TromboneAl said:
Those numbers don't make sense to me. 100WH/day is just 4.166 watts per hour - about half of what a night light uses.
He says it runs just 2 minutes an hour. First, that it probably a really inefficient duty cycle (3.33% on) for a refrigeration unit - I think they need to run longer (at lower power) to overcome start-up losses. Most high efficient devices will actually be sized small to run near 100% - this does not add up.
Further, 4 watts/hour average used in 2 minutes an hour would be a 125 Watts draw ( ~ 1.1 Amp @ 115 V) for those 2 minutes. That is only enough to drive a 1/8 HP motor. I doubt you could find a chest freezer that consumes only 1.1 Amps while running - this does not add up. Well, here is one designed for off-grid applications, it might do it, but it is $590 for a very basic unit, Remember, this is a 10CFt fridge, inconvenient chest style, no freezer in this mode and then add $75 for a refrigerator thermostat:
http://www.backwoodssolar.com/Catalogpages2/refriger2.htm
4.166 W per hour average is 14 BTUs per hour. Refrigeration is only about 50% efficient (probably less, plus insulation losses), so a generous 7 BTUs output. At that rate, it would consume all that cooling power for 34 hours just to bring a gallon of water from 70F to 40F. And about another 170 hours to turn it into ice, if you were to set the thermostat below 32F. So there is no way you can get those kind of numbers if you actually use it and put some room temperature food in there to cool. They probably looked at just steady state with the contents already cooled. I bet the energy-star numbers quoted by the appliance makers take some loading/unloading into account. I bet these numbers are not apples-to-apples at all.
You might have no choice off the grid, but I doubt this makes economic sense for most people. Looking at some units at Sears, I doubt you would realistically save more than $30 a year over a more conventional fridge sized at 10 cubic feet. And it would be much cheaper to buy. Two tips: Avoid putting hot food in your fridge (safely air or water cool it first), Stack up the food you are returning to the fridge - open the door *once* and put it all in at one time. These two things will save $ and require no investment.
Two observations:
One - I think many of these environmentalists (and I know a few like this) get a real ego-stroke by claiming that everyone else is so stupid and the world would be so much better if they just did this simple stuff that they do. Sometimes they may be right about some things, but take it with a huge grain of salt. Their numbers often do not add up, or they ignore the other impacts (like calling an EV pollution free).
Two - I hate these claims about 'look, we could save (put generic big number here) if everyone just did X,Y, and Z'. Trouble is, we use very, very big numbers of energy - so any small, small savings is a big number when taken out of context. 0.001% of our energy usage is a big number. Sure, small things add up, but we need to look at the big picture and prioritize efforts. IIRC, transportation accounts for 40% of our energy usage - some real, meaningful, across-the-board, long-term (but not draconian) CAFE standards could probably have done more to cut energy usage and reduce greenhouse gas than anything else. And if they did it over the past 30 years, we'd probably all be driving 35+ mpg vehicles and not even feel we were compromising in any way - technology would have taken care of that, if there was an incentive.
-ERD50