micro feezer

notsobright · October 2009

Ive been searching for a tiny freezer with no luck so far.

I'd like to be able to freeze a bottle of water as effeciently as possible then use the frozen bottles for keeping my cooler "cool"

it would need to freeze the bottle slightly faster than a frozen one would thaw.

all I need is a tiny freezer! where can I find one or learn how to make one?

thanks

BB. · October 2009

Re: micro feezer

That is tough... Is this going to be a full time freezer (9+ months of the year) or a part time (summer weekends)?

Generally, a part time fridge/freezer would be best addressed with a propane powered unit... You only need the gas on the weekends.

Solar electric tends to favor running most of the year so you can spread the costs of the panels and batteries over a long period of sunny weather (9+ months of the year).

In either case, a small electric fan (even a 24 volt computer fan running on 12 volts) will stir the air and help freeze the water faster without having to crank the cold all the way down (the lower the temperatures, the less efficient the cooling process is).

Once you decide on propane or electric--then you can start running some calculations on BTU's from 1 gallon of water per day (60F to 10F) and how "big" a motor or propane unit you would need to keep up with the cooling (lbs of ice per hour or something like that).

No other options? Making ice for keeping things cool is not always the most efficient use of power (cooling the "product itself" and a very well insulated cooler may be better--depends on your needs).

What is your portable cooling needs? Hiking? Doctor taking medicines to patients in back of truck or what?

-Bill

icarus · October 2009

Re: micro feezer

I have a very small dometic 2 way fridge. Maybe 24X24" cubed. We dial it up to full cold and use it as a freezer. It cools to ~0f and burns about 20# (5 gal) every 3 months. We keep it full (filling excess space with water jugs too keep the mass cold and cover it with a blanket. Since it is only opened only every few days it takes almost no propane.

Tony

notsobright · December 2009

Re: micro feezer

I almost forgot I posted this.

tough.. as usual, I want too little too much. just extream conservation.

I thought that would be the most efficient way to maintain a cooler. seems it would anyway. actually I dont need a bottle of ice for just ice, so you think it would be more efficient to just use a small refridgerator?

I'd like to find a really small 2way or 3way propane/12v system.

thats sounds like a nice unit Icarus.

thanks

RandomJoe · December 2009

Re: micro feezer

It takes more energy to freeze water then use that ice for cooling, than it takes to directly cool the intended target directly. But it does allow you to time-shift when you consume the energy. (Just like charging a battery bank to use at night, there are losses involved.)

I work with HVAC control systems, and one of the things we work on is ice storage systems for commercial buildings. The ONLY reason they make any economic sense is that the businesses are billed for time-of-use and (more importantly) peak-demand rates. So the nighttime kWhs are cheaper than the daytime, and anything they can do to shave off their peak demand during the day is worthwhile. Busting your peak-demand cap anytime in a given month means you pay a lot more for the ENTIRE month's usage.

During the winter, when the utility doesn't charge them for peak demand, almost everyone shuts down the ice storage system. They can run the chillers all day during the day and it uses less kWs (and costs less, the primary goal) than running the ice system.

There is one other use for the system, which a small handful of places use. It does allow them to get by with less chiller capacity than they require during peak usage. One building I worked on is a club / dance hall on a military base. Not very busy most of the time, so they don't need a lot of capacity. But for a few hours a week it'll be a packed house. They have a small ice storage system that carries them through those few hours, and it'll be refrozen during the off-time until needed again. (I'm not so sure the cost and complexity really make this a valid approach, but somebody thought it was a good idea at the time!)

It sure is fun, though, to go into a mechanical room for a large building with full-capacity ice storage on a 100 degree afternoon - and hear almost nothing! Just one or two pumps quietly whirring to circulate the water. So peaceful!

notsobright · December 2009

Re: micro feezer

thanks for the info RandomJoe! intresting.

topic change: micro refridgerator.

time to go dig thru old posts again.

thanks

notsobright · December 2009

Re: micro feezer

anyone have experience with a sundanzer freezer?

http://www.sundanzer.com/Home.html

specifically Im considering their DCF50. they have both small refridgerator and freezer but you cant get both in one unit.

another use I may have for ice beside for a food and beverage cooler is to also use it in a "swamp" cooler for air conditioning. the only problem is my region is high humidity so I wonder if the small sundanzer can make enough ice to use. any thoughts?

just kicking some ideas around..

what Id really like is a three-way combined refidgerator and air conditioner. hmmm

icarus · December 2009

Re: micro feezer

Making ice, then to use it in a swamp cooler sounds line it's going to take a ton of power. Remember, turning water to ice takes a ton of energy, way more than just cooling water down to near freezing.

