A structure comprises at least one outer wall having an internal wall section and an outer wall section with an air flow passage therebetween. A circulation system circulates air through the flow passage to inhibit moisture accumulation and mold growth. A sensing system determines the presence of moisture in the flow passage and generates a signal in response thereto. A controller receives the signal from the sensing system and controls the circulation system to maintain a predetermined temperature and relative humidity in the flow passage.

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a structure having an outer wall system, the construction of which provides for flow of air between an internal wall section and an external wall section for inhibiting moisture accumulation and mold growth on the internal wall section. 
   2. Description of the Related Art 
   In today's construction industry, numerous residential structures, and even a significant number of commercial structures such as, for example, apartment buildings, motels, restaurants, and strip shopping centers, have their exterior surfaces finished with a synthetic stucco-type coating applied over a foam insulation board. Such exterior finishes are generically referred to as Exterior Insulation and Finish Systems, and will be referred to hereinafter as EIFS. 
   While such EIFS constructions have proved to be quite satisfactory for their relative ease of installation, their insulating properties, and their ability to receive a variety of aesthetically-pleasing finishes, a serious problem associated with EIFS construction exists. This problem is one of moisture accumulation behind the exterior wall covering. As used herein, the term “moisture” refers to both liquid and airborne forms of water, including condensation. Such moisture may be the result of condensation or high humidity, but may also be the result of wind-driven water, that may enter behind the exterior wall covering at any point where the exterior surface of the coating is penetrated. Such moisture accumulation may be the result of poor workmanship or design, deterioration of flashing or sealants over time, lesser quality doors or windows, or any other penetration or compromise of the exterior finish. 
   When such water penetration, high humidity, or condensation occurs, absent effective, reliable means for eliminating the moisture from behind the EIFS exterior construction, the moisture can remain trapped long enough before evaporating to damage or rot any moisture-sensitive elements to which the insulation is bonded, typically wood framing, oriented-strand board, plywood, or gypsum sheathing. In addition, the moist environment is a breeding ground for wood consuming insects and health hazards such as various varieties of molds. This problem is accelerated in hot and humid environments. 
   Attempts have been made to prevent entry of moisture into the building wall interior by sealing or caulking entry points in and around wall components as the primary defense against moisture intrusion, or by installing flashing around the wall components to divert the moisture. These attempts have not been completely successful. Sealants are not only difficult to properly install, but tend to deteriorate and separate from the wall component or wall due to climatic conditions, building movement, the surface type, or chemical reactions. Flashing is also difficult to install and may tend to hold the moisture against the wall component, accelerating the decay. 
   The use of sealants and flashing is also limited to the attempted minimization of moisture collection in building walls in new construction, and the further collection in existing structures. These materials are of no value in addressing the problem of moisture that has already entered a building wall interior. Thus, with solutions presented in the prior art, moisture still enters the wall interior, and the problem is further compounded by the prevention of any evaporation of the moisture already in the wall interior. 
   The problems of moisture penetration and accumulation have prevented the full use of new building cladding materials, and has resulted in many buildings with rotting framing structures, requiring extensive and expensive retrofitting. Thus, there is a great need for an system and method to prevent moisture from accumulating in the wall interior of a building at wall components, and for the removal of moisture that has already collected within the wall interior. 
   SUMMARY OF THE INVENTION 
   The present invention contemplates a structure with an outer wall having an internal wall section and an external wall section with a flow passage in between. A circulation system flows air through the flow passage inhibiting moisture accumulation and mold growth. 
   In one embodiment, a structure system comprises at least one outer wall having an internal wall section and an external wall section, where the external wall section is located such that there is an air flow passage between the internal wall section and the external wall section. A circulation system circulates air through the air flow passage to inhibit moisture on the internal wall section. 
   In another preferred embodiment, an essentially enclosed structure system comprises at least one outer wall having an internal wall section and an external wall section, where the external wall section is located such that there is an air flow passage between the internal wall section and the external wall section. A circulation system circulates air through the air flow passage to inhibit moisture on the internal wall section. 
