Abstract:
A device for selectively controlling the passage of thermal energy through the device from a first space to a second space by selectively varying an overall thermal conductivity of the device comprises a structure having at least one component movable from a first position to a second position and an actuator mechanically coupled to the component for moving the component from the first position to the second position. When the at least one component is positioned in the first position the device exhibits a first thermal conductivity and when the at least one component is positioned in the second position the device exhibits a second thermal conductivity different from the first thermal conductivity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/525,848 filed Jun. 18, 2012, entitled “Variable Thermal Insulation”, which claims priority to U.S. provisional application No. 61/498,157 filed Jun. 17, 2011, entitled “Smart Insulation”. The contents of each are incorporated in their entirety herein by reference. 
     
    
     STATEMENT OF GOVERNMENTAL SUPPORT 
       [0002]    This invention was made with government support under grant # DE-EE0004261 awarded by the DOE. The government has certain rights in the invention. 
     
    
     TECHNICAL FIELD 
       [0003]    The invention relates generally to insulating materials and, more particularly, to insulating materials or devices that have the ability to exhibit both thermally insulating and non-insulating states. 
       BACKGROUND OF THE INVENTION 
       [0004]    Improving the energy efficiency of buildings has been one of the main focuses in recent years toward lowering energy consumption and carbon emissions in both the United States and worldwide. As shown in  FIG. 1 , in the United States, buildings account for nearly 40% of overall energy consumption. Within building energy consumption, heating and cooling loads account for 42% and 29% of residential and commercial building energy consumption respectively, resulting in great effort placed toward improvements in the implementation of conventional insulation materials. 
         [0005]    The main purpose of conventional insulation is to passively prevent heat transfer in either direction between the building interior and the hot or cold outside environment, to maintain a desired temperature gradient over the insulation at all times. In general, the only existing ways to improve the energy efficiency of conventional insulation are through either developing higher R-value insulation or insulating to the maximum amount that can be cost-justified. 
         [0006]    There is therefore room for improvement in insulation. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention seeks to improve upon deficiencies in known insulations by providing an insulating system having thermal conduction properties that may be selectively varied to best suit the particular environmental conditions present at a given time. 
         [0008]    As one aspect of the invention a device for selectively controlling the passage of thermal energy therethrough by selectively varying the overall thermal conductivity of the device is provided. The device comprises a structure having at least one component movable from a first position to a second position. When the at least one component is positioned in the first position the device exhibits a first thermal conductivity and when the at least one component is positioned in the second position the device exhibits a second thermal conductivity different than the first thermal conductivity. 
         [0009]    The structure may comprise a number of thermally conductive pathways adapted to be disposed between the first space and the second space. Each pathway of the number of thermally conductive pathways being selectively interruptible by movement of the at least one component such that the overall thermal conductivity of the device is selectively variable between the first thermal conductivity and the second thermal conductivity. 
         [0010]    The structure may comprise a first plate member having a number of fins extending therefrom and a second plate member having a number of fins extending therefrom. At least one of the first plate member and the second plate member may be selectively moveable among: a first position in which the number of fins of the first plate member contact the number of fins of the second plate member creating the number of thermally conductive pathways, and a second position in which the number of fins of the first plate member and the number of fins of the second plate member are disposed a distance apart. 
         [0011]    The first plate member and the second plate member may be disposed the same distance apart when disposed in either of the first position or the second position. 
         [0012]    The first plate member and the second plate member may be disposed a further distance apart when disposed in the second position than in the first position. 
         [0013]    At least one of the first plate member and the second plate member may comprise an insulating material disposed between the fins thereof, the insulating material being formed from a different material than either of the plate members or the fins thereof. 
         [0014]    The fins of at least one of the first plate member and the second plate member may be selectively moveable among: a first position in which the number of fins of the first plate member contact the number of fins of the second plate member creating the number of thermally conductive pathways, and a second position in which the number of fins of the first plate member and the number of fins of the second plate member are disposed a distance apart. 
         [0015]    At least one of the first plate member and the second plate member may be selectively moveable among: a first position in which the first plate member contacts the second plate member creating the number of thermally conductive pathways, and a second position in which the first plate member and the second plate member are disposed a distance apart. 
