Earth Tubes in cold climates (NY)

[speedfunk]

thanks homeschool for sharing that link!

Eco:

I'd really like to see your idea .  I've even given my system a bit more thought and might post a picture as well.  Your question about the weep holes is a good one.  I've noticed that with the pipe I'm using, that if you didn't drill a hole in the low spot there would be no way that it would COMPLETELY drain.  There wouldn't be much water in it, but there would be some.  Another idea would be to not glue the tubes together that way it would eventually works it way out the cracks of the pipe.

The fan sounds like a good backup plan.  trying to make it naturally draw air through the house and if that doesn't work turn the computer fan on.  So if I understand you idea right.  You want to use the heat that your appliances generate to create a draft out your upper earthtubes thus drawing air up ito your house from the lower earthtubes?

I gave a good amount of thought to the earlier posts about the need to have the pipes at different heights.  The tubes that are in the back of house (bermed side) would be higher then the front side (solar collector side).  The more I think about it the more it makes sense.  The trick is that an insualted 20' skirting has to drain the water in the immediate area of the house so it's pitched down (even in the back bermed part of the house).  So my thought is that it can go down for a bit then after the insulated skirting ends go up and out of the ground.  Angle toward wind and done.

I've also given a bit of thought to angling the upper pipes toward the prevailing wind.  So instead of relying solely on temp differentials to create the movement use the wind?   Wind would blow in upper pipes pushing air down into the house.  Coldest air would selttle in bottom tubes and exit.  On the way out some heat would be recovered.  Pic would explain better... lol.

[brucel]

Great thread.

I'm wondering why nobody directly mentioned the classic Hait camel's nose auto-reversing heat-exchanging convective system? He suggests laying both pipes side by side in the same trench once they leave the house.They rely on the difference in temperature between floor level (where the "lower tube" enters the house) and ceiling level (where the "upper tube" comes in), and between the house and the storage zone around it. He says the difference between outside temperature and inside temperature has nothing to do with it. I quote Hait's book:

If we can make the tube "breathe," then the air will take turns going one way and then the other. In this way the wave-front can be kept from reaching the interior and bringing the outdoor weather directly inside. Thus the earth tube becomes a counterflow heat exchanger just like a camel's nose! However, we do not want to use this as an excuse for shortening the pipes since the breaths are not all the same length. Air may still flow in a single direction for quite a while before it reverses, although it will probably balance-out over the entire year.

Later he adds:

The greater the temperature difference between the home and the earthen heat storage (thus the greater the need for heat or ventilation,) the faster the air flows. If anything tries to suddenly raise or lower the temperature the earth tubes will work harder to try to even it out again.
The over all effect is to moderate out the temperature differences which try to occur, just as with conduction.


If I understand this correctly, this means that in spring and autumn, when outside temperatures are agreeable, the airflow will be minimal. Will it be sufficient to ventilate the house (say at night when outside doors and windows must be closed)? A tight house needs permanent ventilation. It may be that an electric fan should be installed in the system and used if there is no air movement. Hait himself suggests that having fans available may be "prudent".

Hait says that earth tubes should always have a slope to them because they must function as heat traps. His tubes, both "upper" and "lower" always seem to slope downwards, away from the house.

Hait's idea is very attractive because it is entirely automatic in summer and winter - no need for thermostats and fans most and maybe even all of the time.

Bruce

[SimonASNG]

I am more than a year since the last posting...  But we all start some time.  I am looking to break ground for my home next spring and have done a lot of research on this topic (including burring hundreds of dollars of sensors in the earth).

Radon was brought up.  In the "old days", people used that kind of 4" flexible drain pipe that was easy to lay but had holes all over it.  The ridges and frequent curves slowed down airflow and all the holes gave a lot of surface area for radon to get in...  I actually know of an Earth sheltered home in my area (Michigan), built in the 1970's, that found they may as well have been smoking 2 packs a day for the past 30 years.  Pretty bad situation.  They said they were sad they had to seal the system because it had worked so well for humidity and temperature moderation, but obviously they couldn't let that continue.   

A more modern design using sealed (or mostly sealed) PVC pipe with a larger diameter and as few turns as possible would work much better and shouldn't have any problems with Radon that it didn't cure by bringing in a lot more fresh air.

As for the humidity problems...

