Patent Publication Number: US-2003221717-A1

Title: Composite thermal system

Description:
RELATED INVENTIONS  
     [0001] This application claims priority to U.S. Provisional application serial No. 60/384,300, filed on May 30, 2002, entitled “Active Building Envelope Systems”, which is hereby incorporated by reference in its entirety. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] This invention is related generally to composite thermal systems incorporating both a thermoelectric system and a photovoltaic system.  
       BACKGROUND OF THE INVENTION  
       [0003] Thermal systems for affecting the temperature of an object, such as a building, are known. For example, some thermal systems are designed to provide an ambient temperature within a building. Typically, such thermal systems for buildings include a thermal envelope, i.e., a structure that inhibits the passing of heat between the inside and outside of the building. Conventionally, thermal envelopes include insulated walls and/or roofs, for example.  
       [0004] Additionally, building thermal systems also typically include heating and/or cooling systems that compensate for the heat flow to or from the buildings. For example, heating and cooling systems such as air conditioning systems, furnaces, heat pumps, etc. are well known for this purpose. Thus, conventional strategies to mitigate thermal envelope losses or gains in buildings often rely on passive insulation approaches, and separate heating and cooling systems then compensate energy losses or gains that do occur.  
       [0005] Approaches to improve thermal systems for buildings include approaches directed to improving the thermal envelope. These approaches include double skin facades, walls with embedded evaporative cooling systems, dynamic insulation, integrated latent heat storage using phase-change materials, and development of multifunctional glazing materials. Efforts to develop enclosure systems with energy harvesting capabilities have also been made, for example, in the area of building integrated photovoltaic cells. Building integrated photovoltaic cells (BiPV) are photovoltaic systems that are fully integrated into the building&#39;s enclosure.  
       [0006] Approaches to improve thermal systems for buildings have also been directed to improving the heating or cooling system. For example, solar powered refrigeration has been studied, where power obtained from a photovoltaic system is used to drive a conventional heat-pump or ventilation system. In the solar powered refrigeration systems studied, solar energy is actively used (via its direct conversion to electricity) to extract heat for refrigeration purposes. In addition to conventional heat-pumps or ventilation units powered via photovoltaic systems, studies have also reported on the use of solid-state thermoelectric heat-pumps powered by photovoltaic cells. In these latter studies the solid-state thermoelectric heat-pumps are separated from the photovoltaic cells.  
       SUMMARY OF THE INVENTION  
       [0007] In accordance with one aspect of the present invention, there is provided a composite thermal system. The composite thermal system comprises a thermoelectric system that converts electrical energy into thermal energy and a photovoltaic system that converts light energy into electrical energy. The photovoltaic system is integral with and electrically connected to the thermoelectric system for providing electrical energy to the thermoelectric system.  
       [0008] In accordance with another aspect of the present invention, the composite thermal system further comprises a substrate. The thermoelectric system comprises a thin film thermoelectric layer formed over the substrate, and the photovoltaic system comprises a thin film photovoltaic layer formed over the thin film thermoelectric layer.  
       [0009] In accordance with another aspect of the present invention, the composite thermoelectric system comprises a plurality of thermoelectric modules, and the composite thermal system further comprises a heat storage layer, the thermoelectric modules disposed adjacent to and thermally connected to the heat storage layer.  
       [0010] In accordance with another aspect of the present invention, the thermoelectric system comprises a plurality of thermoelectric modules. The photovoltaic system is disposed on a first side of the plurality of thermoelectric modules. The composite thermal system further comprises a thermal insulation layer disposed on a second side of the plurality of thermoelectric modules opposite to the first side, the thermal insulation layer having a plurality of ventilation pathways, each ventilation pathway extending from a respective thermoelectric module of the plurality of thermoelectric modules into the thermal insulation layer.  
       [0011] In accordance with another aspect of the present invention, the thermoelectric system comprises a thermoelectric layer and the photovoltaic system comprises a photovoltaic layer.  
       [0012] In accordance with another aspect of the present invention, there is provided a method of controlling the temperature of a structure. The structure comprises a thermoelectric system that converts electrical energy into thermal energy, a photovoltaic system that converts light energy into electrical energy, wherein the photovoltaic system is integral with and electrically connected to the thermoelectric system, for providing electrical energy to the thermoelectric system, and a plurality of thermoelectric regions. The method comprises controlling the electrical energy provided by the photovoltaic system to the thermoelectric system so that at least some of the thermoelectric regions have different temperatures.  
