Man Retrofits Freezer to Make an Ultra-Efficient Fridge
by Justin Thomas, Virginia on 07.25.05
An off-grid experimenter in Australia, Tom Chalko, has retrofitted a chest freezer to create a fridge that uses only 100 watt-hours (0.1 kWh) per day! Why a chest freezer? Tom points out that vertical door refrigerators are inherently inefficient. As soon as you open a vertical fridge door the cold air escapes, simply because it is heavier than the warmer air in the room. When you open a chest freezer, the cool air stays inside, just because it’s heavy. Any leak or wear in a vertical door seal causes significant loss of efficiency.
Tom took a standard chest freezer (a Vestfrost SE255), added a $40 external thermostat, then wired the freezer to turn off when the desired temperature was reached. The thermostat runs on 2 AAA batteries which last for months. The freezer runs for about 90 seconds per hour and then shuts down completely, making it not only very efficient but very quiet.
Full article from Build It Solar (PDF File)
From the article: it uses less power in a day, than a 100W bulb does in an hour. Wow, this is
a significant discovery for getting off grid. Its tough to live without a fridge and then it's an either/or decision. Here's to finding a third way.
From the article: it uses less power in a day, than a 100W bulb does in an hour. Wow, this is
a significant discovery for getting off grid. Its tough to live without a fridge and then it's an either/or decision. Here's to finding a third way.
http://www.nps.gov/renew/appliances.htm -
In the United States 26% of all electricity generated is used to operate refrigerators. The average domestic refrigerator consumes around three kilowatts of electricity per day (3000W/day vs 100W).
What a cool experiment! :)
Seriously, someone needs to replicate this system and see if they get the same performance that this man is reporting. If so, sign me up for one of those things - I hate my fridge.
Hmm. This site suggests that you'd need to open the fridge door about 80 times a day to consume an extra kilowatt-hour's worth of electricty in a vertical fridge:
http://utwired.engr.utexas.edu/conservationMyths/appliances/fridge.cfm
Over on this site, they estimate the average electrical cost for a modern fridge to be $3.76/month, which, at their rate, is about 46 kWh/month, so about 1.5 kWh/day:
http://www.nppd.com/My_Home/Product_Brochures/Additional_Files/electric_usage.asp
So, this guy's freezer/fridge is about an order of magnitude more efficient, probably a combination of the better insulation on the freezer and the top-loading chest design saving around 1kWh/day, depending on how you use your fridge.
On the other hand, we're talking about a difference of $3/month (if you're on the grid; off grid electrical costs would be higher because of comparatively inefficient generation, and your relative costs will change), which is the equivalent of an espresso or two. Possibly, the chest fridge/freezer may result in a slightly greater risk of back injury, but, arguably, you should be doing your sit-ups anyway.
I was expecting some kind of extensive hack that involved taking the whole thing apart, changing insulation, using a high-efficiency compress or, and goodness knows what else. This sounds REALLY simple. What a terrific post! Thanks!
"In the United States 26% of all electricity generated is used to operate refrigerators."
That's a figure for how much electricity kitchen appliances (not refrigerators) consume in households (not across all sectors).
Fridges and freezers consume about 17% of residential electricity and almost certainly have a lower share in commercial, industrial, and transportation electricity end-use.
Commercial verions of this already exist but that run off eithe AC or DC and can alternate between being a freezer or ridge. One has the ability to run directly off a modest solar panel (you should not open it much at night). THe impetus was for keeping medicines cold in developing nations. Unfortunately, prices are very high -- so this hack is great if you live off grid.
I have a Vestfrost refrigerator/freezer and they are already more efficient than most others on the market - except for the Sunfrost.
Good work.
Went to a presentation on fuel cells tonight and the speaker said the USA has an annual energy budget of about 97 quadrillion btu's and waste comprises about 56 quads of that figure. We have a long way to go.
Anyone here know of a two-door, two-section chest refrigerator-freezer?
Access from the top changes a lot of the equation, from kitchen layout to product packaging to how people use the appliance. Maybe that's why chic drawer-style refrigerator designs haven't made their way into mainstream product lines.
The digital temperature readout this guy added is much nicer than the comparatively crude control dial found in the typical refrigerator. I also like the idea of removing the door light -- less late-night browsing for snacks!
Hmmm, well, to get over the layout change, what about putting the fridge on wheels or tracks? Just roll it out from under the counter when you need something, then slide it back. Depending on how you set up that compartment, you might even increase its efficiency, through exterior insulation and ducting heat.
On a house-building TV show here in the UK (Grand Designs - http://www.channel4.com/4homes/ontv/grand-designs/), a couple had drawer fridges and freezers fitted. They looked like regular kitchen drawers, but when opened were actually refridgerated or freezers. This has lots of advantages over the chest design; how long would you need the chest open to find something way down at the bottom? I also assume you could turn off individual drawers, if you did not have enough food to freeze.
Check out "A Solar Ammonia Absorption Icemaker" in issue 53 of Home Power Magazine. You used to be able to download the PDF for free, but I understand the move to charge (webservers aren't free, even when the power running them may appear to be).
