Abstract:
Aspects of the invention support simultaneous operation of a cooling side and a heating side of an apparatus to change the temperatures of a cooling serving surface and a heating serving surface, respectively. A cooling semiconductor device (which may comprise one or more Peltier devices) transfers heat from its top to its bottom while a heating semiconductor device (which may similarly comprise one or more Peltier devices) transfers heat from its bottom to its top. A heat pipe transfers waste heat from the cooling semiconductor device&#39;s bottom to the heating semiconductor device&#39;s bottom and waste cold from the heating semiconductor device&#39;s bottom to the cooling semiconductor device&#39;s bottom.

Description:
This application is a continuation of U.S. patent application Ser. No. 13/495,643, entitled “Heating and Cooling Unit with Semiconductor Device and Heat Pipe” and filed on Jun. 13, 2012, the entire disclosure of which is hereby incorporated by reference, which is a continuation-in-part of U.S. patent application Ser. No. 13/347,229, entitled “Heating and Cooling Unit with Semiconductor Device and Heat Pipe” and filed on Jan. 10, 2012, the entire disclosure of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     Aspects of the disclosure relate to a hot/cold unit for heating and/or cooling an item on a serving surface. In particular, the hot/cold unit uses a semiconductor device, such as a Peltier device, and a heat pipe. 
     BACKGROUND 
     Perishable foods for home, market, catering and restaurant buffets are conventionally chilled by ice or commercially manufactured containers of freezable material, or by refrigeration systems. When the ice melts and the freezable material warms, these cooling media lose their ability to keep foods safe and may render them unsuitable or hazardous for consumption. Refrigeration systems are bulky and costly, requiring condensers, coils and harmful chemicals and, further, must be serviced and maintained. Additionally, they are not easily adapted for portability. 
     Other foods need to be heated or kept warm for home, market, catering and restaurant buffet service. Conventional sources of heat include flame and electricity, e.g. by use of alcohol-based combustible gels or by electric hot plates. Flame sources often produce local hot spots and uneven heating and may produce fumes, odors, or other combustion products. The indoor pollution and health risks to food service workers and patrons from these combustion products may be viewed with concern by those in the industry. 
     In the presentation of food and/or beverages such as for a buffet service, it is often desirable to store, transport, and/or present the buffet items in a convenient, presentable fashion. It is often further desirable to provide the items either above or below the ambient temperature of the presentation environment. Moreover, in-home hosting has trended upward, and could benefit from equipment improvement. Further, the costs and convenience of improved buffet service, storage, transportation, and/or presentation means may be improved such that they are more accessible and feasible in the market place. 
     While traditional servers for heating and/or cooling may not require fuel or ice to achieve a desired temperature of an item, traditional servers may rely on a temperature adjusting element in conjunction with an active exchange device, e.g., a liquid circulation pump, to facilitate energy transfer and thus mitigating the temperature of the temperature adjusting element. This approach may generate noise may typically increases the cost of the traditional server. 
     SUMMARY 
     An aspect of the invention provides apparatuses, computer-readable media, and methods for changing the temperature of a serving surface in order to cool or heat an item on the serving surface. Heat is transferred to or from the serving surface through a semiconductor device (e.g., a Peltier device), a heat pipe and a heat sink. 
     With another aspect of the invention, an apparatus for reducing the temperature of a serving surface includes at least one Peltier device that transfers heat from the serving surface to a heat pipe to a heat exchange device. Alternatively, the apparatus may increase the temperature of the serving surface by reversing the operation of the at least one Peltier device. 
     With another aspect of the invention, a control device activates the at least one Peltier device from a measured temperature of the serving surface and a temperature setting. The control device activates the at least one Peltier device in order change the serving surface according to the temperature setting. Moreover, hysteresis may be incorporated so that control cycling of the at least one Peltier device may be reduced. 
     With another aspect of the invention, a plurality of Peltier devices may be partitioned into different subsets so that the control device may activate different subsets during different time intervals. When the measured temperature of the serving surface is outside a temperature range, all of the Peltier devices may be activated, while only a selected subset may be activated when the measured temperature is within the temperature range and until a hysteresis temperature is reached. 
