THERMOELECTRIC DEVICE FOR DEFOGGING AND DEFROSTING APPLICATIONS

BACKGROUND OF THE INVENTION This application relates to the use of a thermoelectric cooler for providing defogging or defrosting of cold surfaces associated with a climate-controlled space, while not appreciably affecting conditions in the climate-controlled space.

Various enclosure and cabinet structures include surfaces that may be transparent or reflective and typically need to maintain this transparency or reflection functionality over a lifetime, particularly during air conditioning or refrigeration equipment operation. As an example, in grocery stores, items are often displayed in refrigerated cases. In a refrigerated case, a glass door typically seals an enclosed refrigerated space from the outside environment, and at the same time, allows for the content of the refrigerated case to be displayed and be accessible. Cooled air is circulated within the climate-controlled space of the refrigerated case. The door faces the hotter, and typically more humid outside environment on one face, and the cold or refrigerated air of the enclosure on its other face. In fact, an air curtain is often delivered along the inner face of the door to prevent intrusion of the outside air, for instance, during periods of time when the door is opened. Although the glass doors of the refrigerated cases are typically well insulated, frequent opening of the doors, as well as respiration of the produce inside the refrigerated case, can lead to fogging of the glass doors, which is highly undesirable.

Various other transparent or reflective cold surfaces associated with climate- controlled spaces may experience a similar problem. For example, windows or mirrors in stationary applications, such as bottle coolers, wending machines, merchandisers, bathrooms, etc., and mobile applications, such as commercial and personal vehicles, mobile refrigerators, etc., can become fogged. Similarly, some of these type surfaces can be exposed to frost.

One option which has been recently proposed for incorporation into refrigerant systems is the use of thermoelectric coolers. The thermoelectric cooler essentially takes advantage of specific thermoelectric properties of dissimilar semiconductor

materials and is based on two phenomena - the Peltier effect and Seebeck effect, concurrently taking place during operation of the thermoelectric device. The Peltier effect is associated with the release or absorption of a finite heat flux at the junction of two electrical conductors, made from different materials and kept at constant temperature, at the presence of electric current. Similarly, the Seebeck effect is related to the same arrangement, where the two junctions are maintained at different temperatures, which would create a finite potential difference, and an electromotive force that would drive an electric current in the closed-loop electric circuit.

The Peltier and Seebeck effects are presented simultaneously in the thermoelectric cooler that is preferably made from materials that have dissimilar absolute thermoelectric powers. The finite electric current passing through the two junctions triggers two heat transfer interactions with two cold and hot reservoirs kept at different temperatures. For steady thermoelectric cooler operation, heat fluxes associated with the two junctions should have opposite signs. If the external system maintains potential difference and drives electric current against this difference, the two-junction system becomes a thermoelectric cooling device.

A typical thermoelectric cooler consists of an array of P-type and N-type semiconductor elements that act as the two dissimilar conductors. The P-type material has an insufficient number of electrons and the N-type material has extra electrons. These electrons in the N-type material and so-called "holes" in the P-type material, in addition to carrying an electric current, become a transport media to move the heat from the cold junction to the hot junction. The heat transport rate depends on the current passing through the circuit and the number of moving electron-hole couples. As an electric current is passed through one or more pairs of P-N elements, there is a decrease in temperature at the cold junction resulting in the absorption of heat from the object to be cooled. The heat is carried through the thermoelectric cooler by electron transport and released at the hot junction as the electrons move from a high to a low energy state.

Although the thermoelectric devices are inherently irreversible, since heat and electric current must flow through the circuit during their operation, they do not have moving parts that makes them extremely reliable and quiet.

Thermoelectric devices have not been applied to providing defogging or defrosting of cold surfaces associated with a climate-controlled space, to address the problems mentioned above, while not appreciably affecting conditions in the climate- controlled space.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a controlled surface having a direct contact with a flow of cold air circulating within a climate-controlled space is provided. Air conditioning or refrigeration equipment supplies the flow of cold air to the climate-controlled space. A thermoelectric device is associated with the controlled surface and maintains it without formation of fog, frost or condensate. The controlled surface may be predominantly transparent or reflective and will sustain these properties during air conditioning or refrigeration equipment operation without fogging or frosting. On the other hand, the controlled surface may be made of conventional construction materials, such as aluminum, steel or plastic, and will not allow formation of any condensate to cause dripping and wet spot initiation in undesired locations within the climate-controlled space.