       [0013] In accordance with another aspect of the present invention, there is provided a method of controlling the temperature of a building. The building comprises a thermal envelope comprising a thermoelectric system that converts electrical energy into thermal energy, a photovoltaic system that converts light energy into electrical energy, wherein the photovoltaic system is integral with and electrically connected to the thermoelectric system for providing electrical energy to the thermoelectric system. The method comprises converting light energy to electrical energy via the photovoltaic system during the day and transferring the electrical energy to the thermoelectric system, converting the transferred electrical energy via the thermoelectric system to thermal energy to heat a heat storage layer of the thermal envelope, dissipating heat from the heat storage layer to the thermoelectric system towards air external to the building during the night, and using the dissipating heat to generate electricity via the thermoelectric system.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 is a schematic illustrating a composite thermal system according to an embodiment of the invention.  
     [0015]FIG. 2 is a cross-sectional view of a composite thermal system according to an embodiment of the invention.  
     [0016]FIG. 3 is an enlarged cross-sectional view of a portion of the composite thermal system of FIG. 2.  
     [0017]FIG. 4 is a cross-sectional view of a composite thermal system according to another embodiment of the invention.  
     [0018]FIG. 5 is an enlarged cross-sectional view of a portion of the composite thermal system of FIG. 4.  
     [0019]FIG. 6 is a cross-sectional view of a composite thermal system according to another embodiment of the invention.  
     [0020]FIG. 7 is a cross-sectional view of a composite thermal system according to another embodiment of the invention.  
     [0021]FIG. 8 is an enlarged cross-sectional view of a portion of the composite thermal system of FIG. 7.  
     [0022]FIG. 9 is a cross-sectional view of a composite thermal system according to another embodiment of the invention.  
     [0023]FIG. 10 is an enlarged cross-sectional view of a portion of the composite thermal system of FIG. 9.  
     [0024]FIG. 11 illustrates composite thermal system panels as a part of a building. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0025] Reference will now be made in detail to embodiments of the present invention. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
     [0026] The present inventor has realized that a number of advantages can be obtained for building thermal systems and other thermal systems by implementing a composite thermal system incorporating both a photovoltaic system and a thermoelectric system, where the photovoltaic system is integral with the thermoelectric system, i.e., the photovoltaic system is attached to the thermoelectric system. For example, in the case of such a composite thermal system in building thermal envelope applications, an integral system actively addresses the building heat dissipation problems at their source, i.e., the envelope.  
     [0027] In contrast to many conventional systems, according to aspects of the present invention, heat may be pumped in an opposite direction of the passive heat conduction direction in order to maintain a desired temperature gradient. For example, if a higher temperature is to be maintained within a building as compared to the surrounding air temperature, heat is pumped from the building envelope into the building, instead of simply losing heat through the building envelope.  
     [0028] In addition, because energy distribution storage and control technology may be embedded within the building envelope itself, significant reductions in building construction time due to system integration and shop manufacturing may be realized. When the PV system is integrated into the building enclosure system, these systems may also provide other building functions, such as providing protection against weather. In those applications where additional conventional heating and cooling equipment need not be included within the building system, equipment cost savings, and reduced building construction time can be realized.  
     [0029] Further in those applications where the photovoltaic and thermoelectric systems comprise solid state devices, reduced maintenance of the cooling and heating systems may be realized due to the reliability of solid state devices.  
     [0030] Because the heating and cooling functions can be distributed throughout the building envelope, localized control of the temperatures of the inner surfaces of the building envelope are possible, and thus such a system allows for optimization to respond to both local external conditions and internal comfort needs.  
     [0031] The composite system according to the present invention has applications in addition to building thermal envelopes. For example, when the system is implemented using thinner materials, such as thin film thermoelectric and photovoltaic materials, the composite thermal system has packaging and aerospace applications. Furthermore, implementations using thinner materials allows the composite thermal systems to be applied to existing buildings, to new construction, and to transparent materials such as glazing.  
     [0032]FIG. 1 is a schematic illustrating a composite thermal system  10  according to an embodiment of the invention. The composite thermal system  10  includes a photovoltaic system  20  and a thermoelectric system  30 . Photovoltaic systems are systems using photovoltaic devices that convert electromagnetic radiation directly into electricity. The photovoltaic system  20  converts light energy into electrical energy. The photovoltaic system  20  is integral with and electrically connected to the thermoelectric system  30 , and thus can supply electrical energy to the thermoelectric system  30 . In turn, the thermoelectric system  30  converts electrical energy into thermal energy. Thus, the thermoelectric system  30  provides heating or cooling by converting electrical energy into thermal energy. In general, thermoelectric systems are heat engines in which charge carriers serve as the working fluid. The thermoelectric system  30  can be converted from heating to cooling by reversing the polarity of the current supplied thereto.  