         [0016]    The structure may comprises a number of compartments formed therein, each of the compartments being adapted to receive and house a volume of a gas or liquid therein. The device is structured to exhibit the first thermal conductivity when the volume of gas or liquid is housed in the number of compartments and the device is structured to exhibit the second thermal conductivity when the volume of gas or liquid is evacuated from the number of compartments. 
         [0017]    The structure may have a selectively variable thickness, the device exhibiting the first thermal conductivity when the structure has a first thickness and the device exhibiting the second thermal conductivity when the structure has a second thickness different than the first thickness. 
         [0018]    The structure may comprise a number of compartments formed therein, each of the compartments being adapted to receive and house a volume of a gas or liquid therein. The device is structured to have a first thickness when the volume of gas or liquid is housed in the number of compartments and the device is structured have a second thickness when the volume of gas or liquid is evacuated from the number of compartments. 
         [0019]    The structure may further comprise a first plate member disposed on a first side of the structure and a second plate member disposed on an opposite second side of the structure generally parallel to the first plate member. The thickness of the device may be the distance between the first plate member and the second plate member. 
         [0020]    At least one of the first plate member and the second plate member may include an actuator coupled thereto, the actuator being structured to selectively vary the distance between the first plate member and the second plate member. 
         [0021]    The structure may include a mechanical pump fluidly coupled to each of the number of compartments within the structure. The mechanical pump is structured to supply or remove the volume of gas or liquid from the number of compartments. 
         [0022]    These and other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
           [0024]      FIG. 1  shows a breakdown of energy consumption in the United States; 
           [0025]      FIGS. 2A and 2B , respectively, show a comparison between conventional and smart building insulation for an example of a sunny winter day case; 
           [0026]      FIGS. 3A and 3B , respectively, show a comparison between conventional and variable building insulation for an example of a summer evening case; 
           [0027]      FIG. 4  shows a sectional view of a portion of a system according to an embodiment of the present invention disposed in a non-insulating configuration; 
           [0028]      FIG. 5  shows a sectional view of the portion of  FIG. 4  disposed in an insulating configuration; 
           [0029]      FIG. 6  shows a sectional view of a portion of an alternate embodiment of the system of  FIG. 4  disposed in an insulating configuration; 
           [0030]      FIG. 7  shows a sectional view of a portion of a system according to another embodiment of the present invention disposed in a non-insulating configuration; 
           [0031]      FIG. 8  shows a sectional view of the portion of  FIG. 7  disposed in an insulating configuration; 
           [0032]      FIG. 9  shows a sectional view of a portion of a system according to another embodiment of the present invention disposed in an insulating configuration; 
           [0033]      FIG. 10  shows a sectional view of the portion of  FIG. 9  disposed in a non-insulating configuration; 
           [0034]      FIG. 11  shows a sectional view of a portion of a system according to another embodiment of the present invention disposed in an insulating configuration; 
           [0035]      FIG. 12  shows a sectional view of the portion of  FIG. 11  disposed in a non-insulating configuration; 
           [0036]      FIGS. 13A and 13B , respectively, show a portion of another example embodiment in a generalized arrangement for thermal analysis disposed in two different positions; and 
           [0037]      FIG. 14  is a series of graphs showing the ratio of insulated conductive resistances vs. the number of divisions. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    The following description is provided to enable any person skilled in the art to use the invention and sets forth the best modes contemplated by the inventors for carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art. 
         [0039]    As used herein, the term “number” shall be used to refer to any non-zero quantity, i.e., one or any number greater than one. 
         [0040]    As used herein, the term “insulating” shall be used to refer to an arrangement having a generally low thermal conductivity. Conversely, as used herein the term “non-insulating” shall be used to refer to an arrangement having a generally high thermal conductivity. 
         [0041]    The present invention addresses deficiencies in the prior art by providing a new type of insulation that can lower building heating and cooling loads by changing its thermal properties on command. The basic idea behind such variable or “smart” insulation as described herein is that certain temperature differences occur at particular times for buildings where it would be beneficial to remove the insulation and allow some heat transfer to flow between the interior of the building and the outside walls or ambient environment. There are also instances where it would be beneficial to selectively enable or impede heat flow within particular sections of a building or to selectively enable or impede heat flow between components of machinery. 
         [0042]    For example, a commercial or industrial building has high temperature equipment in a specific area, such as a kitchen in a restaurant. In the winter it is beneficial to allow that heat to flow to an adjacent area for secondary heating, such as to the eating area of the restaurant. In the summer, however, it is better to keep that heat from entering the adjacent areas. 
         [0043]    Instead of acting as a passive component, such as conventional building insulation, smart insulation is an adaptive component that is able to be selectively switched between low and high heat transfer states to take advantage of such instances where it would be beneficial to be able to “turn off” the insulation. Two example scenarios in which little or no building insulation would be advantageous would be sunny winter days and cool summer evenings. 
