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Community and Q&A

Earth tube ducted through thermal mass concrete wall

Daniel McKinney | Posted in Green Building Techniques on

OK, here’s the basic idea. I would like to use an earthtube system to bring fresh air into a very tightly sealed home.

I’m also designing the home with a “solar stairwell”, a stairwell that’s exposed to the sun with big windows, with the back wall of the stairwell being made of dark-colored cast concrete.

During cold months, the concrete wall acts as thermal mass, gathering heat during the day and shedding it during the night. Exterior louvered shades above the big windows would keep this wall from getting direct sunlight during the summer.

So, the question is this – would it make sense to duct the earth tube air vertically through the concrete wall? The rationale is that the air moving through the solar-warmed concrete would help distribute that heat through the home.

The fresh air brought in during winter would first be temperature-moderated by the earth, and second, further moderated by the sun-warmed concrete wall before being distributed into the house.

Does this make sense?

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Daniel,
    You are entertaining two ideas from the 1970s -- a Trombe wall and earth tubes. Both ideas have been substantially discredited, but, like the walking dead, it seems that it takes more than a stake through the heart and a bunch of garlic to keep these ideas where they belong.

    Briefly, the added cost to build a Trombe wall or install an earth tube are so high that there is no way that any conceivable future energy savings will ever be enough to justify the investment. In the case of a Trombe wall, the details you describe may actually increase rather than decrease the annual energy load of the house.

    Earth tubes are expensive to do right -- you need a very large diameter duct, buried very deeply, in a very long trench -- and are subject to problems with condensation and mold. They don't save much energy.

    For more on earth tubes, see these articles:

    Belgian Passivhaus is Rendered Uninhabitable by Bad Indoor Air

    Using a Glycol Ground Loop to Condition Ventilation Air

    For more information on passive solar design, see:

    Reassessing Passive Solar Design Principles

  2. Daniel McKinney | | #2

    Thanks for the response!! Give me a little time to absorb this all, and formulate something sensible!!

  3. Brad Hardie | | #3

    Daniel,

    Malcolm Isaacs - depicts a different opinion on earth tubes. See the GBA guest blog from 2014. https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/my-earth-tube-story

    I've been interested in the technology too, especially after reading how efficient his system works. So much so, that I emailed him, and this was our discussion:

    Malcolm,
    My name is Brad Hardie, I'm currently building a Super Insulated/Zero Energy home in the US (NH/Zone 6a/8000HDD). I've considered earth tubes for some time, and was wondering if you additional feedback you can provide on your system since you last published info on Green Building Advisor? I'm going to be heating with Mitsubishi Mini-Splits and ventilating with a Zehnder HRV. I have been considering the Zehnder Comfofond as an add-on to the HRV, but have to admit the idea of using earth tubes has me so much more excited. Is there anything you would change, add, or omit if you could do it all over again? Some other info: I've got a fairly level site, with well draining sandy soil, and I will be doing the excavation myself.

    Here was his response:
    Brad,
    Well firstly I hope you’re aiming to build a Passive House, or close? In my experience that’s the only way to get anywhere near Net Zero at an affordable price. A couple of colleagues have built much more high-end earth tubes than mine recently, with “proper" components, but I feel that if you’re vigilant and careful then you don’t need custom products to do this – the ET approach is remarkably resilient. I did everything “wrong” but it still works very well, so I might use a better quality PE pipe, but otherwise not much would change next time.
    Good luck!
    Malcolm Isaacs
    Director, CanPHI

    Not sure if that helps, but obviously here is a guy who is actually operating one, without issue.

  4. User avatar
    Stephen Sheehy | | #4

    Brad: why consider an earth tube when you plan to install mechanical ventilation? I guess what scares me most is that the tube is pretty much impossible to clean, so over time the " fresh" air is likely to get less fresh.