Tony

notsobright · December 2009

Re: micro feezer

but it should be more efficient than powering a refridgerator AND an air conditioner, no?

Im undecided on freezing or fridging at this point but I'd still like to hear from anyone that has used sundanzer equipment. they seem like good units.

I just noticed my typo in the title.. probably to late to edit.

"feezer"

LOL

icarus · December 2009

Re: micro feezer

I can't say which would be more efficient. My intuition says that it would be less efficient,,but it is only my intuition.

LucMan · December 2009

Re: micro feezer

If you have high humidity a swamp cooler won't give you much cool air. The drier the air the better they work, as water evaporating cools the discharge air.
You will be just wasting ice & the power used to create it.
As far as the 3 way, freezer, refrigerator, A/C. It does not exist, if it did only NASA would be able to afford to buy it.

notsobright wrote: »

anyone have experience with a sundanzer freezer?

http://www.sundanzer.com/Home.html

specifically Im considering their DCF50. they have both small refridgerator and freezer but you cant get both in one unit.

another use I may have for ice beside for a food and beverage cooler is to also use it in a "swamp" cooler for air conditioning. the only problem is my region is high humidity so I wonder if the small sundanzer can make enough ice to use. any thoughts?

just kicking some ideas around..

what Id really like is a three-way combined refidgerator and air conditioner. hmmm

john p · December 2009

Re: micro feezer

You may like to try this web site they have exactly what you want. Waeco and Dometic are same company I think so it should be available from Dometic in USA.
http://www.waeco.com.au/news.asp?id=268

I have the CF15 which is a bit bigger and we use it to make and keep ice candy in it. uses very little battery power and almost totally silent

john p · December 2009

Re: micro feezer

Waeco also sell all components if you want to build a freexer or refrigerator into some ice box or home made container if that is the way you want to go,, the compressor comes in 2 sizes th danfos 35 and danfos 50.. they very reliable and will last even under bad condittions for many years.

System2 · December 2009

Re: micro feezer

Sundanzers are very reliable and should be noticably more efficient than the Waeco unit since they have much thicker insulation. SunDanzer uses 110mm of insulation.

john p · December 2009

Re: micro feezer

sundanzers dont appear to come im sizes below 1.8c ft thats about 50 litre the Waeco small units cone down to 11 litre size,, thats why they not 100mm (4in)thick.. but it means they very portable .easily carried by a child. and Iknow they use very litle power as have one in use. but as I also said you can buy the components and make a container as big or small as you want and wall size as thick as you want.

System2 · December 2009

Re: micro feezer

Waeco is good for transport applications, but the Sundanzer 1.8 c.f. model averages only 5 watts of power in a 32C ambient, so it is better suited for solar PV applications. That's only 2.4 watts/c.f. I love mine.

mike95490 · December 2009

Re: micro feezer

Lightweight? Do they use a fluid/gas cycle and compressor, or what ??

john p · December 2009

Re: micro feezer

most of the Waeco fridge/freezers use the Danfos b35 compressor only the very biggest ones use theDanfos b50 compressor they all run on either 12 or 24 v the unit automatically detects which one its connected to
the 15 l fridge freezer I have weighs about 9kg about 20lbs
they all can be set as freezers or refrigerators. fuly adjustable temp setting

System2 · December 2009

Re: micro feezer

mike90045 wrote: »

Lightweight? Do they use a fluid/gas cycle and compressor, or what ??

The SunDanzers are heavier because of the larger size and thicker insulation. But the 50L has handles. It uses R-134a in a standard vapor compression refrigeration cycle.

notsobright · December 2009

Re: micro feezer

welcome aboard the NAWS Forum solarjoe! thanks for joining and providing the helpful input on this topic.

LucMan wrote: »

As far as the 3 way, freezer, refrigerator, A/C. It does not exist, if it did only NASA would be able to afford to buy it.

