Are frost-free freezers more efficient?
by Stephen
(London, UK)
Frost-free freezers are usually less efficient than manual defrost freezers, because they use a fan to circulate air and prevent frost buildup. But ratings are usually done by running the freezer for 24 hours and extrapolating a yearly kWh use - so they presumably don't take into account the reduction of efficiency from the buildup of frost in a manual freezer. Do you think this actually makes frost-free freezers more efficient? Is there any measure of the amount of additional energy consumed from even a modest frost buildup, less than the 6mm or so which is recommended as the limit beyond which one should defrost? If it is significant, then frost free might be best, even though it uses more energy. Please advise!
Answer from Green Energy Efficient Homes
The good folks at the US EPA actually thought of this when they established energy efficiency requirements for freezers and refrigerator freezer compartments. There are actually separate measurement requirements for manual defrost freezers, partially automatic defrost freezers, auto defrost freezers, and long-time auto defrost freezers (ones with a long defrost cycle). The measurements for those with some level of automatic defrost include a defrost cycle as part of the measured period, and include enough time duration that the likely impact on actual household consumption is reflected in the eventual measurement.
The efficiency requirements for manual and automatic defrost freezers are the same in the US and Canada, and because the measurements required for certification are designed to measure the realistic energy use of the freezer over a year, you should really just go by the estimated kWh per year consumption on the energy label that comes with the freezer.
Freezer efficiency requirements are set as a base allowance of kWh per year, plus an additional allowance per cubic foot of volume. All freezers sold in North America must meet at least the basic efficiency requirements. ENERGY STAR freezers need to be at least 10% more efficient than the base requirements.
In principal, given two freezers of the same size, with one having auto defrost and the other having manual defrost, the manual defrost freezer should be more efficient because of the extra energy used during the defrost cycle. But because the efficiency requirements factor in the defrost cycle and require both types to meet the same minimum and ENERGY STAR efficiency levels, it's likely that manufacturers put a little extra effort into the auto defrost freezers to make sure they meet those same standards. It seems that to get the most energy efficient freezer possible, you really should rely on the annual consumption estimates provided on the appliance energy efficiency label.
© Green Energy Efficient Homes Inc. 2012 Privacy policy