Tag Archives: by-passive

Long Earth Tubes


Posted on September 6, 2014 by

While the trench was open, it was our chance to lay the drain tile and earth tubes.  We didn’t set the timelapse and we were too busy working to take many photos, but it is an important step for any earth sheltered home, so I want to capture a few details.  Sorry, no timelapse.

We had already laid the drain tile and earth tube close to the house as we back-filled that portion. Click here for that story.  But we still needed to run long tubes from the house to daylight.

The bottom of the trench was already sloped to 1% and the septic line, made of 4″ schedule 40 PVC, was already in place (done by the excavator and already approved by the plumbing inspector).  We needed to bury it, but with a constant slope.  Sherri and I used shovels and rakes to pull down dirt and bury the original line by about 6 inches.  We (and the boys) stomped on this layer to pack it down, especially next to the buried septic pipe.  The end result was a nicely sloped flat bottom trench.

We connected 100 ft long segments of 6″ corrugated drain pipe to the ends of the pipe we had already buried up by the house.  We used a proper fitting connector piece and also taped it heavily and covered the connection in landscapers fabric.  We laid these two parallel drain tiles along the trench and periodically placed dirt on them to even everything out and keep them separated by a couple feet.  I would have liked to have separated them by more, and I did where the trench was wide enough.  In all, we added about 150 ft of pipe to each end of the drain tile loop.

Normally, a drain tile loop is connected to a single long pipe that runs to daylight.  However, by connecting each end to its own pipe, I am able to use it as an earth tube circuit with an inlet and outlet or two inlets.  The other end of the pipes goes into the house, but I can simply connect those ends together if I want the air to circulate under the mass of the house without entering it (by-passive annual solar heating).  The extra cost is the additional 150 ft of pipe, which cost me about ~$100.



The second layer of earth tubes was the 8 inch double wall (smooth inside) HDPE pipes.  These come in straight 20ft segments that have a bit of flex to them.  You can connect the pipes directly (bell and spigot ends with soil tight connectors) or you can connect them with 30 or 45 degree joints.  It was a hot day and we did not have the energy to properly bury the 6″ corrugated drain tile before laying the larger earth tubes, so we decided to mount the larger earth tubes to the side of the slope (with stakes) a couple feet above the previous layer.  This still left more than 10 ft of earth above these pipes for most of the distance and gave us more than 6 ft between the two parallel pipes.


At the end of the day, we had 4 earth tubes, each over 150 ft long, going from the house to “daylight” along the trench.

The next step would be backfilling.

Later, while back-filling the trench, we made sure that the 8 inch pipes stayed in place while the excavator back-filled below/between them and the 6″ pipes…  This took some care and probably added at least an hour to the back filling process.  The excavators charged by the hour, so that should probably be counted in the cost of the earth tubes, but seemed like a bargain compared to backfilling that trench manually on that hot day.  I did pull out some of the stakes when they were no longer needed to hold the pipe still, but many were buried in place at an additional cost.

By-Passive Solar

Posted on July 23, 2012 by

(like many pages on my fledgling website… this one is still a work in progress.  Illustrations to come).

Introduction to By-Passive Solar


You can read a lot about Passive Solar on the web or in books.   The benefit of this arrangement is that it is economical…  nothing “extra” to build.  Just rearrange your home’s windows a little so they are mostly on the south side, add some overhangs to keep out the summer sun and tada! you have passive solar.  Adding some mass to soak up those rays (such as a cement slab floor) would be a good idea.  In the winter, the sun’s heat comes in the windows and is already in the living space where you need it.  In many cases, the air just circulates around by natural convection and floors radiate warmth back into the rooms at night.

I am sure I will use some aspects of direct-gain passive solar in my home (all solar homes build on passive solar concepts)…  perhaps even “augmented” with a fan or in-floor pex pipe to move the heat around…

but what is “By-Passive Solar”…?

It starts with the need to fix the main problem with direct-gain passive solar…  The solar collector IS the home.  This requires certain compromises.  For instance, you need to leave the curtains open to let the sunlight in.  You need too keep your floors bare (and many recommend darker colors unless you have masonry walls to capture the reflected energy).  Also, because the home is the collector, the home is often uncomfortably warm during the solar heating hours.

