Fridge flame

Jen pointed me at the website Treehugger.com--an environmentalist information site. Well, I'm afraid that some of what I've seen comes across as environmentalism lite--this is the bamboo flooring that you can install to make yourself feel better, while your house is 3500 square feet.

I came across this particularly painful post, conjecting how a window on the front of a fridge would save energy, because people would not open and close the door too often to figure out what is inside. This flew into the face of a lot of intuitions I have, so I spent my Saturday night researching and rebutting this claim, in painful detail. I posted this as a comment to the site, but it has not appeared yet. [Ed. note: as of Sunday, it is now on the site; the administrator actually contacted me via email to thank me. Pretty cool.] To wit, here are my thoughts:



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I seriously have to question any savings with this type of a fridge window. I will break down my response into a few sections: insulation of the glass, the energy cost from opening the door, and the overall energy performance.

Glass insulation levels: To take a guess at the insulation value of the glass in this fridge (Sub Zero 648 PROG), I looked at the description: a triple-pane low-E coated unit. To estimate an insulating (R) value, I looked around for similar residential windows, for a ballpark number. The Efficient Windows Collaborative gives a center-of glass U value of 0.14, which is equal to R-7. However, according to this APS document, a whole window (including frame) is more in the range of R-4 to R-5.

In comparison, according to Home Energy Magazine, regular fridge insulation is about R-15. Bottom line: the window is a hole in the front of the fridge with 1/3 of the insulating value, tops.

Energy costs from door opening: This idea of opening the door clobbering your energy bill has always bothered me, because of the fact that air has a really low thermal mass. E.g., you can stick your hand in a 350 F oven; sticking your hand into a 350 F fryolator is not a good idea. I did a few calculations comparing the thermal mass of the air in the fridge with, say, an equivalent amount of water. The specs say the fridge portion is 18.4 cubic feet, or 0.52 cu meter, or 0.62 kg. The equal thermal mass of water is 0.15 kg, or 0.15 liters, or 0.62 cups. So: if you dumped out all the air from the fridge and replaced it with room temperature air, that's about equal to putting in 2/3 of a cup of room temperature water. So it's some energy, but trying to save big amounts by not opening the door sounds questionable to me.

This is not to say that you should leave the door open, or not repair leaky gaskets--those are continuously dumping cold air that needs to be conditioned. My parents had a Japanese fridge back in 1991 that dealt with this well: it would have a beeping warning if the door was open for more than a minute, and it would shut off the cooling while the door was open, so it wouldn't be wasting power there.

Incidentally, in terms of the lighting inside the fridge, based on the specifications and installation guide, the lights are LEDs, which are not adding much cooling load.

Overall Energy Use: The web description of this model is pretty cryptic: it consumes "less energy than a 100 watt lightbulb." Most refrigerators are described in terms of kWh (kilowatt-hours) per year--they're giving an answer in mph, while everybody talks about miles. If we assume that it means the equivalent of a 100 watt light bulb running all year, that works out to 876 kWh per year. If you go to the Energy Star Appliance website, you can compare this use to equivalent-size fridges. This model is in the ridiculously oversized high end (29.8 cu ft combined fridge + freezer), but Energy Star rated fridges in the same size range are around 590-650 kWh. Meaning: this fridge is a real power hog, as would be expected by the lousy insulation on the front (see previous section).

But, you might ask, what about the fact that it "conforms to rigorous Department of Energy standards for residential use"? I would guess that on one of those yellow Energy Guide labels, it doesn't actually go all the way off the right hand side of the scale. By analogy, when people talk about a house "that is built to code" as an example of quality, I have to reply that a house that just meets the building code is the worst house you can legally build without getting thrown in jail.

Remember to think of fridges the same way you think of cars and houses: if you're buying bigger, you'll be paying more to run it. Ultimately, I recommend a refrigerator that meets Energy Star--see this Home Energy Magazine article on why a even a 1990's fridge should probably be replaced for energy reasons.

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Given the fact that this was my Saturday night activity, I suppose it's pretty obvious why the babes are all over me. [smirk]