  5. Brad Hardie | | #5

    Stephen,
    I've considered it, only based on stories like Malcolm's.....I live in a very-cold area (8000HDD) and it really improves the efficiency of the HRV. I admit I'm apprehensive, but if others are having success, then there must be a way to make it work (within reason). I've got the ability to do the excavation myself, and the material is fairly inexpensive, compared to say a Comfofond unit for a Zehnder HRV (which I'm using), so I've honestly considered it (along with putting some data loggers in the pipe to research it a bit too)!

    It is tough because you have so many varied opinions, from extremely intelligent folks who have both academic and occupational rigor and experience under their belts who vouch for so many different strategies. This one just seems so low-tech, that if it could be tweaked would be very beneficial to a bunch of folks.

  6. Joe Suhrada | | #6

    I know of a guy who apparently did this kind of thing and used some flexible black pipe that they use for drainage around the footings. I heard he found out later that the stuff is made from recycled detergent bottles and it gave off an odor of clothes detergent. Better than chicken droppings, for sure. But not good.

  7. User avatar GBA Editor
    Martin Holladay | | #7

    Brad,
    Thanks for providing the link (in Comment #3) to Malcolm Isaacs' blog on GBA (My Earth Tube Story).

    As you might have guessed, I'm not convinced that Malcolm Isaacs' example is a good one for green builders to emulate. His article notes, for instance, "My 2004 visit to the Passivhaus Institut predated all these debates about earth tube viability; I returned to Canada with all the enthusiasm of the newly-converted, determined to build myself a passive house — and right away. My understanding was that I needed an earth tube, so that’s what I did."

    He also freely admits several errors (including his decision to use PVC drain pipe for supply air ductwork, in spite of the fact that many green builders worry about PVC off-gassing).

    Moreover, he failed to give a complete financial analysis -- once that balances costs with energy savings. (And by the way, the fact that Isaacs used inexpensive PVC pipe instead of a more appropriate type of ductwork would have skewed his financial spreadsheet in any case.)

    One clue that Isaacs may be unfamiliar with financial payback calculations is his statement that buried glycol loops for preheating ventilation air "have a reasonable cost." In fact, as my article (Using a Glycol Ground Loop to Condition Ventilation Air) showed, these systems have a very high cost compared to the energy benefits they provide.

    Reputable academic researchers have come to different conclusions that those reached by Isaacs. For example, see the CMHC study (Earth Tube Ventilation Systems — Applicability in the Canadian Climate) discussed in the comments section below Isaacs' blog. The CMHC researchers concluded, "This study has shown, through a literature search and interviews with researchers, owners and operators, that EAHXs [earth-to-air heat exchangers, or earth tubes] may have benefits when used under the right conditions and in the right climate, but also that they are very subtle systems which require careful design and operation to be successful. The literature shows that an improperly designed system will not work as expected, or result in poor air quality, etc. leading to disenchantment with the system and in many cases decommissioning: it is often very difficult to fix EAHXs once the trenches are back-filled.

    "The literature also shows that controls, air quality, and thermal memory of the ground are but three of the areas to pay close attention to when considering an EAHX. It also demonstrates that an EAHX can be redundant when used in conjunction with heat recovery ventilators (HRV), and that the economics are rarely favourable."

  8. Daniel McKinney | | #8

    I think the general principle is sound, that fresh air whose temperature is moderated by the earth can be preferable to whatever the outdoor air's ambient temperature is during more extreme seasons. For example, air at 40 degrees F is preferable to air at -10 F!

    Obviously, the system must be designed well, which can be a bit tough, it seems, since there seems to be so little hard data to make such design possible. But I've been using this calculator - http://nesa1.uni-siegen.de/index.htm?/softlab/gaea_e.htm - as a start.

    I don't think that the requirement that a system be designed well should disqualify the idea out of hand. A poorly designed and constructed roof can spell disaster for a new home, but does that mean that the idea of a roof is a bad one?

