Off Grid Cabins, Winter, Freezing Temperatures, On Site Food Storage

[Squirl]

As far as digging goes, would it be easier to dig in instead of down.  It looks as if you have a pretty good slope there.  Or maybe build a small concrete structure and push the dirt over it from above.

Ok.  Let's think about the calculations of electricity to heat.  For all assumptions, let's assume that this is going to be an insulated box.  My initial reaction would be to use an old chest freezer.  Insulated, easy to clean, and many times free.  The cost of a 2 inch  thick home built box would probably cost much more in materials and time.

Would it be more efficient to heat the box directly through a resistance heater or some type of home built heat pump?

I think you said that the lowest temp recorded was 20 degrees F.  That means that you only have 13 degrees temperature rise.  Most fridges and freezers have to combat 2-5 times that in temperature drop.

What is your excess daily production?  IIRC, you have 3 200 watt panels and should get at least 2 hours of sunlight even in the winter.  Seems like you would have at least 200-300 excess watts a day.  That would be around 600 btu.

I was trying to find a conversion for air, and I found this:
http://www.gas-lights.com/form.html

It gave me this answer:
For a temperature Rise of 20 degrees Fahrenheit,
In a space of 8 cubic feet,
Your BTU requirement is 21.28 BTU's

It seems like a small heater should very easily be able to heat a small 2x2 box by 13 degrees with your excess electricity.  My concern would be overheating.  Considering that the purpose of heating a small box would be to keep water from freezing, there should be plenty of thermal mass already from the food to maintain stable temperatures over time.

[suburbancowboy]

Here is a couple of other things that I remembered from my days on the farm in idaho.  They had something call the poorman's rootcellar which was basically an old chest freezer buried in the ground covered with straw.

Another thing I remembered was a program that I saw on homesteading in alaska and some body had a fishing camp.  To keep things from freezing they dug a 2X2X4 hole in the ground.  They then put a foot of horse manure in the bottom.  They then put in one of the old styrafoam ice chests on top of the manure with holes cut in the bottom of the ice chest.  The whole thing was then buried in dirt.  As the manure breaks down it generates heat and keeps things from freezing.  The down size was that you had to clear the dirt off when you wanted to get something out.

[MountainDon]

Thanks for that squirl. I've run across a couple of those calculators in the past. I'll be first to admit I was figuring on a larger space because there has to be enough mass to act as a heat sink to help keep the temperature from late afternoon when there is no power excess through the night till maybe noon or so the next day. That's one advantage of using the battery locker; 800 pounds of heat sink.

(Each day the PV charging system goes through a bulk recharge cycle, then spends a little time in ansorb until the batteries regain float voltage. That could be before noon on a good day, later if it's cloudy and /or snowing.)


However, I find those simple calculators suspect. They have no input for insulation so does that mean an insulated box will perform better than the calculator result? Or is that calculator based on some unknown 'standard' wall? It also has no time factor. BTU's are time rated, as in so-many BTU's per hour, same as watts or KwH.  How is mass and heat input for a limited time taken into account?   

I'll come back to this later. Thanks.

[MountainDon]

The low temperature of 20 degrees that I mentioned was the cabin interior temperature. The exterior temperature makes it into the single digits, 8 or 9 regularly during the coldest. This is according to data from the past half dozen years. Historical data has the lows dipping into the minus singles for several hours a night, but that has not happened much at all since 2001, the oldest area records I have access to. So any storage placed outside the cabin has temperatures of maybe 8 degrees F to deal with.


Solar production:  Here's what I looked at. There's a remote weather station a few miles from our cabin. The weather conditions are similar even with the 800 foot elevation difference. That station collects many data types, one is solar radiation, in watts per sq. meter. The solar radiation value used when testing and rating PV modules is 1000 watts per sq meter. So if the weather data indicates that at high noon (actually 12:08 at my station) the solar radiation was 638 watts/m*m, simple math shows me that the most power my 624 watts worth of panels could produce would be 399 watts.

I do have data collected by the charge controller. Summary data such as KwH put into the batteries. That runs at about 0.3 Kwh a day when we are not using the cabin. That would require a little more power from the panels due to charging loses in the batteries.