         [0044]    During the winter in most areas of the United States, it would usually be beneficial to have building insulation with a very low thermal conductivity to maintain the interior building space at temperatures much warmer than the cold outside environment. In the afternoon of a sunny winter day, however, thermal radiation can cause heat to build up on the building walls and in the attic to temperatures much higher than the interior space of the building. If the building insulation could be selectively “turned off” in appropriate regions of the building where the temperature difference is beneficial, thereby allowing heat to flow across it, the external thermal energy could be used to help heat the building interior, thus lowering building energy consumption.  FIGS. 2A and 2B  show a schematic comparison between conventional and smart building insulation for such a sunny winter day case. As shown in  FIG. 2A , conventional insulation  10  blocks the flow of the thermal energy (shown by arrows  12 ) from the walls and attic to the interior  14  of the building  16 , resulting in any beneficial heating from the external thermal energy  12  being lost. On the other hand, as shown in  FIG. 2B , smart insulation  20  is able to “turn off” the insulator state, effectively raising its thermal conductivity, thus allowing the thermal energy  12  to readily transfer to the interior  22  of the building  24 , thus lowering heating costs. 
         [0045]    For the second case, during summer in most areas of the United States, it would also be beneficial most of the time to have very low thermal conductivity insulation during the day in order to maintain the interior building space at temperatures cooler than the hot outside environment. In the evening or at night on a clear summer day, however, the outside temperature can drop rapidly to a cooler, comfortable temperature. Homeowners commonly try to take advantage of this effect by opening windows or using whole-house fans to allow air to transfer heat from the building interior to the cooler outside environment. However, homeowners will often continue to use their centralized air conditioning system instead of taking advantage of the cool outside environment. If the building insulation could be “turned off” to allow heat to transfer from the building interior to the outside environment, it would have a similar effect to opening windows except on a much larger level, since it would be like “taking the attic off” or “taking the walls off” of the building. However, unlike opening windows, smart insulation would only transfer heat and not air between the building interior and outside environment, which would allow the comfortable humidity level of the conditioned air inside of many buildings to be maintained, while preventing very humid or very dry air from transferring from the outside environment into the building as would occur with open windows.  FIGS. 3A and 3B  show, schematically, a comparison between conventional and smart building insulation for the cool summer evening case. As shown in  FIG. 3A , conventional insulation  26  blocks heat (shown by arrows  28 ) from flowing from the interior  30  of the building  32  to the cooler outside environment, resulting in the loss of any beneficial cooling. On the other hand, such as shown in  FIG. 3B , smart insulation  34  is able to “turn off” the insulator state, thus allowing the heat  28  to transfer from the interior  36  of the building  38  to the outside environment, thus lowering cooling costs by reducing/eliminating the need to run fans or air conditioners. 
         [0046]    From studies conducted by Neeper and McFarland for the U.S. Department of Energy, it was found that the potential exists for solar energy to supply almost all space heating needs in the continental United States. In such studies, an example small rectangular building with 1200 ft 2  (111.48 m 2 ) of floor, a projected horizontal roof area and 8 ft. (2.44 m) high walls, a heating load of 7200 Btu/DD (degree-day), R-20 ft 2  F-hr/Btu (3.52 m 2  K/W) building insulation, and double-glazed windows was utilized. Using the example building with a worst-case heating scenario of the month of January for very cold or cloudy locations, the study found that the solar insulation on the roof alone exceeded 80% of the building&#39;s heating load, and the insulation on the south wall alone exceeded 50% of the building&#39;s heating load at all locations. Accordingly, even in the coldest month in severe climates of the continental U.S., the insulation on the roof and walls of the example building far exceeded the heating requirements of the building. The present invention builds upon that knowledge and teaches that by selectively switching smart insulation from its insulating to its conductive state at desired times to take advantage of this insulation, it is readily apparent how buildings&#39; heating costs and energy consumption can be significantly reduced. In addition, although the environmental cooling resource would not be able to completely supply all of the cooling needs of buildings in the continental U.S., Neeper and McFarland did conclude that the environment provides sufficient resources to potentially supply half of all cooling loads in the continental U.S. Therefore, smart insulation that can take advantage of the environmental cooling resource is able to significantly reduce building′ cooling costs and loads. 
