Freezer to Fridge Conversion: Good performance or shitty Freezer Selection

[Zwy]

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

76W x 12 hours (runs 50% of the time) = 912W

About 1 Kwh over a 24 hour period. I'm not quite sure where they came up with 611Wh........

how often does a refrigerator run at DuckDuckGo

DuckDuckGo. Privacy, Simplified.

duckduckgo.com

From everything I've seen, a refrigerator runs 30 min cycle off/on.

 

[Checkthisout]

Howdy.

You said "I barely have any food inside".

It may have already been said but an empty fridge/freezer runs all the time because the mass/surface ratio is low.

You need stuff in that freezer or it will stay running all the time.

 

[MattiFin]

Sounds reasonable for cheapo unit with no special attention paid to energy efficiency.
Could be much better tho, for example https://www.idealo.de/preisvergleich/OffersOfProduct/201460147_-rb38a7b6as9-samsung.html
4 cu ft freezer and 9 cu ft fridge totalling 295 Wh per day or mere 12w average.

 

[Xhumeka]

Sounds reasonable for cheapo unit with no special attention paid to energy efficiency.
Could be much better tho, for example https://www.idealo.de/preisvergleich/OffersOfProduct/201460147_-rb38a7b6as9-samsung.html
4 cu ft freezer and 9 cu ft fridge totalling 295 Wh per day or mere 12w average.

That Samsung RB38A7B6AS9 looks really cool, but from what I can tell it's only available in Europe at the moment... I can't seem to find any North American supplies for it. Hopefully it makes its way across the pond soon!

 

[MattiFin]

That Samsung RB38A7B6AS9 looks really cool, but from what I can tell it's only available in Europe at the moment... I can't seem to find any North American supplies for it. Hopefully it makes its way across the pond soon!

That seem to be case with many models. North American market is more for reefer size fridges. Compact&efficient models ideal for solar use are difficult to find in NA market based on comments here.

some smaller 4 cu ft models do even better than the mentioned Samsung, 80kWh or so per year. That would allow some serious runtime on battery (Like 1 year with tesla car size battery ? but you would need to get creative with the inverter control or inverter idle losses are 3x actual fridge consumption.

 

[DThames]

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.

If the fridge was full of jugs of water, it would not cycle as often but would require a longer run time to drop the temp, because of increased thermal mass.

 

[Old_Skewler]

Howdy.

You said "I barely have any food inside".

It may have already been said but an empty fridge/freezer runs all the time because the mass/surface ratio is low.

You need stuff in that freezer or it will stay running all the time.

Thanks for this clarification.

 

[Xhumeka]

That seem to be case with many models. North American market is more for reefer size fridges. Compact&efficient models ideal for solar use are difficult to find in NA market based on comments here.

some smaller 4 cu ft models do even better than the mentioned Samsung, 80kWh or so per year. That would allow some serious runtime on battery (Like 1 year with tesla car size battery ? but you would need to get creative with the inverter control or inverter idle losses are 3x actual fridge consumption.

So frustrating - I just spent 30 minutes dealing with Samsung Canada trying to find something equivalent. The lowest consuming model the support/sales person could find was still over 1Kw/day (380/year).

Guess I'm back to looking at the "solar fridge" from Unique for now... :/ I'd rather run off A/C so that I can track my energy usage in one central location (ie my inverter) but if DC is going to be almost twice as efficient (at least here in North America) so be it!

 

[Checkthisout]

So frustrating - I just spent 30 minutes dealing with Samsung Canada trying to find something equivalent. The lowest consuming model the support/sales person could find was still over 1Kw/day (380/year).

Guess I'm back to looking at the "solar fridge" from Unique for now... :/ I'd rather run off A/C so that I can track my energy usage in one central location (ie my inverter) but if DC is going to be almost twice as efficient (at least here in North America) so be it!

What do you think makes one unit more efficient than another?

Are straight dc units more efficient than a/c?

 

[Xhumeka]

What do you think makes one unit more efficient than another?

Are straight dc units more efficient than a/c?

