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Earth Tube Cooling Tips for new house construction

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Started 1 year ago by schnark
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schnark
Member

Hi All,

We're in the process of building a new house (in the Canberra region) and as part of this, we were inspired by a recent Renew magazine to put in earth tubes into the house. The benefit we have is that we're going to be diging the trenches ourselves so the cost of doing should be relatively low.

What I was wondering is if many other people have done this and if there are any tips as we'd like to design the system to be as effect as possible. I've done a fair bit of research so hopefully the design we're going with will be reasonable spot on. Happy for any/all feedback.

Background
- The house itself is reasonably large and is two stories - it will have all the normal insulation (wall / roof etc) and is double brick design
- We're starting the construction phase right now so we have flexibility to do what we want
- We have the ability to dig reasonably deep trenches
- We plan to suplement the earth tube cooling by using Solar Heating/Cooling units - we currently use two Sola-Mate units in our current home with great heating and reasonable cooling results

Current plan
- There will be 2 inlets at 200mm each coming into the house
- These two inlets will be fed back to a common 400mm pipe
- We plan to run the pipe as deep as possible and for as long as possible - this should be at least 2 meters deep for at least 50 meters
- We plan to use pvc piping with vent outlets within the house that can be opened/closed as required
- The two inlets that come into the house will split into 4 outlets total (i.e. each one goes into two) with the outlets being 100mm each. We'll be placing these strategically around the house in the open spaces as well as close to where the stairs are so that the cold air distributes
- We plan to use natural convection to suck out the hot air in by opening the top windows in the house (we'll have a skillion with windows up the top that can be opened) and use the earth tube cooling force cold air into the house
- We plan to put a fan at the far (outside) end (of the tube) and use that to force in the air into the house
- There will be a drop in the inlet vents as well as a drop at the external air inlet to ensure that condensation runs away from the house

That's the current plan anyways so I'd appreciate any thoughts/feedback

Posted Monday 10 Jan 2011 @ 1:54:12 pm from IP #
matas
Member

Sounds like an good plan, especially if you can dig the trench yourself.
Just wondering, are you going to have an electric fan to suck air from the 400mm pipe ?
Any estimate of the ground temperature at 2 or 3 metres deep ?
Apparently the temperature variation reduces with depth and at about 10 metres the Earth's temperature is constant and close to the annual average air temperature.

Posted Sunday 16 Jan 2011 @ 1:50:06 am from IP #
Terrapreta
Member

Geothermal Energy has been used since Paleolithic times for heating with the earths temperature constant at 12.8 c below 3 m .
Air to ground is the least efficient heat exchange medium . Thus heat pumps are normally used to cycle saline water

Posted Sunday 16 Jan 2011 @ 3:39:43 am from IP #
matas
Member

Terrapreta says "earths temperature constant at 12.8 c below 3 m"

Are you sure ?
I thought it depended on the air temperature above.
The deeper you go, the more the fluctuations are averaged.
So eventually you get the annual average air temp.
I averaged the Sydney air temperature figures from the BOM and got a figure of 17.7 °C
Not sure if my averaging maths is exactly correct though.

Of course if you go very deep (>20m) it slowly gets hotter with increasing depth.

Posted Sunday 16 Jan 2011 @ 4:17:29 am from IP #
schnark
Member

Hi,

Matas - thanks for the feedback. We plan to have a electric fan driving the unit at the far end. It's going to be connected to a switch within the house so that we can turn the unit on and off.

In regards to the earth temp/system design, i've tried to do a fair bit of research, but there's been some actual investigation done on it - http://simulationresearch.lbl.gov/dirpubs/SB06/kwangho.pdf

Any other suggestions? I've just read some other stuff about using 45' rather than 90' bends to make it easier to clean as well as putting in a small rope so that you can run a cloth along it if required.

Has anyone actually setup one of these systems at all?

Posted Monday 17 Jan 2011 @ 12:54:16 pm from IP #
dave lawrence
Member

the only commercial installer I know of in Australia :

http://www.geoexchange.com.au/

I had a client a couple of years ago who had a large deep lake next to his house , my idea was to submerge a coil of polypipe in the bottom of the lake and force air through that before introducing to the house . for one reason and another it never happened but I have heard of other people who have installed systems.