    Excavation cost, of course, is a big factor, but I am going to install the system in new construction, and hope to be able to combine some of the excavation duties. For instance, use the trench for the utilities or well line for the earth tube, too. Dig deep for the buried duct, backfill partially, and then lay utilities or well line above and to one side, at the appropriate distance from the earth tube and at appropriate depth.

    Another factor that might be able to help shorten the suggested 100-150' length of the duct would be to use a more thermally conductive material than PVC pipe. I've been considering PCD duct - http://www.smcduct.com/pcd-polyvinyl-coated-ductwork - which is 4 mill PVC-coated galvanized steel. It's not intended to be waterproof, but if buried above the water table, it could work, and might provide much greater thermal conductivity than the PVC pipe usually used.

    Obviously, the pipe must be pitched at an angle that will allow condensation to flow and not puddle, and that condensate must be able to drain at one end or the other. I've seen designs where the tube pitches down toward the building and the condensate drain is in the basement. This seems like a good idea, allowing for that line to be cleaned, and allowing access directly to the earth tube, as long as the desired depth can be achieved and still have the end of the tube accessible inside the basement.

    What about the idea of using simple UV lights to keep mold, bacteria, fungus, etc. to a minimum inside the tube? If the pipe is pitched correctly and drains well, I don't think mold and other biological contaminants would be to big of an issue, but UV lights at either end of the tube could be a helpful prophylactic. A light near the intake end could help prevent contaminants from entering and propagating inside, and the light at the basement end of the tube would help prevent whatever did make it past the first UV light from entering the home.

    And UV lights installed at either end of the tube would be accessible, and easy enough to change.

    Anyhow, those are my thoughts on the subject for now.

    1) Keep excavation costs down by sharing digging duties
    2) Use a more thermally conductive material to keep the run shorter
    3) Design and build it well so condensate doesn't collect
    4) Use UV lights as a safety precaution against bio contaminants

    And I am quite fond of more than a few ideas that were born in the '70s. Porn 'staches notwithstanding, that decade did generate some useful stuff.

  9. User avatar
    Brian Knight | | #9

    Hey Daniel, I'm not sure you've addressed the biggest problem with ET that Stephen mentions. Humidity of incoming air will condense on the inside surface of the pipe and will collect dust, pollen and likely become a petri dish over time. Seriously doubt a UV light, with it's upfront, energy and maintenance concerns will be enough to purify the air coming through the eventual MT (mold tubes). Might want to also plan on a robust cleaning system with a strong wire and rope connected to a cleaning plug or pig because condensate drainage and UV probably won't be enough.

  10. Charlie Sullivan | | #10

    The thermal conductivity of the duct itself is not the limited factor in heat transfer into the air. It's the thermal conductivity of the dirt around it, and that heat transfer between the air and the tube. And in other respects, the PVC/galvanized steel sounds like the worst possible combination to me: the steel will eventually rust out, and in the meantime, the PVC will outgas into your "fresh" air. I would want a smooth-walled seamless polyethylene tube. (Polyethylene is hard to glue, and so regular HDPE drain pipe would not be ideal--the joints could leak soil gas into the system.)

    If you plan to have it drain into the basement, have a way to clean it, and have a filter on the input to keep it reasonably clean, I think you've addressed most of the problems. And although some people say it is a waste in combination with an HRV, I think it's good--it avoids the need for defrosting on very cold days, and it provides dehumidification on most humid summer days.

    It's probably still not a sound recommendation for mass adoption, but might work for you.

    But if you think about it much, you might conclude that it's cheaper to use smaller diameter pipe, buried in a more haphazard layout, with a glycol mixture in it rather than air. Then you spend less money on pipe and take advantage of the better heat transfer with the liquid, which you then connect to a liquid-to-air heat exchanger. That's the Zehnder Comfo-Whatever system, which Martin linked to in the first answer. It's pretty clear that that's not cost effective, but if you are wanting to do a DIY system and you aren't too concerned about cost effectiveness, you could probably DIY one of those for less than the Zehnder system.

