Heat exchange – With timer – programmer – time delay – or condition responsive... – Control of heat pipe heat transfer characteristics
Reexamination Certificate
2000-10-24
2003-07-15
Ford, John K. (Department: 3743)
Heat exchange
With timer, programmer, time delay, or condition responsive...
Control of heat pipe heat transfer characteristics
C165S272000, C165S104140, C165S104210, C062S090000, C062S095000
Reexamination Certificate
active
06591902
ABSTRACT:
FIELD OF INVENTION
The present invention is generally directed to an apparatus and method for use in heating, ventilation, and/or air conditioning systems (“HVAC systems”). More particularly, the present invention is directed to an apparatus and method employing a controllable, multipurpose heat pipe system that provides an improved, more energy efficient HVAC system. Advantages of the present invention are especially apparent when the present invention is applied to buildings utilizing centralized HVAC systems.
BACKGROUND OF THE INVENTION
HVAC systems generally function to heat or cool air to a more comfortable temperature by manipulating the transfer of heat. For example, an air conditioning system may contain a cooling coil that absorbs heat from hot air to lower the air's temperature. Similarly, a heating system may utilize a heated gas or liquid to transfer heat to cold air to increase the air's temperature.
Heat transfer from or to air may be effected within such HVAC systems by the use of a working fluid or refrigerant, such as ammonia, R134a (tetrafluoroethane), or similar fluids. These working fluids are generally capable of changing state under various conditions of temperature and pressure. With each change of state, the working fluid either accepts energy or gives up energy. As a result, this energy is either removed or added to the air, respectively, so that cold air may be heated or hot air may be cooled.
In a conventional air conditioning system, the working fluid generally moves in the following cycle of operation: (1) from a compressor; (2) to a condenser; (3) through an expansion valve; (4) to an evaporator; and then (5) back to the compressor. In one such air conditioning system, the working fluid enters the compressor as a low temperature gas at about 65 F. and leaves the compressor as a high temperature gas at about 150 F. The working fluid then enters the condenser. Within the condenser, the working fluid thermally communicates with, and gives up heat to, surrounding cooler air, and the working fluid is converted from a high temperature gas into a cooler liquid of about 90 degrees F. The working fluid then passes through an expansion valve to a region of low pressure. As a result, the working fluid begins to change state from a liquid to a low temperature gas of about 45 degrees F. The working fluid then moves to the evaporator, where the working fluid thermally communicates with, and absorbs heat from, hot air surrounding the evaporator. As heat is transferred from the hot air to the working fluid, the hot air is cooled, and the working fluid is heated to become a gas of about 65 degrees F.
In general, an air conditioning system may provide sensible cooling and latent cooling. Sensible cooling is associated with reducing the temperature of air, while latent cooling is associated with decreasing the moisture content of air (dehumidification). For example, when air is cooled, but is not cooled below its dewpoint, only sensible cooling has occurred. On the other hand, when air is cooled to its dewpoint (approximately 60 degrees F.), moisture in the air begins to condense, and dehumidification (latent cooling) of the air begins. If the air is cooled below its dewpoint, further dehumidification occurs. Therefore, when air is cooled below its dewpoint, both sensible and latent cooling have occurred, because the air's temperature has been reduced (sensible cooling), and moisture has been removed from the air (latent cooling). In order for conditioned air to be comfortable to humans, the air must be at a comfortable temperature, and it must contain an appropriate level of moisture.
In some air conditioning systems, air is reheated after being cooled and dehumidified. In one such air conditioning system, warm air enters at approximately 80 F. The air then moves through the system's evaporator and is typically cooled to approximately 55 degrees F. or lower. During this cooling process, when the air temperature reaches its dewpoint (approximately 60 degrees F.), moisture in the air condenses (dehumidification begins). As the temperature of the air falls below the dewpoint, additional moisture is removed from the air. Such cooling normally produces air that is colder than desired for human comfort. However, this degree of cooling is often required to provide the necessary amount of dehumidification. In essence, the air conditioning system's evaporator generally overcools the air in order to remove an appropriate amount of moisture. Accordingly, some air conditioning systems reheat the dehumidified air to a more comfortable level. Such systems are very energy inefficient, because excess energy is used in the overcooling (dehumidification) and reheating processes.
Heat pipes are passive devices that may be used to heat or cool air by manipulating the transfer of heat from a heat source to a heat sink, or vice versa. Heat pipes may contain a precise amount of working fluid or refrigerant, such as ammonia. The working fluid is generally contained within the heat pipe and may be cycled continuously through at least two elements: an evaporator and a condenser. Adiabatic section(s) may be included in the heat pipe to allow the working fluid to pass between the evaporator and the condenser without transferring heat to or from the surroundings.
Evaporators and condensers are generally configured to allow heat exchange with the environments that surround them. For example, a heat pipe evaporator may be configured to absorb heat from a heat source, such as hot, unconditioned air that passes around the evaporator. Similarly, a heat pipe condenser may be configured to release heat into a heat sink, such as cool, conditioned air that passes around the condenser. As such, a heat pipe may act as either a heater or a cooler depending on its orientation.
In general the heat pipe's working fluid enters a heat pipe's evaporator in a liquid state. The working fluid in the evaporator absorbs heat from a heat source, such as hot, unconditioned air. As a result, the hot air may be cooled, and the working fluid is transformed from a liquid to a vapor. The vaporized fluid then passes from the evaporator, through an adiabatic section (in some embodiments), into a condenser. In the condenser, the vapor releases heat to a heat sink, such as cool, conditioned air. As a result, the cool air may be heated, and the working fluid is transformed from a vapor to a liquid within the condenser. The condensed working fluid is then returned to the evaporator, in a liquid state, by the force of gravity and/or capillary forces through a wick. The return path may be through an adiabatic section or other connecting section.
To improve conditioning performance, some air conditioning systems utilize heat pipe heat exchangers. In these systems, heat pipe technology is used to increase moisture removal capacity and/or to provide passive reheat capability. Such systems are disclosed in U.S. Pat. No. 2,093,725 to Hull; U.S. Pat. No. 4,607,498 to Dinh; U.S. Pat. No. 4,971,139 to Khattar and U.S. Pat. No. 5,695,004 to Beckwith.
Generally, conventional dehumidification heat pipe systems have been used in the following manner. Hot air enters the HVAC system. The heat pipe may be used to precool the hot air before the hot air is cooled by the air conditioning system. In such a system, a heat pipe may be disposed around the air conditioning system's main cooling coil (or main evaporator). Generally, the heat pipe's evaporator will be positioned upstream of the main cooling coil, while the heat pipe's condenser is positioned downstream of the main cooling coil. As such, the hot air passes over the heat pipe's evaporator and heat may be absorbed from unconditioned hot air by the heat pipe's evaporator. This precool the air. Then the precooled air passes over the system's main cooling coil and is cooled further and becomes dehumidified. The heat may then be transferred via the heat pipe's condenser to cool the dehumidified air that leaves the cooling coi
Dvtkiewicz Edward P.
Ford John K.
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