Patent Application
20100223870
The present invention generally relates to a system for use in building construction, and, in particular, to a structural member for use in constructing walls in a building for increasing the resistance to the flow of heat into, out of, and/or through the building.
The energy consumption associated with environmental control systems for buildings has become one focal point for development and application of “green” technologies and energy conservation. In particular, the energy consumption by a Heating Ventilating and Air Conditioning (HVAC) system that controls the temperature and other parameters of the inside areas of a building is associated with the construction of the building, specifically with the way in which the building is constructed and the materials from which it is constructed. For example, the outer wall of a building separates an outdoor weather temperature from an indoor, conditioned temperature. The materials in the wall determine, at least in part, the heat flow into and out of the building. The rate of heat flow from the hot to the cold side of the wall is driven by the thermal energy differential across the barrier and the heat flow path through the barrier from the hotter environment to the colder environment. As heat is lost from or gained by the temperature conditioned environment, the HVAC system uses energy to add or remove heat, respectively, from the conditioned temperature environment. For instance, heat lost from the inside of the building (e.g., during the winter season) through the wall must be replaced by the HVAC system. Similarly, heat gained by the temperature conditioned environment (e.g., during the summer season) must be removed by the HVAC system. As such, barriers to heat flow, such as the exterior walls of the building, are one primary medium that controls the inexorable flow of heat from the hot environment to the cold environment. The barrier, therefore, has a direct impact on energy consumption by the HVAC system. In general, reducing heat flow through the barrier reduces energy consumption.
The structure of a barrier, like the exterior wall, between two environments has an insulative value that is often referred to as the “R value.” The R value is a useful numerical rating of the wall's resistance to heat flow. R values are derived from the reciprocal of a “U value,” which is the effective thermal conductivity of the barrier. For example, the U value of a wall is the combined result of (a) the structure of the wall; (b) the thermal conductivity values (i.e., the heat energy transfer property of each individual material comprising of the structure of the wall) or k values of the components of the wall; and (c) the heat transfer mechanisms (e.g., conduction, convection, and radiation) through the solid/air pathways in the wall. The R value of a wall may be increased, for example, by adding bulk insulation to the wall that reduces the flow of heat due to at least one of the heat transfer mechanisms. For example, drywall and sheathing supported by framing members may form a part of a wall's outer surface and glass wool battens or blown or foamed insulation may be added to interior cavities that are bordered by the framing members and the drywall and the sheathing. In this case, the R value of the wall increases as a result of highly insulating nearly static air pockets formed by the solid insulation masses within the wall cavity, the barrier(s) to air flow, and insulating properties of the sheathing. However, all components of a barrier affect the overall R value of the barrier. Thus, the structural framing components of a building, e.g., studs, joists, rafters, beams, etc., which may be formed from wood and/or sheet metal, also contribute to the R value of the wall. Accordingly, these components contribute to the consumption of energy by HVAC system.
Because wooden and metallic portions of the wall, such as, wall studs and joists, have a lower R value than bulk insulation, significant heat transfer may occur through those studs and joists. For example, while wood is generally somewhat resistant to heat transfer, a wooden wall stud may still transfer heat through a wall approximately 3 times as fast as through glass wool insulation. Even more noteworthy, a steel-fabricated wall stud may be 1,000 times more heat conductive than glass wool insulation. Therefore, heat may flow into, out of, and/or throughout a building from the hotter to the cooler wall surfaces through the wooden or metal studs more quickly, essentially creating a “thermal bridge” that bypasses any insulation in the wall cavities. In this way, the actual R value of a wall may be 40-60% less than design R value due to heat loss through the wall principally due to heat flow through the wall studs.
