8" drain-tile,( non-perforated of course).

Posted By ICFconstruction on 09 Sep 2010 09:20 PM
8" drain-tile,( non-perforated of course).

PVC, poly or clay?

oh I don't know the black corrugated stuff, poly?

Posted By ICFconstruction on 10 Sep 2010 07:09 AM
oh I don't know the black corrugated stuff, poly?

Brad;

thats kind of what I was fearful about.  Unless the tube was absolutely watertight like glued sch.40 PVC, the pipe will most likely take on water. If it has water several problems could occur, now it is a source for water vapor to enter the conditioned space and create humidity. It is also is a breeding ground for mold and bacteria.
Water sourced bacteria is how Legionaire's disease starts, for those of you too young to rember what that is:

The bacteria that cause Legionnaires' disease are found in warm, stagnant water and the soil it seeps into. People inhale the bacteria when it becomes airborne, usually through air conditioners, humidifiers, shower heads and faucets, whirlpool spas, and even the water misters found in grocery stores. The bacteria has also been found in soil and groundwater at construction sites. Some people can be exposed to the Legionella bacteria

Corrugated tile would also trap condensation since it isn't smooth like PVC. This trapped water could cause mold, mildew, bacteria... something that you don't want your fresh air going through.

Yes, it must be smooth walled-goods to limit water stagnation and to make it easy to clean, but the Legionaires breeding threat is almost vanishingly small at water temps below 80-85F. Mere presence of the bacteria in groundwater doesn't make it a threat- the concentration (or the ability to multiply rapidly) are key. In most of the US the deep soil temps are well below the threat temp:

http://mb-soft.com/solar/soilmap.gif

But that's not to say molds & other potential pathogens won't be an issue if water is allowed to stagnate there. All ground tubes are better off installed with sufficient slope to drain, and with a reasonable system for disposing of the condensation/groundwater/rain that might that will inevitably find it's way in at some point. (In dry soil well above the water table weep hole at low points would suffice. In swampy-rainy areas it'll need something else.)

It doesn't need to have full schedule-40 PVC wall thickness & pressure specs- just the smoothness. Less expensive low pressure thin-walled drain/sewer pipe will do (backfill carefully to keep from breaking it.)

The Passivhaus folks have been moving away from earth tubes in residential applications in favor of closed loop PEX systems for pre-tempering ventilation air. Unless you can climb into the earth tube to inspect and clean it (which might be the case in a big commercial building with tons of fresh air intake, labs, hospitals, etc), there are some inherent risks in the system as others have pointed out (critters, mold, mildew, etc). As well, the German systems tend to only use cement or tile for their earth tubes to limit microbial growth, they stay away from buried wet plastic.

The pex systems are very simple, and sealed. Basically, you put a few hundred feet of PEX under your slab or footings before you pour, and circulate brine or glycol with a very small low-wattage pump into a small heat exchanger located in the fresh air intake of the HRV or ERV, which can reduce humidity, and cool or heat the air slightly. This can reduce the load on an air-conditioner in a cooling climate, or keep the core of an ERV from freezing up in a heating climate and avoid electric resistance reheat.

Controls are critical, from what people tell me, it's the main reason to buy a packaged unit instead of home-brewing it. From the numbers I've seen, they can be tough to justify economically, but with very low-energy buildings can start to be viable.

Some links to these systems:
http://www.zehnderamerica.com/products/comfofond.asp
http://www.sole-ewt.de/index-e.html#CWK
http://www.luefta.com/pdfs/Zubehoerkomponenten.pdf

I've heard rumors of dehumidifiers running on groundwater-temp fan coils like that too, but haven't seen details. In humid climates with sub-55F well-temps it should work.

Cost-wise is another thing...

Posted By Dana1 on 10 Sep 2010 10:06 AM


It doesn't need to have full schedule-40 PVC wall thickness & pressure specs- just the smoothness. Less expensive low pressure thin-walled drain/sewer pipe will do (backfill carefully to keep from breaking it.)