     With another aspect of the invention, an apparatus has a cooling side for changing the temperature of a cooling serving surface and a heating side for changing the temperature of a heating serving surface. A cooling semiconductor device transfers heat from its top to its bottom while a heating semiconductor device transfers heat from its bottom to its top, where each semiconductor device may comprise one or more Peltier devices. A heat pipe transfers waste heat from the cooling semiconductor device&#39;s bottom to the heating semiconductor device&#39;s bottom and waste cold from the heating semiconductor device&#39;s bottom to the cooling semiconductor device&#39;s bottom. The cooling side and the heating side of the apparatus are thermally isolated so that the cooling service surface and the heating serving surface can operate simultaneously without adversely affecting the temperature of the other serving surface. 
     Various aspects described herein may be embodied as a method, an apparatus, or as one or more computer-readable media storing computer-executable instructions. Accordingly, those aspects may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Any and/or all of the method steps described herein may be implemented as computer-readable instructions stored on a computer-readable medium, such as a non-transitory computer-readable medium. In addition, various signals representing data or events as described herein may be transferred between a source and a destination in the form of light and/or electromagnetic waves traveling through signal-conducting media such as metal wires, optical fibers, and/or wireless transmission media (e.g., air and/or space). 
     Aspects of the disclosure have been described in terms of illustrative embodiments thereof. Numerous other embodiments, modifications, and variations within the scope and spirit of the disclosure will occur to persons of ordinary skill in the art from a review of this disclosure. For example, one of ordinary skill in the art will appreciate that the steps illustrated herein may be performed in other than the recited order, and that one or more steps illustrated may be optional in accordance with aspects of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features and wherein: 
         FIG. 1  shows a block diagram of a serving apparatus operating in a cooling mode in accordance with an embodiment of the invention. 
         FIG. 2  shows a block diagram of a serving apparatus operating in a heating mode in accordance with an embodiment of the invention. 
         FIG. 3  shows a Peltier device in accordance with an embodiment of the invention. 
         FIG. 4  shows a heat pipe in accordance with an embodiment of the invention. 
         FIG. 5  shows a serving apparatus in accordance with an embodiment of the invention. 
         FIG. 6  shows a control device in accordance with an embodiment of the invention. 
         FIG. 7  shows circuitry for controlling Peltier devices in accordance with an embodiment of the invention. 
         FIG. 8  shows an arrangement of Peltier devices for changing a serving surface temperature in accordance with an embodiment of the invention. 
         FIG. 9  shows an arrangement of Peltier devices for changing a serving surface in accordance with an embodiment of the invention. 
         FIG. 10  shows a flowchart for controlling a serving apparatus in accordance with an embodiment. 
         FIG. 11  shows a flowchart for controlling Peltier devices in accordance with an embodiment. 
         FIG. 12  shows a flowchart for controlling Peltier devices in accordance with an embodiment. 
         FIG. 13  shows a serving apparatus with a heating side and a cooling side in accordance with an embodiment. 
         FIG. 14  shows a serving apparatus with serving surfaces in accordance with an embodiment. 
         FIG. 15  shows a portable serving tray in accordance with an embodiment. 
         FIG. 16  shows a plurality of portable trays stacked in a rack in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the various embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. 
       FIG. 1  shows a block diagram  100  of a serving apparatus operating in a cooling mode in accordance with an embodiment of the invention. Block diagram  100  shows the basic elements of the serving apparatus but may not explicitly show the dimensions and relative placement of the elements. For example, heat pipes  105  and  104  may be bent in a horizontal plane rather than a vertical plane so that the operation of the heat pipes is not adversely affected (e.g., by gravity). 
     The measured temperature of serving surface  101  is changed by transferring heat from Peltier devices  102  and  103  through heat pipes  104  and  105  and through heat sinks  106  and  107 , respectively. 
     Control device  108  activates and deactivates Peltier devices  102  and  103  based on an indication from temperature sensor  109  that is indicative of the measured temperature of serving surface  101 . Temperature sensor  109  is typically placed against serving surface  101  in order to provide thermal coupling. For example, when the measured temperature is above a cooling temperature setting (i.e., the desired temperature) control device  108  provides electrical power to Peltier devices  102  and  103  through electrical connections  110  and  111  and connections  112  and  113 , respectively. 
     With some embodiments, heat transfer may be enhanced by fans  114  and  115  producing air circulation from heat sinks  106  and  107 , respectively, and through vent openings  116  and  117 , respectively. 
       FIG. 2  shows a block diagram  200  of a serving apparatus operating in a heating mode in accordance with an embodiment of the invention. With some embodiments, the serving apparatus may be the same serving apparatus as with block diagram  100 . 
