Chest freezer as a chest refrigerator

System · July 2005

I came across this on another list. A clever guy in Austrailia has converted a chest freezer to a chest refrigerator and it only consumes 100 watt hours per day. It all makes sense.

Here is the link.

http://www.builditsolar.com/Projects/Conservation/chest_fridge.pdf

I have been very seriously considering replacing my frig but I may give this a go instead.

Jay

PS: The original link is apparently dead:

ILFE wrote: »

Bill, the link for the write up in the first post of that thread is no longer valid.

I found it here, though: http://mtbest.net/chest_fridge_1.pdf

Perhaps, one of you staff folks may change it in that post?

Thank you ILFE. -Bill 3/25/2014

niel · July 2005

Re: Chest freezer as a chest refrigerator

jay,
that was interesting and it does make you wonder about refrigs today. the biggest problem i could see doing this is fitting it where the refrig used to be. that's not much space for it as most kitchens are designed to allow only a small section for it.
niel

System2 · July 2005

Re: Chest freezer as a chest refrigerator

That was great to read. We have two propane-powered upright refrigerators and one chest-type propane freezer at a cabin. I can certainly attest to the fact that the freezer has absolutely no trouble coping with the hottest days, while the freezers on the two refrigerators struggle mightily.

We're going to remodel our kitchen at our house one of these days...I wonder how my wife would feel about a chest refrigerator? As Niel notes, they eat up a lot more floor space.

--Tad

crewzer · July 2005

Re: Chest freezer as a chest refrigerator

Interesting idea, but hardly novel. For example, Danzer makes an 8 cf DC chest fridge, but, at ~$1,000, it’s not cheap. See: http://www.backwoodssolar.com/Catalogpages2/refriger2.htm

Note that the Vestfrost SE255 freezer described in the article is a 9 cf unit (= 255 liters). That’s pretty small by U.S. standards. I have to admit that I question the author’s energy numbers and environment (103 Wh/day at ~ 18 C, or ~64 F, which is rather cool). That’s ~ 28% less than the Danzer’s 70 F requirement, and it probably doesn’t include inverter losses.

Nonetheless, it’s a nifty idea, and converting a “standard” chest freezer may be worthwhile. However, the interior may need a small circulation fan (= higher energy consumption) to avoid stratifying interior temperature layers.

HTH,
Jim / crewzer

System2 · July 2005

Re: Chest freezer as a chest refrigerator

Here are 2 thermostats specifically meant for controlling the temperature of chest freezers, with a different outcome in mind: creating the right temperature for beer and wine. It would serve the same purpose, though, to convert a freezer to refrigerator temperature.

http://ceisites.com/9025.html
http://www.morebeer.com/product.html?product_id=16663

System2 · July 2005

Re: Chest freezer as a chest refrigerator

:? I too question the author’s energy numbers. Two minutes of run time would hardly be enough for the system build up pressure, let alone do any cooling of the interior, and 90 seconds? come on - - .
I agree that it should be much more efficient than a "normal" refer, but his numbers and run times are pure bull **** The only way his thermostat (if not defective) could possibly shut down the compressor that quickly would be if the thermistor happened to be glued to the interior wall, right over the evaporator nozzel and that would give no indication of the interior tempature at all!
Not putting down the whole idea, just offering a reality check.
Would be great if someone else could try it and report proper numbers and tempatures after a bit of experience.
Just a note on adding a length of wire to between the thermostat and it's thermister sensor: It may well be sensitive to rhe length of wire. Have run into this with indoor-outdoor electronic thermometers and it doesn't seem to have so much to do with wire resistance, but more a capacitance thing. To save energy and avoid heating the thermistor, the circuts usually only check the temp every minute or two, by sending out a HF AC pulse. So, confirm operation after any modification.
Wayne

