You know the cool feeling on your feet every time you open the refrigerator door? If you didn’t know, that’s the feeling of all your cold air falling out on the ground. Cold air is heavy and naturally sinks down, which makes the design of most refrigerators suboptimal for conserving that cold air when opened. Though convenient, this means that your refrigerator will be using a lot more energy than is necessary.
Well, what can you do about it? In Japan there are refrigerators with pull out drawers that help eliminate some of the problem, but importing a massive Japanese appliance isn’t likely to happen for most of us. Luckily, there is a DIY solution that involves converting a deep freeze into an incredibly efficient refrigerator chest.
You can check out the DIY PDF here, but in summary, what the creator, Tom Chalko, did was get a chest freezer and modify the temperature control so that it held foods at the normal temperature a standing refrigerator would. In the end, Tom had a fridge with a slightly non-traditional organization of foods, but one that only used about 100 watt hours of power a day, compared to most refrigerators, which use between 1 and 2 kilowatt hours per day. If you’re interested, be sure to check out the PDF for some more specifics. Tom also put together a web page, and aparts list to make duplicating his efforts quite easy.
Also, check out our article on a DIY Passive Cooled Fridge, and our series on DIY improving your freezer’s efficiency.
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i’ve actually built this, kind of.
i just used standard cheap chest freezer and instead of dealing with a bunch of electronics i got a device from the beer and wine store that brewers use when they are laggering.
the temp guage plugs into the wall and the appliance plugs into gauge. when the temprature goes outside of the user selectable range it turns the freezer on or off as applicable.
there are a few problems with the setup that he doesnt tell you about.
for example, you know how ice builds up on the inside of a chest freezer? you’re always fighting a puddle in the bottom of the fridge.
also you need to add a pancake fan in the fridge to stableize the temprature otherwise the top will be above 50 while the bottom will freeze.
on the other hand, i built a fridge that runs on 400 watts a day for around $250.
One problem is that there is no freezer section so a second freezer is needed.
KW per day ?
that doesn’t make sense, you mean KWh/day or KJ/day or something
> that only used about 100 watts of power a day, compared to most
> fridges, which use between 1 and 2 kilowatts per day
Just to whine about one of my nerdy obsessions: Watt is a flow-measurement (energy per second), and so cannot be used to indicate an absolute amount. You can use Joule or Watt-hour, but not “Watt”. Saying a fridge uses 100 Watts a day is a meaningless statement. Does it use 100 Watts continuously? Then it uses 2.4 kWh per day. Or do you mean 0.1 kWh per day?
Please don’t be offended. My intent is to inform, not to insult :).
Jeroen
Something I haven’t see yet is someone putting the coil underground, so you maintain a constant temperature of the refrigerant. This would be very helpful in the summer.
merccom – that’s /exactly/ what he described in the PDF, he controlled the power supply with an external thermostat, when it gets to the temperature that he wants it turns off. There’s no bunch of electronics involved – it’s just a thermostat.
The fact yours is 4x less efficient is just a shame.
This is a fine idea and interesting user experiences from merccom. However I’m confused by the reports of energy consumption of these modified freezers. When you say 100 W/day, is the machine running continuously with a 100 W electrical draw from the wall outlet? Most vapor compression machines are use an on/off control scheme which means they aren’t running continuously, in which case 100 W per day must be some averaged power draw, but it’s not clear.
In any case (and at the risk of being pedantic), “100 W per day” is a confusing way to report energy consumption: especially for non-constant power draw. A watt is a unit of power or energy flow (energy per unit time). So, if your machine draws 100 W when it’s on, you multiply (not divide) this power draw by the amount of time it draws this power to get the energy consumption for that period of time. Energy consumption for a day should be reported either in joules/day or more conveniently in Watt-hr/day, for example.
For example, if the power draw is 100 W, and the machine is drawing this power for 10 h/day, then the energy consumption is 3.6 MJ/day or 1 kWh/day. It is this number you should be comparing to energy consumption of state-of-the-shelf home refrigerators (although an “on” time of 10 h/day is just a guess on my part).
The title is a little confusing but is attention getting.
The freezer is subject to room temp. By lowering the start/stop temp. the unit does not run as long. The PDF states that the compressor is running 3 min/hour. He also states the freezer is 10 to 20 times more effi.
It use to run 30 min to 60 min every hour now it runs 3 min.
another idea i had due to reading this, and i’m wondering if it sounds plausible: have each shelf of a regular standing fridge have some transparent curtains across the front of it to try to reduce the amount of cold air leaving when you open the door.
I have a question about the thermostat. Is it just your run of the mill, big box store thermo? Because this would be of great interest to the brewing community. Because the unit that is mentioned above starts at $55 and goes up. I would love to be able to convert a chest freezer into a energy efficient fermentation/lagering chamber/kegerator!
John
You guys are getting caught up in semantics here….
