Abstract:
A wall plate for a wall thermostat blocks intrusion air from the thermostat. The wall plate has a wire passage aligned with the wall penetration through which the thermostat wires emerge. The wall plate member directs any intrusion air that flows out the penetration away from the cavity of said thermostat. An insulating layer, e.g., a closed-cell foam sheet, in the wall plate insulates the thermostat from direct thermal contact with the wall. The closed-cell material closes around the thermostat wires. Bosses or feet on the thermostat back plate create a standoff between the wall plate and the thermostat.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to control devices for controlling the temperature, humidity, and/or other environmental conditions in an interior comfort space, and is more particularly concerned with an improvement to a wall thermostat to prevent inaccuracies and misoperation that may result from intrusion air which may enter the thermostat from a hollow wall on which the thermostat is mounted. 
   Wall thermostats are typically installed on an interior wall of a house or other building to control the operation of a furnace, air conditioner, heat pump, or other environmental control equipment. The thermostat is intended to monitor the temperature of the room or other interior comfort space continuously, and to adjust the operation of the associated environmental control equipment to keep the interior comfort space parameter (e.g., temperature) within some range (e.g., 68° F., ±1.0° F.). Other controls may be sensitive to other parameters, such as humidity or particulate level. The thermostat is connected to the furnace, air conditioner, heat pump or the like by means of a run of thermostat wires, which pass from the furnace control board up through spaces in the interior walls, and emerge at an opening in one of the walls, and this is the place the thermostat is to be mounted. An opening is provided in the back of the thermostat for the wires to pass through, so that the wires can be connected to appropriate contacts inside the thermostat housing. 
   In practice, the opening or penetration in the wall for the thermostat wires allows some intrusion air to enter the room, and this air passes out of the wall cavity, through the thermostat opening, into the interior of the thermostat housing. As a result, the sensors inside the housing are influenced to a significant degree by intrusion air that comes through the hollow wall, and this air can be warmer or cooler than the rest of the air in the room. Even if a contractor plasters or caulks the wire opening during construction of the house, the plaster or caulk can eventually dry and crack, and permit intrusion air to enter the thermostat. As a result, the actual room air temperature (or humidity) can be outside the range set on the thermostat (or humidistat), and this can occur without any malfunction of either the thermostat or the environmental control equipment. 
   In addition, accurate control over room temperature is made difficult when the thermostat housing is in direct contact with the wall, which may be significantly warmer or cooler than the room air. That is, if the thermostat is in direct thermal contact with the wall, and if the wall is warmer or cooler than the air in the room, the accuracy of the thermostat can be impaired, even in the absence of intrusion air from the wall cavity. However, no one to date has considered thermally isolating the thermostat from the surface of the wall. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an improvement to a wall thermostat that overcomes the above-mentioned drawback(s) of the prior art. 
   It is another object to provide an effective solution to the above-mentioned problem, which solution is of a straightforward, one-piece design, and which is simple to install. 
   It is a more specific object to provide a barrier that diverts or blocks intrusion air from entering the thermostat or other similar control device. 
   It is yet another object to interpose a thermal barrier between the wall and the thermostat to avoid direct thermal contact between the wall and the thermostat. 
   In accordance with one aspect of the present invention, a thermostat arrangement that is adapted for mounting on a wall of a controlled space includes a thermostat having a front cover and a back plate adapted to be mounted on the interior wall. The back plate and the cover define a cavity, and the temperature sensor and other control circuitry are contained within this cavity. The circuitry includes contacts which are adapted to receive two or more thermostat wires that protrude through a penetration in the wall. The back plate has mounting screw openings for mounting the thermostat on the wall over the penetration, and also has a thermostat wire opening adapted to receive the two or more thermostat wires. As a means for blocking or redirecting intrusion air flow that may come out of the wall penetration and to avoid having the intrusion air enter the interior cavity of the thermostat, a wall plate member may serve as a barrier to block intrusion air from the thermostat. In this case, the wall plate member is adapted to be installed between the wall and the back plate of the thermostat. The wall plate has a wire passage that is to be aligned with the wall penetration and through which said thermostat wires are passed. The passage closes over the thermostat wires. The wall plate member serves as a barrier to direct intrusion air that flows out the penetration away from the cavity of said thermostat. In addition, an insulating layer, e.g., a closed-cell foam sheet, is included as part of the wall plate, which serves as a thermal barrier so that the body of the thermostat is insulated from direct thermal contact with the wall on which it is mounted. The closed-cell material is of a type that will close around the thermostat wires that pass through it, so as to block any air flow. There can be small bosses or feet on either the wall plate or the thermostat back plate so that there is also a small standoff between the wall plate and the back plate of the thermostat. 
