Only using fridge to make ice...?

[rruff]

Seems like a decent idea, but I've never heard of anyone doing it, so maybe not! What I'm thinking is having a small fridge (15-20L) and using it only to freeze icepacks... and only when there is sun or the truck is running. It'll be turned off the rest of the time. Food and frozen icepacks will go in a good cooler.

Advantages:

a) lower battery requirements with the ice providing a buffer
b) not having the fridge noise at night
c) better insulation of the cooler
d) easy to just buy ice in town if you are looking at a week of rainy weather
e) if it's sunny you can make ice for other people

Downsides:

a) fridge will have lower efficiency at a lower temperature... but may be offset by the higher efficiency of the cooler.
b) futzing around exchanging icepacks and monitoring temperatures
c) temperature control is less precise

Anything I missed?
Anyone tried it?

 

[shade]

I think you'll find that it takes significantly more power to freeze enough ice (or ice packs) to do as you suggest than to just refrigerate food. I'm not sure what the second half of this means: "fridge will have lower efficiency at a lower temperature... but may be offset by the higher efficiency of the cooler."

Freezing ice packs to place in a cooler won't be more efficient than just refrigerating the contents of the cooler. Better to just buy a good fridge of the right capacity and be done with it.

 

[rruff]

I think you'll find that it takes significantly more power to freeze enough ice (or ice packs) to do as you suggest than to just refrigerate food.

It certainly does while you are freezing them, but if you are looking at the overall W-hr consumed by the fridge it should be very close. The energy it takes to freeze the water = the energy to thaw it. Nothing lost there. The cooler will be much better insulated than the refrigerator; that's why I said that it might compensate. Maybe even over-compensate, resulting in less W-hr of energy consumed.

 

[AbleGuy]

What about instead just getting and using a small ice maker? know some folks who do that, but they make their ice using shore power while at a powered camp site or using their generator. I don’t know if there are any models out there that would run off pf 12v power tho.

You may have already looked at the portable 13v refers that can be switched over to act 100§ as freezers instead...why would they not suffice for your plan?

 

[rruff]

What about instead just getting and using a small ice maker? know some folks who do that, but they make their ice using shore power while at a powered camp site or using their generator.

I've looked at those; they are cheap and inefficient and only work on AC that I've found. They also only make cubes! I won't ever have shore power or a generator, just solar fulltime. I need an energy efficient freezer.

 

[john61ct]

Polar tubes, filled with eutectic fluid or saltwater at the density appropriate for your desired freezing / melting point.

The phase change is where the major energy transfer takes place.

That said a system equipped to do this effectively will be very expensive.

And it is inherently much less energy efficient than just "as usual" keeping the contents at the desired temperature directly.

 

[shade]

It certainly does while you are freezing them, but if you are looking at the overall W-hr consumed by the fridge it should be very close. The energy it takes to freeze the water = the energy to thaw it. Nothing lost there. The cooler will be much better insulated than the refrigerator; that's why I said that it might compensate. Maybe even over-compensate, resulting in less W-hr of energy consumed.

Cutting out the middle man with a better insulated fridge would make much more sense to me. Otherwise, energy consumption is increased simply by opening the freezer & cooler during those transfers, even if the efficiency you propose is accurate.

 

[rruff]

Cutting out the middle man with a better insulated fridge would make much more sense to me. Otherwise, energy consumption is increased simply by opening the freezer & cooler during those transfers, even if the efficiency you propose is accurate.

It's inherently difficult to make a refrigerator insulate as well as a good cooler. Heat is transferred through the plumbing. Something will be lost with opening and closing, but if transfers are done at times when you are getting in the cooler anyway (like dinner time and in the morning), it won't be much. The main advantage is to create a buffer for the electrical system (less battery needed to weather cloudy spells).

And it is inherently much less energy efficient than just "as usual" keeping the contents at the desired temperature directly.

Why would that be?

 

[john61ct]

don't have the time to detail the various thermodynamics involved, maybe an HVAC guy will lay it out for you.

Tests, pretty well controlled A/B, showed 130+ Ah per day vs ~40 for the same loading.

Lots more cooled space involved is a big one, also freezing is **much** thirstier than cooling.

 

[john61ct]

Any well insulated custom space can be converted to a fridge / freezer box, only adds $1200 or so if you do it yourself.

 

[john61ct]

Eutectic "holding plate" systems can replace battery capacity if you reliably have a lot of "free surplus" energy for a few hours.

Once a day is OK, but two such periods is much better.

Adds a lot of total space needed inside the box, ad only works out cheaper over a decade or so, if you would otherwise be running a genset instead.

 

[rruff]

Tests, pretty well controlled A/B, showed 130+ Ah per day vs ~40 for the same loading.

I can understand the thermodynamics. What exactly are you comparing? The condenser temperature will not be that different. Just over freezing vs just under. According to some Secop data I found the COP difference for a 10F difference in condenser temperature is ~15%. So there is that. But I don't think it would be hard for a simple but decent cooler to beat the fridge by much more than that for heat loss.

 

[dreadlocks]

I just got an ice maker for my old lady, its like 120W and makes a cup of ice in like 6mins, run it when solar conditions are good and its free ice, it dont refrigerate em so I dump the ice into a thermos and toss it into the fridge and I can keep drinking ice in there for at least a week, but it normally dont last that long w/our consumption. I can keep pre-frozen foods frozen in the bottom of my Engel at 0C for at least 10 days from my testing.. had a big slab of bacon and hamburger and stuff I hadda thaw out on our last vacation as it just would not thaw out in the fridge after being pre-frozen.

 

[john61ct]

I don't think it would be hard for a simple but decent cooler to beat the fridge by much more than that for heat loss.

Of course the insulation makes more difference than any other factor.

A lousy cooler will make a well-insulated fridge look better and v/v

The comparison was like with like, obviously a super insulated box like 4+ inches will help in either case.

I really don't feel like arguing about it, just do testing yourself if you like.

 

[rruff]

I just got an ice maker for my old lady, its like 120W and makes a cup of ice in like 6mins, run it when solar conditions are good and its free ice, it dont refrigerate em so I dump the ice into a thermos and toss it into the fridge

Sounds cool, but not ideal for me. Loose ice is just another thing to mess with. Prefer to use home-made ice packs. For $180 the 15l Alpicool portable fridge/freezer would work, or the similar size model from Truckfridge with a Danfoss compressor for $420. I need to do some calculations to see what I'm looking at...