But what really pushed me down this path is that I am in Michigan where I can’t rely on a daily solar charge.  I can only expect one sunny day a week in January or February.   I needed my solar charge to last longer.  Therefore, I needed to heat more mass; not just my home, but a huge mass of earth around my home (PAHS Umbrella style).  Collecting that much energy requires letting the heat in during the summer, at the same time that I would like to enjoy a cool earth sheltered home…  I don’t want the heat to be building up in the home and surrounding earth all summer,   I want the heat of summer to enter my home 6 months later, when I need it…  So the key is to flip things upside down and heat the earth 10ft away/below my home all summer.  By the time that energy reaches my floors, it will have saturated the earth around my home and be ready to carry me thru the cloudy SE Michigan winter.

This sort of by-passive solar heating system would need two extra components.

  • Solar Air Heater to absorb the sunlight energy and transfer it to air
  • Earth Tubes to carry the heat under the earth by convection or perhaps a small solar powered fan


Solar Hot Air Collector


It is called a collector, but really it is a generator.  It takes in air at some temperature and then heats it up with solar energy.  You can find many different designs on the internet…  But the best ones seem to be a shallow box with a glazed front and an insulated back.  The glazed front lets in sunlight and heats up air, the high temps drive the air thru by convection (or augmented by a small fan on a thermostat switch).  There is an inlet and an outlet and some means of snaking the air thru the box to gather as much heat as possible, but without creating too much back pressure… that’s it 😉

I plan to make my boxes somewhat modular so I can experiment with different configurations and swap them out later.  Each module should start with a 4×8 sheet of plywood.  You could nail a 2X6 frame around the plywood such that the plywood is approximately 1/3rd of the way thru the frame.  On the back of the plywood, you glue a 2 inch thick sheet of poly iso rigid foam insulation, such as Super Tuff-R that won’t melt under the heat.

On the front of the plywood, you build the “solar absorber”.  This is where the innovation happens.  The solar heat should be transferred to internal airflow and not lost thru the frame or glazing.  Air should not be moving near the glazing as this will result in more heat lost.  The absorber should not reflect any light, so paint it flat black (not glossy or metallic).   It should have lots of surface area to exchange heat with the air. If you design with ducts across the absorber, the spaces between the ducts should be a material that can conduct heat to the back of the ducts.

You need a way for the air to enter and exit the absorber.  In some designs you also need to turn the air within the absorber.  The performance of the Solar heater is very sensitive to the plenum or manifold design.  You want to distribute the air evenly and with a minimum of back pressure or leakage.  Adding simple turning vanes can make a huge difference.  A back flow damper may also be a good idea.

The Glazing is attached to the front of the frame… Ideally, it is something cheap and easy to work with such as Suntuff or Tuff Tecs or some other UV stabilized plexiglass.  The experts warn against using double pane glass because its seals can’t handle the heat.

Controls can be as simple as letting the sun drive the flow thru buoyancy, or you could augment the flow by adding a fan on a thermostat switch ($10 snap switch).  Some fancy designs even use 2 fans with the second one kicking in at a higher temperature.  You can buy some pretty high efficiency duct fans or use something as simple as a PC fan.  Many attic fan assemblies come with solar panels so the system can operate off the grid while the sun is shining, which is the only time you will need to pump the air anyway.

For materials, I think I will start with an “aluminum downspout design”.  This design uses rows of Aluminum downspouts glued to an aluminum back plate, all painted flat black.  The air comes in at the bottom of the left side and turns around in a plenum on the right side before returning and exiting on the top left side.  I may also try a vented soffit or double layer fiberglass screen design, but I suspect they are not as efficient because they don’t keep the air in the channel and away from the glazing.

One other interesting aspect of my design (images or sketches to come) is that it will be adjustable.  I plan to pivot my assembly by the lower intake.  The output will be able to pivot. between two positions.  The lower position (~30°) is for summer use (when the sun is higher in the sky) and will pump the heated air under the house for thermal storage.  This closed earthtube loops back to the solar heater inlet where the air is reheated.   Above this earth tube is a second earth tube, an inlet opening that takes fresh air directly into the home, moderated thru the cool earth.   In winter, I tilt the heater up to the winter angle (~60°).  This connects the outlet of the heater to the inlet earthtube and pumps the hot air directly into the home.  Meanwhile the closed circuit earth tube is now open to the winter air, since this is actually the inlet for the heater, air is first drawn under the home and tempered before running thru the solar heater and then up into the house.  Get it?  Maybe not.  I made a 2D sketch, but it doesn’t do it justice, I will cad it up some time…


A Freebee Earth Tube!