System2 · July 2005

Re: Chest freezer as a chest refrigerator

Thought more about this today - when I was “working”.
The following numbers are rounded off and do not take into consideration the inverter losses etc.
One chest freezer listed as using 274 kWh per yr, average temp 0F inside and 70F room temp.
Since energy consumption is directly related to temp differential across the walls of the freezer, (inside to outside) it follows that energy consumption would be 274KWH / 70F= 3.9 KWH per yr, per degree F difference.
It follows that when using the freezer as a “chest refer”, a good inside temp would be 35F, which would result in a 35F differential across the walls.
35X3.9=135.5KWH per yr. Just half the energy consumption and that makes sense.
Per day consumption would be 135.5/365=.37KWH, or 370watt hours/12Volts=31AH per day at 12 Volts. NOT BAD!! One could easily install a small brushless 12VDC fan such as used in computers etc and run it at reduced speed and power to prevent stratification of internal temps. Easily less than 1 watt. No need for a hurricane inside, just a very little air movement.
I think this is very interesting and very doable.
If someone has a chance to try this before I do, please let us know the real world results.
Thanks
Wayne

kc8adu · July 2005

Re: Chest freezer as a chest refrigerator

the reason a chest unit is more efficient is because the cold air sinks.
not as much loss as an upright unit where you lose a bunch each time the door is opened.

System2 · August 2005

Re: Chest freezer as a chest refrigerator

Thanks for all the feedback!

I agree, the numbers don't add up in a number of ways.

If you take the link that Crewser sent (I look at Backwoods all the time. Can't believe I missed chest refrigerator there) it seems that the Sundazer 'frig' uses 27 percent less electricity than the identical freezer. Given that, then a Kenmore 7.2 cu ft freezer that normally uses about 274 kWh/yr would use .2 kWh/day. Double the Aussies numbers but still very descent.

BUT If one gives up the top freezer refrigerator then one has to buy a chest freezer to replace the top freezer. I looked at a 5 cu ft Kenmore chest freezer and it uses .67 kWh/day. Add the two together and now you are back to almost a kWh per day (.87 kWh/day) for only 12 cu ft of cool/cold space.

My 12 year old 21.5 cu ft Amana uses about 1.3 kWh/day with the temp set at the warmest settings. It doesn't add up. A new Kenmore 15 cu ft top freezer refrigerastor uses 1.0 kWh/day. I t seems then that most of the energy used is to keep the freezer cold, than to cool food.

Maybe a freezer is more an electical luxury that I realized. Maybe I need to look at not having a freezer. hmmmmmmmmmm.

Thanks,

Jay

Brock · August 2005

Re: Chest freezer as a chest refrigerator

Maybe I am wrong, but isn't it more then a 2 to 1 gain halfing the temp? I mean the regular chest freezer is say 70 degrees different at 35 degrees different wouldn't it work about 1/4 as much or more realistically 1/3 as much? It seems to me when I push my chest freezer temp way down (-15F) it runs proportionally longer.

What is the temp drop on the evaporator from ambient? Maybe as you approach that it isn’t a flat ratio?

System2 · August 2005

Re: Chest freezer as a chest refrigerator

So did anybody try it yet??

System2 · September 2005

Re: Chest freezer as a chest refrigerator

I have the digital control coming and think I have settled on a Frigidaire FFC0723 7.2 cu ft freezer. It uses more electricity than the Crosley but is local. At $200 it can always become a real freezer again.

More in a couple of weeks.

Jay

System2 · October 2005

Re: Chest freezer as a chest refrigerator

Controller was backordered but just arrived. Will pick up freezer tonight.

Found this website. Excellant data for all refrigerator and freezers, even older models.

http://www.homeenergy.org/consumerinfo/refrigeration2/refmods.html

The 7 cu ft Crosley in 2004 used 276 kwh/yr. The Frigidaire listed above in 2004 uses 281 kwh/yr and the compressor warranty is better.

Will report more later.

Jay

System2 · October 2005

Re: Chest freezer as a chest refrigerator

The manual for the Ranco digital controller has a registration problem when it was printed and I couldn't reliably tell where the wires where to go, so it took me a couple days to get it sorted out with their tech support.

