Abstract:
A method of conditioning the air supplied to a paint application booth having a separate air supply from a paint application building housing the paint application booth includes determining a booth psychometric condition preferred to apply paint inside the paint application booth. Air is removed from the paint application building and conditioned obtaining the preferred booth psychometric condition of the air removed while maintaining a generally constant enthalpy. The air removed from the paint application building is transferred into the paint booth at the booth psychometric condition preferred to apply paint inside the paint application booth.

Description:
RELATED APPLICATION  
       [0001]     This application claims priority to Provisional Application Ser. No. 60/729,676 filed Oct. 24, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally toward an improved method for controlling the environment inside a paint booth. More specifically, the present invention relates toward an energy efficient method of using heat generated inside the paint application building to reduce the cost associated with conditioning the environment inside the paint application booth.  
       BACKGROUND OF THE INVENTION  
       [0003]     The operation of a paint application building, and more specifically, a paint application booth, has proven to be one of the most costly elements of mass producing articles that are coated with protective and/or decorative coatings. In a mass production setting, articles are conveyed through a paint application booth where atomized paint is applied to the article, such as, for example, automobile bodies, at a high rate. The increased use of environmentally friendly coating materials such as, for example, water borne base coats, urethane clear coats, and powder coatings has required a narrow psychometric condition be maintained inside the paint application booth during operation. This has resulted in increasing costs associated with achieving the preferred psychometric condition to achieve the necessary coating quality.  
         [0004]     Presently configured paint application buildings generally make use of segregated ventilation systems for the paint application booth, working areas, and non-working or general building areas. In each case, fresh ambient air is drawn from the outside environment and treated by either heating, cooling, humidifying, or dehumidifying to obtain the desired psychometric condition. This is best represented in  FIG. 1  where a conventional paint application building ventilation schematic is generally shown at  10 . The conventional application building  10  generally includes three separate areas, namely, a general building or non-work area  12 , a work space  14 , and a paint application booth  16 .  
         [0005]     The general building area  12  includes all of the areas inside the building  10  where no significant work is performed on the articles being coated. This includes aisle ways, article accumulation areas, and article transport areas. The general building area  12  includes an independent air inlet  18  that draws air from outside the building  10  via a building air supply house  20 . In Northern regions, this air is generally heated and humidified particularly during the Winter months, and in the Southern region, this air is generally cooled and dehumidified, particularly during the Summer months. The building  10  also includes a building exhaust  22  where air is generally, continuously exhausted from the general building area  12 . Thus, air that has been conditioned in the building air supply house  20  by either heating, cooling, humidifying, and dehumidifying is exhausted back to atmosphere without making further use of the desired psychometric condition established in the building air supply house  20 .  
         [0006]     Various work spaces  14  are also included in a conventional paint building  10  where various functions are performed on the article being painted, both before and after paint application. Some of these functions include detacification, dust and other particle removal, both dry and wet sanding, sealer application, and other necessary operations to make ready the article to be painted. Each of these processes are known to increase air temperature inside the various work spaces  14 . Each work space  14  includes a work space air inlet  24  that draws air into the work space  14  via a work space air supply house  26 . Air is generally, continuously exhausted from the work space  14  through a work space exhaust  28 . The temperature of the air exiting the work space  14  is typically greater than the air entering the work space  14  as the work being performed on the articles generates heat. This heat energy along with the energy used to condition air received from the work space air inlet  24  to reach the desired psychometric condition in the work space  14  is exhausted through the work space exhaust  28  to the atmosphere.  
