Abstract:
In a system for cleaning, and for maintaining a desired temperature in, the air within the interior of a building, an activated carbon filter is disposed in a filter housing forming part of a conduit connected from a supply duct to a return duct. Air flows through the activated carbon filter as a result of the difference between the pressures of the air in the respective ducts, and substantially the entire quantity of air within the building is passed through the carbon filter in a short time.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to systems for maintaining the air within the interior of a building at a desired temperature, such as forced-air heating systems, air-conditioning systems, and combined forced-air heating and air-conditioning systems (HVAC) systems. The invention relates particularly to an easily installed apparatus for cleaning the air as it circulates through the system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many homes and commercial buildings are plagued by indoor pollutants and odors from various sources such as new construction materials, cleaning chemicals, cooking, and pets. Pollutants also enter buildings from the outside, and can be troublesome especially where there are high levels of outdoor pollution. The problem of pollutants and odors can be especially severe in commercial establishments such as nail salons, hair salons, pet stores, and other buildings in which chemicals are used regularly. Even in buildings where there is no noticeable contamination, inhabitants frequently desire clean and healthy indoor air, free from unknown pollutants. In addition, airborne volatile organic compounds (VOCs) are known to cause formicary (“ant tunnel”) corrosion of system components, including corrosion that results in leaks to evaporator coils in air conditioning apparatus. 
       SUMMARY OF THE INVENTION 
       [0003]    Conventional filters, including fiber filters and electrostatic filters, although effective in removal of airborne particulate matter, are ineffective in the removal of odors and pollutants in gas or vapor form. Carbon filters are capable of adsorption of gas and vapor, but require a relatively long contact time to be effective. Carbon filters have been used to replace and upgrade existing fiber filters, and are sized to fit the openings used for fiber filters in existing ductwork. These carbon filters can remove chemical gases and odors, but, because they replace fiber filters, they must also filter both particulate dust and dirt. Carbon filters quickly become clogged with dirt, and also tend to restrict air flow. Since they cover the entire cross-section of a return duct, they need to allow a large volume of air to pass through them at a high speed. Therefore, the amount of carbon in these filters is limited in order to minimize restriction of air flow. The limitation on the amount of carbon, in turn, limits the filters&#39; adsorption capacity. A carbon filter can be preceded by a fiber filter in an air return duct. However in such an arrangement, and also when a carbon filter is used by itself, the air velocities are such that the contact time is too short for the carbon filter to remove pollutants efficiently. 
         [0004]    There is a need for a simple and effective apparatus for removal of odors and gaseous and vapor-form pollutants in heating and air conditioning systems. There is also a need of an apparatus that can be added to an existing system without the need for major modifications to the ductwork of that system, and that will not impair the air flow in the system by excessive restriction. This invention answers these needs. 
         [0005]    Briefly, the invention is a simple and easy-to-install, add-on, by-pass carbon filtration system for removing indoor air pollutants, odors, VOCs and other gases, and from residential and commercial buildings. The system is effective in homes and buildings with moderate to high levels of indoor pollutants or odors emanating from various sources, such as new construction materials, cooking, pets, cleaning chemicals, and outdoor environments having high levels of outdoor pollution. The system can be used in commercial buildings such as nail or hair salons, pet stores, and other buildings in which VOCs and other chemicals of various kinds are used, and in any residence or commercial building the interior of which is liable to be contaminated by airborne gases, vapors and odors. The system can also be used in homes or buildings having no noticeable contamination, but in which the residents or inhabitants desire to remove unknown indoor air pollutants in order to be confident that they are breathing clean, healthy, indoor air. 
         [0006]    Unless otherwise indicated, the term “air handler” as used herein means a heating system, an air conditioning system, or a combined heating and air conditioning system. 
         [0007]    The preferred system utilizes a filter housing that holds a removable, high capacity activated carbon air filter. In an air handler system of a building, the filter housing is connected to existing supply and return ducts, using conduit parts lengths of flexible, insulated duct, so that the filter-housing and the flexible conduit parts form a by-pass path allowing a portion of the air that would otherwise flow into the interior of the building to flow through the carbon filter through by-pass path. The system is easily retrofitted to an existing air handler, requiring only a small amount of time and labor. 
