Abstract:
A method for cleaning a heat exchanging coil in an air conditioning unit using a low-pressure cleaning system to remove foreign particles that have accumulated on the heat exchanging coil. The low-pressure cleaning system discharges air at a low pressure, high velocity, and a high volume in order to clean the heat exchanging coil. Further, the low-pressure cleaning system can inject a substance into the discharge air flow to aid in cleaning the heat exchanging coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 60/404,880, filed Aug. 21, 2002. 
    
    
     
       BACKGROUND OF THE INVENTION  
         [0001]    Air conditioning systems, such as roof top units that cool the air inside a building, rely on the efficient transfer of heat from a refrigeration fluid to the air through heat exchangers. Heat exchangers generally comprise a “heat exchanging coil” comprising one or more tubes interconnected by a plurality of thin metal fins that serve to increase the surface area of the tubes that is exposed to the air. As compressed refrigeration fluid passes through the tubes, a fan draws unfiltered air through the fins and around the tubes to facilitate cooling of the refrigeration fluid inside the tubes. The unfiltered air tends to carry dirt and debris from the surrounding environment, some of which becomes trapped in the spaces between the tubes and the fins. The efficiency of a heat exchanging coil in transferring heat from a refrigeration fluid to the air depends on how freely the air moves through the spaces between the tubes and the fins. If the spaces between the tubes and the fins are clogged by dirt and debris, the efficiency of a heat exchanging coil drops significantly.  
           [0002]    Regular maintenance of the heat exchanging coil is important to maintain efficient heat transfer. Traditionally, heat exchanging coils are cleaned in a variety of ways, including, but not limited to, the use of high pressure “pressure washers.” Pressure washers force high-pressure (1000 pounds per square inch (“psi”) or higher) air or water through a small, usually hand-held nozzle that directs high-pressure air or water toward the heat exchanging coil to blow dirt and debris from the spaces between the tubes and the fins. The effective cleaning area of the air or water stream is approximately the size of the small nozzle orifice, which may be one-eighth inch to three-eighths of an inch (⅛-⅜″) in diameter in some cases. Significant labor costs are incurred when using small orifice, high-pressure nozzles because of the number of passes that must be made by the operator to clean a desired region of the heat exchanging coil.  
           [0003]    The use of water-based pressure washers has several disadvantages. Water-based pressure cleaners typically require even higher pressures than do air-based pressure cleaners, because water has a much higher drag coefficient than air and is more difficult to “push” through a typical heat exchanging coil. Moreover, the large volume of water gallons per minute typically needed to clean a heat exchanging coil can cause damage to other components of an air conditioning system, which could lead to an electrical short in the circuitry of the air conditioning system. Further, the use of a large volume of water can cause damage to an adjacent building or other surrounding materials near the air conditioning system that is being cleaned. In order to prevent this damage, significant labor time is required to mask-off air conditioner components and the surrounding building to prevent or limit water damage during water-based cleaning of a heat exchanging coil.  
           [0004]    Any type of high-pressure cleaning method can cause damage to a heat exchanging coil because the high pressure tends to bend the fins and/or fold the fins over, which closes the space between the tubes and the fins and leads to a loss of heat exchanger efficiency. In addition, high pressure water cleaning methods always impose extreme force on the coil bundle which can loosen the tight fit between the fin and tube causing reduced efficiency and mechanical damage. Thus, there is a need for an improved system for cleaning heat exchanging coils that reduces the labor time required to clean a coil, reduces the risk of damage to the coil fins, reduces the labor time needed to mask and clean a coil, and reduces the possibility of damage to the building on which the heat exchanging coil is installed.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    The subject invention relates to the cleaning of an exposed heat exchanging coil with high velocity, high volume, low pressure air and when needed a cleaning fluid mist. Specifically, it relates to a method for cleaning a heat exchanging coil using a low-pressure cleaning system to remove foreign particles that have accumulated on the heat exchanging coil. An operator of the low-pressure cleaning system can discharge air at a low pressure from the low-pressure cleaning system so that the air passes through the heat exchanging coil. The discharge air flow from the cleaning system will dislodge foreign particles that have accumulated on the heat exchanging coil. Further, the low-pressure cleaning system can inject a substance, such as a cleaning fluid mist, into the discharge air flow so that the substance will pass through the heat exchanging coil and aid in the cleaning of the coil if needed.  