Go to http://www.homepower.com/archive/ and search for "solar ice" and you will find it. Zero electricity, but not for everyone (and it is only really an ultra-efficient ice-maker). Have yet to try it out myself, but it isn't unproven technology.
I remember watching a TV program on inventor/artist Bill Lishman about ten years ago. He was the guy the movie "Fly Away Home" was based on.
Anyway, he invented a lazy susan chest refrigerator for his house. The lazy susan would pop up out of the refrigerator when you opened it. It was very efficient and I imagine much easier to use than a simple chest refrigerator. You can see a picture on his webpage.
http://www.williamlishman.com/underground.htm
This looks great and seems easy. But as soon as I would finish doing this at home my wife would ask me where the freezer is--this design eliminates it. If you want to continue to use a freezer you'll have to add in the additional power usage and space for the freezer.
This seems too good to be true. In fact i love not to use the fridge but this day in age it has become impossible. I have one more suggestion for some people who live in high in Nothern Hemoshphere or southern hemisphere.
Why not find a way to harness the winter and the cold air to flow into the fridge. That way you would not have to use the electicity at all, if not to the bare minimum???
Is it possible??? I wonder!!
You can harness low temperature differences the way your great-grandparents did: in the northernmost corner of your kitchen or pantry insulate a space and provide a low and high opening to the outside, screen those openings and you have a cold(er) box to store perishables in, a kind of root cellar without the cellar. You can make it more efficient by installing temperature sensitive controls to operate baffles for the openings.
Also keep in mind that a fridge that uses less energy like this one will probably vent less waste heat into the house. I have found that I can keep the whole house cool without A/C except for the kitchen (even when none of the cooking appliances are in use).
OK, I'm going to try this, sort of.
I've been wanting a backup fridge, solar powered, for all the hurricane power outages we get in FL.
So I bought a 5cf Fridgidaire chest freezer (not as efficient as the VestFrost, but the $800 savings will pay for more solar panels). Problem is, I can't find a thermostat with a latching relay. Or even one that switches 120V. Apparently they are not as common in the US as in OZ. They all work on 24V here.
I could hack something together, but had hoped it would be easier.
Anybody got any ideas?
I use a chest fridge with a high efficiency 12V motor, which tends to consume about 300Wh/day. This is more realistic. I've read his article and it's clear that his 100Wh figure is overly optimistic because there is only a 7C difference between inside and out for most of the time. Winter has long nights. Summer has short nights. This radically increases summer power usage beyond just a temerature difference. I've seen my type fridge in a cooler climate use 100WH, even with cold temps inside.
Another problem with modern freezer chests is that they have the heat sinks in the outside skin, which heats up the outer skin and makes the outer temperature effectively about 55C-60C. You can burn your hand on it in summer when the fridge is on all the time, trying to cope with all the heat that it applies to itself. It's ridiculous. If you want to build an efficient fridge, you have to have the heat mesh apart from the skin and sink it in water.
As the back of my normal fridge is sealed, ie it does not have cooling piped attached there, I am wondering if I can just lay it down?
I am sure that the cooling unit will object, but I am almost tempted to give it a go after reading this. Had I read it before I bought this (fairly) new fridge I would have implemented it rather than buying a normal one. I too am keen on three of the things Tom mentions: noise, low power, and top loading. Naturally the kitchen layout is a problem too.
We used to have a top loading freezer at my parents home - they are miles better, and it is little trouble to get at the things in them, particularly if you load them correctly. A note to the the fellow who was concerned on this issue: you may be forgetting about how many things are loaded low in a normal fridge!
I did try an upside down fridge to get the normal part up high too - now there is a really inefficient and noisy solution, and the salespeople do nothing to point these disadvantages out at the time that you are buying the beast!
Nevertheless I can imagine that a lot of people will not be so accepting, we human beings do not accept new ideas well.
Well done Tom.
To the guy Larry that was asking about thermostats with a latching relay:
A latching relay is only neccesary if you choose to operate the thermostat (and relay) on battery power. A simpler and cheaper way to control a freezer would be to use a 120 VAC baseboard heater thermostat, and reverse it's operation with a SPDT (or DPDT) relay. Make sure the relay coil is 120 VAC, and that the contacts have an amp rating that exceeds what your freezer will draw. I've sketched a diagram of how to hook this up:
href="http://img479.imageshack.us/my.php?image=relay1jb.png
Keep in mind that everything in this circuit runs at line voltage! All components need to be inside a junction box or other suitable enclosure. The entire thermostat needs to mounted inside the freezer as well.
Baseboard heater thermostats go for about $10 at any hardware store, and you can get the relay for about $15 from an electrical supply or electronic parts store.
A note about power consumption. The relay in my diagram will be drawing power continously whenever the freezer is "off" (as determined by the thermostat). The coil itself is very small, and probably only consumes a few fractions of a watt, but may become an annoying parasitic load if this is being powered by off-grid electricity. The relay consumes no power at all when the freezer is operating.