the evaporator and to generate a detected light signal that corresponds to the amount of the emitted light reflected by the evaporator. The control module is configured to receive the detected light signal from the light sensor and to compare the detected light signal to a preset threshold. The control module is also configured to generate a termination signal when the detected light signal is less than the preset threshold and to generate the lockout signal when the detected light signal is greater than the preset threshold.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Application No. 62/128,485 filed on Mar. 4, 2015. That application is incorporated into this patent application by this reference. 
    
    
     FIELD OF THE INVENTION 
     This disclosure is directed to a system for defrost termination, and, more particularly, to a system for terminating a defrost mode of an evaporator for a refrigeration system. 
     BACKGROUND 
     Conventional refrigeration systems reduce the temperature of commercial and residential spaces, such as homes, offices, commercial freezers, and refrigerated delivery trucks. Such systems typically operate on the vapor-compression cycle and include four major components: a compressor, a condenser, an evaporator, and an expansion valve. 
     In conventional operation, refrigerant is compressed by the compressor and exits the compressor as a vapor at a temperature higher than the inlet temperature. The vapor is then condensed by the condenser, turning the vapor into a liquid. The expansion valve rapidly decreases the pressure of the liquid refrigerant, resulting in a mixture of liquid and vapor at a lower temperature and pressure. Next, the refrigerant passes through the evaporator. A fan typically blows relatively warm air, from the space being cooled or refrigerated, across the evaporator. As the warm air passes the evaporator, and more particularly, the fins or coils of the evaporator, the warm air vaporizes the refrigerant in the evaporator since heat from the air is transferred to the refrigerant in the evaporator. And the refrigeration cycle repeats. In this way, the temperature within the space to be cooled is reduced. 
     One drawback of such conventional systems is that frost tends to build up on the evaporator when moisture condenses out of the relatively warm air and freezes on the outside of the relatively cold evaporator. This happens mostly on the fins or coils of the evaporator. To reduce or eliminate such frost, conventional systems typically include a defrost operation mode, where the evaporator is heated so that its surface temperature is above the freezing point of water. In that way, frost on the evaporator is melted and the resulting water is either blown off by a fan or drips off of the evaporator, thus eliminating the frost and the condensed moisture. 
     Typically, conventional defrost modes are periodically initiated by a timer. In such systems, the defrost mode generally ends when the temperature of the evaporator increases to a certain level, such as a few degrees above the freezing point of water. The temperature of the evaporator may be read, for example, by a thermostat. Other conventional defrost systems use an infrared source to direct infrared radiation through the region where frost would accumulate on the evaporator. The radiation is received by an infrared detector on the opposite side of that region. In such systems, the infrared detector can determine if frost is present by detecting the presence or absence of infrared energy. 
     But there are shortcomings with the conventional systems. For example, since such systems initiate the defrost mode based on a timer, the systems might engage the defrost cycle even if no frost is present on the evaporator. This can lead to an unnecessary and inefficient use of electrical power. Also, infrared systems are typically expensive and require a large amount of labor to install and maintain because of their complexity. 
     Embodiments of the invention address these and other issues in the prior art. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of the disclosed subject matter provide mechanisms for terminating a defrost mode of a refrigeration system based on an absence of frost or ice on an evaporator rather than only on the temperature of the evaporator. 
     Accordingly, at least some embodiments of a system for controlling a defrost cycle of an evaporator may include a sensor module and a control module. The sensor module is configured to attach to the evaporator. The sensor module includes a light source configured to emit light toward the evaporator when activated and to deactivate in response to a lockout signal. The sensor module also includes a light sensor configured to determine an amount of the emitted light reflected by the evaporator and to generate a detected light signal that corresponds to the amount of the emitted light reflected by the evaporator. The control module is configured to receive the detected light signal from the light sensor and to compare the detected light signal to a preset threshold. The control module is also configured to generate a termination signal when the detected light signal is less than the preset threshold and to generate the lockout signal when the detected light signal is greater than the preset threshold. 
     In another aspect, at least some embodiments of a system for terminating a defrost cycle of an evaporator may include a sensor module, a control module, a set-point calibrator, and a defrost timer. The sensor module is configured to attach to the evaporator. The sensor module includes a light source configured to emit light toward the evaporator when activated and to deactivate in response to a lockout signal. The sensor module also includes a light sensor configured to determine an amount of the emitted light reflected by the evaporator and to generate a detected light signal corresponding to the amount of the emitted light reflected by the evaporator. 