     [0033] The photovoltaic system  20  supplies electrical energy to the thermoelectric system  30  via an electrical distribution system  40 . The electrical distribution system  40  includes the circuitry as necessary to distribute the electrical energy from the photovoltaic system  20  to different thermoelectric regions  35  of the thermoelectric system  30 . The electrical distribution system can consist of conventional wiring, integrated circuits, or adaptive solid state circuitry, for example. The thermal system  10  may also include an electrical storage system  70 . In this case electrical energy produced by the photovoltaic system  20 , which is not distributed to the thermoelectric regions  35  may be diverted to the electrical storage system  70 . In this regard the electrical storage system  70  may be a battery as is known in the art for storing electrical energy. The electrical storage system  70  may be integrated with the remaining structures of the system  10 , or may be separate therefrom.  
     [0034] When the photovoltaic system  20  is not producing enough electrical energy to supply the thermoelectric regions  35 , such as at night, during a cloudy day, or when the temperature gradient to be maintained is large, the electrical energy stored in the electrical storage system  70  may be diverted to the thermoelectric regions  35 .  
     [0035] The thermal system  10  may also include temperature sensors  50  and a thermal control system  60  to provide thermal feedback and temperature control. For thermal systems where temperature control of the individual thermoelectric regions  35  is desired, the thermal sensors  50  are individually associated with a respective thermoelectric region  35 . For example, individual thermal sensors may be disposed near or at respective of the thermoelectric regions  35  to measure the temperature near or at that respective thermoelectric region. Alternatively, the thermoelectric regions  35  can also serve as the thermal sensors themselves. In the latter case, no separate temperature sensors  50  are needed.  
     [0036] The thermal control system  60  receives signals indicative of the temperatures detected by the thermal sensors  50 , and based on these signals, and desired temperature setting of the thermoelectric regions  35 , controls the electrical distribution system  40  to provide an appropriate amount of electrical energy in the form of current and voltage to the thermoelectric regions  35 . In this regard, the thermal control system  60  may include an interface with control software, allowing for smart control.  
     [0037] The thermoelectric regions  35  may have different individual temperature settings, and thus these regions  35  may be controlled to have different temperatures as desired. Thus, the present system  10  can provide flexibility in providing different temperatures for the different thermoelectric regions  35  as desired. Because the heating and heat dissipation are localized, the temperature may be controlled to vary over a relatively short distance.  
     [0038] As an alternative to providing different temperature control for each of the thermoelectric regions  35 , the thermoelectric regions  35  may be controlled to provide the same temperature. The temperature control in this case may be simplified, and a single thermal sensor  50  may be used. Also in this case the control may be simplified by controlling the different thermoelectric regions to be provided with the same electrical energy.  
     [0039] The thermal sensors  50  may be any conventional thermal sensors such as a thermocouple, for example. Alternatively, the thermoelectric regions  35  can also serve as the thermal sensors themselves.  
     [0040] The thermoelectric regions  35  may each comprise one or more thermoelectric devices, such as thermoelectric modules for example. The present invention is not limited to any particular type of thermoelectric device, and suitable thermoelectric devices may comprise thermoelectric materials such as filled skutterdites, chlathrate structured compounds, fine grain sized thermoelectric materials, and film shaped thermoelectric materials, for example. The thermoelectric devices may comprise single stage devices, or multistage cascade structures, for example. The thermoelectric devices may also comprise thin-film thermoelectric materials, or may be thermoelectric devices comprising organic thermoelectric materials.  
     [0041] The photovoltaic system  20  may comprise one or more photovoltaic devices. The present invention is not limited to any particular type of photovoltaic device, and suitable photovoltaic devices may comprise materials such as conventional crystalline silicon, thin film silicon, amorphous silicon, gallium arsenide and other semiconductor materials. Suitable photovoltaic devices also include single junction or multi-junction solar cells, and dye-doped solar cells based on titanium dioxide. Suitable photovoltaic devices also include photovoltaic materials such as ceramic-based semiconductors, polymeric or polymeric hybrid materials. The photovoltaic devices may also include optics such as concentrator lenses and mirrors, antireflective coatings, textured cell surfaces and back reflectors.  
     [0042] In addition to a photovoltaic system and a thermoelectric system, the following embodiments may include an electrical distribution system, thermoelectric regions, temperature sensors, thermal control system and electrical storage system.  