         [0007]     Air is delivered to the application booth  16  through a booth air inlet  30  via a booth air supply house  32 . The psychometric condition of the air entering the application booth  16  is defined by the processing parameters of the coating material being applied to the article. Therefore, the energy used to condition the air received from the booth air inlet inside the booth air supply house  32  to heat, cool, humidify, and dehumidify is significantly greater and more precisely controlled than the conditioning that takes place in the building air supply house  20  and the work space air supply house  26 . As stated previously, the air drawn through the booth air inlet  30  is generally heated and humidified in Northern regions primarily during the Winter months and cooled and dehumidified in Southern regions, primarily during the Summer months. The air flowing through the spray booth  16  is generally, continuously exhausted through a booth exhaust  34  where the energy used to condition the air is exhausted to the atmosphere.  
         [0008]     The conventional paint building design set forth above has proven to use an excessive amount of energy to condition air for each of the building  12 , the work space  14  and the application booth  16 . In each case, air is exhausted to the atmosphere without taking full advantage of the energy used to condition the air to obtain the preferred psychometric condition in each of the various areas. Therefore, it would be desirable to provide a coating process having reduced energy requirements by taking advantage of more efficient flow of energy, particularly during an era of increasing energy costs.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is directed toward a method of conditioning the air supply to a paint application booth disposed within a paint application building. A booth psychometric condition preferred to apply paint inside the paint application booth is determined based upon specifications set forth by the paint or coating supplier. Air is removed from the paint application building and is conditioned to obtain the preferred booth psychometric condition. The air is conditioned while maintaining a generally constant enthalpy and is transferred into the paint booth at the preferred booth psychometric condition.  
         [0010]     The inventive method of conditioning the air supply to the paint application booth takes advantage of the psychometric condition of the air disposed in the paint building exterior to the paint booth. Generally, air makeup supplied to the paint application building is conditioned by either heating and humidifying and cooling and dehumidifying depending on the seasonal condition and the regional location of the building. Therefore, energy is used to condition the air received from the atmosphere to provide a building environment that is more conducive to processing articles through a paint booth than is the atmosphere. Furthermore, the mechanical operations and machinery generally provide heat energy to the air disposed inside the application building that results in an increase in temperature of the air. Prior art buildings partly vent this air to the atmosphere when circulating fresh air through the paint application building resulting in the loss of the heat energy provided to the air by virtue of the work functions performed inside the building and the energy associated with conditioning the air to make the building interior more conducive to processing the articles through the paint booth than is the atmosphere outside the building.  
         [0011]     By taking advantage of the energy associated with the air inside the building and making use of the psychometric condition of the air disposed inside the building, a significant energy reduction is achieved by routing the building air through the paint application booth as opposed to exhausting the air from the building back to the atmosphere. Specifically, the preferred psychometric condition inside the paint application booth is obtained by merely converting the sensible heat of the air being transferred from the building to the application booth to latent heat. The preferred psychometric condition is obtained when converting sensible heat to latent heat by merely adding humidity to the flow of air from the application building through the paint application booth. This provides the opportunity to either eliminate cooling and heating systems associated with the paint application booth or significantly downsizing heating and cooling apparatus because the heat energy already disposed in the building air is being recycled. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates a cross sectional view of a prior art paint application building;  
         [0013]      FIG. 2  illustrates a cross sectional view of a paint application building of the present invention;  
         [0014]      FIG. 3  is a psychometric table representing an application booth of the present invention being operated at a target psychometric condition;  
         [0015]      FIG. 4  is another psychometric chart representing a range of temperature and humidity known to produce equivalent paint quality; and  
         [0016]      FIG. 5  illustrates an alternative embodiment of the paint application building. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Referring to  FIG. 2 , a paint building of the present invention is generally shown at  110 . The inventive paint building  110  generally includes a non-working or general building area  112 , a work space  114  and an application booth  116 . As is known to those of skill in the art, the general building area  112  includes aisle ways, office space, transfer conveyors, accumulators, and storage areas. The work spaces  114  are areas where additional work is performed on articles, such as, for example, vehicle bodies  117  being processed through the paint application building  110 .  
