RE: SB: air Cooling tubes

["David Wagner" <dwagner@sa.kevric.com>]

Rob Tom raised some concerns, and I have a few comments to add.  I
worked with and taught a bit about indoor air quality issues when
active duty in the US Air Force, and have been looking into earth
tubes for air cooling recently.

On Mold
The cause of indoor mold problems in commercial buildings I've seen is
almost always insufficient servicing of heating and (especially)
air-conditioning filters and ductwork.  These concerns are important,
but simple, straight earth tubes opening downhill to daylight behind a
grate would be extremely easy to clean.  One idea: hire a chimney
sweep and explain the opening is at ground level, the 'chimney'
extends horizontally, and the concern is water and mold rather than
creosote.

Chuck's plan, to have the tubes buried in a gravel trench foundation,
could be a bit more problematic, but should not be beyond the reach of
a hose with a spray head snaked into the tube if cleaning is needed.

With this said, I question the assumption improperly serviced hospital
and school HVAC systems (and I've seen more than one of each) are
similar enough to earth tubes to warrant hazard comparison.  Typically
these large HVAC systems become problems because of (usually
extremely) nasty filters, or in dead spaces in the system.  These
relatively small, moist, static, and previously sterile environments
hidden in a large and complicated ventilation system provide nice
protected pockets for a mold or three particularly suited to grow in
the specific conditions provided.  Earth tubes are very simple things,
and as long as there is at least a constant trickle of fresh air, seem
unlikely to become a problem.  I would, however, be wary of using an
earth tube only to recirculate air without mixing in at least some
fresh.

I have visited a few natural caverns and never noticed others in the
tour group having sudden allergy attacks, nor have I heard of mold
being a concern underground.  Algae is a concern where there are
artificial lights, but obviously this is outside my current knowledge,
and if somebody could confirm or correct me about cave mold, I'd
appreciate it.

On Radon
If you are using some kind of perforated tube underground and actually
drawing air through the soil, then yes, you will be able to draw radon
into the house along with fresh air filtered through the soil.
However, if you are considering earth tubes to precondition fresh air
prior to supplying it to your straw bale house, you are likely doing
so because you realize the need for fresh air supplied to your
superinsulated home and are planning to increase the air exchanges
without blowing your energy budget.  Radon can build up in homes or in
portions thereof where there is insufficient fresh air supply.  If you
can increase the amount of fresh air you use because it is thermally
preconditioned in an earth tube, you can likely more than offset the
amount radon drawn in.  However, it may be worth locating your radon
monitor at the point of earth tube fresh air supply if this gas is a
problem in your area.

If your earth tube is not perforated, you will not be sucking any more
radon into it than is present in the fresh or recirculated air going
into the tube. I am not sure if chuck is planning to recirculate home
air through the tube, or draw fresh air in from outside, but in either
case, radon in the surrounding earth will not get into a imperforated
tube.

With all of this said, I am probably not going to be installing air
tubes myself, mainly because my site is nearly flat and the ground
occasionally saturates under a few inches of water when it rains
faster than it can run off.  A large open pipe from a shallow monsoon
lake into my home seems like a bad idea.  I may use water to move heat
through tubes between the house and its environment, but those things
are for considering next year.

-David






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