  11. User avatar GBA Editor
    Martin Holladay | | #11

    Charlie,
    Neither approach -- neither the glycol loop approach nor the earth tube approach -- is cost-effective. They both cost more to install than can ever be justified by future energy savings.

    But at least the glycol loop approach has a lower risk of introducing bad air into your house.

  12. User avatar
    Stephen Sheehy | | #12

    Adding to the cost would be some sort of device to assess air quality, if such a device even exists to measure mold spores or other nasty stuff.

  13. Daniel McKinney | | #13

    The PCD duct I mention is specifically designed to work as underground air duct, and apparently has been used successfully as such for years, so I don't know if it would decay the way you say, Charlie.

    What about copper? Setting aside cost considerations for the moment. Would the antimicrobial action of copper be enough to keep the nasty stuff at bay?

  14. User avatar
    Brian Knight | | #14

    Aside from the questionable use of a precious resource, I doubt it. I suspect the innermost buildup on the inside of the pipe would overcome the influence of the copper surface. Better to regularly scrub/clean the entire inner pipe surface. I admire your determination though! Maybe worth an experiment if you find used pipe, but for the substantial scrap value, there are probably better indoor air or energy saving investments.

  15. Daniel McKinney | | #15

    I had been thinking of semi-rigid copper air duct. Of course, the drawback is that it's corrugated - and not waterproof! And in my radon-heavy neighborhood, I don't want any gas exchange between the earth and the air in the pipe. So perhaps HDPE with an antimicrobial treatment is ideal after all.

  16. Brad Hardie | | #16

    Martin,

    Yes PVC pipe....no good. Would definitely be interested to see some financials on it too - using material/products that we should actually be using.

    So the only safe ground source option seems to be glycol filled piping, - which I know you aren't a fan of because they aren't financially prudent. I'm wondering though, in your article on using glycol ground loops in April last year https://www.greenbuildingadvisor.com/articles/dept/musings/using-glycol-ground-loop-condition-ventilation-air - Peter Schneider from Vermont Energy Investment Corp, discusses two houses that he compared (one used an electrical defroster for the HRV and the other used a glycol ground loop).....what specifically stuck me about the article is that he mentions its not necessarily "just" about the financial return. He states, " “At the end of the day, if you install a ground loop, you're not doing it for the BTUs saved. It’s for the increased comfort — to raise the delivery temperature of the ventilation air delivered to remote spaces. With the ComfoFond, that air will be within 2 degrees of your setpoint. With Zehnder's electric preheater, the air will be cooler.” ."

    For me this is the driving factor for wanting to use a ground loop (air or water) to precondition the HRV.

    Do you have studies you know about, that researched this?

  17. User avatar GBA Editor
    Martin Holladay | | #17

    Brad,
    Increased comfort? Maybe. But I'm not convinced.

    If you build a superinsulated house with triple-glazed windows and very low levels of air leakage, and you install a Zehnder HRV with a built-in electric-resistance heater (because the electric-resistance heater is more cost-effective than a glycol ground loop) -- and discover that you are uncomfortable, you are a more delicate flower than me. I can't imagine how many people are so frail and delicate that they would be uncomfortable in such a house.

  18. User avatar
    Stephen Sheehy | | #18

    Brad- I just lived through a mild, for Maine at least, winter. I never notice the HRV and certainly never experienced any cold air coming from the supply vent, even on the rare below zero F nights. I think placement of the supply vents may be an important factor. Obviously, you don't want air blowing on your head while you sleep or eat dinner, but that is true even for relatively warm air. Unless you live at the North Pole are you implementing a solution for a non-existent problem?

    Daniel or Brad: Getting back to the earth tube, how would that work? Would you directly connect the HRV intake to the pipe? What diameter and length pipe would be sufficient to let in enough air for ventilation and at the same time allow the air from outside to stay in the pipe long enough to warm the air? You'd obviously need to screen the pipe to keep out critters.

    And I still don't understand how you would clean a long, underground pipe. Does antimicrobial coating last forever?

