Patent Publication Number: US-7712350-B2

Title: Apparatus and method for determining density of insulation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional application of U.S. patent application Ser. No. 10/969,427 filed Oct. 20, 2004 now abandoned. 

   TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION 
   This invention relates in general to an apparatus and method for determining the density of insulation, and in particular, to an apparatus and method for determining the density of a loose-fill, blown-in-place fibrous insulation. 
   BACKGROUND OF THE INVENTION 
   In recent years, a greater emphasis has been placed on the use of insulation materials in dwellings or other structures to promote energy conservation and noise reduction At the same time, innovative architectural designs have created a variety of shapes and sizes that do not always lend themselves to the use of a conventional fibrous batting, which is often available in rolls of uniform width. This has created a need for a technique for applying fibrous insulation that does not use uniform width batting. 
   This need has been fulfilled to a limited extent by developing various blown-in-place insulation techniques, wherein loose-fill fibrous insulation is blown into a cavity between the flaming member&#39;s of the wall, ceiling, or floor of a dwelling. The loose-fill insulation is provides a low cost installation techniques and is perceived as capable of completely filling the cavity, regardless of its shape and size, achieving a uniform volume of insulation for optimum energy conservation, as well as sound insulation purposes. 
   While blown-in-place insulation techniques provide a low cost method of installing insulation, one of the advantages of batting lost to blown-in-place insulation is the batting&#39;s ability to provide a predetermined insulation value, also known as the “R-value”. The R-value can be determined by the thickness (T) of the fibrous insulation and the insulation constant (k) using equation 1. 
   
     
       
         
           
             
               
                 R 
                 = 
                 
                   k 
                   T 
                 
               
             
             
               
                 ( 
                 1 
                 ) 
               
             
           
         
       
     
   
