greenspree.ca at The Sietch

I came across this discussion in the comments section of Peak Oil Debunked’s post on the chest fridge idea from the famous mtbest article. The gist of the argument, and I have posted the relevant parts of the argument against the chest fridge, was that the orientation of the cooling device would make no difference and that the original author was sacrificing a large amount of food storage. Seeing as the original post and discussion took place two years ago I doubt I will get a response, but have decided to post my thoughts on it here.

My take on the subject is that you can buy two 15cf deep freeze’s for the same price as one side by side refrigerator freezer unit and have one set up to be a fridge and use the other as is. In my research, the standard 25cf fridge/freezer has a 15cf fridge side and 10 cf freezer side. My research also shows that similarly sized chest freezers use less energy than upright refrigerator only models. So you can in fact have more storage and pay less in utility bills for it!

More after the fold.

Comments #1-9 are from Quantoken, an apparent math and physics whiz, who argues at great length about the futility in trying to save electricity by using the chest fridge idea. He posts lots of equations and theoretical math but does not back any of his claims up with real world examples.

Comment #1:

The energy comparison is misleading. It does not take into consideration that this chest frige is much smaller than a regular refrigerator, as well as the fact that regular refrigerator also has a freezer, which is much more energy intensive because you need to maintain a much larger temperature difference between the freezer temperature and room temperature, than the chest frrige does, which is between the 5C interior temperature, and 18C room temperature, as claimed by the paper.With all other conditions equal. The energy consumption is roughly proportional to the square of the temperature difference. The amount of energy require to transport one calorie of heat from a cold source to a hot source is roughly proportional to the temperature difference, for one thing. The heat leak, hence the number of calories needed to be transfered per unit time, is proportional to the temperature gradiant, too. Combine the two you get the square proportionality relationship.Therefore, to maintain a freezer of comparable size to -10C from the 18C room temperature, compare with a frige at 5C from the 18C. The energy cost is the square of (28/13), 4.64 times bigger. And the frige in the picture is less than one half the refrigerator at my home, so that’s another 2 times factor. Combined, his chest frige really is not that much more energy efficient after all.The claim of the factor of leaking cold air has been greatly exagerated. Let’s do some calculation. Each time you open a regular refrigerator, let’s say half of the cold air (which is an exageration) is replaced with room temperature air. That’s 12 cubic feet going from 5C to 18C. 12 cubic feet air is about 0.34 cubic meter, at 1.29 kg per cubic meter that’s 0.438 kg. Specific heat is about 0.4 cal/(gram*degree) so that’s 2280 calories lost.

The refrigerator operates between 5C and 18C, which is 278K and 291K. Assuming a 100% efficient heat pump, it costs 13 calories of net energy to transport 278 calories from the cold source to the hot source. So it costs 107 Calories of net energy to make up the loss of 2280 calories lost due to each door opening.

107 calories times 4.1855 cal per joules, gives you 448 Joules, which is 1.244×10^-4 kw*hour. That’s a totally insignificant energy cost comparing with the 1 kwh per day consumption. Even if you open the refrigerator 20 times a day, and the peak pump is only 25% efficient instead of 100%, you are still talking about 80 times more energy, which is still just 1% of the 1 kwh per day energy cost, still very insignificant.

So lying the frige down instead of sitting up, really doesn’t make much difference after all. So other factors are much more important.

Quantoken

Comment #2:

Roland:
I am not disputing the 1/10 power figure. I am saying it’s merely due to the fact that it is just a frige without a freezer, compare with the regular refrigerators that come with a freezer, and also it is way much smaller than a regular refrigerator, meaning less food can be stored.

It of course uses less electricity and it is also 10 times less useful as a refrigerator. The energy saving has nothing to do with whether it lies down or stands up, and has everything to do with cutting the capacity and usefulness.

Comment # 3:

Look at the photo I insist that it is much smaller than a regular home refrigerator. The author claims that it is converted from a regular chest freezer. It looks like the kind of chest freezer slightly lower than the kind I see near the wal-mart checkout that contains kids icecreams. If that’s the case then the volume is only 1/4 of a regular home refrigerator.

Saving energy on saving size and capacity is really no improvement of efficiency. If that is then I propose you just don’t eat any food that needs to be preserved in a refrigerator, and get rid of it altogether. If you return to the caves, eat raw meat and forfeit all modern lifestyles, then you could practically cut energy use to zero. Is that what you want?

Comment #4:

Now that your numbers make sense. 239 litre is 8.44 cubic feet, that’s way much smaller than a stand up dual door 25 cubic feet refrigerator, which is pretty much the standard equipment of an American single family home.

But the bigger factor is you are cutting off the freezer and use it as a frige only. It makes a big difference what kind of temperature difference (between room temp and the interior) you try to maintain. Since theoretically the power consumption is roughly proportional to the SQUARE of the temperature difference. The author maintained only a 13 degree difference in his frige (5C versus 18C). A typical freezer would maintain 33 degree difference (-15C to 18C), which consumes (33/13)^2 = 6.44 times more power. Combine that with the almost 3 times volume (25/8.44). That’s a 19 times difference in cooling capacity!!! So if you save only 10 times electricity, not only it is not impressive at all, it is actually running at lower efficiency after all.

Like I said, cutting capacity to save electricity is not an improvement of efficiency at all.

Comment #5:

Roland:
You don’t get it. You lose a major chunck of the food preserving capacity by not having the freezer in this chest frige. And you settle for a much smaller volume. It is not a saving by efficiency. It is a saving by cutting corners. You might as well just eat food that does not need preservation, and go without a refrigerator that way.

At the end of day it does not save you any thing. You save 330 kwh electricity per year by having this smaller frige without a freezer, which is about $33 saving if each kwh is 10 cents.