         [0008]    In the operation of the apparatus, whenever the air handler is running, a small fraction of the supply air is diverted through the carbon filter to the return side of the system. Over time, substantially all of air in the building will have passed through the carbon filter, and large quantities of indoor air pollutants will have been removed by the activated carbon. Because of the relatively slow flow of air through the by-pass path in which the carbon filter is situated, the contact time of the air with the activated carbon in the filter is increased, and efficient adsorption of airborne contaminants is achieved. The air that flows through the carbon filter will have been filtered already by the existing particulate air filter or filters in the air handling system. Therefore, the carbon filter will not be readily fouled by dust, which would shorten its life. In an air handling system utilizing the invention, the carbon filter should be changed about every six months. The flow through the carbon filter in the by-pass path in a typical domestic air handling system is approximately 50-70 CFM, which represents an insignificant loss, but is nevertheless enough to filter substantially all of the air in the building many times over between filter changes. 
         [0009]    In more particular terms, the invention is a system for cleaning, and for maintaining a desired temperature in, the air within the interior of a building. 
         [0010]    The system comprises a first air flow path, a heat exchanger forming a part of the first air flow path, and apparatus, connected to the heat exchanger, for modifying the temperature of the air in the first air flow path. A supply duct, which is a part of the first air flow path, is arranged to deliver air from the heat exchanger to the interior of the building. A return duct, which is also a part of the first air flow path, is arranged to deliver air from the interior of the building to the heat exchanger. 
         [0011]    A blower, which constitutes part of the system, is arranged to cause air to flow from the return duct, and, through the heat exchanger, to the supply duct. 
         [0012]    A conduit, connected from the supply duct to the return duct, provides a second air flow path that by-passes the first air flow path. An activated carbon filter in this conduit is arranged to filter air flowing through the second air flow path from the supply duct to the return duct. As result of a difference between the pressure of air in the supply duct and the pressure of air in the return duct resulting from operation of the blower, a fraction of the air in the interior of the building passes through the activated carbon filter when the blower is operating. 
         [0013]    The system preferably includes at least one fiber filter disposed in the first air flow path upstream of the heat exchanger. 
         [0014]    The conduit preferably comprises a filter-containing unit for containing the activated carbon filter, a first conduit part connecting the filter-containing unit, to the supply duct on one side of said activated carbon filter, and a second conduit part connecting the filter-containing unit to the return duct on an opposite side of said activated carbon filter. The activated carbon filter preferably has an air flow cross-sectional area, larger than the air flow cross-sectional areas of either of the first and second conduit parts. In a preferred embodiment, the filter-containing unit has a central filter-containing part, a first tapered transition on one side of the central filter-containing part for connection to the first conduit part and a second tapered transition on an opposite side of the filter-containing part for connection to the second conduit part. 
         [0015]    Preferably, the activated carbon filter is removable from the conduit for replacement. 
         [0016]    Among the advantages of the invention are the fact that it enables a high capacity carbon air purification device to be added easily to existing air handling system. In addition, the disposition of the carbon filter in a by-pass path eliminates air restrictions, and avoids fouling of the carbon filter by particulate matter, thereby extending its life. 
         [0017]    Another advantage is ease of installation. Atypical installation of the carbon filter and by-pass conduit in an existing air handling system requires less than one hour. No additional electric wiring is required for installation of the carbon filter. 
         [0018]    Finally, the carbon filter can use blends of activated carbons designed to remove the wide ranges of indoor air pollutants, and can remove the VOCs that cause formicary corrosion and leaks in evaporator coils. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic diagram of a system, in accordance with the invention, for cleaning, and for controlling the temperature of, the air in the interior of a building; and 
           [0020]      FIG. 2  is an exploded perspective view of the by-pass conduit including the carbon filter and the carbon filter housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]      FIG. 1  shows a heating, ventilating and air conditioning (HVAC) unit  10  for a building. The HVAC unit includes a blower  12  for circulating air through a heat exchanger  14 . The heat exchanger can be used to heat or cool the air, or both to heat and cool the air, depending on the relationship between the desired temperature and the current air temperature. Air exits the heat exchanger through a supply duct  16 , which can be connected to heat vents throughout the building by a network of branches (not shown). Air is returned to the HVAC unit through a return duct  18 , which is similarly connected to return ports throughout the building by another network of branches. A fiber filter  20 , for removal of particulate matter from the circulating air, is disposed in the path of the air flowing into the HVAC unit through the return duct  18 . Thus, the return duct, the blower, the heat exchanger, the supply duct, and the interior of the building, are all parts of a first air flow path, through which air is circulated by operation of blower  12 . The system described so far is conventional, and typical of a forced air heating, ventilating and air conditioning system in a residential or commercial building. Other arrangements are of course possible in conventional HVAC systems. For air can be returned to the HVAC unit through two or more return ducts, each having its own particulate filter, and air can be supplied to the building interior through two or more supply ducts, each being connected to receive air passed through the heat exchanger. The heat exchanger can also be designed simply for the purpose of heating, or for cooling, but not both, and in the case of a system designed both for heating and cooling, the heating and cooling parts of the heat exchanger can be separate from each other. In all cases, however, the system will have a heat exchanger, a supply duct, a return duct and a blower. 
