ok I bought 250 acres in BC and built a home depot kit house on it. http://www.vrh2.com/clier/ClierLake.html I put 3 inches of styrofoam on the outside so the walls are about r34. I closde in the crawl space and insulated the floor so downstairs has r44 wlls but is still dirt. the roof rafters are 2 by 8 and I compressed 2 r22 pieces into that. Probably around r 30 or so. Anyways the whole house cost under 50 grand and stays cool in summer and hot in winter. But to keep the pipes from freezing I leave base boards on in the house and the crawl space. it cost me $50 a month in power. so I want to build a dirt battery to store solar energy in thermal mass. Right now lets say the design is: -Build a 32*16 hole in the yard. -build 2 r22b oxes in the hole, fill the box with compressed earth, interwoven with white pipe. Heat water with black hose coils? Heat dirt in box to about 100farenheit. In september put lid on box. Install radiant heating in house and have the hot water from the box keep the house above freezing all winter. Will this work? the 32*16 is arbitrary. How big would such a battery have to be? Are there ways to calculate? thanks for any advice.

Interesting idea. I am sure this can be calculated, but there are an awful lot of factors to consider, and it won't be easy. Do you live in this house, or are you just looking to keep it above freezing? You'll need to know the heat loss of the house. You'll need to determine the specific heat capacity of the dirt/earth you'll use (determine this factor alone will be a challenge). You'll also need to know what the ground temperature is at depth so you can calculate losses to the earth. If you plan to store 100F temperatures, your heat loss to the ground will likely be quite significant. You will probably have to dig rather deep in order to get below the frost line and get to where earth temperature is stable.

As I am thinking more about this, and trying to find the heat carrying capacity of dirt, I am thinking this is going to be quite a challenge. You might be better off getting one or two large used industrial tanks and storing warm/hot water. In my brief look, water can store 4x more energy than dirt. It is also easier to heat with home made solar panels. All you'd need to extract the heat would be a circulator pump. Search for used tanks on eBay.

I wish you good luck. This is definitely out-of-the-box thinking.

Regards,
Ed

Do you live in this house, or are you just looking to keep it above freezing? its pretty empty right now but as it gets finished I hope to do some kind of weekly rental..(at least for the summer when the horses are in the field below) really its pretty much passive annual heat storage. Get it warm during the summer and heat it up for the winter. Right now the water comes from the well about a kilometer away and is all buried to the house about 4 and a half feet deep. I think this whole thing would have to go lower than that. Water flows fine at 20 below.. Maybe this year I build a small bit of it and test it to see how big it would have to be . I know water has better thermal mass, but what about how long it holds that heat?

You and dragmit should start a club!

Do a manual-J type heat loss analysis on it and/or carefully analyze the power use during your away times to calculate how many BTUs you need to store as a starting point.  ($50 means nothing to me. What's that in kwh?)

To avoid freezing you have to both

A: store enough heat and

B: be able to deliver it at a fast enough rate during the coldest hours of the year.

Part A should be easy to calculate, but difficult to implement.

Part B could be easy to implement but may be pretty fuzzy to calculate if you don't have a good handle on just how cold "cold" is when you're not there. It's likely the electric baseboards can put out a lot more heat per hour than you'll need to avoid freezing, but for yuks, use their total wattage as an upper bound.

For the record- the size of your underground heat store (and therefore the amount of insulation you'll have to buy) will be much smaller if you use water rather than dirt as your storage medium.  The specific-heat of soil varies with soil type, but is universally much lower than that of liquid water. Using soil as the storage medium also makes the heat-exchanger much larger, since it will have both poorer surface contact and lower thermal conductivity than water.

But it's still gonna take a heluva big tank to coast you through a winter, and the heat loss through the buried R22 will also be quite significant over 3-5 months of sub-freezing weather.

As a start, add up the total kwh of energy you think you might need, based on your whole-winter power bill and we'll see how far we can get. (I'm thinkin' it's about a third to half the energy that dragmit would need to store, which is still a heluva lot.)

hm

This forum software sucks by the way. I wish they would fix it so you can get a decent layout when you quote or edit posts.

ya sorry for that attempt. Usually [quote] and [/quote] do it. I just gave up.

So, assuming $0.07/kwh, and 4 months of sub-freezing weather @ $50/month, you're looking at ~715kwh, which is ~2,400,000 BTUs. A 10,000 gallon tank of water (dragmit's case) contains ~83, 400 lbs of water, so to store the whole shebang the water would have be 2,400,000/83, 400= 288F above your desired room temp, and that's assuming ZERO storage or distribution loss.

