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result of their efforts was ready in less than five months, and was
unveiled to the world at Domotechnica in Cologne, Germany, in
February.
Challenges Met
The key element of the ATR is the
system's ability to efficiently deal with heat loads. "When you
look at reducing the amount of heat that has to be pumped, there is
a crossover point at about 20 watts to 30 watts," say John
Nelson, Vice President, Marketing and Sales, Marlow Industries,
"As you lower the heat level in a refrigerator, compressors are
forced to cycle on and off more, which decreases their efficiency.
So as heat loads become smaller, thermoelectric coolers are able to
approach the efficiency levels of compressor-based systems.
"Since we
couldn't put 10 inches of foam around the the refrigerator cabinet
and have it be of any value, incorporating the Aura Superinsulation
vacuum panels was the only way to get the heat loads down to the
range we needed."
Aura is a
CFC-free, thermally tailored fiberglass media encased in stainless
steel and hermetically sealed. A vacuum is pulled on it to produce
vacuum panels.
While
the Aura vacuum panels are being used in compressor-refrigerant
systems in Europe and the U.S., the ATR represented Aura's greatest
challenge, says Ralph McGrath, global product and technology
manager, Owens-Corning. "With this prototype, we decided to
avoid the use of polyurethane foam in the design. A
fiberglass-reinforced plastic cabinet was designed to eliminate the
need for polyurethane foam used to enhance structural integrity (and
for its thermal-insulation properties in conventional refrigerator
designs). The inner and outer shells of the refrigerator were
fastened together to provide a freestanding arrangement with a
cavity for the Aura panels."
While the ATR
technology can be incorporated into more traditional refrigerator
designs requiring polyurethane foam for structural integrity, the
prototype proves that it is possible to effectively eliminate the
need for Polyurethane form.
"What this
means is that it is possible for even "greener" systems
using water blown or CO2 urethane foam, with the
insulation properties being provided by Auro.
Another
key to the ATR's ability to lessen heat loads is the phase-change
material. This is basically a paraffin material that melts during
periods of high heat loads, absorbing heat and maintaining the
chamber at low temperatures explains
Nelson: "When the user stocks the refrigerator with vegetables
and/or meats at ambient temperature, heat from those foods must be
removed. We didn't want to do that by increasing power to the
thermoelectric assembly, because if we did, then the efficiency of
the system would be decreased. Instead, we remove the heat from the
products by using the heat pumping capacity of the phase-change
material." During low heat loads,
the thermoelectric cooler assembly regenerates the phase-change
panel material. And when the material is completely regenerated, the
whole system shuts off until needed.
Another
environmental advantage of the ATR is its use of recyclable
components, such as the Aura panels and thermoelectric cooler
assembly (aluminum and semiconductor materials).
Article courtesy
of Appliance Manufacturer ©, Joe Jancsurak, July 1995
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