About The Fridge

I’ve been thinking about the refrigerator. You’re probably not going to like this one, because as I did here and here, I am again going to wind up being contrary to what seems like common-sense green thinking.

The winter before last, my fridge compressor was broken for ten days (aside: good luck getting warranty service from Amana, Inc.) This was inconvenient, but we managed to keep the fridge functioning pretty well as an icebox. I filled three or four big tupperware containers with water, and rotated them from outdoors (where they froze to ice) to the fridge compartment (where they chilled the fridge, and melted). This is not a novel idea: my new heroes over at Experiments In Efficiency started living without a fridge altogether last year, using this same strategy in the winter (they put their food in a cooler, but same idea.)

During that broken-fridge episode, I started to feel that it was absurd to use electricity to keep things cold in New England, in winter. It seems there is no shortage of natural coldness available right outside, and that we should not be using electricity to make more.

But deeper thought shows things aren’t quite so simple. In fact, there is no “abundant cold”. Cold, indeed, does not exist– only the relative lack of heat exists. To “make” something colder, you have to move its heat somewhere else. The fridge cools its interior by moving heat to the room outside. Of course it also generates some extra heat in the process, exactly equivalent to the amount of electricity it uses. In effect, the fridge (like all electrical appliances) is a space-heater that happens to do something else handy along the way.

In other words, when you have the fridge plugged in, it pulls heat from the inside and puts it in the kitchen. As the heat seeps back in, the fridge pumps it out again. Each time, it adds a little “waste” heat. But in winter that’s not really wasted, since it helps keep the house warm, which you want also. As a way to heat the house, it’s not as efficient as using the furnace– unless I’m only trying to keep a couple rooms warm, in which case, it’s actually more efficient and cost-effective to “heat” the kitchen with the fridge than heat the whole house with the furnace (previous post on that concept.)

Now, consider the alternative strategy: unplugging the fridge and rotating containers of water outdoors to freeze. What this seems like is bringing a valuable commodity (cold) from a place where it is naturally produced (outside) to a place you want it (the fridge.) What it actually is, though, is taking a valuable commodity (heat) from a place you have produced it and want it (the house) and disposing of it in a place where it is useless (outdoors).

I know. This seems like whacknut thinking. But ponder it. Each time I brought in a tub of ice, and let it melt in the fridge, it drew heat from the fridge interior, which in turn drew heat from the kitchen, which ultimately was replaced by heat from the furnace. So the end product was a tub of water with a lot more heat than it started with when frozen. And then what? I took the tub and put it outside to cool off. I took perfectly good heat from the house (contained in water) and purposefully tossed it outside. And repeated for a week. (And this doesn’t even consider the heat-losing effect of opening the front door all those extra times to bring water in & out…) Really, this is wasteful in the same as filling the toilet tank with cold water, warming it to room temp, then flushing it down the sewer.

So it comes down to this: In winter, is it better to (a) unplug the fridge, make heat with the furnace, then throw the heat outdoors, or (b) run the fridge with electricity, but keep the heat it produces indoors? No longer such an easy question. And answerable only in considering that heating with a furnace is 2-3 times a more efficient use of fossil fuels than using them to generate electricity. So again, roughly, I’ve decided that if I’m only trying to keep 1/2 or 1/3 of my house warm, then electricity is as or more efficient than the central oil heat. And so long as that’s the case, it’s as or more efficient to keep the fridge plugged in.

There are two ways I can think of to short-circuit this whole problem and make the fridge actually efficient.

1) Bring ice/snow in from outside for the fridge, but after you’ve melted & warmed it up, don’t just toss it back outside with its heat. But this means you have to keep all that melt water in the fridge till spring… which starts to become unwieldy…

2) Run the fridge directly from fossil fuel in winter. This isn’t a loony idea. Propane fridges have been around forever. I’ve used them. They work great. Here’s one that can run off either propane OR electric. That fridge uses either 3.9kWH/day of electricity, or 1.1lbs of propane. As 1.1 lbs of propane contains about 6.9kWH of energy, at first glance it appears more efficient to use electricity– but only if you ignore the horrible efficiency of electrical generation in the first place. It takes about 12kWH worth of coal to generate that 3.9kWH of electric… the rest of the coal energy goes up the generator smokestack as wasted heat. Whereas, if you run the fridge with propane, every single kilowatt of energy it uses will ultimately stay in the kitchen as heat. Nifty, huh? Then in the summer you might want to switch back to electric.

Okay, bring on the rants.

P.S. Possibly the best thing about a propane fridge: No moving parts. No compressor. I wouldn’t have had to deal with Amana, Inc. and live without a fridge for a week in the first place…

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9 Responses to “About The Fridge”

  1. Anonymous Says:

    Something’s wrong with number 1. You don’t throw heat out with the meltwater. The heat has, effectively, already been used up. You brought in a tub of ice and it took X amount of energy to melt. Once it has melted, it doesn’t matter what you do with the water – the heat has been used and needs to be replaced with new heat from your furnace (or fridge, or toilet tank water, or typing furiously onto blogs).