   At least one sensor generates a signal indicative of moisture and generates a signal in response thereto. A controller receives the signal from the at least one sensor and controls the circulation system to provide a predetermined relative humidity of the air flow in the air flow passage. 
   In one embodiment, a method is described for inhibiting moisture accumulation in an outer wall of a structure, comprising:
         providing an outer wall with an internal wall section and an external wall section with an air flow passage therebetween; and   supplying air into the flow passage by an air circulation system to inhibit moisture accumulation on the internal wall section.       

   Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals, wherein: 
       FIG. 1  is a perspective drawing of a structure according to one embodiment of the present invention; 
       FIG. 2A and 2B  are schematics of a structure according to one embodiment of the present invention; 
       FIG. 3  is a block diagram of a circulation system according to one embodiment of the present invention; and 
       FIG. 4  is a schematic of a structure according to one embodiment of the present invention. 
   


   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 ,  2 A and  2 B,  FIG. 1  shows a perspective view of a structure and  FIGS. 2A and 2B  show alternate sectional views of an outer wall  25  of a structure, and  FIG. 2B  shows an alternative sectional view of an outer wall of a structure according to certain embodiments of the present invention. The structure  30  comprises a foundation slab  20  having a dual section outer wall  25  attached thereto. The dual section outer wall  25  has an un-insulated internal wall section  26  and an insulated external wall section  27  displaced a distance away from internal wall section  26  such that an air flow passage  17  is established between them. Conditioned air  16  is forced out through the air passage  17  by the air circulation system  45  shown in  FIG. 2  and described below, thereby inhibiting the accumulation of moisture and mold on the internal wall section  26 . 
   The external wall section  27  is constructed with an exterior insulation and finish system, commonly referred to as EIFS, which comprises a weather resistant outer surface  2 , typically of synthetic stucco, attached to a thermal insulating layer  21 . Alternatively, any suitable weather resistant material may be used, including, but not limited to, brick tile, stone tile, wood siding, pressed board siding, and cementicious siding. The thermal insulating layer  21  is typically formed from an expanded polystyrene foam, but may alternatively be made from a polycyanurate or polyurethane foam, or from any suitable insulation material. The insulating layer  21  is, in turn, attached to a sheathing layer  4 , typically a cementicious material known in the art. The external wall section  27  is attached to furring strips  6  which are in turn attached to the internal wall section  26  using attachment techniques known in the art. The furring strips  6  serve to establish the size of the flow passage  17  and to secure the outer wall section  27  to the inner wall section  26 . Furring strips  6  can also be positioned to direct the flow of air  16  in the passage  17 . The furring strips can be any suitable furring strips known in the art, with a “Z” shaped galvanized steel strip being preferred. Drain channel  18  is located near the bottom of passage  17  and is sloped to provide a drainage for any condensation or water which may need to be expelled from passage  17 . Channel  18  may be solid and thereby used to direct the air flow  16  exiting from the passage  17  at a base of the outerwall to the outside environment, as shown by arrow  16 . Alternatively, channel  18  may have multiple holes allowing moisture and air flow  16  to exit at the base of the exterior wall  25 . 
   The inner wall section  26  comprises a commercially available liquid barrier  8  attached to an external sheathing  10  which is typically a commercially available plywood or oriented stranding board (OSB). The liquid barrier  8  prevents the passage of liquid water but allows for the passage of gases and water vapor and is well known in the art. The external sheathing  10  is attached to and supported by the framing studs  12 . Any suitable framing stud material can be used including wood and metal materials. An interior sheathing  14  such as paneling, drywall board, or other suitable interior surface is attached to the interior side of the framing studs  12 . The inner wall section  26 , contrary to common construction, has minimal, or no insulation in its internal cavities. The lack of insulation minimizes the temperature gradient between the interior sheathing  14  and the external sheathing  10  in order to inhibit any condensation in the internal spaces of the inner wall section  26 . The flow of appropriately conditioned air  16  through the flow passage  17  bordered by external sheathing  10  provides an air temperature at the external sheathing essentially the same as the air temperature inside the structure  30  thereby inhibiting condensation on the liquid barrier  8  or the sheathing  10 . 