Posted Monday 17 Jan 2011 @ 7:42:22 pm from IP #
Diver
Member

dave,

Just quickly as I am off topic.

How did you propose to pump air through a closed system? I have been working on a simple unpowered 'pump' that raises water to a height above its head by using air generated by another unpowered device I have invented. The 'pump' will not be subject to patent. Am I able to contact you?

Posted Monday 17 Jan 2011 @ 9:01:06 pm from IP #
dave lawrence
Member

it was not proposed to be a closed system .
i am on davelawrence@exemail.com.au

Posted Monday 17 Jan 2011 @ 10:24:55 pm from IP #
matas
Member

schnark thats an interesting paper - I am really interested in temperatures at different depths.
You seem to have done a lot of research on the subjuect, and would know a lot more than most of us.
I get the impression that earth tubes aren't economic if you hire a company to build them.
But if you could do it yourself that would probably be different.
This website has some great solar information, including some on earth tubes.
Just in case you haven't seen it.
http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm#Other
I particularly like these two:
http://www.builditsolar.com/Projects/Cooling/EarthtubeNotes.htm
and this:
http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12460
A bit negative though -
"In the 1970s and early 1980s, earth cooling tubes received a great deal of attention from architects, builders, and homeowners as an alternative or aid to conventional air conditioning. While the concept of routing air through underground tubes or chambers to achieve a cooling effect seems like a good idea, in practice it is not very effective, both technically and economically. Perhaps a few hundred systems were constructed, but information on the practical application of the concept is limited. There are few functioning installations, and limited quantitative performance data exists."

Posted Tuesday 18 Jan 2011 @ 6:59:58 am from IP #
Buzzman
Member

Did anyone bother to read the 'happy customer' letter from the Wagga Wagga installation on the Geoexchange website?

39kW per day to maintain 22degC in the home. 39kWh/day!!!!!!!

No wonder this technology has not taken off here. Might make sense in colder climates where winter heating is unavoidable - northern hemisphere - but this sort of consumption is ludicrous from an energy efficiency perspective.

If I assessed a home with that sort of consumption I'd tell them to turn it off.

Even if it was only used for 6 hrs/day (rather than the 24hrs of this example) that would still add almost 10kWh/day to a households energy consumption.

This is consistent with a 3.0kW R/C A/C unit running 3-5hrs/day - and most people don't use it that much or even every day.

I'd say R/C A/C is more efficient and more economical on that basis alone.

This Waterfurnace technology relies on water flowing through the ground loop, so maybe requires more energy to pump water than air????

But according to the paper linked previously, the difference in temperature is only a few degrees when using air exchange and would still require A/C.

Or did I miss something?

Posted Wednesday 19 Jan 2011 @ 6:00:37 am from IP #
dave lawrence
Member

yes my understanding of geoexchange is that does not make much economic sense installing in domestic situation , like many technologies most efficient on large scale.
also may be more suited to colder climates, utilising earths warmth rather than coolth ?
I noticed on grand designs shows most of the time used for warming rather than cooling

Posted Wednesday 19 Jan 2011 @ 6:29:18 am from IP #
schnark
Member

Hi guys,

We looked into commercial vendors with this, but the quote we got from a geothermal solution (a different vendor) was $100k for it (we've got a reasonable size hosue). For obvious reasons, we decided not to go with it, but there are some pretty decent discounts for commercial and public installations (http://www.business.vic.gov.au/scripts/nc.dll?BUSVIC:STANDARD:1001:pc=PC_62714.html) if you live in Victoria to do geothermal.

Just to clarify, we're not doing geoexchange - in general, that's about drilling down 10-20 meters and then putting fluid through it and then using this to drive a traditional (style) air-con system.

We're doing earth tube which is plain pipes dug into the ground as deep as practical, run over a long distance and then coming into the house. It's not overly complex.

I do like the lake idea, but we don't have one handy (we do have a river about 1km away but it's not practical to put it up that long distance!), so hopefully going under the ground long and deep enough will work.