         [0047]    A separate DOE study conducted by Caskey suggests that large energy savings could result from the implementation of varying thermal properties of building materials. In the study, reflective aluminum foil was installed in the rafters of a pitched-roof single-family dwelling in Albuquerque, N. Mex., in order to prevent high heat losses through the roof during the winter from high radiative heat transfer to the outside environment. Experimental results in the study eventually showed a 25% decrease in roof heat losses during the winter nights, which were approximately 12 hours in length. Unfortunately, the reflective aluminum foil also caused a 40% decrease in roof heat gain from solar heating during the sunny winter day periods, which were approximately 8 hours in length, canceling out the decrease in heat losses during the winter nights. This led to the reflective aluminum foil having a zero net total effect on the heat losses through the roof of the building during the winter. Although the reflective aluminum foil did not produce good results, it shows that if smart insulation, such as described herein, were implemented in the roof of the building tested instead of the aluminum foil, large energy savings could result. During the winter nights the smart insulation could serve as a good insulator, as with the reflective aluminum foil, to prevent high heat losses through the roof. Later, during the winter days, unlike the aluminum foil, the smart insulation could change to a high heat transfer state to take advantage of the roof heat gain from solar heating. Thus, the smart insulation would be able to have the large decrease in roof heat losses during the winter nights and also still maintain the roof heat gained from solar heating during the winter days, resulting in a large net decrease in heating loads needed for the building over the winter and large heating cost savings. 
         [0048]    Accordingly, it is an object of this disclosure to provide a smart insulation and insulating system whose thermal conductivity can effectively be selectively turned on and off. 
         [0049]    The present invention utilizes conduction as the main method of heat transfer. Smart insulation must be able to be selectively switched between a low and high thermal conductivity state (i.e., insulating and non-insulating state) whenever it is desired to inhibit or allow heat transfer. The switch between low and high thermal conductivity is activated by an external trigger. Although other designs are foreseeable, the following example embodiments of the present invention focus on two general concepts: 1) plate/fin devices which utilize conduction pathways that may be selectively formed and broken and 2) inflatable or expandable devices having a thickness which is selectively variable. Different example embodiments are presented for each of these concepts. 
         [0050]    A first embodiment of the present invention will now be discussed in the form of a shifting fins thermal semiconductor concept. This concept involves the connecting and breaking of a number of thermal conduction pathways in order to regulate the heat transfer across a device. 
         [0051]      FIGS. 4 and 5  illustrate a schematic sectional view of a portion of an example smart insulation system  40  consisting of highly conducting (e.g. metal) fins  42  extending from plates  44  that can be shifted (either one or both of plates  44 ) by one or more actuator(s) (not shown) or other suitable mechanism(s) so that the fins  42  are positioned in either a contacting position ( FIG. 4 ) or non-contacting position ( FIG. 5 ). It is to be appreciated that  FIGS. 4 and 5  illustrate only a selected example portion of the system  40  that would be disposed between two selected spaces, shown generally as A and B. Such spaces may, for example, without limitation, respectively be an interior and exterior environment (including material that is a part of these environments such as wall or roof material not generally considered to be part of the insulation) of a building or other generally sealed structure and system  40  accordingly would be used as a portion of a wall and/or roof of the building or structure separating the interior and exterior environments. In such application the “spaces”, such as identified as A and B in  FIG. 4 , could be air in an interior or exterior environment, or they could be the brick or wall board, or other building material that would be adjacent to the insulation device. Additionally, the system  40  could be used to separate two interior spaces in a building or machine. For example, one could choose to close off a room of a building that is not used in the winter or summer, and this system could prevent heat transfer from/to the conditioned part of the building. 
         [0052]    When the fins  42  are positioned in a contacting state, such as shown in  FIG. 4 , a number of thermally conductive pathways  46  are formed between the fins  42  of the plates  44  so that high heat transfer by conduction will be able to take place between the first space A and the second space B. By breaking the contact between the fins  42 , such as by using an actuator (not shown) to shift one or both of the plates  44  and associated fins  42  laterally with respect to each other, such as shown by arrows  48  in  FIG. 5 , the thermally conductive pathways  46  from  FIG. 4  are eliminated, thus vastly reducing the thermal conductivity of the system  40  and thus making the system insulating.  FIGS. 4 and 5  illustrate the shifting fins thermal semiconductor concept in both its low (insulating,  FIG. 5 ) and high (non-insulating,  FIG. 4 ) thermal conductivity states. It is to be appreciated that there are many other foreseeable embodiments of this concept in which the key feature is the ability to selectively break and form conduction paths (which could be done at many different scales, ranging from the macro scale, depicted herein, to the micro or nano scales within materials) to change the device from conducting to insulating states. For example, without limitation, folding or hinged conductive pathways and pathways that slide or rotate into and out of contact are readily foreseeable. 
         [0053]    In order to eliminate the natural convection of the air between the fins  42 , the area (not numbered) between the fins may be filled with an insulating material, such as, for example, without limitation, pieces of polyisocyanurate foam building insulation  50 , such as shown in the embodiment of the system  40 ′ of  FIG. 6  which is shown positioned in a low thermal conductivity (insulating) state similar to the system  40  of  FIG. 5 . 
