Abstract:
When products to be shipped are temperature-sensitive, it is necessary to maintain a substantially uniform and constant temperature to avoid spoilage. As a result, thermal shields are often placed on top of the products. Many designs for thermal shields have been considered in the past but improvements are still desired. Accordingly, there is provided a multilayer thermal shield ( 100 ) comprising a thermally conductive layer ( 108 ), and at least one heat exchange fluid circuit ( 120 ) coupled to a first surface of the thermally conductive layer, the at least one heat exchange fluid circuit comprising at least one inlet ( 124 ) configured to permit the ingress of heat exchange fluid. The thermal shield further comprises an outer insulation layer ( 104 ) connected to a first surface of the thermally conductive layer ( 108 ) and comprising grooves designed to receive the heat exchange fluid circuit. The thermal shield further comprises an inner insulation layer ( 110 ) connected to a second surface of the thermally conductive layer ( 108 ).

Description:
FIELD 
       [0001]    The subject application relates to a thermal shield for maintaining a generally constant temperature. 
       BACKGROUND 
       [0002]    It is common to ship products over vast distances by ground, sea and/or air transportation. In many instances, the products being shipped are placed in containers. When the products are not temperature-sensitive, there is typically no need to provide the containers with temperature control systems. When the products are temperature-sensitive, it is necessary to maintain a substantially uniform and constant temperature to avoid spoilage. As a result, thermal shields are often placed on top of the products. Many designs for thermal shields have been considered. 
         [0003]    For example, U.S. Pat. No. 5,100,016 to Wischusen discloses insulation material configured to provide improved insulating properties in a shipping container. An insulated bottom section is placed along the bottom of a container under the contents of the container. An insulating blanket constructed of plastic sheets sealed to form pouches for containing paperboard and mineral wool is configured to have an inverted U-shape and is placed over a bottom half of the container. A top half of the container is then placed over the bottom half such that the legs of the inverted U-shaped material are between the overlapping sides of top and bottom of the container and the middle portion of the U-shaped material is between the top of the container and the contents within the container. 
         [0004]    Although thermal shields have been considered, improvements are desired. It is therefore an object to provide a novel thermal shield for maintaining a generally constant temperature. 
       SUMMARY 
       [0005]    Accordingly, in one aspect there is provided a thermal shield comprising a thermally conductive layer, and at least one heat exchange fluid circuit coupled to a first surface of the thermally conductive layer, the at least one heat exchange fluid circuit comprising at least one inlet configured to permit the ingress of heat exchange fluid. 
         [0006]    In an embodiment, the at least one heat exchange fluid circuit extends about the first surface of the thermally conductive layer. In an embodiment, the at least one heat exchange fluid circuit extends about the first surface of the thermally conductive layer in a serpentine path. In another embodiment, a first insulation layer having a first surface is connected to the first surface of the thermally conductive layer. 
         [0007]    In an embodiment, the first insulation layer comprises at least one groove defined in the first surface, the at least one heat exchange fluid circuit being defined by the at least one groove. The at least one heat exchange fluid circuit comprises at least one tubular member. An inlet header is coupled to the at least one inlet of the heat exchange fluid circuit and is configured to direct heat exchange fluid received from a storage unit to the at least one inlet. The heat exchange fluid circuit comprises at least one outlet configured to direct the egress of heat exchange fluid. An outlet header is coupled to the at least one outlet of the heat exchange fluid circuit and is configured to direct heat exchange fluid received from the at least one outlet to the storage unit. 
         [0008]    According to another aspect there is provided a system for maintaining a generally constant temperature, the system comprising a thermal shield comprising a thermally conductive layer, and at least one heat exchange fluid circuit coupled to a first surface of the thermally conductive layer, the at least one heat exchange fluid circuit comprising at least one inlet configured to permit the ingress of heat exchange fluid, and a pumping unit configured to pump heat exchange fluid into the at least one heat exchange fluid circuit. 
         [0009]    In an embodiment, the system comprises a storage unit for storing heat exchange fluid, the pumping unit configured to pump heat exchange fluid from the storage unit into the at least one heat exchange fluid circuit. 
         [0010]    According to another aspect there is provided a method for maintaining a generally constant temperature in a container comprising one or more temperature sensitive products, the method comprising providing a thermal shield comprising a thermally conductive layer and at least one heat exchange fluid circuit coupled to a first surface of the thermally conductive layer, the thermal shield being placed over the one or more temperature sensitive products, and selectively pumping a heat exchange fluid from a storage unit through the at least one heat exchange fluid circuit via a pumping unit. 