           [0006]    In one of the embodiments, the low-pressure cleaning system comprises a pressure source that creates movement of air and a discharge tube with a first end connected to the pressure source so that air will pass from the pressure source into the discharge tube and a second end with or without an attachment that allows air to exit out of the discharge tube at a pressure of less than about 50 pounds per square inch, at a velocity greater than about 180 miles per hour (“mph”) and at a volume greater than about 440 cubic feet per minute (“cfm”). The second end and/or the attachment on the second end usually ranges in diameter from one inch to two-and-a-half inches in size (1-2½″). In another embodiment, an injector is placed within the discharge tube. The injector has a spray nozzle connected to a valve by a hose so that a substance can enter through the valve and be emitted into the discharging air flow from the spray nozzle. The subject invention has applications in many industries, particularly the air conditioning industry, for cleaning heat exchanger coils in air conditioning condensers. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 shows a side view of an exemplary embodiment of the low-pressure cleaning system being used to clean a heat exchanging coil in an air condition unit;  
         [0008]    [0008]FIG. 2 shows a cross-sectional side view of the discharge tube of another embodiment of the low-pressure cleaning system;  
         [0009]    [0009]FIG. 3 shows a cross-sectional side view of the discharge tube of FIG. 1 with an attachment with a horizontal opening; and  
         [0010]    [0010]FIG. 4 shows a cross-sectional side view of the discharge tube of FIG. 1 with an attachment with a vertical opening. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    [0011]FIG. 1 shows a side view of an embodiment of the subject invention being used to clean an exposed heat exchanging coil  62  in an air conditioning unit  22 . As shown in FIG. 1, the embodiment comprises a low-pressure cleaning system  20 . Low-pressure cleaning system  20  comprises a pressure source  24 , such as a centrifugal fan, for creating the movement of air. Pressure source  24  is coupled to an air admitting end  28  of a discharge tube  26 . Discharge tube has a flexible portion  30  and has a discharge orifice  32 . In this embodiment, discharge tube  26  has a flexible portion  30 . Further, a handle  35  is attached to discharge tube  26  to aid in the operation of low-pressure cleaning system  20 . Although handle  35  and flexible portion  30  are not required, they do allow the discharge tube  26  to be aimed in different directions. In this embodiment, discharge tube  26  and discharge orifice  32  have approximately the same diameter of at least approximately two and three-eighths inches (2⅜″). However, the diameter of the discharge tube can be adjusted to any diameter to adjust the volume and velocity of the discharge air flow, as needed. Ideally, the diameter of the discharge tube and/or discharge orifice will be between one inch and two-and-a-half inches (1-2½″) in size. It will also be appreciated by one skilled in the art that the capacity of the pressure source can be adjusted to adjust the volume and velocity of the discharge air flow. Moreover, it will be appreciated by one skilled in the art that the low-pressure cleaning system is not limited to air conditioning units but, rather, can be utilized to clean anything with a heat exchanging coil that allows air to pass through it.  