With 2 of dragmit's tanks that drops to 144F above the desired minimum room temp (again zero loss), which at least gets you to sub-boiling storage temps.

With 4 of dragmit's tanks you're at 72F above the desired minimum room temp, so if you set the thermostats to 40F you're almost down to the desired 100F storage temp.

With 8 of dragmit's tanks you're at 36F above the desired minimum room temp, which is now down to where you don't need R500 of insulation to not lose it all to standby..

You may have a shot with 100,000-150,000 gallons of storage water and R50 of insulation (depending on the average subsoil temp and the geometry of the tank.) 150,000 gallons is roughly a cube 27 feet in all dimensions. 100,000 gallons is a cube ~23 feet on a side.

But this could be off by 100%, given the imprecision with which we've estimated the average heat load. If you want the thing to be even remotely affordable you need to do better than a WAG as to how much you actually need.

Do you have REAL kwh per season numbers, rather than some WAG on billing $/month and a guess on utility rates?

What temperature are you actually keeping the place with that power use? (40F? 55F?) And does it ever drop below the setpoint?

How many kilowatts of baseboard are installed?

How long is the freeze risk actually real? (50 days, 100 days, 150 days?) Don't guess- use weather data from a tracking station close to you of similar altitude, or use your own data logger on outdoor temps for a full season.

so what I'm getting is that a water tank is the way to go but every way I've looked at storing water underground is expensive. A tank with underground structure and insulation is going to cost huge amounts. Really underground stuff caves in so even the dirt idea may not work...

ok thought a bit more now and an underground swimming pool may be an answer.

We go for water storage. Plenty big and deep.

underground in a cement pool. And you can swim in it, so only a little warmer than room temp.

Seems like making something that wont rot is hardest.

hmm I wonder if most water storage systems use pressurized? Or is it ok to make a very well insulated indoor pool. I mean I think some windows would add solar gain many days, but they would have to have some kind of auto shutter for cold cloudy days This is getting way too expensive again I think I'll just burry a 16*16*16 box and fill it with dirt and see how it does.

If you don't start with carefully calculating how much heat you actually NEED to store, there's no way to get a handle on this. Flailing around in the dark is a recipe for failure.

A 16' cube of dirt wouldn't likely have even 10% of the storage capacity needed at peak temps that wouldn't melt the insulation.

An indoor pool insulated to at least R15 against the subsoil would provide a substantial thermal mass to the equation- enough to average out daily (even weekly) loads bringing your peak kw needs down, but hardly enough to coast through a month or a season on at temps safe to swim in. If you have access to off-peak rate structures like Brock you could pump heat into it on off-peak hours to bring the bill (if not the energy use) down.

the reason I've gone back to dirt is I think it's possible http://www.earthshelters.com/Ch_1.html I'm trying to develop a technology that joe in the suburbs could do in his back yard. the hole is going to have to be really deep. BTW this is canada. The CODE in the mountains around the ranch is R50 in the attic. if I did a pool I'd blow most of the money to make the whole structure about r50. Spend money on regeneration not generation. Also:this is the okanagen where people grow peaches and wine. It gets really hot in summer. Short but powerful solar collection season, but also lots of sunny days in winter where thermal solar panels that work to minus 20 would work. I want something really really cheap. The pool might happen, but not as a way to heat the house. Maybe a hot tub in the basement could help with that but Ithe 'dirt batteries' can be assembled over years in stages. I can do some, check the hydro readings. do some more...the year its free I've done enough.. (I cant dig deep if I do it in stages but there's 250 acres to sprawl on)

I'm getting the impression that you feel much more comfortable running a shovel than a calculator. LOL

Most earth-dome shelters in colder areas need an unbroken 30+ over the top to work, and uses the thermal mass of the enclosed soil to moderate the interior temps. The temperature in the thermal mass (the storage temperature) is never above room temp. Heat gains in the summer have to be carefully managed to boost the temp of the soil within the thermal envelope without cooking the occupants in the summer. By remaining earth-coupled the occupied space won't stabilize a temps much higher than the average deep-soil temp for the region. I'm not sure what that is in the Okanogan valley, but it's certainly not going be comfortable in much of the Canadian midwest, where the deep soil temps are well under 10C.

