Patent Document

This application claims the benefit of provisional application Ser. No. 60/366,829 filed Mar. 22, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to managing freezer operations as a function of off-peak energy demand periods. 
     A freezer typically includes a thermally insulated compartment that maintains subfreezing air. Some freezers are attached to a refrigerator while other freezers are freestanding. Many freezers permit a consumer to set an internal air temperature of the freezer to between −20 degrees and 20 degrees Fahrenheit (F.) (−29 degrees to −7 degrees Celsius (C.)). To rapidly freeze and store food items and to save energy, most consumers maintain the freezer air temperature at around zero degrees F. (−18 degrees C.). 
     In contrast to a refrigerator, a freezer typically has only one energy-using device: a compressor. A thermomechanic device such as a thermostat typically controls the on/off operations of the compressor to create and maintain subfreezing air. When energized, the compressor is used to draw out heat from the interior of the freezer. However, freezers require a significant amount of energy to create subfreezing air. 
     The energy costs to create subfreezing air in a freezer may depend upon the time of day. In areas of the United States where energy is at a premium, utility companies often divide their rates into off-peak and on-peak energy rates based on off-peak and on-peak energy demand periods. Energy used during off-peak may cost the consumer in United States dollars around 2¢ to 3¢ per kilowatt-hour (kWh) while on-peak energy may cost anywhere from 6¢ per kWh to 50¢ or more per kWh. The utility companies eventually pass these extra costs to the consumer. In a recent California energy crisis, the wholesale cost of energy rose to $3.00 per kWh. 
     Without some sort of management, a freezer that creates subfreezing air based on the demand of a household most likely will operate when energy demand on a utility company is at its highest. Drawing power to create subfreezing air during these on-peak periods increases a consumer&#39;s monthly energy bill. In the collective, this lack of demand side management places excessive wear on a power plant to shorten the overall life of the plant. 
     Many utility companies have off-peak energy usage programs that provide lower energy rates. These lower energy rates apply so long as the consumer&#39;s appliance draws power only during off-peak times. Off-peak energy usage programs typically aid in reducing on-peak demand. However, there may be times during the on-peak periods when the temperature of the consumer&#39;s freezer is above levels at which food may be stored safely. Here, the consumer may override the clock timer to bring the temperature within safety levels but will incur significant kWh energy charges. What is needed is a system that manages the creation of subfreezing air in a freezer during the off-peak periods to supply needs of a consumer during the on-peak periods, to time shift consumer demands on power plants, and to save the consumer money. 
     SUMMARY OF THE INVENTION 
     In light of the above noted problems, the invention works towards providing a system that creates subfreezing temperatures in a freezer during the off-peak periods. During the off-peak periods, the freezer system invention may subfreeze the interior temperature in a freezer to very low temperatures that may last throughout a normal day&#39;s use of the freezer, including during the on-peak periods. Since the freezer subfreezes during off-peak periods, consumer demands on power plants may be shifted away from on peak periods and the consumer may save money. 
     Thus, in a preferred embodiment, the invention provides a freezer system having a freezer, a thermoelectric device, and a controller. The freezer may include a compressor and a compartment, where the compartment may store subfreezing air. The thermoelectric device may be a temperature sensor positioned in thermal communication with the compartment. The controller may be coupled to the compressor and the thermoelectric device. The controller is configured to deliver power to the compressor based on a temperature signal and a control signal. The temperature signal may be from the thermoelectric device and the control signal may be selected from an off/on peak signal and an override signal. 
     These and other objects, features, and advantages of the present invention will become apparent upon a reading of the detailed description and a review of the accompanying drawings. Specific embodiments of the present invention are described herein. The present invention is not intended to be limited to only these embodiments. Changes and modifications can be made to the described embodiments and yet fall within the scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevated isometric view of a freezer system. 
     FIG. 2 is a graph illustrating a typical off-peak and on-peak demand over a twenty-four-hour operating period. 
     FIG. 3 is a schematic diagram of components and interconnections of the freezer system. 