         [0011]    In an embodiment, the selective pumping is based on one or more criteria. The one or more criteria comprises in the event that the temperature is above or below a threshold value, pumping the heat exchange fluid. The one or more criteria comprises in the event that a blockage condition is detected in the at least one heat exchange fluid circuit, shutting down the pumping unit. The one or more criteria comprises in the event that a blockage condition is detected in the at least one heat exchange fluid circuit, closing a valve associated with the at least one heat exchange fluid circuit. 
         [0012]    In an embodiment, the method comprises monitoring a temperature of heat exchange fluid leaving the storage unit, monitoring a temperature of heat exchange fluid coming into the storage unit, and if the monitored temperatures are not equal, continuously pumping heat exchange fluid through the at least one heat exchange fluid until the monitored temperatures are approximately equal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Embodiments will now be described more fully with reference to the accompanying drawings in which: 
           [0014]      FIG. 1  is a block diagram of a system for maintaining a generally constant temperature in a container; 
           [0015]      FIG. 2  is an isometric view of a thermal shield forming part of the system of  FIG. 1 ; 
           [0016]      FIG. 3  is a cross-sectional view of the thermal shield of  FIG. 2 ; 
           [0017]      FIG. 4  is an enlarged partial view showing an inlet and outlet header of the thermal shield of  FIG. 2 ; 
           [0018]      FIG. 5  is an isometric view showing the thermal shield of  FIG. 2  positioned in a container during use; 
           [0019]      FIG. 6  is a block diagram of another embodiment of a system for maintaining a generally constant temperature in a container; 
           [0020]      FIG. 7  a flow chart showing a method of operation of a controller forming part of the system of  FIG. 6 ; 
           [0021]      FIG. 8  a flow chart showing another method of operation of a controller forming part of the system of  FIG. 6 ; and 
           [0022]      FIG. 9  is an isometric view of another embodiment of a tubular member. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    Turning to  FIG. 1 , a system for maintaining a generally constant temperature in a container is shown and is generally identified by reference numeral  10 . The system  10  comprises a storage unit  50  fluidly coupled to a thermal shield  100 . The system  10  is configured to be placed in a container such that the thermal shield  100  overlaps one or more temperature sensitive products. 
         [0024]    The storage unit  50  comprises a storage tank and a pumping unit. In this embodiment, the storage tank stores heat exchange fluid. The pumping unit is configured to pump heat exchange fluid from the storage tank to the thermal shield  100 , as will be described in more detail below. 
         [0025]    The thermal shield  100  is best shown in  FIGS. 2 to 4 . The thermal shield  100  is made of a layered construction. The thermal shield  100  comprises an outer protective layer  102  which in this embodiment is made of protective material such as for example canvas. 
         [0026]    The thermal shield  100  also comprises an outer insulation layer  104  coupled to an interior surface of the outer protective layer  102 . The outer insulation layer  104  is made of a thermally insulative material such as for example polyurethane. In this embodiment, three (3) spaced-apart U-shaped grooves  106  are defined in the outer insulation layer  104 . Each U-shaped groove  106  extends the length of the outer insulation layer  104  such that the two arms are positioned adjacent a first end of the outer insulation layer  104  and the U-shaped portion is positioned adjacent a second end of the outer insulation layer  104 . 
         [0027]    The thermal shield  100  also comprises a thermally conductive layer  108  coupled to an interior surface of the outer insulation layer  104 . The thermally conductive layer is made of a thermally conductive material such as for example aluminum. 
         [0028]    The thermal shield  100  also comprises an inner insulation layer  110  coupled to an interior surface of the thermally conductive layer  108 . The inner insulation layer  110  is made of a thermally insulative material such as for example polyurethane. 
         [0029]    The thermal shield  100  also comprises an inner protective layer  112  coupled to an interior surface of the inner insulation layer  110 . The inner protective layer  112  is made of a protective material such as for example canvas. 