         [0022]    As shown in  FIG. 1 , in addition to the conventional components described above, the system includes a conduit  22 , which provides a second air flow path that by-passes the first air flow path composed of the return duct, the supply duct, the blower, the heat exchanger and the building interior. Conduit  22  comprises a filter-containing unit  24 , a first conduit part  26  connecting the filter-containing unit  24  to the supply duct  16 , and a second conduit part  28  connecting the filter-containing unit  24  to the return duct  18 . The filter-containing unit  24  can be made from sheet metal, or any of a variety of other materials. For example, it can be molded from synthetic resin. 
         [0023]    A removable activated carbon filter  30  is disposed within the filter-containing unit  24 . Thus, the conduit parts  26  and  28 , which connect the filter-containing unit  24  respectively to the supply and return ducts, are on opposite sides of the activated carbon filter. 
         [0024]    As shown in  FIG. 2 , the activated carbon filter  30  is removable from the filter-containing part  24  for replacement, and has a cross-sectional area through which air can flow that is greater than the internal cross-sectional areas of each of the conduit parts  26  and  28 . A central, filter-containing part  32  of the filter containing unit is made large enough to accommodate the filter  30 , and the filter-containing unit is formed with tapered transitions  34  and  36 , which connect the central part  32  to the respective conduit parts  26  and  28 . 
         [0025]    The central part  32  has a rectangular opening  38  for insertion and removal of the filter, and a closure  40 , which fits frictionally onto the central, filter-containing part  32 , is provided to close the opening when the filter is in place. Various other forms of closures, such as a hinged door, can be used as alternatives to closure  40 . 
         [0026]    The conduit part  28  is preferably formed from a length of flexible duct  42 , typically having a circular cross-section and an internal diameter of four inches. The length of duct  42  is surrounded by a quantity of glass fiber insulating batting  44 , which is in turn contained within a flexible tubular cover  46 . Conduit part  28  is similarly constructed. The conduit parts are connected to tubular end portions  48  and  50  of the tapered transitions on the filter-containing part  32 , and to the supply and return ducts through adapters  52  and  54 . Resilient wire loops(not shown) can be used to clamp the ends of the flexible ducts to the tubular end portions and adapters, and duct tape can be used to seal the connections. 
         [0027]    In the operation of the apparatus, the pressure difference across the filter unit will typically produce a flow in the range from about 50-70 CFM through the filter when the blower is operating, depending on the static pressure within the duct system. The loss in air flow through the building resulting from flow of air through the by-pass path through the carbon filter is not significant. Nevertheless, with good air circulation within each of the individual rooms of a typical family dwelling, substantially all the air in the building will have passed through the filter within a few hours, e.g., 4 to 5 hours, of blower operation. 
         [0028]    Various forms of activated carbon can be used in the filter  30 . An activated carbon blend, known as “Carbon Z,” a mixture of activated carbon and potassium permanganate (KMnO 4 ), is preferred. Carbon Z is capable of high capacity removal of a wide range of airborne pollutants. The activated carbon component is capable of adsorption of most VOCs and other gases typically found in indoor air. However formaldehyde, which can be emitted into the air from various sources including building material and furnishings, poses a serious health risk, is not adsorbed well by carbon, but is efficiently removed by potassium permanganate. Various other mixtures of which activated carbon is a principal component can be used in this application. 
         [0029]    A typical filter in this application can be expected to operate satisfactorily in a 10 ton HVAC system for nine months, depending on the level of airborne contaminants. However, since contaminant levels are unknown, the activated carbon filter should be replaced every six months.