     [0043]FIGS. 2 and 3 are cross-sectional views of a composite thermal system  210  according to an embodiment of the present invention. FIG. 3 is an enlarged view of a portion of the composite thermal system illustrated in FIG. 2. The composite thermal system  210  of FIGS. 2 and 3 is an active building envelope system where the photovoltaic system  220  and the thermoelectric system  230  are part of a building thermal envelope. The composite thermal system  210  also includes a heat storage layer  262 , a thermal insulating layer  264 , first heat sinks  266 , second heat sinks  268 , first supporting structure  274 , second supporting structure  276  and third supporting structure  278 .  
     [0044] The first  274  and third  278  supporting structures support the thermoelectric system  210 , heat storage layer  262 , and thermal insulating layer  264 . The first  274  and third  278  supporting structures may comprise the external skin of a structural load bearing panel  280 , for example. In this case, in addition to the first  274  and third  278  supporting structures, the heat storage layer  262 , thermal insulating layer  264 , first heat sinks  266 , and second heat sinks  268  are all integrated into the load bearing panel  280 . The load bearing panel  280  as a whole, including insulating layer  264  and heat storage layer  262 , may provides structural support as a building panel. The panel  280  in application may be a part of the building thermal envelope of a building. The first  274  and third  278  supporting structures may comprise plywood or some other building materials such as metals or fiber reinforced polymer composite, for example.  
     [0045] The second supporting structure  276  may comprise a metallic or fiber reinforced polymer composite material, or any other material suitable for supporting photovoltaic materials. The second supporting structure  276  acts to support the photovoltaic system  220 . The second supporting structure  276  is attached to the first supporting structure  274 , and thus the structures are integral. In this regard, the first supporting structure  274  may include a number of supporting brackets  275  that extend outwardly from the first supporting structure  274 . These supporting brackets  275  can be made from a metal or any other suitable material. The second supporting structure  276  may be hung and secured on the supporting brackets  275  to attach the second supporting structure  276  to the first supporting structure  274 .  
     [0046] The thermoelectric system  230  includes a plurality of thermoelectric modules  232 . The present invention is not limited to the particular thermoelectric module, and the thermoelectric modules may comprise any thermoelectric module or thermoelectric system, as disclosed above with respect to FIG. 1. The thermoelectric modules  232  may be grouped as desired, and may be arranged to correspond to thermoelectric regions  235  as also disclosed above with respect to FIG. 1. Each thermoelectric region  235  may be associated with one or more of the thermoelectric modules  232 .  
     [0047] The grouping of the thermoelectric modules  232  according to thermoelectric regions  235  allows for a particular region to be heated or cooled as desired, and provides for much flexibility in differential heating/cooling of the different regions  235 . For example, if the composite thermal system  210  is to be used as part of a building thermal envelope for a building having several rooms, the regions  235  may be grouped according to the different rooms of the building, and the different rooms heated or cooled to have different temperatures.  
     [0048] The composite thermal system  210  of FIGS. 2 and 3 may be particularly suited for a building thermal envelope in a heating dominated climate. In this regard the composite thermal system  210  includes the heat storage layer  262 . The heat storage layer  262  comprises a material with a high heat storage capacity. The heat storage layer  262  may comprise a phase change material, for example, where heat supplied to the phase change material is stored as the latent heat of phase transformation of the material. Suitable phase change materials may include salt hydrates, paraffins, or fatty acids. Alternatively, these phase change materials can also be incorporated into conventional building materials such as concrete or drywall, for example by means of micro-encapsulation. In the latter case, the heat storage layer  262  may also provide structural support for the thermoelectric layer  30 , and act as a load bearing structure for the building, for example to support a roof load. Heat generated by the thermoelectric modules  232  is transferred to the heat storage material of the heat storage layer  262 , or vice versa if the modules  232  are in cooling mode.  
     [0049] Heat is transferred between the thermoelectric modules  232  and the heat storage layer  262  via thermal conduction paths between thermal insulation regions  263  of the thermal insulating layer  264 . The thermal conduction paths may be extensions of the heat storage layer  262  through the thermal insulating layer  264  towards respective thermoelectric modules  232 . In this regard, the thermal insulation regions  263  are disposed adjacent the heat storage layer  262  and laterally adjacent the plurality of thermoelectric modules  232 . Alternatively, the thermal conduction paths may comprise a material with good heat conduction properties extending from the heat storage layer  262  through the thermal insulating layer  264  towards respective thermoelectric modules  232 . Appropriate materials with good heat conduction properties include metals such as copper or aluminum, for example.  