   Alternatively, a resilient plug is fitted into said thermostat wire opening in the back plate. This plug may be a grommet of cross section to match that of the opening, and may be formed of a soft, resilient material, i.e., a rubbery material. The plug has a passage through which the thermostat wires are passed, with this passage closing over the thermostat wires. The resilient plug can be used in addition to the insulated wall plate mentioned above. 
   In either case, any intrusion air ends up being mixed in with the room air, and does not pass directly into the thermostat, and the thermostat is held out of direct thermal contact with the wall itself, which may not necessarily be at the same temperature as the room air. The thermostat then senses the room air parameters, e.g., temperature or humidity, much more accurately, and permits the furnace, air conditioner, heat pump, or other environmental control equipment to keep the interior room air within the comfort range that is set on the device. 
   The above and many other objects, features, and advantages of this invention will be more fully appreciated from the ensuing description of certain preferred embodiments, which are to be read in conjunction with the accompanying Drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is an exploded assembly view of a thermostat with a thermostat wire grommet. 
       FIG. 2  is an exploded assembly view of a thermostat with a wall plate. 
       FIG. 3  is a front plan view of a thermally insulated thermostat wall plate according to an embodiment of this invention. 
       FIG. 4  is a plan view of the back of the wall plate of this embodiment. 
       FIG. 5  is a perspective view of a wall thermostat and its associated wall plate according to this embodiment. 
       FIG. 6  is a bottom view of the thermostat and wall plate of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the Drawing,  FIG. 1  shows a wall thermostat assembly  10  that is to be mounted onto a wall W of a room of a dwelling, commercial building, or other structure where a human comfort space is to be maintained within some desired range of temperature. Here the thermostat  10  comprises a front cover  12  which fits onto a back plate  14 . There are sensors, switches, and electrical and electronic components mounted on the back plate  14 , which elements are of any well known configuration, and are not shown in detail and not discussed here, except that a contact strip  16  is present for connecting some number of thermostat wires  17 , here shown protruding out a hole or penetration P in the wall W. In this thermostat  10 , there are screw holes  18  provided at the left and right sides of the back plate  14 , and a pair of threaded fasteners  19  that mount the back plate  14  onto the wall W. The back plate is positioned on the wall so that a thermostat wire opening  20 , which is at or near the center of the back plate  14 , is aligned over the wall penetration P. 
   A grommet or plug  22  is formed of rubber, or of another generally soft, resilient material, and is dimensioned to fit snugly into the wire opening  20  in the back plate  14 . There is an opening  24  in the center part of the grommet  22 , and the thermostat wires are passed through this opening  24 . When the grommet  22  is then pushed into the opening  20 , the rubbery material is squeezed against the thermostat wires, closing off the opening. Then, the back plate is installed onto the wall W, using the screws or other fasteners  19 . The grommet  22  blocks the opening  20 , so that the path of least resistance for any intrusion air from the penetration P is around the grommet, and into the room space, where the intrusion air mixes with the rest of the room air and does not directly affect the action of the thermostat. 
   As shown in  FIG. 2 , the thermostat  10  is again shown in an alternative embodiment, in which a wall plate  26  is disposed between the wall W and the back plate  14  of the thermostat. Here, the elements of the thermostat  10 , wires  17 , and wall W are identified with the same reference numbers as in  FIG. 1 , and do not need to be discussed in great detail. 
   In  FIG. 2 , prior to installation of the back plate  14  onto the wall W, the thermostat wires  17  are threaded through a small central wire opening  28  in the wall plate. Then the wires are passed through the opening  20  of the back plate, and the latter is installed onto the wall W using the threaded fasteners  19 . Slots  29  or similar passages for the fasteners  19  are provided on the left and right sides of the wall plate  26 . Then, the wires  17  are attached to the appropriate contacts in the strip  16 , and the cover  12  is snapped in place on the back plate  14 . 
   In the  FIG. 2  arrangement, the wall plate can be made, either entirely or partially, of a resilient material, so that the opening  28  closes snugly over the wires  17 , and blocks any flow of intrusion air from entering the interior space of the thermostat  10 . Alternatively, the wall plate  26  can be made of a more rigid material, with a central insert of a resilient material, and with the opening  28  being in this insert. 