I chose a typical recent January. Looking at the solar data, most days the power generated before noon should be sufficient to ensure the batteries are full. This is borne out by personal readings on mornings when we arrive after having been absent for several days or more.

The next step was to do the math to add up the watt-hours that would theoretically be generated until late afternoon when the output generally would fall to a figure of 5 to 10% or less. I selected 10 random January days and came up with an average of 1.25 KwH that could be called excess power.

My conversion calculator indicates that 1250 watts/hour is = to 4267 BTU/hour
averaging 4267 BTU/hour out over a 24 hour day = 177 BTU/hour
OR
1250 watts/hour averaged out over a 24 hour day = 52 watts/hour

However, the excess power is not available spread over 24 hours. The excess energy is produced over 5 hours and therefore must be stored in some sort of mass, concrete, water, something.

Not only that when I was calculating the average data I did not select any cloudy days. There were not that many of them and the exterior temperatures were sometimes actually higher than clear days. The cloudy days though, most often came in sets of two or three days in a row. So that would be two or three days, during which the container would cool down. How far down, I don't know. Guessing at what the container inside temperature would be, is just a guess.


Using a calculator similar to the one squirl provided I came up with a theoretical value of 167 BTU/hr for my battery locker. That seems to be too close to the the theoretical calculation for the excess power. Too close for comfort and too close to allow for a three cloudy day factor.


I realize that a smaller space would require less heat to keep warm. However there is the issue of needing it to be large enough to contain sufficient mass, plus whatever heating equipment is involved, plus the food items we wish to keep from freezing. On the subject of heating equipment one of the more workable heating loads would seem to be a resistant coil designed for water heating. That could be used in a small tank filled with anti freeze solution 'just in case'. That adds to the heat sink and also takes up more space.


Anyhow, possibly there is some defect to my reasoning process. I think I'd welcome that as long as the surplus numbers came out more favorably.

   

Perhaps I should link this to the Off Grid topic?

[MountainDon]

    whoa!

So I figure let's have a look at what sort of dollars I'd have to put out to take advantage of this free electricity.

water heater element, 24 volt 600 watt  .......................................................................................   $70 to $110
120/240 volt won't work or you need a whole bunch of them. Ohm's law thing.
thermostat, water,   ...    $20
relay, solid state; use with charge controller to turn heater on/off when excess power is available  ..........   $70 to $100

that's $160 to $240 not to mention the cost of a water tank, insulation, fuse, etc. etc.......................


That makes me go back to square one (more or less) and stash some canned goods in the oven with the pilot light on. Last year we used less than $80 worth of propane for the entire year's worth of propane to cook, heat water, operate the refrigerator and warm up the cabin with the wall heater! (we used the wood stove for primary heat).

But a part of me would still like to use that 'wasted' electrical power.     Call me nuts.  

[Squirl]

I think you are missing that the food itself can be the thermal mass. If the food didn't have water in it, you would not have to worry about keeping it above freezing.  This is why fully stocked fridges and freezers require less electricity and fluctuate less in temperature.  Fluids make excellent thermal mass.   

Also, I have seen many cheaper 12v heating appliances. for $10-$25. Off the top of my head they are air heaters from Harbor Freight, coffee cup water elements, and heating blankets.  Most of these products can be picked up at the local Wally world.  I used to have to keep my eye out for these. I had an older jeep.

A well insulated box with a small heater on for 2-3 hours should keep the food above freezing for a day or two, especially if it is indoors.  Personally, I would worry more about overheating.  It sounds like a fun experiment.

[NM_Shooter]

That hole in the ground is looking better and better 

[OlJarhead]

What about a passive solar 'box' (something like a greenhouse) over by the pv panels?  THen you could install an incandescent light, 60w solar power system and a cutoff to protect the battery.

Maybe even a timer so the light only comes on at night.

Some cheap aluminum windows, 6" walls, black concrete wall on the northside with 6" wall behind it and all heavily insulated with a STRONG shed roof so the snow would bury it and not collapse it.

