Refrigeration – Processes – Circulating external gas
Reexamination Certificate
2002-12-12
2004-03-30
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Circulating external gas
C062S271000
Reexamination Certificate
active
06711907
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to air conditioning and dehumidification equipment, and more particularly to an air conditioning method and apparatus using desiccant wheel technology.
It is well known that traditional air conditioning designs are not well adapted to handle both the moisture load and the temperature loads of a building space. Typically, the major source of moisture load in a building space comes from the need to supply external make-up air to the space since that air usually has a higher moisture content than required in the building. In conventional air conditioning systems, the cooling capacity of the air conditioning unit therefore is sized to accommodate the latent (humidity) and sensible (temperature) conditions at peak temperature design conditions. When adequate cooling demand exists, appropriate dehumidification capacity is achieved. However, the humidity load on an enclosed space does not vary directly with the temperature load. That is, during morning and night times, the absolute humidity outdoors is nearly the same as during higher temperature midday periods. Thus, at those times there often is no need for cooling in the space and therefore no dehumidification takes place. Accordingly, preexisting air conditioning systems are poorly designed for those conditions. Those conditions, at times, lead to uncomfortable conditions within the building and can result in the formation of mold or the generation of other microbes within the building and its duct work, leading to what is known as Sick Building Syndrome. To overcome these problems, ASHRAE Draft Standard 62-1989 recommends the increased use of make-up air quantities and recommends limits to the relative humidity in the duct work. If that standard is properly followed, it actually leads to a need for even increased dehumidification capacity independent of cooling demands.
A number of solutions have been suggested to overcome this problem. One solution, known as an “Energy Recovery Ventilator (ERV),” utilizes a conventional desiccant coated enthalpy wheel to transfer heat and moisture from the make-up air stream to an exhaust air stream. These devices are effective in reducing moisture load, but require the presence of an exhaust air stream nearly equal in volume to the make-up air stream in order to function efficiently. ERVs are also only capable of reducing the load since the delivered air will always be at a higher absolute humidity in the summer months than the return air. Without active dehumidification in the building, the humidity in the space will rise as the moisture entering the system exceeds the moisture leaving in the exhaust stream. However, ERVs are relatively inexpensive to install and operate.
Other prior art systems use so-called cool/reheat devices in which the outside air is first cooled to a temperature corresponding to the desired building internal dew point. The air is then reheated to the desired temperature, most often using a natural gas heater. Occasionally, heat from a refrigerant condenser system is also used to reheat the cooled and dehumidified air stream. Such cool/reheat devices are relatively expensive and inefficient, because excess cooling of the air must be done, followed by wasteful heating of air in the summer months.
A third category of prior art device has also been suggested using desiccant cooling systems in which supply air from the atmosphere is first dehumidified using a desiccant wheel or the like and the air is then cooled using a heat exchanger. The heat from this air is typically transferred to a regeneration air stream and is used to provide a portion of the desiccant regeneration power requirements. The make-up air is delivered to the space directly, or alternatively is cooled either by direct or indirect evaporative means or through more traditional refrigerant-type air conditioning equipment. The desiccant wheel is regenerated with a second air stream which originates either from the enclosure being air conditioned or from the outside air. Typically, this second air stream is used to collect heat from the process air before its temperature is raised to high levels of between 150° F. to 350° F. as required to achieve the appropriate amount of dehumidification of the supply air stream. Desiccant cooling systems of this type can be designed to provide very close and independent control of humidity and temperature, but they are typically more expensive to install than traditional systems. Their advantage is that they rely on low cost sources of heat for the regeneration of the desiccant material.
U.S. Pat. Nos. 3,401,530 to Meckler, 5,551,245 to Carlton, and 5,761,923 to Maeda disclose other hybrid devices wherein air is first cooled via a refrigerant system and dried with a desiccant. However, in all of these disclosures high regeneration temperatures are required to adequately regenerate the desiccant. In order to achieve these high temperatures, dual refrigerant circuits are needed to increase or pump up the regeneration temperature to above 140° F. In the case of the Meckler patent, waste heat from an engine is used rather than condenser heat.
U.S. Pat. No. 4,180,985 to Northrup discloses a device wherein refrigerant condensing heat is used to regenerate a desiccant wheel or belt. In the Northrup system, the refrigerant circuit cools the air after it has been dried.
The invention as described in our parent application Ser. No. 08/795,818 is particularly suited to take outside air of humid conditions, such as are typical in the South and Southeastern portions of the United States and in Asian countries and render it to a space neutral condition. This condition is defined as ASHRAE comfort zone conditions and typically consists of conditions in the range of 73-78° F. and a moisture content of between 55-71 gr/lb. or about 50% relative humidity. In particular, the system is capable of taking air of between 85-95° F. and 130-145 gr/lb. of moisture and reducing it to the ASHRAE comfort zone conditions. However, that system also works above and below these conditions, e.g., at temperatures of 65-85° F. or 95° F. and above and moisture contents of 90-130 gr/lb. or 145-180 gr/lb.
As compared to conventional techniques the invention of the parent application has significant advantages over alternative techniques for producing air at indoor air comfort zone conditions from outside air. The most significant advantage being low energy consumption. That is, the energy required to treat the air with a desiccant assist is 25-45% less than that used in previously disclosed cooling technologies. That system uses a conventional refrigerant cooling system combined with a rotatable desiccant wheel. The refrigerant cooling system includes a conventional cooling coil, condensing coil and compressor. Means are provided for drawing a supply air stream, preferably an outdoor air stream over the cooling coil of the refrigerant system to reduce its humidity and temperature to a first predetermined temperature range. The thus cooled supply air stream is then passed through a segment of the rotary desiccant wheel to reduce its moisture content to a predetermined humidity level and increase its temperature to a second predetermined temperature range. Both the temperature and humidity ranges are within the comfort zone. This air is then delivered to the enclosure. The system also includes means for regenerating the desiccant wheel by passing a regeneration air stream, typically also from an outside air supply, over the condensing coil of the refrigerant system, thereby to increase its temperature to a third predetermined temperature range. The thus heated regeneration air is passed through another segment of the rotatable desiccant wheel to regenerate the wheel.
It is an object of the present invention to treat outside supply air at any ambient condition and render it to practically any drier and cooler psychrometric condition with lower enthalpy.
Yet another object of the present invention is to provide a desiccant based dehum
Dinnage Paul A.
Young Kevin H.
Doerrler William C.
Munters Corporation
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