  19. Brad Hardie | | #19

    Martin,

    Did you call me fragile - no wait it was a "delicate flower"?!!!! Haha that is one of your most fantastic posts I've ever read!

    You know I can't imagine it either (folks being uncomfortable in such a house), delicate flower.....maybe! I do agree with Stephen about supply vent placement though. I've got plenty of PV to supply the increased KWH demand (which still isn't a lot). Can you believe that growing up, I asked "why" a lot and challenged conventional thinking????? Don't answer that!

  20. Daniel McKinney | | #20

    Stephen,

    I've been using this calculator to determine the particulars for the pipe.

    http://nesa1.uni-siegen.de/index.htm?/softlab/gaea_e.htm

    It takes into account the length of the run, the diameter and number of pipes, the desired airflow, the temperature profile of the earth at your geographic location, the soil type (makes a big difference for thermal conductivity), the air intake temperature based on your location, the distance from the foundation, the depth of pipe, and more. The calculator itself is based on this paper...

    http://www.ibpsa.org/proceedings/bs1997/bs97_p008.pdf

    As far as the microbe/mold issue, there are people in the US who have buried corrugated pipe with a slit cut down the bottom middle to allow for continuous drainage along the length of the pipe so water never has a chance to sit in the thing. But that would allow radon infiltration, which is a big problem here. (Or so the radon mitigation industry has led us to believe!) And it presents the problem of water infiltration, too, if the water table rises.

    So, it seems to me that a completely sealable HDPE pipe length would be best. And one that inclines toward the basement where there'd be an accessible drain line inside, and not a drain into the ground, where, again, there's the issue of gas and/or water from the earth getting into the system. I feel best keeping the thing completely shut off from the earth!

    There are those who say that an inclined, smooth-walled HDPE pipe with constant airflow and no area for moisture to collect and stagnate does not present a good environment for mold, etc. to grow.

    And there are those who say it does! Not sure if we have much real proof one way or another - at least, I don't have the proof in hand. The naysayers seem to be saying, "Yuck! dark + damp = mold" The promoters say it's not the proper environment for such growth, backed by the notion that HDPE is inherently resistant to fungal & bacterial growth.

    So it's good to ask, what does mold need to grow, and does an HDPE earth tube present the right conditions for such growth?

    Mold needs...

    !) moisture - well, yes, we've got that, at least part of the year. But we've got moving moisture, not stagnating moisture.
    2) stagnant air - no
    3) food - no, at least not supplied by the pipe itself
    4) favorable temperature (best between 77 & 86 degrees F) - depends on where in the tube the air is! And what season, too.

    So, I'm a little unclear on what favorable conditions we DO have. Does drippy, flowing condensate provide a comfy home for mold? If so, then mold likes point #1. Mold does not like point #2 or #3, and let's say we DO have a favorable temperature for #4.

    It looks like #3 is the biggy, with the jury out on whether we really are providing the right kind of moisture for mold in #1.

    HDPE is not penetrable by water, and so by itself presents a hostile environment for mold to grow. Unlike paper or fabric or drywall, there's nothing for the mold to feed on. I imagine mold could eventually find a source of food in dust and organic particles that collect over time in the tube, but the HDPE itself doesn't give a mold a foothold on which to thrive.

    So, mold could be a problem if outside material is allowed to settle and eventually cake onto the surface of the pipe. But I wonder, if in a humid climate, or at least a climate where there's high humidity during the warm months, if the action of condensation forming, collecting into drops and eventually flowing to the drain end would have any cleaning action. i.e. carrying dust & pollen with it as it flows to the drain?

    Or would it make it worse by creating a "dust mud" that would cake and collect on the HDPE surface, and eventually provide a comfy bed and food for the mold?

    So, the idea is to deprive the mold the possibility of growing in the tube by draining whatever condensate does form, and maybe by killing whatever mold spores we can with a UV light near the intake, and by depriving whatever spores did get into the pipe of food by filtering dust/food/growing surface material at the intake.