With enough southern exposure the windows would heat the black wall with the sun and the concrete wall would retain the heat for a long time augmented by the light.

Well insulated it will likely remain above freezing.

My neighbor tells me that even in 10 degree weather his uninsulated porch can get to 60 degrees because of the greenhouse effect his windows on the south provides.  He plans to insulate and make it a green house.

[Redoverfarm]

What about a passive solar 'box' (something like a greenhouse) over by the pv panels?  THen you could install an incandescent light, 60w solar power system and a cutoff to protect the battery.

Maybe even a timer so the light only comes on at night.

Some cheap aluminum windows, 6" walls, black concrete wall on the northside with 6" wall behind it and all heavily insulated with a STRONG shed roof so the snow would bury it and not collapse it.

With enough southern exposure the windows would heat the black wall with the sun and the concrete wall would retain the heat for a long time augmented by the light.

Well insulated it will likely remain above freezing.

My neighbor tells me that even in 10 degree weather his uninsulated porch can get to 60 degrees because of the greenhouse effect his windows on the south provides.  He plans to insulate and make it a green house.

OJ I think that the amount of snow in that area during his absense would restrict the sun penetration into the window. Thats what I had mentioned in my earlier post.  I suggested using a solar " tube skylight" but even this would have to be elivated several feet above the actual top to keep from being covered over by snowfall.

[considerations]

Root cellar.... and latching storage boxes.  You will not be the only mammals who notice the relative warmth of the root cellar. Anyway in the winter you can thaw out in the cellar after walking in while the fire is heating up the cabin! 

[MountainDon]

Well, I think we should dig a hole back into the hillside. That will wait until spring or early summer though as my neighbor with the skid steer, who will work for us for fuel, has a project going on that has removed the skid steer from the mountains for at least a month.   

However, I have thought out a way to test out the excess solar output manually without spending a lot of money. I need to locate an old freezer or refrigerator box first though. I'll have a look at the local freecycle site as soon as I figure out what my login is.   

[Pritch]

Don,

I'm not sure if you're going the same direction, but last night I had a different idea.  Rather than expend energy trying to prevent freezing, perhaps you could use it to assure freezing.  If you were to take an old freezer (outside but roofed against snow/rain/sun) and keep frozen food such as vegatables, meat and the like.  Your winter weather will usually keep the food frozen so the freezer wouldn't need to cycle to maintain temperature.  Short warmer periods would be defeated by the insulation of the freezer and thermal mass of the food.  The only time the freezer would need to use energy (propane or electricity) would be during periods of sustained warmer weather.

[UK4X4]

12 Volt bed warmer already has a thermostat, just need to add a timer to only come on during the afternoons when you have the spare power.

Under $100 us- adds to existing system- timer should not be that expencive

low wattage- low heat.

In walmart they also have a 3 way vehicle 12 v adapter with a battery saver circuit too, I use one in my truck with my 12v fridge, works perfectly to protect your battery bank < $ 10

[MountainDon]

Perhaps build a false bottom on your kitchen cupboards (or in your pantry) that would allow you to install lines through which your pilot-light-only water heater could thermosiphon?

A manual valve tapped into the outlet side of the water heater would allow you to bypass the 'heat-bars' when you're not away, and some very thin rigid insulation placed inside the cupboards should be enough to keep things above freezing when the water cycles through.

True it would involve some construction, but it would be a one time thing and use no more energy than you already use keeping your tank from freezing (assuming you don't drain it every time you leave).

I have located my propane adapter!!    This weekend I'm going to run a pilot only test on the RV water heater using a disposable propane cylinder. I'll weigh a cylinder, record the start weight, and check every so often. I believe the cylinder will last longer than the weekend. Anyhow, we'll see how much gas gets burned in what time period and then extrapolate the data. Full report later.

A loop with a small aluminum oil cooler in it could likely succeed as a thermo-siphon radiator to heat the under cabinet space. I have one of those lurking someplace in the attic storage IIRC.

