'free' heating and cooling using PAHS

PAHS:  Passive annual Heat Storage. 

Len wrote:
Actually my idea is based on that... and on a writeup I saw from NY state (I think), where the guy runs his fridge from a cooling coil that freezes a brick of ice in his cool cabinet. I have also seen someone who has done sidewalk clearing using "7" or upside down "L" shaped tubes full of RV antifreeze. The fluid at the top gets cooled by the icy walkway and falls to the bottom of the down tube, while the relatively warm water at the bottom rises and warms the earth. If I put a tank of white plastic pipe (PVC?) at the bottom of the upright, I should be able to store cool in the mass of the ground and concrete. I think I shouldn't need to put an isolating layer like a PAHS because water sinking through should bring the cool down too.... but I only have a little room to work with anyway (5 by 8 feet or so), so it wouldn't hurt to isolate the bottom part and insulate the concrete wall on the outside above the tank while I am at it. Right now that room is only a few degrees less than the "crawl space" beside it.... The inside walls and roof have 4inch foam insulation, but the outside wall are just concrete and while one of them is NE, the other is SE and gets full sun till about 1pm. It is right next to a driveway, so I can't put bushes there to shade it either. I may have to give up the mass on that wall and insulate inside.

This is a continuation of the thread under LED lights.

It's about using the (geothermal) characteristics of soil and containing it somehow in an 'envelope' and then using pressure differences to let air vent and flow through the house.  This concept was introduced by Dr. John Haitt in the 70's (of Rocky mountain Institute) and is started to get some newly found traction. An umbrella house version of this can be found at: http://www.norishouse.com/PAHS/UmbrellaHouse.html
I'll be building one of these in a 'tiny house' version later this year.

The quote is from Len using this concept to cool a root cellar and melt the snow on his sidewalk - BRILLIANT concept.  Len, I wonder if one can use wax instead of RV anitfreeze.  Probably too cold for wax.  I don't care for the toxicity (even food grade glycol).    How about borrowing from the solar HW drainback system and just use water that's heated by the sun and then gravity drain it into a reservoir tank to avoid any freezing?  Also, one of solar thermosiphon principles is there's gotta be an 18" height difference to get thermosiphon action to work.  I wonder if some solar HW system would work better for keeping winter sidewalks warm... and then use the PAHS principles to preheat the SHW incoming water? 

What's the freezing temp of masonry on a clear nite?  For SHW collectors it's about 41F.

winsol3 wrote:
PAHS:  Passive annual Heat Storage. 
This is a continuation of the thread under LED lights.

thankyou for starting the new thread

The quote is from Len using this concept to cool a root cellar and melt the snow on his sidewalk - BRILLIANT concept.  Len, I wonder if one can use wax instead of RV anitfreeze.  Probably too cold for wax.  I don't care for the toxicity (even food grade glycol).

The heat transfer fluid has to be liquid down to below -10C(14F?). In my area I may be able to get away with salt water as I don't think it gets down to -18C air temp and the ground even 4 inches down will be warmer. I don't know if the salt would settle out at all or stratify with fresh(er) water on top. I could make it saltier than seawater of course.

    How about borrowing from the solar HW drainback system and just use water that's heated by the sun and then gravity drain it into a reservoir tank to avoid any freezing? 

But I don't want to avoid freezing temperatures, I want to use them... The coldest temperatures will do me the most good. Avoiding freezing temperatures in this set up would be like avoiding heat in a solar heater 

Also, one of solar thermosiphon principles is there's gotta be an 18" height difference to get thermosiphon action to work.  I wonder if some solar HW system would work better for keeping winter sidewalks warm... and then use the PAHS principles to preheat the SHW incoming water? 

The first purpose of this set up, is to keep my root cellar cooler, the heating of side walks would be just a bonus... permaculture principle.... try to make any change do more than just one thing (the Len paraphrase). Anyway, the height difference should be around 36 inches, so thermo-siphon should work... and be the least complex. The tube(s) from the lower tank to the top would be straight. I may put a valve in to stop heat penetration in the summer.... but a steel valve would conduct heat just as well as the fluid... hopefully cooling the earth around the lower tank will make up for that.... and the coolest fluid should fall too. I need to find the smallest pipe that will still work to join the two tanks.

