Abstract:
A rapidly assembled pre-fabricated array of heating elements, such as tubing or wire, on a rigid mesh, for use in radiant panel heating and/or cooling systems, reduce costs by streamlining both the design layouts and the labor operations to fabricate and install the systems. The pre-fabricated arrays may be installed with the mesh on the finish floor side for additional protection of the heating elements during and after installation.

Description:
[0001]     This invention was made with State of California support under California Energy Commission contract number 500-02-026. The Energy Commission has certain rights to this invention.  
       BACKGROUND  
       [0002]     This subject matter of this application relates to radiant floor heating and cooling systems, and particularly to systems that place hydronic tubing or electrical heating cables in contact with indoor room or outdoor surfaces.  
         [0003]     Radiant floors are widely recognized as the most comfortable choice among heating systems. As a result, the radiant floor market has grown rapidly. However, the market could be much larger if installed system costs could be lowered significantly. Installations have been largely limited to custom homes where the owners are willing to pay more for improved comfort. Current radiant heating systems are more likely to be installed at sites where cooling systems are not necessary. Cooling is generally provided by ducted forced air systems, which for a modest additional expense can deliver heating as well. By comparison, combining radiant heating with forced air cooling is much more expensive to install. However, there is the potential in dry climates to install ductless systems that can deliver cooling as well as heating through floor tubing. Many rapidly growing housing market areas are in the dry climates of the U.S. southwest and mountain states. Production builders construct more than 75% of new homes in these areas. These volume homebuilders are more likely to consider radiant systems if costs can be reduced, because homebuyers are attracted to many radiant system features including superior comfort, high energy efficiency, and low noise.  
         [0004]     There are additional market opportunities for lower-cost outdoor panel heat transfer systems. These include snow-melt and patio heating systems, patio cooling systems, and swimming pool solar heating systems that circulate pool water through tubing in surrounding or nearby concrete paving.  
         [0005]     The most economical radiant floor systems place linear tubing or electrical conductors (wires) in concrete slabs, where reinforcing steel provides a matrix for securing the linear heat transfer elements in a desired pattern. The concrete transfers heat laterally, allowing wider spacing of the elements. For concrete slab construction, a typical method involves a concrete crew placing steel reinforcing wire, which is typically a grid-type reinforcing mesh that arrives in a rolled form and then is straightened, cut, and laid throughout the formed area. A radiant floor specialty crew then manually secures the tubing or wire onto the top of the reinforcing grid at 2′ to 3′ intervals with wire or cable ties. Tying the tubes or wires in place is a labor intensive, time consuming, process. The installers must either repeatedly bend over or be on their hands and knees for extended periods of time. In addition to working for long periods in uncomfortable positions, the installers must have considerable dexterity to secure the ties without damaging the tubing or wires.  
         [0006]     The heating elements typically arrive at the site in rolls, and if the element is hydronic tubing, its “memory” of the rolled shape complicates the task of securing it in straight runs on the mesh. Radiant floor designs typically use customized serpentine and rectangular spiral layouts. These layouts or circuits can be complex because interior wall locations must be marked before the circuits are placed. The layout patterns are usually configured room-by-room with connecting lines entering through doorways to avoid passing under interior walls, thereby minimizing the danger that wall framing fasteners will penetrate and damage the tubing or wire.  
         [0007]     The ends of the heating elements ultimately meet at a manifold or panel that becomes the distribution point for a group of “circuits,” whether hydronic or electrical. After the circuits are run, the concrete crew that formed the slab edges returns to pour the slab over the heating elements. During the pour, they typically reach blindly through the wet concrete with “J-hooks” to pull the reinforcing mesh up near the horizontal centerline of the slab. Because the mesh is not typically flat, and the ties are widely spaced, this operation sometimes results in pulling heating elements too near the surface, where they are more vulnerable to damage. If the system is hydronic, the tubing is pressurized during the pour, and a sudden loss in pressure indicates that the tubing has been punctured.  
         [0008]     Radiant systems that are not placed in concrete slabs are relatively more expensive because they require the addition of a layout matrix to guide the layout patterns. Such systems usually require either closer spacing of the heating elements or additional components to spread heat laterally. The prior art includes several novel strategies for reducing the cost of “raised floor” radiant technologies that do not surround the linear heat transfer elements with concrete. For example, the Applicant&#39;s “low mass” radiant system shown in U.S. Pat. No. 4,782,889 uses a corrugated deck that spans across the framing members to hold the tubing, and spread heat laterally across the floor. A subsequent technology (U.S. Pat. No. 5,788,152) uses a composite plywood-aluminum deck to accomplish the same three functions. Both of these systems would benefit from use of a tubing product that arrives in a serpentine pattern rather than in rolls.  