         [0012]    During operation, pressure source  24  causes air to travel through discharge tube  26  so that a discharge air flow  36  emits from discharge orifice  32  at a low pressure. “Low pressure” comprises a pressure of less than about 50 psi. While the low-pressure cleaning system emits an air stream at a low pressure, the total energy of the air velocity and volume is sufficient to dislodge dirt and debris from the heat exchanging coil. Thus, the low-pressure cleaning system will emit air at not only a low pressure but also a high velocity and a high volume. While the velocity and volume can be any level sufficient to dislodge dirt and debris from the heat exchanging coil, it is recommended that the velocity be greater than about 180 mph and the volume be greater than about 440 cfm. For example, low-pressure cleaning system  20  of FIG. 1 could comprise a gas-powered leaf blower of a type known in the art. Such as a gas powered leaf blower produces a pressure of less than 5 psi while moving about 640 cfm of air at a velocity of approximately 210 mph. Discharge air flow  36  will enter air conditioning unit  22  at a sufficient pressure, velocity and volume to dislodge dirt and debris from the heat exchanging coil  62 . FIG. 1 shows the dirt and debris being blown out of the top of the air conditioning unit through the exhaust fan of the unit with exiting air  38 . The low pressure of discharge air flow  36  reduces the possibility of damaging the heat exchanging coil. Further, the large diameter of discharge orifice  32  provides a larger area of discharge air flow  36  and makes cleaning the heat exchanging coil faster. Flexible portion  30  of discharge tube  26  and handle  34  allows the operator to direct the air flow  36  in different directions.  
         [0013]    [0013]FIG. 2 shows a side cross-sectional view of the discharge tube of another embodiment of the low-pressure cleaning system. As shown in FIG. 2, low-pressure cleaning system  20  further comprises an injector  40  that can inject a cleaning fluid into discharge air flow  36  to improve or alter the cleaning characteristics of the air. For example, a small amount of water or a water/detergent mixture can be provided as a mist  48  (or a low volume stream) to improve cleaning of some surfaces and to help remove oily residue in some cases. As shown in FIG. 2, the cleaning fluid is induced through injector  40  located inside and attached to discharge tube  26 . Injector  40  has a spray nozzle  46  connected to one end of a hose  44  that connects the spray nozzle to a valve  42 . Valve  42  can be connected to a reservoir that contains the cleaning fluid. In operation, the operator of this embodiment of the low-pressure cleaning system can open valve  42  and cause the cleaning fluid to be fed through hose  44  and into and out of spray nozzle  46  so that mist  48  of the cleaning solution can be injected into the discharge air flow  36 . Other nozzles can be placed in the discharge tube or can engage the discharge tube so that not only cleaning agents can be injected into the discharge air flow, but also so that other useful substances, such as rinsing agents, fogging agents, and dry powders can be injected into the discharge air flow.  
         [0014]    A variety of attachments can be attached to discharge orifice  32  to improve/modify operation of low-pressure cleaning system  20 . For example, as shown in FIG. 3, an attachment  50 , having a horizontal opening  52  and an open end  54  that fits over discharge orifice  32 , can be attached to the discharge orifice to focus and direct discharge air flow  36  horizontally relative to the axis of the discharge tube. Alternatively, as shown in FIG. 4, an attachment  58 , having a vertical opening  56  and an open end  54  that fits over discharge orifice  32 , can be attached to the discharge orifice to focus and direct discharge air flow  36  vertically relative to the axis of the discharge tube. Other attachments may engage discharge orifice  32  to aid in directing the discharge air at variable angles from the horizontal axis of the discharge tube or to improve the cleaning of the heat exchanging coil. For example, an attachment that causes the air to exit discharge tube  26  at a forty-five degree angle or a ninety degree angle relative to the axis of the discharge tube can be used to fit into tight spaces in order to effectively clean all of the heat exchanging coil. Moreover, an attachment with an opening and a brush around the opening may be engaged with the discharge orifice to help remove surface residue. While FIGS. 3 and 4 show attachments  50  and  58  being used with discharge tube  26  without injector  40 , such attachments can be used with a discharge tube that has injector  40  attached thereto. Furthermore, any fan or blower capable of producing low pressure at a high volume and a high velocity can be used as a pressure source. Alternatively, an air compressor of a type known in the art that produces high velocity compressed air can be used along with a pressure-reducing attachment so that the air emanating from the discharge tube is of the desired pressure.  
         [0015]    While the subject invention has been described in considerable detail with references to particular embodiments thereof, such is offered by way of non-limiting examples of the invention as many other versions are possible. It is anticipated that a variety of other modifications and changes will be apparent to those having ordinary skill in the art and that such modifications and changes are intended to be encompassed within the spirit and scope of the pending claims.