What's the freezing temp of masonry on a clear nite?  For SHW collectors it's about 41F.

Depends on altitude, sky view, cloudiness... maybe latitude too. Even surface colour affects this.

Len, you have any web links or illustrations on this?  I'm a bit confused... wouldn't freezing temps (frozen transfer fluid)  stop any kind of thermal transfer - as in delivering something warmer for the top part to heat the sidewalks?

Also - have you ever seen any look-up tables on freezing temperatures for various surfaces in different configurations?

thanks

winsol3 wrote:
Len, you have any web links or illustrations on this?  I'm a bit confused... wouldn't freezing temps (frozen transfer fluid)  stop any kind of thermal transfer - as in delivering something warmer for the top part to heat the sidewalks?

That is why I specified something that remains liquid below our (admittedly mild) winter temperatures. I don't have an illustration just now.... but think of the cartoon dumb bells with a pipe and two globes one at either end. Now put that at 45 degrees with the lower one close to the bottom of the root cellar and the top one just under the side walk. Fill the whole mess with liquid that doesn't freeze. The pipe joining the two globes might be two tubes, one higher than the other.... warm fluid in the lower globe rises up the upper tube into the upper globe where it gives up its heat to the ground and sidewalk. it then falls to the bottom of the upper globe and down the lower tube to the lower globe where it gains heat from the ground at that level and completes the circuit.

Now make those globes into bigger longer tanks.... big tubes in fact. That is the idea.

Also - have you ever seen any look-up tables on freezing temperatures for various surfaces in different configurations?

No I have not. I would suggest that the math is complex. It involves black body radiance. There is the temperature of the sidewalk(0C is an ok value), the temperature of deep space (around 0K), The emittance of the sidewalk (colour, smoothness etc.), the percentage of sky view of the sidewalk (50% minus any nearby trees, buildings, etc.) and the transparency of the atmosphere (altitude, latitude, cloudiness, etc.). That does not include The mass of the side walk nor the length of time therefore required to freeze before the sun comes up. I don't think it is possible to come up with a simple table considering the number of variables. I get the idea that freezing water at +10C is possible at 5000feet above sea level on a flat plain if the water is no more than a few inches deep.... but that is just a guess from some of the things I have read. I am within 50 feet of sea level, in a generally cloudy area, looking at an area with maybe 20 to 25% sky view.... I might freeze things at +3 0r 4C if I am lucky.... and the ground is already close to 0C... late winter early spring with a clear sky.

Len wrote:
I get the idea that freezing water at +10C is possible at 5000feet above sea level on a flat plain if the water is no more than a few inches deep....

I routinely get ice this way... i'm at around 4500 ft, and on a clear sky nite I take a bunch of $5 cement mixing pans and put about 2" of water in them... and have solid ice in the morning.  That's how the pioneers got ice into town... hi-altitude ice pond skimming... there's even an area up off Hwy50 here called 'Ice House'

I'm still trying to figure out how to do the 'quote' copying here... guess I should read the directions...

Great explanation on the cartoon dumb bells.  You need to have some sort of expansion tank/vent valve to allow for expanding and contracting fluid and air.  Setting up a constant, no-maintenance capillary action will require some fine tuning.  When are you going to do this?

winsol3 wrote:
Great explanation on the cartoon dumb bells.  You need to have some sort of expansion tank/vent valve to allow for expanding and contracting fluid and air.  Setting up a constant, no-maintenance capillary action will require some fine tuning.  When are you going to do this?

I would like no air, but guess it would get there somehow anyway. The best place for an expansion tank would be straight up from the lower tank so it's close to the house out of the way.... the most effective place is the top of the upper tank so the fluid can be contacting the ground closest to the surface. I tried making a picture... below.