     FIG. 4 is a flow chart illustrating a method to manage the freezer system through software of a demand side management (DSM) controller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is an elevated isometric view of a freezer system  100 . The freezer system  100  may include a freezer  102 , a control panel  104 , and a thermoelectric device  106 . The control panel  104  and the thermoelectric device  106  may be retrofit into a freezer already in existence or in service. Moreover, new freezers may include the control panel  104  and the thermoelectric device  106 . 
     The freezer  102  may be any device having a compressor and a compartment, such as a cabinet, or room, to maintain subfreezing air. The freezer  102  may include a door  108 , a cabinet  110 , and a compressor  112 . When closed against the cabinet  110 , the door  108  and the cabinet  110  may form a compartment  114  that acts as a reservoir for subfreezing air. 
     The compressor  112  may include refrigerant, an evaporator, and a condenser. The compartment  114  may include coils attached to the compressor  112  to circulate the refrigerant through the compartment  114 . In operation, the compressor  112  may exert pressure on a vaporized refrigerant and force the refrigerant to pass through the condenser, where the refrigerant loses heat and liquefies. The refrigerant may then move through the coils of the compartment  114 . There, the refrigerant may vaporize in the evaporator, drawing heat from whatever is in the compartment  114 . The refrigerant then may pass back to the compressor  112  to repeat the cycle. A power cord  113  may deliver power to the compressor  112 . 
     The control panel  104  may include a timer  116  and an interface  118 . The timer  116  may be a switch or regulator that controls or activates and deactivates another mechanism at set times. The timer  116  may be a programmable seven-day timer. Moreover, the timer  116  may include at least one variable state output to indicate whether a current time is on-peak or off-peak. 
     The interface  118  may be a manual user interface having buttons, displays, and the like to permit a user to communicate to the control panel  104  and receive information from the control panel  104 . The interface  118  may permit a user to input a plurality of on-peak and off-peak settings for each day into the control panel  104 . The on-peak and off-peak settings may be independent from each other. 
     The control panel  104  also may include a power cord  120  and a socket  122 . The power cord  120  of the control panel  104  may be plugged into a socket  123 . The socket  123  may be a household wall outlet. The power cord  113  of the compressor  112  may be plugged into the socket  122  of the control panel  104 . 
     The power cord  120  may receive electrical power from the socket  123  and deliver the electrical power to the control panel  104 . In turn, the control panel  104  may deliver electrical power to the compressor  112  through the power cord  113 . The delivery of this power to the compressor  112  from the control panel  104  may be a function of the on-peak and off-peak settings. 
     The control panel  104  may communicate to one or more control sources through a signal line  124 . The signal line  124  may be any pathway configured to pass a signal from one location to another location. The signal line  124  may be in communication with devices within a home or outside of the home. For example, the signal line  124  may receive remote information. This remote information may include off-peak and on-peak information from a power plant or status information from devices within the home. The off-peak and on-peak information may be input into the control panel  104  automatically as a plurality of on-peak and off-peak settings for each day. The signal line  124  may transmit and receive information through a variety of techniques, such as over a telephone line, over the Internet, or through free space such as by radio waves. 
     Conventionally, a user may plug the freezer  102  directly into the socket  123  to receive power to run the compressor  112 . The power may be routed through a circuit controlled by a thermomechanic device  128 . In general, the thermomechanic device  128  may be a device that mechanically responds to temperature changes to either make or break the power circuit. The thermomechanic device  128  may be a thermostat. 
     One of the components of the thermomechanic device  128  may expand or contract significantly in response to a temperature change. For example, heated mercury may expand to touch an electrical contact to complete a circuit as part of a mercury thermostat. A different design may use a bimetallic strip made of two thin metallic pieces of different composition bonded together. As the temperature of the strip changes, the two pieces change length at different rates, forcing the strip to bend. This bending may cause the strip to make or break the circuit. 