         [0009]     The above factors suggest a need and opportunity for improved radiant panel methods that reduce costs and enhance installation reliability.  
       SUMMARY  
       [0010]     The subject matter of this application is directed to an improved heating element product and methods for fabricating and installing such elements, including radiant panel systems that reduce costs by streamlining both the design layouts and the labor operations to fabricate and install the systems. The improved products and methods include forming a heating element, such as hydronic tubing in a “figure-8” pattern that facilitates installation of the tubing in certain layouts. The subject matter of the application also provides, a method of rapidly assembling pre-fabricated arrays of heating elements, such as tubing or wire, on a rigid mesh. According to the subject matter of this application, the pre-fabricated arrays may be installed with the mesh on the finish floor side for purposes of protection of the heat transfer elements. These and other improvements will be further described in the following sections. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The subject matter of this application will be described in detail with reference to the following drawings in which like reference numerals refer to like elements and where:  
         [0012]      FIG. 1  is an isometric view showing an exemplary method for winding figure-8 tubing;  
         [0013]      FIG. 2  is a plan view showing an exemplary method for deploying tubing from a narrow figure-8 pattern;  
         [0014]      FIG. 3  is a plan view showing an exemplary method for deploying tubing from a wide figure-8 pattern;  
         [0015]      FIG. 4  is an isometric view showing an exemplary method for pre-fabricating tubing in a narrow figure-8 pattern to a grid substrate;  
         [0016]      FIG. 5  is a cross-sectional view showing an exemplary method for placing a pre-fabricated assembly and enclosing it in a concrete slab;  
         [0017]      FIG. 6  is a cross-sectional view showing an exemplary method for placing the pre-fabricated assembly on a framed floor with cementitious topping; and  
         [0018]      FIG. 7  is an isometric view showing an exemplary method for folding two pre-fabricated assemblies that form a single tubing circuit. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0019]     Although features of the subject matter of this application may be implemented use in a variety of deployment patterns, standardization can be maximized using a serpentine pattern in which the linear heat transfer element, such as tubing or wire, enters near one corner of a rectangular grid and is placed in a repetitive back-and-forth alignment of parallel runs. The “memory” problem for plastic tubing wound on a spool can be minimized an/or eliminated with a “figure-8” winding, which can be accomplished according to the subject matter of this application.  
         [0020]      FIG. 1  is an isometric view showing an exemplary method for winding figure-8 tubing. As shown in  FIG. 1 , tubing  1  is extruded from an extruder  2 . The tubing  1  is received on a winder  6  having two mandrels  3   a  and  3   b . Because the extruder  2  is typically a large machine that must remain fixed in position, a preferred exemplary embodiment uses a two-mandrel winder  6  with double-axis movement. The exemplary version of the winder  6  has two vertical mandrels  3   a ,  3   b  and a bed  6   a  that tilts about a horizontal axis  6   b . The spacing between the mandrels  3   a ,  3   b  can vary from as little as about 3′ to as much as about 20′, as shown in exemplary applications further described with reference to  FIGS. 2 and 3 .  
         [0021]     During the winding process, tubing  1  being produced by the extruder  2  is wound on two mandrels  3   a  and  3   b  of a winder  6  rather than on one larger mandrel as used in a standard tubing extrusion process. The diameter of the mandrels  3   a ,  3   b  will typically range from 6″ to 12″. As the tubing  1  from the extruder  2  is freshly wound about the mandrels  3   a  and  3   b , the tubing  1  takes a “set” such that curved tubing segments  4  remain curved and straight sections  5  remain straight after removal from the winder  6 . In an embodiment, the winder  6  tilts and rotates relative to the extruder  2  so that the tubing  1  clears the mandrels  3   a ,  3   b  as winding proceeds. As shown in  FIG. 1 , the winder  6  next rotates counter-clockwise about axis  9  as viewed from above. As rotation proceeds, the tubing  1  winds about the mandrel  3   b  and the winder  6  continues to rotate counterclockwise until the mandrel  3   a  approaches the tubing  1 . An end  7  of winder  6  then pivots downward until the tubing  1  fully clears the top of mandrel  3   a . The end  7  then pivots back up before rotation reverses, and clockwise rotation continues until the mandrel  3   b  approaches the tubing  1 . An end  8  of the winder  6  then pivots downward until the tubing  1  fully clears above the mandrel  3   b . The end  8  pivots back up, and rotation changes back to counter-clockwise.  