     Control device  208  reverses the transfer of heat with respect to block diagram  100  by reversing the electrical polarity of electrical connections  210  and  211  and connections  212  and  213 . (As will be discussed, the Peltier effect is a reversible process.) Consequently, heat flows to serving surface  201  to heat it. 
       FIG. 3  shows Peltier device  300  in accordance with an embodiment of the invention. However, some embodiments may use other types of semiconductor devices that provide similar heating and/or cooling characteristics. Heat is transferred between top side  351  and bottom side  352  based on the Peltier effect. Thermoelectric cooling by Peltier device  300  uses the Peltier effect to create a heat flux between the junctions of two different types of materials. Peltier device  300  may be classified as a heat pump. When direct current is provided to Peltier device  300 , heat is moved from one side to the other. Peltier device  300  may be used either for heating or for cooling since the Peltier effect is reversible. For example, heat may be transferred from top side  351  to bottom side  352  to cool a serving surface by providing electrical power at terminals  314  and  315 . Moreover, the direction of the heat transfer may be reversed (i.e., from bottom side  352  to top side  351 ) in order to heat the serving surface by reversing the polarity of the electrical power at terminals  314  and  315 . 
     Peltier device  300  comprises a plurality of N type and P type semiconductor grains  301 - 309  that are electrically interconnected through electrical conductor arrangements  310  and  311 . Ceramic layers  312  and  313  provide thermal conductivity as well as electrical isolation so that Peltier device  300  is able to cool or heat a serving surface. With some embodiments, the serving surface and heat pipe are thermally coupled to ceramic layers  312  and  313 , respectively. 
     With some embodiments, one or more Peltier devices may be used to exchange heat with the serving surface. For example, with the embodiment shown in  FIG. 5 , four Peltier devices may provide faster cooling than with one Peltier device. Additional Peltier devices may be used; however, electrical power and physical constraints may be factors that limit the number of Peltier devices. 
       FIG. 4  shows heat pipe  400  in accordance with an embodiment of the invention. With some embodiments, heat pipe  400  is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces. At the hot interface within heat pipe  400 , which is typically at a very low pressure, a liquid (fluid) is in contact with a thermally conductive solid surface that turns into a vapor by absorbing heat from the surface. The vapor condenses back into a liquid at the cold interface, releasing the latent heat. The liquid then returns to the hot interface through either capillary action or gravity action, where it evaporates once more and repeats the cycle. In addition, the internal pressure of the heat pipe may be set or adjusted to facilitate the phase change depending on the demands of the working conditions of the thermally managed system. With some embodiments, heat pipe  400  does not contain mechanical moving parts and typically requires little or no maintenance. 
     Heat pipe  400  may be a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two ends. With traditional systems, a radiator using single-phase convection with a high-speed motor often provides heat transfer. However, heat pipe  400  can transfer the heat efficiently without a high-speed motor. 
     Heat pipe  400  transports heat from portion  452  to portion  451 . Heat pipe  400  comprises casing  401 , wick  402 , and vapor cavity  403 . Casing  401  may comprise a sealed pipe or tube made of a material with high thermal conductivity such as copper or aluminum at both hot and cold ends. Working fluid evaporates to vapor absorbing thermal energy at event  404 . Examples of such fluids include water, ethanol, acetone, sodium, or mercury. The vapor migrates along cavity  403  from portion  452  (high temperature end) to portion  451  (low temperature end). The vapor condenses back to fluid and is absorbed by wick  402  at event  406 , and the fluid flows back to portion  402  through wick  402 . 
     With some embodiments, referring to  FIG. 5 , heat pipe  503  comprises a sealed pipe or tube made of a material with high thermal conductivity, i.e., copper at both hot and cold ends. For example, a copper pipe or tube may be approximately 300 MM long with a diameter of approximately 8 mm. Heat pipe  503  is typically constructed with a tube shell, wick and end caps. Heat pipe  503  may be drawn into negative pressure and may be filled with the fluid such as pure water. Wick  402  is typically constructed with a capillary porous material. Evaporation of the fluid occurs at one end of heat pipe  503 , while condensation occurs at the other end. When the evaporation end is heated, the capillary action in the fluid evaporates quickly. With a small gravity difference between two ends, the vapor flows to the other end, releasing heat. The vapor is then re-condensed into fluid, which runs along the porous material by capillary forces back into the evaporation end. This cycle is repeated to transfer the heat from the one end to the other end of heat pipe  503 . This cycle is typically fast, and the heat conduction is continuous. Good performance of the wick is often characterized by:
         1. Large capillary action or small effective aperture of wick,   2. Smaller fluid flow resistance, which have higher permeability,   3. Good thermal conductivity characteristics, and   4. Good repeatability and reliability in the manufacturing process.       