Dave - We're in Canberra so we're got pretty cold temps - however we'll be putting in solar heaters (Sola-Mates) to help supply the heat. From what that report says though, it would help with heating the house.

Would the other people that you mention be happy to be contacted? We're keen to leverage off other people's ideas/experiences as we're trying to be as green as possible with this house.

Posted Wednesday 19 Jan 2011 @ 12:28:01 pm from IP #
Jeffbloggs
Member

schnark
Have you considered a heat recovery ventilation (HRV) heat exchanger instead/as well?

Also have you considered the thermal capacity and conductivity of PVC pipes in your design? I could imagine that a PVC pipe underground, with only 62m2 of surface area will not add much temperature difference to the incoming air(it is only the same surface area as a 12m wall section of your proposed double story house), especially so because PVC is more a insulator, and that a large diameter pipe (400mm) allows air to flow from one end to another without contacting the outside (no heat transfer at all!), and because your design doesn't "meander" much. I'm not trying to dissuade you in any way, but there are other possible solutions.

With all forms of heat exchangers (which is essentially what your building underground), the most important features are:
- Turbulent flow (rough sidewalls that produce turbulence, or spiral walls, that continually change the direction of flow, alternatively at a minimum place deflectors at every pipe join to create swirling effect throughout the pipe. Imagine tiny air particles that need to contact the walls as often as possible to transfer heat)
- Use Heat conductive materials like Aluminium is one of the best, and not corrosive
- Flow velocity needs to be according to heat transfer capacity/design of tube
- Delta temperature of in/out air/ground are critical when designing the HE (the higher the temp difference the more heat can transfer in that time)

On the point of trying to harvest some "energy" via the earth tubes, you'd be better off scrapping your double brick, and going for brick veneer with as much insulation and sealing as possible. Why harvest energy just to loose it in the house construction? Personally I'd go with a SIP (Structurally Integrated Panel) design if you can/want.
I can offer some assistance with design recommendations for free, we are currently developing SIPs buildings to be used in up northern WA for a 300 block mining suburb, but many issues are similar regardless of building construction.

Let me know if I can help.
Regards
JB

Posted Wednesday 19 Jan 2011 @ 3:47:26 pm from IP #
Buzzman
Member

YEah, you should read that article by the academics posted higher up - it's quite specific about the ratio of pipe size to cooling capacity, flow rates and so on.

Basically the smaller the pipe, the longer the pipe, the deeper the pipe and the slower the air passes thru it, the more heat it gives up or takes up.

In winter you might have some success with cold air sinking and warmer air rising, but it seems from the academic tests that some kind of force is usually required - ie: fans - which then adds an electricity component and thus a cost.

As DM69 has posted elsewhere, when looking at purging fans (which is essentially the same thing) you need a fan/pump flow rate that will cause the total volume of air to be replaced every half to one hour.

Do your sums carefully!!!

Posted Thursday 20 Jan 2011 @ 6:22:43 am from IP #
matas
Member

If the earth tube was only going to be used for cooling (not heating) then you could put the tube on a south facing slope (if possible), so the ground temp would be lower.
And also have the tube opening in the shade (and near vegetation and creek/pond etc)
Not sure sure if schnark wants to do heating as well as cooling.

There are probably a few successfully operating earth tubes around Australia.
I read this on another forum
"saw a house in Adelaide hills that was built with 30 metres of underground air piping and on a warm sept day it had a nice flow fo cool air rising from below."
http://forum.homeone.com.au/viewtopic.php?f=20&t=1790&start=0

Posted Thursday 20 Jan 2011 @ 6:53:39 am from IP #
schnark
Member

Hi Guys,

First of all, thanks for the feedback - this is exactly what I wanted.

Jeffblogs - In regards to HRV systems, I looked into it, but they don't seem to have very favourable reviews from either customers or reviewers. We're more than happy with our Sola-Mate for our heating.

In regards to PVC vs Alluminum - sounds like a solid idea, I'll look into this further - as you noted, in this case, we don't want it to insulate!

