Abstract:
An exterior wall is kept free of moisture condensation in both heating and cooling seasons by four one-way valves that utilize pressure differentials of a chimney effect to ventilate the insulating cavity with air from the drier colder side, while maintaining a vapor barrier on the more humid warmer side.

Description:
BACKGROUND 
       [0001]    Water is a building&#39;s worst enemy. Whether it comes from precipitation, groundwater, or condensation, water can, over time, cause mold and mildew, rotting of wood structures, corrosion of metals, separation of paint from surfaces, spalling of masonry and concrete, and health problems for building occupants. Moisture problems are a principal factor limiting the useful service life of a building. 
         [0002]    Groundwater can be shunted away by drains and water barriers; buildings can be sheltered from rainwater by roofs and walls that shed water; but condensation is particularly insidious because it originates within the building itself. 
         [0003]    Whenever a building is heated or cooled, a danger exists that moisture-laden air may travel from the warmer side of an exterior wall to the colder side, condensing when it reaches any surface colder than its dewpoint. 
         [0004]      FIG. 1  illustrates the condensation problem in a heating season  102 . Moisture may be added to the air  101  inside a building by various sources, such as tub baths and showers, respiration and perspiration of pets and humans, humidifiers, cooking, dishwashing, internal clothes dryer venting, floor mopping, houseplants, and gas range pilot lights. A chimney effect within the building may cause a chronic exfiltration of air  103  from the upper part of the structure, through cracks and other imperfections in the wall. A temperature gradient exists within the wall, from the warm inside wall  105  through the insulation  100  to the cold outside wall  106 . When the airflow reaches a surface that is below the air&#39;s dewpoint, condensation  104  occurs. The condensation can continue over long periods of time, resulting in a significant accumulation of liquid water within the wall assembly. 
         [0005]      FIG. 2  illustrates the basic method that has historically been used to combat winter condensation. The basic rule is, “Put a vapor barrier on the warm side of the wall.” In  FIG. 2 , as in  FIG. 1 , a temperature gradient exists in winter  202  from the warm inside wall  205  through the insulation  200  to the cold outside wall  206 . In  FIG. 2 , a vapor barrier  204  has been added, which prevents the humid inside air  203  from traveling into the wall. As a result the dewpoint of the air within the wall cavity is equal to the lower dewpoint of the dry outside air. Therefore no condensation occurs within the wall. Humid interior air  201  is in contact with the interior side of the vapor barrier, but the vapor barrier is warm because it is on the warm side of the wall. In particular, it is warmer than the dewpoint of the humid interior air, and so no condensation forms on the vapor barrier. The vapor barrier does not have to be perfect to be effective. It is sufficient if the vapor barrier is significantly less gas-permeable than the wall structures between the vapor barrier and the outside. When this requirement is met, the wall will dry to the outside, and so the dewpoint of the air within the wall cavity will be approximately the same as the dewpoint of the dry outside air. No condensation will form. 
         [0006]      FIG. 3  depicts the problem for a building that is air-conditioned in a cooling season  302 . The temperature gradient now runs in the opposite direction, from a warm outside wall  306  through the insulation  300  to a cold inside wall. Air  301  inside the building is dehumidified as well as cooled. A reverse chimney effect induces an infiltration  303  of warm humid air in the upper part of the structure, from the outside to the inside. When this air contacts materials colder than its dewpoint, condensation  304  accumulates. 
         [0007]      FIG. 4  illustrates the basic method that is recommended for warm climates, to combat this condensation. Now the exterior temperature is higher, so the vapor barrier  404  is placed on the outside. The vapor barrier prevents high-dewpoint exterior air from traveling through the wall. As a result the dewpoint of the air within the wall is equal to the lower dewpoint of the dry inside air. Therefore no condensation occurs within the wall. Humid exterior air  403  is in contact with the vapor barrier  404 , but does not condense because the vapor barrier is on the warmer side of the wall, and is at a higher temperature than the dewpoint of the outside air. Again, the vapor barrier does not have to be perfect, only significantly less gas-permeable than the structures of the wall between it and the interior. 
         [0008]    The solution for a heated building is  FIG. 2 . The solution for an air-conditioned building is  FIG. 4 . But what about the usual case, where the building is heated at various times, and cooled at various other times? One possibility that presents itself (U.S. Pat. No. 5,027,572) is to put vapor barriers on both the inside and outside of the wall. But this does not solve the problem because the dewpoint of the air between the two barriers will be at some value intermediate between the dewpoint of the outside air and the dewpoint of the interior air, depending on the relative amount of leakage on the two sides. If either side of the wall is below this value, condensation will form on that side. Merely placing a vapor barrier on the warm side is not sufficient. It is also necessary that, at the same time that the vapor barrier is blocking humid air on the warm side, any moisture within the wall must be allowed to leave toward the dry side. Otherwise moisture can be trapped between the two vapor barriers, leading to condensation. In other words, the air inside the wall must be the air from the dry side, with its lower dewpoint. During the heating season this is the exterior air, and during the cooling season it is the interior air. 