I have my first day's results and it used 260 watts in 24 hours with a 30F temp differntial. (I started the 24 hours after it initially cooled) The temp probe is about 6 inches down from the top and the set point is 37F with a 3 degree differential. That means on above 40F and it is off when below 37F. Thermal stratification is not what I would have suspected. The cooling coils are near the top on the sides of the unit and it is colder at the top than on the bottom. Right now the temp probe says 37F, above that is 32F and on the bottom is 38F.

The unit only had beer, maple syrup, eggs, bread, and rice in it to cool. It appears that it may be a more effiecent use of space, than a front fridge, but time will tell. It has tons of room left right now.

260 watts per day is not 100, but if one only needs cooling it appears like an enegy effecient way and inexpensive way to go.

Jay

System2 · October 2005

Re: Chest freezer as a chest refrigerator

:-) Wow! If your info holds, that's less then 25 amp hours per day from a 12 volt system!
Thanks a lot for sharing your findings.
Wayne

crewzer · October 2005

Re: Chest freezer as a chest refrigerator

Jay,

How are your numbers holding up? You may be able to help with this project: http://www.wind-sun.com/smf/index.php?topic=1211.0

Thx,
Jim / crewzer

System2 · October 2005

Re: Chest freezer as a chest refrigerator

Hey Crewser,

It has been 18 days and it is averaging 240 watts per day for a ~30 F temp delta. Not the 100 that the Aussie claimed, nor the 200 that I anticipated but not bad either.

For the first 17 days I had the setpoint at 37 F with 3 F temperature differential, ie, meaning it came on at 40 and turned off at 37. The probe is 6 inches down from the top. There is a lag in the cooling system and I routinely see the temp go as low as 31F a number of minutes after the compressor turns off. Yesterday I changed the setpoint to 38 F and the temp differential to 2 F and I am still running about 10 watts an hour. I will continue to experiment with it and post my results. I must say it is very quiet, much quieter than my frig which is about to be put on freecycle. ;-)

HTH,

Jay

System2 · December 2005

Re: Chest freezer as a chest refrigerator

Well it has been 40 days with the setpoint at 38 with a 2 degree temp differential. It has averaged about 230 watts a day.

Overall I am happy with the experiment. In fact my old frig was picked up today and I won't be going back to a normal frig again. I had unplugged my freezer before, so I was living with my standard combo frig for over a year. Now the old freezer (12 cu ft) is up and running and ALL of my frozen items are in it and it resides in my detached garage. The chest frig fits in quite nicely where the old frig did, but it was also at the end of a line of cabinets and I had a couple of inches to spare. I find that 7 cubic feet is adequate for refrigerated items but has little capacity for more (like the extra food that you buy at the holidays). I have two baskets that hang from the top and there is a section on the left where the compressor is, that provides another convenient shelf. The rest is below the baskets and needs to have the baskets slid to one side or removed to acquire items from the lower section. It is not filled so lotsa left overs from a holiday meal can fit there, but are not convenient to get to. I am also single so I don't have to please anyone else with this arrangement. ;-)

My freezer is using less than .5 kWh per day and adding in the chest frig, I am about .7 kWh/day for the both. It will go up in the summer, but don't they all. Overall the size of the mix, 12 cu ft freezer and 7 cu ft frig, works very well for me, I think better than the ratio on the standard combo frig.

Unless something profound happens, this will be my last report on it.

Jay

System2 · December 2005

Re: Chest freezer as a chest refrigerator

Thanks a lot Jay for the update.
One question, how do you handle the moisture in the chest fridge? Condensation is showing up on the top foot of the walls in my 5 cu ft unit. I'm thinking of installung a sort of mini eves trough to catch it as it runs down and direct it into a tube that drains outside the chest.
Thanks
Wayne.

System2 · December 2005

Re: Chest freezer as a chest refrigerator

Wayne from NS Cana wrote:

One question, how do you handle the moisture in the chest fridge?

