Earth Tubes in cold climates (NY)

[ListerD]

So are your walls the only mass?

I'm assuming you'll do another poor for the floor, what thickness?

[HomeschoolMom]

It's always fun to see progress!  Thanks for sharing your journey   

[glenn kangiser]

That is cool.  Thanks for the pix.

John does not have room to load files to the forum so they have to be loaded elsewhere and linked to.  Scribd is one place for some kinds of files.

[bgarrett]

Some websites say that earthtubes were a fad in the 70s and 80s but nowhere do I find any other information telling whether they succeeded or failed.

Has anyone seen any results?

If mine doesnt work I will say so  and of course if it does work I will tell that too.

...

It sure is quiet here

[glenn kangiser]

It seems most final results are lacking.  We look forward to hearing of yours.

Jonesy in Australia was going to report  but got busy and we never heard if he finished. 

The report I did hear of was from a friend of Whitlock's who put them dowhill and as I suspected they work in reverse drawing warm air into the house and expelling the cooled air downhill.  A fan in this situation would have to overcome the heavier cooled air to reverse it's natural flow and push it backward into the house. 

This would not then use the natural heaviness of the cooled air to power the system.

[John Raabe]

Let me do a bit of thinking here on earth tubes, insulation and seasonal heat storage.

When thinking about earth tubes you have to start with the soil temperature (and moisture content, but let's just deal w/ temp for now).

Down 2'-3' in the soil the temperature tends to stabilize at the annual average temp plus a degree or two from warming from the core of the earth.

In my Pacific NW cool climate the earth temperature is 50º to 53º. This is most easily determined by measuring the water temp of a fresh draw from a deep well. In strong four season climates with high summer temps that seasonal average may be 60º or higher. What is your soil temperature Glenn?

Dry soil is a very poor conductor of heat  so don't expect much heat transfer from slightly warmed air running through a plastic tube and conducting into soil. You could set up a simple experiment with a couple of thermometers and compare soil temps a foot away from the earth tube to an undisturbed area of soil at the same depth. You could then put insulation on top of the soil over the tube and see how much that raises the temp.

In cold climates earth tubes can be used for cooling purposes in the summer as it will cool outside air. Some folks have also used these tubes for preconditioning incoming air to a furnace or heat pump reasoning that if the outside air is -10º and we can warm it up a few degrees this is heat we don't have to purchase.

To attain the goal of seasonal heat storage so that you can have a yearly flywheel of thermal energy you can make deposit to in the summer and withdrawls in winter you will need:
• A container that will hold the BTU value of your winter heat load.
• The container will need to be highly insulated since insulation r-value is a measure of resistance to heat flow over time and we are counting on holding the heat for 6 months or more.
• In order that we do not need to build an enormous, highly insulated container we will want to store these BTUs in something with high heat content such as water. (Soil is not good for this as it is tiny bits of rock separated by air.)

About the time you get to this point in the calculation you start thinking about ground source heat pumps and realize that it can do the job for less money and it provides both heating and cooling while taking advantage of the soil temperatures.

[John Raabe]

I have just uploaded Bruce's spreadsheet. Click on the file name and "save link as" to your own computer or open with Excel.

http://www.countryplans.com/Downloads/heat_exchanger.xls

[John Raabe]

Bruce replies to my post above about seasonal storage

"Soil temperature here is about 58 degrees.

I will have some water going into the sand around the earthtubes, think soaker hose. Seasonal heat storage is not my goal nor any part of my plan.

Since I own a backhoe and will ignore the cost of diesel to operate it, the cost of earthtubes is the cost of the pipe, the sand to fill around it and fans to get the airflow required.

I see this as the cheapest possible way to have a constant flow of 58 degree air thru my building. At 58 degrees, I will not need Air Conditioning and will  need to add only about 10-14 degrees of heat in the winter."

Please put a minimum of two digital temp probes in with at least one the tubes. One probe reading the air temp at the inlet side of the tube and one at the outlet or exhaust side. Then you can track these two numbers with the interior temp and this will let you do simple experiments like turning fans off and on for two days when the outside temps are similar. Did it change the house temp? Did I use more or less heat?

Your theoretical maximum heat transfer between the soil and air would be attained if you were always able to get air into the house at the same temperature as the deep soil temp. Then you would get the benefit you mention above. Since the conduction between the air and the deep soil is a long way from perfect, your actual temperature rise or fall in the tube will be something different - how different depends on lots of things we don't need to get into and it doesn't matter anyway. Your probes will tell you all you need to know.

I am sure your tubes will be a help for summer cooling. I wouldn't expect the air coming in to be 58º, but even if it's 78º that will be useful for cooling. This is the benefit I get from my earth coupled crawlspace air loop.

I am not convinced you will have any benefit in the winter time. I will venture a guess that if you do the experiment I suggest above that you will find you will use less purchased BTUs to get the interior temperature to your comfort point when the earthtubes have the fans turned off and are capped closed.

[bgarrett]

Thank you John!
I like the  statement below your posts.....None of us are as smart as all of us.