Turbulent flow sounds like a reasonable idea - i'll investigate this further. In regards to flow velocity, we've done the maths and we'll have one 200cm cylindrical tube splitting into 5 100cm outlets where infact, we could have 5.8 outlets. This should ensure positive flow. We'll be using a fan to drive it, but at low speed as per the pdf file I referenced as this ensures the best cooling.

In regards to the ditching of double brick, at this stage we've got double brick with polystyrene insultation so we should be pretty well insultated in the walls. We're also planning on insultation the slab as well to prevent loss from that.

We've got a (split) skillion roof so the idea of a solar chimney (for the bit that with the false roof as opposed to the other section with the open rafters and then windows with vents at the top) makes sense as well.

Buzzman - thanks for the feedback, do you know of any sums I could check my numbers against? Happy to get feedback/suggestions.

Matas - At this stage, we'll probably be putting the inlet at the east side of the hosue, but i'll investigate moving it to the south. The catch is that the house is on a slope so that's not likely to be practical. I think i'll work around this by planting trees around where the point will be to shade it.

Posted Tuesday 25 Jan 2011 @ 5:52:03 am from IP #
Jeffbloggs
Member

schnark
In regards to HRV I mean a ventilation system of the house itself and not of the roofspace.

What a HRV does (or should do!) is provide continuous fresh air and ventilation without needing to open any windows. This leads to better overall climate control and increases efficiency by using a simple air to air heat exchanger to "pre-treat" the incoming fresh air with energy from the outflowing "stale" air. This works for both winter and summer and can re-claim over 90% of your loses through normal window ventilation. For this reason our current building designs are mostly very conservative with window placement, area and openings, as they are thermally "holes" in the wall. Even when regarding passive heating and cooling through windows, if it is not designed correctly or has insignificant protection, both in shade and insulation, windows (or the lack of!) are one of the most important house features for climate control. One of the problems with passive designs using windows is that people need to actively contribute to its control, they need to open them, shade them, insulate them and of course close them! A HRV allows you to have very limited opening windows and simplified controls without sacrificing climate quality, and actually increases efficiency if you have active AC/heating components, by reducing loses from normal ventilation practices by reusing the otherwise outflowing heat/cold. Obviously, seeing that you are already planning on installing a form of ducted ventilation to the house, it would make sense to use a simple and relatively cheap (under $2k) HRV heat exchanger as a part of the system to take further advantage of the installation costs involved.

On the point of double brick with insulation, be careful that you minimize thermal bridging and droughts. Remember heat convects, conducts and radiates, and you need to identify how the heat might transfer.

In Europe they commonly insulate on top of the slab, which has hydronic heating, and screed across the top for flooring. This actually helps reduce the internal thermal mass whilst providing a good way to integrate the tubing for hydronics. Remember uncontrolled thermal mass is a liability, especially when the required temperature needs to be artificially produced with AC or heating. It only works well if it can stabilize temperature in the comfort zone, as soon as it is allowed out of the temperature comfort zone, you need to change it's temperature as well.

Further on the subject of earth tubes: Have you considered to do this using a hydronic/water based system instead? The difference is that it allows you to integrate the following into the design:
1. Heat and cold storage with simple compact insulated tanks (Water's heat capacity is nearly 4000x that of air per unit volume) This allows you to cycle the system according to occupancy (work day, home at night), and store heat/cold from night to day or vice versa, and with enough tank capacity from day to day
2. You can then supplement this hydronic system with solar HWS/heat pump AC or even timber stove or gas to boost the temp output required
3. Allows you to use small diameter PE heating tubing for earth source temperature harvesting with 20W electric water pump, running literally km's of easily installed tubing in the ground and the house (available in 300m lengths), small tubing has greater surface area per volume of water, and the heat capacity of water means longer single runs without affecting temp delta performance, and no air quality contamination issues through the air earth tubes. You can also emulate turbulent flow by simply zig-zaging tubing before burying.
4. You can install a simple air-to-liquid HE in HRV ventilation ducting for complete house dispersal or use hydronic radiative floor to ceiling panels with natural fanless convection, or hydronic floor tubes with screed as above, or simply poured in just under the top of a normal slab (only costs you the tubing if you install it yourself, very easy to do)

All in all a fairly good alternative with a good cost/performance ratio. BTW I have some more pointers on the "Sustainable Housing (Climate, Natural Disaster and Flood Proof)" thread if you are interested.