I meant three-way power as in 12vdc, 120vdc, or propane aswell as combined cooling units. still, I dont see how it would be so difficult or expensive to make a refridgeration unit that could combine a refridgerator/freezer with an air conditioner. Im no expert but refridgeration isnt exactly rocket surgery ;-)

john p wrote: »

You may like to try this web site they have exactly what you want. Waeco and Dometic are same company I think so it should be available from Dometic in USA.
http://www.waeco.com.au/news.asp?id=268

I have the CF15 which is a bit bigger and we use it to make and keep ice candy in it. uses very little battery power and almost totally silent

that is great! unfourtunately it doesnt seem available in the USA, I can only find the next size up. (no suprise)

here is the most affordable portable unit I have found available

http://www.truckfridge.com/tf32.html

john p wrote: »

Waeco also sell all components if you want to build a freexer or refrigerator into some ice box or home made container if that is the way you want to go,, the compressor comes in 2 sizes th danfos 35 and danfos 50.. they very reliable and will last even under bad condittions for many years.

thats intresting.

anyone know if there is a portable unit that runs off propane and 12vdc? or where one might be able to purchase a Waeco CDF11 in the USA?

BB. · December 2009

Re: micro feezer

The mix is a bunch of different animals...

The tri-power refrigerators, such as those in RV's (from what little I have seen), are all normal ammonia cycle propane type fridges and the 12 volt or 120 volt version of them simply substitute the propane heat source for the electric heat source and they are not terribly efficient in electric mode.

Peltier effect coolers are even less efficient.

The most efficient electrical driven still seem to be the mechanical compressor types.

Usually, to optimize any mechanical device, you need to know its operating conditions.

For refrigeration, you need to know the operating temperatures (evaporator and condensers) and how much heat you will need to remove.

Obviously, a freezer needs to run much cooler than an A/C system. A refrigerator also needs to be cooler than an AC system.

So, a system optimized to do one of the above three functions will probably not do the other two nearly as well.

Also, a fridge/freezer is designed to move a relatively small amount of heat... A full sized US Energy Star fridge or freezer probably runs a 100-200 watt compressor.

Even a relatively small mini-split AC system (like the Sanyo and such we have been talking about here on other threads), when operating on "low" still takes over 300 watts to run the compressor and fans for 3,000 BTU of cooling (or even heating if running in heat pump mode).

So, running a mini-split A/C system to also cool your small fridge would probably end up being pretty inefficient (pump/condenser/fans don't match heat load of small fridge).

It is really interesting to me to go through the US Energy Star Fridge/Freezer listings...

You can get a

cu.ft micro refregerator that uses ~260 kWhrs per year or a 15 cu.ft. Fridge/Freezer that uses 350 kWhrs per year.

Now is that because nobody has made optimized cooling system (compressors and such) for the very small fridges or is it because nobody would put the same amount of insulation and a small fridge (the volume of the cube would become mostly insulation with just a small place to put a few cans of soda).

I don't know--but I suspect it is a combination of both less insulation and using over-sized compressors (cheaper to use standardize full sized compressors vs developing and manufacturing ones optimized for a lower volume 3' cu.f.t fridge).

They can obviously make more efficient refrigerators--Sun Frost (from Engery Star link above) has a 16 cu.ft. fridge that rates at 204 kWhrs per year, and a 11 cu.ft. fridge/freezer that runs 171 kWhrs per year.

Or, you can purchase a cheap 7-10 cu.ft. chest freezer, swap in some sort of refrigerator temp. range thermostat and run at ~95 kWhrs per year.

Apparently way under the power usage of any store bought unit--and a heck of a lot cheaper than any "off grid solar fridge".

I guess that I am still confused about what it is you want. I don't think you will get an efficient Frdige/Freezer that will run off both propane or AC/DC power. Even a small Dometic RV 3 way power fridge still has 150/175 watt (12/120 volt) heaters to operate. Whereas their small/portable compressor based models take only 35-55 watts. I don't know the duty cycle--so we can't know the kWhrs / day or year ratings for these units without doing our own measurements. They did make a 3 way portable unit--but I don't know if it is still in production (I would not bet on it being very efficient when electrically powered).

If you have mixed needs, your best bet may to get a used propane RV fridge from a recycler and get a dedicated AC or DC powered compressor based fridge/freezer based on your needs (portable, fixed, etc.

