I just talked to a guy selling 6" aluminum irrigation pipe for $1.50 a lf, but he said it seals with the water pressure inside the pipe, so it may not be water tight.

Does ABC pipe conduct thermal well.

I would think that you could seal those aluminum irrigation pipe joints with a tube of RTV silicon as you slip them together and not have to worry about any leaks.

By ABC did you mean ABS? If so, ABS thermal conductivity is just slightly better than PVC, but not much.

From the link I posted previously, Thermal Conductivity of Thermoplastics:

PVC = 1.1
ABS = 1.35
PE = 3.2

Aluminum thermal conductivity is orders of magnitude higher than those.

Ya, sorry, ABS. Would condensation be an issue with the aluminum?

What is the cost of the PE?

I think I will go with 6" sewer PVC, I found it for $1.30 lf. I will put in two in case I put in an HRV. I will pitch it so any water will run out.

Is 6" big enough?

The normal thin skin sewer PVC pipe is easily crushed.  Be careful installing it.  Some backhoe operators will run the tires in the trench to pack the earth but this can crush the pipe if there is not much dirt on top of the pipe.  Thicker pipe or schedule 40 is safer but will cost more.  I am assuming that the sewer pipe you mentioned is truly sewer pipe that is non-pressurized.

Is 6" big enough?

I've looked at this a few different times and 6" is workable. It's right on the small end of the range, though.

Any kind of thermoplastic is probably fine.

Other than the price, SDR-35 gasketed sewer seems pretty ideal.

Posted By ICFconstruction on 04 Sep 2010 08:11 AM
How well would an earth tube work for a air intake for make-up air or HRV?

We measured less than 1 degree difference between the return air and extract air from a number of FiWi HRV units this winter, this means its not necessary to use earth tubes to pre-heat ventilation air. Fine Wire heat exchangers are the most efficient in the world!

The sewer line I am getting is thicker wall, almost as thick as schedule 40. I am committed to going under-ground, as my walls and roof are on, my utility room is in the middle of the house. My parents have an earth tube and my dad stuck a thermometer in the intake and had, as I recall, a twenty degree difference.

I agree with you that its possible to get a twenty degree lift using earth tubes but if the heat exchanger in your HRV unit is efficient enough you won't need earth tubes. It was 4 degrees F outside and 68 degrees inside the house I tested, the fresh air coming in through the FiWi HRV heat exchanger was 66 degrees F.

I suppose it would depend on the temperature differential.

Posted By Viking House on 31 Jan 2011 06:38 AM

Posted By ICFconstruction on 04 Sep 2010 08:11 AM
How well would an earth tube work for a air intake for make-up air or HRV?

We measured less than 1 degree difference between the return air and extract air from a number of FiWi HRV units this winter, this means its not necessary to use earth tubes to pre-heat ventilation air. Fine Wire heat exchangers are the most efficient in the world!

Viking - It was minus 35 F this morning. Are you suggesting that an HRV (with no power or coil) will raise this to 67ºF? Seems to defy physics!

Yes that's correct, it was invented by a Dutch professor.

My preference for earth tube is spiral duct wrapped in plastic embedded in concrete. A couple of other thoughts. The slower the air is moving, the more heat it can pickup/give off. If you can introduce turbulence it will be even more effective. I myself would not us plastic pipe as I feel it is too smooth and does not transfer heat as well as aluminum or steel. But that's me. I'm sure some math types will differ ;-) My system is 250 cfm exhaust fan coupled to 3 6" parallel spiral tubes with a fan coil pulling air from 3 tube over the 3 exhaust tubes. Its not in full use yet but I'm happy with the results so far. An HRV would definitely be cheaper but at the price we pay for electricity I'm will to go for the long run.

My concern is to have the intake water-proof and smooth. Smooth so any condensation runs away from the house. I am doing the earth tube, as much to not have the intake and exhaust on the side of the house.

Posted By FBBP on 01 Feb 2011 10:36 PM
My preference for earth tube is spiral duct wrapped in plastic embedded in concrete. 

I would think a smooth pipe would be preferable. As someone else noted it would be able to drain. It also will allow it to be “swabbed” after construction and at regular intervals (once every few years?) to remove construction dirt, dust and any mildew  that may be trying to grow. Not to mention allowing you to clean it if an animal was able to get in there. I still have hopes that the Rehau earth-tube system will become available in my area before I start construction. It has an antimicrobial silver-treated lining and a filter tower at the intake.

