AC vs DC fridges for off-grid use

[DougfromdaUP]

Would you be able provide any references to support that statement?

I'm going from many years of working with heating professionals, so maybe it's just the local gas company, but I don't think so. I did a little looking, and here are some interesting links.

https://www.hsph.harvard.edu/c-chan...gas supplied,ethylbenzene, xylene, and hexane.

https://www.e-education.psu.edu/fsc432/content/natural-gas-composition-and-specifications

https://www.propane101.com/propanegradesandquality.htm

But I had better modify my statement to, " in my area, and in areas where heating professionals I have worked with are very familiar, there are far more impurities as measured by pipe scaling, erosion, valve plugging and drip-leg residue in natural gas than in propane. "
None of my local providers will say what's in their gas. I hope someone can find better info.

 

[wholybee]

For the most efficient fridges, look to what is being done on cruising boats. The best are homemade, and could be either AC or DC, with either an evaporator or an Eutectic holding place. The key is in the box design and build. Commercial boxes are built to a price, and don't use enough insulation, cheap seals, etc.

I just bought a book "Refrigeration for Pleasureboats" by Nigel Calder. It details the construction, different methods of refrigeration, and how to calculate energy requirements given box dimensions an amount and type of insulation used.

 

[Tecnodave]

Years ago I switched from adsorption refrigeration powered by propane to DC compressor referigerators. I have 2 Grape Solar 5 cu.ft uprights and one 3.2 cu.ft. Volvo (diesel line truck) upright refrigerators. All 3 use 42 watts each maximum at 10 to 15 volts or 20 to 30 volts DC or 120 volts AC. The logic in the referigerators auto select between the power sources.

I use about 200-250 watt/hours/day with each of the refrigerators

In a test I ran one Grape Solar referigerator on one Arco Solar 50 watt 33 cell self regulating panel with no solar controller and one very used Honda car 12 volt 50 a.h. battery. In sunny coastal California on hot (85-100 deg days) Temperatures were always in the set zone...35 degrees F.

Grape Solar does recommend one 100 watt panel and a 100 a.h. battery but I wanted to see what the minimum requirements were. I have a place in Alaska where we are quite remote and I pretest everything here in California before I ship stuff there, I need to know the minimum requirements.

I still have a Servel gas refrigerator there in Alaska but the winters cold drops the gas pressure in the cylinder so low that the referigerator will not ignite!, the gas stove has a very lazy dirty flame. Door in the wall fridge works great there but freezing and bears is a problem there.

Can you believe that we Alaskans have resorted to heating water on a wood stove to heat the propane enough to come out of the tank!

Yes DC powered fridges are expensive! I paid about $900 USD for the first Grape Solar fridge from home depot and it failed in a minor way, the freezer door hinges broke! Grape Solar replaced it with a new one and I made a styrofoam plug in door for the 1st fridge. Now I have a veggie box, a dairy and meat box, and a beer box, all with correct temperature. I have about $1000 in all three fridges, one bought new, one warranty , and one from a wrecking yard
I have about 10 years now with DC powered fridges and very satisfied with the outcome for the investment.

My neighbor has a very large Sundanzer Chest Referigerator about 15 cu.ft. which draws very little more power than my Grape Solar units (same power 42 watts but a bit longer run time) , but it has much better insulation than my Grape Solar units

I have way more Solar than needed with 2 X 2.4 kw arrays each with a Midnignt Solar Classic 150 for Summer use ( I know...very conservative, they can do 5kw. or so)....and 2 more arrays 2.5 kw direct water heating in summer and battery charging in winter , here on coastal Califofnia in the winter sometimes I have no visible sun for two weeks at a time so I have a rather large system and run with NO generator or utility power used to run house. I do have a utility hookup but its only 30 amps 120 volts (1928) but I use only $5.00 /month to run yard lights,,need to consume some power to keep my occupancy permit

I was born in Territorial Alaska on a homestead just south of Denali Mount so Ive a bit of a head start to living off the grid....

 

[KITROBASKIN]

Have not mentioned it yet here on diysolarforum but our discontinued Dometic propane refrigerator has a very cold freezer section on top but the refrigerator temp is above what is considered proper. We are careful to not leave scary perishables in there very long (shrimp, etc.) because even if the temp setting is placed really low, the refrigerator is only a few degrees colder and still not at 40 degrees F in many areas inside. Maybe that is why Dometic discontinued that model. Our portable electric small fridge made by Dometic is fine.

 

[12VoltInstalls]

Our portable electric small fridge made by Dometic is fine tiny

I couldn’t live with it.
Plus I have a 7.5CF 120V fridge that was $215US and the extra panels to support it were not that expensive.

 

[Tecnodave]

Two things that I learned from years of expereince with Dometic and other adsorption referigeration is that the cooling fins on the rear of the units need to keep clean of dust and a bit of air over the radiator on the back will help a lot, a small computer type fan will greatly improve cooling of the unit. The large cooling loop on the back is to condense the vaporized ammonia back to liquid. One of the problems with the design is the need to keep the unit vertical in both planes (both fore and back and side to side) . The reliquidifed ammonia wants to puddle in spots and does not drain back to the boiler.