         [0022]     The winding process continues until the winder  6  is full. The tubing  1  is then cut and the cut end from the extruder  2  is connected to a second winder. The coiled tubing  1  is then removed from the first winder  6 . If the heating element being extruded from the extruder  2  is a cross-linked polyethylene tubing (PEX), the coil of tubing then proceeds to a cross-linking operation. The completed coil of tubing may either be packaged for shipment or deployed and secured immediately to a grid in a process to be described below.  
         [0023]      FIGS. 2 and 3  are plan views showing exemplary methods for deploying tubing from narrow and wide figure-8 patterns, respectively. In  FIG. 2 , tubing  1  from a bundle  10  is partially secured to a mesh grid  11 . In  FIG. 3 , tubing  1  is shown secured to the grid  11 . In various exemplary embodiments, the grid  11  will typically serve both as a base for attaching the tubing  1  and as a source of reinforcement for a concrete slab or other floor topping, and is usually made of steel in a square grid pattern, e.g., reinforcing wire. For example, a mesh of rigid #10 steel wires (approximately 0.10″ diameter) are often used in a 6″×6″ spacing arrangement, and the grid is typically produced in the U.S. in 5′ and 7′ widths. Heavier wire and/or tighter grid spacing can be used where stronger reinforcement is required. The mesh is relatively rigid but can be obtained in either rolls or flat sheets. Flat sheets are preferred for use with the subject matter of this application because such sheets more reliably retain the tubing  1  in a flat plane. The most common and appropriate sheet size is 7′ by 20′, as shown in  FIGS. 2 and 3 .  
         [0024]      FIG. 2  shows how the bundle  10  of “figure-8” tubing  1  can be deployed into a narrow serpentine pattern  13   a . Compared to a wide serpentine pattern  13   b  shown in  FIG. 3 , the narrow serpentine pattern  13   a  requires less factory space for the winding process, and facilitates pre-fabrication of the tubing/grid arrays, as discussed with reference to  FIG. 4 . The tubing  1  is sufficiently flexible that the curved tubing segments  4 , which in packing make turns of more than 180°, quite easily open to 180° during deployment of the tubing  1 . In an exemplary preferred layout, “tails” of the heating elements from each pattern  13  connect to a supply box or “manifold center”. Thus, it is beneficial to have both the supply end  16  and the return end  15  leaving the grid  11  in close proximity to one another. For example,  FIG. 2  shows a “tail”  15  of the heating element that proceeds straight from the left end to the right end of the grid  11 . When installed at the job site, the tail  15  will proceed with the second tail/supply end  16  to the manifold center connection point.  
         [0025]     A common spacing of the tubing  1  on the grid  11  is 12″ on center. The configuration or pattern shown in  FIG. 2  uses tubing nominally wound on 12″ mandrels with axes spaced 4′ apart, so that the “outside-to-outside” serpentine pattern is 5′ wide. Located on the grid  11  as shown, this pattern allows side-by-side grid placement that essentially maintains a spacing of about 12″ between the tubing  1  including the tail  15 . In  FIG. 2 , tubing segments  17  and the tail  15  have already been secured to the grid  11  with ties  18 . Various devices can be used for the ties  18 . Field-placed tubing is typically held to the mesh grids  11  with either wire ties or (“zip”) cable ties placed by hand. An example of a motorized wire tie system is discussed with respect to  FIG. 4 . Spacing of the ties  18  varies with location of the tubing  1  on the grid  11 . For example, along the straight segments  5 , the ties may be spaced up to 36″ apart, but at the 180° curved segments  4 , ties  18  are recommended at the intersection of the straight and curved segments  5 ,  4 . A spacing of about 24″ between the ties  18  is recommended along the tail  15  ( FIG. 2 ) where the curved segments  4  have been opened to form a continuous straight segment  5 . The dotted line  19  shows where the “not yet secured” tubing will be placed, and how the other tail  16  will leave the grid parallel to the first tail  15 .  