It is cold where I live, at least in winter.  But in summer it can be hot and muggy.   If I make my tube go deep as soon as possible (slightly upward but deep into the side of a hill), then the summer temp drops quickly (as my expensive research grade probes will tell you).  If the temp outside is 95 degrees and 100% humid, and then is cooled down to something like 60 degrees by the earth tube (the earth temp is 51 degrees), then that would drop its humidity to 100% for that temp (fully saturated at 60 degrees).  Then the air enters my 70 degree home and as it warms up, the relative humidity would immediately drop to 70%...  Not ideal, and some dehumidification will still be needed, but better than 100% humidity from outside air.   If my tubes are a bit longer, and I could some how get the air temp down to closer to my 51 degree ground temp, that air would warm up to 70 degrees with a RH of 50%, with is considered ideal. 

As for the camel nose...  I don't believe that the exchange is direct enough...  I think I am better off keeping the tubes as far apart as possible and letting the earth moderate.  I have read John Haits book (I actually own a copy), I am just not convinced.  I am sure I will read it one more time before I build.

Anyway, like several others on this thread, I plan to take good data from my full sized experiment and will try to let the world know how it all worked out...  Even if it is embarrassing.   

[SimonASNG]

Oh yea, one more quick thought.  Some people on here were concerned about the cool air falling and escaping out the lower air tubes when you would prefer to keep it in the house...  Someone even suggested running a small computer fan just to keep that from happening...

The passive way to sort that out is a light, but stiff, flap over the lower air tube entrance.   When air is coming up the airtube, the flap should be light enough to easily flutter out of the way...  But when the air tries to reverse (seasonally or daily), the flap needs to be stiff enough to close the tube...  Typically, the flap is hung so that in zero air flow, gravity would bring the flap down and close the pipe (the pipe opening should be parallel to the ground).

A friend of mine did this for the air intake into his wood shop and it works perfectly.  He just taped a piece of thin transparent plastic over the opening and let gravity and back pressure take care of the rest.  It is important that the "closed" air tube have a nice flat pipe end to rest against and that the angle is right so that gravity puts the flap in the closed position if no air is coming up in the right direction...  Otherwise "slow" air may leak down without moving the flap into the closed position. 

Barn fans do something similar with thin metal louvers that open when the cooling fan is on and close (too keep the heat in) when it is off.

[MartyM]

 I'm glad to see this thread resurrected, and anxious to hear how things are working for those that are farther along in there build.

I must say my knowledge of earth tubes has come mostly from this thread and the links provided here.  Thanks folks!

I have been giving the earth tube idea a fair amount of thought and I have a few ideas I would like to bounce off you guys.

My build will be in the Ozarks so I have more cooling days to deal with than heating days.  I think the point made about being  sure to include the house it self as part of the system is a big one and it seems to me that thinking of the house as a heat separator only makes sense.  If the house is closed up with no fans or HVAC systems moving the air around the heat will naturally separate.  The lowest floor being cooler and high spots holding the warm air.  It seems to me that 1 set of exhaust vents up near the ceiling for moving heat out in the summer, and another set near the floor  for moving heat in for the winter would be the best solution.  It was mentioned that a small fan or flaps could be used to prevent unwanted back flow.  Here is my twist, why not add a simple solar heat collector to replace the fan.   https://sites.google.com/site/glenssolarheater/   This is just an example, I think a big insulated  box of rocks to make a heat sink would work better for our use and we probably don't need a fan. If you had your summer air drawn in to the house through earth tubes and  vented high on the north side of the house then the exhaust tube exiting the house on the south side connected  to the bottom intake of the solar collector. Its seems to me the collector would stay much hotter than the indoor air and keep everything moving.   During the winter months have the incoming earth tube air connected to the collector to pre heat it further before entering the house low on the south side.

  Clear as mud right!   

What do you think?

[laranxo]

Hello, I'm newcomer,  and don't speak english very well, so forgive me please.

I realised this is an old thread, but most interesting, so I'd like to share one idea.

As we are trying to get a flyweel from winter through summer, why not to split it in two?

if for instance we divide the heat storage zone by isolating the north side of the ground from the south one, and arrange the earth tubes to operate independently.

the idea would be to have a set of permanent earthtubes collecting heat,  and other set collecting cold.

another adjustable set would connect the house to the storage zones.

in a cold climate you can place the hot storage zone under the house, in a hot climate should be better the cold one.

that way you could possibly get more heat and more cold than with only one common storage zone.

the cold one always shaded, the hot one in the sun,
if you think about it, it has many possibilities (place of tubes openings, dedicated solar collectors, etcétera)

just an idea, waiting for your thoughs and knowledge.

cheers
Manu