         [0018]     Many of the functions performed in the application building  110  and the work spaces  114  produce heat resulting in an increase in the air temperature within the work spaces  114 . For example, unpainted vehicle bodies generally referred to as body in white are first treated with the application of a phosphate coating, which is applied at about 130° F. and is subsequently coated with an electrodeposition primer and baked at a temperature approaching 400° F. Each of these operations result in an increase in air temperature resulting in an altering of the psychometric condition of the air disposed in the work space  114 . Further operations include sanding and cleaning the primered surface to remove particulate matter known to result in paint defects and also increase the temperature of the air in the work space  114 .  
         [0019]     The application booth  116  is maintained in the most precise psychometric condition out of any area in the paint application building  110 . The type of paint being applied to the vehicle body  117  dictates a temperature and humidity range required to optimize the finished paint quality on the paint vehicle. For example, applying paint at an unrecommended high temperature or humidity may result in paint defects known as sags or orange peel on the vehicle body  117 . Therefore, the paint supplier generally sets a humidity and temperature range known to reduce the potential for finish paint defects. Generally, the paint supplier recommends a target temperature and humidity known to produce optimum paint finish on the vehicle body  117 . While a narrow range is also generally identified by a given paint supplier, it is recommended by that paint supplier that the target temperature and humidity be maintained at all times. It is contemplated by the inventors that the target temperature and humidity actually define a desirable range that provides an optimum paint application performance. It has also been contemplated by the inventors that the temperature and humidity target can be broadened along a line on a psychometric chart plotting dry bulb temperature against absolute humidity of air. The advantages of the present inventive paint building  110  are explained further below.  
         [0020]     Ambient air is drawn through a building air inlet  118  from the atmosphere into a building air supply house  120  by fans sized and powered to produce the desirable amount of fresh air to the general building area  112 . The building area supply house  120  includes air conditioning assemblies (not shown) that heat, cool, humidify, or dehumidify the air being drawn through the air inlet  118  from the atmosphere to the preferred temperature and humidity of the general building area  112 .  
         [0021]     Ambient air is also drawn from the atmosphere through a work booth air inlet  124  into a work booth air supply house  126  by fans (not shown) sized to provide the desired amount of fresh air to the various work booths  114  disposed within the paint application building  110 . Like the building air supply house  120 , the work booth air supply house  126  also includes air conditioning equipment to heat, cool, humidify, or dehumidify the air being drawn from the atmosphere  124  to the preferred temperature and humidity inside the various work booths  114 . As represented in  FIG. 2 , the air from the work booth  114  is optionally vented through a work booth exhaust  128  to the atmosphere after appropriate abatement procedures are performed.  
         [0022]     Air is drawn through a transfer  136  from the general building area  112  into a paint application booth air supply house  132  via fans sized to provide the desired amount of make up air to the application booth  116 . The booth air supply house includes an air conditioner  133  to adjust the psychometric condition of the air entering the paint application booth  116 ,  216 . The air conditioner  133  either increases the humidity, decreases the humidity, increases the temperature, or decreases the temperature of the air entering the paint application booth  116 . As is known to those of skill in the art, this requires air conditioner to include a heater, chiller, humidifier, or dehumidifier. It is expected that the concepts of the present invention eliminates the need for a heat, or, in the alternative, enables the heater to be reduced in size. Air is exhausted from the application booth  116  through application booth exhaust  139  after the appropriate abatement is conducted in a known manner.  
         [0023]     The method by which the advantages of the inventive paint building  110  is derived is best explained referring to a psychometric table set forth in  FIG. 3 .  FIG. 3  represents the application booth  116  being operated at a target psychometric condition  138  (spray booth requirement). In this example, ambient air delivered through one of the general building air inlet  118  or the work space air inlet  124  is identified at dry bulb temperature and humidity at  140  (building delivery). It should be understood by those of skill in the art that the temperature and humidity of the ambient air  140  changes depending on seasonal and regional factors.  