         [0026]      FIG. 3  also shows the tubing  1  placed 12″ on center. In this exemplary embodiment, the tubing  1  having a figure-8 pattern was wound on 12″ diameter mandrels spaced 17′ apart, and the “outside” serpentine dimension is 18′. Most features of this wide figure-8 pattern  13   b  are similar to those discussed with respect to  FIG. 2 , including tails  15  and  16  leaving the grid  11  at the same corner. However, this wide or “long serpentine” pattern  13   b  would better integrate with grid sheets  11  of even footage width increments (for example, 6′ or 8′ wide) so that identical grid/tubing panels  11  could provide even spacing of the tubing  1  in side-by-side placement. With the 7′ grid  11  or other “odd” footage widths, uniform spacing of the tubing  1  across multiple panels can only be achieved by adding an extra serpentine element to each alternate sheet  11 . For example, alternating 7′ panels can have four serpentine pairs each, and their alternating neighbors can have three pairs, like the panel shown in  FIG. 3 .  
         [0027]      FIG. 4  is an isometric view showing an exemplary method for pre-fabricating tubing  1  in the narrow figure-8 pattern  13  to a grid substrate  11 . The pre-fabricated tubing/grid panel  24 , shown in  FIG. 4 , is similar to the grid  11  discussed with respect to  FIG. 2 . In an exemplary embodiment of the method, the grid  11  is supported in a vertical position so that the tubing installer  20  can work in a more convenient and comfortable position compared to installing the tubing  1  on the floor or at a horizontal table. In the embodiment, the grid  11  is hung from above its horizontal centerline on pegs  21  that project from a support rail  22 . The support system may also include a lower support rail (not shown) to stabilize the grid during assembly. Assembly proceeds starting with placement of the grid  11  onto the pegs  21  of the support rail  22 . The tubing bundle  10  (not shown) is then deployed onto the grid  11  by hanging the curved segments  4  over the pegs  21 , with one peg  21  per serpentine loop. The installer  20  may preferably use a motorized tie gun  23  to quickly attach the tubing  1  to the grid  11  at ties  18 . The top tail  15  may be tied to the grid  11  either before or after the serpentine loops are tied. After all ties  18  are completed, the “off panel” tubing in the tails  15  and  16  may be bundled and lightly secured to the edge of tubing/grid panel  24  for transporting. The assembled grid/tubing arrays  24  may be stacked in any position for storage and delivery.  
         [0028]      FIG. 5  is a cross-sectional view showing an exemplary method for placing pre-fabricated panels in a concrete slab. In a typical slab-on-grade application, edge forms  25  confine the concrete pour, and are partially supported by a concrete footing  26 . Grid/tubing panels  24  are supported by standoffs  27  above a prepared base layer  28 . In an exemplary embodiment, the panels  24  are placed with the tubing  1  at an underside of, rather than above, the grid  11 . Locating the tubing  1  below the grid  11  is an advantage of the pre-assembly process as it keeps the tubing  1  lower in the concrete slab where it is less vulnerable to puncture from above, and it keeps the tubing  1  from floating upward between its tie points  18 . Before a slab  29  is poured, the tails  15 ,  16  (not shown) from the panels  24  are deployed to the manifold center (not shown) and connected for a leakage test. Typically, the tubing  1  remains pressurized during the pour, and pressure is monitored to verify continuing integrity during the labor activities. In a typical 4″ thick slab, the grid panels  24  are placed at a vertical centerline of the slab  29 . Several types of standoffs  27  are available and are well known in the art. Alternatively, instead of using standoffs, the panels  24  may be placed directly on the base layer  28 , and then lifted using a “J-hook” during the pour, to place the panels  24  near the vertical centerline of the concrete slab  29 .  
         [0029]      FIG. 6  is a cross-sectional view showing an exemplary method for placing the pre-fabricated assembly on a framed floor with a cementatious topping in conjunction with metal fins that improve heat transfer. The floor construction includes joists  30  that support the subfloor  31  and a cement topping  32 . This floor construction method is used where the mass of a concrete or gypsum cement topping is valued for its thermal and/or acoustical benefits. The topping  32  does not as effectively spread heat laterally compared to the full slab shown in  FIG. 5 , and the absence of a steel mesh grid also reduces lateral heat transfer. Aluminum channel fins  33  may be secured to the subfloor  31  in close contact with the tubing  1  to improve heat transfer and to minimize the likelihood that occupants will feel “hot lines” on the floor surface  34  directly above the tubing  1 . The channel fins  33  are only placed over straight sections  5  of the tubing  1 .  