Posted Tuesday 25 Jan 2011 @ 9:13:29 am from IP #
Catopsilia
Member

schnark

http://simulationresearch.lbl.gov/dirpubs/SB06/kwangho.pdf
I like the above paper that you quoted, as a way to bring the discussion "down to earth", rather than "off with the fairies" as energy saving enthusiasts are sometimes tempted to be.

I have not attempted to predict soil temperature myself, and I see from the paper that it is no simple exercise. Air temperature is not used as the basis of the calculation.
I had expected that air temperature would predict soil temperature, based on the broad generalisation that mean annual soil temperature is close to mean annual air temperature. It is not VERY close.
I have posted some observations of soil and air temperature relations here (and in subsequent posts):
http://forum.weatherzone.com.au/ubbthreads.php/topics/856013/Re_Observations_of_climate_var#Post855531
There is also discussion of soil temperature prediction in the same thread:
http://forum.weatherzone.com.au/ubbthreads.php/topics/868319/Re_Observations_of_climate_var#Post868319

Posted Wednesday 26 Jan 2011 @ 1:02:15 am from IP #
matas
Member

Catopsilia, thats some really interesting subsoil temperature you have collected.
You have done a great recording job.
I noticed that you say "Mean annual temperature at 750 mm was 2 degrees warmer than mean annual air temperature"
Can you tell me again the mean annual air temperature at Manilla ?

Posted Thursday 3 Feb 2011 @ 10:34:58 pm from IP #
schnark
Member

Hi Jeffbloggs,

Firstly, thanks for taking the time to respond in much detail - it gave me much to think about.

We did look at a commercial Hydronic solution but it was riduculously expense. Are you proposing a DIY one instead? I'll have a look at your thread, but at this stage, we could put still put it in if it is going to have a significant, positive effect.

I did consider a similar idea to what you were proposing but with air (e.g. air tubes in the slab), but concluded that air wasn't a particularly good conductor and it most likely wouldn't work that well. Wasn't aware it was 4000x as bad, but that makes sense.

We are planning to insulate the slab edges anyway as part of the house design as we're right on the edge of what the US Gov's energy site recommends for doing starting.

The concept that you're talking about with the HRV system is exactly what we want. We are keen to ensure that here is good airflow. Are you able to send me the info about the $2k system you were talking about - i'm assuming it can manage air based systems fine?

We've slightly tweaked the system since we last spoke - we're now running 2 * 225mm pipes into the house and then sending one of those upstairs into the cavity (between the ground/1st floor) and the other one being split into 5 outlets on the ground floor.

I'm trying to work out some rough numbers for how this will work so if anyone has any suggestions - i'm happy to take feedback.

Cheers,

Kieran

Posted Saturday 5 Feb 2011 @ 10:56:12 am from IP #
matas
Member

I am interested in claims that the tube should be metal, instead of plastic.
I thought because heat transfer from earth is slow, plastic would be just as good.
And much longer lasting and cheaper.
Also that it is important to introduce as much turbulence into the air as possible.
Does this really make a difference thermally in an earth tube scenario ?
Because it would be harder and more expensive to build, and the air would take more energy to pump.

Posted Saturday 5 Feb 2011 @ 10:29:56 pm from IP #
Catopsilia
Member

matas

My data is not official. I use as my standard period the ten years beginning April 1999.This time is perhaps a degree warmer than the 1961 to 1990 period used by the Bureau of Meteorology.

My figures for Manilla NSW (30deg45S; 150deg44E) are:
Mean air temperature in the screen: 17.9 deg.
Mean Subsoil temperature at 750 mm: 20.1 deg

For the seasons:
Autumn: Air: 17.7; Subsoil: 21.7;
Winter: Air: 10.5; Subsoil: 14.3;
Spring: Air: 18.4; Subsoil: 19.0;
Summer: Air: 25.1; Subsoil: 25.5.

