Can't stop thinking about fridges and winter...
February 21, 2008 8:07 AM   Subscribe

I can't stop thinking about fridges and winter. Would it save much energy to freeze gallon containers of water outdoors and put those in the fridge now and then? It's Minnesota winter over here and I want to make the most of it ;)
posted by advicepig to Home & Garden (17 answers total) 1 user marked this as a favorite
Yes that would save energy. Probably be worth doing as long as you reused the water. That is to say, did not pour it out and refill. As a mater of fact, just keeping your fridge full is helpful. The more thermal mass in the fridge, the less energy lost when you open and close the door. Other things are make sure the seal around the doors is good and vacuum the coils now and again.
posted by d4nj450n at 8:13 AM on February 21, 2008

I've heard that a fridge full of gallons of water uses less energy than an empty one. Someone else would have to do the math to demonstrat the initial cooling doesn't wipe out your gains, otherwise it makes sense, imagine the gallons of water as reducing the internal area your fridge has to cool.

If you pre-freeze the water and put it in your fridge, it seems clear it would cause the fridge to use less energy. If it's a measurable change, I have no idea.
posted by These Premises Are Alarmed at 8:14 AM on February 21, 2008

Or, what Dan said.
posted by These Premises Are Alarmed at 8:15 AM on February 21, 2008

Yes, it would save some energy. Some of the energy you save might go out the door when you set out and retrieve your water bottles. An exact answer to this sort of question isn't possible because there are too many variables like size and age of your fridge, etc.
posted by kuujjuarapik at 8:16 AM on February 21, 2008

If you put frozen gallon containers of ice in the fridge, they would melt and just be gallon containers of cold water. These gallons of water, however, are better conductors of heat than air is, and since they'd displace some of the air in the fridge, in theory you'd have some energy savings. How much is another question. I once left my fridge plugged into my Kill A Watt for a month and discovered that it only used about $7 worth of electricity. And I have a pretty old fridge. So maybe it's not worth worrying about.
posted by Dec One at 8:17 AM on February 21, 2008

Yep, water has a high specific heat so keeping cool water in the fridge and frozen water in the freezer can only help.
posted by damn dirty ape at 8:18 AM on February 21, 2008

I think the trick is that you would have to remove them at some equilibrium point. Otherwise you would be spending money to keep them below room temperature.
posted by smackfu at 8:18 AM on February 21, 2008

But, smackfu, it still uses less energy to keep gallons of water below room temperature than air.
posted by These Premises Are Alarmed at 8:23 AM on February 21, 2008

You could get an old-fashioned ice box, which doesn't use any electricity and is probably better designed to handle ice (not sure how often the ice needs to be replaced tho). Neat pictures on Wiki! Or, how about the more recent pot-in-pot refrigerator.
posted by Melismata at 8:23 AM on February 21, 2008

If you want to save energy, don’t start by speculating on how to make small improvements to arbitrary appliances. Take a look at your electric bill and see how many kWh you are consuming. Then look up the Energy Star stats on your refigerator. What portion of your energy consumption is drawn by your refrigerator? Does it make sense to focus on a 10-15% portion of the bill? Or can you make more significant improvements in other areas, like replacing incandescent bulbs with CF, or making sure that your electronics aren’t drawing standby power. Your computer is probably pulling as many or more kWh as your refrigerator.
posted by breaks the guidelines? at 8:24 AM on February 21, 2008

Your computer is probably pulling as many or more kWh as your refrigerator.

Doubtful if it's a laptop. My laptop pulls about 30 watts, or .03 kilowatts. If it's on 24 hours a day, 30 days a month, that's 21.6 watts. At 8 cents per kilowatt-hour (which is approximately the rate where I live), that's $1.73. My fridge cost $7 monthly.
posted by Dec One at 8:32 AM on February 21, 2008

I think the idea is to put frozen water into the fridge, the phase change of ice into water taking heat out of the rest of the system (the fridge), and once liquid, being moved outside for refreezing. The phase change energy for ice into water will take up 334 kilojoules per kilogram of water, so it will take your fridge less energy to run, exactly how much is left as an exercise for the reader. But I imagine any gains will be nullified by the tendency to keep opening the fridge door to check on the ice.
posted by borkencode at 8:33 AM on February 21, 2008

Best answer: Let's say you put 4 gallons of water outside in 10 F (-12 C) weather, then put them in your refrigerator which you keep around 40 F (5 C). For the 12 C where it's ice, you get 2 J/g*K, and in the 5 C of water you get 4 J/g*K. There's also the specific melting heat of 333 J /kg. You've got 15 kg of water, so that's a total of (12 * 15000 * 2) + (5 * 15000 * 4) + 333 * 15 = 665,000 Joules, which is about 0.2 kilowatt-hours. Multiply that by the inverse of your fridge's efficiency for a final answer, let's assume a worst case of 20% efficiency and call it 1 kWh. We'll also assume you take the jugs out as soon as you reach equilibrium temperature and don't lose any gains opening and closing the door (of your fridge or your house, which you also spend energy to heat).

My apartment with 2 people in it (and electric heat) used an average of 57 kWh per day last month, so even if you're hauling these water jugs in and out every day, it's probably not a good use of your time.
posted by 0xFCAF at 8:34 AM on February 21, 2008

Response by poster: Thanks all. I was mostly curious how much effect it would have. Now to start working on an icebox and a way to harvest ice from the lake just like the old days.
posted by advicepig at 9:23 AM on February 21, 2008

Something else to consider is that your electric refrigerator is an excellent source of heat inside your house. So please take into consideration how the added cost of electric refrigeration actually warms your home.
posted by thomas144 at 9:40 AM on February 21, 2008

If you have room in your kitchen, you could build a pantry like I have in my 1913 era house. It's cupboard doors are sealed like a fridge door, and it has two small (8" x 12") window style cut-outs that are screened, on an outside wall. I'm in a somewhat milder climate, but it functions as a second fridge in winter. If you could figure out how to make separate compartment temperatures for fridge and freezer, you could turn your appliance off in winter.
posted by lunaazul at 9:59 AM on February 21, 2008

DIY Super Energy Efficient Refrigerator
posted by Floydd at 2:12 PM on February 21, 2008

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