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Murray

Underground pipe work to stabalise temp

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Somewhere I read of underground pipe system to stabilise temp. Evidently about 2 mtrs down the earth temp is 20 to 22 deg C all year round.

By burying a qty of pipe at that depth and pumping water through fish tank water temp could be kept stable.

Was it you FF who did this ?

I have searched but cannot find info.

Can someone help with some good links please ?

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From what I understand, geothermal temperature is the average year round temperature of your area. It changes with the distance from the equator,with greater distance meaning a greater temperature drop. This occurs as shallow as 2 meters deep.

http://gladwell.typepad.com/gladwellcom/2006/08/the_case_for_ge.html

This thread might be of use.

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When I built my next house I'm going to install pipes under the ground. Heat from the ceiling leaving the roof pulls air from the rooms and in turn pulls air from under the ground. Like having free air con that uses no power. Green houses can be set up to use the same thing for cooling. And FT's seem to respond well to using underground pipes.

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Yea it was me havent realy tried it yet as the ground temp is close to tank temp13.5 deg atm on the first test run seems to make a difference i think to realy work you would need a lot more pipe and deeper than i have but connected to the freezer system as well i think i can give the trout a few more weeks because as it is here one or two hot days then back to cold for two weeks .

1 oclock yesterday 9 deg and a foot of hail on the hill a mile away

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http://sunnyjohn.com/

The answers are in here but these folks aren't the best at explaining themselves. You'll have to chase a bunch of the links pertaining to greenhouses and "SHCS" (subterranean heating and cooling system).

It's worked well for them in the American southwest where daytime summer temps exceed 110 degrees F and the nights drop as low as 35 deg. F.

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My experiment had only limited success it needs to be a lot deeper and a lot larger [as the ground warmed up it had little effect] so i will just leave it there for the archaeologists to find in 500 years:)

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You'll have archaeologists in 500 years telling people they used to grow fish in pipes burried in the ground because they find pipes with fish poo in it.:D

FF I can't remember the size of the pipe you used. Can it be hooked up to your shed and air get pulled through it. Interested in how it cools air flow for buildings.

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http://sunnyjohn.com/

First, please forgive my limited knowledge of American standard measurements to metric. I'll put together a conversion table and post it on my monitor.

On the above listed site they modulate the air temp with 4inch/90mm perforated corrugated PVC drainage pipe. It's sandwiched in between layers of 1/2 inch pea gravel. Heat of the day is stored and released at night. They use a dual thermostat system to maintain a desired range of temperature.

Conduction of heat via water to the soil is only effective with adequate moisture in the soil. There must be nearly 100% contiguous contact for it to be efficient and you would need to put 12 inches of soil between each loop and layer. Soil works as a heat sink but must have greater mass ratio than the water pipes. Here in the States ponds are used as heat exchangers for cooling liquid conveyed in pipes.

With air exchange through the gravel you also carry excess humidity out of the sealed greenhouse. This aids in the efficiency of the exchange and the need for slotted pipe. Large amounts of moisture merely drain into the subsoil. The SHCS works at its best in a dry climate like the southwestern desert regions of America. SHCS uses a closed greenhouse environment to work more efficiently, even with hot summer weather. Roof venting is for exceptionally hot days only.

Fish tanks are thermal mass, grow beds dissipate moisture into the air creating a mild cooling effect. If the humidity is controlled with the SHCS the cooling effect of the grow beds could keep the water temps more even. I'm not sure if it would cause a dramatic cooling effect but if your problems are related to excess heat build up then it might be worth a closer look.

Dramatic temperature swings are what effect fish the adversely. Granted some varieties do go off their feed if the temps are too low or too high out of their normal comfort range. But fish are adaptable too. Freshwater fish can be made to tolerate saltwater conditions with gradual change and vice versa. Perhaps with a gradual adjustment of temperature they will adapt as well.

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Hi all,

I'm by no means an expert regarding geothermal technologies, but researched it a little when considering it for a "green" housing project.

From what I could establish, the depths required to reach "stable" temperatures was not as deep as mentioned in this thread. The order of magnitude was around 500mm below surface.

I do not have enough space (and it's a rented house) to perform a test, but feel that this concept is sound. I would set up a seperate pump to circulate water through the underground pipes, perhaps with a timer which could allow the water to remain underground long enough for it's temp to reach equilibrium with the soil, or experiment with variable flow rates to achieve a similar result. Also, the thinner the "radiator" pipes the move effective the system should be, which obviously requires a better pump.

I hope my ramblings help formulate ideas.

Dave

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Hi Dave,

I follow what you're saying and agree if that was what I had in mind. However, that's not what I'm proposing. The SHCS doesn't move water around to use geothermal benefit but moves the greenhouse air into the ground and uses it as a huge thermal mass. The tubes are layered in the soil or in some cases gravel to evenly distribute the warmth.