    One other point I want to make is to counter the "yuck" factor, that distasteful idea that we're drawing in air through a damp pipe in the summer. The air we're drawing in will actually be drier than if we pulled in air directly from outside since the tube has a dehumidifying effect on the air. Which makes it less yucky, not more.

    I appreciate those who counter my thoughts!! Preaching to the choir never did much good when it came to solving problems, so I do want to be told I'm an idiot for even considering such a project.

    Critics are always more valuable than cheerleaders.

  21. Brad Hardie | | #21

    Stephen,

    There is a very excellent chance that considering a ground tube is (insert negative adjective). I never knew how clean it either. I never thought the commercial antimicrobial coatings would really work. My understanding is that the ground tube gets connected directly to the air intake on the HRV. I researched the commercial options, and one product has a charcoal filter/screen on the end of a stainless pipe. The price was extremely excessive to say the least.....

  22. User avatar GBA Editor
    Martin Holladay | | #22

    Daniel,
    It's clear that you want to install an earth tube. Here's my advice: go ahead and install an earth tube.

    Keep track of how much it costs to install the earth tube (including an estimate of excavation costs, backfilling costs, and landscaping costs).

    Install some monitoring equipment for temperature and RH. You want to measure the temperature and RH of the air right before it enters the HRV. Ideally, you also want to log outdoor temperature and outdoor RH.

    After you live in your house for two years, write a blog for GBA about the experience.

    And remember -- if you have mold problems, you can always cut off the earth tube in your basement with a hacksaw and cap it. Then you can install an air intake for your HRV somewhere else.

  23. User avatar
    Stephen Sheehy | | #23

    Daniel- any ballpark sense of pipe length and diameter? My HRV intake looks like it is about 6" inside diameter, so I assume you'd need something at least that large if hooking up to an HRV, but if you just use it to precondition ventilation air without the HRV, maybe smaller would work. You'd need to consider how much the bug/snake/skunk screen would hinder air flow.

  24. Daniel McKinney | | #24

    Martin - If I go ahead with it, I will most definitely monitor it and keep track of how it works. And if it goes in at my proposed new construction, it will share some of the excavation costs with other necessary digging, i.e. well line, septic line, or utility trenching.

    But I am building a garage at my present house this spring, and while my excavator is here, I want him to dig for an earth tube for my present home. That'll be my test before I try it in new construction.

    And, as you say, if it turns out to be a disaster, cap the thing! Or use it as a very long pet door...? Pneumatic mail tube...?

    But if it works, I do reserve the right to say "told you so". As do you, of course, if it's a big stinking fail.

  25. Brad Hardie | | #25

    Daniel,

    I wouldn't install the UV light, just go with the carbon filter at the end. The UV light electrical needs seem to negate any benefit you'd get from the energy savings the tube provides.

    I've got to say the commercial options are really very simple in application and well thought out.

  26. Brad Hardie | | #26

    Daniel,

    I would think it would also be prudent to keep it several feet away from any water line, as it could potentially cause freezing of those pipes - just like a glycol ground loop can do, when placed too close to water lines.

    I can't wait to read the future post about your future success or failure!

  27. User avatar GBA Editor
    Martin Holladay | | #27

    Daniel,
    Feel free to tell me "I told you so" in two years.

    Here's my view: I acknowledge that there are earth tubes that work (and that there are happy earth tube owners). I also think that many earth tubes don't work -- some are disastrous -- and that almost all of them are too expensive to justify their installation costs (especially in light of the fact that they save only very small amounts of energy).

    One more point: the risk of mold and stinky air increases with the passage of time. The likelihood that homeowners will clean a buried air tube on a regular basis drops off steeply with the passage of time. So just because the owner of an earth tube is happy during Year 1 and Year 2, doesn't mean that he or she will be happy in Year 6 or Year 10.

  28. Daniel McKinney | | #28

    Two years. Got it.

