Gas separation – With separate flow line access means or filter media passage... – Access means is clamping or coupling means for unit filter...
Reexamination Certificate
2001-06-26
2003-09-23
Simmons, David A. (Department: 1724)
Gas separation
With separate flow line access means or filter media passage...
Access means is clamping or coupling means for unit filter...
C055S481000, C055S492000, C055S493000, C055S508000, C055S511000, C055SDIG003, C055SDIG003
Reexamination Certificate
active
06623540
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to forced air heating, ventilating and air conditioning systems and more particularly to a filter unit used at the end of a duct in such a system. The invention is particularly suited for use in an evaporative cooling system.
2. Description of Related Art
Virtually all modern buildings, whether residential, commercial or industrial, are equipped with systems for maintaining the air inside the building at a comfortable temperature and humidity, and reasonably free from airborne contaminants. A substantial art and industry supporting the design, fabrication and installation of such systems has grown up. This is often identified as the heating, ventilating and air conditioning (HVAC) art and industry, the term HVAC comprehends heating, cooling, filtering and related treating of air inside the building. Many such systems incorporate the forced movement of air within the structure through the HVAC apparatus; this type of system may be termed a forced air system.
The present invention is most closely related to the residential segment of the HVAC industry, though it will be recognized that HVAC apparatus for commercial and industrial structures comprise many of the same features as residential apparatus, differing primarily in size.
Those skilled in the HVAC arts recognize that there are many types of HVAC apparatus in widespread use today; they will also recognize that although the following discussion is couched in terms of representative types of apparatus, it is applicable to many other types of apparatus.
In temperate climates, which will be arbitrarily defined for this discussion as having frequent daily summertime temperatures in excess of 80° F. and frequent overnight wintertime low temperatures below 40° F., one very common type of HVAC system comprises a central heating/cooling apparatus, with a system of supply ducts for distributing the heated or cooled air throughout the structure and a system of return ducts for collecting air from various portions of the structure and returning said air to the heating/cooling apparatus. A filter is typically incorporated in such a system; it is typically situated in a return duct immediately adjacent to the heating/cooling apparatus. As the air inside the structure is recirculated through the living space in the structure and the HVAC apparatus, this HVAC system is termed a closed-loop system.
One purpose of filter elements in HVAC systems is to keep dust and dirt inside the structure down to a manageable level. Another purpose is to reduce the likelihood of injuries to the lungs of occupants of the building, where such injuries may result from breathing dirty air. However, the effectiveness of any filter apparatus depends on its design, and whether it is properly maintained. Maintenance typically means replacement of disposable filter elements or cleaning of reusable filer elements. If the heating/cooling apparatus is situated in a basement or utility room, maintaining or cleaning the filter element is relatively easy. However, if the heating/cooling apparatus is situated in a crawl space or attic, access to a filter is very difficult.
The type of filter element most commonly used in residential HVAC systems is comprised of a batt of glass fibers supported by expanded or perforated metal screens and a paper frame. Such filter elements are inexpensive, but also ineffective. Such filter elements typically remove less than ten percent of airborne particulate matter from the air passing through the filter element. Even where access to the filter element in an HVAC system is reasonably convenient, all but the most conscientious occupants of the structure are likely to maintain the filter less frequently than should be done. Where access to the filter is difficult, maintenance may be nonexistent.
Another type of HVAC system is frequently employed in hot dry climates, which will be arbitrarily defined for this discussion as having frequent daily summertime temperatures in excess of 95° F. and prevailing dew points below about 60° F. This is an evaporative cooler, also known as a swamp cooler. In such an apparatus, ambient air is drawn from the exterior of the structure across constantly moistened evaporator elements. Water on the evaporator elements vaporizes, absorbing the requisite heat of vaporization from the moving air stream. If the dew point of the ambient air is low enough, the air stream can absorb enough moisture to reduce its temperature to a comfortable indoor temperature. Because the effectiveness of an evaporative cooler depends upon the low dew point of the incoming air, these systems are operated as open-loop systems. Air is discharged from the interior of the structure to the outside air through exhaust ducts or open windows.
Because evaporative coolers operate as open-loop systems, all air entering the living space of the structure will contain whatever dirt and dust may be present in the ambient outdoor air. Typically, in a hot, dry climate, the air is very dusty and likely to contain dead vegetative matter. Also, any solids dissolved in the water used to moisten the evaporator elements will add to the airborne particulate matter as the water is evaporated. In addition, bacteria and mold may grow in the HVAC apparatus, creating another class of undesirable contaminants in the moving air stream. For structures of similar size, the volume of air passing through a swamp cooler is generally several times that passing through a closed-loop HVAC system. All of these factors point to a greater need for effective filtration in an open-loop HVAC system than in a closed-loop system. As evaporative coolers are frequently situated on the roof of a structure, rendering access to a filter located near the cooling unit impossible, filters are generally omitted from such HVAC apparatus.
In summary, filters in closed-loop HVAC systems are ineffective and filters in open-loop HVAC systems are nonexistent. Recognition of the need for more effective and more easily maintained filters for both closed-loop and open-loop HVAC systems led to the present invention. However, recognition of that need was only one factor in the present invention. Another factor was the realization that occupants of a structure can most easily maintain the filters in the HVAC system of that structure if the filter is situated within the living space thereof. Yet another factor was the discovery that those skilled in the HVAC arts had not heretofore adequately addressed that need.
The most relevant prior art known to the inventors comprises three patents issued to Hodge (U.S. Pat. Nos. 5,525,145, 5,690,719 and 5,989,303) and patents issued to Mack et al (U.S. Pat. No. 5,944,860) and Liedl (U.S. Pat. No. 5,176,570). The Hodge '145 and '719 patents and the Liedl patent are particularly relevant, for they identify a most preferred location for a filter in an HVAC system, namely, over a duct end at the point where that duct is joined to the living space within a room. The Hodge patents also provide an extensive survey of the HVAC arts existing as of the filing dates thereof, 1993 and 1995, respectively. Accordingly, disclosures of the Hodge '145 and '719 patents are incorporated herein by reference. Liedl's teachings differ from Hodge's to the extent that the only location he teaches for his filter apparatus is over a return air duct end.
The Hodge '303 and Mack et al patents disclose pleated or fanfold filter elements that are situated within the air distribution or collection ducts. While the latter two patents disclose filters installed near the duct end, those filters are actually installed within the duct, which creates considerable inconvenience in installing the filter apparatus and considerable difficulty in maintaining the filter elements. As for filtering effectiveness, a pleated filter element does have a larger filter surface area than a planar element, thereby reducing the restriction to the air passing theretrough, but at the expense of
Clayton Robert L.
Hodge Michael T.
Bardes Bruce P.
Pham Minh-Chau T.
Simmons David A.
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