| There are several types of evaporators used in boat
refrigerators and the holding plate is also an evaporator. Evaporators are
the component in the refrigerator where the liquid refrigerant vaporizes
and absorbs the heat. Evaporators are made in four different styles each
having different design application advantages.
- Flat
thin plates (shell type) used to line the inside walls of the
refrigerated box. The main advantage is it can absorb heat over a
large area at a fast rate.
- A
thin plate formed into a box providing a dual, purpose refrigerator, a
chamber for freezing and refrigeration for the rest of the box. The
main advantage is it allows even the smaller boxes to be separated
into a freezer- refrigerator.
- Fin
tube type with forced air circulation. This type of evaporator is used
for better overall box heat absorption and frost-free refrigeration. I
sold this type of unit years ago and called it a Freeze Blast a
similar unit is now marked by WACO.
- Holdover
type evaporator better know as Holding Plates are designed to hold a
eutectic solution. The solution freezes at a certain temperature, 0 to
+10 °
for a freezer box or 24 to 26 °
for a refrigerator. The latent heat of melting increases the length of
holdover time while holding a more constant temperature.
The major advantage of a holding
plate type of evaporator is that it stores energy and the larger the plate
the more energy is stored.
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There are disadvantages
associated with each type of evaporator:
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The thin plate units do
not store energy and require a continuous power source around the
clock
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Thin plates are generally fabricated from Aluminum and are
easily damaged by sharp objects
and corrosion.
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Holding
plates are much slower in lowering the temperature of the surrounding
area than the thin plate evaporators, this is due to surface area of
the plate and heat transfer through the plate.
The chart below compares a 15inch Adler/ Barbour thin
plate box chamber evaporator and a holding plate.
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Chamber Evaporator Versus a Holding Plate
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TEST
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Evaporator Type
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Hours Compressor
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Total AMP=Hrs
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Avg.Temp
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Box Temp High
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Box temp
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Run
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High
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Low
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115
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Adler Barbour
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55.4
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38.3
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38.3
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37.4
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129/130
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Holding Plate
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50.2
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39.7
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46.9
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36.5
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The holding plate in this comparison was 9.4% more
efficient than the chamber evaporator. The box temperature swing is
much greater from a low of 36.5° to a high of 46.9°F.
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