   In the manufacture of fiberglass batts it is a relatively simple matter to determine the nominal thickness and insulation constant to determine the R-value of the batt. This R-value is then printed on the batt during manufacture. When insulation batting is purchased, for example, to place in a new dwelling, it is often purchased by specifying a desired R-value. If installed in accordance with minimal prescribed installing techniques, the purchaser, due to uniform dimensions of insulation batting, can be count on at the insulation value having a certain thermal resistance. 
   The R-value of blown-in-place insulation is determined by Eq. 1 (above), however k is dependent on the density of the insulation. Therefore, one advantage of the easily determined R-value associated with batting is typically not applicable. As a consequence, it is necessary to also employ a secondary technique fox determining the density of the blown-in-place insulation for assuring that the insulation has the desired R-value. 
   Various secondary techniques have been employed for the determining density in blown-in-place fibrous insulations. In one technique, a known mass of loose-fill is blown into a cavity of a known volume. The mass is divided by the cavity volume to determine density and R-value. A problem with this technique is that it slows down the installation process of the insulation and therefore, may not be easily used in the field. It is also difficult to calculate the actual volume of the cavity because there are typically features such as windows, doors, devices in the area that take up volume. Further, inexperienced insulation installers may not provide an even volume filling density that causes the density and R-value to vary between cavities. 
   In another known technique, a space is first filled with blown-in-place insulation. Then, a sample of insulation of a known volume is removed from a wall cavity and weighed. Using the volume of the sample, it is possible to determine the density of the insulation in the cavity by weighing the sample and dividing the weight by the known volume. The R-value of the insulation may then be determined in a known manner simply by knowing the thickness of the insulation in the cavity. In some instances, the quantity of insulation may be loose or compressed. As a consequence, error in determining the density of the insulation can be magnified if care is not taken to correctly remove the sample or average a number of samples. This is also a very time consuming technique and consequently is not preferred by insulation installers. 
   In yet another known technique, netting is secured to wall studs to enclose an underlying cavity Insulation is blown into the cavity through a hole in the netting. The netting retains the insulation in the cavity. U.S. Pat. No. 4,712,347 to Henry V. Sperber discloses observing the bulging out of the netting as a signal that a sufficient amount of insulation has been fed into the cavity behind the netting. This technique is unreliable because it is based on the subjective observation of the insulation installer s and the tension of the netting applied to the cavities. Moreover, the mechanical properties such as the modulus of elasticity of the netting material affect the resiliency of the netting and the appearance of the bulge. In addition, the modulus of elasticity of the insulation, which is affected by the fiber diameter and the presence or absence of a binder, controls the resiliency of the insulation Environmental conditions, such as humidity, may also affect the accuracy of the technique Another disadvantage of this technique is that installers, in an effort to insure that a cavity is adequately filled, often overfill the cavity. Overfilling the cavity is undesirable because it causes the netting to bulge too much and wastes insulation. If the netting bulges too much, wallboard is difficult to install on the framing members This has been recognized as a problem and thus has led to the use of a shield during installation, whereby the shield is held against the netting while the cavity is being filled to prevent the netting from bulging undesirably. 
   In view of the above techniques, it is apparent that there exists a need in the art for an improved apparatus and method for installing insulation that is blown into open wall cavities to a prescribed density wherein the improved apparatus and method provide increased accuracy. 
   SUMMARY OF THE INVENTION 
   The above objects, as well as other objects not specifically enumerated, are achieved by an apparatus for determining the density of insulation in a cavity of a dwelling of other structure The apparatus is in the form of a sensor that is held within the cavity of the structure and relative to the insulation in the cavity for sensing the force of the insulation against the sensor. The force is used to determine the density of the insulation, which, in turn, is used to determine the thermal resistance or R-value of the insulation. 
   An alternative apparatus includes a sensor and a fixture supporting the sensor The fixture is structured and dimensioned to hold the sensor against the insulation within the cavity to measure a material property of the insulation and therefore determine density and R-value The material property may be resistance to an applied force, pressure within the cavity, resistance to air flow, or any other material property that may be used effectively to calculate density or R-value. 
   A method for determining the density of loose-fill, blown-in-place insulation comprises the initial step of providing a structure that includes flaming members and a sheath forming at least one cavity having a known depth. An exposed side of the cavity is covered with netting. The cavity is then filled with insulation. A sensor is held in contact with the netting or the insulation in the cavity The sensor then detects a material property of the insulation that may be converted to a density or R-value. For example, a force may be exerted by the sensor on the insulation. The force may include mechanical force, air pressure differential, ultra-sonic response or any other force that may be used to calculate density. The thermal resistance of the insulation is determined from the known cavity depth and insulation density. 
   Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a diagrammatic representation in plan of a partial structure of a dwelling or other structure. 
       FIG. 2  is a schematic representation in plan of an apparatus for determining the density of a loose-fill, blown-in-place fibrous insulation in a cavity of the structure illustrated in  FIG. 1 . 
       FIGS. 3A and 3B  are diagrammatic representations in plan of sensors of the apparatus according to the invention supported within the cavity of the structure illustrated in  FIG. 1 . 
       FIG. 4  is a schematic representation in plan of a fixture for supporting a sensor according to the invention outside the cavity. 
       FIG. 5  is a diagrammatic representation in plan of a fixture according to one embodiment of the invention. 
       FIG. 6  is a diagrammatic representation in plan of a fixture according to another embodiment of the invention. 
       FIG. 7  is a diagrammatic representation in plan of a fixture according to yet another embodiment of the invention. 
       FIG. 8  is a diagrammatic representation in plan of a sensor according to one embodiment of the invention. 
       FIG. 9  is a diagrammatic representation in plan of a sensor according to another embodiment of the invention. 
       FIG. 10  is a block diagram of a method for determining the density of a loose-fill, blown-in-place fibrous insulation. 
       FIG. 11  is graph of empirical data relating to the relationship between the density and the spring force of the loose-fill insulation and a polynomial used in a regression to arrive at the empirical data. 
       FIG. 12  is graph of empirical data relating to the relationship between the density and the pressure drop through the loose-fill insulation and a polynomial used in a regression to arrive at the empirical data. 
   

   DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION 
   Referring now to the drawings, there is illustrated in  FIG. 1  a partial structure of a dwelling or other structure, indicated generally at  10 , including flaming members  12 , such as wall studs, ceiling joists, or floor joists. Various other flaming members, not shown, the purpose of which will be apparent to those skilled in the art, maybe included in the structure  10 . A cavity  14  is formed between the framing members  12 . An inner side of the cavity  14  is covered with a sheet or netting  16 . An outer side of the cavity  14  is covered with an exterior sheathing  18 , which sheathes the structure  10  except at locations of doors and windows, not shown. 
   Insulation  20  is installed in the cavity  14  to prevent heat passage either outwardly or inwardly through the structure, and to minimize sound transmission therethrough The insulation  20  is preferably a loose-fill, blown-in-place fibrous insulation. The insulation  20  may consist of any suitable material useful for insulation purposes. Such insulation  20  may be installed in a conventional manner, such as through use of a blower apparatus, not shown, which picks up the insulation in an air stream and carries the insulation to the cavity  14  through a tube or hose, also not shown. 
   The netting  16  is preferably relatively thin, yet are capable of containing the insulation  20  in the cavity  14  to hold the insulation  20  in place, and serves to permit air to escape from the cavity  14  while filling the cavity  14  with insulation  20 . The netting  16  terminates at lower and upper ends of the cavity  14  at flaming members, such as a sill plate and a header, not shown, that traverse the flaming members  12 . 
   An apparatus for determining the density of insulation  20  in the cavity  14  is schematically represented at  30  in  FIG. 2 . The determination of density leads to the determination of thermal resistance, or the R-value, of the insulation  20 . The apparatus  30  comprises a sensor  32  that is adapted to be held in a substantially fixed position relative to the insulation  20  in the cavity  14  The term “substantially” with respect to the term “fixed” means that the sensor  32  will be held in a position relative to the insulation that allows reliable density determinations to be repeatedly made by the sensor  32 . That is to say, the sensor  32  may suffer some minor deviation in position as long as the density determinations remain reliable. 
   According to the present invention, the sensor  32  senses force F, or a change in force, which is used to determine density, as will be described in greater detail in the description hereinbelow. Numerous embodiments of the apparatus  30  can be used to catty out the invention Some examples of such embodiments are set forth in the following paragraphs. 
   In one embodiment of the invention, the sensor  32  is supported within the cavity  14 . This may be accomplished by attaching the sensors to the sheathing  18  or the netting  16 , as shown in  FIGS. 3A  or  3 B. When the insulation  20  is blown into the cavity  14 , the sensor  32  senses the force F of the insulation. In accordance with this embodiment, a measurement of force F may be taken from within the cavity  14  via a physical or wireless connection, not shown, by the sensor  32 . 
   In another embodiment of the invention, the sensor  32  is supported against the netting  16  and the insulation  20  but is located outside the cavity  14 . This can be accomplished in any suitable manner. For example, a fixture  34  could be provided for supporting the sensor  32 , as schematically illustrated in  FIG. 4  The fixture  34  can be any suitable structure that is adapted to hold the sensor  32  in a substantially fixed position relative to the insulation  20 . 
   In  FIG. 5 , there is illustrated a fixture in the form of a standard  36  that may be supported by a supporting surface  22  adjacent the cavity  14  with the insulation  20  therein The sensor  32  is adapted to be supported by the standard  36  in a manner so that the sensor  32  can be repeatedly held in a fixed position relative to the netting  16  and the insulation  20 . For example, the standard  36  may include a foot  38  for establishing a set distance for the standard  36  away from the netting  16  and the insulation  20 . 
   In  FIG. 6 , there is illustrated a fixture in the form of a plate  40  that is adapted to be repeatedly held in a fixed position relative to the netting  16  and the insulation  20 . The plate  40  can be held in contact with the netting  16  and the insulation  20 , or, as shown in  FIG. 6 , spaced from the netting  16  and the insulation  20 , as long as the position is substantially consistent to permit correlated determinations of density to be made. In the illustrated embodiment, the plate  40  is adapted to be held a fixed distance D from the netting  16  and the insulation  20  in the cavity  14  with each determination of density made by the apparatus. This can be accomplished with legs  42  that extend from the plate  40  to engage the flaming members  12 , although such is not required. The distance D is preferably a distance whereby the sensor  32  does not extend beyond a plane P that is coplanar with the inner sides of the flaming members  12 , or into the cavity  14  between the flaming members  12 . 