Earth domes are also by-design very low-loss from a glazing point of view (all glazing is S-facing, with movable shutters for managing gain/loss. I suspect your heat loss is currently dominated by glazing, and it could be that installing R15+ insulating exterior shutters on your place would leave it sufficiently earth-coupled and low loss enough to keep from freezing, if not exactly warm. This would be far less expensive to build custom removable insulation panels to bolt over the windows when you leave for the season (including a shed to store them in) than insulating a big box o' dirt and pumping a gazillion BTU of solar heat into it. For the windows on the S side you could even make removable insulated passive or photovotaic-operated thermal air panels, to bag what winter insolation you DO get. Thermal air panels are inherently low temperature/high-efficiency with no freeze-up hazard of their own, and dead-easy to design & build.

By insulating over the dome, earth dome shelters become earth-coupled on 5 sides out of 6 of the house-cube, whereas your place is only earth-coupled on one (the crawlspace floor.) You need to protect against a far higher heat loss, far lower earth-coupled condition. But raising the temp of the dirt battery above the surrounding soil temps by even 5-10C will prove very lossy compared to the earth-dome structure, yet you need much higher temps than that to make up for your higher winter loss aspects with soil-stored heat.

If you haven't already, make that place as absolutely air-tight as you can with foam & caulk, and TEST it. Use window fans to pressurize/depressurize the place and smoke-pencils (incense sticks, whatever) to find & fix every possible draft. Otherwise infiltration will also be a large contributor to heat loss (another issue that earth-domes inherently don't have much of.)

BTW: A buddy of mine has a cabin on the Colville res in WA, not too far from Republic. I've been up to Pendicton several times, Kelowna once- gorgeous country, that!

ok now we're talking

so first summer we add the shutters.

Finish and insulate the crawlspace

Tighten and cauls anything we can (the woodstove needs a shutoff, the kitchen has a vent)


then, with the r40 walls and such its a very insulated structure. Maybe as much as an earth dome?


(while we finish the basement I think I should add some hot water storage)


The plywood box I'm talking is 2*12, r44 with an r66 roof) it's burred under the ground for geothermal warming..

Since you're going for a high-performance building envelope, you should probably model it with either the HEED freebie  or using the proprietary PassiveHouse tools. 

With R40 walls, R50 attic, R40 crawlspace you will find that the heat load is very small indeed with even minimal glazing up grades or insulating shutters.  Earth coupling of the crawlspace can be further enhanced by buried EPS insulation parallel with the ground extending a few feet from the foundation all the way around.  Judicious treatments of thermal bridges from plumbing, structural timbers, etc can reduce the heat load even further without nearly the cost of active solar and large thermal storage to make up the shortfall.

Your heat loss will still be higher, and your earth coupling substantially lower than with an R30 earthdome, but it'll be at a "who cares" level.  I suspect that, as with the Saskatchewan Conservation house in the '70s, you'll be opening up the windows to cool off every time you fire up the woodstove.

There has been a lot of GREAT proof-of-concept buildings for low energy housing built in Canada.  Do a google search on "net zero housing", and similar.  Learning from what has gone before is a good way to avoid problems and lower your expenses.  In general, storing seasonal amounts of heat has never been demonstrably cost effective, but super-insulation has, and that seems to be the very good path you're on.  If you do it as best you can with the best available design tools it'll just work. 

Earth coupling is great, if your subsoil temps are near a desirable room temp and you actually have the house build into a S-aspect hillside or berm (which you don't.)  I'm suspecting your deep-soil temps are well into the low side of where this would be easy, projecting the isotherm lines on the deep well map into southern BC:



It's a lot easier to do a good job heating with just earth-coupling & a small amount of passive solar if your deep soil temps are in the high 50s/low 60s Fahrenheit than at 50F or lower although mere freeze-protection in a 5-side earth-coupled scenario is dead easy even at 45F. I wouldn't count on a subsoil temp substantially higher than 50F in the Okanogan valley, and no matter what your R-values are, you're still only earth coupled on 1/6 of the exterior, not 5/6.  But if your true clear-wall R-values are over R40, and you use insulated shutters (exterior or interior) at R15+, that single side of earth coupling will count from a freeze control point of view.

If your freeze-control monthly heating bills in the less-insulated non earth-coupled structure are $50, by the time you've doubled the R-value and insulated the crawlspace walls to earth-couple it, your heating bills will likely have fallen to $20.  Add some passive thermal air panels, and your freeze control costs will likely go to zero.