Aside from the poor energy efficiency that may be associated with significant heat egress or ingress of a building, there are other problems that may be associated with rapid heat loss. For example, freezing damage may occur in the event of prolonged HVAC interruption or equipment failure due to overheating and/or human error. Further, in certain cold climates, rapid loss of heat through a wall stud or joist may result in localized cold regions on the interior wall surface that is in contact with structural member. In turn, this may cause localized condensation of humidity that may cause an undesirable appearance and, in certain instances, cause actual dampness on the wall that coincides with the underlying stud or joist. In a similar manner, wall studs or joists may promote the transfer of sound into, out of, and/or throughout a building's walls, floors, and/or ceilings.
Therefore, what is needed in the art is a system and a structural member to improve the energy efficiency of a building. In particular, what is needed in the art is a structural member having a reduced thermal conductivity that may be used in the construction of a building, that may reduce the consumption of energy by the HVAC system, and that may be durable. What is further needed is a method of manufacturing such a structural member that is both cost effective and sufficiently durable when exposed to normal construction site handling.
In one embodiment, a structural member for use in constructing a barrier having a covering is provided. The barrier separates a first environment having a first temperature from a second environment having a second temperature. The structural member comprises a core of a first material having a first thermal conductivity, the core being adapted to support the covering and being used in constructing the barrier, and a thermal barrier layer of a second material disposed on at least one exterior surface of the core. The thermal barrier layer has a second thermal conductivity lower than the first thermal conductivity. The thermal barrier layer is positionable between the first environment and the second environment to reduce heat flow between the first and second environments.
In one embodiment, a method of manufacturing a structural member for use in constructing a barrier having a covering is provided. The barrier separates a first environment having a first temperature from a second environment having a second temperature. The method comprises applying a thermal barrier layer of a first material to a core of a second material. The first material has a thermal conductivity lower than that of the second material. The thermal barrier layer is positionable in the barrier between the first and second environments to reduce heat flow between the first and second environments.
In one embodiment, a system for use in constructing a building and that is configured to separate a first environment having a first temperature from a second environment having a second temperature is provided. The system comprises a barrier that is positioned between the first environment and the second environment. The barrier includes a plurality of structural members for supporting the barrier. The structural members each have a first side and a second side with at least one structural member that comprises a core of a first material and a thermal barrier layer of a second material that is disposed on the core and that coats at least one of the first and second sides of the structural member. The thermal barrier layer has a thermal conductivity that is less than a thermal conductivity of the first material. The first side of each structural member is oriented toward the first environment and the second side of the structural member is oriented toward the second environment. A first barrier covering is secured against the first sides of the plurality of structural members, and a second barrier covering is secured against the second sides of the plurality of structural members, whereby the thermal barrier layer is positioned between at least one of the core and the first barrier covering and the core and the second barrier covering.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the brief description given above and the detailed description given below, serve to explain various aspects of the invention.
With reference generally to the
The structural member 10 may be located in any part of a building (not shown) and may have appropriate configuration for a particular structural purpose. By way of example and not limitation, the structural member 10 may be included in a ceiling, in an interior or exterior wall, and/or in a floor or in another load bearing or non-load bearing structure in the building. As such, the structural member 10 may be dimensioned similar to standard dimensional lumber or other standard components used in construction. For instance, the structural member 10 may be dimensioned similar to a two-by-four, a four-by-six, or a ten-by-twelve, as are known in the art, to name only a few. In addition, the structural member 10 may form a portion of other components. For example, the structural member 10 may be configured as a track or other attachment device that may or may not have standardized dimensions for use with, for example, metallic framing members. In still another example, structural member 10 may support or otherwise contact a heating and/or cooling device and/or its associated ductwork as well as the building's water pipes and drains. Thus, it may reduce the heat flow to or from those components. As will be described in more detail below, a system that comprises a barrier to heat flow that may be used in constructing a building may be a composite assembly of many individual components that are made of different materials. For example, an exterior stud wall or other barrier that separates the interior, temperature controlled environment of a building from the uncontrolled weather outside of the building may be constructed of a plurality of structural members that support one or more air barriers, vapor barriers, drywall sheets, plywood sheets, chip board sheets, planking, flooring, corrugation, insulating sheathing, siding, shingles, brick, and/or other materials.