         [0054]    Another variation on the shifting fins smart insulation concept involves flipping the bottom and top sections over so that the plates  44   a  and  44   b  are positioned back-to-back, and the fins  42  of each plate  44   a ,  44   b  thus extend outward, away from each other, as shown in the example embodiment of  FIGS. 7 and 8 . The rationale behind this design is to utilize the large amount of surface area provided by the number of fins  42  to capture heat to quicken the heating of the bottom plate  44   b  for cases such as the sunny winter day case previously described in conjunction with  FIG. 2 . In a high thermal conductivity (non insulating) state, such as shown in  FIG. 7 , the top plate  44   a  is disposed directly against the bottom plate  44   b  so that the two plates are in direct thermal contact. When positioned as shown in  FIG. 7 , the fins  42  of the top plate  44   a  are positioned sticking upward to act as a heat sink (or drain) with a large amount of surface area to dissipate (or absorb depending on the application) heat quickly when the system  40 ″ is in conducting mode, as opposed to the non-conducting mode shown in  FIG. 8  in which one or both of plates  44   a ,  44   b  have been moved away from the other plate in a direction indicated by the arrows  50 . Alternate configurations to  FIG. 8  can be formed in which the fins are folded flat or otherwise placed in a position such that they do not project from plates  44   a  and  44   b , thereby reducing their heat transfer coefficient. In addition to the embodiments described herein, it is readily foreseeable that other device variations that involve foam, fiberglass, or other insulating material with imbedded conductive paths that can be selectively interrupted or broken in order to vary the conduction/insulation properties thereof may be employed without varying from the scope of the present invention. 
         [0055]    It is to be appreciated that although shown as having fins  42  disposed on, and extending from both plates  44   a ,  44   b , such fins may also be employed on only one plate. In such embodiment the conduction pathways would be created and/or broken by selectively moving the fins directly into and out of contact with the second plate. 
         [0056]    It is also to be appreciated that although shown as being integrally formed therewith, fins  42  of any of the embodiments thus far discussed may be formed separately, either from the same or from a different material than the corresponding plate  44 , and then coupled via any suitable manner to the corresponding plate  44 . Additionally, it is to be appreciated that the fins  42  may be designed to fold in and out from the corresponding plate  44 . For example, in the insulating case one would want the fins to “disappear”, thus reducing the heat transfer. 
         [0057]    The second general concept of the present invention generally utilizes an inflatable structure, such as structure or panel  60  of  FIGS. 9 and 10 , which includes a series of adjacently-connected compartments  62  delimited by a thin material  64  (shown having a thickness tb and referred to herein as a partition or membrane), such as plastic or other suitable material. As used herein, the term “inflatable” is generally used to indicate that a particular device includes compartments that may be filled with gas or liquid either through pumping or by expansion of the volume through movement of the boundaries. By expanding the volume. the compartments need not be filled with fluid but may reach low pressure or near vacuum states. 
         [0058]    As shown in  FIG. 9 , the compartments  62 , having a height H b  and a cross-sectional width W b , can be inflated or expanded (e.g., via an air pump—shown schematically in  FIGS. 11 and 12  as element  72 , actuator imparting motion—shown schematically in  FIGS. 11 and 12  as element  74 , or other suitable mechanism) with a low conductivity gas, such as air or other suitable liquid to create an insulating state, in which the structure  60  has an overall height H and a cross-sectional width W and separates two regions A, B having temperatures T i  and T e  respectively. In other embodiments the compartments  62  may be in a vacuum or low-pressure state thereby further reducing the heat transfer properties, and the compartment&#39;s shape is maintained by mechanical forces in the material  64 , the outer walls  65 , 66 , and the top  67  and bottom  68  of the panel  60 . Conversely, when the smart insulation device needs to have a high thermal conductivity, the inflatable or expandable structure  60  is selectively deflated or collapsed by suctioning the air from the compartments  62  or by moving one or both of the outer walls  65 ,  66  (e.g., via an air pump, actuator imparting motion, or other suitable mechanism) to create a conducting (non-insulating) state, such as shown in  FIG. 10 . In the deflated or collapsed state the structure  60  becomes thin, having a cross-sectional width W 2 , since the deflated or collapsed structure  60  only consists of thin layers of the material used to contain the air or vacuum state. In the deflated case, the thickness of the device is decreased greatly, thus increasing the thermal conductivity of the device, resulting in much less thermal conduction resistance and a conducting state for the structure. 
         [0059]      FIGS. 11 and 12  show a modified version of the embodiment of  FIGS. 9 and 10  in which boundary plates  70  are added to the inflatable structure  60  to help to prevent small air spaces between layers when the inflatable structure is disposed in its conducting state by enabling the structure  60  to be compressed to a higher degree. In addition, the boundary plates  70  tend to improve the insulating states of the device.  FIGS. 11 and 12 , respectively, show the conducting and insulating states for this embodiment. In an example embodiment, each of the boundary plates  70  are formed from aluminum or other suitable material. Although not particularly described herein, it is to be appreciated that many other embodiments of the device shown in  FIGS. 11 and 12  are readily foreseeable, including the incorporation of folding fins to even further improve performance of the conduction state. It also to be appreciated that the embodiment shown in  FIGS. 11 and 12  utilizes a matrix of inflatable compartments or bubbles to reduce the unwanted heat transfer effects of convection currents within the structure  60 . Yet another point to be appreciated is that the embodiment presented in  FIGS. 11 and 12  does not require inflation, but rather the boundary plates  70  can serve as structural members to push and pull the structure  60  together or apart (through the use of actuators or other mechanisms not shown), thereby enabling a low pressure state between the boundary plates  70  in one or more chambers thus providing even better insulating properties. 