         [0030]     Another advantage of the figure-8 tubing  1  is apparent in considering installation of the channel fins  33 . For example, conventional rolled tubing must first be secured to a subfloor to straighten the tubing before the channel fins can be placed. With the figure-8 tubing  1 , the tubing  1  need not be secured to the subfloor  31  before the channel fins  33  are placed. Instead, the tubing  1  can be held by the channel fins  33  which are secured to the subfloor  31 . This process works because the channel fins  33  can readily be snapped over the straight sections  5  of the figure-8 tubing  1 .  
         [0031]     The figure-8 tubing  1  may also benefit installations of the “Low Mass Hydronic Radiant Floor System” shown in U.S. Pat. No. 4,782,889 (1988). In this application (not shown), tubing is held by and in the grooves of a corrugated metal deck that replaces the subfloor in framed construction. As with respect to  FIG. 6 , the pre-formed serpentine patterns afforded by the figure-8 tubing  1  simplify installation by eliminating the need to wrestle with continuously curved tubing. Instead, the tubing  1  can be quickly deployed in its approximate final position, and then secured by pushing it down into the grooves in the corrugated metal deck.  
         [0032]     In practice, one of the most cost-effective radiant heat designs combines low piping and manifold costs with relatively low pressure drop to minimize pump size and energy use. Optimal circuit lengths, tubing sizes, and tube spacings often dictate arrays that require two grid panels. For example, two 7′×20′ grids may be placed end-to-end to form a 7′×40′ assembly, or side-by-side to form a 14′×20′ assembly. For U.S. markets where ½ diameter (nominal) tubing is most common, the resulting 280 square foot area is appropriate for the optimal circuit.  FIG. 7  shows a folded panel with a tubing circuit pattern known as a “spiral pair.” This pattern is similar to the “long serpentine” shown in  FIG. 3 . For both patterns, folding a “two grid” panel in the middle requires bends in all the parallel tubes in the array. The narrow serpentine pattern shown in  FIG. 2  only requires two bends, but in either event, the tubing must not be damaged by bending. Tubing manufacturers typically specify minimum bend radii for their products. For example, the minimum bend radius for most cross-linked polyethylene (PEX) tubes is 10 diameters. Thus, a ½″ tube (actually 0.625″ diameter) can be formed to a 6.25″ bend radius- or roughly to a 12″ semi-circle in a serpentine pattern.  
         [0033]      FIG. 7  is an isometric view showing a method for folding two grid sections that support a single tubing circuit. With two end-to-end grids  11   a ,  11   b  joined only by the tubing  1 , and with the tubing  1  not joined to the grids  11  near the intersection of the grids  11   a ,  11   b , one grid  11  may be offset with respect to the other grid  11  by a predetermined bend diameter. A folded width of the assembled grids  11   a ,  11   b  is then the width of the grid plus the tubing bend diameter. As shown in  FIG. 7 , the tubing  1  is secured to a folded pair of grids  11   a  and  11   b . The two grids  11   a ,  11   b  are folded about line  37 . When the pair of grids  11   a ,  11   b  is unfolded, the top corner  40  on the left grid  11   a  will meet the top corner  41  on the right grid  11   b . When folded, the tubing  1  is contained between the two grids  11   a  and  11   b . With the grids  11   a ,  11   b  in the folded position, the two top corners  40  and  41  are displaced by a length  19  (typically the minimum tubing bend diameter), allowing the tubing  1  to form arcs  17  without crimping the tubing  1 . In the case shown where the bend radius equals the grid wire spacing, the arcs  17  are inset by a distance  18  equal to approximately 0.57 times the bend radius. For the 6″ spacing and bend radius shown, the distance  18  equals approximately 3.4″. Thus, the ties  38  and  39  should be no closer than 9.4″ (6″+3.4″) to the fold line  37 . After unfolding and placement in the prepared foundation, the grids  11   a  and  11   b  may be wired together along the fold line  37 , with the corners  40  and  41  intersecting.  
         [0034]     Although the subject matter of this application has been described with reference to various exemplary embodiments, it is to be understood that the subject matter is not limited to the exemplary embodiments or constructions. To the contrary, the subject matter of this application is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, others combinations and configurations, including more, less, or only a single element, are also within the spirit and scope of the invention.