In the exemplary embodiment depicted in
With further reference to
The core 12 may be formed from any suitable material as will be apparent to one of ordinary skill in the art. By way of example, and with reference to the exemplary embodiment shown in
In one embodiment shown in
In yet another embodiment, while the core 12 may have a smooth surface, the core 12 may have a surface that has a specific texture or topography that may include peaks, ridges, and valleys that reduce the effective contact surface area between the core 12 and the thermal barrier layer 14 thereby creating “dead air” spaces that impede heat and/or sound flow. However, it will be appreciated that other regular or irregular surface topography or textures may allow the thermal barrier layer 14 to bridge across the deeper features of the topography of the core 12 and create pockets beneath the core 12 and the thermal barrier layer 14. In this regard, the thermal conductivity of the structural member 10 may be further reduced because of the reduced contact area between the core 12 and the thermal barrier layer 14.
With reference to
In one embodiment, as with the topography of the core 12, described above, the surface of the layer 14 may have a roughness or topography sufficient to limit the contact between a wall covering and the structural member 10. The topography of the surface of the layer 14 may depend upon how the layer 14 is formed, as described below. By way of example, the layer 14 may be smooth or may be rough, such as being pebbled, dimpled, pocked, fissured, ridged, crackled, to name only a few. Such surface topography or profiling may be produced, with a particular coating application technique, by molding, or other forming operation and/or by adding other materials. These features may be used in combination with the topography or surface texturing of the core 12, described above. In one embodiment, topography of the layer 14 may have a predetermined design including having a unique color and/or pattern, applied design, or other surface features. For example, the layer 14 may have a topography that identifies the manufacturer, architect, or builder by name or by trademark. In these ways, insulative spaces, such as, bubbles, pockets, gaps and other discontinuities may be induced at the interface between the core 12 and thermal barrier layer 14 and/or between the thermal barrier layer 14 and any wall covering secured against the structural member 10. In one embodiment, the thermal barrier layer 14 includes internal porosity that inhibits heat flow through the structural member 10. By way of example, the insulative spaces within the thermal barrier layer 14 may be formed by the process parameters used when the thermal barrier layer 14 is applied, such as, with variation in the chemistry of the thermal barrier layer 14 or by incorporating beads, particulates, or other fillers in the thermal barrier layer 14 during or following application of the layer 14. In these embodiments, the filler may therefore be dispersed in the thermal barrier layer 14 and/or be attached to the thermal barrier layer 14. It will be appreciated that internal porosity, fillers, and surface topography of the core 12 and/or the layer 14 may be used in any combination.
The layer 14 may be of any suitable thickness or depth, though the layer 14 may be limited by the application technique or final design parameters. For example, layer 14 may be in a range from about 0.005 inch to about 0.500 inch thick, in the range of about 0.040 inch to about 0.250 inch thick, or in the range of about 0.080 inch up to about 0.125 inch thick. In another example, the thickness of the layer 14 may not be constant along the length and/or across the width of a side of the core 12. However, the thickness of the layer 14 is not so limited and may depend upon the particular material of the thermal barrier layer 14, the use for the structural member 10, and/or the material of the core 12.