One rumor is to roll the fridge over several times.......DO NOT DO THAT....The correct procedure is to tip the fridge 5-10 degrees left for 15 minutes then tip the fridge 5-10 degrees right for 15 minutes. Repeat several times to remove all liquid water/ammonia mix from the large cooling loops on the rear of the fridges. The reasoning for that is to drain puddled ammonia/water solution back to the boiler. The water should remain in the boiler, only the ammonia should be boiled off and remain as a vapor as the recondensation of the vaporous ammonia to a liquid is what does the cooling of the refrigerator. The water in the cooling loops recondenses the ammonia in the heat exchanger on the rear of the units leaving not enough vaporized ammonia to complete the refrigeration cycle.

This procedure is covered in the “Dometic dealers service manual” found very well hidden on Dometic’s website buried deep down in the service manuals for older and obsolete units. You have to search for it, it’s not meant for end users but is for dealers servicing the units. It is a veritable “gold mine” of information on theory of operation and use of not only dometic units but all adsorption refrigeration units.

I have a tough time uploading this manual but if you PM me I will send you a copy of it.

Of all the brands of adsorption units that I have owned Servel, Dometic and Norcold the Servel units are by far the best made units out there. They were meant for household use but being unvented they were outlawed in housing units as they do emit UBH....Unburned hydrocarbons...which are a health hazard. They are still being manufactured in Brazil or Argentina.....(not sure but in South America in any case)

One of the “MUST DO” maintaince items is to keep the burner and exhaust stack cleaned of built up soot from the combustion process. This is a problem with all adsorption units. Most units have a stack cleaner built in. On the Servel it is easily accessable but in R.V. installations it is often necessary to remove the top vent above the refrigerator (on the R.V. roof) and clean out the stack. An accumulation of soot is often seen in the burner area as well which can be accessed from the exterior of the R.V. through the access door.

Absolutely required is the use of two monitors , one a CO monitor located high on the wall away from the referigerator but in the same room , which will alert you to CO (carbon monoxide) CO rises and collects in corners of the space. the second monitor is for UBH.....Unburned Hydrocarbons...leaking unburned propane gas located low on the wall just above floor level.....propane gas sinks and collects in the low spot ...unlike Natural gas which rises and dissapates

One of the unspoken hazards of adsorption refrigeration is the presence of Acetylene gas in the refrigeration mix.
Acetylene gas is highly combustable and burns at 5900 degrees when stociometrically correct mixture with oxygen at about 6000 feet per second! Can you say EXPLOSION......

Do not under any circumstances attempt to cut into the boiler or cooling lines in these units.

read the Dometic diagnostic manual, it’s a gold mine for information on these units

Again covered in the “Dometic dealers repair and service manual”

 

[KITROBASKIN]

Is this the service manual you are writing about?

https://www.nationalserroscotty.org/resources/dometic-service-manual.pdf

 

[Tecnodave]

That is a much newer version than I have but the same information. I applaud Dometic for making this information available. It greatly helps with systems diagnostics. so many companies “Just buy a new one” Thanks for posting this

<EDIT> maybe I forgot it was Hydrogen gas, not Acetelyne gas but I do remember being suprised by a highly flammable gas in a cooling loop.

<EDIT> NOT a newer version, publication date is the same

 

[spuds]

Propane was THE option when solar wasnt.Nephews new Toy Hauler trailer just had a propane fire.He ripped out everything that ran on propane.
Propane is expensive,can get scarce,and hauling tanks are a major PIA says Fred Flintstone,hauling electrons arent says George Jetson.
Propane was nice in 1975,now its time is way over.

Chest freezer 7cf converted to refer uses 175 w/hrs a day in a room thats 90F,thats efficient!
EDIT to add,thats with an inkbird set at 34-37F,thats a dang good root cellar,very cool!

Need a regular sized freezer/reefer this is what is extremely popular for solar in the USA.

 

[12VoltInstalls]

a regular sized freezer/reefer this is what is extremely popular for solar in the USA.

Is this 12V? Because his 5 amp claims and 53 watt claims they don’t calculate out at 120V
0.5A at 120V makes math sense

 

[spuds]

Watch the video 120 volt,he has several on the setup.2 friends off grid both upgraded to them,says best theyve ever had and thats the consensus bigtime,all I know about em.

Im using the chest conversion Im currently using as a freezer,will refer it back when needs may come.

 

[spuds]

Is this 12V? Because his 5 amp claims and 53 watt claims they don’t calculate out at 120V
0.5A at 120V makes math sense

My freezers 7 cf and 14 cf run 55-80 watts on high end,
sounds spot on to me?

 

[SilverbackMP]

Regular fridge. And bigger. More panels and batteries if needed. DC (and gas) fridges were needed back when panels were expensive.

Just threw out a still working 12 cu foot propane unit of my mom’s and replaced it with a 22 cf French door electric model in anticipation of me firing up the new (shared) system . Quality of life has doubled.

(The propane unit was 30 years old with failing hinges, thought about keeping it, but I’m trying to get rid of excess junk).

 

[spuds]

Regular fridge. And bigger. More panels and batteries if needed. DC (and gas) fridges were needed back when panels were expensive.
Quality of life has doubled.

Weve come a long way in last few years,great times for solar!

 

[12VoltInstalls]

My freezers 7 cf and 14 cf run 55-80 watts on high end,
sounds spot on to me?

5 amps is 600W at 120VAC. I think he was reading battery current not AC current.

 

[spuds]

5 amps is 600W at 120VAC. I think he was reading battery current not AC current.

Agree,sometimes he misspeaks,he isnt a pro,just an average guy learning on the journey so I take him at that face value.Good guy IMO.