         [0009]    Before the advent of air conditioning, buildings only had to cope with being heated. Any exterior wall that had more ventilation to the exterior than to the interior, whether by design or by accident, was safe from condensation. Most buildings today in temperate zones will be cooled in the summer and heated in the winter, and so will face the quandary described above. Indeed, buildings that are retrofitted with air conditioning commonly develop condensation problems as a result. Buildings that have survived for decades, or even centuries, may be destroyed when air conditioning is installed, by rotting of their structural wood members. 
         [0010]    Various other proposals have been made to deal with the problem. US-2003/0205129, US-2004/0211315, and U.S. Pat. No. 6,793,713 propose periodically placing desiccant within the insulation cavity. US-2010/0233460 and US-2010/0229498 propose ventilating an insulating cavity with manually operated valves. US-2007/0094964, US-2007/0084139, and U.S. Pat. No. 7,247,090 describe systems with a dehumidifier that forces dehumidified air into the insulating cavity. 
         [0011]    What is needed is an inexpensive insulating system that automatically, throughout all seasons, ventilates to the colder side, while blocking ventilation to the warmer side. 
         [0012]    A component, that will be used in the current invention, and that is well known in the art, is a one-way valve that operates with low-pressure differential between inlet and outlet. U.S. Pat. No. 8,464,715 describes one-way valves that are used in non-rebreathing facemasks. US-3993096 describes a one-way valve operated by air pressure, used in air conditioners. U.S. Pat. No. 4,565,214 describes a flapper check valve that is operated by a low-pressure differential. U.S. Pat. No. 6,210,266 describes a flap valve for pressure relief in an automobile passenger compartment. 
         [0013]    The requirements for a one-way valve in the current invention are that it be durable, and operate in response to a low-pressure differential between its inlet and outlet. It need not perfectly seal against wrong-way flow, but only restrict wrong-way flow to be significantly lower than right-way flow. It does not need to have a large flow rate, only a flow rate that is larger than whatever leakage exists in the vapor barriers of the current invention. 
         [0014]      FIGS. 5 ,  6 ,  7 , and  8  depict a low-pressure differential one-way valve  500 , as is well known in the art.  502  is the inlet, and  501  is the outlet. A lightweight and flexible but strong membrane  504  in the shape of a disc is secured at its periphery  505  to be held above a barrier  506  with inlet holes  507 . When inlet  502  pressure is higher than outlet  501  pressure ( FIGS. 5 and 6 ), a flow  503  is established through the inlet holes  507  and out through the outlet  501 . The schematic symbol depicting the flow condition is shown in  FIG. 6 . When inlet  502  pressure is lower than outlet  501  pressure ( FIGS. 7 and 8 ), the membrane  504  presses against the barrier  506 , blocking the holes  507  and preventing backflow ( 703 ). The schematic symbol depicting the non-flow condition is shown in  FIG. 8 . 
       SUMMARY 
       [0015]    The air in an insulating cavity is at a temperature intermediate between the temperatures of the interior and exterior of a building. This fact is exploited to induce a chimney effect in the insulating cavity, relative to the colder of the two adjacent temperatures. In the heating season, ventilation takes place between the insulating cavity and the exterior but is blocked between the cavity and the interior, thus replacing any humid air with dry outside air. In the air-conditioning season, ventilation takes place between the insulating cavity and the interior but is blocked between the cavity and the exterior, thus replacing any humid air with dry inside air. In effect, the system obeys the rule of thumb “Put the vapor barrier on the warm side of the wall,” in both heating and air-conditioning seasons. 
         [0016]    The flows of air are very small, because they only need to be larger than any leakage in the vapor barriers situated on the exterior and interior sides of the cavities. In particular, the flows of air do not cause any significant reduction of the insulating ability of the system. 
         [0017]    Four one-way valves regulate the flows. Each valve opens and closes exclusively in response to differential pressure between its inlet and outlet. The system is entirely automatic, requires no human control or regulation, and no external power source other than the temperature differential between the inside and the outside of the building. The only moving parts of the system are the flap membranes inside the one-way valves. 
         [0018]    By always ensuring that the air inside the cavity comes from the drier side, condensation is prevented. 
     