Additionally, the layer 14 may be sufficiently strong such that it resists being crushed or compressed under normal loads associated with attachment of wall coverings, and it remains sufficiently flexible such that is does not flake or spall off of the core 12. That is, the layer 14 may be sufficiently robust such that the layer 14 may remain adherent and intact on the core 12 when subject to rigors of manufacturing and construction operations, such as when impacted, handled, cut, banded together, drilled, pried against, etc. The layer 14 may furthermore be resistant to water and other chemicals. For example, the layer 14 may not be substantially compressed when a sheet of dry wall is secured thereto with dry wall screws normally used to hang dry wall. In these applications, the layer 14 may substantially retain its predetermined or applied thickness, and may not require any on-site re-application and/or thickness adjustment. Advantageously, any predetermined specifications for the layer 14, i.e., thickness, coverage, texturing, and other structural characteristics, which collectively achieve a predetermined R value of the structural member 10, may be retained to meet or exceed industry standards. It will be appreciated that the size or dimensions of the core 12 may be adjusted to accommodate a specific predetermined R value by allowing an increase or decrease in the thickness of the thermal barrier layer 14 while providing the structural member 10 with standardized dimensions. For example, if a thermal barrier layer 14 that is about 0.500 inch thick is attached to two edges of the core 12, the width of the core 12 may be reduced by about 1 inch to keep the width of the structural member 10 at a nominal 4 inches or to match other industry standard dimensions.
As set forth above, the thermal barrier layer 14 is a material having a lower thermal conductivity than the material of the core 12. In one embodiment, the thermal barrier layer 14 is any suitable insulating material that provides an increase in the R value of the structural member 10. In this regard, the thermal barrier layer 14 impedes heat flow through the structural member 10 when the structural member 10 is positioned such that thermal barrier layer 14 resides between the core 12 and one or both of the environments that are separated by the structural member 10. By way of example, the thermal barrier layer 14 may be a material having relatively high thermal resistance and sonic insulation properties. For instance, the thermal barrier layer 14 may comprise a polymer, such as, polyethylene, polyurethane, polypropylene, polyamide, or polyester, or a combination thereof. By way of additional example, the layer may be an epoxy. Such polymers may be represented, though not limited to common trade-named products as Styrofoam®, Kevlar®, Nomex®, Lexan®, Plexiglas®, Teflon®, Nylon 6®, or Rilsan®. However, it will be appreciated that other thermoplastic or thermosetting polymers may also be used. Furthermore, the layer 14 may be in a solid form, in the form of porous foam, in the form of a composite comprising a combination of materials, or in another insulative-enhancing form. For example, a polymer layer may include one or more common filler materials, such as a mineral, like vermiculite, or other insulating material in particulate or fiber form or in another insulating form, for example, solid or hollow spheres, HOSP® powder, solid or hollow fibers, porous particulates, fragmented particulates, or pellets, to name only a few, which when dispersed in, composited into, and/or impinged onto or otherwise attached to the thermal barrier layer 14, may increase insulative properties thereof. In another example, layer 14 may be thermally sprayed ceramic oxides of zirconium or aluminum, or may comprise glass, one or more ceramics (e.g. oxides and nitrides), or minerals, or glass.
As set forth above, the layer 14 is made of a material that has a lower thermal conductivity than the thermal conductivity of the material of the core 12, for example, polyethylene foam has a thermal conductivity k value of approximately 0.114 BTU-[in]/hr-ft2-° F. and a related reciprocal insulative R value of around 8.770 hr-ft2-° F./BTU. Materials of the core 12, for example, pine wood and plain C-steel 1020, are characterized by thermal conductivities of about 0.828 BTU-[in]/hr-ft2-° F. and about 324 BTU-[in]/hr-ft2-° F., respectively. As such, the layer 14 may have a thermal conductivity that is a fraction of the core 12. Accordingly, in one embodiment, the thermal barrier layer 14 has a thermal conductivity that may be 25% or less than that of the core 12, though the thermal conductivity of the thermal barrier layer 14 may be less than about 15% of the core 12. However, the thermal conductivity of the thermal barrier layer 14 may be greater than or equal to the thermal conductivity of air that is about 0.114 BTU-[in]/hr-ft2-° F.