         [0030]    The thermal shield  100  also comprises a heat exchange fluid circuit  120  thermally coupled to the thermally conductive layer  108 . In this embodiment, the heat exchange fluid circuit  120  comprises three (3) U-shaped tubular members  122  each of which is positioned within a respective U-shaped groove  106  defined in the outer insulation layer  104 . Each tubular member  122  comprises an inlet  124  and an outlet  126 . A portion of each tubular member  122  is thermally coupled to the thermally conductive layer  108 . As such, the tubular members  122  are partially encapsulated by the outer insulation layer  104  and exchange thermal energy with the thermally conductive layer  108 . As will be appreciated, a coating such as for example thermally conductive grease may be used to increase thermal energy exchange between each tubular member  122  and the thermally conductive layer  108 . 
         [0031]    In this embodiment, the three (3) U-shaped tubular members  122  are coupled to the storage unit (not shown) via an inlet header  130  and an outlet header  140 . The inlet header  130  is coupled to the inlets  124  of the tubular members  122 . The inlet header  130  comprises an inlet  132  configured to receive heat exchange fluid from a storage unit (not shown) and an inlet header body  134  configured to direct the ingress of heat exchange fluid into each of the inlets  124 . 
         [0032]    The outlet header  140  is coupled to the outlets  126  of the tubular members  122 . The outlet header  140  comprises an outlet  142  configured to receive heat exchange fluid from the outlet  126  of each of the tubular members  122  and an outlet header body  144  configured to direct the egress of heat exchange fluid back into the storage unit (not shown). 
         [0033]    During use, as shown in  FIG. 5 , the storage unit  50  containing heat exchange fluid and the thermal shield  100  are positioned inside a container C containing one or more temperature sensitive products. The thermal shield  100  is positioned such that it at least partially covers the one or more temperature sensitive products, like a blanket. 
         [0034]    Heat exchange fluid is pumped from the storage unit  50  into the inlet header  130  by the pumping unit. Heat exchange fluid travels from the storage tank and through the inlet header  130 . As heat exchange fluid travels into the inlet header  130  it is directed into the inlet  124  of each tubular member  122 . Heat exchange fluid travels into the inlet  124 , through each tubular member  122  and out of the outlet  126 . Heat exchange fluid travels out of the outlet  126  to the outlet header  140 , where it is directed back into the storage unit  50 . Heat exchange fluid that returns back to storage unit  50  is mixed with any heat exchange fluid contained in the storage unit  50 . In this embodiment, heat exchange fluid is continuously pumped from the storage unit  50 , through the thermal shield  100  where it returns back to the storage unit  50 . 
         [0035]    As the heat exchange fluid travels through the tubular members  122 , thermal energy is exchanged with the thermally conductive layer  108 . As a result, the thermal shield  100  is selectively heated or cooled. A generally uniform temperature is maintained in the container C during shipping operations such that any item covered by the thermal shield does not spoil. 
         [0036]    In this embodiment, when used as a heating thermal shield, the storage unit stores heat exchange fluid in the form of a heating liquid, such as for example glycol or a glycol solution. 
         [0037]    In this embodiment, when used as a cooling thermal shield, heat exchange fluid in the form of a combination of ice slurry and water is used. 
         [0038]    Turning now to  FIG. 6  another embodiment of a system for maintaining a generally constant temperature in a container is shown and is generally identified by reference numeral  200 . As can be seen, system  200  is similar to system  10 . However, in this embodiment, system  200  comprises a sensor and control unit  210  electrically coupled to the storage unit  50  and the thermal shield  100 . The sensor and control unit  210  is used to control the operation of system  200  such that heat exchange fluid is selectively pumped from the storage unit  50  to the thermal shield  100 . 
         [0039]    In this embodiment the sensor and control unit  210  comprises three inlet (3) flow sensors (not shown) each positioned within the inlet  124  of a respective tubular member  122  and three outlet (3) flow sensors (not shown) each positioned within the outlet  126  of a respective tubular member  122 . The sensor and control unit  210  also comprises three (3) electrically controlled valves (not shown) each positioned in the inlet  124  of a respective tubular member  122 . A controller (not shown) is coupled to the inlet and outlet flow sensors to monitor the flow rate of heat exchange fluid as it travels through each tubular member. A power source (not shown) is used to provide power to the various components of the sensor and control unit  210 . 
         [0040]    During operation, system  200  operates similar to system  10  described above. However, as heat exchange fluid is pumped from the storage unit  50  into the inlet header  130  by the pumping unit, the controller operates according to a method  300  shown in  FIG. 7 . 