If I am way off base, someone speak up and save me a lot of money and work!

I do plan to keep a record of outside air temperature, earthtube outlet temperature and room temperature  thru the summer and winter in order to see what is accomplished.
(You dont know what you have unless you take inventory)
As you mention, I dont expect to get exactly 58 degrees as the earthtube outlet temperature, but anything cooler than outside air should be a benefit.

You mention winter benefits from the earthtubes....in my naivety I imagine that 16 degree air drawn thru the earths temperature of 58 degrees will warm the air coming out of the earthtubes...Are you saying, maybe not?

[John Raabe]

I suspect that if the outside air is 16º you may well get air that is still close to freezing at the interior of the tube. Unless you immediately feed this into a heater and raise it to perhaps 10º above room temp you will feel a cold draft. That's why I suggest you design the tubes with tight fitting caps.

In the winter you don't want a lot of outside air to heat up - doing so is expensive.  The normal stack effect of a well sealed house provides plenty of air change and drying when you have such a high temperature differential between inside and outside.

With super-insulation cold climate techniques you try to cut down the air change rate with tight construction and then install a simple heat exchanger to supply fresh air that is heated with the stale air headed out. These have a much higher heat transfer rate than would an earth tube and even they need heaters to warm the air when the outside is 16º.

[speedfunk]

To attain the goal of seasonal heat storage so that you can have a yearly flywheel of thermal energy you can make deposit to in the summer and withdrawls in winter you will need:
• A container that will hold the BTU value of your winter heat load.
• The container will need to be highly insulated since insulation r-value is a measure of resistance to heat flow over time and we are counting on holding the heat for 6 months or more.
• In order that we do not need to build an enormous, highly insulated container we will want to store these BTUs in something with high heat content such as water. (Soil is not good for this as it is tiny bits of rock separated by air.)

About the time you get to this point in the calculation you start thinking about ground source heat pumps and realize that it can do the job for less money and it provides both heating and cooling while taking advantage of the soil temperatures.  

Check.  we have a container that will hold the heat designed.  
Check.  We will have 2 layers of r10 techfoil and a vapor barrier (6 mil plastic), which will also act as shingles under the ground to keep water from changing thermal properties.  The house will have 4" of rid polystrene on outside of brick wall.  the roof will have 4 inches of polyurethane rigid foam board.

I bet a ground source heat pump will be more expensive overall.  There is the advantage of using the earth's conductivity rather then water for transfer of heat. It's still mass just less dense. It requires no electric,this for me personally is big. I want a very passive simple home. There is also no equipment to service or maintain.  I'm not sure the exact cost differences though, varies by sitituation i'd imagine.  The main costs of using earth as storage and conduction is the large area that needs to be excavated and the insulation blanket.  Maybe some  one can share what a whole house geothermal ground source heat pump costs to install and keep running!  if I remember right somewhere between 10-20 Grand for initial install and 1/3 the cost of heating from then on.   I know of a few people around here who love their geothermal heat pump setup.   The idea of a utility bill scares me and is going against my goal of VERY affordable living  .

[speedfunk]

bgarrett:  I'd love to see pics and some posts on your setup while your installing .  Please consider starting a thread.  Maybe between all of us we can start to make earthtube science more open for all to examine and customise!  I believe there is a lot of promise and look forward to any real world info.  I've been debating with my self over the intakes and whether two 4 inch pipes will be enough.   However with fans I can increase the draw and suck MORE air if needed.  I know what info i need to figure out, just have not done it lol.  To be honest I'm not at that stage of the building.

1. Whole house volume of air.
2. how much air a 4" tube x 125' (approx) with a variable speed fan can exchange ( x'2 x for my situation)
3. how much air exchange is needed for "healthy" air    Maybe someone can shine the light on this one.  I'm going to talk to a guy I work with who runs a k-12 school.  The state mandates a certain air exchange rate and that would be good info to know when designing a system.

The trick though is how quickly air will take to (in my case pre-heating) warm up.  This can be changed if using fans by regulating air draw. The only real numbers that matter in the end are what john and bgarrett mentioned.  The inlet and and the where the tube enter home.  If for some reason the air doesn't have enough time to get to whatever temp you want adding more pipe would help.  I would think that in the beginning of the earthtube where your temp differentials are highest the most work will take place.   As the air travels farther along and gets close to it's in house destination and the temp starts creeping toward ground temp the less the difference the less quickly the air will be affected.  So there is probably a point of diminishing returns based on how long the pipe is.  So getting the same exact temp as ground would seem difficult, however getting temps very close should be obtainable.

[glenn kangiser]

John, measuring the soil that does not get sun, I get 70 degrees.

Interesting that the area in the sun is at 89 degrees at 8:35 AM/

[EcoHeliGuy]

I to fully plan to incorporate earth tubes in my house. But I also do not plan them for a heating/cooling source.

During the summer I will have a very open house concept lots of windows and doors open allowing fresh clean lively air to flow through.