     Referring to  FIG. 4 , heat pipe  400  may have bends in order to route the heat transfer to or from a heat exchange device providing that the bends to not adversely affect the capillary or gravity action of heat pipe  400 . For example, referring to  FIG. 5 , heat pipe  503  is bent in a horizontal plane to route the heat between Peltier device  502  and heat sink  505 . 
       FIG. 5  shows serving apparatus  500  in accordance with an embodiment of the invention. While serving apparatus  500  is depicted in the cooling mode, apparatus  500  may be used to heat aluminum plate  501  (which functions as the serving surface on which an item is placed) based on the previous discussion. 
     Peltier device  502  is thermally coupled to serving surface  501  and copper block  504 , where the top side (corresponding to ceramic layer  312  as shown in  FIG. 3 ) is physically situated against serving surface  501  and the bottom side (corresponding to ceramic layer  313 ) is physically situated against copper block  504 . Thermal conductivity may be enhanced by ensuring the flatness of the installation surface, and coating the contact surface with a thin layer of heat conduction silicon grease. Also, in order to avoid fracturing the ceramic layers of Peltier device  502 , the pressure against the layers should be even and not excessive when fixing device  502 . 
     Heat pipe  503  is thermally coupled to Peltier device  502  through copper block  504  so that heat flows along heat flow  509   a  and  509   b . However, with some embodiments, heat pipe  503  may be directly placed against Peltier device  502 . Heat pipe  502  transports heat along heat flow  509   b  by traversing through copper block  504  via branches  507   a - 507   c  and heat sink  505 . Heat is thus transported along heat flow  509   c  and into the surrounding environment of serving apparatus  500 . 
     With some embodiments, heat sink  505  may be constructed from copper and/or aluminum in order to achieve performance, size, and cost objectives. 
     With some embodiments, fan  506  operates when apparatus is operating in the cooling mode. However, with some embodiments, fan  506  may operate in the heating and/or cooling modes. Fan  506  assists in the transfer of heat by drawing in cool air  510   a  and  510   b  so that heat sink  505  may be kept to a smaller size than without fan  506 . With some embodiments, the speed of fan  506  may be changed based on the temperature of serving surface  501 . For example, the speed may be increased when the difference of measured temperature of serving surface  501  and the desired temperature increases. However, with some embodiments, the speed of fan  506  may be fixed when fan  506  is activated and may operate during the entire duration of operation. 
     With some embodiments, while not explicitly shown in  FIG. 5 , a cooling fan may circulate air to provide inner air convection within the serving chamber (within serving cover  508  and serving plate  501 ) to enhance the cooling of food within the chamber. With some embodiments, a fan may support inner air convection when the apparatus is operating in the heating mode. 
       FIG. 6  shows control device  600  for controlling apparatus  100  (corresponding to control device  108  as shown in  FIG. 1 ), apparatus  200  (corresponding to control device  208  as shown in  FIG. 2 ), and apparatus  500  (as shown in  FIG. 5 ) in accordance with an embodiment of the invention. Processing system  601  may execute computer executable instructions from a computer-readable medium (e.g., storage device  604 ) in order provide verify communication redundancy for a network, Memory  602  is typically used for temporary storage while storage device  504  may comprise a flash memory and/or hard drive for storing computer executable instructions and a profile image. However, computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media include, but may not be limited to, random access memory (RAM), read only memory (ROM), electronically erasable programmable read only memory (EEPROM), flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by processing system  601 . The executable instructions may carry out any or all of the method steps described herein. 
     With some embodiments, processing system  601  may correspond to one or more processors and storage device  604  may correspond to one or more memories. 
     Control device  600  may be implemented as one or more ASICs or other integrated circuits (e.g., a single chip computer) having instructions for performing operations as described in connection with one or more of any of the embodiments described herein. Said instructions may be software and/or firmware instructions stored in a machine-readable medium and/or may be hard-coded as a series of logic gates and/or state machine circuits in one or more integrated circuits and/or in one or more integrated circuits in combination with other circuit elements. 