         [0041]    The controller polls the inlet and outlet flow sensors to receive sensor data representative of the flow rate of heat exchange fluid (step  305 ). For each tubular member, the flow rate at the inlet is compared to the flow rate at the outlet (step  310 ). If the flow rate at the outlet is not approximately equal to the flow rate at the inlet, it is assumed that there is a problem with the tubular member. The problem may be due to a leak or a crack in the tubular member. As such, the controller communicates a signal to close the electronically controlled valve to prevent heat exchange fluid from entering the problematic tubular member (step  315 ). If the flow rate at the outlet is approximately equal to the flow rate at the inlet, it is assumed that there is not a problem with the tubular member, and the method returns to step  305 . 
         [0042]    Although in embodiments above the sensor and control unit is described as comprising inlet and outlet flow sensors, those skilled in the art that other sensors may be used. In another embodiment, temperature sensors may be placed in the storage unit to measure the temperature of heat exchange fluid leaving and coming into the storage unit. In this embodiment, heat exchange fluid is pumped from the storage unit into the thermal shield, as described above. Heat exchange fluid is pumped into the thermal shield until the temperature of heat exchange fluid going into the thermal shield is approximately the same as the temperature of heat exchange fluid coming back into the storage unit. Once the temperature of heat exchange fluid going into the thermal shield is approximately the same as the temperature of heat exchange fluid coming back into the storage unit, the pumping unit is shut off and thus heat exchange fluid is stored in the thermal shield. Once the pumping unit is shut off, the controller operates according to a method  350  shown in  FIG. 8 . 
         [0043]    When the pumping unit is shut off, the system is idle in that heat exchange fluid that is within the thermal shield is stored in the thermal shield. A check is performed to determine if the system  200  has been idle for a predefined period of time (step  355 ), that is, if the pumping unit has been shut off for the predefined period of time. If the system has been idle for less than the predefined period of time, the system remains idle. If the system has been idle for the predefined period of time or longer, the controller activates the pumping unit to pump a portion of heat exchange fluid from the thermal shield into the storage unit (step  360 ). As the portion of heat exchange fluid is pumped into the storage unit, the controller polls the temperature sensor placed in the storage unit to determine the temperature of the heat exchange fluid entering into the storage unit (step  365 ). The temperature of the heat exchange fluid is compared to a temperature threshold to determine if the temperature of the heat exchange fluid is at an acceptable level (step  370 ). If the temperature of the heat exchange fluid is at an acceptable level, the method returns to step  355 . If the temperature of the heat exchange fluid is not at an acceptable level, the pumping unit is activated to replace the heat exchange fluid in the thermal shield with heat exchange fluid from the storage unit (step  375 ). 
         [0044]    In another embodiment temperature sensors may be used to monitor the temperature of the container. If the temperature of the container is too hot or too cold, the controller activates the pumping unit to pump heat exchange fluid to the thermal shield, as described above. If the temperature of the container is not too hot or too cold, depending on the temperature sensitive products contained therein, heat exchange fluid is not pumped from the storage unit. 
         [0045]    Those skilled in the art will appreciate that the sensor and control unit may comprise various combination of the embodiments described above. Further, the sensor and control unit may be used with additional sensors such as for example water sensors to detect condensation, fluid level sensors to detect fluid levels in the storage unit, etc. 
         [0046]    Although step  355  of method  350  is described as determining if the system  200  has been idle for the predefined period of time, those skilled in the art will appreciate that alternatives are available. For example, method  350  may be performed such that heat exchange fluid is pumped into the thermal shield periodically, for example, every 5 minutes. In this example, a calculation may be performed based on the temperature of the container to determine how often the heat exchange medium stored within the thermal shield needs to be replaced. 
         [0047]    In another embodiment, the sensor and control unit may comprise an alarm module configured to indicate to a user when a problem or leak has occurred. For example, in the event that one of the tubular members has a problem, an emergency light may be illuminated or an audible alarm may be triggered. 
         [0048]    In another embodiment, the sensor and control unit may comprise a timer configured to track the time the system has been active. In the event that the system is active for greater than a threshold period of time, the system is shut down. Other sensors may be used to ensure the system does not malfunction due to extended use. 
         [0049]    Although in embodiments above electronically controlled valves are used to block heat exchange fluid from entering a potentially problematic tubular member, those skilled in the art will appreciate that alternatives are available. For example, in another embodiment the electronically controlled valves may be used to selectively permit or block heat exchange fluid from entering a tubular member. In this embodiment, only one or more of the tubular members may permit heat exchange fluid from entering. As such, only a portion of the thermal shield may be heated or cooled as desired. 
