Refrigeration – Processes – Circulating external gas
Reexamination Certificate
2000-02-05
2002-08-06
Tapolcai, William E. (Department: 3744)
Refrigeration
Processes
Circulating external gas
C062S176100, C062S176600
Reexamination Certificate
active
06427454
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of air conditioning by refrigeration and in particular to the control of the level of humidity independently of the temperature, while using fresh, return or ambient air from the controlled space to preventing over cooling. The invention provides independent humidity control while preserving as much heat as possible from the inlet air thus limiting sensible cooling relative to latent cooling without using expensive reheat or additional coils.
BACKGROUND
Air conditioning and controls for adjusting the air-conditioning equipment, to achieve a desired comfort zone by controlling the temperature and humidity levels, are well known. Such devices are shown in numerous patents described below. Any such air conditioning system typically uses a chilled fluid or a circulating refrigerant in a heat exchanger coil as a conditioning means to cool and dehumidify air before it is forced into an indoor controlled space. The rate of cooling provided by some systems of this kind, such as chilled fluid systems, is varied in response to a thermostat placed within the indoor space being cooled, with variations occurring in a smooth manner to maintain a chosen temperature level at the thermostat. In other systems, such as split-systems and package units, the air conditioning system compressor turns on and off in response to the thermostat. In recent years, some manufacturers have incorporated humidity sensing into their controls. Humidity control has typically been accomplished through adjustment of the temperature set point or calculation of a comfort condition based on a combined temperature-humidity setting, rather than through a control strategy based on user selectable separate temperature and humidity set points.
It has long been recognized that proper air conditioning systems should not only lower the temperature of the interior space being served when the temperature therein has exceeded a predetermined level but should also control the relative humidity of the space as a function of the air conditioning. During operation of a typical air conditioning system, air from the space to be conditioned is circulated over a heat exchanger. The heat exchanger absorbs heat energy from the air lowering its dry bulb temperature. If the temperature of the air is lowered below its dew point, then moisture from the air is condensed onto the heat exchanger surfaces and the actual amount of moisture contained in the air is reduced.
Most air conditioning systems provide dehumidification passively as a byproduct of cooling. In most systems, the amount of dehumidification delivered by the system is not sensed, controlled, or responsive to the user's needs. Most currently available systems control the amount of cooling delivered by the heat exchanger coil, but not the amount of dehumidification. The space temperature or temperature of a room for example, is maintained within a few degrees of the user's setting, however, the space humidity typically swings up and down, as temperature varies. At times of low load and humid conditions, this swing in humidity can be plus or minus 20% rh resulting in space humidity levels that exceed the maximum comfort levels of 60-70% rh recommended by ASHRAE (American Society of Heating Air-Conditioning and Refrigeration Engineers). Supply duct humidity typically exceeds 90% rh in such systems. The maximum recommended humidity level for supply ducts is 70% rh to prevent fungal growth. These recommended humidity levels are independent of temperature. Present-day air-conditioning system's have not adequately addressed these problems. Excessive energy consumption, complexity, expense, coil freezing, and/or premature compressor failure have confined the practicality of systems that claim to address these problems to specialized applications.
One such system shown in U.S. Pat. No. 5,802,862, which describes a combined, reheat coil runaround system. U.S. Pat. Nos. 4,350,023 and 4,448,597 describe a control scheme for a reheat apparatus that has an additional coil located downstream of the evaporator coil, referred to as a sub-condenser. A similar arrangement is described in U.S. Pat. No. 4,182,133, which uses one coil with multiple circuits, and in U.S. Pat. No. 5,622,057. One of the earliest examples of reheat is described in U.S. Pat. No. 2,451,385, with a variation described in U.S. Pat. No. 2,685,433, in which first cooling and then heating are sequentially provided through separate air streams. By its very nature, heating air after considerable energy has been expended to cool said air is wasteful and results in significantly increased energy expense. The additional heat exchanger coils that are required make such systems expensive to install and more difficult to maintain.
Reheat can be provided with no additional energy expense by exchanging heat from the air entering the coiling coil to the air exiting the cooling coil, as described in U.S. Pat. No. 4,428,205. A current example of this technology is wrap around heat pipes, which significantly increase equipment cost.
U.S. Pat. No. 4,984,433 describes an air conditioning system with a variable sensible heat ratio. The system includes a variable speed supply air fan and a plurality of subcooling coils. The controller senses temperature and humidity and tracks their change over time to predict if the latent and sensible needs will be satisfied simultaneously. When it is desired to remove more latent heat than sensible heat, the supply air fan speed is reduced and subcoolers are activated. This system requires expensive components including a variable speed fan and additional refrigerant coils and solenoids. As with previous inventions of this type, energy waste and the problems of coil freezing and liquid entering the compressor are not solved.
U.S. Pat. No. 3,938,348 describes a unit in which an evaporator coil is maintained at a selected cool or dew point temperature constantly, regardless of whether cooling is required. The compressor is turned on and off, or it is a two-speed, or two compressors are used to constantly maintain the evaporator at a selected temperature. U.S. Pat. No. 5,346,127 describes an air handler arrangement where air flow through the coil is varied, according to the sensible load, via face and bypass dampers.
U.S. Pat. No. 4,485,642 describes a heat exchanger air bypass for humidity control by a manually set damper apportioning the air flowing through the heat exchanger and bypassing the heat exchanger. U.S. Pat. No. 5,303,561 describes a controller that produces a slower fan speed when conditions are humid, based on temperature and humidity sensors. The system modulates the indoor fan speed to attempt to stay within the comfort envelope defined by combined relative humidity and temperature measurements. Other examples are disclosed in U.S. Pat. No. 2,236,058 which describes a variable speed fan; U.S. Pat. No. 2,296,530 which describes a face damper only; U.S. Pat. Nos. 2,685,433; 3,251,196 which describes three staged fans; and U.S. Pat. No. 4,003,729 which, describes a variable speed fan in conjunction with a coil temperature sensor. U.S. Pat. No. 5,346,129 describes a controller that starts a condensing unit in response to an error signal that is a combination of temperature and humidity. Another combined controller is described as in U.S. Pat. No. 5,850,968, which is a comfort controller replacement for a conventional thermostat.
U.S. Pat. No. 4,105,063 discloses an air conditioning system with a sensor responsive to a predetermined maximum moisture content, operated in parallel with the normal dry-bulb temperature control. U.S. Pat. No. 4,889,280 discloses an auctioning controller wherein the predetermined dry-bulb temperature set point is modified in response to an absolute humidity error signal. Another controller is described in U.S. Pat No. 5,195,473, which operates a system having an HVAC control and a humidity limiting control.
SUMMARY OF THE INVENTION
According to the inventive principles as disclosed in connection with the p
Ali Mohammad M
Rosenblatt Joel I.
Tapolcai William E.
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