    My attraction to the idea comes from the fact that it presents the tantalizing possibility of gathering energy for one's home quite literally from one's own backyard, just as PV is attractive because it gathers energy from the light that's already falling, and a wind turbine grabbing it from the breeze that's already blowing. The home is fed by the natural elements that surround it. Nice. Comfy.

    I like the idea of the home emulating how a tree works, getting what it needs from what's around it. The '70s are calling, but, whatever.

    That and the simplicity of the approach. Buried duct. Fan. The end. I can understand it, in a world where the vast majority of devices we use on a daily basis are completely beyond me.

    I remember my grandmother asking me how an ATM knows to give you YOUR money, and not someone else's. I had no answer as I quickly realized that I haven't a clue how it works. However, the earth tube I could have explained to Nana.

    Of course, there's nothing simple about excavating a 10' trench the length of 100-150', but if I can use excavation that's already happening, then that problem's licked, more or less.

  29. Jason Morosko | | #29

    Interesting conversations. I'll just add my two cents as someone referred me to the post. I am a CPHC, i gave a presentation at the 7th annual PHIUS conference on earth air tubes.. looking at three installs (one is mine).. cost and benefit. I am also an ERV manufacturer, as well as able to provide the glycol loop equipment (UltimateAir). Here's a link to my meager assessment back then… http://www.phius.org/NAPHC2012/Morosko_EarthAirTubes.pdf . I have been living with my tubes running continuous for 4 years now. I used SDR35 pipe.. cheap form of PVC yes- Does anyone have some science about the off-gassing of this product? I have not come across any. I regularly check CO2, formaldehyde, and radon levels in my passive house duplex. All remain at acceptable levels. From my experience- you may gain 500 – 3500 BTU/H worth of ‘free energy’ using the tubes. Lots of factors there.. but that is just measuring mine. Make note- some of that ‘energy’ is wasted. Depends on the season, ground temp, depth, EAT length.. outside temp… all that. I have less than $1200 in my earth air tubes.. two pipes, 8” diameter, 100 foot each, SDR35 pipe. I think I paid $54 per 14’ joint of gasketed pipe. I made mine so they drain water, and are able to be cleaned. I have never cleaned them. Are they worth it? Well.. in my climate, my ERV would require preheat to ventilate at cold outside conditions (times below 12 F). Hence- I would have need of some type of duct heater to keep incoming air warm during cold snaps. Hence- the duct heater is generally an electric resistive device- meaning large instant amp draw- short pulses. Not a lot of energy- but if you are looking at off grid / solar, you do not want spikes of energy use….bad for batteries/capacity and it happens at the worse condition (climate timing speaking) So that is something to consider. Given my cost, and experience of four years thus far- yes it was worth it. Financially. maybe break even at year 4 ?

  30. User avatar
    Paul Kuenn | | #30

    Daniel, you may want to contact the Aldo Leopold foundation in Portage WI.
    http://www.aldoleopold.org/Visit/leopoldcenter.shtml
    They've had their massive earth tube (3' in diameter) working for many years now at the teaching center. However, they did install a very large and expensive ultra violet filter at the inboard side where it enters the utility room. Keep in mind some very wealthy donors and many not so much (like us) kept their cost down. I think they would have done better with better windows and more insulation in the long run. PK

  31. Daniel McKinney | | #31

    Thanks paul. Speaking of balancing cost with green approaches, I spoke with someone yesterday who spent $80K on a geothermal system, who then bragged about how low their air conditioning costs were in the summer!

  32. KEVIN ZORSKI | | #32

    Daniel - Thank you for this interesting post. The idea of these tubes seems so logical and pretty simple, until you hear about the potential problems. As I'm reading through these comments, I did have the thought, " What's the point?" A new, well constructed, efficient home will spend far more on heating domestic hot water than it ever will heating the home ( assuming the house is reasonably sized). If this is true, and it seems to be so, it seems like it would be more worthwhile to figure out how to save on hot water. In other words, why reinvent the wheel ? If earth tubes made sense, I think more people would have tried them at this point. If it's not CLEARLY worthwhile, and if it has possible negative consequences, move on to some other aspect of your project to save energy. My 2 cents. Best of luck to you on your project!