         [0050]    In another embodiment, the sensor and control unit may comprise one or more temperature sensors to monitor the temperature of heat exchange fluid in the storage unit. In the event that the temperature of the heat exchange fluid is approaching a threshold value, it is assumed that only a small amount of thermal energy remains. As such, the sensor and control unit may close one or more of the electronically controlled valves to ensure the remaining thermal energy is efficiently used. 
         [0051]    In another embodiment, the amount of thermal energy in the storage unit may be estimated and this estimate may be used to selectively pump heat exchange fluid into the thermal shield. In one embodiment when the storage unit is initially filled with heat exchange fluid, the initial thermal energy may be determined. As heat exchange fluid is pumped from the storage unit into the thermal shield, the remaining amount of thermal energy may be calculated. For example, as heat exchange fluid flows from the storage unit, through the thermal shield, and back into the storage unit, the amount of energy transferred may be calculated by multiplying the average flow rate of the heat exchange fluid by the specific heat capacity of the heat exchange fluid and by the difference between the temperature of the heat exchange fluid leaving the storage unit and the temperature of the heat exchange fluid retuning back to the storage unit and by the time the pumping unit is active. The average flow rate may be measured using a flow meter or sensor. The temperature may be measured using one or more temperature sensors. The time for which the pumping unit is active may be measured using a timer. The amount of thermal energy remaining may be converted to the time remaining until the thermal energy approaches zero. This time may be displayed to a user using an LED display. 
         [0052]    Although in embodiments above the tubular members are described as being generally U-shaped, those skilled in the art will appreciate that alternatives are available.  FIG. 9  shows another embodiment of a tubular member generally identified by reference numeral  400 . In this embodiment, the tubular member  400  comprises an inner tube  402  and an outer tube  404  disposed around the inner tube  402 . The inner tube  402  comprises an inlet  406  configured to direct the ingress of heat exchange fluid. The inner tube  402  comprises a pair of apertures  408  positioned at an end opposite that of the inlet  406 . The outer tube  404  comprises an outlet  410  positioned adjacent to and circumscribing the inlet  406  of the inner tube  402 . 
         [0053]    During use, the tubular member  400  receives heat exchange fluid through the inlet  406  of the inner tube  402 . The heat exchange fluid is pumped through the inner tube  402  as indicated by arrow A. The heat exchange fluid exits the inner tube  402  through the apertures  408  and through the outer tube  404  as indicated by arrow B. The heat exchange fluid travels through the outer tube  404  and out through the outlet  410 . 
         [0054]    One or more tubular members of the type of tubular member  400  may be used with thermal shield  100  similar to tubular member  22  described above. 
         [0055]    Although in embodiments above the heat exchange fluid circuit is described as comprising three (3) tubular members, those skilled in the art will appreciate that alternatives are available. For example, in another embodiment five (5) tubular members may be used. In another embodiment, a single tubular member may be used. For example, the single tubular member may extend about the surface of the thermally conductive layer, thereby defining a serpentine channel to direct the ingress of heat exchange fluid. In another embodiment, no tubular members are required. For example, the grooves defined in the outer insulation layer may be used as the heat exchange fluid circuit such that heat exchange fluid may be pumped therethrough. In another example, channels may be formed between two layers of a thermally conductive material. In yet another example, a moisture absorbing material may be used and may have channels formed therein. In this example, heat exchange fluid may be pumped into the moisture absorbing material such that at least some of the heat exchange fluid is absorbed by the moisture absorbing material. 
         [0056]    Although in embodiments above the outer insulation layer is described as comprising spaced-apart U-shaped grooves and the tubular members are described as being positioned within the U-shaped grooves, those skilled in the art will appreciate that alternatives are available. For example, in another embodiment the U-shaped grooves may be configured such that when the tubular members are positioned therein, arms of neighboring tubular members are coupled to one another such that thermal energy is exchanged therebetween. A coating such as for example thermally conductive grease may be used to increase thermal energy exchange between the arms of neighboring tubular members. 
