Refrigeration – Automatic control – Humidity sensor
Reexamination Certificate
1999-05-28
2001-07-10
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Humidity sensor
C062S515000, C062S272000
Reexamination Certificate
active
06257006
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for cooling air through use of a heat exchanger, and more particularly to a cooling method and cooling apparatus which can maintain the relative humidity in a refrigerator or a room at a level close to 100%, which improves energy efficiency, and which allows humidity control.
BACKGROUND ART
In order to cool air, there has conventionally been employed a method in which from, a refrigerant that substitutes for fron, water, a thermal accumulating medium, or an antifreeze agent is caused to flow through a heat exchanger disposed inside a refrigerator or a room, and in which forced circulation or free convection of air is caused such that air passes through the heat exchanger in order to cool the air. Also, in order to obtain a high humidity, there has been developed and employed a cooling method, called a “chilled scheme” in which cooling is effected over an entire wall surface through use of a similar refrigerant. Further, a cooling scheme based on the Peltier effect or the like has recently come into use.
In order to improve heat absorption by a refrigerant, a metal having a high heat conductivity such as copper or aluminum is utilized as a constituent material of a heat exchanger. In a Peltier element as well, heat exchange is performed through a metal or ceramic having a high heat conductivity. In such case, due to high heat conductivity, the temperature of a refrigerant becomes equal to the surface temperature of a heater exchanger, and in the case of fron, the surface temperature is determined by the evaporating temperature of fron. This holds true in the case where water, a thermal accumulating agent, or an antifreeze agent is used; in such a case the temperature of the water, thermal accumulating agent, or antifreeze agent becomes equal to the surface temperature of the heat exchanger.
Humid air has been known to contain water vapor. Although the amount of water vapor in humid air is 1-2% by weight or less, the latent heat of the water vapor has an effect that must be taken into account in the design of a cooling method and a cooling apparatus, because evaporation and condensation occur even at room temperature. The maximum amount of water vapor contained in air increases with temperature. Air containing the maximum amount of water vapor is called saturated air, whose absolute humidity is the highest for the given temperature and pressure. When air in a certain state is cooled to have a decreased temperature, the air comes into a saturated state, so that water vapor condenses. The temperature at which air comes into a saturated state is called the dew-point temperature. When wet air is cooled to a temperature below the dew-point temperature, water vapor condenses so that a phenomenon of dew formation occurs. Changes in the state of air in a conventional cooling apparatus will be described with reference to an air chart of FIG.
1
. Point A indicates a state in which air has an absolute humidity x
1
and a temperature T
1
. In order to cool the air, the air is circulated over a heat exchanger having a surface temperature t
d
equal to the temperature t
d
of a refrigerant. As indicated by the solid line E, the temperature of the circulated air—which flows along the surface of the heat exchanger—changes from T
1
to T
2
, while the humidity changes from x
1
to x
3
, so that the air reaches an equilibrium point D. By this time, the absolute humidity of the air has decreased to a value corresponding to the maximum amount of water vapor that can exist at the surface temperature t
d
of the heat exchanger, which is identical to the temperature of the refrigerant, so that the relative humidity of the circulated air decreases accordingly. In the conventional cooling scheme in which the surface temperature of the heat exchanger becomes equal to the temperature of the refrigerant, since the surface temperature of the heat exchanger decreases and the dew-point temperature decreases accordingly, the absolute humidity of air decreases, resulting in a dehumidification operation. Accordingly, in such an heat exchange system, moisture within air is cooled excessively and thereby dew-condensed, and dewed moisture is discharged to the outside in the form of water or frost. In other words, energy is wasted.
Meanwhile, the specific enthalpy of wet air is known to increase with the absolute humidity even at constant temperature. When air is subjected to heat exchange by a conventional heat exchanger, the air is dried, and the amount of latent heat in the air decreases considerably. Therefore, a temperature difference of 10° C. or more between the inlet and outlet of the heat exchanger has been considered a necessary condition for effecting cooling. That is, since the amount of latent heat of air is small, a required temperature cannot be maintained unless a certain temperature difference is provided for the internal and external thermal loads. Accordingly, when cooling is performed through use of the conventional heat exchanger, air is dried and energy is wasted, due to the very nature of the heat exchanger.
When the conventional cooling apparatus and cooling method are applied to a cooling apparatus in which a refrigerant is caused to flow through a heat exchanger disposed in a refrigerator or room in order to perform heat exchange, the space inside the refrigerator or room is dried, and in the case of the refrigerator, the cooling apparatus and cooling method are not suitable for storage of flesh foods for a prolonged period of time. In the case of cooling the space inside the room, air is dried excessively, so that a larger amount of moisture transpires from the skin, which causes cooling-related diseases. Further, as described above, moisture within air is cooled and discharged outside a refrigerator or room in the form of water, resulting in loss of energy.
DISCLOSURE OF THE INVENTION
Recalled here is cooling by use of ice. Conventional cooling through use of ice is known to provide a high humidity. In cooling through use of ice, the melting temperature of the ice is constant, and the surface temperature of the ice is always constant. That is, while heat is exchanged between the ice and air, heat is absorbed by the ice at the surface thereof in the form of heat of fusion. Therefore, during heat exchange between the ice and air, the dew-point temperature is constant, and only the temperature of the air changes without a decrease in the humidity of the air, so that cooling can be effected while a high humidity is maintained.
An object of the present invention is to realize a cooling apparatus which does not decrease humidity as in the case of ice, and which produces a smaller temperature difference between an inlet and an outlet of a heat exchanger, i.e., reduces energy loss. In order to achieve the object, in a cooling method and cooling apparatus of the present invention, a material having a low heat conductivity is employed as a material of a heat exchanger, in place of a conventionally-employed material having a high heat conductivity such as cooper or aluminum which makes the surface temperature of the heat exchanger equal to the temperature of a refrigerant. Due to employment of a material having a low heat conductivity, a thermal gradient is produced between the refrigerant and the surface of the heat exchanger, so that the temperature at the surface of the heat exchanger becomes higher than that of the refrigerant. Some materials cause the heat exchanger to have a surface temperature close to the temperature of circulated air. That is, since the heat exchanger has an increased surface temperature, the dew-point temperature increases accordingly, so that the absolute humidity is increased. Since cooling is performed in a state in which the absolute humidity is maintained at a high level, the relative humidity is increased, and cooled air having a high humidity can be obtained.
Although the refrigerant exchanges heat in the form of sensible heat, only the temperature of circulated air can be changed without a decrease in
Michaelson Peter L.
Michaelson & Wallace
Tanner Harry B.
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