     The control module includes a comparator circuit, a lockout circuit, and a termination relay. The comparator circuit is configured to compare the detected light signal to a preset threshold. The comparator circuit is also configured to generate a termination signal when the detected light signal is less than the preset threshold and to generate the lockout signal when the detected light signal is greater than the preset threshold. The lockout circuit is coupled to the comparator circuit and is configured to activate in response to the lockout signal to prevent the termination signal from reaching the termination solenoid of the defrost timer. The termination relay is coupled to the lockout circuit and is configured to relay the termination signal from the lockout circuit to the termination solenoid of the defrost timer. 
     The set-point calibrator is coupled to the control module and is configured to adjust and establish the preset threshold. The defrost timer is coupled to the control module. The defrost timer is configured to initiate a periodic defrost cycle of the evaporator and to provide electrical power to the control module only during the periodic defrost cycle. The defrost timer has a termination solenoid configured to terminate the defrost cycle in response to the termination signal. 
     In yet another aspect, at least some embodiments of a method of detecting frost in an evaporator may include activating a light source to emit light at the evaporator; determining, with a light sensor, an amount of the emitted light reflected by the evaporator; comparing, with a control module, a preset threshold to the amount of the emitted light reflected by the evaporator; generating a termination signal by the control module when the amount of the emitted light reflected by the evaporator coils is less than the preset threshold; generating a lockout signal by the control module when the detected light signal is greater than the preset threshold; and deactivating the light source in response to the lockout signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of a system for defrost termination, according to embodiments of the invention. 
         FIG. 2  is a diagrammatic, side view of an example sensor module, according to embodiments. 
         FIG. 3  is a partial schematic drawing of a system for defrost termination integrated with a conventional defrost heater system, according to embodiments. 
         FIG. 4A  is a diagrammatic, front view of an example sensor module, according to embodiments.  FIG. 4B  is a diagrammatic, side, sectional view of the sensor module of  FIG. 4A  shown in relation to an evaporator coil. 
         FIG. 5  is a diagrammatic front view of an example system for defrost termination installed on an evaporator assembly, according to embodiments. 
         FIG. 6  is a side, diagrammatic view of the example system of  FIG. 5 . 
         FIG. 7  is a diagrammatic view of an example system for defrost termination with multiple sensors, according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     As described herein, embodiments of the invention are directed to a system for terminating defrost. In general, embodiments of the described system provide mechanisms for terminating a defrost mode of a refrigeration system based on an absence of frost or ice on an evaporator. In embodiments, the presence or absence of frost is determined by sensing visible light that is reflected from the evaporator. If frost is present, the amount of reflected visible light differs from the amount reflected when frost is absent. 
       FIG. 1  is a functional block diagram showing material portions of a system for defrost termination according to embodiments of the invention. As illustrated in  FIG. 1 , a system  100  for defrost termination may include a defrost timer  101 , a control module  102 , a sensor module  103 , and a set-point calibrator  104 . The defrost timer  101  may include a power connection  105  and a termination solenoid  106 , and the control module  102  may include a power supply  107 , a comparator circuit  108 , a termination relay  109 , and a lockout circuit  110 . The set-point calibrator  104  may include an adjuster  111  and an indicator  112 , while the sensor module  103  may include a sensor  113  and a light source  114 . 
     The defrost timer  101  communicates with the control module  102 , while the control module  102  communicates with the sensor module  103  and the set-point calibrator  104 . The communication may be by way of one or more electronic couplings or connections. 
     The power connection  105  may be coupled to an outside power source, such as line, or mains, electric power. The power connection  105  provides electrical power  115  to the power supply  107 . The power supply  107  may include an alternating current (AC) voltage to direct current (DC) voltage converter or rectifier. The sensor  113  may include, for example, a photocell, a photo resistor, or a light-variable resistor. The light source  114  may be any source of visible light that generates light that may be detected by the sensor  113 . The visible light may be white light or another color. The visible light may be, for example, generated by an incandescent, fluorescent, or LED (light-emitting diode) source. For instance, the light source  114  may be an LED emitting white light at between 0.1 and 2 lumens, such as about 0.5 lumen. 
     In use, a user may preset a desired level, or a set-point, on the set-point calibrator  104 , for example, by varying the adjuster  111 , which may include an adjustable potentiometer. When the defrost timer  101  begins a defrost cycle or mode, the power connection  105  provides electrical power  115  to energize the control module  102 , the sensor module  103 , and the set-point calibrator  104 . 
