Abstract:
A contamination barrier for protecting heat exchanger units, for example, condensers of heating, ventilation, and air conditioning (HVAC) systems. The contamination barrier includes a filtration media which allows particles small enough to pass through a condenser assembly to pass through the contamination barrier, while preventing larger particles from passing therethrough. The contamination barrier inhibits the buildup of debris and other contamination within the condenser assembly while reducing or eliminating the need to clean the barrier, and without significantly reducing airflow through the condenser assembly, thereby promoting the ability of the condenser assembly to maintain operational efficiency. The contamination barrier is adaptable to be applied to a variety of heat exchanger units.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/713,781, filed Oct. 15, 2012, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to methods and apparatuses suitable for maintaining the cleanliness of heat exchangers, a nonlimiting example being condenser units of heating, ventilation, and air conditioning (HVAC) systems. 
     Condensers are a type of heat exchanger primarily used to transfer heat between two mediums, for example, air and a refrigerant, in various heat transfer systems, including but not limited to space heaters, air conditioners, and automotive radiators. In typical HVAC systems, a compressed refrigerant vapor enters a condenser that serves to condense the refrigerant to its liquid state. In particular, the refrigerant vapor flows through hollow cooling coils or tubes of the condenser, where heat is released from the refrigerant and transferred to the surrounding atmosphere, for example, air drawn through fins in contact with the tubes. Thereafter, the condensed refrigerant, which is cooler but still under pressure, is forced through an expansion valve to form a mist before entering an evaporator where the refrigerant is evaporated to its vapor state before again being compressed. The evaporator draws heat from the surrounding atmosphere, which is thereby cooled. In an HVAC system, the cooled air can be circulated through a room, building, passenger compartment, etc. 
     Condensers for commercial HVAC systems installed in buildings are often located on the roofs of the buildings. As a result, the heat transfer efficiency of a condenser, and therefore the efficiency of the entire HVAC system, declines over time due to debris and outdoor contaminants becoming entrapped within the condenser&#39;s tubes. Such a scenario is depicted in  FIG. 1 , which represents a condenser assembly  10  comprising at least two sets of tube and fin assemblies  12 , each having at least one tube  14  (optionally configured as a coil) contacted by multiple fins  16 . Contaminants are represented as including relatively coarse debris  18  and relatively finer particulate debris  20 . The condenser assembly  10  can be manually cleaned, though doing so can be difficult, time-consuming, and possibly result in damage to the condenser assembly  10 . In addition, and as represented in  FIG. 2 , it can be difficult to remove the debris  18  and  20  from between the tube and fin assemblies  12 . Coarse debris  18  can be particularly difficult to remove, with the result that the remaining coarse debris  18  entraps both coarse and particulate debris  18  and  20  during subsequent operation of the condenser assembly  10 . 
     Another approach involves protecting the condenser assembly  10  with a filter that serves to filter the air being drawn through the condenser assembly  10 . Commercial examples of such filters are often constructed of a plastic or rubber-coated nylon or some form of loosely woven plastic fibers, configured as a single-layer or multiple-layer mat that is often very thin, for example, less than one centimeter. Filters of this type can be designed to be cleaned periodically or as needed, though at least annually, and are designed for a service life of roughly ten years. These filter products are typically designed and sized for use with a specific HVAC system. 
     Existing filter products for HVAC systems have several shortcomings, including cost due to the product being designed for specific HVAC systems, and efficiency and energy losses due to the accumulation of contaminants on the products between cleanings and replacements. In particular, filter products require inspection, cleaning or replacement on a regular basis to ensure that the filter product does not become an upstream obstruction that reduces airflow through the condenser unit. As a result, there is considerable resistance to placing any type of airflow restriction upstream of a condenser unit because of the concern for significantly reduced heat transfer efficiency that will result in increased operation and energy consumption by the HVAC system. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides a contamination barrier and method particularly well suited for use with heat exchanger units, for example, condenser units of types used in HVAC systems. 