     [0050] The thermal conduction paths from respective thermoelectric modules  232  to the heat storage layer  262  may also include first heat sinks  266 . Each heat sink of the first heat sinks  266  is disposed adjacent to a respective of the thermoelectric modules  232  in the thermal conduction path, and thus acts to provide a thermal conduction path between its respective thermoelectric module  232  and the heat storage layer  262 . In this regard, it is preferred that the first heat sinks  266  have good thermal conduction properties, and may be made of a material with good heat conduction properties such as a metal, such as copper or aluminum, for example. The heat sinks  266  should be in good thermal contact with the thermoelectric modules  232 , for example by applying an adhesive with good thermal conductivity. The first heat sinks  266  should also be of a shape such that heat is dissipated between the first heat sinks  266  and the heat storage layer  262 . For example, the heat sinks  266  may comprise a number of extending portions that provide a large surface area to be contacted by the material of the heat storage layer  262 .  
     [0051] The composite thermal system  210  also includes a plurality of second heat sinks  268 , each of the second heat sinks  268  adjacent to a respective of the plurality of the thermoelectric modules  232  on an opposing side from a respective of the first heat sinks  266 , and providing a thermal path from its respective thermoelectric module  232  in a direction opposite from the heat storage layer  262 . Thus, each of the second heat sinks acts to conduct heat between a respective thermoelectric module  232  along a path on the opposite side of the thermal conduction path to the heat storage layer  262 .  
     [0052] The second supporting structure  276  may be attached to the first supporting structure  274  such that there is an air space  282  between these two structures. Heat conducted by each of the second heat sinks  268  is conducted from a respective thermoelectric module  232  and dissipated at the air space  282 . The second heat sinks  268  should also be of a shape such that heat is dissipated between the first heat sinks  266  and the air space  282 . For example, the heat sinks may comprise a number of extending portions that provide a large surface area to be contacted by the air in the air space  282 . Air exchange between the air space  282  and air outside of the thermal system  210  may occur through natural ventilation, such as through vents in the second supporting structure  276 , or via forced air.  
     [0053] The photovoltaic system  220  together with its supporting structure  276  may also act as a rain screen for the building, protecting the structural load bearing panel  280  from the weather. No other material or structure is therefore needed to weatherproof the building.  
     [0054] In operation as part of a building thermal envelope, the thermal system  210  receives and converts light energy during the day to thermal energy, and stores the thermal energy in the heat storage layer  262 . During the night, presuming the night time external temperature is below the ambient internal building temperature desired, there is a temperature gradient between the outside air and the heat storage layer  262 . In this case, the heat storage layer  262  slowly dissipates the heat stored towards the inside air. In addition, the heat storage layer will also dissipate stored heat outwards through the thermoelectric system towards the external air. In one embodiment this dissipating heat may be used to generate electricity by the thermoelectric system  230 . The thus generated electrical energy may be stored, such as in a battery, or used immediately.  
     [0055]FIGS. 4 and 5 illustrate cross-sectional views of a composite thermal system  310  according to another embodiment of the present invention. FIG. 5 is an enlarged view of a portion of the composite thermal system illustrated in FIG. 4. In a similar fashion to the system of FIGS. 2 and 3, the composite thermal system  310  of FIGS. 4 and 5 may be an active building envelope system where the photovoltaic system  320  and the thermoelectric system  330  are part of a building thermal envelope. While the embodiment of FIGS. 2 and 3 may be most appropriate for use in a heating-dominated climate where heat storage in night time is important, the embodiment of FIGS. 4 and 5 may be most appropriate for use in a cooling-dominated climate where heat storage in night time is not as important.  
     [0056] In the embodiment of FIGS. 4 and 5, the composite thermal system  310  also includes a thermal insulating layer  364  in a similar fashion to the thermal insulating layer  264  of the embodiment of FIGS. 2 and 3. The embodiment of FIGS. 4 and 5, however, does not include the heat absorbing layer of the embodiment of FIGS. 2 and 3. The embodiment of FIGS. 4 and 5 also includes in a similar fashion to the embodiment of FIGS. 2 and 3, thermoelectric regions  235 , first heat sinks  266 , second heat sinks  268 , a first supporting structure  274 , a second supporting structure  276 , a third supporting structure  278 , load bearing panel  280 , and other components denoted by the same numerals as in FIGS. 2 and 3.  