         [0060]    Although the embodiments of  FIGS. 9-12  show embodiments having several compartments  62  stacked vertically, it is to be appreciated that the quantity of compartments  62  arranged vertically or horizontally may be varied without varying from the scope of the present invention. For example, in an example embodiment a panel or structure having a plurality of compartments each extending the entire height of the panel (i.e., no stacking) was found to exhibit acceptable properties in accordance with the present invention. 
         [0061]    In addition to changing the spacing between boundary plates, heat transfer in the conductive state of any of the embodiments described herein can be enhanced by improving circulation of fluid (gas or liquid) between spaces A and B, and insulation can be enhanced by limiting the fluid circulation (or removing the fluid). This could be done by opening and closing passageways at any size scale, and/or pumping liquid or gas. 
         [0062]    In addition to the embodiments described herein, it is to be appreciated that other embodiments may be employed within the scope of the present invention in which the total thickness of the conducting pathway is changed, either by changing the thickness of individual elements, or by adding or removing a subset of many conducting pathways (for example, without limitation, n conducting paths are available to be put into place, and m conducting paths are connected at any given time, where m≦n). It is to be further appreciated that the interruptible conductive pathways do not have to be limited to the building layers described herein, but could extend further into the interior of the structure (for example to the interior walls, floors, ceilings, or new structural elements designed specifically for heat transfer) and out to the exterior of the structure (for example roof, exterior walls, into the ground, or new structural elements designed specifically for heat transfer). As previously discussed, it is also to be appreciated that embodiments of the present invention could also be disposed within selected portions of machines as well as other applications where the variable insulating properties could be utilized. 
         [0063]    It is also to be appreciated that further devices may be employed to enhance heat transfer in the conductive state. For example, without limitation, devices utilizing circulation (either passively or actively driven) of air or other fluid (gas or liquid) may be employed. Similarly, devices or structures that limit the fluid circulation (or removal of the fluid) may be employed to enhance insulation in the non-conductive state. Such enhancement may be accomplished, for example, without limitation, by opening and closing passageways at any size/scale, and/or pumping liquid or gas. 
         [0064]    Additionally, it is to be appreciated that elements from these such general concepts can be combined to produce further example embodiments of the present invention. As an example, a generally rigid structure (i.e., having fixed boundary plates/walls) could utilize partitions formed therein in which generally thermally conductive fluid (gas or liquid) could be supplied or conversely removed, thus creating a non-conductive vacuum within the structure. 
         [0065]    Having thus described a number of example embodiments in accordance with the present invention, the determination of optimum criteria for a smart insulation application will now be described in conjunction with the example structure  80  illustrated  FIGS. 13A and 13B , namely a one-dimensional analysis with full-height compartments. Referring to  FIGS. 13A and 13B , the insulated (expanded wall) configuration is shown in  FIG. 13A  and the conductive (collapsed wall) configuration is shown in  FIG. 13B . Similar to the embodiments of  FIGS. 11 and 12 , the structure  80  includes a plurality of interior compartments  81  (labeled  1 -N), each compartment  81  being separated from an adjacent compartment by a partition  82  formed from a layer of thin material (e.g., without limitation, a polymer membrane). Such compartments may be defined by both horizontal and vertical members as depicted in  FIG. 9 , or the compartments may extend the full height of the panel, for example H in  FIG. 9 , as depicted in  FIGS. 13A and 13B  (where there are no horizontal members separating compartments). Other embodiments may involve other shapes of compartments, for example diamond, tetrahedron, oval, spherical, etc., that may extend the full height of the panel or may be smaller than the full panel height. Structure  80  also similarly includes a pair of boundary plates  84 , disposed adjacent regions A and B which are separated by structure  80 . It has been found that the spacing δ between partitions  82  (i.e., the cross-sectional width of each compartment  81 ) is the primary factor of importance for optimum performance in the insulated configuration, while the total thickness t cond  of the compressed structure  80  dictates the performance during the conductive configuration. The thickness t cond  is dependent on the thickness t p  of each of the partitions  82 , the number N of compartments  1 -N and the thickness t w  of the boundary plates  84 . The thermal performance is also dependent on the aspect ratio, and although the analysis considers very large aspect ratio compartments, the same optimization procedure can be applied for compartments with smaller aspect ratios. 
         [0066]    For the insulated configuration, the thermophysical properties of the interstitial fluid (in this case air) were evaluated at 300 K and are shown in the table below along with other important variables. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 Thermal conductivity (k) 
                 0.0263 W/mK 
               