  33. Malcolm Taylor | | #33

    Kevin,
    I don't want to disparage the idea. as I really don't know if they can be tweaked to work well, but I suspect a lot of the recent enthusiasm for earth tubes came from them being adopted as part of architects search for a green sales pitch to tack onto their creations. Architects are suckers for metaphors, or ideas that translate well into being sketched on napkins during business lunches with clients. Earth tubes suit both enthusiasms. Touted as coming from a close observation of how some creatures deal with cooling, and, unlike complex insulation strategies, they are easy to explain. I don't think it is a coincidence that they have caught the attention of tech publications like Wired, where once something is possible it is promoted as desirable using the most dubious justifications
    http://www.wired.com/2015/11/building-skyscrapers-like-termite-mounds-could-save-energy/

  34. Brad Hardie | | #34

    Daniel,

    Here is a link I found about earth ground loops.....http://www.ventilation-system.com/cat/geo/
    These guys sell a nice thru-the-wall ERV like the Lunos too.

  35. Daniel McKinney | | #35

    Brad,

    For a system that meets with such doubt and trepidation here in the US, it seems to have been embraced wholeheartedly in Europe. I'd like to hear more from the Europeans' side of the story. Is it an idea on the wane, a product of outdated thinking as Martin suggests, or is it still considered good practice?

    Interestingly, they do sell products in the US, just not their earth tube stuff!

    (The system represented by this company shows a condensate drain somewhere in the middle of the tube, accessible by a manhole. But I do like the idea of the drain in the basement.)

  36. User avatar GBA Editor
    Martin Holladay | | #36

    Daniel,
    Q. "I'd like to hear more from the Europeans' side of the story. Is it an idea on the wane, a product of outdated thinking as Martin suggests, or is it still considered good practice?"

    A. I asked Dr. Wolfgang Feist, the founder of the Passivhaus Insititut in Germany, about earth tubes when I interviewed him in December 2007. Here's a transcript:

    Martin Holladay: "In North America, many energy-efficient builders associate earth tubes with condensation and mold. Have earth tubes in Europe experienced these problems?"

    Wolfgang Feist: "There were problems in northern Europe, especially in Scandinavia. In Central Europe we haven’t had any hygienic problems so far. Actually, I’m not sure why we don’t have these problems in Central Europe. But I don’t advertise these systems any more, mainly because they are too expensive. If you have a good heat-recovery ventilator, you don’t need it."

    The entire interview (available online) was published in the January 2008 issue of Energy Design Update.

  37. Daniel McKinney | | #37

    https://www.youtube.com/watch?v=7eI6pxFKW-s

    http://www.greenenergyfutures.ca/blog/save-money-pipe-ground-story-earth-tube

    Two links on Green Energy Future's story on earth tubes and the (apparently) successful installation in a 29-story office tower in Edmonton.

  38. User avatar GBA Editor
    Martin Holladay | | #38

    Daniel,
    The Epcor Towers video mentions that the air picks up heat from glycol embedded in a concrete wall -- perhaps from the HVAC system. Moreover, it looks to me like the air in these tubes is being heated by heat pulled from the concrete floor of the parking garage (thereby lowering the temperature of the parking garage slightly). That makes these earth tubes somewhat different from typical earth tubes.

  39. Daniel McKinney | | #39

    Right - so instead of drawing air directly into the building from the tubes, the glycol-embedded concrete wall acts as the heat exchanger? And the air is looped back into the tubes? Or is exhausted into the city? Either way, the air that passes through the tubes is never used directly used as breathing air, it seems.

    Why, I wonder, go this route instead of burying the glycol pipes directly into the ground? Why use air flow to effect heat transfer from ground to glycol?

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