     According to a first aspect of the invention, a contamination barrier includes a filtration media that prevents passage therethrough of relatively coarse contaminants of a size that would be entrapped within the heat exchanger unit but allows passage therethrough of relatively finer contaminants that are sufficiently small to pass entirely through the heat exchanger unit so as to reduce accumulation of contaminants within the heat exchanger unit and reduce the need for cleaning the contamination barrier. 
     Another aspect of the invention is a method of protecting a heat exchanger unit comprising fins in thermal contact with at least one tube. The method includes securing a contamination barrier upstream of the fins and tube of the heat exchanger unit. The contamination barrier includes a filtration media that prevents passage therethrough of relatively coarse contaminants of a size that would be entrapped within the heat exchanger unit but allows passage therethrough of relatively finer contaminants that are sufficiently small to pass entirely through the heat exchanger unit so as to reduce accumulation of contaminants within the heat exchanger unit and reduce need for cleaning the contamination barrier. The heat exchanger unit is then operated to cause air to be drawn through the fins and tube thereof, wherein the filtration media prevents passage therethrough of the relatively coarse contaminants that would be entrapped within the heat exchanger unit and allows passage therethrough of the relatively finer contaminants that subsequently pass entirely through the heat exchanger unit. 
     A technical effect of the invention is the ability to maintain the cleanliness of various types and designs of heat exchangers, including but not limited to condenser units used in HVAC systems, thereby improving their efficiency and reducing the operation time and costs, prolonging the service lives of the HVAC systems and their condenser units, and significantly reducing if not eliminating the need for cleaning the condenser units. The contamination barrier achieves such benefits by primarily filtering relatively coarse contaminants that would likely become entrapped within the condenser unit, while allowing the passage of relatively finer contaminants that are sufficiently small to pass entirely through the condenser unit. In this manner, the contamination barrier can also operate for relatively long periods without the need for cleaning and without significantly reducing airflow through the condenser unit. The contamination barrier is also capable of functioning to protect a condenser unit from damage from human contact and the environment. 
     Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically represents relatively coarse and fine contaminants trapped within and between two sets of tube and fin assemblies of a condenser assembly of a type used in commercial HVAC systems. 
         FIG. 2  schematically represents the appearance of the condenser assembly of  FIG. 1  after removal of the contaminants from an outermost set of the tube and fin assemblies and subsequent entrapment of additional coarse and fine contaminants between the two sets of tube and fin assemblies. 
         FIG. 3  schematically represents a contamination barrier placed upstream of the condenser assembly of  FIGS. 1 and 2 , whereby relatively coarse contaminants that are likely to become trapped within and between the tube and fin assemblies are trapped by the contamination barrier and the contamination barrier permits passage of finer contaminants that are capable of passing through the condenser assembly. 
         FIG. 4  illustrates an exemplary installation of a contamination barrier on a condenser unit of an HVAC system. 
         FIG. 5  represents a technique for installing the contamination barrier on the condenser unit of  FIGS. 4 and 5 . 
         FIG. 6  represents a clip configured for securing an edge of the contamination barrier to the condenser unit of  FIGS. 4 and 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  represents a contamination barrier  22  particularly suitable for installation on condenser units of commercial HVAC systems, including condenser units located on the roofs of the buildings. For convenience, the barrier  22  is represented as being installed upstream of the condenser assembly  10  represented in  FIGS. 1 and 2 . As previously discussed, the condenser assembly  10  is shown as comprising at least two sets of tube and fin assemblies  12 , each having at least one heat transfer tube  14  (optionally configured as a coil) contacted by multiple fins  16 , though in many applications a single tube and fin assembly  12  may be present in the condenser assembly  10 . As a condenser assembly  10 , a fluid flows through the tube  16  and heat is transferred from the fluid to the surrounding environment (e.g., atmospheric air) via the fins  16 , though in the case of a different type of heat exchanger, heat may be transferred from the surrounding environment to the fluid within the tube  16 , and such an operation is also within the scope of the invention. The representation of  FIG. 3  is merely for illustrative purposes, and the invention is not limited to condenser units of any particular configuration, and more generally is applicable to a variety of heat exchanger units that comprise one or more tube and fin assemblies  12 . 