Inter-seasonal temperature range:
Air: 14.6; Subsoil: 11.2.

Note that spring is warmer than autumn for air temperatures, but the reverse is true for subsoil temperatures.

Posted Sunday 6 Feb 2011 @ 12:25:39 am from IP #
petacat
Member

hi Schnark. I am in Canberra too and have investigated a number of these options too.

First thing is that you will certainly get more benefit from good double glazing and north facing glass with very good shading of the North in Summer.

A Solar Chimney works far better than geothermal approaches in Canberra because of the low overnight temperatures with low humidity in Summer. That makes more difference than anything else and is totally passive (taking advantage of heat rising and drawing cooler air in through ordinary windows.

Supplementation with active solar heating works. I have used the Solamate/HRV approach and I am able to keep my house thoroughly comfortable in Winter. I use a heater (because it is Canberra and we get -5 degrees in Winter) in the evenings and early mornings. It is a small rinnai "room heater" suitable for a small room according to the manufacturer. It is all I need to keep the whole house warm - even when the sun has not been seen for 2-3 days. Do not buy the hype about HRV/HVAC systems efficiently cooling your house for you in Summer. They do not unless you set them up to do that job rather than heat in Winter - you choose one or the other.

After doing similar analysis to your own on the feasibility of using pipes (and seeing a similar design on Grand Designs) I found that spending $15,000 on double glazing, the Solamate/HRV and a simple solar chimney was better value. An additional $3500 on retractable shading of the north side glass area made more difference in Summer than was obvious form my initial calculations. This is because I neglected to take into account reflected (from the ground) radiation. More shade cooler house (no kidding!).

If you can build in more thermal mass and get the Winter sun on it then you will be increasing your internal temperature by 5-18 degrees overnight in mid Winter, depending on how much window and thermal mass. I have dark slate on a very thick concrete slab and 26 sq M of glazing on the north side. I walk on that floor in bare feet when the outside temperature is below -5.

Compartmentalising the house so you do not waste the retained heat by venting it through bathrooms, laundry etc makes a bigger difference than you might think.

Specifying double the insulation on the North and West of the house will almost certainly mean that you will be comfortable in Summer extremes as well as getting the benefits in the Canberra Winter.

hope this helps a bit.

Posted Sunday 6 Feb 2011 @ 2:58:29 am from IP #
pulpo
Member

I'm not convinced on earth tubes, for many reasons.

I think Jeffbloggs is on the money with his thoughts and suggestions.

I'm currently building in the Goulburn region so similar climate to Canberra.

I have installed hydronic piping in the slab; DIY, 5 zones.

I will heat with evacuated tubes large tank.

How it will all work, is something to work out down the track.

With hydronic there has to be some suck it and see approach as all homes vary.

Professional installations are just over the top.

Have a look at http://www.solarsatisfaction.com.au.

Seems very knowledgeable on the subject and is in Canberra well worth a chat.

I have not used him but spoken with him.

Enjoy

Pulpo

Posted Sunday 6 Feb 2011 @ 6:37:25 am from IP #
schnark
Member

Hi guys,

Cheers for the suggestions, luckily we're owner/building ourselves so we can make changes as we need. Here's my feedback on the points we've raised, appologies for the long reply however lots of points have been raised!:
- Already doing double glazing on all windows
- Already got adequate north facing windows and all windows on all sides will have external awnings with eaves (additionally) used to protect the top floor against summer sun/allow for winter sun to come in
- petacat: i'm interested in what you've said about the ground reflecting the sun - did you use any specialised awnings to protect against this? I also read your blog a bit and was interested in the issues you've had with curtains so i'll definately investigate the issues you've raised
- House compartmentalisation is a good idea - we've done that already for the main entrance that we will be using (from the garage in through the laundry, into the house). We haven't bothered with compartmentalising the main entrance as it will only be used when guests come over - bathrooms are partially covered as well and we'll make sure we've got good sealing vents
- We've got a 100mm slab and will be insulating it (regardless of if we go with Hydronics) so combined with north windows, I believe we've got this well covered for winter passive heating.
- Insulation wise we'll have 70mm insulation the whole way round the house in a double brick house so this should give us a pretty high rating
- I'm convinced on the idea of solar chimney so are planning on putting this in - i'm going to go have a look round for some info about this, but if anyone has any suggestions, that'd be appreciated
- We already have two SolaMates in the current place and love the things in Winter - they're simply gold. In summer, it's a partial help - we're only seeing it bring down the temp a little bit. We'll definately be getting them on the new place.