I would avoid the use of corrugated drainage pipe as a fresh air Earth Tube because of the water that gets trapped in the corrugations and the potential for mold entering your home…  It is highly advisable that all earth sheltered homes be equipped with as many waterproofing measures as possible, including foundation perimeter drains made with these corrugated drainage pipes.    I have heard of earth sheltered home owners who are both glad and a little sad that their drainage pipes never get any water in them.  What if we used them for a dual use as by-passive solar earth tubes.  The loop would never enter the home, so there would be no risk of mold or radon from the corrugated pipes.   The modifications could be small, instead of branching your drain pipes, you would need to make a continuous loop that would start and end at the solar heater.   All summer these pipes would be warming the foundation under the umbrella and helping to increase the temperature of the earth under the home…   I might take it a bit farther and use the more expensive 6 inch corrugated drain pipe for easier air flow.


Earth Shelter Origins (at least for me)

Posted on June 24, 2012 by

  1. Origins

I keep checking with my wife and a few other people (architect, engineer, builder, friends, etc. but no qualified psychiatrist yet) and I am told that I am not crazy.  So then, why would I want to build an earth sheltered house?


I had just bought my first home when the “Northeast Blackout of 2003” occurred.  My new home was poorly built and thinly insulated and had no backup systems.  The blackout clearly demonstrated that my home was not designed to keep us comfortable without consuming vast amounts of energy.  Maybe at some point I will share some of our regular electricity and gas bills, but suffice it to say they are large.   However, I was thankful that the 3 day power outage had not happened in winter, because we also had no backup heat.   Since that time, there have been several shorter-term winter power outages where I felt my homes temp drop to the low 50’s in just a few hours.  A number of other times we have had the natural gas shut off while the gas company was doing repairs.   Our furnace (like most) was designed so it would be worthless if either the electricity or the natural gas stopped flowing.    I thought back to the Quebec power outage of 1989 where 4 million people lost power in the middle of winter for up to 33 days.  Can you imagine if some freak storm did that in our area?  Neighborhoods like the one I currently live it would be devastated.   I became interested in moving my family to somewhere more stable.