   As shown in  FIG. 2 , in a preferred embodiment, the circulation system  45  is located in an attic space  36  of structure  30 . The attic  36  is bounded by roof  22  and ceiling  29 . Roof  22  is connected to and essentially sealed with external wall section  27  by flashing  28  which extends around the periphery of structure  30 . Conditioned air  16  from the circulation system  45  is forced through duct  33  into the interior  50  of structure  30 . The air  16  exits the interior space  50  through a plurality of ceiling vents  34  which exhaust into the attic space  36 . The attic space acts as a plenum for circulation system  45 . Air enters the circulation system  45  through inlet damper  43  in attic  36  and outside makeup air  44  enters through makeup damper  46  and the combined intake air flows through blower  42  and into heating and cooling elements in conditioner  40 , through duct  32  into humidifier  38  for maintaining a predetermined relative humidity. The heater elements (not shown), in conditioner  40  may be electric or gas type elements common in the art, or any other suitable heating elements. The cooling system (not shown) in conditioner  40  may be a conventional compresser/condenser type system. Alternatively, a heat pump system may be used for heating and cooling the air. Guidelines for selecting the predetermined relative humidity are available in published documents of The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE), Standard 62-1999, Ventilation for Acceptable Indoor Air Quality, which indicates that the relative humidity should be maintained below about 70% to inhibit fungal contamination including, but not limited to, molds and mildew. The actual relative humidity and air flow requirements will be structure specific and are determined using procedures and standards known in the art. 
   The conditioned air flows through duct  33  and into interior space  50  and as previously described, exhausts through vents  34  into attic  36 . The addition of the outside makeup air  44  to the air volume existing in the essentially sealed structure creates a suitable positive pressure in the structure  30  and attic  36  relative to the outside environment, and causes conditioned air to flow  16  through the air flow passage  17  in the outer wall  25 . In a preferred embodiment, the blower  42  operates continuously forcing an essentially continuous flow of conditioned air  16  through the passage  17 , thereby inhibiting the buildup of moisture and mold on the inner wall section  26 . 
   The dampers  43  and  46  may be manually set to provide the appropriate flows. Alternatively, the dampers  43  and  46  may have actuators (not shown) which may be controlled remotely. 
   In one preferred embodiment, see  FIG. 3 , temperature and relative humidity sensors  62  and  63  are disposed in passage  17  to measure the temperature and relative humidity of conditioned air flow  16 . Signals from the sensors are received by a control system  60 , which may contain sensor interface circuits, a processor, and output control circuits for actuating devices in the circulation system  45 . As shown in  FIG. 3 , control system  60  receives signals from sensors  62  and  63  and acts according to programmed instructions to actuate makeup air damper  46 , intake damper  43 , blower  42 , conditioner  40 , and humidity controller  38  to maintain a predetermined temperature and relative humidity in conditioned air flow  16 . 
   In another preferred embodiment, see  FIG. 4 , conditioned air is split from duct  33  and travels in header  52  around the periphery of the attic space  36 . Multiple discharge ducts  54  direct conditioned air  16  from the header towards the opening of passage  17 . The air flow is controlled by multiple dampers  56  on multiple discharge ducts  54 . The dampers  56  may be manually set or, alternatively, may be fitted with actuators (not shown) which may be remotely controlled by control system  60 . 
   In another preferred embodiment, a plurality of blowers (not shown) may be mounted so as to intake the conditioned attic air and discharge the air directly into the passage  17  at a plurality of predetermined locations around the perimeter of the structure. The passage of the discharged air passing between the furring strips  6  act to create a venturi effect to induce flow from between adjacent furring strips  6 . 
   It will be appreciated by those skilled in the art, that the circulation system  45  may be wholly located external to the structure  30  with air flow to and from the structure  30  through suitable conduit or ducting (not shown). Alternatively, the circulation system  45  may be partially located in the structure  30  and partially located external to the structure  30  as is common in home systems. It is also to be understood that local environmental conditions and local building codes will, to some extent dictate the individual components used. 
   The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.