Freezer to fridge conversion?

Has anyone built their own fridge out of an old chest freezer that was more efficient and  cheaper than a Sundanzer? (for example)

I'm thinking of doing the "old freezer to fridge conversion" I've seen online to be used in the tropics, but I'm thinking of taking it a couple steps further.
1. Cut the freezer in half horizontally.
    - the normal depth of a chest freezer isn't practical for daily use. I'm thinking if it were half as deep, it
      would require less electricity and provide easier access to what's inside.
    - so I would take a skill saw to it all around to cut it down to size then reattach the lid?
2. Increase or even double the insulation.
    - I always wondered why there aren't manufacturers out there who haven't done this?
    - I would remove the outer shell of the chest freezer and just double the thickness of the insulation (especially on the bottom and side walls) to increase the r value and again reduce energy consumption.

It would ultimately be used in the Philippines on a solar system.
Any thoughts? Has it been done before?

Yes. The thermostat has an adjustment screw. I was lucky enough that I could turn it far enough to make it a fridge.
On this model cutting it in half would not (easily) work, as there are cooling pipes on the inside and heat radiating pipes (condenser) on the outside.

Instead a two boxes could be used. One for the less used things below and one for the common things above.
Energy use is not much of a problem. It uses 75W when running, but does not run often. (I have to measure it).

to reiterate Sebastian's point about the condenser: at least on the models I'm familiar with, adding more insulation would actually dramatically reduce efficiency. the condenser is placed under the outer skin of the freezer so the whole surface acts to radiate heat away. if you add insulation over that, the heat will not be radiated away and the compression cycle won't be able to cool the freezer.

for more insulation to work, it would have to be placed toward the inside of the freezer from the condenser tubes, which would not be a trivial undertaking, to put it mildly.

Is there any reason why you can't add the insulation inside the freezer instead of cutting the unit down and then adding insulation to the outside? I'm thinking about the practice of storing gallons of frozen water in freezers as I say this.

yeah, Casie. for the same reason it won't work on the outside, it won't work on the inside: instead of condenser tubes, there are evaporator tubes under the skin on the inside. insulation there would just keep energy from traveling out of the freezer box, which is how it's cooled. any additional insulation would have to go between the evaporator and condenser tubes, at which point you're probably better off starting from scratch.

So now I'm curious about whether the old technique with the water gallons even works. We've never had an empty enough freezer to try it ourselves.

adding water isn't about insulation, it's about adding mass. you're making a sort of thermal flywheel so that the compressor doesn't cycle as frequently. it might run a little longer when it does cycle on, but it should work out to be a bit more efficient that way and last a little longer. the beginning of a compressor cycle is when the bulk of wear on the moving parts takes place, so if there are fewer cycles, there's less wear.

New chest freezers are cheap,so cheap they rival used refrigerators on a cubic foot basis.
As far as hard to access space, filling the bottom with one gallon jars of lacto fermented foods seems ideal.
Buy a second freezer for more space, repeat with the gallon jars.
I would add a  tempature controller .
For about 20 bucks, it will hold the temp at 40.
It has a tempature probe and a place to plug in the appliance,no fancy wiring needed.

Now that I'm thinking about it, I should order one for my ancient huge basement upright freezer, and buy a 5 cubic foot chest freezer for upstairs.

Clearly chest freezers are more efficient, but an upright freezer converted to a fridge is probably more efficient than a standard refigerator.
I could fill it with ferments,out of the way of my family's everyday fridge use.

The same temp could controllers might be useful for sous vide and smoking.

About the water trick… Before converting it to a fridge, it was filled with water bottles which were then frozen (and some exploded…).
While freezing took 3 days, the result was ice/cool water for the the 7 days of travel under rather warm conditions.

If you can find someone who repairs fridges/freezers, you could build your own from spare parts. I don't like the idea of cutting into the coolant pipes…

William Bronson wrote:Clearly chest freezers are more efficient, but an upright freezer converted to a fridge is probably more efficient than a standard refrigerator.

I'm not sure this is true. chest freezers are more efficient primarily because of the orientation of the door, not because they're freezers. the heat pump apparatus is optimized for freezer temperatures, not refrigerator temperatures. so I would guess that an upright freezer would be slightly less efficient than the same size upright refrigerator.

one advantage of most upright freezers and refrigerators is that the condenser tubes aren't usually in the skin, they're on the back or bottom. if that's the case, you could actually add insulation to the outside as long as you didn't restrict airflow past those tubes. my guess is that a chest freezer conversion would still come out ahead, but that might depend on how often you'll be opening the thing. the more it's opened, the better the chest option looks.

You might be right, but the extra insulation alone might make the difference.
Here is one source that claims as much, though the method seems more involved:
Convert a Freezer into a High Efficiency Fridge

Thanks everyone for your time, the education and contributions to the discussion!
I now understand that the condenser tubes make my idea impossible.