     [0057] As noted above, the composite thermal system  310  of FIGS. 4 and 5 may be particularly suited for a building thermal envelope in a cooling dominated climate. In this regard the composite thermal system  310  includes a number of ventilation pathways  386 . Each of the ventilation pathways  386  extends from a corresponding thermoelectric module  232  through the thermal insulating layer  364 . Heat generated by the thermoelectric modules  232  is convected through the ventilation pathways  386  from the thermoelectric modules  232 , or vice versa if the modules  232  are in cooling mode. Air flow in the ventilation pathways  386  can be accomplished by means of natural ventilation or forced air ventilation, for example.  
     [0058] The composite thermal system  310  also includes a plurality of filters  388 , each filter  388  disposed in a respective ventilation pathway  386 . The filters act to inhibit dirt or bugs from entering the ventilation pathways  386 . The filter  388  may be open pore filters, for example.  
     [0059] The thermal system  310  may also include first heat sinks  266 , each of the first heat sinks  266  adjacent to a respective of the plurality of the thermoelectric modules  232  and providing a thermal path between its respective thermoelectric module  232  and a respective of the ventilation pathways  386 . In this regard, it is preferred that the first heat sinks  266  have good thermal conduction properties, and may be made of a material with good heat conduction properties such as a metal, such as copper or aluminum., for example. The heat sinks should be in good thermal contact with the thermoelectric modules, for example by applying an adhesive with good thermal conductivity. The first heat sinks  266  should also be of a shape such that heat is dissipated between the first heat sinks  266  and the ventilation pathways  386 . For example, the heat sinks may comprise a number of extending portions that provide a large surface area to be contacted by the air in the ventilation pathways  386 .  
     [0060] When the thermoelectric modules  232  are operated to provide cooling, heat is dissipated from the air in the ventilation pathways to first heat sinks  266 , and when operated to provide heating, heat flows in the opposite direction.  
     [0061] The composite thermal system  310  also includes a plurality of second heat sinks  268 , each of the second heat sinks  268  adjacent to a respective of the plurality of the thermoelectric modules  232  on an opposing side from a respective of the first heat sinks  266 , and providing a thermal path from its respective thermoelectric module  232  in a direction opposite from the thermal insulation layer  364 . Thus, each of the second heat sinks  268  acts to conduct heat between a respective thermoelectric module  232  along a path on the opposite side of the thermal conduction path to the thermal insulation layer  364 .  
     [0062] In a similar fashion to the embodiment of FIGS. 2 and 3, in the embodiment of FIGS. 3 and 4, heat conducted by each of the second heat sinks  268  is conducted from a respective thermoelectric module  232  and dissipated towards the air space  282 . The second heat sinks  268  should also be of a shape such that heat is dissipated between the second heat sinks  268  and the air space  282 . For example, the heat sinks  268  may comprise a number of extending portions that provide a large surface area to be contacted by the air in the air space  282 . Air exchange between the air space  282  and air outside of the thermal system  310  may occur though natural ventilation, such as vents in the second supporting structure  276 , or via forced air.  
     [0063]FIG. 6 is a cross-sectional view of another embodiment of a composite thermal system similar to the embodiment of FIGS. 4 and 5 in that both systems include ventilation pathways. The ventilation pathways in this embodiment, however, extend in directions on both sides of the thermoelectric modules.  
     [0064] The composite thermal system of FIG. 6 includes a front structural support  676  and a rear structural support  678 , with a thermal insulation layer  668  between the front  676  and rear  678  structural supports. A thermoelectric system  630  comprising a plurality of thermoelectric modules  632  is embedded within the thermal insulation layer  668 . A photovoltaic system  620  is disposed at the front of the thermoelectric system in line with or on the front structural support  676 . A power distribution layer  690  may be located near the rear structural support  678  to distribute the electrical energy received from the photovoltaic system  620  to the thermoelectric modules  632  as needed.  
     [0065] Each of a plurality of ventilation pathways  686  extend from the front of the system to respective of the thermoelectric modules  632  and then to the back of the system. In operation, the air in the ventilation pathways  686  is either cooled or heated by the thermoelectric modules (depending on whether they are operated to provide heating or cooling).  
     [0066] Each of a plurality of valves  696  allows the air to pass directly past the thermoelectric modules  632  when opened. The valves  696  may be controlled to be opened when desired to allow flow of air past the thermoelectric modules  632 . This mode of operation allows for direct ventilation through the composite wall system.  
     [0067]FIGS. 7 and 8 are cross-sectional views of a composite thermal system  410  according to an embodiment of the present invention. The composite thermal system  410  of this embodiment may be adapted to both heating-dominated and cooling-dominated climates. FIG. 8 is an enlarged view of a portion of the composite thermal system illustrated in FIG. 7. The composite thermal system  410  of FIGS. 7 and 8 includes a thermoelectric system, which in this embodiment is a thermoelectric layer  430 , and a photovoltaic system, which in this embodiment is a photovoltaic layer  420 , integral to the thermoelectric layer  430 .  