     When the freezer  102  is plugged directly into the socket  123 , the thermomechanic device  128  may provide sole control over the flow of power to the compressor  112  to maintain a predetermined temperature in the compartment  114 . If the thermomechanic device  128  provides the sole control over the flow of power to the compressor  112 , then the compressor  112  undesirably may operate during on-peak rates. To provide more control over the operations of the compressor  112 , the freezer system  100  may include the thermoelectric device  106 . 
     In contrast to the mechanical on/off actions of the thermomechanic device  128 , the thermoelectric device  106  may perceive the actual temperature inside the compartment  114  and generate a signal proportional to the actual temperature. The generated signal may be a voltage signal in millivolts (mV), for example. The thermoelectric device  106  may transmit the voltage signal to the control panel  104  over a signal line  126 . The control panel  104  may convert the voltage signal to related temperature in degrees F. or degrees C. In one embodiment, the thermoelectric device  106  may be a temperature switch. As an example, the thermoelectric device  106  may consist of two dissimilar metals joined so that a voltage difference generated between points of contact is a measure of the temperature difference between the points. 
     Through the interface  118  of the control panel  104 , a consumer may input the Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday off-peak/on-peak demand periods and/or off-peak/on-peak rates into the timer  116 . The consumer may also input a vacation schedule, a holiday schedule, or a business schedule, each as a function of the on-peak or off-peak entries. The signal line  124  also may deliver this information into the control panel  104  from, for example, a power plant. The control panel  104  may respond to this information by managing whether the freezer  102  operates during an on-peak demand period or operates above particular energy rates. 
     FIG. 2 is a graph  200  illustrating a typical off-peak and on-peak demand over a twenty-four-hour operating period. From midnight to about six in the morning, the demands for energy may be low, such that off-peak rates  202  may apply. From about six in the morning to about eleven in the morning, demands for energy may be high, such that on-peak rates  204  may apply. The energy demands may drop in the afternoon and pick up around five in the afternoon. From around five in the afternoon to around nine in the evening, the demands for energy again may be high. These high demands may increase the cost of energy to on-peak rates  204 . The demands for energy may be so great that special on-peak rates  206  may apply. Off-peak energy may cost in United States dollars around 2¢ to 3¢ per kWh. Significantly, on-peak energy may cost the consumer anywhere from 6¢ per kWh to 50¢ or more per kWh. 
     FIG. 3 is a schematic diagram  300  of components and interconnections of the freezer system  100 . The timer  116  may be in direct communication with a controller  302  through a signal line  304 . The controller  302  may be part of the control panel  104 . The controller  302  may control the compressor  112  through power supplied into the power cord  113 . In some instances, the thermomechanic device  128  may provide further control over the delivery of power to the compressor  112 . 
     The controller  302  may include an internal clock synchronized with the local time of day as the current time. When the timer  116  closes a switch  308 , the timer  116  may send a constant high-input to the controller  302  during off-peak periods of each day of the week. This high-input signal may contribute to the control over the operations of the compressor  112 . The terms “high-input” and “low-input” are relative and a low-input signal may operate the devices of the invention. 
     The freezer system  300  may include an override switch  310  connected to the controller  302 . The override switch  310  may be connected in parallel with the thermoelectric device  106 . A demand request from either the override switch  310  or the thermoelectric device  106  may augment or bypass the control of the timer  116  over the operations of the compressor  112 . The demand request may be manual or automatic. 
     To provide a manual demand request, the override switch  310  may bypass the signals from the timer  116  and instruct the compressor  112  through the controller  302  to begin subfreezing the air in the compartment  114 . Manually depressing the override switch  310  may activate the override switch  310 . In view of this manual demand request, the compressor  112  maybe limited as to how much heat the compressor  112  removes from the air in the compartment  114 . For example, the compressor  112  may subfreeze the air in the compartment  114  to only about 2 degrees F. (about −17 degree C.) if activated by this manual demand request. 