Here's a follow up question. I can't find anyone online that has ever built there own chest type fridge (plywood shell, a ridiculously high R value walls, salvaged condenser tubes, etc) with components from an old freezer.
I'm not asking if it's worth the effort, but only if it's possible just to see how far we can take the energy efficiency?

I do think it's possible. to get it right, you might need coils from two different freezers: a bigger one for the condenser coil and a smaller one for the evaporator so that you can have thicker walls and more insulation. the alternative would be to re-bend one set of coils to fit the new arrangement, which would also be difficult.

some things to consider:

most refrigerants are potent greenhouse gases. beyond that, I don't know much about them chemically. they may be horribly toxic, or they may be inert. but if you lose any, and you most likely would, you would very probably be creating more problems than you're solving, at least on any scales bigger than your immediate financial savings.

fitting coils together without leaks is not easy if you haven't done it before.

and the compressor that you get out of one of the old freezers may not be tuned as well to the new arrangement and you may, again, lose efficiency there. I don't know that you would, but you might.

Dany Richard wrote:Here's a follow up question. I can't find anyone online that has ever built there own chest type fridge (plywood shell, a ridiculously high R value walls, salvaged condenser tubes, etc) with components from an old freezer.
I'm not asking if it's worth the effort, but only if it's possible just to see how far we can take the energy efficiency?

I have a thought, but lack knowledge. That is to say: this may not be a good idea, but it is an idea. Maybe some good could come from the discussion of it. How about the home made shell you describe, with a coolbot and a small and efficient air conditioner?

It is possible to get affordable compressor for solar/DC usage (low starting current), where as DC/off-grid fridges are usually quite expensive. Building your own might save quite a bit. (And even allow to turn an entire cellar into a fridge/freezer!)

Sebastian Köln wrote:Yes. The thermostat has an adjustment screw. I was lucky enough that I could turn it far enough to make it a fridge.

I would like more info on this... by far the easiest-sounding solution!  Do all chest freezers have an adjustment screw on the thermostat?  How common is it for the low end of the range to be in fridge territory?  Anyone have any comment on brands or types that lend themselves best to this sort of tweaking?

I bought a used chest freezer from a coworker for $20, there's no adjustment that I saw and it has a target temp of 0F. I then bought a digital thermometer on Amazon for around $20, which has the temp probe and 2 outlets, on for "cooling power" and one for "warming power". I set it for 35F, +/- 2F. So when it hits 37, power is sent to the cooling outlet, which the freezer is plugged into, and it turns on to cool it to 35. If I needed to keep the temp within a tight range, say for brewing beer, then a heater can be plugged into the other outlet, and if the temp dropped below the lower number (33F for my example), then power goes to the other outlet and a heater could turn on.

This old chest "fridge" was using 240 watt hours per day in my 80-90F garage over 4 days of testing, compared to nearly 1kwh per day in regular freezer mode of 0F.

What is the initial start up surge like for freezer to fridge conversions? Is it the same as it would be running it as a freezer, or is it around 5x75w?

And does the surge happen every time to compressor switches on by itself, or just when the power is switched on?

I wonder if filling the bottom with tubs of water as thermal mass, it could be switched off overnight without getting too warm?

surge should be the same. it's the same motor that's being started. there may be a small difference because of viscosity changes of the refrigerant due to temperature, but I would expect that to be negligible.

I have a chest freezer conversion on a timer so it doesn't turn on and make noise between 9:00 pm and 7:00 am. it's set to 2° C. on a really warm night, it might get up to 5° by the time it switches back on, but 3.5° is more common, even in the summer. I've got up to 10 gallons of water and beer in there, though, which certainly adds some thermal mass.

Thank you! It's good to hear real life experiences with these. I only need to keep raw milk cool in there for a day or three before cheesemaking so this might work well if I have it on during the day, as I don't need it to strictly be below 4°c.

Hey, Dany and others! I've got a thread running over in Solar where I talk about our chest freezer to fridge conversion on the way to describing our current project: https://permies.com/p/949880.

Our current project might interest you, too, since you're thinking outside the box. It started its life as a decades-old small upright RV fridge with ammonia cooling, but we removed the cooling set-up from what was its back (apparently the ammonia had leaked out years ago), turned that into its bottom, added insulation, and installed peltier chip units in the door, which is now its lid. It runs on 140 watts of solar panels with no batteries, so not at night or when it's overcast (but then it's cooler, and we put ice bottles or the equivalent in there as well; more cold ballast would be good).

It's not working so well now at the hottest time of the year, but we're still playing with it. We're getting another panel, a couple more peltier chips, and the components for a liquid-cooled rather than air-cooled system that we'll add on to the existing system by mounting those in the box's small sides, keeping the existing units in the lid.

We're far from experts on thermodynamics and how all this stuff should work ideally, so we're making plenty of mistakes and what I say should therefore be taken with copious grains of salt, but the project is cheap and educational and -- since we got frustrated with that initial power surge of compressors -- more manageable for us than what we were trying before.