     [0068] Preferably the thermoelectric layer  430  comprises thermoelectric modules  432  that are not spaced apart, but have an almost 100% density over the surface of the thermoelectric layer  430 . Thus, the thermoelectric modules  432  cover substantially all of the surface of the thermoelectric layer  430 . The thermoelectric layer  430  may comprise one or more thermoelectric devices, such as thermoelectric modules for example. The present invention is not limited to any particular type of thermoelectric device or material. In applications where the thermoelectric system  410  constitutes a building envelope, the thermoelectric layer  430  covers the entire building envelope running parallel to the photovoltaic layer  420 .  
     [0069] The composite thermal system may also include a heat dissipation layer  440  disposed over the thermoelectric layer  430 . The photovoltaic layer  420  is disposed over the heat dissipation layer  440 . The heat dissipation layer can be composed of a metallic material with open cell structure, for example. Heat from the thermoelectric layer  430  flows to the heat dissipation layer  440  when the thermoelectric layer  430  is warmer than the heat dissipation layer  440 , and is dissipated thereat. Conversely, when the thermoelectric layer  430  is cooler than the heat dissipation layer  440 , heat from the heat dissipation layer  440  flows to the thermoelectric layer  430 .  
     [0070] The composite thermal system  410  may optionally include a heat storage layer  460  disposed adjacent the thermoelectric layer  430 . Heat from the thermoelectric layer flows to the heat storage layer  460  (and vice versa if the thermoelectric layer is in a cooling mode). The heat storage layer can be a phase change material, where the heat is stored as the latent heat of phase transformation of the phase change layer.  
     [0071] The composite thermal system  410  also may include a structural support layer  450  supporting the heat dissipation layer  440 , thermoelectric layer  430 , photovoltaic layer  420 , and heat storage layer  460 , if present. The structural support layer  450  may be made from a metallic or fiber reinforced polymeric composite material, for example. Alternatively, the heat storage layer  460  can also serve as a structural support layer. In the latter case, no separate support layer  450  is needed.  
     [0072] In this embodiment the total thickness of the photovoltaic layer  420 , thermoelectric layer  430 , heat dissipation layer  440 , structural support layer  450  and heat storage layer  460 , if included, may be less than 100 mm, for example. Thus, this embodiment provides the possibility of allowing for a thin thermal system, which can be readily incorporated into building envelope applications for new or existing building envelopes. In this regard, the thermal system  410  could be mounted to the outside of an existing building envelope  490  of an existing building. The system  410  may be mounted on the existing building envelope  490  as shown in FIG. 7 so as to provide a closed air space  492  between the system  410  and the existing building envelope  490 . A closed air space  492  is formed in between the building envelope and the composite system  410 . This air space  492  may be well insulated at the edges so that no external air is allowed to enter the space. In this case, the system  410  is used to thermally control the airspace in between the system  410  and the existing building envelope  490 . Indirectly, this system  410  acts to thermally control the building.  
     [0073]FIGS. 9 and 10 are cross-sectional views of a composite thermal system  510  according to an embodiment of the present invention. FIG. 10 is an enlarged view of a portion of the composite thermal system  510  illustrated in FIG. 9. The composite thermal system  510  of this embodiment may be adapted to both heating-dominated and cooling-dominated climates. The composite thermal system  510  is similar to that of FIGS. 7 and 8 in that the overall thickness of the system can be made relatively thin. In the embodiment of FIGS. 9 and 10, because thin film thermoelectric systems and thin film photovoltaic systems are employed, the overall thickness can be even lower than that of the embodiment of FIGS. 7 and 8.  
     [0074] Returning to FIGS. 9 and 10, in the composite thermal system  510  the thermoelectric system comprises a thin film thermoelectric layer  530 , and the photovoltaic system comprises a thin film photovoltaic layer  520 . In a similar fashion to the embodiment of FIGS. 7 and 8, the total thickness of the thermal system in the Embodiment of FIGS. 9 and 10 may be quite thin. In fact, because thin film materials are used, the total thickness may be even less, 500 micrometers or less for total thickness of the layers other than the structural support layer  550 , or even  100  micrometers or less.  