     With some embodiments, control device  600  supports different control capabilities for heating and/or cooling. For example, device  600  may obtain a temperature setting (desired temperature) from a user through an input device and control one or more Peltier devices (e.g., Peltier devices  802 - 805  as shown in  FIG. 8 ) to compensate for environmental factors in order to approximate the desired temperature. Control device  600  may also sense when cover  508  (as shown in  FIG. 5 ) is open (e.g. through a switch not explicitly shown), and control the Peltier devices accordingly. For example, control device  600  may activate the Peltier devices for a longer period of time when cover  508  is open than when it is shut. 
       FIG. 7  shows circuitry  700  for controlling Peltier devices in accordance with an embodiment of the invention. While some of the functionality of a serving apparatus may be implemented with a control device (e.g., control device  600  as shown in  FIG. 6 ), some or all of the functionalities may be implemented with separate circuitry, e.g., circuitry  700 . For example, circuitry  700  controls the activation of the Peltier devices by a comparator  701  comparing temperature setting  704  and measured temperature  703 . Comparator  701  may have hysteresis characteristics so that once Peltier device  706  is activated by providing electrical power from source  705  through power switch  702 , activation continues until the serving surface reaches a hysteresis temperature. 
       FIG. 8  shows a collection of Peltier devices for changing a serving surface temperature in accordance with an embodiment of the invention. Embodiments may support one or more Peltier devices in order to increase or decrease the temperature of a serving surface. With some embodiments, as shown in  FIG. 8 , four Peltier devices  802 - 805  may heat or cool serving surface  801 . Some or all of the Peltier devices may be activated at one time. For example, when the temperature of serving surface  801  is within a temperature range, Peltier devices  802 - 805  may be deactivated. When the measured temperature of serving surface  801  is outside the temperature range, all of the Peltier devices  802 - 805  are activated. (This approach is incorporated in flowchart  1100  as shown in  FIG. 11  and will be further discussed.) However, with some embodiments, only a proper subset of Peltier devices (e.g., devices  802  and  805  or devices  803  and  804 ) is activated at a given time when the temperature is outside the temperature range. Moreover, different subsets may be activated in a sequenced manner in order to provide more consistent thermal properties, such as more even cooling and/or heating, over serving surface  801 . For example, a first subset and a second subset may be activated and deactivated, respectively, during a first time duration while reversing activation states during the second time duration. 
     Some embodiments may support a greater number of Peltier devices. However, the number of Peltier devices may be limited by physical constraints and/or electrical power limitations.  FIG. 9  shows a collection of sixteen Peltier devices  902 - 917  for changing serving surface  901  in accordance with an embodiment of the invention. As discussed previously, some or all of devices  902 - 917  may be activated at the same time. Devices  902 - 917  may be partitioned into a plurality subsets, e.g., a first subset including devices  802 ,  805 ,  807 ,  808 ,  811 ,  812 ,  814 , and  817 , a second subset including  802 ,  804 ,  807 ,  809 ,  810 ,  812 ,  815 , and  817 , and third subset including devices  803 ,  805 ,  806 ,  808 ,  811 ,  813 ,  814 , and  816 , where some or all of the subsets may have overlapping members. 
     With some embodiments, the same Peltier devices may be used for different modes of operation. For example, referring to  FIG. 8 , Peltier devices  802 - 805  may be used both for heating and cooling. 
     With some embodiments, different Peltier devices may be used for different modes of operation. For example, Peltier devices  802  and  805  may be used for cooling while Peltier devices  803  and  804  may be used for heating. As another example, Peltier devices  802 - 805  may be used for cooling while only Peltier devices  502  and  805  are used for heating. 
       FIG. 10  shows flowchart  1000  for controlling a serving apparatus in accordance with an embodiment. At block  1001 , a control device (e.g., control device  108  as shown in  FIG. 1 ) reads the measured temperature of the serving surface (e.g., surface  101 ) from the temperature sensor (e.g., sensor  109 ). At block  1002 , the control device determines whether to activate some or all of the Peltier devices at block  1003 . With some embodiments, selected Peltier devices (i.e., all or some of the Peltier devices) may be activated until the measured temperature reaches a hysteresis temperature so that a hysteresis characteristic is incorporated. For example, the temperature setting may be 35° F. when the serving apparatus is operating in the cooling mode. In such a case, the selected Peltier devices may be activated until the serving surface is cooled down sufficiently so that the measured temperature reaches 33° F. (the hysteresis temperature). The hysteresis temperature is typically offset from the temperature setting by several degrees so that control cycling is reduced. Different exemplary procedures for controlling the Peltier devices will be discussed in  FIGS. 11 and 12 . 