And of course, if we give up on the project, we can move those panels to our main array and only the peltier chips and fans (both of which are ridiculously cheap) will be wasted, at least until we find another use for them. I think the current plan is to use salvaged motorcycle radiators for the liquid cooling system (partner is a motorcycle mechanic and has plenty of bikes for parts, plus friends with other bikes for parts).

Beth's mention of motorcycle radiators gave me an idea: increasing the area of a freezer's heat exchangers.

freezers have two heat exchangers. one cools the inside, the other heats the outside. adding surface area to either one could improve efficiency by accelerating the transfer of heat energy from the inside to the outside. the surface area on both the inside and outside are pretty much minimized in many chest freezers. adding fins (or even vertical tubes to use the stack effect) to the outside of a freezer that has the condenser under the external skin should improve heat transfer at the expense of a bigger footprint and hideous appearance.

on some upright freezers and refrigerators, this strategy is already used. the condenser coils often have their surface area increased with fins, much like an automotive radiator.

you could also add fins to the evaporator on the inside, but that would take up useful space. I think augmenting the condenser is a better bet.

this is sort of the opposite of adding external insulation, which was suggested earlier as a possible way to improve efficiency.

as far as Beth's issue with the surge on startup, that could be fixed by manually giving the motor a boost to get it started. it would mean digging into the guts a little bit to access the pulley wheel, and maybe adding another pulley to the works. it would also mean less automation, though the process could certainly be automated with a little ingenuity.

it also occurs to me that replacing the AC motor on a freezer with a DC motor and skipping the inverter could solve some solar startup problems, but electrical engineering is well outside my expertise. in my limited understanding, though, a DC motor can handle variable voltage, so just hooking a PV panel up relatively directly would result in the motor turning at different speeds. unless the speed gets way too high, neither the motor nor the compressor should be negatively affected (again, I'm not at all certain about this, so feel free to correct/educate me). if the freezer had a dedicated PV system, it could just always be on.

of course, I have no idea what variable speed DC motors cost, or how difficult it would be to retrofit one. my guesses are, respectively, a lot and very.

tel jetson wrote:it also occurs to me that replacing the AC motor on a freezer with a DC motor and skipping the inverter could solve some solar startup problems, but electrical engineering is well outside my expertise. in my limited understanding, though, a DC motor can handle variable voltage, so just hooking a PV panel up relatively directly would result in the motor turning at different speeds. unless the speed gets way too high, neither the motor nor the compressor should be negatively affected (again, I'm not at all certain about this, so feel free to correct/educate me). if the freezer had a dedicated PV system, it could just always be on.

of course, I have no idea what variable speed DC motors cost, or how difficult it would be to retrofit one. my guesses are, respectively, a lot and very.

Our Sundanzer freezer is on a dedicated PV system, and it does work without an inverter, but it still requires a battery and charge controller. We tried connecting directly without the battery, but it couldn't provide the necessary power for the surge even with the Arizona sun shining brightly. If at some point we have sufficient funds and desire to do so, we may expand this dedicated system and add a second DC chest at fridge temperatures with a Danfoss compressor like Sundanzer uses.

The thicker the insulation the more efficient your fridge will be. It's pretty easy to construct and convert a freezer/fridge if you know the trade. If you dont know refrigeration then have someone do this part and you can only do the body works. I use to repair these kind of devices. All of the thermostats have adjusting screws although I am not sure if  all freezer thermostat can be adjusted enough for it to function as fridge. However thermostat here in the Philippines is pretty cheap. The last time I bought it cost me  P350.00. That was 2 or 3 years ago. I no longer do these sort of job. Refrigerant is very toxic. every time I inhale just a bit I feel the effect on my health the following day. So be very careful. You can also salvage thermostat from broken fridge. If adjusting the thermostat dont work try to relocate the sensing bulb of the thermostat at the lowest part. If you do pursue with the conversion I would suggest to add a few more length of condenser coil. Perhaps a fourth of the total length. Your fridge will consume less power and last longer. Nearly all devices on the market implement some sort of " planned obsolescence" a shorter condenser coil adds more stress to the motor.

It is my intention to use Marine refrigeration conversion kit from West Marine, these kits have all the components for the fridge except the insulated box allowing for remote locating of the compressor radiator unit outside my house. A salvaged/broken freezer would make a great base for such a system as they are already better insulated than a fridge. I'm also brain storming a secondary cooling system that utilizes the cold outside air of winter to keep fridge cool.

For many years  I have cringed every time I opened the fridge door, all that cool air falling to the floor.  
I figured a chest fridge would be perfect, but all the wife could see is counter space disappearing.

Dennis Barrow wrote:For many years  I have cringed every time I opened the fridge door, all that cool air falling to the floor.  
I figured a chest fridge would be perfect, but all the wife could see is counter space disappearing.

there are kits that let you add runners to the bottom of a chest freezer so you wouldn't have to lose counter space. build a counter over the top of it and slide the freezer/fridge out when you want to open it. you might actually gain counter space by adding counter where before there was only an upright refrigerator.