Freezer to Fridge Conversion: Good performance or shitty Freezer Selection

[Old_Skewler]

I am on a off-grid situation so I tried solving my fridge problem with the infamous "chest freezer" conversion.

I bought a brand new Magic Chef Chest Freezer from Home Depot and a digital controller from Amazon. I also have a EcoFlow River Pro battery that runs the fridge.

The battery is 720Wh. I can power the fridge for about 20 years before the portable battery hits 15% capacity. I tried multiple setpoints and the best battery performance was at 47.4F <---> 39.3F

I honestly cannot tell if this is great performance or if I picked the wrong freezer to convert. i just feel like the setup should perform better - I barely have any food inside, rarely open the fridge, and it is brand new.

Anyone else with a similar conversion to share performance data?

Cheers!

 

[BentleyJ]

The battery is 720Wh. I can power the fridge for about 20 years before the portable battery hits 15% capacity.

Did you mean 20 minutes or 20 hours. I doubt its been 20 years!!!

 

[littleharbor2]

Really hard to give a complete answer without more info. 12 volt system with inverter? What is supposed to keep this battery charged? What type of battery are you using?
Please note, some inverters draw more power than a full sized fridge. Clearly your battery is undersized for the application.

 

[circus]

I'm no chest fridge expert but sounds reasonable. (720w-15%)/20 hours= 30.6w per hour. My dinky 12v fridge advertises 45w per hour.

 

[efficientPV]

47.4F <---> 39.3F where? I find most of the newer fridges are highly stratified with cooling coils near the bottom. To make it useful at all I run mine at 34F. Even then I use a computer fan attached to one of the upper baskets. I only run in the day never discharging the battery more than 10% and storing cold thru the evenings in large amounts of liquids. I had a 5cf and switched to a 7cf to ease locating stuff. If in anything but a dry climate, it will fill up with water from condensation. Use about 800WH a day.

 

[Old_Skewler]

47.4F <---> 39.3F where?

In the fridge temperature control. The one I am using is this one here:

Temp Control

Use about 800WH a day.

Seems high to me.

 

[Old_Skewler]

Did you mean 20 minutes or 20 hours. I doubt its been 20 years!!!

20 hours!

I can run the setup for 20 hours then I need to run the generator to charge the EcoFlow portable battery. Then I get another 20 hours and repeat cycle.

 

[Old_Skewler]

Really hard to give a complete answer without more info. 12 volt system with inverter? What is supposed to keep this battery charged? What type of battery are you using?
Please note, some inverters draw more power than a full sized fridge. Clearly your battery is undersized for the application.

The fridge is 120V.

The battery is a EcoFlow River Pro 720 Wh portable battery with 120V outputs.

Once the portable battery hits 15% capacity, I'll run the generator for about 1.5 hours and fully charge the Ecoflow portable battery.

 

[BentleyJ]

Sounds about right. I concur with circus who posted the same info above.
85% of 720Wh = 612Wh
612Wh/20hrs = 30.6 Watts per hour which is quite efficient.
Of course the compressor doesn't operate on only 30.6 Watts its probably more like 70 to 100 Watts when its running but it cycles on and off and doesn't run all the time.

 

[Old_Skewler]

85% of 720Wh = 612Wh
612Wh/20hrs = 30.6 Watts per hour which is quite efficient.

When you present it like that it sounds correct.

It just feels like the temperature inside the fridge (freezer) drops very fast therefore the unit constantly cycles on and off. I was hoping someone would have a better freezer recommendation with better insulation so that the overall efficiency of the system would increase.

 

[BentleyJ]

Realistically there is no way to significantly improve the insulation on the freezer because the compressor is inside the cabinet producing heat and in some cases the "skin" is used as the condenser so you can't even insulate that area either or block the airflow around the compressor. You need a bigger battery.

 

[MurphyGuy]

Okay.. a couple of things to consider and an observation.

1) I have a 7 cuFt freezer in my 65 degree basement and it uses 600 Wh of power every 24 hrs. During the winter when the basement temps drop into the high 40's, it uses about 500 Wh, and during the hottest part of the summer when basement temps climb into the 70's, it uses almost 700Wh.

2) You said "you hardly have any food in it at all".. This will lower the efficiency of your freezer and cause it to draw more power. Refrigeration systems are a bit like diesel engines in that they're not very efficient when they start running.. As the refrigeration system runs for longer and longer, its efficiency goes up.. at first its a big jump, then it tapers off.
Since you don't have much stuff in there, it means your thermal mass is very low, which means your refrigeration system is turning on and off a lot.. which is bad in all kinds of ways. Fill that bugger up, even if you have to put water in there.

3) The type of inverter you're using will also make a difference. Crappy inverters put out noisy messy power that lowers the energy efficiency of anything running on it.
You are expecting too much.. and a 720wh battery is not sufficient to run anything significant, especially a refrigeration system.