    
     
       DRAWINGS 
       Figures 
         [0019]      FIG. 1  (Prior Art) shows the problem of moisture condensation during a heating season. 
           [0020]      FIG. 2  (Prior Art) shows the usual method of preventing moisture condensation during a heating season. 
           [0021]      FIG. 3  (Prior Art) shows the problem of moisture condensation during an air-conditioning season. 
           [0022]      FIG. 4  (Prior Art) shows the usual method of preventing moisture condensation during an air-conditioning season. 
           [0023]      FIG. 5  (Prior Art) shows the usual direction of airflow in a one-way valve. 
           [0024]      FIG. 6  (Prior Art) schematically shows the usual direction of airflow in a one-way valve. 
           [0025]      FIG. 7  (Prior Art) shows how a one-way valve stops backflow. 
           [0026]      FIG. 8  (Prior Art) schematically shows a one-way valve stopping backflow. 
           [0027]      FIG. 9  shows the operation of the current invention in a heating season. 
           [0028]      FIG. 10  shows the operation of the current invention in an air-conditioning season. 
       
    
    
     DRAWINGS 
     Reference Numerals 
       [0000]    
       
           100 —fill insulation 
           101 —building interior 
           102 —exterior of building in heating season 
           103 —exfiltration of air from interior to exterior 
           104 —condensation where humid air touches material colder than air dewpoint 
           105 —interior wall 
           106 —exterior wall 
           200 —fill insulation 
           201 —building interior 
           202 —exterior of building in heating season 
           203 —exfiltration of air blocked by vapor barrier 
           204 —vapor barrier 
           205 —interior wall 
           206 —exterior wall 
           300 —fill insulation 
           301 —building interior 
           302 —exterior of building in air-conditioning season 
           303 —infiltration of air from exterior to interior 
           304 —condensation where humid air touches material colder than air dewpoint 
           305 —interior wall 
           306 —exterior wall 
           400 —fill insulation 
           401 —building interior 
           402 —exterior of building in air-conditioning season 
           403 —infiltration of air blocked by vapor barrier 
           404 —vapor barrier 
           405 —interior wall 
           406 —exterior wall 
           500 —one-way valve 
           501 —air outlet 
           502 —air inlet 
           503 —airflow 
           504 —membrane 
           505 —membrane securement 
           506 —barrier 
           507 —air holes 
           703 —blocked backflow 
           900 —fill insulation 
           901 —building interior 
           902 —building exterior in heating season 
           903 —upper interior one-way valve 
           904 —upper exterior one-way valve 
           905 —lower interior one-way valve 
           906 —lower exterior one-way valve 
           907 —interior wall with vapor barrier 
           908 —exterior wall with vapor barrier 
           909 —airflow into cavity from exterior 
           910 —airflow within cavity 
           911 —airflow from cavity to exterior 
           912 —blocked airflow between interior and cavity 
           913 —cavity 
           1002 —building exterior in air-conditioning season 
           1009 —airflow from building interior into cavity 
           1010 —airflow within cavity 
           1011 —airflow from cavity into building interior 
           1012 —blocked airflow between exterior and cavity 
       