     As evident in  FIG. 3 , the barrier  22  comprises a filtration media that has trapped certain potential contaminants of the condenser assembly  10 . In particular, the barrier  22  has trapped relatively coarse debris  18  of a size that would have resulted in the debris  18  becoming entrapped within the condenser assembly  10 , for example, between adjacent fins  16  and/or between the two sets of tube and fin assemblies  12 . However, the barrier  22  is configured to intentionally allow the passage of relatively finer contaminants, for example, particulate debris  20 , whose individual particles are sufficiently small to pass completely through the condenser assembly  10 , in other words, between adjacent fins  16  of the condenser assembly  10 . For example, the contamination barrier  22  is intended to prevent relatively large contaminants, for example, leaves, paper, fibrous materials, and other relatively large debris often present in an outdoor environment, from reaching the tube and fin assemblies  12 , while allowing passage of relatively fine contaminants, for example, dust particles, dirt, etc., that are capable of passing between adjacent fins  16  of the condenser assembly  10 . As such, the filtration media is preferably sized so that openings within the media are sized to correspond to the particular spacing between the fins  16 . As a nonlimiting example, the openings within the filtration media may be roughly the same size or slightly smaller than the distance between adjacent fins  16 . 
     In contrast,  FIG. 1  illustrates the contamination of the condenser assembly  10  resulting from the condenser assembly  10  being unprotected, such that both coarse and fine debris  18  and  20  have become trapped within and between the tube and fin assemblies  12 . Even after an intensive cleaning process,  FIG. 2  illustrates that further contamination buildup occurs as a result of the remaining coarse debris  18  within the condenser assembly  10  promoting entrapment of the finer debris  20 . 
     The contamination barrier  22  preferably utilizes a filtration media having a lofty, high-weave configuration that, as schematically represented in  FIG. 3 , enables certain individual coarse debris  18  to wrap itself around an individual fiber at the outer surface or within the interior of the media, thus reducing the surface area of the debris  18  that would present itself as an obstruction to incoming airflow through the barrier  22 . In turn, the lofty configuration of the filtration media enables incoming air to flow around an obstruction created by a coarse debris  18 , thereby minimizing the total pressure drop through the barrier  22 . Furthermore, finer debris  20  (for example, less than about 100 micrometers) is able to freely pass through the barrier  22 . Examples of finer debris  20  observed to be capable of passing through the barrier  22  include, but are not limited to, cottonwood seeds, small insects, pollen, dust, etc. 
     In a particular commercial embodiment of the invention, the filtration media of the barrier  22  is constructed of 100% polyester material with a stiffening agent applied during manufacturing for strength and a UV additive to withstand prolonged sunlight exposure. The media may have a thickness of about one to two centimeters, for example, about one-half inch (about 1.3 cm), which is sufficiently lofty to allow airflow around contamination trapped in its fibers. Significantly thicker filtration media tend to reduce thermal transfer efficiency by increasing the initial pressure drop through the barrier  22 , whereas significantly thinner filtration media tend to not enable sufficient airflow around coarse debris  18  trapped within the barrier  22 . 
     The contamination barrier  22  can be produced in rolls of a mat or sheet material, whose length can be cut according to the dimensions of the heat exchanger unit on which the barrier  22  is to be installed. This allows the contamination barrier  22  to be applied to the vast majority of existing HVAC systems. An example of an installation of the contamination barrier  22  on a roof-mounted condenser unit  24  of a commercial HVAC system is schematically represented in  FIG. 4 . The contamination barrier  22  is applied across an exposed face of the condenser, such that the one or more tube and fin assemblies (e.g.,  12  in  FIG. 3 ) of the condenser unit  24  are concealed by the contamination barrier  22 . In this manner, the contamination barrier  22  may also serve to protect the tube and fin assemblies from accidental damage from human or other activities. 