   In  FIG. 7 , there is illustrated another fixture, which is also in the form of a plate  40 . Extending from the plate  40  are pins  44  that are adapted to pierce the netting  16 , pass through the insulation  20  in the cavity  14  without substantially affecting its density, and engage the inner side of the sheath  18  The length L of the pins  44  may be fixed or adjustable to accommodate framing members  12  having different dimensions For example, the length L of the pins  44  may be approximately 3-½inches in length if the flaming members  12  are nominal 2×4 studs or approximately 5-½ inches in length if the framing members  12  are nominal 2×6 ceiling joists. Adjustment of the pins  44  may be accomplished in any suitable manner, such as, for example, providing apertures, not shown, through the plate  40  and a clamp  46  in fixed position relative to the plate  40  and in alignment with the apertures. The pins  44  may pass through the apertures and the clamps  46  may secure the pins  44  in a desired position relative to the plate  40  Alternatively, the pins  44  may be telescopically adjustable, or adjustable in some other suitable manner. 
   The sensor  32  according to one embodiment of the invention may be in the form of a load cell for measuring the force of the insulation  20  in the cavity  14 . Such a sensor  32  would be suitable for use within or outside the cavity  14 , as schematically represented in  FIGS. 2 and 4 , or in any of the embodiments of the invention described herein. Any conventional load cell may be suitable for carrying out the invention. 
   In  FIG. 8 , there is illustrated a sensor in the form of a force transducer  48 . The force transducer  48  is adapted to measure the force F encountered by a contact plate  50  held against the insulation  20 . The force transducer  48  may be a digital transducer or an analog transducer. The force transducer  48  can be held in a fixed relation to the insulation  20  in any suitable, such as with the use of any of the fixture  52  shown, or any of the fixtures described above. Alternatively, an analog spring-force meter may be used in the place of the force transducer  48 . In accordance with the invention, the insulation  20  will exert a force t against the force transducer  48 , and that force F will be directly related to the density of the insulation  20 . 
   In  FIG. 9 , there is illustrated another embodiment of a sensor in the form of an air cup  54 . The air cup  54  includes a contact surface  60 . The contact surface  60  is configured to press against the netting  16  and the insulation  20  in the cavity  14  behind the netting  16 . As shown in  FIG. 9 , the air cup  54  can be mounted to an air cup fixture  62 . The air cup fixture  62  is configured to support the air cup  54  and hold the air cup  54  in a fixed position relative to the netting  16  and the insulation  20 . In the embodiment shown in  FIG. 9 , the air cup fixture  62  includes an air cup plate  64  and a plurality of air cup legs  66 , similar to the plate  40  and legs  42  as shown in  FIG. 6 . In another embodiment, the air cup fixture  62  could be any suitable structure configured to support the air cup  54  and hold the air cup  54 , such as for example, the fixture  36  shown in  FIG. 7 . In the embodiment shown in  FIG. 9 , the air cup fixture  62  is mounted to framing members  12 , although other mounting methods could be used In yet another embodiment, the air cup fixture  62  could be a free standing structure, such as for example, the fixture  36  shown in  FIG. 5 . As previously mentioned, the contact surface  60  is configured to press against the netting  16  thereby forming a hollow space  68  within the air cup  54 . A pressure differential between the air cup  54  and the atmosphere is created within the air cup  54 . The pressure differential may be produced by introducing air, through a source connector  67   a , into the air cup  54  from a pressure device  56 . The pressure device  56  may be in the form of an air tank, an air pump or any other suitable device to increase the pressure within the air cup  54 . Similarly, air may be evacuated from the air cup  54  by air pump, a vacuum, or any other suitable device to decrease the pressure within the air cup  54 . As further shown in  FIG. 9 , a gauge  58  is connected to the air cup  54  by a connector  67   b . The gauge  58  is configured to determine the air pressure differential between the air cup  54  and the atmosphere. The gauge  58  is configured to determine the density of the insulation from the air pressure differential by, for example, using a predetermined equation providing the relationship between the air pressure differential and the density of the insulation  20 . The pressure in the air cup  54  will be directly related to the density of the insulation  20  behind the netting  16 . 