According to another embodiment of the invention, the structural member 10 may be made by applying the thermal barrier layer 14 to a side of the core 12, each described above, in any suitable manner. With reference to
By way of additional example, the thermal barrier layer 14 may be applied by other powder coating techniques known in the art where polymer powder particles may be attached to the surface of the core 12 by electrostatic “cling.” The attached particles and/or the core 12 may then be heated in a conventional oven, for example, via infrared or ultraviolet radiation or with electric induction, to melt the particles or otherwise chemically convert the attached polymer particles into the thermal barrier layer 14. While applying the thermal barrier layer 14 to the core 12 may be achieved by the aforementioned methods, embodiments of the invention are not so limited, as other techniques, such as atomic force or cold spray processes (e.g. those processes that rely on kinetic energy or the velocity of particles to form a coating) or other methods of adhering particles of the material of the thermal barrier layer 14 to the core 12 may be utilized.
By way of further example, a polymer or other low thermal conductivity ingredient in liquid form or solid form contained in a suspension may be applied by a paint spraying process to form a coating on the core 12. As referred to herein, “coating” may also constitute a surface conversion whereby one material may be applied to the side of the core 12 and a subsequent physical or chemical modification of the coating occurs to form the thermal barrier layer 14. The thermal barrier layer 14 may then be formed following, for example, evaporation or chemical reaction of the sprayed coating. A material may also be applied to the core 12 by coating with a brush, a roller, a putty knife or other similar tool or by extruding a material onto the core 12 to form the thermal barrier layer 14. In another example, the core 12 may be dipped into a liquid or a solid-state fluidized bed to form a coating thereon such that following evaporation, thermal treatment, and/or chemical reaction, the thermal barrier layer 14 is formed. It will be appreciated that other application techniques are contemplated, such as, coating the core 12 by physical vapor deposition (PVD) or chemical vapor deposition (CVD) techniques, with a sol-gel precursor, and other similar techniques.
In one embodiment, the thermal barrier layer 14 may be formed by intentional conversion of a portion of the side of the core 12 or on all sides thereof to form the thermal barrier layer 14. This may be achieved by treating the core 12 to form a surface layer having different chemistry. For example, wood cores may absorb chemicals and/or solids to form the thermal barrier layer 14. By way of additional example, metallic cores may be chemically or metallurgically reacted to form a surface layer of an oxide, a nitride, or another composition that has a lower thermal conductivity than the material of the core 12. This result may be achieved by placing the core 12 in a controlled atmosphere, such as, a vacuum atmosphere and/or other specific reactive atmospheres, and then heating the core 12 to react the atmosphere with the core 12 to form the thermal barrier layer 14. For example, the process may include a pack cementation process or another reactive method that modifies the surface of the core 12 by additive thickening and/or atomic lattice penetration to produce the thermal barrier layer 14.
With reference to
It will be appreciated that any of the aforementioned application processes may be implemented in an automated system. For example, the thermal barrier layer 14 may be thermally sprayed onto the core 12, as shown in
Furthermore, embodiments of the invention may include preparation of the surface of the core 12 prior to applying the thermal barrier layer 14. Such surface preparation processes may include degreasing and surface roughening by grit blasting or other surface activation processes known in the art. Other associated processes may include pre-heating to facilitate rapid application of the layer 14 and adherence of the layer 14 to the core 12. Further, post-coating air jets or other means may be used to rapidly cool and solidify the heated material.
With reference to
Furthermore, it will be appreciated that a layer of material may alternatively, or in combination with the structural member 10, described above, be applied to either or both surfaces of the barrier covering 52, 54 in
In order to facilitate a more complete understanding of the invention, the following non-limiting examples are provided.
Structural members and applied coating samples, according to embodiments of the invention were tested to demonstrate the performance characteristics thereof. The test determined heat transfer reduction between two thermocouple-instrumented aluminum alloy bars when respective samples were placed between the bars.