A thermoelectric device associated with the controlled surface is located within the climate-controlled space, with its hot junction positioned in the path of the airflow, and provides defogging, defrosting or condensate evaporation for the controlled surface. A cold junction of the thermoelectric device may be positioned downstream of the hot junction on the path of the airflow to reduce the air temperature towards its original value and relieve the air stream from at least some amount of moisture. This condensate collected on the cold junction is directed to a drain pan and removed from the climate-controlled space, while the controlled surface is defogged, defrosted or dried out. This defogging or defrosting functionality is provided by the thermoelectric device without interruption of the cooling mode of operation.

A thermoelectric device may be continuously operated or it may be activated on demand, for instance, based on a timer setting or a sensor feedback. Such sensors are generally known in the industry and could be of a chilled mirror type, capacitance

type, resistance type or any other type. Furthermore, a thermoelectric device may be provided with a variable power supply, and therefore various amounts of heating and cooling can be transferred respectively by a hot junction and a cold junction to the passing airflow, for instance, by varying voltage to the power supply, in order to adjust thermoelectric device operation to variable environmental conditions.

A thermoelectric device and its junctions may be incorporated into the controlled surface structure or may be applied as an add-on device.

If a power supply polarity for a thermoelectric device is reversed, the hot junction and the cold junction are swapped. This in turn allows for additional cooling to be provided by the cold junction of the thermoelectric device to the associated controlled surface.

This invention can be applied to any transparent or reflective controlled surface, such as glass doors, windows or mirrors, or any other general purpose controlled surface positioned within the climate-controlled environment. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically shows a refrigerated enclosure incorporating the present invention.

Figure 2 is an enlarged view of a portion of the Figure 1 refrigerated enclosure.

Figure 3 shows a generic representation of a controlled surface incorporating the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a refrigerated enclosure 20 incorporating a glass door 22 allowing access to the refrigerated produce as well as providing a transparency function for a consumer to observe the content of the refrigerated enclosure 20. The refrigerated enclosure 20 may include various construction elements such as shelves

24 and the like. Cold air is circulated within the climate-controlled space of the

refrigerated enclosure 20 to provide cooling to the produce that may be placed inside the refrigerated enclosure 20. In addition, an air curtain is provided along the glass door 22 to prevent intrusion of the outside air as well as escape of the cold air to the ambient environment during the door openings. A return air duct 18 delivers air from the climate-controlled space of the refrigerated enclosure 20 to a refrigeration system heat accepting heat exchanger, such as an evaporator 30. The air then returns through a return air duct 32 and through vents 36 and 37 into the climate-controlled space of the refrigerated enclosure 20. The vent 37 is generally positioned to provide the air curtain 26. The evaporator 30 is incorporated within a refrigeration system including at least basic components such as a heat rejecting heat exchanger, a compressor, an expansion device and a pair of air- moving devices associated with heat rejection heat exchanger and evaporator 30. The refrigeration system may be an integral component of the refrigerated enclosure 20 or may be of a slide-in configuration. An air-moving device, such as fan 28, associated with and typically positioned downstream of the evaporator 30, provides cold airflow to the climate-controlled space of the enclosure 20 that is cooled and often dehumidified while passing through the evaporator 30.

The air curtain 26 is thus typically at the same cold temperature as the air circulated within the interior of the refrigerated enclosure 20. The glass door 22 has its outer face exposed to the ambient environment 100 and its inner face in contact with the air curtain 26. Typically, the air curtain 26 has much lower temperatures and moisture content than the ambient environment 100. Therefore, it is typical that the glass door 22 can become fogged, for instance, during the door openings. The glass door 22 may also become fogged due to respiration of the produce placed within the refrigerated enclosure 20.