  2. Turboglacier Says:

    Respectfully, and cautiously, I disagree with Anon. Anything warm (and by “warm”, I mean warmer than outdoors) that you take out of your house and dispose of outside is giving away heat. It doesn’t matter if it’s toilet water, or water from the fridge, or the sofa. And it doesn’t matter if it’s the coldest object in your house– if it’s warmer than outside, it’s helping hold on to heat that you’ve already paid for. (If things in your house are COLDER than outside, congratulations– you made it to spring! Open the windows!)

  3. Kelly Says:

    Huh. Well, I’ll agree that when you remove something from inside the house, additional air will enter the house to fill the volume formerly occupied by the object you removed. That new air is going to obviously be cold. But it takes a lot less energy to heat that new air than it did to heat the bucket of water in the first place. The heat you’ve invested in heating the water to room temperature is lost to you. Yes, putting it outside warms the outside – but it doesn’t chill the inside (with the small exception I described above).It seems to me that the only way to reclaim the heat you invested in that bucket of water is to somehow lower the temperature of the water and extract the heat. I don’t know of any way to do that. I just don’t see how once you’ve warmed the water (and invested a bunch of energy doing so), it makes any difference what you do with that warmed water. The energy is invested, and gone.I have to admit I’m absolutely fascinated by your discussions on these issues. Anon (now exposing my identity)

  4. Johanna Says:

    Ok, given that the furnace is a more efficient use of fossil fuels, it follows that you want to maintain a constant temperature with as high a proportion of the heat achieved from the furnace (as opposed to electricity) as possible. Thus it further follows that you want to minimize how long your fridge runs – no exceptions. To do that, you need to avoid introducing warm items in the fridge, and to keep it as full as possible. If putting a tub of snow in there means that it a) runs less (and consequently a lower proportion of the heat in the kitchen is a byproduct of refridgeration) and b) the additional meltwater using space helps maintain the temperature better – i.e. with less time of compressor running – than in an empty fridge, then logic would dictate that you use the tub and keep water to use available space. Presumably, the water inside the fridge is kept lower than room temperature now that the cold house is the heated house, so once you need the space for other things or more snow, you need to pitch the water outside. Yes, you are pitching the equivalent latent energy as you absorbed letting it melt. However, since the cold house will not drop below freezing, there is no way to recapture this latent energy, and you get a net negative benefit if you keep it anywhere in the house that is warmer than the fridge. Key to my understanding is that the energy used to achieve the change of state came from *inside* the fridge, thus circumventing the process of using electricity to move heat from the inside to the outside. Comes back to your statement that the oil furnace is a more efficient use of fossil fuels than electricity, no?

  5. Marlene Says:

    By insisting on keeping cold food in the warm part of your house, you create a need for a fridge and justify it by claiming it to be an efficient space heater. Why don’t you just put your fridge outside? Then it would never run, and your food would stay cold. Of course, where I live, your food would be frozen solid, but it sounds like your climate is a bit more forgiving. Alternately, you could put the fridge in the coldest room of the house, whereby you would lose your space heater, but since the fridge would run even less, if at all, you wouldn’t be losing much.

  6. Turboglacier Says:

    Kelly,After pondering this for far too long, I’m going to say we’re both half right. This part of what you wrote I still disagree with: “I just don’t see how once you’ve warmed the water (and invested a bunch of energy doing so), it makes any difference what you do with that warmed water. The energy is invested, and gone.”Energy can’t just be “gone”– the heat you put into the water (well, ice, then water) is still in the water. But on this part I do now agree with you: “It seems to me that the only way to reclaim the heat you invested in that bucket of water is to somehow lower the temperature of the water and extract the heat.”Agree. If you throw the water away while it’s fridge-temp, it’s a wash. If you warm it further before tossing it, you’ve wasted more heat. If you can get it colder than fridge temp (without using even more energy to do so) before you toss it, then you’ve extracted some of your energy back. How to do that? Well… maybe there’s a corner of the house that’s even colder than the fridge… but for practical purposes, this is getting a little absurd…

  7. Green Grrl Says:

    Aww, shucks. [blush] :-)This isn’t fridge related but thought you might be interested in this link:http://noimpactman.typepad.com/blog/2009/01/how-to-cut-out.html

  8. Green Grrl Says:

    Oh and also, a heat exchanger might be able to capture some heat from room temp water. Certainly it can be used with warm/hot waste water (the heat exchanger then pre-heats water coming into the house and into the hot water tank). Last thing… tubs of snow in the fridge should be covered. Uncovered liquids release moisture which makes the compressor work harder. (from what I understand)

  9. Turboglacier Says:

    “Last thing… tubs of snow in the fridge should be covered. Uncovered liquids release moisture which makes the compressor work harder. (from what I understand)”Ooh! Good point! (I better run home and put Saran wrap over my ice cube trays!)

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