4) Your ecoflow (or whatever it's called) is probably made in china, but regardless of where its made, none of the specifications list the inverter efficiency.. with that in mind, I think we can assume something in the lower 80% range, so your 720wh battery minus 20% losses in really only 576Wh by the time it powers something, and that's assuming you charge to 100% and discharge to zero.

 

[efficientPV]

I would not recommend that temperature control because it does not have a time delay to prevent hot starts. Any control should have a five minute delay. The timed output seems nice, but I suspect that is for total time. I have a timer in my control which turns off the inverter after 20 minutes. This insures any inverter fault will be reset. I can leave my fridge for days assured that it will keep working.

I think 800WH is a very reasonable number. That power is DC going into the inverter and it is a heavily used fridge opened quite a bit with liquids being constantly added. I don't feel the need to be dramatic with numbers. I remember it being in the 700's, I round up. Hope is not a strategy in solar. Your fridge is only safe for drinks in that temperature range. What do you have monitoring that gives you those numbers?

From your own numbers 612WH/ .83 = 737WH in 24 hours, close to what I use. And mine is colder and is used more. Numbers are basically the same.

 

[Shimmy]

If you don't need the depth, fill the bottom of the freezer with 1Qt/L covered plastic bins filled with water to add thermal mass to the system. You could also try putting a thin layer of insulation above the bins and run the temperature a little lower, relying on the stratification to keep it more ideal above.

 

[efficientPV]

I arrived at my summer place June 13 and started my chest fridge. Had a small bag of ice left over from the trip cooler. Two days ago I found the bag and it still had ice. My fridge only runs daylight hours, is set to 35F mid level and even has a fan to help break up stratification. Yes, they are really stratified.

 

[Zwy]

I am on a off-grid situation so I tried solving my fridge problem with the infamous "chest freezer" conversion.

I bought a brand new Magic Chef Chest Freezer from Home Depot and a digital controller from Amazon. I also have a EcoFlow River Pro battery that runs the fridge.

The battery is 720Wh. I can power the fridge for about 20 years before the portable battery hits 15% capacity. I tried multiple setpoints and the best battery performance was at 47.4F <---> 39.3F

I honestly cannot tell if this is great performance or if I picked the wrong freezer to convert. i just feel like the setup should perform better - I barely have any food inside, rarely open the fridge, and it is brand new.

Anyone else with a similar conversion to share performance data?

Cheers!

My less than a year old standard refrigerator uses 1 KWh per day, I've checked it over a few weeks with a Kill O Watt.

It has auto defrost. Freezer on bottom. I have to ask what you are gaining with a chest type freezer over a newer standard upright fridge?

 

[sparrowhawk]

My less than a year old standard refrigerator uses 1 KWh per day, I've checked it over a few weeks with a Kill O Watt.

It has auto defrost. Freezer on bottom. I have to ask what you are gaining with a chest type freezer over a newer standard upright fridge?

Lower energy usage should be one advantage of using a chest freezer, but it's harder to keep fresh food in it without stacking it. I personally wouldn't use a chest freezer as a refrigerator, but would, and do use a chest freezer instead of an upright freezer for the energy savings it offers over the upright freezer.

One of the reasons for the uprights energy use penalty is when you open the door a lot cold air falls out of the freezer and is replaced by warm air which has to be cooled. Also with that air exchange comes more moisture which also has to be removed more often which also takes additional energy. A refrigerator has the same energy penalties but I will take that along with the additional convenience.

 

[Zwy]

I have a commercial upright freezer I purchased new. We only use it for times when we need extra freezer space and quick cool down such as larger parties or get together's where it fits the purpose well. We don't even have it in the house, it is in a shed. I put a Kill O Watt on it, it came out to using the same Kwh in one month that one of my 2 chest type freezers would use in a year.

 

[Xhumeka]

I was hoping someone would have a better freezer recommendation with better insulation so that the overall efficiency of the system would increase.

I'm about to replace my propane fridge with a "solar" fridge from Unique... they have quite a few options these days:

Solar DC Refrigerators & Freezers

Complete the look of your kitchen with a matching fridge/freezer and rangehood!

uniqueappliances.com

They run off DC power (you can buy an AC adapter if you want though) and are very efficient. The 14 cubic foot model I'm considering reports:

Operation:DC Power, 12V / 24V
Total Watt. hr. draw (24V DC):611 Wh/ 24 hrs (set to -14˚C / 6.8ºF freezer/+4˚C / 39.2ºF refrigerator performance in a +25˚C / 77ºF ambient)
Total Watt. hr. stable (24V DC):535 Wh/ 24 hrs (set to -14˚C / 6.8ºF freezer/+4˚C / 39.2ºF refrigerator performance in a +25˚C / 77ºF ambient)
Power consumption:75 W on 12V/24V
Average run current:3.2A on 24V
Fridge temp. range:-3°C to +10°C / 26.6ºF to 50ºF
Freezer temp. range:-15°C to +6° / 5ºF to 42.8ºF

 

[Bluedog225]

Shame they don’t have 48v