A schematic of the testing apparatus is shown in
As shown in
During testing, the hotplate HP, bars 4B and 4T, and samples started at room temperature. The hotplate HP was then set to 212° F. (100° C.). The heating rate was controlled by the hotplate HP, which was monitored for consistency of each test by a third thermocouple (not shown) inserted into a fixed position within the HP heating element. Temperature rise of 4B and 4T was recorded at intervals of 4, 12, and 20 minutes. The final temperature difference, ΔT° F., was essentially calculated as 4B° F. minus 4T° F. at 20 minutes and was used as an indicator of the relative insulative characteristics of the samples. Accordingly, a larger ΔT° F. indicated better insulative property. In other words, larger differences in temperature ΔT° F. indicated that bar 4T remained cooler and 4B retained heat. The difference in temperature was due primarily to the thermal insulation characteristic of the interposed sample S, which simulated an insulative factor or the “R” value of a structural member.
Calibration of the testing system was performed periodically to confirm reproducibility of the experimental test method. The heating rate curve of the hotplate was determined to be consistent within the selected 20 minute test duration. Also, all metallic sample surfaces and hotplate HP surfaces were polished with emery for each test to minimize surface oxide accumulation and other interfacial contamination effects on the heat transfer through the bars 4B and 4T and sample S, if any.
Temperature data from calibration of the temperature measurement system and data from measurement of the temperature difference for one sample are compiled in Table 1. As provided in the table, Mode A provided a baseline measurement of the temperature of the bar 4B when subject to heating with the hotplate according to the above procedure. According to the Mode A measurements, the hotplate HP heats most rapidly in the first four minutes, then heats with a more gradual, nearly linear tangential temperature as the set point of 212° F. is approached.
As provided in Table 1, Mode B data provides information regarding the thermal conduction between the two bars 4B and 4T when they are placed in contact with one another and without any material intentionally inserted between them. As noted in Table 1, the heat transfer between the aluminum bars in Mode B is rapid because the two abraded bar surfaces are in direct contact with one another. In Mode C, a specimen of galvanized sheet steel, obtained from Clark-Western Building Systems, Inc. and representing material used for fabrication of metal framing members, was interposed between the bars 4B and 4T. According to the data in Table 1, the ΔT° F. is relatively small, slightly less than about 2 times more than for the very high conductivity aluminum bars. This indicated comparatively rapid heat transfer, as would be expected from the high thermal conductivity of metal. In other words, Mode C data is evidence of the undesirable rapid heat transfer that a galvanized steel wall stud provides between environments having differing temperatures in building structures.
In Mode D, a sample of a polyethylene layer of about 0.082 inch effective bulk thickness on a galvanized steel strip was tested. The coating was applied utilizing an XIOM® X1000™ thermal spray system onto a 1 inch×6 inch strip of about 0.045 inch thick galvanized steel. As indicated in Table 1, the Mode D samples provided an increase of about a factor of 5 times in the ΔT° F. difference in temperature between bar 4B and bar 4T, as compared to the uncoated galvanized steel sample of Mode C. Mode D data demonstrated that a substantial thermal insulative benefit was achieved. Cross sections of the sample were mounted in epoxy for subsequent microscopic examination using traditional metallographic mounting and polishing procedures.
Mode E samples were tested to provide temperature difference data for other materials, including air, that were compared to the Mode A-Mode D samples. Mode E samples were performed on materials having known thermal conductivity. Samples in Mode E were 1 inch by 6 inch strips of the material having the thicknesses noted in Table 1. From the data in Table 1, the exemplary sample exhibited ΔT° F. that is of similar magnitude to those materials having known low thermal conductivity values. In essence, this testing demonstrated that the thermally sprayed polyethylene composite layer improved the thermal conductivity of underlying metal substrate and may thereby decrease the costs associated with maintaining the temperature within a building when a structural member, according to the embodiment of the present invention, is used in the construction thereof.
While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those of ordinary skill in the art. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user.
The present application claims priority to U.S. Ser. No. 61/157,254, filed Mar. 4, 2009, the disclosure of which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61157254 | Mar 2009 | US |