     With reference to  FIGS. 1 and 2 , when the control module  102  is activated, that is, when the power connection  105  energizes the control module  102 , the light source  114  emits light  116  and illuminates at least a portion of an evaporator  117  of a refrigeration system, such as the evaporator  117  of  FIGS. 5 and 6 . The sensor  113  receives the reflected light  118  from the light source  114  that is reflected off of the evaporator. 
     Returning to  FIG. 1 , the sensor  113  generates a detected light signal  119 , which corresponds to the amount of the emitted light  116  that is reflected by the evaporator. The comparator circuit  108  compares the detected light signal  119  to a threshold level that corresponds to the set-point preset by the user. If frost or ice is present on the evaporator, more light is reflected back to the sensor  113  than if frost or ice is not present. Thus, for example, the threshold level may be set to correspond to the detected light signal  119  at transition between the two states: with frost and without frost. 
     If the detected light signal  119  is below the threshold level for the set-point, the comparator activates the termination relay  109  in the control module  102 . For example, the comparator  108  may generate a termination signal  120 . The termination relay  109  then activates the termination solenoid  106 . Thus, the defrost timer  101  exits the defrost mode and the power connection  105  stops energizing the control module  102 . The control module  102  and the sensor module  103  then remain without power until the defrost timer  101  initiates the next defrost mode or cycle. In this way, the system  100  terminates the defrost cycle when the system  100  determines that no frost is present on the evaporator. 
     If the detected light signal  119  is above the threshold level for the set-point, the comparator circuit  108  locks out the termination relay  109  by activating the lockout circuit  110 . For example, the comparator  108  may generate a lockout signal  121 . This places the control module  102  in a sleep mode, and the light source  114  is turned off so that it no longer illuminates the evaporator. In this sleep mode, the defrost timer  101  may continue with the defrost cycle until the cycle terminates in a conventional manner. For example, a conventional termination thermostat may indicate that the evaporator has reached a temperature high enough to melt the frost on the evaporator and signal the termination solenoid  106  of the defrost timer  101  to terminate the cycle. As described above in the Background section, the termination thermostat is typically part of the evaporator in a conventional system that relies on the evaporator&#39;s temperature to end the defrost mode. 
     When the defrost timer  101  enters another periodic defrost cycle, the power connection  105  energizes the control module  102 , and the described process repeats. 
     The system for defrost termination may interact or be integrated with a conventional defrost heater system. For example,  FIG. 3  is a partial schematic drawing showing material portions of a system for defrost termination integrated with a conventional defrost heater system, according to embodiments of the invention. As illustrated in  FIG. 3 , a system  300  for defrost termination may include a defrost timer  101 , a control module  102 , a sensor module  103 , a sensor  113 , and a light source  114 . The comparator circuit  108 , the termination relay  109 , and the lockout circuit  110  may be within the control module  102  as illustrated in  FIG. 3 . These features are generally as described above for  FIG. 1 . 
     Also illustrated in  FIG. 3  are a defrost heater  122 , a defrost termination and fan delay switch  123 , and an evaporator fan  124 . Those components, along with the defrost timer  101 , are typically already included in a conventional evaporator. 
     The sensor module may include one or more clips or hangers to mount or attach the sensor module to an evaporator, such as the evaporator  117  shown in  FIGS. 5 and 6 . The clips, for example, may be one or more alligator clips connected to the sensor module. The hanger may be, for example, one or more hooks configured to suspend the sensor module from a portion of the evaporator. The sensor module  103  may be connected to the control module  102  with a connecting cable  126 . 
     Preferably, the sensor module  103  is configured to shield the sensor  113  from ambient light that might interfere with the desired operation of the sensor  113 . As used here, ambient light is light other than the emitted light of the light source  114 . Thus, for example, the sensor module  103  may partially enclose or encapsulate the sensor  113  in a housing  125  having an opening  127  for the sensor  113  to receive light from outside of the housing  125 . An example of this is shown in  FIGS. 4A and 4B . The opening  127  of the housing  125 , containing the sensor  113 , may be placed against the coils  128  of the evaporator  117 . Preferably, the opening  127  of the housing  125  is immediately adjacent the evaporator coils  128 . As an example, the opening  127  of the housing  125  may be no farther than about 1/32 of an inch (about 0.8 mm) from the evaporator coils  128 . The light source  114  may also be enclosed or encapsulated with the sensor  113 . 