There are lots of options out there,

-Bill

icarus · December 2009

Re: micro feezer

I think that on a per cu ft basis, smaller is much harder to make efficient. The volume of insulation relative to the size of the box is greater in a small freezer for example. 4" of foam in a 1 cu ft box makes the box 2 cu ft for example, but the same 4' of foam in a 2 cu fit box only makes the box 3 cu ft say.

Also dissipating the heat is easier, the bigger the box, as the condenser coils can be bigger, as can the evaporator coils, (as a percentage of box volume.

As for chest fridges. Yes they certainly can be an efficient use of power, but they are a damn pain to use in the real world. (Unless you are using them just for bulk cooling like fresh mild from a dairy) The net result of which, is that they may be efficient use f power, but in all likely hood a poor use of volume. Imagine for example if you had a 10 cu ft chest freezer now working as a fridge. As a freezer, you might open it once a day, rifle through, rearranging stuff for the day, then close it. But it it were a fridge, you would open it often, and stuff would always be on top of other stuff, (or you would only fill it 1/2 full). Imagine having to take all the produce out to get to the mayo for example.

It seems to me, there is efficiency, and then there is efficiency.

Tony

PS Bill is right in that all three way fridges (or even two way) are ammonia/ absorption type fridges. Their primary power is a Propane/kerosene/butane/gas flame that "boils" the ammonia solution. The 12vdc or 120vac versions rely on a resistance electric heating element to boil the solution. On it's face, it is a pretty clever idea, but the electric heaters run ~350 watts for a moderate size fridge, and the duty cycle is way longer than it is on propane. I have rigged a couple of mine to switch to electric when the batteries are full and I have power to spare, but it provides so little benefit as to be useless. 1 hour of electric run time cuts propane run time by maybe 15 minutes at most, or ~300 btus worth of propane.

Imho, the best thing you can do is add insulation to any fridge cabinet, and provide good ventilation to the condenser. Keeping the cold in is priority one, getting rid of the heat quickly is priority two. 2" of styro foam (R-10+-) on the top and sides of a fridge box makes a huge difference.

notsobright · January 2010

Re: micro feezer

notsobright wrote: »

I dont see how it would be so difficult or expensive to make a refridgeration unit that could combine a refridgerator/freezer with an air conditioner.

after some digging I have found a unit that do this.

http://www.myboatsgear.com/mbg/product.asp?prodID=49

intresting! but GlazierBay is known to be expensive so no doubt this unit will be out of my range but still worth mentioning.

System2 · February 2010

Re: micro feezer

Bill mentioned the possibility of altering a chest freezer to operate as a refrigerator. I have given this a try and have had great results. The chest "refrigerator" now uses about 0.2 kwh a day so that is even less than Bill's estimate of 95kwh per year. All I needed was a line voltage heating thermostat and a relay switch. I have posted a circuit diagram and all the other information here:
It's pretty easy to find a cheap freezer somewhere and the right relay switch could be found at your local electronics store.

edited by niel.
if somebody wants the link they can pm him for it, but he is selling books right along side of the pertinent info he wants to convey to us. eliminate the book selling and the link will be allowed to stand.

notsobright · March 2010

Re: micro feezer

BB. wrote: »

They did make a 3 way portable unit--but I don't know if it is still in production

I am trying to find out more about this one but it seems to be hard to get for customers in the US.

the only info about them available in the US is from the link you provided so I called and got a weird message to press star for more info then after pressing star it sent me a text message that says I need to join some type of service for $9.95 a month.

not sure what thats all about but Im just looking for info on possible purchase in the US for this one.

any ideas?

edit: I contacted Dometic and found these units available from campingworld http://www.campingworld.com/shopping/item/dometic-portable-refrigerator/27837

also for anyone intrested, I found here for much less than campingworld
http://www.pplmotorhomes.com/parts/rv-refrigerators/compact-refrigerator-rc4000.htm

RWB · March 2010

Re: micro feezer

Anybody have any experience with these units?

http://www.dometic.com/enus/Americas/USA/Marine/Refrigerators/Refrigeration/?productdataid=85492

http://www.dometic.com/01253888-348b-4ae2-89f7-decf22f257c4.fodoc

micro feezer

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