         [0024]     The first line on the psychometric chart in  FIG. 3  represents heat added to the air in the general building area  112  and through operation of necessary equipment in the paint building  110 . In this example, the ambient air temperature is increased from generally 65° F. to around 95° F. Converting the sensible heat disposed in the general building area  112  air to latent heat by merely increasing humidity of the air transfer from the general building area  112  to the application booth  116 , the psychometric condition of the transferred air becomes closer to the desired spray booth psychometric condition  138 . This reduces the amount of the heating required in the booth air supply house  132  as represented by line  144  of the psychometric chart shown in  FIG. 3 .  
         [0025]     A second example is represented in the psychometric chart of  FIG. 3  where the temperature of the air in the building is increased from point  140  along line  146  to approximately 115° F. As set forth above, the sensible heat is converted to latent heat by merely adding humidity to the air transferred through transfer  136  from the building  112 , or more likely in this example, from the work area  114  to the application booth  116 . At generally constant enthalpies, the air temperature remains higher than its required psychometric condition  138  in the application booth  116  requiring additional cooling in the booth air supply house  132  as represented by line  148  of the psychometric chart in  FIG. 3 .  
         [0026]     It has been determined by the inventors that the booth requirement  138  shown in the psychometric table in  FIG. 3  is achievable through a range of temperature and humidity known to produce equivalent paint quality. The range is represented in the psychometric chart shown in  FIG. 4  by the spray booth control line  150 . By adopting the spray booth control line  150  as a process control parameter, the necessity for adding heat or removing heat from the air being transferred into the application booth  116  through transfer  136  from the general building  112  or the work booth  114  is eliminated further reducing the cost associated with conditioning the air inside the application booth  116 . The point identified in the psychometric chart of  FIG. 4  as  140  increases in temperature along lines  142  and  146  depending upon the various processes being performed in the paint application building  110 . In each case, humidity is added converting sensible heat to latent heat in the continuous flow of air flowing from the paint application building  110  to the application booth  116 . As the spray booth control line  115  is adopted providing a range of enthalpies neither heat needs to be added nor removed further reducing the cost associated with conditioning the air being delivered to the application booth  150 .  
         [0027]     A further alternative embodiment of the paint application building as shown in  FIG. 5  as  210 . In this embodiment, a work space air inlet  224  provides air to the application building  210 . Air is drawn through the work space air inlet  224  by fans disposed in a work space air supply house  226  for use in a work space area  214 . As set forth above, heat is added to the air by virtue of the work being performed on the vehicle body  17  inside the work space  214 . A work space transfer line  252  exhausts air from the work space  214  and may pass the air through a filtration system  254  before the air is introduced through the non-work area  212  of the application building  210 . In this embodiment, air passes through transfer  236  after being exhausted from the non-work space  212  to the booth air supply house  232  via air supply fans (not shown). The psychometric condition of the air passing through the transfer  236  is determined prior to transferring the air into the application booth  216 . As set forth above, the air is humidified in the booth air supply house  232  prior to transferring the air into the application booth  216 . Air is continuously exhausted from the application booth through the application booth exhaust  239  where abatement is performed prior to releasing the booth air to the atmosphere. In this embodiment, costs are further reduced through the use of only a single exhaust  239  for the entire application building  210 . It should be understood by those of skill in the art that fresh air may be added to the transfer  236  at a predetermined ratio for this and the previous embodiments if necessary.  
         [0028]     The paint application booth  116 ,  216  of each of the embodiments set forth above include a sensor  119 ,  219  that signals a controller  121 ,  221  the temperature and humidity of the air inside the paint application booth  116 ,  216  to establish a feed back control loop. Preferably, the controller  121 ,  221  is a proportional integral derivative controller providing a level of control known to those of skill in the art to limit the amount of variability of the temperature and humidity in the paint application booth  116 ,  216 . Therefore, the controller  121 ,  221  maintains the temperature and humidity inside the booth  116 ,  216  with the predetermined psychometric control range  150 .  
         [0029]     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.  
         [0030]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.