Dana1;

"be carefull not to break it" is right , I have seen 4" sched. 20 pipe become oval in just 2 years under only 4 ft. of clay soil. I have also seen a sharp stone pushed thru the thin wall PVC in similar soil conditions.
I would be afraid to do an earth tube in anything less than sch 40

I wish I knew that earlier. But the pipe is one piece and pitched well.

Now what? Is this a risk significant enough to remove it? I don't foresee what entering the pipe, but condensation? I read somewhere a filter was put on the end to prevent mold from entering.

I'd be careful about anything that could cause an underslab area to freeze.

If an earth tube is watertight and only used in cold weather, then I don't see any moisture problems. For warm weather, I agree that a water based system has advantages. Preheating/cooling might even be worth it for geothermal users that already have a ground loop - just connect the loop to the HRV.

If one has a supply of say 45F air, then one could eliminate all infiltration of colder ambient air. Just keep the house very slightly pressurized. Of course that can create other problems.

Update, we got 4" of rain last week and the house filled with water so did the earth tube. I knew right away that there had to be a hole(s) in the tube, below grade since both ends were up and out of the water. Upon close examination I found an area full of pin holes that look like they resulted from the manufacturing process.
I am looking at removing it. I don't know what I will put back. The utility room has no exterior walls and I don't want any air duct going through the living space to get to one, so I want to put a underground tube back. I would like to use Schedule 40 PVC but 8" will cost a fortune. How small could I go?

Brad;

if it is getting connected to and HRV/ERV then you can only go as small as the specs call for 6 - 8" (check)  But if it is just a fresh air intake 3-4" is big enough

If you go smaller than 8" your friction goes up very quickly. I too have looked at placing an earth tube and it seems like there is few options that don't put it at a $1000 project

I was not going to do a HRV, but I could for what this tube will cost. The 8" corrugated tube, 240' was $460, but it would not have to be that long.

And although I was not going to use an HRV I would like to be able to in the future.

I was planning on installing a fresh air intake pipe before I backfill around my basement. I can get ~100 linear feet of pipe in the ground at an average depth of ~5'. I was initially planning on running two parallel runs of 4" lightweight smooth PVC pipe, but am now considering multiple runs of 2" 80# rated polyethylene (PE) black plastic pipe since PE pipe has ~3x greater thermal conductivity than that of PVC. Larger diameter PE pipe was considered but eliminated due to the cost relative to the 2" pipe than can be procured at many agri supply stores.

http://www.engineeringtoolbox.com/physical-properties-thermoplastics-d_808.html

This would just be a fresh air makeup system to compensate for discharged air due to bathroom vent fans, clothes dryer, kitchen vent fan, etc. The intent is to temper the air somewhat prior to it entering the home. The intake (filtered) would be near grade level on the walkout side of the basement and then pass around two sides of the basement before passing through the basement wall into a utility room several feet higher than the intake so that any condensation that might form in warm months will drain back down to the inlet.

Has anyone actually found a supplier in the US for the Rehau system of earth tubes? On paper at least it addresses all the big issues (anti-microbial coating, water and radon tight, filtered air inlet, drains). If it is available and not grossly more expensive it would be logical to use them. However I really have not seen anything other than one magazine article a few years ago stating they are coming to the US. A PEX ground-loop system would be overkill in my small house design.

I dug out the 8" corrugated drain tile, which had holes in it. I am commited to getting fresh air from through the floor. So what should I put back?

How much do you want to spend?

Polyethylene (PE) pipe has much better heat transfer characteristics than PVC, but large PE pipe can get expensive. Aluminum pipe would be even better with respect to heat transfer characteristics. I have looked for used aluminum irrigation pipe locally, but have not found what I need at a reasonable price. You can find it anywhere from 3" up to 10" generally in 30' lengths with connectors and fittings as required.

If interested in the used aluminum irrigation pipe option, you might try searching www.craiglook.com near you and see what is available.