     At block  1004 , the control device determines whether to activate one or more fans (e.g., fans  114  and  115 ). For example, with some embodiments the fans may be activated at block  1005  only when the measured temperature is outside a temperature range to assist transferring heat with the environment of the serving apparatus. However, with some embodiments, a fan may be activated only for specific operating modes, e.g., a cooling mode or a heating mode. 
       FIG. 11  shows flowchart  1100  for controlling Peltier devices in accordance with an embodiment. At block  1101  a control device obtains a measured temperature of a serving surface from a temperature sensor and the temperature setting (desired temperature) of the serving surface from a user input. At block  1102 , the control device determines the mode of operation, i.e., cooling or heating. Based on the mode of operation, the control device determines whether to activate the Peltier devices based on the measured temperature, temperature setting, and hysteresis temperature at blocks  1103 - 1108 . 
     At block  1103 , the control device operates in the cooling mode and determines whether the measured temperature exceeds the cooling temperature setting. If so, the control device activates the Peltier devices until the measured temperature is less than or equal to the cooling hysteresis temperature at block  1104 . Otherwise (i.e., the measured temperature does not exceed the cooling temperature setting), the control device deactivates the Peltier devices at block  1105 . 
     At block  1106 , the control device operates in the heating mode and determines whether the measured temperature is less than the heating temperature setting. If so, the control device activates the Peltier devices until the measured temperature is greater than or equal to the heating hysteresis temperature at block  1107 . Otherwise (i.e., the measured temperature does not exceed the cooling temperature setting), the control device deactivates the Peltier devices at block  1108 . 
       FIG. 12  shows flowchart  1200  for controlling Peltier devices in accordance with an embodiment. Flowchart  1200  is similar to flowchart  1100 , where blocks  1201  and  1202  correspond to blocks  1101  and  1102 , respectively. However, process  1200  activates all of the Peltier devices when the measured temperature is outside a temperature range (e.g., between the temperature setting and the hysteresis temperature) at blocks  1204  and  1207  and a selected subset of the Peltier devices when the measured temperature is within the temperature range at blocks  1205  and  1208 . When operating at blocks  1205  and  1208 , the control device may select different subsets from the plurality of Peltier devices and sequence through the different subsets. For example, referring to  FIG. 9 , the control device may first select and activate the first subset for a first time duration, followed by the second subset, followed by the third subset, followed by the first subset, and so forth. 
       FIG. 13  shows a serving apparatus  1300  with a heating side  1301  and a cooling side  1302  in accordance with an embodiment. Heating side  1301  and cooling side  1302  may operate at the same time so that heating serving surface  1305  may be heating one food item (e.g., hot cereal for breakfast) while cooling serving surface  1303  may be simultaneously cooling another food item (e.g., orange juice for breakfast). 
     Cooling serving surface  1303  is cooled by Peltier device  1304  transferring heat from its top to bottom, where Peltier device  1304  is thermally coupled to surface  1303 . Heating service surface  1305  is thermally coupled to Peltier device  1306 , which transfers heat from its bottom to its top. Consequently, waste heat is generated at the bottom of Peltier device  1304  while waste cold (loss of heat) is generated at the bottom of Peltier device  1306 . 
     With some embodiments, Peltier device  1304  and/or Peltier device  1306  may comprise a plurality of plurality of Peltier devices similarly shown in  FIGS. 8 and 9 . 
     A first portion of heat pipe  1307  is thermally coupled to Peltier device  1304  while a second portion of heat pipe  1307  is thermally coupled to Peltier device  1306 , in which the operation of heat pipe  1307  is similar to the operation of heat pipe  400  as shown in  FIG. 4 . Consequently, waste heat is transferred from Peltier device  1304  to Peltier device  1306 , which absorbs some of the waste heat. On the other hand, waste cold is transferred from Peltier device  1306  to Peltier device  1304 , which utilizes the cold in order to lower its operating temperature. As a result, waste heat and waste cold may be used by Peltier devices  1304  and  1306  that would have otherwise been expended into the surrounding environment. 