     Returning to the example illustrated in  FIG. 3 , when the defrost timer  101  activates a defrost cycle, such as discussed above, contact points N and  3  of the defrost timer  101  provide power to the sensor module  103 . The defrost timer  101  preferably operates on any voltage from about 100 VAC to about 240 VAC. 
       FIG. 5  is a front, diagrammatic view showing material portions of an example system  500  for defrost termination installed on an evaporator assembly, according to embodiments.  FIG. 6  is a side, diagrammatic view of the system of  FIG. 5 . The illustrated evaporator assembly  117  includes evaporator fins and tubing  128 , a fan and motor assembly  124 , and a defrost-termination and fan-delay switch  123 . The control module  102  may be mounted within the evaporator  117 , or the control module  102  may be mounted at the defrost timer  101 , which is typically remote from the evaporator  117 . Other configurations are also possible. The sensor module  103  may be mounted on the fan side of the evaporator  117 , such that the light source  114  faces the evaporator coils  128 . The cable  126  connects the sensor module  103  to the control module  102 . These features are generally as described above. 
     Thus, embodiments of the system for defrost termination may work with conventional defrost timers to improve the defrost process. For example, embodiments provide defrost capability with a more efficient use of electrical power since the defrost cycle can be terminated, if no frost is detected on the evaporator, before the temperature of the evaporator increases to the temperature set for the conventional thermostat. Also, embodiments of the system for defrost termination requires much less labor to install and maintain when compared to infrared systems, particularly since embodiments of the system for defrost termination may be mounted on just one side of the evaporator. 
     Accordingly, embodiments of the system for defrost termination interact, or are integrated, with a conventional defrost heater system for an evaporator  117  of a refrigeration system. When the conventional defrost timer  101  begins a defrost cycle, the control module  102  activates and the light source  114  illuminates at least a portion of the evaporator  117 , such as the coils  128  of the evaporator. If frost or ice is present on the evaporator  117 , more light is reflected back to the sensor  113 , which is detected by the sensor module  103  and analyzed by the comparator circuit  108 . The comparator circuit  108  then activates the lockout circuit  110 , and the light source  114  turns off so that it no longer illuminates the evaporator  117 . The defrost timer  101  then continues with the defrost cycle until a conventional termination thermostat terminates the defrost cycle. If frost or ice is not present on the evaporator  117 , relatively less light is reflected back to the sensor  113 . In such cases, the comparator  108  activates the termination relay in the control module  102 , which in turn activates the termination solenoid  106  in the defrost timer  101 . Accordingly, the defrost cycle ends, and the control module  102  is no longer energized. 
       FIG. 7  is a diagrammatic view showing material portions of an example system for defrost termination with multiple sensors, according to embodiments of the invention. As illustrated in  FIG. 7 , a system  700  for defrost termination may include a control module  102  and a plurality of sensor modules  103   a - 103   n  that are remote from the control module  102 . Each sensor module  103  in the plurality of sensor modules is attached to a different one of a plurality of evaporators  117   a - 117   n . The control module  102  may be coupled to a defrost timer  101 . Each sensor module  103  in the plurality of sensor modules is coupled to the control module  102 , for example, by one or more connecting cables  126 , and perhaps through a plurality of connectors  129   a - 129   n . In this way, a single control module  102  may operate with a plurality of sensor modules  103  to terminate a defrost mode of each of the plurality of evaporators  117 . 
     The previously described versions of the disclosed subject matter have many advantages that were either described or would be apparent to a person of ordinary skill. Even so, all of these advantages or features are not required in all versions of the disclosed apparatus, systems, or methods. 
     Additionally, this written description makes reference to particular features. It is to be understood that the disclosure in this specification includes all possible combinations of those particular features. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment, that feature can also be used, to the extent possible, in the context of other aspects and embodiments. 
     Also, when reference is made in this application to a method having two or more defined steps or operations, the defined steps or operations can be carried out in any order or simultaneously, unless the context excludes those possibilities. 
     Furthermore, the term “comprises” and its grammatical equivalents are used in this application to mean that other components, features, steps, processes, operations, etc. are optionally present. For example, an article “comprising” or “which comprises” components A, B, and C can contain only components A, B, and C, or it can contain components A, B, and C along with one or more other components. 
     Although specific embodiments of the invention have been illustrated and described for purposes of illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.