         [0057]    Although in embodiments above the heat exchange fluid is described as being circulated through a storage unit, those skilled in the art will appreciate that alternatives are available. For example, rather than being recycled in the storage unit, the heat exchange fluid may remain contained in the tubular members. In this example, rather than a storage unit, a heat exchanger containing a heat exchange medium such as for example paraffin wax may be used. In this example, a circulation circuit is coupled to the inlet and outlet heaters and extends through the heat exchanger. The heat exchange fluid may be circulated through the heat exchange fluid circuit and passed through the heat exchanger via the circulation circuit to recharge the heat exchange fluid. As the heat exchange fluid passes through the circulation circuit it may be heated or cooled due to heat exchange between the heat exchange fluid and the heat exchange medium. The heated or cooled heat exchange fluid may then continue back into the heat exchange fluid circuit as described above. 
         [0058]    Although in embodiments above the pumping unit is described as pumping heat exchange fluid into the heat exchange fluid circuit, those skilled in the art will appreciate that in other embodiments the pumping unit may be a vacuum unit used to draw heat exchange fluid from the heat exchange fluid circuit. 
         [0059]    Although in embodiments above the heat exchange fluid is described as being pumped continuously from the storage tank through the thermal shield, those skilled in the art will appreciate that alternatives are available. For example, the heat exchange fluid may be pumped intermittently. As another example, the heat exchange fluid may be pumped through the thermal shield in a first flow direction for a period of time, and then may be pumped through the thermal shield in a second flow direction, opposite the first flow direction, for another period of time. 
         [0060]    Those skilled in the art will appreciate that the thermal shield may comprise a connection mechanism configured to secure the thermal shield inside the container. Further, the thermal shield may comprise mechanisms to help a user position it within the container. For example, the outer protective layer of the thermal shield may comprise one or more riveted openings configured to couple to a strap system to help the user positioned the thermal shield over the one or more temperature sensitive products. Other mechanisms that may be used include suction cups, magnets, Velcro, a linear track mechanism, a cable system, etc. 
         [0061]    The thermal shield may comprise one or more rigid members configured to provide support to the thermal shield. For example, in an embodiment a plurality of axially extending rigid members in the form of aluminum bars may be connected to the outer protective layer at positions intermediate the tubular members. 
         [0062]    The thermal shield may be configured to be rolled or folded up when not in use. For example, in an embodiment all components of the thermal shield may be made of flexible materials such that the thermal shield may be rolled up when not in use. As another example, the thermal shield may comprise one or more spines or lines-of-weakness that are configured to operate in a hinge-like manner such that the thermal shield may be folded up when not in use. 
         [0063]    Although in embodiments above the inner and outer protective layers are described as being made of a protective material such as for example canvas, those skilled in the art will appreciate that alternatives are available. For example, in another embodiment the inner protective layer may be made of a low-friction material to protect the thermal shield from internal impact during loading/unloading. 
         [0064]    Although in embodiments above the inner insulation layer is described as being made of a thermally insulative material such as for example polyurethane, those skilled in the art will appreciate that alternatives are available. For example, in another embodiment the inner insulation layer may be formed as an air gap or may be made of one or more vacuum insulated panels. In this embodiment, by having an air gap between the heat exchange fluid circuit and the one or more temperature sensitive products, the risk of exposure to condensation is reduced. 
         [0065]    As will be appreciated, the storage unit may comprise a valve configured to selectively drain unwanted liquid from the storage unit during transportation. In another embodiment, liquid from the storage unit may be discharged at another location within the container where it may be used to cool the temperature within the container through evaporation. 
         [0066]    Although in embodiments above the thermal shield is described as having inner and outer protective layers, those skilled in the art will appreciate that the thermal shield may have a single protective layer or no protective layer. 
         [0067]    Although in embodiments above the thermal shield is described as comprising a heat exchange fluid circuit positioned interior of an exterior insulation layer, those skilled in the art will appreciate that alternatives are available. For example, in another embodiment two heat exchange fluid circuits may be positioned on opposite sides of an insulation layer or on opposite sides of the thermally conductive layer. In this example, the pumping unit may be configured to selectively pump heat exchange fluid to one or both of the heat exchange fluid circuits. For example, in the event that it is desired to prevent temperature sensitive products from overheating and if the temperature exterior of the thermal shield is less than the temperature underneath the thermal shield, then pumping heat exchange fluid through both heat exchange fluid circuits will cause heat to be extracted from underneath the thermal shield and to be emitted to the exterior of the thermal shield. Further, the heat exchange fluid circuits may be in fluid communication with one another. 
         [0068]    Although embodiments have been described above with reference to the accompanying drawings, those of skill in the art will appreciate that variations and modifications may be made without departing from the scope thereof as defined by the appended claims.