     [0075] The composite thermal system  510  may include a thin film heat dissipation layer  540  disposed over the thermoelectric thin film layer  530 . The photovoltaic thin film layer  520  is disposed over the thin film heat dissipation layer  540 . A thin film metallic material can be used as the heat dissipation layer, for example. Heat from the thermoelectric thin film layer  530  flows to the heat dissipation thin film layer  540  when the thermoelectric thin film layer  530  is warmer than the heat dissipation thin film layer  540 , and is dissipated thereat. Conversely, when the thermoelectric thin film layer  530  is cooler than the heat dissipation thin film layer  540 , heat from the heat dissipation thin film layer  540  flows to the thermoelectric thin film layer  530 .  
     [0076] The composite thermal system  510  may also include a structural support layer  550  supporting the heat dissipation thin film layer  540 , thermoelectric thin film layer  530 , and photovoltaic thin film layer  520 . The structural support layer may be a metallic, polymeric, or ceramic material, for example.  
     [0077] In this embodiment the total thickness of the photovoltaic thin film layer  520 , thermoelectric thin film layer  530 , and heat dissipation thin film layer  540 , may be less than 500 micrometers, or even less than 100 micrometers, for example. Thus, this embodiment provides the possibility of allowing for a very thin thermal system, which can be readily incorporated into a number of applications. In addition, since thin film thermoelectric and thin film photovoltaic materials are used in this embodiment, this embodiment can be made transparent or translucent. For example, for building envelope applications, the structural support layer  550  could be made of a transparent glass or other transparent material, and the composite thermal system  510  can be used as a glazing system for buildings. Alternatively, when attached to an opaque structural support layer, the composite thermal system  510  can be attached to the outside of an existing building envelope  590  of an existing building in a similar fashion to the embodiments of FIGS. 7 and 8. In this regard, the system  510  may be mounted on the existing building envelope  590  as shown in FIG. 9 so as to provide a closed air space  592  between the system  510  and the existing building envelope  590 . A closed air space  592  is formed in between the building envelope and the composite system  510 .  
     [0078] In addition to building applications, the composite thermal system  510  could be employed in packaging applications, for example. For example, the composite thin film thermal system  510  could be applied to the surface of a bottle of refreshment or other storage container, or to the surface of other objects that are intended to be kept cool. The composite thermal system  510  could then actively cool the object when the object is in the sunlight. Other applications include the use of transparent thin film thermal composite systems  510  for automobile windows. The internal automobile space could then actively be cooled when exposed to sunlight. Alternatively, the thin film composite thermal system of embodiment  510  can also be used to heat objects or surfaces above ambient temperatures.  
     [0079] In addition to building and packaging applications, the composite thermal system could also be employed in aerospace applications, for example. For example, the composite thermal system could be applied to construct the external skin of a space station or space transport vessel. In this application, solar energy is directly used to thermally condition the internal space of the space station or space transport vessel. In addition, the composite thermal system in this application actively counteracts thermal structural stresses that are encountered in these structures when the structures are unevenly exposed to solar radiation. The thermal control capabilities of the composite thermal system may also be used to thermally condition the fuselage or wing structures of airplanes, for example.  
     [0080]FIG. 11 illustrates composite thermal system panels  910  as part of a building  900 . The composite thermal system panels  910  may comprise the composite thermal system of any one of the earlier embodiments of FIGS.  1 - 9 . The composite thermal system panels  910  may comprise part of a roof  920  and/or walls  930  of the building  900 . Some or all of the overall building thermal envelope may comprise the panels  910 . For example, the panels  910  may be disposed only in the roof  920 , only in the walls  930 , or as a portion of the walls  930  or roof  920 .  
     [0081] Preferably the panels  910  are disposed at least as part of the walls  930  and roof  920  that face in different directions. Thus, the electrical power generated at panels receiving sunlight may be redistributed to those panels which are in shade or in little sunlight. This allows the photovoltaic system (not shown in FIG. 11) of the panels  910  to receive sunlight generated power during most of the day time, even if only some of the panels  910  are in sunlight during part of the day time. The panel  910  may remain stationary as opposed to tracked panels that are moved to track the movement of the sun. Although such stationary panels may have a lower efficiency than the tracked panels, the efficiency may be sufficient in many applications because the panels  910  are incorporated throughout the building  900 .  
     [0082] While the above embodiments illustrate the layers of the composite thermal system in a particular order, the invention is not so limited. The layers may be arranged in an order other than that illustrated in the drawings. For example, in the embodiment of FIGS. 9 and 10, the thermoelectric thin film layer  530  may be disposed between the heat dissipation thin film layer  540  and the photovoltaic thin film layer  520 .  
     [0083] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.