               
                   
                 Thermal diffusivity (α) 
                 22.5 × 10 −6  m 2 /s 
               
               
                   
                 Kinematic viscosity (v) 
                 15.89 × 10 −6  m 2 /s 
               
               
                   
                 Prandtl number (Pr) 
                 0.707 
               
               
                   
                 Expansion coefficient (β) 
                 (300 K) −1   
               
               
                   
                 Overall temperature difference (ΔT) 
                 15 K 
               
               
                   
                 Partition membrane thickness (t p ) 
                 2 mm 
               
               
                   
                 Wall layer thickness (t w ) 
                 5 mm 
               
               
                   
                 Partition wall thermal conductivity (k p ) 
                 0.2 W/mK 
               
               
                   
                 Wall layer thermal conductivity (k w ) 
                 0.2 W/mK 
               
               
                   
                   
               
             
          
         
       
     
         [0067]    The spacing δ between partitions  82  is a function of the overall cross-sectional width W and the number N of compartments  1 -N according to: 
         [0000]      δ= W/N   (1)
 
         [0068]    Natural convection between the partitions  82  will be the dominant source of heat transfer and from a global point of view, the thermal performance will be “N” convective resistances in series. The Rayleigh number should therefore be based on δ as shown in the equation below. 
         [0000]    
       
         
           
             
               
                 
                   
                     Ra 
                     δ 
                   
                   = 
                   
                     
                       g 
                        
                       
                           
                       
                        
                       
                         
                           β 
                            
                           
                             ( 
                             
                               Δ 
                                
                               
                                   
                               
                                
                               T 
                             
                             ) 
                           
                         
                         δ 
                       
                        
                       
                         δ 
                         3 
                       
                     
                     
                       v 
                        
                       
                           
                       
                        
                       α 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where g is the acceleration of gravity (units m/sec 2 ). 
         [0069]    But the local temperature difference between compartments (ΔT), can be expressed in terms of the global temperature difference ΔT according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       ( 
                       
                         Δ 
                          
                         
                             
                         
                          
                         T 
                       
                       ) 
                     
                      
                     
                       Δ 
                       δ 
                     
                   
                   = 
                   
                     T 
                     / 
                     N 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0070]    Making these substitutions into Eq. (2) allows a relationship to be formed between the local and global Rayleigh numbers according to: 
         [0000]    
       
         
           
             
               
                 
                   
                     Ra 
                     δ 
                   
                   = 
                   
                     
                       
                         g 
                          
                         
                             
                         
                          
                         βΔ 
                          
                         
                             
                         
                          
                         
                           TW 
                           3 
                         
                       
                       
                         
                           N 
                           4 
                         
                          
                         v 
                          
                         
                             
                         
                          
                         α 
                       
                     
                     = 
                     
                       
                         Ra 
                         W 
                       
                       
                         N 
                         4 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0071]    Therefore, to minimize heat transfer for the insulated scenario, one would simply want to create as many compartments  81  as possible (increase N) so that the local Rayleigh number is as small as possible. A small Rayleigh number suggests a Nusselt number very close to unity. One standard correlation used to quantify the heat transfer characteristics through window panes is the following: 
         [0000]        Nu   δ =0.0673838 Ra   δ   1/3  for  Ra   δ &gt;5×10 4   (5)
 
         [0000]        Nu   δ =0.028154 Ra   δ   0.41399  for 10 4   &lt;Ra   δ ≦5×10 4   (6)
 
         [0000]        Nu   δ =1+1.75967×10 −10   Ra   δ   2.2984755  for  Ra   δ ≦10 4   (7)
 
         [0072]    Therefore, when the Rayleigh number is small, only Eq. (7) is applicable, revealing a Nusselt number that approaches a value of 1 as the Rayleigh number continues to decrease. Since the thermal resistance from each layer acts in series with its neighboring layers, the total wall resistance during the insulated state (R ins ) can be expressed as: 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     ins 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             Nu 
                             δ 
                           
                           · 
                           k 
                         
                         δ 
                       
                       ) 
                     