In the winter when things are closed up (Western canada) I will have a fire place, gas water heater, gas dryer, gas stove. these things need an air supply. also in a tight house the Range fan, and bathroom fan also need an air supply. This is where my Earth tubes will come in, these appliances drawing air will pull fresh air through the earth tubes.

I will have a slap floor and the tubes will run below the floor and insulation before entering the house. The tubes will flow up hill to the house with no weeping holes in the pipe. At the entrance to the tubes will be a vertical pipe with a rain cap coming out of the ground. air will be drawn into this vertical pipe into a Dry well. then enter the earth tube, all condensation from the tube will flow back down hill to the dry well. This air as said before will be mechanically pulled by appliances in the house. As the air travels the earth tube and warms up it will become lighter and a natural air flow will want to occur. Remember the out side is cold and heavy, the air inside the house is warm and light. The ceiling is well above ground level so the air will naturally want to escape the house at a high point and enter at a low point. This is basic physics. The problem people are having is only looking at the Earth tubes, the house is part of the system too. And the Ceiling will be well above the ground level in all seasons.

I'm not looking to heat air with the earth to heat the house, I'm looking to reduce a cold draft.

[speedfunk]

Sounds like a smart way of looking at thing mcbane!     .  You will have to update us with info when you eventually get to installing.  You mention also that the house is part of this equation , insightful!  I'm thinking of a wood stove heating up the air , then exhausting through the upper earthtube and CREATING that pull of air.   No doubt will be interesting to play with. 

[poppy]

John, interesting discussion on earth tubes and seasonal heat storage.  There is a thread in General about Noble Homes.  Here is a link to a part of the Noble web site that talks about heat storage.

http://noble-home.net/design.html

If I read it correctly, they are offering to help a home owner with material costs for a heat storage system.

Hope this is on topic.

[speedfunk]

Very helpful!  It's nice to know others want to advance building earth stored heated homes.  I'm still " digging"    through their site thanks!

[ListerD]

http://countryplans.com/smf/index.php?topic=4752.80 Additional thoughts this morning on humidity control for the earthtubes for our home in Missouri.

[llamaman]

http://mb-soft.com/solar/saving.html
above is a link that some may find interesting. 
Im  installing three hundred feet of four inch tubing that is house to house.  and five hundred feet of four inch tubing that is fresh air to house. there will be 8 -  100 ft runs.   Im now thinking ill run  my last three fresh air tubes up hill away from the house. that makes sense to me.   My house is a little over 1600 sq feet and will have a vented stack in the roof to let hot air out and hopefully pull air threw my tubes to cool my house.   
the link above explains its not so much the size of the tubes it's the number. hope this helps
I love the topic 

[speedfunk]

llamaman great to hear it.  I like your idea of 100' run and more of them. 

I just upgraded my house to 6 total earthtubes 3 intake 3 exaust.  I also think I'll run it about 100' also.

Here is a link I wanted to share from sugar mountain farm.  He ran earthtubes 70' and describes his experience.

http://sugarmtnfarm.com/blog/2008/09/earth-air-tubes.html

I think we have to most comprehensive list of earth tube related material on the web lol. woohoo.

[rickeyleee]

Someone else may have addressed this, but I was contemplating the feasability of venting the earthtubes into an atatched garage or outbuilding and installing a heat pump in it to let it do its job.  Not sure if this would be good for the heat pump or the garage though?  My first thought is that it is generally too cold in Iowa for a heat pump to work effeciently but using the earth tubes as a source of much warmer or cooler air than outside temperatures in the winter and summer seems to be a plausable soloution but not sure if it is a viable answer.  What problems would a person run in to in such an install?

[glenn kangiser]

Likely the experimentation may be the bigger problem.  Some of the expensive systems use extensive trenching and buried pipes - tubes etc.  I only vaguely know of them - have seen a few but never followed up on them.

[rickeyleee]

Sorry about the confusion but I'm talking about a typical heat pump and not a geothermal heat pump.  I would be making my own heat tube system that would be vented into the garage or out building where I would install the outdoor portion of a typical heat pump.

[EcoHeliGuy]

One of these days I'll place some drawing up of the system I'm planing, but until then I have a few questions.

first off, if your tubes are on a slight slop descending from the house, do you feel you need drain holes in the tube, or just let the condensation flow down the 100ft to the end and trickle out?

Also I have been thinking of placing an 80mm computer case fan at one end of the tube to try and make sure that the air always flows one direction, this is not to "force" air into the house, but to resist backward flow down vent pipes in hot water heaters and such. Any ideas?

AS I said before it will be the appliances in the house drawing the air in my earth tubes, (ei bathroom fan, dryer, gas hot water heater, fireplace ect) I'm just thinking of ways to make sure the air current is always in the right direction, I have thought of using the dryer type vent doors on the inside of the house, that would only allow air movement one way, but not sure how they would work with natural draw, compared to the forced air they are designed for.

[HomeschoolMom]

I came across this system today.  While I don't know much about earth tubes I thought of this thread.  While it might not be useful info, it also might be useful...   Just thought I would share.

http://na.rehau.com/construction/renewable.energy/ground-air.heat.exchange/system.overview.shtml