Please read the FAQ's at this link if you want a better picture of what I'm saying.

http://www.sunnyjohn.com/indexpages/shcs_faq.htm#faq1

If you use the ground to stabilise your water temps you'll have water that's too cool for proper fish growth and in your breeding tanks there would be no breeding as the temps would be too low to trigger the natural response.

Since their FAQ's cover a lot of questions it should give a more precise picture than I did.

The SHCS works off the principles of refrigeration phase change. This is a partial quote from that link.

Simply put, how does the SHCS work?

"To put it in a nutshell, hot moist daytime air of the greenhouse is circulated through underground tubing and then back into the greenhouse cooled and dryer. The result is a greenhouse cooled in the day by soil that is heating up, and a nighttime greenhouse that is much, much warmer because of the high soil temperatures. It makes perfect sense, but we never discovered how great it would work until we did it in a number of projects and noticed that because the air is so moist and dropped in temperature, that the phenomenon of dewpoint occurs. Because it reaches dewpoint it "acts" as a refrigerator using the phase change of water rather than the phase change of freon."

So what you get is good temperature control in the daytime and geothermal warmth at night from the thermal mass of the heated soil. If the ground under your greenhouse is insulated and thereby isolated from the surrounding soil, then you have the added advantage of "caching" the warmth of your Aussie winter to counteract the cold of your summer. The reverse is true on my side of the equator.

You still get some solar advantage in the cold season but in the case of Australia the further south you are located the less advantage you receive. We have USDA growing zones here in America. I'm sure you have the something similar there. Zone 1 is the polar region and Zone 10 is Key West, Florida. At the southern tip of Lake Michigan is zone 5 and this system works into Zone 4 which reaches up into Maine. Canada has some zone 4 and mostly zone 3 and lower. Mexico is zone 9 or 10 and up.

The beauty of the SHCS is that it requires only a fan, thermostat and some venting during extremely hot days to heat and cool a greenhouse. No more heaters and massive vent fans. Cooling a greenhouse with 55 to 75 degree F air from below is much more efficient than trying to do it with whatever the hot air outside the greenhouse has to offer, which can be in excess of 100 degrees F on a real scorcher. Conversely, 50 to 55 degree air from below on a cold day with some solar advantage during the colder season is a plus as well. There might be a much shorter period where the fish go off feed or none at all depending on the breed of fish.

Add in a tank heater or use bubble wrap floating on the fish tank surface during cold weather inside a greenhouse environment and the water temps will probably remain warm enough. I once insulated a small greenhouse years ago with clear bubble wrap attached to the frame inside the greenhouse and I was able to keep it warm enough to grow kales, onions and lettuces during our cold winter here at the southern tip of Lake Michigan. Then I started my garden flats a month ahead of all my neighbors and friends.

Figuring out what is the optimal depth and amount of underground drainage tubing for conveying the air is every individual's task to calculate. But, there is a calculator on the http://www.sunnyjohn.com website. "Mr. Hobbit" is the fellow that has had a lot of experience with the SHCS, there's video and picture galleries and links galore to help you put the pieces together. He also has a forum of his own listed on there too.

At the age of 55 being retired and with a disabled back from being an urban paramedic, I do a lot of homework first. That's mainly why I'm on this forum is to learn from all of you that know more about AP systems than I do. My introduction page will tell you a bit more about me. I really enjoy quid pro quo information exchange.

Dean

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Hi David, I am very interested in making an underground heat exchange system and using water filled pipes to do it.

I am interested that you say only 500mm will do it. That would be great, as the cost of digging 2000mm deep trench is a whole lot more.

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Think they go deeper to increase the amount the heat exchange(soil) can handle. At 500mm the soil will have a limit to the amount of heat it can take in. Also at that depth the temp change in the topsoil will have an effect on lawns and the dirt garden. I've heard of lawns dying in winter because of topsoil pipes used to heat pools. Plus if your digging a hole anyway, and the backhoe is there. Why not go down deeper.

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Thanks Dean, obviously 2 different systems, both as interesting as the other.

Dufflight, yes agreed that if it's been done by machine it's easier, but a cut-and-cover scenario at shallower depth is obviously a better option.

The depth below ground for the system which I was looking at in my studies (and I'm sorry I don't have that info readily available - will try to get it) was being employed in extreme climates (winter freezing and snow and summer heat of about 35 deg C). The experiments were based on underground pipe length vs depth, and essentially the theory goes that there's more financial benefit (cheaper) in laying slightly more pipe at shallower depth (order of 500mm) than less at deeper depth, since the change in the temp range between this depth and deeper is not significant enough to warrant the additional excavation costs.

Please remember that going deep in an open excavation has massive cost implications regarding temporary shoring of the sides (health and safety legislation, etc.) unless you have a lot of space then you can batter the sides. So a larger shallower layout would be more economical. Or say, one layer at -750mm do some backfill and the next layer at -500mm - thereby half the footprint.

By the way - this type of geothermal technology is now being used extensively. In new builds, such an array of piping is even being installed in concrete cast in-situ piles. The pipes are tied to the reinforcing cage once concreted they are essentially installed in an environment which has a stable temperature with a huge capacity to transmit heat.