[DirtyLittleSecret]

Maybe I missed it, but... Back when I was doing a good deal of expedition climbing in Alaska we would bury our caches about 3-4' deep in the snow.  Snow is an excellent insulator.  Have you taken this into consideration? 
I'd think that the partially buried refrigerator (use some popcorn packaging foam for backfill) with an above ground substructure (thinking of a "double door") insulated with 4" foam insulation glued into place and heated by the heating element out of a DC cup warmer would do the trick nicely....if it snows, you will have even more insulation.  Any cheap refrigerator off Craigslist would work.  Betcha that the total cost would be under $120.  Just think of the $$$ you'd save by not having to plan on buying a plot at the funeral home...

[MountainDon]

DLS,  we can't depend on snow. It may snow 3 to 6 feet in a winter, but daytime temps go above freezing with some regularity and it does melt down. It would likely help for a couple months of the winter.

[MountainDon]

Okay now, FWIW the propane pilot test happened this weekend. I started the Suburban brand RV water heater, 6 gallon, Saturday afternoon. The control was set to allow only the pilot light to be lit, no main burner. I had a 20# tank hooked to one side of the changeover regulator. The other side had a Coleman disposable cylinder hooked up with an adapter. At 4 PM Saturday I switched the regulator to the disposable cylinder. Monday at 2 PM I switched the disposable cylinder out of the system and removed it.

The disposable cylinder weighed 304 grams less at the end of the test.
304 grams for 46 hours of operation = 6.608 grams per hour.
6.6 X 24 hours = 160 grams per 24 hour day.
I'm going to round that up to 175 grams per day.

175 per day X 30 = 5250 grams per month; 11.57 pounds per month

At 4.24 pounds of propane per gallon that would be approximately 2.75 gallons.

So one of my 40# portable tanks should last about 3.6 months if feeding only the RV water heater on pilot light only.

[NM_Shooter]

Wow!  That's a lot of gas.

[Pritch]

Still think it might be easier to keep frozen food cold. . .   

[upa]

175 per day X 30 = 5250 grams per month; 11.57 pounds per month

At 4.24 pounds of propane per gallon that would be approximately 2.75 gallons.

So one of my 40# portable tanks should last about 3.6 months if feeding only the RV water heater on pilot light only.

Not to nitpick but depending on your refiller there is a good chance that your 40# tank could be only filled to a max of 80% per stated tank capacity so figure on 2.8 months of run at previously mentioned consumption. I hate to say it but it might be worth actually weighing your filled tanks occasionally and making sure you actual get what you think you are paying for.

[MountainDon]

Experiment in progress.... link from here....


http://countryplans.com/smf/index.php?topic=2335.msg123471#msg123471

[rniles]

Sorry for the resurrection of an old topic but I found this thread quite interesting. The root cellar idea I think has merit and doesn't have to be complicated.

http://extension.umd.edu/publications/pdfs/fs803.pdf

Is a good publication and even mentions just using an old barrel or building a box. The publication talks mostly about storing vegetables but storing canned goods would easily work as well.

[MountainDon]

Thanks for that!

[MelFol]

Late comer to the thread.  Loved the plutonium idea.  Got me thinking.  How about a wench (I didn't misspell winch) to transport the stuff?  I'm trying to think outside the (thermal conditioned) box. 

[Cowboy Billy]

I was looking for ways to keep my horse's water trough from freezing with out power. One way was to bury a pipe 48 inches below the frost line insulating it above the frost line. And ground heat coming up the pipe would help keep it from freezing. You may be able to make your insulated storage area  with a ground heat pipe coming into it to keep it from freezing.

The upright pipe to your tank or waterer must also be well insulated. Some companies sell an insulated earth tube that can be put down the hole where your riser pipe comes up. This 16-inch-diameter tube is made of two-inch styrofoam and helps insulate the pipe. Ground heat will then surround the pipe, even above ground level.

If you dig a deep hole, down past the frost line—an extra four to six feet down past the water line itself—this generates ground heat for your riser. The hole enables warm air to come up through the insulation tube around the vertical water pipe and keep the water from freezing. Ground temperature below frost line is usually 48 to 56 degrees. The earth tube is durable PVC on the outside and foam insulation on the inside.