The present invention positions a thermoelectric device 44 associated with the glass door 22 and the air curtain 26 within the climate-controlled space of the refrigerated enclosure 20 such as the hot junction 38 of the thermoelectric device 44 is in the path of the air leaving the vent 37 and before it flows over the glass door 22. Due to heat transfer interaction between the curtain air stream leaving the vent 37 and the hot junction 38 of the thermoelectric device 44, the air curtain 26 will be at a

higher temperature than the rest of the air circulating within the interior of the refrigerated enclosure 20. Therefore, the warmer air of the air curtain 26 will be able to absorb moisture that could accumulate on the interior face of the glass door 22 in the form of fog, condensate or frost. As a result, the transparency function for the glass door 22 will be maintained, as desired.

The cold junction 40 of the thermoelectric device 44 is positioned near the end of the air path of the air curtain 26, and will serve to cool the air toward the original temperature, as well as dehumidify the air, as it returns to flow through the evaporator 30. The condensate removed from the air stream by the cold junction 40 of the thermoelectric device 44 is collected in a drain pan 45 and then removed from the refrigerated enclosure 20.

The airflow in the air curtain 26 over the hot junction 38 is shown in detail in Figure 2. It has to be pointed out that both the hot junction 38 and the cold junction 40 of the thermoelectric device 44 are shown schematically and may have any shape or configuration. For instance, to enhance heat transfer, the hot junction 38 and the hot junction 40 may have airflow channels of any suitable cross-section, extended secondary heat transfer surface, such as heat transfer fins or ribs, and heat transfer enhancement elements, such as louvers or boundary layer disruptors. Generally, these heat transfer enhancement elements are known in the art. Further, the cold junction 40 may have incorporated condensate drainage paths in the form of troughs or valleys that may be shielded from the airflow to prevent condensate carryover. Further, elements of the thermoelectric device 44, such as the hot junction 38 and the cold junction 40, may be attached to the structure of the glass door 22 or may be even integrated into the door structure, for instance, in the form of lamination positioned close or at the inner face of the glass door 22.

It should be understood that the thermoelectric device 44 can provide defogging or defrosting functionality without interruption of the cooling mode of operation for the refrigeration unit associated with the refrigerated enclosure 20. Moreover, the thermoelectric device 44 may be continuously operated or it may be activated on demand, for instance, based on a timer setting or a sensor feedback. Such sensors are generally known in the industry and could be of a chilled mirror type,

capacitance type, resistance type or the like. Furthermore, a thermoelectric device may be provided with a variable power supply, and therefore various amounts of heating and cooling can be transferred respectively by a hot junction and a cold junction to the passing airflow, for instance, by varying voltage to the power supply, in order to adjust thermoelectric device operation to variable environmental conditions. Such variable environmental conditions may be caused, for instance, by less or more frequent door openings, higher or lower respiration items placed into refrigerated enclosure and changing ambient conditions.

Moreover, if a power supply polarity for a thermoelectric device 44 is reversed, the hot junction 38 and the cold junction 40 will be swapped. This in turn allows for additional cooling to be provided by the cold junction (now 38) of the thermoelectric device 44 to the associated controlled surface, such as the glass door 22, and to the entire climate-controlled environment of the refrigerated enclosure 20. This mode of operation could be executed during the periods of time when defogging or defrosting of the glass door 22 is not required. The heat generated by the hot junction (now 40) in this mode of operation, will be removed by the refrigeration unit associated with the refrigerated enclosure 20.

As shown in Figure 3, rather than the glass door 22, other controlled surfaces 46 associated with the thermoelectric device 44 may benefit from the positioning along the path of the airflow moving over a hot junction 48, and then over the cool junction 50, in sequence. Surfaces such as windows, glass partitions and separators or mirrors in stationary or transport applications can benefit from this invention. Also, any general purpose controlled surface 46 positioned within the climate-controlled environment that tends to accumulate condensate, fog or frost can benefit from the invention. Some examples may include, but are not limited to, windows in buildings, mirrors in the bathrooms, glass partitions in the refrigerated displays, windows and mirrors in the cars, shelves in the merchandisers and many others. In addition, in appropriate circumstances, this invention can be utilized to defrost or remove condensate from the controlled surface 46. While several embodiments and applications are disclosed, a worker of ordinary skill in this art would recognize that the disclosed applications are exemplary

and many other applications could benefit from the disclosed invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.