     To provide an automatic demand request, the thermoelectric device  106  may work as an automatic demand to bypass the signals from the timer  116 . The thermoelectric device  106  may be set to begin the subfreezing of the air in the compartment  114  under certain circumstances. For example, if the air temperature in the compartment  114  is approaching an unsafe value, the thermoelectric device  106  may activate the compressor  112 . Although the thermoelectric device  106  may activate the compressor  112  during on-peak energy periods, this may be a more efficient option than permitting food to spoil. An example of an unsafe temperature value may be about 10 degrees F. (−12 degrees C.). 
     Activating the compressor  112  during on-peak energy periods may drive up operation costs. The controller  302  may place a limit on its operation to avoid excessive expense. For example, if the air temperature in the compartment  114  rises above a predetermined level and more subfreezing is requested, the controller  302  may activate the compressor  112  only if the compressor  112  has not been activated within the past ninety minutes, for example. A ninety-minute inhibit timer may be used for this purpose. Even if activated by this automatic demand request, the compressor  112  may be limited as to how much heat the compressor  112  removes from the air in the compartment  114 . For example, the compressor  112  may subfreeze the air in the compartment  114  to only about 5 degrees F. (about −15 degrees C.) if activated by this automatic demand request. 
     FIG. 4 is a flow chart illustrating a method  400  to manage the freezer system  100  through the software of the controller  302 . A machine-readable medium having stored instructions may implement the method  400 . For example, a set of processors may execute the instructions to cause the set of processors to perform the method  400 . A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). A machine-readable medium may include read only memory (ROM), a random access memory (RAM), a magnetic disk storage media, an optical storage media, and flash memory devices. The machine-readable medium may include electrical, optical, acoustical or other form of propagated signals such as carrier waves, infrared signals, and digital signals. 
     The method  400  may start at  402  and proceed to step  403 . At step  403 , the method  400  may determine whether the thermomechanic device  128  is closed. A close thermomechanic device  128  may mean that heated mercury touches an electrical contact or that a bimetallic strip bends to bridge a power circuit. If the thermomechanic device  128  is not closed, the method  400  may return to step  403 . If the thermomechanic device  128  is closed, then the method  400  may proceed to step  404 . 
     At step  404 , the method  400  may determine whether an input to the timer  116  is high. A high-input into the timer  116  may close the switch  308 . A closed switch  308  may imply an off-peak demand period such as seen in certain areas of region  202  of FIG. 2. A closed switch  308  may imply an off-peak demand rate. 
     If the input to the timer  116  is high, the method  400  may determine at step  406  whether the output of the controller  302  is high. A high output of the controller  302  may provide subfreezing signals to the compressor  112 . 
     If the output of the controller  302  is not high at step  406 , then the method  400  may proceed to step  408 . At step  408 , the method  400  may determine whether the air temperature of the compartment  114  is above a first preset temperature. An example of the first preset temperature may be about 5 degrees F. (about −15 degrees C.). If the air temperature in the compartment  114  is not above the first preset temperature, then there may be no need to reduce the air temperature in the compartment  114 . Thus, the method  400  may then return to step  403 . If the air temperature in the compartment  114  is above the first preset temperature, then the method  400  may set the output of the controller  302  to high at step  410 . A high output received at the compressor  112  from the controller  302  may activate the compressor  112 . With the compressor  112  activated, the method  400  may set the inhibit timer to off at step  412 . The method  400  may then return to step  403 . 
     If the output of the controller  302  is high at step  406 , then the method  400  may proceed to step  414 . At step  414 , the method  400  may determine whether the air temperature in the compartment  114  is above a second preset temperature. The second preset temperature may be about −10 degrees F. (about −23 degrees C.). If the air temperature in the compartment  114  is above the second preset temperature, then the compressor  112  may continue to subfreeze the air in the compartment  114 . The method  400  then may return to step  403 . If the air temperature in the compartment  114  is at or below the second preset temperature, then setting the controller  302  to low at step  416  may turn off the compressor  112 . With the air temperature at or below the second preset temperature, the freezer  102  may supply a consumer with an entire day&#39;s worth of subfreezing air. From step  416 , the method may return to step  403 . 