     
       DETAILED DESCRIPTION 
       [0085]    The function of the building insulation system is to minimize the flow of heat, without allowing condensation to form.  FIG. 9  shows the system in operation during a heating season  902 , and  FIG. 10  shows the system in operation during a cooling season  1002 . An insulating cavity  913  is interposed between the interior  901  of a building, and the exterior ( FIG. 9   902  or  FIG. 10   1002 ). An optional insulating material  900 , such as fiberglass or cellulose, may be interposed between an inner wall  907  and an outer wall  908 . Both inner  907  and outer  908  walls are impermeable to gas, including water vapor. Four one-way valves  903 ,  904 ,  905 , and  906  control all airflow into and out of the cavity. 
         [0086]    Situated at the top of the inner wall  907  is an upper interior one-way valve  903  that is configured to allow air  1011  to flow from the cavity  913  to the interior  901 , but not in the opposite direction. 
         [0087]    Situated at the bottom of the inner wall  907  is a lower interior one-way valve  905  that is configured to allow air  1009  to flow from the interior  901  to the cavity  913 , but not in the opposite direction. 
         [0088]    Situated at the top of the outer wall  908  is an upper exterior one-way valve  904  that is configured to allow air  911  to flow from the cavity  913  to the exterior  902 , but not in the opposite direction. 
         [0089]    Situated at the bottom of the outer wall  908  is a lower exterior one-way valve  906  that is configured to allow air  909  to flow from the exterior  902  to the cavity  913 , but not in the opposite direction. 
         [0090]    When the structure is being heated ( FIG. 9 ), the temperature in the interior of the building is higher than inside the cavity, which in turn is higher than the exterior. Thus a chimney effect is created within the cavity, relative to the exterior: the pressure at the top of the cavity is greater than the exterior pressure at the same height, and the pressure at the bottom of the cavity is less than the exterior pressure at the same height. Thus air flows from the exterior through the lower exterior one-way valve into the cavity, up the cavity, and out the upper exterior one-way valve to the outside. Any moist air inside the cavity is flushed out and replaced by dry exterior air. Meanwhile, because the temperature inside is greater than the temperature in the cavity, a potential chimney effect is created within the interior, relative to the cavity. However no flow of air takes place between the interior and the cavity, because the pressure at top of the interior is greater than the pressure at the same height within the cavity, and the pressure at the bottom of the interior is less than the pressure at the same height within the cavity. Thus the upper interior and lower interior valves block the flow of air between the interior and the cavity. 
         [0091]    When the structure is being air-conditioned ( FIG. 10 ), the temperature in the interior of the building is lower than inside the cavity, which in turn is lower than the exterior. Thus a chimney effect is created within the cavity, relative to the interior: the pressure at the top of the cavity is greater than the interior pressure at the same height, and the pressure at the bottom of the cavity is less than the interior pressure at the same height. Thus air flows from the interior through the lower interior one-way valve into the cavity, up the cavity, and out the upper interior one-way valve to the interior. Any moist air inside the cavity is flushed out and replaced by dry interior air. Meanwhile, because the temperature in the exterior is greater than the temperature in the cavity, a potential chimney effect is created within the exterior, relative to the cavity. However no flow of air takes place between the exterior and the cavity, because the pressure at top of the exterior is greater than the pressure at the same height within the cavity, and the pressure at the bottom of the exterior is less than the pressure at the same height within the cavity. Thus the upper exterior and lower exterior valves block the flow of air between the interior and the cavity. 
         [0092]    We see, then, that the system obeys the rule “Put a vapor barrier on the warm side of the wall,” in both heating and cooling seasons, while allowing the wall to dry out to the drier colder side. The air inside the wall cavity is always the air of the colder and drier side and thus has its lower dewpoint. Condensation is prevented during all seasons.