The recent thread on icebox design got me going again on the topic of ice. More precisely, how much does it cost to make ice. There have been reports that people are making it for "free" in their freezers at home. Unfortunately the laws of thermodynamics state there is no "free lunch" (or ice for that matter) and in fact you don't ever get quite what you pay for!
Anyway I thought I'd figure out how much "free ice" really costs.
Here are the numbers:
To make ten pounds of ice you have to remove about this much heat:
70f to 32f water = 38f * 1btu/pound * 10# = 380 BTU
10# water to 10# ice = 144btu/# * 10# = 1440 btu
380 btu + 1440 btu = 1820 btu
1880btu = 0.533 Kilowatt Hours (http://www.mhi-inc.com/Converter/watt_calculator.htm)
Typical cost of electricity = $0.15/kilowatt hour (http://michaelbluejay.com/electricity/cost.html)
If you were making heat with an electric resistance heater you would get one watt of heat out for one watt of electricity. Making cold is a bit different. You are moving heat not making it. Soooo, for every watt of electricity you can typically move three watts of heat. So, to make 10# of ice it would take about .3333 * 0.533 Kilowatt Hours = 0.178 Kilowatt Hours of electricity or 0.178 KWH * $0.15/KWH = $0.0265 for ten pounds of ice. In short about two cents!!!!!!
There you have it. My two cents on “free iceâ€