Funny you should mention that. I pulled out some maple syrup tonight, that I wanted to boil down to 224F (107C), continuing a experiment from last spring. There was a little syrup on the bottom of the frig, so I cleaned it up and it was then that I noticed a little puddle of water in a corner. A wash cloth cleaned it out with a couple of wrings, so it wasn't much, but it was there. It doesn't seem to be a large problem now, but might be when the weather gets warmer and more humid.

I like your idea, but I am going to give it some thought.

Thanks for sharing that. I will report on what I do and how it works. I would be interested to hear your results also.

What are the temps you are controlling your frig to BTW?

Jay

System2 · December 2005

Re: Chest freezer as a chest refrigerator

Thanks Jay, the temp; taking into account the overshoot, ranges from about 33 to 41.
The first thermometer I used was giving wrong readings, It told me I was centered on 32. Thought it strange nothing was freezing. I'm still looking for something to use for the "eves trough", I'll know what I want, but haven't seen it yet.
As things develop, I'll let you know. It's a real learning experience, that's for sure. Great to be able to discuss it with someone who knows what I'm talking about. LOL
Grateful for this form.
Later
Wayne

System2 · December 2005

Re: Chest freezer as a chest refrigerator

Wayne from NS Cana wrote:

the temp; taking into account the overshoot, ranges from about 33 to 41.

Wayne,

With the 38F setpoint and two degree temp differential, that is about what I see, 33F to 40F. I don't see the frost forming around the top of the inner unit like I did when I had the settings of 37F and 3 degree differrential. I don't like the extra cycling, but I do like the lack of frost. The moisture in the bottom may have been worse then and I didn't know it.

Most of what I use are in the upper baskets and they are plenty cold. I am finding that food is keeping much longer than my old frig running at 40F. I am wondering is I should bump up the setpoint to 39 and keep the 2 degree differential. I may get less moisture that way also.

Yes it is nice to have someone to talk to about it. On the RefrigeratorAlternatives at Yahoo Groups there is a guy from Missouri who is using the Sear model that has a lower drawer and his temperature gradient was huge, 20F. He had to drill holes between for air circulation and now gets a 10F temp gradient. I usually see 5F. But the lower drawer would be fine for veggies and more convenient.

Thanks,

Jay

System2 · December 2005

Re: Chest freezer as a chest refrigerator

One thing about the Chest Fridge's high moisture level, the vegies should last MUCH longer than in a "real" fridges "wilter" drawers. The manufacturers love to call them "crispers". HA! what a joke that is.

System2 · June 2006

Re: Chest freezer as a chest refrigerator

Update
Finally had time to set up my "chest fridge" to my liking.
Installed the mini water catcher about a foot below the rim and it drains through a tube, into a container outside the "fridge". Works great. Only thing is the upper inside walls, above the water catcher are usually wet. No problem except if you brush against it, your sleeve gets wet. Otherwise, the moisture is well taken care of. I modified a furnace thermostat to operate near freezing and reversed the little glass bulb containing the mercury which closes the circut, so that the switch closes on temp rise. That, through a long small gauge wire, operated a little 12 volt relay in the outside shed where the batteries are, which jumps across the "on/off" switch on the 1000 watt MSW inverter, which is dedicated to the fridge. This relay doesn't switch the supply to the inverter, rather, it just tells the inverter to start up and run. That way, the inverter is never on unless the "fridge" is running. Used another relay with a 5 second delay, to give the inverter a chance to start and stabilize before the load is connected. It's been running this way for a month now and I'm very pleased. With nothing in the fridge, it runs about 6 minutes every 40 minutes. With the fridge full (installed 2 racks at two levels that come from the back wall, to about 2/3 of the way to the front, so you can reach down to the lower shelves/racks) it runs 13 minutes on - 90 minutes off (thats a 103 minute cycle) and the draw from the 12 volt battery, (after it gets started) runs from 12 to 14 amps. Generally starts out around 14 amps 12 volt and drifts down to around 12 amps by the time it's ready to stop, 13 minutes later. The compressor never gets the chance to get much more than the chill off it before it stops again.
That's 3 hours run time every 24 hour day. 13amps X 3 hrs = 39 AH @12 volts! Not bad!
The average temp is set close to 1'F above freezing. I like ice water and I have it!
The 5 year old upright Sears energy pig is now silent (it was a noisy SOB) and the new one is all but silent when it does run.
If I can do it, why can't some big manufacturer? Could it be that the utilities have them in their pocket?
Cheers
Wayne

crewzer · June 2006

Re: Chest freezer as a chest refrigerator

Waye,

Great report! I'm curious, though: How big is the "chest fridge"?