BUT - Dean's point is the most crucial. If Murray's aim is to maintain a reasonably constant temp using this approach, the temperarture that one achieves is not necessarily the right temp, ie: the ground temp may not be optimal. With Geothermal technology generally the ambient air temp is vastly different to the sub-soil temp, thus a heat-exchange system can function well. If one uses this system as I understand it, you're achieving and equilibrium temp ie: fish tank temp = sub-soil temp. Is it the right temp? I, for one, have no idea.

Murray, drive a couple of PVC pipes (20mm dia) to various depth (close their ends with heat gun) drop a few cheap thermometers (tied to string for retreival) and pug the tops with corks. Take occasional temp measurements to see what the approximate equilibrium temp will be. It's probably worth investigating it.

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I'm running a sewage line to the shop in the next couple of months and will be adding some PVC to the 2.5mtr ish trench that is dug. It will be 50mtrs long. But the house we are going to build next door will incorporate both under slab piping as well as more piping layed under ground. I might lay pipe at 2 levels and get some running temps.

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Thanks David, The option to only dig 500 or 750 ml is very appealing due to cost and the lack of mess involved.

I do not know what the soil temp is in this part of the world, but your suggested experiment is worth a go.

We do have fairly mild winters here in Brisbane, but for about 6 weeks we have night temps as low as 5 or 10 deg and maybe 10 nights when it will drop below zero.

Long enough to cause difficulty for my Jade Perch and Sleepie Cod. So the thought of being able to pump the fish tank water via some underground pipes that will stabilise the temp is very appealing.

Last winter I racked up a hefty power bill. Makes the fish dinners a bit expensive.

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The most difficult factor in this whole equation is the variable of each person's ambient subsoil temperatures at any given time of year. I've seen geothermal heat pump systems that go nearly 100m deep in a continuous loop using special coolants to get optimal results.

If you have or know someone with a basement or someone with an underground home, it's obvious there's a difference in temperature just one meter below the exposed surface.

In general what I'm finding in most of the publications I've been reading from the USDA and numerous university studies that are documented on the internet for free is the mean ambient temperature of subsoil at least one meter in depth is 12 to 25 deg. C around the world. Warm and cold seasons have an effect as well.

On either side of the equator, sunny slopes are warmer, shaded slopes are cooler and flat lands are fairly consistent depending on moisture and organic material content. Rocky soils have a small factor in ground temps too.

Going to a depth of 150cm to 200cm you'll find it is generally closer to 12 deg. C which would have an adverse effect on your Jade Perch and Sleepy Cod. If you were to raise fish from a cooler climate using geothermal water temp regulation you might get along just fine. I don't think the reverse would be true of cooler climates using geothermal to raise warm climate fishes.

One very simple method of raising water temps used for swimming pools in cooler regions is a floating bubble wrap cover. It's cut to the shape of the pool, or for AP purposes, a fish tank and it merely floats on the surface. It acts like a solar heater for the water and the bubble wrap insulates reducing heat loss. It would heat a 35K liter swimming pool from 10 deg. C to nearly 30 deg. C in a day or two. The air temp would only be about 20 deg. C when we used the "floating solar heater" as it was named by the manufacturer. The bubbles were about 3cm in diameter.

Mind you, with the solar cover you would need to monitor the temps closely or you could even experiment with using a partial solar cover and see what results that would bring. I would venture a guess that it has solar heating abilities even during the colder seasons as long as there is direct sunlight to the surface of the tanks. It could be a cheap fix to an expensive problem and most office supply outlets have rolls of it for packing material.

Here's some references for light reading. It's tedious but has a lot of data.

http://books.google.com/books?id=rJsVoRw1geoC&pg=PA207&lpg=PA207&dq=ambient+soil+temperature+at+one+meter&source=bl&ots=IylPreSWQi&sig=zqKNzvBcPBGc20jil43uNZmS1LE&hl=en&ei=RfCwSauHAqWoM-25yfkE&sa=X&oi=book_result&resnum=1&ct=result

Pages 210 and higher have some interesting facts.

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Organicusrex,

i was going to send you a PM with regard to the beard, but I thought bugga rit!, I'll just change my avatar.

We have a charity event here each year called World's Greatest Shave, where you can shave your head, beard or Mo (or just get it coloured) for the Leukaemia Foundation.

This year I have decided to make people pay to shave off this piece of artwork next Saturday! Have nearly reached my target amount!

Anyway, just wanted you to know that youre not the only one with a whorth while hirsuite pursuit!:D

Cheers IanK.

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Murray see OBO post temps vary little at 1 m deep I was in adelaide at the weekend [at an ap meating] and there was a bloke there that is having success with a cooling tower he still has trout just waiting for photos ,will post when available.

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Cooling towers are great. Just got to watch out for build ups because of the evaporation. And they do get legionella etc. But AP water, salt levels and the size may need to be taken in account.

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