   It is entirely possible to employ both the wall plate  26  of  FIG. 2  and the plug or grommet  22  of  FIG. 1  in the same thermostat, although each alternative can function independently. While not specifically shown here, there may be slots or channels provided in the wall-facing side of the wall plate  26 , so that intrusion air has a pathway into the general room air space. However, the small irregularities and texture of the wall W will generally provide sufficient clearance for this diversion air flow. 
   Here, the thermostat  10  is of generally rectangular shape, but the concepts of this invention will perform equally well with thermostats of other shapes and designs. The same is true for the shape of the opening  20 , and grommets  22  can be made to suit thermostat wire openings of other shapes and dimensions. A slot may be provided in some embodiments in place of the wire opening  24  shown for this embodiment. While the above design is preferred, an alternative design for either a grommet or a wall plate could comprise two or more sections. 
   An embodiment of a wall plate  30  with thermal isolation is illustrated in  FIGS. 3 and 4 , with further reference to  FIGS. 5 and 6 . As shown in  FIGS. 3 and 4 , the wall plate  30  has on its front or proximal side a flat, rectangular central section  32  that is matched to the profile or footprint of the thermostat  12 , and a surrounding tapered edge portion  34 . The edge portion  34  forms a border or margin around the thermostat. There are small circular recesses  36  at each corner of the central section. As with the plate of  FIG. 2 , the wall plate  30  has a central wire opening  38  that lines up with the opening  20  on the back plate  14  of the thermostat  12 , and slots or passages  39  for fasteners that line up with the holes  18  in the back plate of the thermostat. Now turning to  FIG. 4 , which shows the reverse side (i.e., distal or wall-facing side) of the wall plate  30 , there is a ridge  40  that proceeds in a rectangle on the reverse side that is aligned with the central portion  32 , which defines a shallow rectangular recess in which is situated a thermal barrier  42 , which in this embodiment is a sheet of a closed cell resilient flexible plastic material. The thermal barrier  42  is visible in  FIG. 3  through the wire opening and slots  39 . There are also reinforcing ridges  44  formed on the reverse side of the tapered edge portion  34 . 
   There is an X-shaped cut  46  at the center of the thermal barrier  40 , aligned with the wire opening  38 , and this is adapted to permit passage of the thermostat wires  17 . The resilient material of the barrier  42  will close around the wires to seal against passage of air into the housing of the thermostat. There are also X-shaped cuts  48 ,  48  aligned with the slots  39  to permit passage of the threaded fasteners. In this embodiment, the sheet or barrier  42  has a nominal thickness of ⅛ inch. The foam material used as the barrier  42  can be a closed-cell urethane foam or a closed-cell polyethylene foam, which has characteristics of resilience and flexibility, and will close around the thermostat wires  17  where they pass through the X-shaped cut  46 . Other plastic foam materials can be used. Also, the section of the thermal barrier  40  where the opening or cut  46  exists can be made of an insert, with the rest of the barrier made of another material. 
   The thermostat  12  is mounted onto the wall W with the wall plate  30  in between, as shown in  FIG. 5 . 
   The back plate  14  of the thermostat housing has a small cylindrical foot or post  50  situated at each corner, with each foot  50  extending distally, i.e., towards the wall W, and fitting into a respective one of the circular recesses  36  on the wall plate. This creates a small amount of stand-off  52 , i.e., air space, between the front of the wall plate  30  and the back plate  14  of the thermostat, as shown in  FIG. 6 . Here, some room air circulates in the space behind the thermostat back plate  14 . The combination of the insulating thermal barrier  42  and the stand-off  52  ensures that the temperature of the wall W will not affect the operation of the thermostat  12 , and that the thermostat will accurately track room air temperature. 
   The wall plate  30  may be molded of a suitable plastic material, or may be made of any other suitable material. Also, while the thermal barrier  42  in this embodiment is a rectangular piece of a closed cell foam, in other embodiments the barrier can be made of other materials, or other shapes, so long as it is capable of both blocking air flow from the hollow wall into the interior of the thermostat and also blocking thermal contact between the wall and the thermostat. 
   Optionally, the grommet or plug  22  can also be used in combination with or in addition to the thermal barrier wall plate  30 . 
   In an alternative embodiment, which could have the same front and rear appearance as shown in  FIG. 5  and  FIG. 4 , respectively, the thermal barrier wall plate  30  could be incorporated into the back plate  14  of the thermostat, rather than being a separate element. This may be provided either with or without the stand-off air space  52 . 
   While the invention has been described with reference to specific preferred embodiments, the invention is certainly not limited to those precise embodiments. Rather, many modifications and variations will become apparent to persons of skill in the art without departure from the scope and spirit of this invention, as defined in the appended claims.