                      
                     N 
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0073]    In contrast to the goal of having as many layers as possible for the insulated state, the opposite is true for the desired performance in the conductive state (i.e., as few layers as possible). The resistance for the conductive state can be expressed as that shown below. 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     cond 
                   
                   = 
                   
                     
                       ( 
                       
                         N 
                         - 
                         1 
                       
                       ) 
                     
                      
                     
                       
                         t 
                         b 
                       
                       
                         k 
                         b 
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
         [0074]    Conduction through the innermost and outermost walls (i.e., boundary plates  84 ) will be present for both scenarios, and is calculated as: 
         [0000]        R   W   =t   W   /k   W   (10)
 
         [0075]    The total resistance in the insulated configuration can be expressed as function of the overall width and number of compartments  81  as: 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     ins 
                   
                   = 
                   
                     
                       2 
                        
                       
                         R 
                         W 
                       
                     
                     + 
                     
                       N 
                        
                       
                         ( 
                         
                           
                             
                               Nu 
                               δ 
                             
                             · 
                             k 
                           
                           δ 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0076]    The total resistance in the conductive region is then expressed as: 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     cond 
                   
                   = 
                   
                     
                       2 
                        
                       
                         R 
                         W 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           N 
                           - 
                           1 
                         
                         ) 
                       
                        
                       
                         
                           t 
                           P 
                         
                         
                           k 
                           P 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
         [0077]    It is important to recognize that to increase R ins , one would have as many partitions  82  and compartments  81  as possible. On the other hand, to decrease R cond , the opposite approach would be required. Therefore, for a given overall wall thickness and temperature difference, there will be an optimum spacing such that the ratio of insulated resistance to conductive resistance is maximized. 
         [0000]        R   ratio   =R   ins   /R   cond   (13)
 
         [0078]    Using the data in Table 1 above, Eq. (13) is now plotted as a function of the number of divisions (N) in  FIG. 14 , revealing a clear optimum condition, which is a function of the overall width of the wall itself. 
         [0079]    To better understand the optimum conditions, Eq. (13) can be differentiated with respect to the parameter “N” and setting the result equal to zero. The expression shown below is then developed for the optimum width as a function of the optimum number of compartments  81 . In other words, the number of compartments (N) can be an input to determine the wall width W which would yield the optimum results. 
         [0000]    
       
         
           
             
               
                 
                   
                     W 
                     opt 
                   
                   = 
                   
                     
                       { 
                       
                         
                           
                             
                               
                                 N 
                                 4 
                               
                               · 
                               α 
                               · 
                               v 
                             
                             
                               
                                 β 
                                 · 
                                 g 
                                 · 
                                 Δ 
                               
                                
                               
                                   
                               
                                
                               T 
                             
                           
                           [ 
                           
                             1 
                             
                               
                                 C 
                                 1 
                               
                                
                               
                                 ( 
                                 
                                   
                                     4 
                                      
                                     
                                       q 
                                       1 
                                     
                                   
                                   - 
                                   
                                     
                                       4 
                                        
                                       
                                         q 
                                         1 
                                       
                                     
                                     N 
                                   
                                   - 
                                   1 
                                   + 
                                   
                                     
                                       8 
                                        
                                       
                                         
                                           t 
                                           W 
                                         
                                         · 
                                         
                                           k 
                                           P 
                                         
                                         · 
                                         
                                           q 
                                           1 
                                         
                                       
                                     
                                     
                                       N 
                                       · 
                                       
                                         t 
                                         P 
                                       
                                       · 
                                       
                                         k 
                                         W 
                                       
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                           ] 
                         
                         
                           1 
                           / 
                           
                             q 
                             1 
                           
                         
                       
                       } 
                     
                     
                       1 
                       / 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
         [0080]    Where C 1 =1.75967×10 −10  and q 1 =2.2984755 as given in Eq. (7). 
         [0081]    As a check, using the graph above, the bottom curve (W=10 cm) suggests the optimum number of compartments  81  is close to 4. Substituting N=4 into Eq. (14) reveals W opt =9.813 cm. Indeed the result is what was expected (a value very close to 10 cm). For reference, if a wall with an overall thickness of 10 cm were partitioned into 4 equal divisions, then the following R values are theoretically achievable using this smart insulation: R ins =20.55 hr·ft 2 ° ΔF/BTU and R cond =0.454 hr·ft 2 ° ΔF/BTU. 
         [0082]    Having thus described the basic concepts of the invention, it will be apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not intended to be limiting upon the invention. Various alterations, improvements, and modifications are intended to be suggested and are within the scope and spirit of the present invention. Additionally, the recited order of elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed concepts to any order except as may be specified in the claims. 
         [0083]    All publications and patent documents cited in this application are incorporated by reference in their entirety for purposes to the same extent as if each individual publication or patent document were so individually denoted.