If you’re confused by his “100 watts per day” statement and want to convert to your typical kWh unit that you get charged by your utility company you just do (100 W)(1 kW/1000 W)(1 Day/ 24 Hours). Presto. You have an average usage of 0.0042 kWh every day using this fridge. It doesn’t matter how long the machine is on every hour. You could figure this out if you knew the power rating of the motor on the compressor and any other power draw the thing has for temp control……but who cares? You’ve got the overall power draw per day, and when it comes down to it, that’s all you need.
@Raoul, that’s a common thing used in grocery and convenience stores to prevent cold loss. Even putting flat panels in on the wire rack shelves that are standard in many fridges would prevent some loss.
What always struck me as odd is that the “upside-down” fridges (with freezer on the bottom) that seem popular now are all *less* efficient than the conventional ones. You’d think that cold air falling would make it more efficient to have the coldest things on the bottom, but it doesn’t work out that way. In practise, I think part of the problem is that the upside-down fridges all have wire rack drawers on the bottom, which let *all* of the air out every time you open the freezer.
Still, as others have pointed out, the setup as proposed is missing some items that will detract from the practicality… A fan for air circulation (which isn’t needed in a deep freeze, you want everything well below zero anyway), a water-removal system, the nuisance of having to bend double to get things out of the bottom when you need them, and on top of it all, you’ll need two of these because you still need a freezer somewhere.
Ultimately you’ll want both fridge and freezer, so you’ll probably want to start with two smaller freezers, which on their own will be less efficient right off the bat than a single larger unit. I can see that at the end of the day you might end up a little more efficient, but I doubt you would see 100x or even 20x improvement over a conventional fridge with freezer when you add up the total costs. But i’d like to be proven wrong! 🙂
Excellent article! Two things popped into my mind when I read this:
1) As most of the cold air stays in when the door is closed, how about exchanging the one large lid for a number of wire shelves that each have their own lid, slide up on drawer slides, and are mated with counterweights hanging down behind the fridge? Anything anywhere in the fridge could quickly and easily be raised up to a convenient height, while minimizing the amount of cold air escaping because of having to dig for something near the bottom.
2) Could the cooling pipes be placed in a ‘grey water’ jacket that feeds things like the toilet, washer, outside taps, etc., where the slightly higher temperature wouldn’t matter? That should make it even more efficient.
@Greg —
Semantics! Heh heh . . . uuum what? Please re-read my comment and try my example which shows that the energy consumption at 100 W for 10 h/day is 1 kWh, not the silly result you’ve calculated (4 Wh is closer to the energy draw of some portable electronic device than a refrigerator). Even the units in your calculation (as written) aren’t Wh per day — more like W*day/hour.
On the more important point of comparing the energy consumption of refrigerators (or anything applicance, for that matter), the only quantity that makes sense to measure/report is the energy consumption (measured in joules or more conveniently Watt*hours) not the power flow, which is usually variable and in any case, requires knowledge of the time for which that power has flowed.
Answer this question as an example. Which light bulb uses less electricity, a 60 W incandescent bulb or a 100 W incandescent bulb?
Answer: indeterminate. If the 100 W bulb is switched on for only 10 minutes, while the 60 W bulb is switched on for hours, the 60 W bulb will have drawn more electrical energy.
Congratulations! A really good idea, i just made an accurate thermostat with lcd display and i will employ it soon in my fridge chest. Just one question: in your pdf-article, it is a normal-closed swicth there, so to use the chst as fridge you have to power it 90 sec/hour. To keep the relay switch open you have to “fire” the relay-coil with power 3600 sec. – 90 sec. = 3510 sec/hour. Why not use a normal-open (NO) switch insteed of the NC one? In this case you will power the coil of the relay only 90 sec/hour and save more energy?
The issue with most refrigerators is not mainly cold air falling out.
It is simply that they have half or less the insulation thickness of even a cheap chest freezer.
What makes most of the difference when using a chest freezer as fridge like this is that the freezers have twice or more the insulation.
If one does the heat equation math on the mass of the air inside a fridge, one sees that the loss from the air is pretty insignificant.
Be sure to put containers full of water in the bottom level of the freezer to stabilize the temperature. This will result in even lower power usage, especially when there’s not much else inside. Also makes a nice way to raise the lowest contents up so they’re easier to reach in this chest setup.
This is a commonly known hack for those of us living off-grid – a way to get a very efficient refrigerator without having to buy a very expensive specialty off-grid unit such as Sundanzer, SunFrost, etc.
BTW the main reason the specialty units are so efficient is because they use a whole lot more insulation. The reason they’re so expensive is because they’re small-scale production.
If all mass-market fridges had twice the insulation – which would by no means double the cost – everyone could use half or less the energy for refrigeration.
SunDanzer also makes chest freezers and chest refrigerators which are extra-insulated and use variable speed compressors. They are also DC based, making them ideal for off-grid scenarios. They are a bit pricey, however.
http://www.sundanzer.com/Home.html
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