Earth Tubes: Earth Air Tube Health After Two Years and Two Massive Rain Storms
|Inspection of Earth Tube Interior Coupling|
Certainly as ERVs become even more efficient at transferring temperature and moisture from one air space to another the incremental benefits of utilizing an earth air tube system may continue to be marginalized in passive house construction.
Despite these apparent negatives and the fact that earth air tubes are generally misunderstood, the notion of getting cooled and dehumidified air (during the summer) and heated air (during the winter) for "free" without any mechanical system, remains extremely appealing to me. While passive houses are certainly very high tech in design and material composition, they are actually very low tech in principle.
To my way of thinking, eliminating mechanization in our living space harkens back to the simple living conditions created by the Cliff Dwellers or the Inuit. These historically advanced cultures understood how to create comfortable living conditions year-round simply by working with nature and without requiring electricity. I suspect had it not been for Carrier, our collective building technology today would be further along than it is.
I had considered several earth tube designs but ultimately went with a design created by Larry Larson of Earth Air Tubes. Larry and his brother's design broke all of the conventional rules. Their system utilized corrugated instead of smooth wall tubing; serpentine configuration instead of straight, level instead of pitched placement. Everyone one of their design ideas sounded quite proper to me, however.
By using corrugated tubing, the tube surface to air contact ratio was far greater than would otherwise be with a smooth walled tube allowing for much more efficient heat transfer between the incoming air and the ground.
Bending the tubes during installation encouraged internal turbulence which again would increase the total air to surface contact area resulting in superior heat transfer efficiency. With smooth wall tubing the outside circumference of the air flow would tend to experience the heat exchange, while the interior spaces of the air flow cavity would tend to be neglected. Creating interior turbulence maximizes the contact area of all of the air flow through the tubes.
Since the tubes were slit along the bottom, they didn't have to be pitched to allow for drainage of the condensate away towards the inlet end of the tube. The drainage occurs immediately below the area of condensation into a drain field consisting of small stone and filter cloth.
When asked about their long-term reliability, I was told that he has had great success with his installations and that his earth tubes are self-maintaining and self-cleaning by their very nature.
With those assurances, I made the leap of faith and went ahead with their installation. Larry was kind enough to fly out to our house from Iowa to oversee their construction and installation. They were installed two years ago. To my knowledge, our project remains the first (and only) passive house that has incorporated Larry's earth tube design.
Initially things were terrific. During hot and humid days, the temperature and humidity drops of our intake air were exceptional. I have read a number of articles suggesting that earth tubes don't work well in hot humid climates. Are you kidding me? They are exceptionally well suited to these conditions!
But soon after their installation, the unthinkable happened. Twice.
Before the site was graded properly, we got hit with two back-to-back massive rain storms over the course of about two weeks. Unfortunately since we didn't have our grading completed, the storm water wasn't able to drain from our foundation area sufficiently. And while we have long since established a proper gravity fed drainage system away from our foundation, my fear was that the damage to the earth tube system had already occurred--that they had been flooded with muddy water from underneath.
Shortly after, I believe I was, at times, monitoring elevated levels of relative humidity coming into our ERVs from the earth tubes, instead of lower levels. I was afraid that the drainage slits created to allow for immediate drainage of condensation had clogged with dried mud preventing draining and instead creating a condition of standing water in the tubes--definitely not a good thing to be sure.
I wasn't about to the throw in the towel just yet, though. So I continued using them through the following winter season and into the next summer. It was during this following summer that I believe the levels of humidity removal were improving over time. As the tubes dehumidified the air, they were rinsing/cleaning themselves out as Larry had suggested they would.
Fast forward now to this coming summer season, I have been anxious to know what the current actual condition of the tubes are--two seasons after the earth tubes were flooded. To find out, I contacted a sewer and drain cleaning service company to come out to scope the tubes with a video camera. If problems were found they would be able to jet wash the interior of the tubes and vacuum any material away and return them to optimal condition.
|Interior View of Earth Air Tube Draining Slits (Lower Right)|
I believe these experiences are a testament to the superior design principles of this earth tube system.
I will continue to post my experiences with these earth air tubes going forward.
P.S.: While it does appear that these tube fared well with water infiltration, any day we are about to experience yet another event that could create another problem for us--Brood II. The 17 year cycle of cicada mating. Anyone who uses mechanical ventilation would be well advised to make sure both their intake and exhaust ports are screened and/or filtered.