Thx,
Jim / crewzer

Brock · June 2006

Re: Chest freezer as a chest refrigerator

Hey where did you get a relay with a 5 second delay? I have a bunch of loads that are all on contactors and all kick on at once. Even delaying 1/2 of them would make a huge differnce.

Nice job on the fridge!

System2 · June 2006

Re: Chest freezer as a chest refrigerator

Thanks for the positive feedback guys.
The size is 5 cu ft. and it's a Woods, model # CO5WA. I believe that a 10 cu ft unit would not use double the power. Probably about 30% more.
By the way, this one has 2 inches of foam insulation, but there are now freezers available with 3 or more inches.

The "time delay relay" LOL, I play around a lot with this stuff. Used a 12 volt relay with 10 amp contacts, put a resistor in series with the relay coil and a capacitor across the coil. The resistor lets through slightly more than just enough current to operate the relay, but with the cap across the coil, when the power is first applied, the capacitor must first charge up before there is enough voltage to pull in the contacts. The resistor limits the current, thus it takes time for the capacitor to charge up.
The values of the resistor and capacitor will depend on the characteristics of the relay. You will have to play around with it until you hit the right combo. I used a 4000 mfd cap but forget the resistor value I finally settled on.
Cheers
Wayne

Brock · June 2006

Re: Chest freezer as a chest refrigerator

LOL, that is what I have done in the past using the Radio Shack relay's I forgot about that, I will have to try that again.

System2 · June 2006

Re: Chest freezer as a chest refrigerator

:-) Way to go Brock! Hopefully this thread will help someone out there who may be thinking about going off grid, or is already off grid.

ALSO, forgot to mention, the high moisture had resulted in a small bit of rust showing up at the seams where the inside metal walls of the "fridge" come together. Solved that one by drying it out and running a bead of silicone in all seams and corners at risk. Also ran a bead of silicone along the front edge of the racks. That prevented items from sliding off the rack and crashing to the bottom.
One other thing, for anyone who doesn't do much thinking, when first turned on, expect it to run for 1/2 an hour or so, to get the initial cool down. Same thing if you load it up with items not already cooled down.

Good night all
Wayne

System2 · August 2006

Re: Chest freezer as a chest refrigerator

jay.. you ordered a controller for your new refrigerator, did you get it from the aussie guy?

System2 · November 2006

Re: Chest freezer as a chest refrigerator

:-) Interesting update on my woods, 5 Cu Ft freezer converted to fridge.
Just moved "home" (where my electricity so far in from the utilities) for the winter, from the solar summer camp and brought the chest fridge with me. Connected it to my Kill a Watt meter at 8:00 PM last evening and just checked the useage 24 hours later. Today was cold outside, just above freezing, but full sun all day, which due to all the south facing windows, drove in the inside temperature to about 80F for most of the day.
The total power used by the "fridge" for the last 24 hours was 0.28 KWh !!
The fridge temp is set for about ONE degree F above freezing. Cycles between +2.5, to --2.5 C.
Things are very cold, but don't quite freeze. I have Ice water without the ice.
Seriously folks, I find things stay fresh much longer than in a regular fridge, probably because it holds a colder temp without freezing. Runs 10 minutes, then is off for 90 minutes. That's a one hundred minute cycle. Am I pleased with it? You bet! Would I ever go back to a regular energy pig fridge? Can't see it! Would I get a bigger one? Probably a 7 Cu Ft next time.
Cheers
Wayne

Chest freezer as a chest refrigerator

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