In 2006, Al Gore released his award-winning “inconvenient truth” about global warming and sea level rise and then (several years later) infamously purchased a 9 million dollar, 10,000 square foot ocean side (sea level) home in Malibu CA.   The irony between his stated belief in an impending carbon-induced global-warming seal level rise and his actions to purchase such a huge (carbon footprint) home right at sea level helped push the story all around the world.   While others were laughing, I had to think, “If you really believed in global climate change bringing extreme weather, what sort of house would you build?”   What if you also believed energy prices would continue to rise?  Or if you believed our energy distribution systems were crumbling or threatened?
There have not been very many generations that made it thru their whole lives without being impacted by war or weather or at least a fuel shortage.  Consider England 100 years ago…  In 1912, two years before the first world war, England had the largest army in the world (and its first airforce), the most advanced education system, a large number of colonies that kept resources and fuel flowing cheaply to its shores, the Titanic had just been built, but not yet sunk, non-stop flights to Paris had just begun, etc.  England was on top of the world and I am sure that many Englishmen assumed it would stay that way, but the only constant is change.
If we look at our current situation, do we expect things to remain stable for the rest of our lives? What do we expect will happen to the costs of energy (barring the invention of a nuclear fusion power plant)?  Every one expects energy prices will continue to rise.  Do we see our energy distribution infrastructure getting better?  Nope, crumbling.   How about our governments ability to look after us?  Soon they will be struggling just to pay the interest on the debt.  Taxes will rise, jobs will be lost, etc.  If you agree that one or more of these things are likely, then what sort of home should you build?
How about the weather?  Regardless of if you agree that global warming is caused by our pollution or just some natural cycle thousands of years long, the data does seem to indicate that it is getting more extreme…  (perhaps weather like this has happened before, but can we at least agree that extreme weather is possible?)  More tornadoes, hotter summers, colder winters (the winter between 2011 and 2012 was an anomaly with the jet stream (arctic oscillation) that kept the bottom half of Michigan very warm by keeping all the cold further north, but next winter could very well see the Jet stream come lower and blast us with a colder than usual Canadian winter.)   The thought of riding out any of these sorts of events, or even a regular Michigan summer, where my AC struggles to keep the house at 80°, in my flimsy 2×4 and vinyl siding home was not appealing.  Tornadoes and strong winds could easily rip my home apart.  We had a hail storm last year that put a number of holes in my siding.   I always chucle when I see people on the news after a storm (or fire) vowing to “rebuild” after their homes were totally destroyed.  Why do most of them build the same type of weak structure that blew away last time…?  “Oh no, ya see, this time I used these here hur-can’ straps to hold my roof down…”  “Great, much better.”   Instead of just hoping for mild weather, why not build a safer way?
So I started looking around.  I started with more traditional passive solar concepts, along with the super insulated “passivhaus” concepts.   Some how, I don’t even remember when exactly, I became aware of this “earth sheltered home” idea as a way to moderate the volatile environment around the house.   I liked it and started researching, casually at first, but then heavily.   I couldn’t find an “off the shelf” idea that I liked.   For instance, many of the homes combined earth sheltering with passive solar.   This was a good combination, especially in sunny/freezing Minnesota, because the passive solar energy could be stored by the massive cement structures needed to support the earth, and then returned to the home over night.  But in S.E. Michigan, we only have 21% sunshine in January, so traditional passive solar with a daily cycle probably wouldn’t work very well.    Then I discovered this idea that I could cheaply incorporate the earth around my home into my “solar mass” so I could store even more energy, perhaps several days worth.  John Hait takes it further by suggesting you include enough mass to hold the home thru a cold dark winter.   I liked that idea, but it called for letting solar heat gain directly into my home during the summer.   This would result in over heated summers, and then thanks to losses found in any system, colder than comfortable winters.  Then I started reading about solar hot air collectors and it occurred to me that I could reserve my home for living in and build an external solar collector to “by-passively” heat the earth under my home.  If the pipes were buried the right distance under the home, the stored heat would take months to reach my floors at just about the time that I needed it.   Also, since I could push the solar heater up to much higher temperatures, I could drive much more heat into the earth (ΔT), and I could be charging up the earth away from the home to take greater advantage of the earths heat conduction lag time.  I will talk about many of these ideas in the “Tech Notes” pages of this site, such as Earth Shelter Basics, Umbrella Basics, Passive Solar, Soil Properties and Earth Tubes (still working on this last one ;^).
I now had the basic idea, I would look to build a “by-passive” (my own term) solar earth-sheltered home in S.E. Michigan…    I shared the idea with my wife and she actually LIKED IT!   Well that was helpful.  This is not the sort of thing you embark on without your significant other.  Of course the kids were on board, they put in their requests for secret rooms and tunnels.   So I started planning.  I used Autodesk Revit for the drawings and tried a number of different configurations.   I crunched numbers for engineering and cost, etc.
Back in 2007, I told my friends that I would probably start building in about 2 years…   Well, breaking ground as been at least 2 years away for quite a while now.   The 2008 housing crash slowed us down on the sale of our current house (its value dropped to 1/3 of its 2003 purchase price), but it did make it cheaper to buy the land we would need.   Buying the land in 2009 was clearly a serious step, however, the orientation of the lot forced a serious redesign.  Now that we have hired an architect and an engineer (two serious steps toward the final goal), had meetings with a builder, got quotes on windows (and more),  I would adjust that estimate down to less than one more year (giver or take a few).   In fact, we would like to start building in 3 or 4 months, but a lot would have to fall into place for that to happen.
This website will journal my progress as I prep for building and then eventually (Lord willing) as I break ground and begin to actually build this crazy home…  We will probably start with some past-tense posts to catch you up to where we currently are…

“The distance between insanity and genius is measured only by success.” Bruce Feirstein