Refrigeration – Processes – Defrosting or frost inhibiting
Reexamination Certificate
1999-06-15
2001-05-08
Tanner, Harry B. (Department: 3744)
Refrigeration
Processes
Defrosting or frost inhibiting
C062S265000, C062S275000, C454S192000
Reexamination Certificate
active
06226995
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to prevention of frost accumulation on a freezer door using an air mover.
2. Background of the Invention
Condensation and frost accumulation on machinery and other useful apparatus is an undesirable effect in many industrial applications. Depending on the particular apparatus, frost and/or condensation may impede air flow, create an unwanted layer of insulation, accelerate rusting and fouling processes, or distort the output from measurement instruments. Frost accumulation is of special concern with respect to freezer, cooler, and refrigerator doors. Frost tends to bind and reduce spatial tolerances of the moving mechanisms of such doors, and impairs visibility of door windows. Frost also engenders the formation of ice and water on the floor area near such doors, creating a safety hazard.
In one known method for preventing frost accumulation on the warm side of freezer doors, air is taken from the warm side of the doors, passed over heating apparatus, and redistributed to the warm side to establish convection currents along the warm side surfaces of the doors. This method is not optimally designed in that the water vapor content of the warm side air is not removed during the heating process. It is well known that the process of passing air over a typical dry surface heater, such as a heater coil, is a sensible heating process which increases only the dry bulb temperature of the air. Since no moisture is added to or removed from the air during this process, the humidity ratio, dew point temperature and latent heat content of the air do not change. This process can be graphically approximated by a horizontal line on a psychrometric chart. Therefore, frost accumulation is prevented only because of the increased air velocity of the redistributed air along the surface of the doors.
The present invention is directed to a process and apparatus that take advantage of the cold side air already conditioned by the pre-existing refrigeration equipment in the freezer. In many freezer applications, the cold side air is both cooled and dehumidified such that the cold side air is drier than the warm air on the other side of the freezer doors. For many food storage lockers, this will also be true even though the refrigeration equipment maintains a desired level of humidity to reduce the rate of respiration and subsequent dessication of the stored food. Accordingly, the process and apparatus of the present invention described below act to draw air from the freezer, and heat and distribute this air across the warm side of the doors. As a result, prevention of frost accumulation is achieved not only because of increased air velocity, but also because the localized region of warm air adjacent to the warm side surface of the doors has a decreased dew point temperature.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, a frost control system for preventing the accumulation of frost on components of a freezer door assembly is disclosed. The system comprises a movable door disposed between a cold space and a warm space, and a header assembly. The header assembly comprises an outer housing, an electrically powered air mover disposed within the housing, and an air inlet adapted for drawing air from the cold space to an inlet of the air mover. A conduit is provided for conducting air from an outlet of the air mover to a region of the warm space proximate to the door, and a thermostatically-controlled heater is disposed within the conduit. The conduit includes a first portion inside the header in communication with the air mover and a second portion outside the header, within the warm space, and adjacent to the door. The second portion communicates with a first heated air exhaust vent. A transition portion is connected between the first and second portions. Also provided is control circuitry for managing the operation of the heater and air mover.
In another embodiment, an air mover assembly is disclosed in combination with a frost control system comprising a movable door disposed between a cold space and a warm space, a header disposed above the door and housing the air mover assembly, and ductwork containing air heaters and adapted to direct heated air to a region of the warm space adjacent to the door. The air mover assembly comprises a blower housing having a front side, a rear side, a top side, a bottom side and two opposing transverse sides. The front side is adapted to receive air within the header drawn from the cold space, the rear, top and bottom sides are closed, and the transverse sides communicate with the ductwork. An impeller is mounted within the blower housing and has an inlet communicating with the front side. The impeller is adapted to radially discharge air from the inlet.
In another embodiment, a heated air exhaust duct section is disclosed in combination with a frost control system comprising a movable door disposed between a cold space and a warm space, a header disposed above the door and housing an air mover assembly adapted to receive air from the cold space, and duct work containing an air heater and adapted to direct air discharged from the air mover assembly to a region of the warm space adjacent to the door. The exhaust duct section includes a heated air discharge vent on an outside surface of the exhaust duct section. The exhaust duct section is removably connected to the ductwork downstream from the air heater and rotatable with respect to the ductwork. The heated air exhaust duct section may include means for adjusting a discharge area of the discharge vent. Additionally, the heated air exhaust duct section includes a band clamp for removably and rotatably attaching the exhaust duct section to the ductwork.
A method is also disclosed for preventing the accumulation of frost on a door assembly situated between a cold space and a warm space. Cold air is drawn from the cold space into a manifold and then directed into an inlet of a centrifugal blower. The cold air is discharged from the centrifugal blower into ductwork. One or more heaters disposed within the ductwork are used to heat the cold air. The heated air is discharged from a vent formed in the ductwork at a location disposed downstream from the heater and proximate to a lower region of the door assembly adjacent to the warm space, to develop convection currents of heated air flowing across a width of the door assembly and across a length of the door assembly towards an upper region of the door assembly. An exhaust vent may also be installed in the ductwork at a location proximate to windows of the door assembly to better ensure that a sufficient amount heated air flows across surface of the windows.
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Drifka Brian Norbert
Kalempa Walenty
Rytec Corporation
Tanner Harry B.
Wallenstein & Wagner Ltd.
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