In the United States and elsewhere in
the world, refrigerators are a nearly universal kitchen appliance.
Refrigerators perform the fundamental tasks of preserving food,
keeping beverages chilled, and making ice.
Of all household appliances, the
refrigerator consumes the most energy. Unlike the intermittent use of
other applicances, it must fight a 24/7 battle to keep the kitchen's
heat from invading its interior. Specifically:
- Heat is constantly conducting
through its walls
- Its doors are opened many times
throughout each day, exposing its interior to the warmer kitchen
- Its fan motor and compressor
generate heat underneath the unit
[Diagram of the heat flows]
The refrigerator itself is basically
a steel box with doors on one side and a refrigeration system in its
base. To minimize the conduction of heat through its walls, insulation
is packed in between its inner and outer shells. Until recently,
polyurethane foam was most common insulating material. Environmental
concerns have forced the replacement of foam with xxxxx, which, though
more expensive, has superior insulating performance.
Cooling the air inside the
refrigerator is accomplished through a series of coils that run
through the back wall of the unit. A refrigerant fluid runs through
these coils. Until recently, the most commonly used fluid was Freon.
As with the foam insulation, manufacturers have stopped using Freon
for environmental reasons. Its replacement, CRC XX, does not have any
adverse effect on the environment.
As the refrigerant itself passes
through evaporator coils inside the refrigerator's walls, it draws
heat away from the inside air, causing the air temperature to drop. As
the heat conducts through the walls and coils, the temperature of the
refrigerant increases, causing the refrigerant to transform from a
liquid to a vapor. This vapor routes through the compressor where its
temperature and pressure increase. Next, the vapor passes through the
condensing coils mounted on the outside of the refrigerator. As a fan
blows room air over the coils, the temperature of the vaporized
refrigerant falls, causing it to condense back to a liquid. During the
transformation, the latent heat of the refrigerant is transferred
through the coils to the room air. As the condensed refrigerant is
passed through an expansion valve on its way back to the evaporator
coils, its pressure drops, and the cycle begins again.
[Diagram of cycle]
Although a refrigerator is
"on" all the time, almost all of its energy consumption
takes place when its compressor is turning. A thermostat inside the
refrigerator activates the compressor whenever the inside temperature
drops below the set point.
Over the last twenty years, energy
consumption of comparably sized refrigerators has dropped an average
of 75%. This is not a misprint. Higher efficiency compressors,
improved insulation, and better door seals have been responsible for
most of this improvement. In 2006, the U.S. Department of Energy (DOE)
will raise energy standards by another 20%.
With the magnitude of these
efficiency gains, almost every refrigerator more than 15 years old can
be justified for immediate replacement based on energy savings alone.
The table below illustrates the payback potential.
Under present standards, any
refrigerator using at least 10% less electricity per year than the DOE
standard is designated as an Energy Star appliance. When shopping for
a new refrigerator, look for the Energy Star label and the Energy
Guide label. The latter will explicitly state the annual operating
cost for the unit at an average $/kilowatt-hour. To obtain your actual
cost, multiply the given annual cost by your marginal $/kilowatt-hour
and then divide by the average $/kilowatt hour shown.
Source: U.S. DOE
If you have the original
documentation from your current refrigerator, it may show the annual
electrical consumption. By comparing your current annual cost to the
new unit's annual cost, you can establish your annual savings
potential. The higher the savings, the quicker your payback on the
purchase price. A payback of 3 years equates to a tax-free return on
investment of 30%. Do you have a better investment opportunity?
Next: Energy Savings
Opportunities - No Cost
Copyright © 2003 HEM Technologies, LLC. All rights reserved.