     Heat pipe  1307  may be directly coupled to Peltier device  1304  and/or Peltier device  1306 . However, heat pipe  1307  may be thermally coupled to ambient air adjacent to the bottom of Peltier device  1304  and/or Peltier device  1306 . With some embodiments, heat pipe  1307  may be thermally coupled to Peltier device  1304  and/or Peltier device  1306  through another material (e.g., similar to copper block  504  as shown in  FIG. 5 ). 
     With some embodiments, heat pipe  1307  may be directly routed between Peltier devices  1304  and  1306 , where heat pipe  1307  provides a continuous connection between the hot side and the cold side of Peltier devices  1304  and  1306 , respectively. Consequently, separate heat sinks (heat exchange device) and fans (e.g., as shown in  FIGS. 1, 2, and 5 ) may not be required because the opposite Peltier device may function as the heat sink for the other Peltier device. For example, the phase change (liquid to gas and/or gas to liquid) of heat pipe  1307  may cause heat/cold flow from one Peltier device to the other so that separate heat sinks and/or fans may not be needed to cause the temperature change to influence the heat/cold flow. 
     With some embodiments, heat pipe  1307  may be routed through a heat exchange device to assist in expending waste heat and/or waste cold. Heat pipe  1307  may have bends (not explicitly shown in  FIG. 13 ) in order to route the heat transfer to or from a heat exchange device providing that the bends to not adversely affect the capillary or gravity action of heat pipe  1307 . One or more fans  1308  and  1309  and/or heat exchange devices (not explicitly shown in  FIG. 13 ) may be positioned in the vicinity of heat pipe  1307  to assist in the exchange of waste heat and/cold. 
     Thermal barrier  1308  provides thermal separation (isolation) between heating side  1301  and cooling side  1302  so that heating serving surface  1305  and cooling serving surface  1303  do not adversely affect each other. 
     While serving apparatus  1300  may support one heating surface (surface  1305 ) and one cooling surface (surface  1303 ), a serving apparatus may support more than two serving surfaces with some of the embodiments. For example,  FIG. 14  shows a top view of apparatus  1400  that has heating surface  1401  (that may be used for the main course) and two cooling surfaces  1402  and  1403  (that may be used for a salad and cold desert, respectively). The surface areas and the temperature changes may be different for the different serving surfaces. For example, apparatus  1400  may have a plurality of cooling zones, where cooling surface  1402  chills a salad while cooling surface  1403  keeps ice cream from melting. Moreover, while serving surfaces  1401 - 1403  are depicted as rectangularly shaped, some embodiments may have differently shaped serving surfaces. Also, with some embodiments, surfaces  1401 - 1403  may have flat or concave surfaces in order to better contain the served item. 
     With some embodiments, heat pipes  1404  and  1405  may be routed between serving surfaces  1401 ,  1402 , and  1403  to assist in expending waste heat and/or waste cold. Different heat pipe configurations may be supported such as routing a heat pipe between a pair of serving surfaces (e.g., between serving surfaces  1401  and  1402 ) or routing a heat pipe across more than two serving surfaces (e.g.,  1401 ,  1402 , and  1403 ). 
       FIG. 15  shows portable serving tray  1500  that supports serving surfaces  1501 - 1503  that may be used to heat or cool different items in accordance with an embodiment. Portable serving tray  1500  contains at least one Peltier device (not explicitly shown in  FIG. 15 ) to provide desirable temperature changes for serving surfaces  1501 - 1503 . In order to have portable operating characteristics, portable serving tray  1500  may be powered by portable electrical source  1504  that may be inserted into tray  1500 . With some embodiments, portable electrical source  1504  may include a battery and/or fuel cell. 
     Portable serving tray  1500  may be used in different serving environments, including a hospital, hotel, or restaurant. Also, different types of items may be heated or cooled, including food, liquids, and non-eatable items. 
       FIG. 16  shows serving apparatus  1600  with a plurality of portable trays  1500  (as shown in  FIG. 15 ) and  1602 - 1603  stacked in rack  1601  in accordance with an embodiment. Portable trays  1500  and  1602 - 1603  may be stacked into rack  1601  so that trays  1602 - 1604  can be transported to a desired location. In addition, rack  1600  provides a holding means (e.g., slots or shelves) so that the portable trays can be inserted into and removed from rack  1600 . 
     As can be appreciated by one skilled in the art, a computer system with an associated computer-readable medium containing instructions for controlling the computer system may be utilized to implement the exemplary embodiments that are disclosed herein. The computer system may include at least one computer such as a microprocessor, digital signal processor, and associated peripheral electronic circuitry. 
     While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.