     It may be desirable to subfreeze the air in the compartment  114  during an off-peak demand period or when an off-peak rate applies. Step  404  through step  416  address the situation where the timer  116  indicated an off-peak demand period or off-peak rate. If the input to the timer  116  is low at step  404 , then the timer  116  may indicate an on-peak demand period or on-peak rate. There may be circumstances where a user desires to subfreeze the air in the compartment  114  during an on-peak demand period or when an on-peak rate applies. 
     If the input to the timer  116  is low at step  404 , the method  400  may determine at step  418  whether the air temperature in the compartment  114  is above a third preset temperature. The third preset temperature may be, for example, about 10 degrees F. (about −12 degrees C.). This part of the method  400  may provide for manual, automatic, or semi-automatic demand overrides of the timer  116  settings. 
     If the air temperature in the compartment  114  is above the third preset temperature at step  418 , the method  400  may determine whether the controller  302  recently activated the compressor  112 . The method  400  may make this determination at step  420  by determining whether the inhibit timer is high. 
     If the inhibit timer is not high at step  420 , that is, if the controller  302  has not recently activated the compressor  112 , then the method  400  may permit automatic demand overrides of the timer  116 . For example, the thermoelectric device  106  (FIG. 3) may have indicated that the air temperature in the compartment  114  is too high for current demands made on the air in the compartment  114 . The method  400  may proceed to step  410  if the inhibit timer is not high at step  420 . At step  410 , the method may set the output of the controller  302  to high. 
     If the inhibit timer is high at step  420 , that is, if the controller  302  recently activated the compressor  112 , then the method  400  may prevent automatic demand overrides of the timer  116 . However, the method  400  still may permit manual demand overrides of the timer  116 . The method  400  may proceed to step  422  if the inhibit timer is high at step  420 . 
     At step  422 , the method  400  may determine whether the override switch  310  (FIG. 3) is high. A high override switch  310  may present a request for a manual demand override. If the override switch  310  is high at step  422 , then the method  400  may proceed to step  410  and set the output of the controller  302  to high. If the override switch  310  is not high at step  422 , then the method  400  may return to step  403 , recognizing that the consumer most likely did not request a manual override. 
     If the air temperature in the compartment  114  is not above the third preset temperature at step  418 , then the air temperature in the compartment  114  may be at a safe level. The method  400  may proceed to step  424  and determine whether the output of the controller  302  is high. Recall that a high output of the controller  302  may activate the compressor  112 . 
     If the output of the controller  302  is not high at step  424 , then the method  400  may return to step  403 . If the output of the controller  302  is high at step  424 , then the method  400  may then turn off the compressor  112 . The method  400  may turn off the compressor  112  by setting the controller  302  to low at step  426 . The inhibit timer may be initialized to zero minutes and turned on at step  428 . From step  428 , the method  400  may return to step  403 . 
     Among other differences, the freezer system  100  may differ from conventional Systems in that the freezer system  100  may utilize the lowermost temperature setting of the freezer  102 . This may subfreeze the air in the compartment  114  (FIG. 1) to a very low, initial temperature. When the door  108  is open to mix warm air with very cold air, the freezer system  100  may maintain a subzero temperature where the initial temperature of the freezer  102  is very low. This generally is true even if the door  108  is opened several times a day. Importantly, this subfreezing may be performed during the off-peak demand period when energy rates may be at their lowest. This saves consumers money and time shifts demands on power plants. By subfreezing the air in the compartment  114  in the early morning hours to very low temperatures, the freezer  102  may retain the subzero temperature air needs of a typical household throughout the day and night without requiring a resubfreezing of the air in the compartment  114 . 
     The present invention has been described utilizing particular embodiments. As will be evident to those skilled in the art, changes and modifications may be made to the disclosed embodiments and yet fall within the scope of the present invention. The disclosed embodiments are provided only to illustrate aspects of the present invention and not in any way to limit the scope and coverage of the invention. The scope of the invention is therefore to be limited only by the appended claims.

Technology Category: 4