But because your frige is 3 times smaller, and do not preserve food very well (by not having the freezer). You need to make more frequent trips to grocery stores to get fresh food. If you take one extra trip per week, and each trip is 6 miles one way, that’s 624 extra miles traveled per year, at 24 miles per gallon, you are consuming 26 gallons extra gasoline, at $2.5 per gallon that’s $65. Just to save $33 in electricity. That’s not only a waste of money but also a waste of energy!!!

Instead I would encourage bigger refrigerators that come with a freezer, so that you can take less number of trips to grocery stores.

Comment #6:

Roland said:
“Yup, here’s the thing – if orientation makes no difference to power use, then this fridge, having a third the volume, should use a third the electricity. But it doesn’t, it uses one-tenth the electricity. Is a normal fridge ten times larger? Yes, I know Quantoken, vertical fridges use more energy, but does this really account for the whole difference? Here’s a quote from the fridge’s inventor:”

Roland: How many time do I need to repeat this: A bigger factor even than the volume is that a regular refrigerator has a freezer, while this chest frige does NOT has one. That factor plus the volume difference accounted for all of the 1/10 power consumption. Whether it’s layed down or stand up has virtually no effect.

There is a huge difference between a freezer, which maintains a much larger temperature difference, and a frige, which maintains a much smaller temperature difference. Of course, if you maintain a zero temperature difference, you save 100% of the energy.

Comment #7:

The author of that article showed a complete lack of basic physics knowledge.

He suggested that when the temperature difference doubles, the energy consumption is only slightly more than double. The fact is the amount of heat needed to pump from the cool interior to warmer outside is doubled, so is the amount of energy required to pump each calorie of heat across the temperature difference. So the energy consumption should actually be quadrippled, not doubled.

He also suggested that solar panels work more efficiently during hot days versis cold days. The fact is consider thermal dynamics, hot weather actually REDUCES the efficiency of solar panels, not increasing it. That’s proven both by actual numbers and by established physics theories. You may have less days of good sunshine. But when you do have clear sky and your solar panel is aligned properly, you get more power on winter days.

It is true that you lose more cold air when opening a stand up refrigerator. But any reasonable calculation shows this is a totally insignificant loss compare to typical operational energy cost, unless you are opening the frige every 5 or 10 seconds during the day, which none of us do. You just got to remember the air is very dilute. And that constant heat leak through the material of the refrigerator is much larger than instantaneous heat loss through opening doors.

Comment #8:

To make my point, please have a look at this commercial product.

Especially look at the R4 model, which is a refrigerator only. It consumes 0.1 kwh, same as the so called chest frige the author invented. But the volume is 23 cubic feet, almost three times bigger. And Yes the R4 is a stand up model, not a chest model!!!

Comment #9:

My fault. The interior dimention of the R4 is actually 3.91 cubic feet, not 23, which is the shipping dimention.

But then in the article of the chest frige. The author gives the room temperature as 15 to 21 C, averaging 18C, and the interior temperature is between 4C to 7C, averaging 5.5C. So that’s merely a 12.5C temperature difference.

The commercial product I cited is rated at 21C and 32C. Let’s take the 32C figure for a comparison. If the interior temperature is 3C, that is a 29C temperature difference, at 0.14 kwh, which is 1.4 times of the check frige.

(29C/12.5C)^2 = 5.38 times
(3.91 cf)/(8 cf) = 0.49 times

The commercial product has total cooling capacity of 2.64 times of the chest frige, at 1.4 times energy consumption. So it’s more efficient.

My Comment:

Quantoken,

Perhaps your calculations can explain away these specs:

18-20cf (freezer 1.7cf bigger) freezer 100 kWh more
Chest freezer (19.7cf) stated energy consumption: 435kWh per year

Upright “all refrigerator” (18cf) stated energy consumption 335 kWh per year

15-18cf (freezer 0.5cf bigger) freezer 78kWh less
Chest freezer (16.5cf) stated energy consumption: 360kWh per year

Upright “all refrigerator” (16cf) 438kWh

10-15cf (freezer 1.8cf bigger) freezer 17 kWh more
Chest freezer (12.8cf) stated energy consumption: 362kWh per year

Upright “all refrigerator” (11cf) 345kWh

6-10cf (freezer 1.2cf bigger) freezer 66 kWh less
Chest freezer (7.2cf) stated energy consumption: 279kWh per year

Upright “all refrigerator” (6cf) 345kWh

3-6cf (freezer 1 cf bigger) freezer 98kWh less
Chest freezer (5cf) stated energy consumption: 242kWh per year

Upright “all refrigerator” (4cf) 340kWh

If design (horizontal doors vs vertical) makes such little difference and the delta of degree difference of inside and outside air does, why do many similar sized chest freezers meet or exceed their refrigerator only equivalents?

You keep mentioning that the upright refrigerator used in the original experiment was only more energy intensive because of size and that it also had a freezer attached. I say you are half right, the loss of cold air from the freezer probably does account for a lot.

The usability and convenience arguments are purely subjective and if you are in a position (building new or remodeling) to plan around such considerations you can have high function and usability. It make take more floor space but a chest fridge allows more upper cabinets to be installed and can be used as a temporary work surface. Rack and baskets systems can be made or purchased to make the food access issues minor.

The fact is you haven’t sufficiently refuted this idea, real world evidence is much more compelling than theoretical calculations.

Tell me what you think, am I wrong in thinking that there is something to the chest fridge idea? Is it merely that chest freezers have more insulation that they are more efficient? And if that is the case does it matter? Also, if that IS the case, why aren’t manufacturers building refrigerators as efficiently as the usually much cheaper chest fridges out there?