Posted By Bigrig on 02 Feb 2011 11:33 AM

Posted By FBBP on 01 Feb 2011 10:36 PM
My preference for earth tube is spiral duct wrapped in plastic embedded in concrete. 

I would think a smooth pipe would be preferable. As someone else noted it would be able to drain. It also will allow it to be “swabbed” after construction and at regular intervals (once every few years?) to remove construction dirt, dust and any mildew  that may be trying to grow. Not to mention allowing you to clean it if an animal was able to get in there. I still have hopes that the Rehau earth-tube system will become available in my area before I start construction. It has an antimicrobial silver-treated lining and a filter tower at the intake.

Smooth pipe will just let the air slide by it, which means the same air is in contact with the pipe the whole way. If you can create turbulance you will be mixing the air that comes in contact with the pipe therefore all the hot/cold air has a chance to absorb/release its heat value. I believe it is called the K value but I'm sure some of the HVAC guys on the forum can explain this better. If you have ever looked at the twisted flat iron in the center flue of a gas hot water heat you get the picture. There is indeed value to be able to clean any duct work. No, animals should not be able to get in. Screen it!!

Hey,

I have used earth tubes in many homes. They work great if you understand how to install them. They replace the ERV. You should have inlet and exhaust tubes next to each other. 4" tubes are cleanable, 8" is difficult to clean. 4s are usually cheaper, but more tubes. Smaller tubes also give better exchange. Drainage has to be designed into the system. The number of tubes depends on air exchange requirements. 50 feet of drop and you can use natural convection to drive the system.

Brian

Hi I was doing a little research about earth tubes and I found this website http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm#ActiveVent. I think this would provide information to all readers of this forum.

I ended up putting in two 6" sewer pipes, glued together pitched the about 100' underground each. A 6" duct fan fits nice on the tubes. The other day was hot out, I took an infrared temp gun. Air temp was 84 the intake outside, because they are in the sun, 90; and the air inside as it leaves the tube 66 degrees. I suppose as the ground warms it will a smaller temp differential. I will keep checking

I doubt I will put in an HRV, the house leaks plenty with the overhead doors and sliding door.

http://www.greenbuildingadvisor.com...indoor-air



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As it turned out, the earth tubes installed at the Belgian house were a big mistake. Hens wrote, “The search for causes [of the IAQ problems] started with a camera inspection of the overall ventilation system. … [The camera] revealed the presence of stagnant water and construction dust in the supply ducts." According to Hens, the source of the water was rainwater intrusion.

Hens continued, "In 2006, the contractor renewed [repaired] the ground pipe, however without success. Again, it collected water. A second renewal in 2007 brought some upgrade; however, still, the ground pipe did not remain dry. In fact, in summer, relative humidity in the pipe passed 80% during prolonged periods of time, creating favorable conditions for mold to germinate on the pipe walls.”

IAQ testing “revealed the presence of spores of penicilium, aspergillus fumigatus, aspergillus versicolor and aspergillus niger.” Hens noted, “High relative humidity in the supply air leaving the ground pipe also caused humidification of the filter at the supply side of the heat recovery unit, turning it into a preferred medium for mold to germinate and sporulate. That most probably explained the presence of aspergillus spores in the indoor air.”

Hens concluded, “Ground pipes are potentially a risky technology. Though solely promoted as energy savers, their impact on energy consumed is too minimal [for] the possible risk they create in terms of degrading supply air quality.”

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Scrolling down to the take-away on this failed high-performance house:



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• If earth tube ventilation systems are well designed, properly installed, and regularly inspected, they can perform well. However, earth tubes are expensive to install, provide limited energy savings, and incur a significant risk of developing moisture and mold problems
• Most walls with vapor-permeable exterior sheathing and interior OSB perform well. However, it’s probably not a good idea to specify OSB with formaldehyde on the interior side of your walls.
• Vapor-permeable exterior sheathing does nothing to slow inward solar vapor drive. If you plan to install a “reservoir” cladding like brick veneer, it’s safer to use rigid foam sheathing than a vapor-permeable sheathing like fiberboard.
• Homes with high-R walls and low air-leakage rates are vulnerable to a variety of problems if details aren’t well thought out or if contractors are sloppy.

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Bottom line, keep an eye on it. A leaky house is no guarantee of good indoor air quality either.