       FIG. 5  is another possible embodiment of the invention, representing a process of installing the contamination barrier  22  on a condenser unit  24 . The barrier  22  is in the form of a roll of sheet material having two oppositely-disposed parallel edges that run the as-manufactured length of the barrier  22 . The installation length of the barrier  22  can be selectively sized to correspond to a first dimension of the condenser unit  24  (for example, the widths that can be seen in  FIGS. 4 and 5 ) of the condenser unit  24  by cutting transverse to the length of the barrier  22 . In preferred embodiments, the width of the barrier  22  (transverse to its length) can be pre-sized to correspond to the dimension of the condenser unit  24  transverse to its first dimension, for example, the particular height of the condenser unit  24  visible in  FIG. 4 . 
       FIG. 6  illustrates a method by which the contamination barrier  22  may be attached to the condenser units  24  of  FIGS. 4 and 5 .  FIG. 6  is a cross-sectional view showing one of the parallel edges  38  of the contamination barrier  22  and a clip  26  that preferably extends the entire width of an opening  36  of the condenser unit  24  through which the tube and fin assemblies  12  (not shown) are exposed to incoming air. The clip  26  is mounted to a wall  34  of the condenser unit  24  that defines the opening  36  of the condenser unit  24 . The clip  26  can be manufactured from various materials, for example, extruded PVC, and can be secured with any suitable fasteners, including mechanical fasteners, adhesives, etc., for example, threaded fasteners (not shown) that pass through a flange  32  of the clip  26  and into the wall  34 . The barrier  22  is subsequently secured with the clip  26  by pushing the edge  38  of the barrier  22  through a narrow slot  28  defined by and between two opposing appendages  30  of the clip  26 . In preferred embodiments of the invention, the slot  28  is sufficiently narrow to enable the use of a blunt blade (not shown) to push the edge  38  of the barrier  22  through the slot  28  in the direction of the arrow in  FIG. 6 . The orientation of the example shown in  FIG. 6  corresponds to the upper edge  38  of the barrier  22 , and a similar operation can be envisioned for the oppositely-disposed lower edge of the barrier  22  as a mirror image of that illustrated in  FIG. 6 . This simple technique is able to securely hold the contamination barrier  22  in place, while being capable of withstanding a wide variety of environmental extremes. 
     The contamination barrier  22  can be fabricated from various materials. However, as previously discussed, the filtration media of the contamination barrier  22  must provide filtration of relatively coarse debris  18  while allowing passage of finer particulate debris  20  that is sufficiently small to pass through the condenser assembly  10  and, in particular, between the fins  16  thereof. In doing so, the barrier  22  is preferably capable of achieving several notable benefits. First, the barrier  22  is adapted to promote the efficiency of the condenser assembly  10  be excluding the buildup of debris and other contaminants within the assembly  10 . Furthermore, the barrier  22  preferably provides this benefit without significantly reducing airflow through the condenser assembly  10 , particularly in comparison to prior art contamination barriers intended to not only prevent coarse debris  18  but also finer and particular debris  20  from entering a condenser unit. As a result of the barrier  22  not intentionally entrapping finer particulate debris  20 , buildup of contamination on the barrier  22  itself is reduced, thereby extending the service life of the barrier  22 . In certain environments, the contamination barrier  22  is self-cleaning, in other words, wind and rain effectively remove coarse debris  18  from the out surface of the barrier  22 , with the result that the barrier  22  requires little or no regular maintenance. Because of the potential for an extended service life, the contamination barrier  22  can be economically constructed of disposable materials and disposed of at the end of its useful life. 
     As a result of promoting the cleanliness of the condenser assembly  10 , the overall efficiency of an HVAC system can be maintained, thereby reducing energy consumption over the life span of the system. In some instances, energy consumption has been reduced between 12.5% and 30% as compared to unprotected HVAC systems. 
     As also previously noted, the barrier  22  also has the potential for protecting the tube and fin assemblies  22  of a condenser unit  24  from environmental or human contact. For this purpose, the filtration media preferably has sufficient strength and durability to remain secured by the clips  26  (or other suitable securing means) while withstanding adverse environmental and operating conditions. 
     While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the contamination barrier  22  and the heat exchanger unit  24  on which it is installed could differ from those shown, and various materials and processes could be used to construct and install the contamination barrier  22 . Therefore, the scope of the invention is to be limited only by the following claims.