   In  FIG. 10  there is illustrated a method for determining the density of loose-fill, blown-in-place insulation in a cavity defined between framing members of a dwelling or other structure. A method according to a preferred embodiment of the invention may comprise an initial step  110  of providing a structure having framing members and a sheath forming at least one cavity having a known depth of thickness. In step  112 , an inner side of the cavity is covered with netting. In step  114 , the cavity is filled with insulation. The insulation is preferably a loose-fill, blown-in-place fibrous insulation. The netting is preferably capable of containing the insulation in the cavity while permitting air to escape from the cavity while the cavity is filled with insulation. 
   In a subsequent step  116 , a sensor is held in a substantially fixed position relative to the insulation in the cavity. In step  118 , the sensor measures force exerted on the sensor by the insulation. In step  120 , the force is used to determine the density of the insulation. In step  122 , the thermal resistance of the insulation is determined from the known cavity depth and insulation density. 
   In optional step  124 , the sensor is supported within the cavity. The sensor may be attached to the netting or the sheathing prior to filling the cavity with the insulation. When the insulation is blown into the cavity, the sensor senses the force exerted against the sensor by the insulation. 
   In an alternative step  126 , a fixture is provided for supporting the sensor outside the cavity and holding the sensor in a substantially fixed position relative to the netting and the insulation. The fixture may be in the form of a standard supported by a supporting surface adjacent the cavity and the insulation therein. Alternatively, the fixture may be in the form of a plate that holds the sensor against the netting and insulation. The plate could be held a distance from the flaming members by legs that engage the framing members. Alternatively, the plate could be held a distance from the sheathing by pins that pass through the netting and the insulation and engage the sheathing. The pins could be adjusted in length to accommodate flaming members having different dimensions. 
   The sensor of step  116  may be in the form of a load cell that senses the force of the insulation against the sensor. Alternatively, the sensor may be a digital or analog force transducer. The transducer can be held in a fixed position relative to the insulation with the fixture provided in step  126 . A spring-force meter may be used in the place of the transducer Alternatively, the sensor may be in the form of an air cup that is pressed against the netting and insulation. It will be appreciated that if the sensor provided in step  116  is an air cup, then an optional step  128  may be performed in which a pressure differential between the interior of the air cup and the atmosphere is created. In step  118 , the force (air pressure) exerted is then determined by measuring the air pressure in the air cup, such as by using a gauge. The pressure in the air cup is directly related to the density of the insulation behind the netting. 
   The aforementioned force transducer  48  and spring-force meter rely on the natural spring force of the loose-fill insulation to gage density. As the density of loose-fill insulation increases, the spring force increases proportionally. Using polynomial regression, an empirical relationship can be found between the density and the spring force of the loose-fill insulation. An example of a polynomial and empirical data relating to the relationship between the density and the spring force for is shown in  FIG. 11 . 
   The embodiment of the apparatus or method that uses the air cup relies on the natural resistance to flow of the loose-fill insulation to create a pressure drop. For a given source pressure, the loose-fill insulation has a characteristic pressure drop for a given density. Further, back pressure created on the high-pressure side of the loose-fill insulation is directly proportional to density. Using polynomial regression, an empirical relationship can be found between the density and pressure drop. An example of a polynomial and empirical data relating to the relationship between the density and the pressure drop through the insulation is shown in  FIG. 12   
   Factors that can affect either embodiment of the invention include the morphology, diameter, characteristic length, and shape of the fibers of the insulation factors, the binder content, if a binder is used, and other factors that are not mentioned. 
   The loose-fill thermal conductance, which is inversely proportionate to thermal resistance, can be related to the density by laboratory testing. The data can then curve fitted, as shown in  FIGS. 11 , and  12 . 
   The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below.