Okay - i'm convinced about the hydronics DIY - just need to get some more info about it. I'll talk to the person you've suggested Pulpo. If it's okay, can I contact you?

That said, we're still going to go ahead with the earth tubes as (a) I've just finished up tonight jackhammering and digging the trenches (b) we've already got the pipes at trade prices and (c) I think it'll work as a supporting part of the overall goal of passively/effectively cooling/heating the house. The solution itself will cost a couple of thousand but I know this going in.

We're using plastic (PVC) tubes for a variety of reasons but cost is the main one and given we can just run the tubes longer for minimal extra digging cost, I don't believe that there's going to be much difference. According to Rehau who make turn Earth Tube systems for Europe/USA (but not distributed into Aus by Rehau for some reason), PE tube is the best, but its also more expensive - I haven't seen anyone in the research i've done recommend anything bar plastic variants

Worst case scenario - we can use the earth tubes as pre heating/cooling for an air-conditioning system. We're putting in filters to mitigate against the risk of air contamination issues.

I've found this info on the subsoil temperature in Canberra - http://www.bom.gov.au/products/IDN65176.shtml - seems to match up with Catopsilia's data.

Anyway, thanks again all.

Posted Tuesday 8 Feb 2011 @ 10:48:04 am from IP #
pulpo
Member

Schnark welcome to email me about Hydronics, but frank will be much better informed than I. (solarsatisfaction.com.au)

Good luck with the earth tubes.

The question will be "would I do it again?"

And that holds for most things associated with building a new house.

I'm building with ICF unlikely to build that way again.

Cheers

Posted Wednesday 9 Feb 2011 @ 11:48:29 pm from IP #
dave lawrence
Member

why not build with ICF again . I am very interested in your comments.

Posted Wednesday 9 Feb 2011 @ 11:50:50 pm from IP #
Catopsilia
Member

schnark
You have found a site for soil temperature data.
These are facts, but they are rather enigmatic facts that are hard to get one's head around.
As you see, it is standard practice to observe soil temperatures at 9 am at depths of 5, 10, 20, 50 and 100 cm (note the antique units!).
Each day, as the solar radiation builds up to a maximum about noon, a wave of heat passes down through the soil. It takes (IIRC) about a day to get to 100 cm (one metre). Just millimetres below the soil surface the cycle of temperature can be larger than that of air temperature, and there is hardly any lag between the two cycles.
At the first observation depth, 5 cm, the cycle is still large, and not much lagged. The 9 am observation, being some hours later than the time of overnight minimum, may be not very far from the mean for the day.
This is not true for the next observation depth: 10 cm. There, the lag of the temperature wave is such that the recorded 9 am value may be close to the minimum temperature for the day at that depth.
At deeper levels the relation of the observed 9 am temperature to mean temperature at that depth becomes obscure. It will be different for different sites, soil types and moisture conditions.
By one metre depth the size of the daily temperature cycle becomes less than one degree, and is of no concern. One should appreciate, however, that major changes in the weather will not be felt there until a day later.

Posted Thursday 10 Feb 2011 @ 1:21:49 am from IP #
pulpo
Member

ICF decision probably should be another thread.

Bottom line I think there must be a better product.

I have seen all the ICF on the markets some better than others.

I'm coming from an owner builder perspective.

Anyway will start another thread.

THings to consider embodied energy, thermal mass in walls only used for strength.

Cheers

Posted Thursday 10 Feb 2011 @ 11:39:54 am from IP #
schnark
Member

Hi pulpo,

Can you please drop me an email @ spamie @ internode.on.net

Cheers,

Kieran

Posted Friday 11 Feb 2011 @ 10:53:17 am from IP #

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