The energy use reported by the Samsung RB38A7B6AS9 (108 kWh/year) is almost unbelievable... I wonder if they get those numbers running it in an igloo or something

As for DC being more efficient than A/C, it definitely seems that way. In another thread, it was mentioned "Unique said that when you use the AC converter on a DC fridge, it consumes just as much energy as a regular AC fridge": https://diysolarforum.com/threads/using-dc-fridge-with-ac-converter.36916/post-467597

 

[sparrowhawk]

The energy use reported by the Samsung RB38A7B6AS9 (108 kWh/year) is almost unbelievable... I wonder if they get those numbers running it in an igloo or something

As for DC being more efficient than A/C, it definitely seems that way. In another thread, it was mentioned "Unique said that when you use the AC converter on a DC fridge, it consumes just as much energy as a regular AC fridge": https://diysolarforum.com/threads/using-dc-fridge-with-ac-converter.36916/post-467597

It's bad enough all consumer appliances have taken a steep downward drop in quality and reliability, but as an appliance repair man I can say that Samsung & lg tend be the worst.

Samsung made great plasma TVs at one time and I still own one, but quit using it because plasma TVs are extreme energy hogs. Samsung makes some of the worst dvd/blue-ray players.

 

[Checkthisout]

The energy use reported by the Samsung RB38A7B6AS9 (108 kWh/year) is almost unbelievable... I wonder if they get those numbers running it in an igloo or something

As for DC being more efficient than A/C, it definitely seems that way. In another thread, it was mentioned "Unique said that when you use the AC converter on a DC fridge, it consumes just as much energy as a regular AC fridge": https://diysolarforum.com/threads/using-dc-fridge-with-ac-converter.36916/post-467597

In principle, there should be less reactive power in a DC motor so it should be more efficient.

Defrost strategy? I dunno. The Defrost coil wattage and run time has to use a significant amount of that total consumption but maybe not.

I would not want a fridge that didn't have auto Defrost. Going to guess the ones that don't show better efficiency numbers.

 

[efficientPV]

DC fridges are all three phase, a lot of power in a small packace and far more efficient than fractional HP single phase motors. If I had an auto defrost fridge, defrost would be scheduled for peak sun hours.

 

[keepsake]

I do so wish that every fridge would abort and stop defrost if the power was interrupted. No reason not to let defrost cycle WAIT to when its been powered for lets say four hours. This is such a off-grid battery killer issue.

 

[Checkthisout]

I do so wish that every fridge would abort and stop defrost if the power was interrupted. No reason not to let defrost cycle WAIT to when its been powered for lets say four hours. This is such a off-grid battery killer issue.

Does the defrost timer require power to advance?

That aside, it seems pretty easy to put a user-controlled relay in there somewhere.

 

[keepsake]

"Does the defrost timer require power to advance?"

I'm sure it does. That's the issue. Need defrost control and only run when the sun shines.

 

[efficientPV]

Older refrigerators simply use a compressor time mechanical timer powered by the thermostat. When it reaches one revolution it switches from compressor to heating element. The element thermostat turns off when it is up to temperature and when the timer times out it goes back to compressor run. Find that little timer motor and break the connection. Or the heater connection, timer will continue to run and fridge won't work in that time period. Use a relay to close only in daylight hours with a nearly full battery charge.

 

[keepsake]

Thinking ...

Bring the heater wire outside and power it separately.

 

[sparrowhawk]

I do so wish that every fridge would abort and stop defrost if the power was interrupted. No reason not to let defrost cycle WAIT to when its been powered for lets say four hours. This is such a off-grid battery killer issue.

Most refrigerators go into defrost maybe once a day. The defrost heater typically stays on for about 20 minutes and draws between 4 and 5 amps which ends up being less than 300 watts for the duration of heater on time, which I would hardly call an off grid battery killer.
Most modern refrigerators use computer controlled timing of the defrost cycle that takes into account the number times the doors are opened and compressor run time to maximize efficiency.
If your off grid battery's are so small that a defrost cycle draw down could be an issue than it might be time to look at getting a manual defrost refrigerator.

 

[No Idea]

Many different perspectives on this.

I joined this forum because it is geared towards a robust and safe build that avoids the system becoming an ignition source. In the fridge / freezer threads I have not come across discussions on considerations for their selection to avoid them too being an ignition source.

I would like to contribute by sharing a link here to include some perspective on other important safety considerations when getting into the details of specific brands / models / features that are well worth your awareness before committing to a specific purchase.

Causes, Consequences and Prevention of Refrigeration Fires in Residential Dwellings : LSBU Open Research

Open Research at LSBU | A repository of internationally recognised and world-leading research generated by our staff and students

openresearch.lsbu.ac.uk