Don't know when. It has been added to my list of projects and will have to figure out where it's priority ends up. Heating the house, RMH or solar or both would be the most bang for the buck as I spend the most money for that now. However, this is something where I could dig a bit when I get bored with other things and it is cheap to build.

In the picture below, nothing is to scale. The upper tank would be smaller and probably the lower one too. They are big to show things clearly. The tanks would likely be an extruded shape and the tubes connecting them may be at opposite ends of the tanks. The cellar is much bigger than shown.

There are supposedly, two PAHS houses in Missoula.  If anybody can get me addresses, I will go, knock on the door, and attempt to make a video.

There's PAHS and there's PAHS... the discerning difference is using soil as a contained + reflected thermal mass and insulating envelope at the same time.  There's gotta be a barrier (plastic/fiberlass layer) around and under the house.

What amazes me is that Dr. Hait  published this in 1983 (reprinted in 2005).  I was turned onto it by a Danish engineer while at Sieben Linden.... long way around.  So why haven't these become more common-place?  simple: Water leakage. 

Even semi-underground homes are notorious for leaking after a while.  My careerwith large commercial building operations verifies that... if commercial AEC's (architects/engineers/contractors) with unlimited funds and smarts can't make an underground wall waterproof and foolproof for more than 5-10 years, what chance do residential AEC's have?  Dr. Hait and others explicitly say to redirect drainage and water away from the building site.  i think a 12 step permaculture approach to doing that is needed.

Maybe a double envelope with a french drain in between would work.  That's what i'm going to try on a tiny PAHS guest house I'm building.  Would love to have other suggestions.

I'm intrigued by how comfortable everyone says a PAHS house is.  I've designed + built 3 passive (latest is a C2C home) and there were still temperature fluctuations until I added 14+tons of internal thermal mass (Trombe wall/granite masonry fireplace) - I got an instant 12F + improvement in both coolth in summer and warmth in winter... with nothing else - just interior thermal mass.

As Dr. Hait states in his e-book about a regular passive home: 'the surface is designed to lose heat all winter, only at a slow rate because of all the insulation'.
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here's a quote from a PAHS builder:   "While we don't measure up to Hait's performance, this is by far the most comfortable house we've experienced.  Since then, I've built another PAHS for a client and have a replacement started for us. There were very few changes made to our original plan, other than size and interior details. These have proved to be wonderful houses."

http://paccs.fugadeideas.org/tom/index.shtml

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Also, here's an article by Dr. Hait on the Missoula Geodome...
http://earthshelters.com/green-blog/passive-annual-heat-storage-improving-the-design-of-earth-sheltered-homes-mother-earth-news/

and a picture of it:    http://earthshelters.com/green-blog/underground-hous-from-space/

winsol3 wrote:
There's PAHS and there's PAHS... the discerning difference is using soil as a contained + reflected thermal mass and insulating envelope at the same time.  There's gotta be a barrier (plastic/fiberlass layer) around and under the house.

What amazes me is that Dr. Hait  published this in 1983 (reprinted in 2005).  I was turned onto it by a Danish engineer while at Sieben Linden.... long way around.  So why haven't these become more common-place?  simple: Water leakage. 

I don't think the house has to be (semi)underground for this to work.... The under ground part may make it more effective..... and I must add, I live in a milder climate than many of the other posters. I might be chilled, but I could live in a basement with no added heat (OK I know, bodies and any electric appliance will add warmth, but no area heaters). I don't think I would have to go down 20feet to find a stable temperature either. In fact even in colder climates than mine (see Sugar Mountain Farms) An entirely above ground high mass house with no surrounding umbrella seems to be working quite well. This past winter it seems he went over a week at a time with no heat. So water leakage is easy to get around with a PAHS house by using standard building practices for the roof and staying above ground with the walls. The roof should be well insulated above any mass.

the more I think about it, I am realising that a PAHS house is a lot like a brick/cob oven with a solar collector to charge it and enough mass to last longer than a week.

There's two parts to a PAHS house... the contained thermal storage of the soil, and the long tube air circulation... both of which are totally static.. in that there is no auxiliary energy required... just intelligent design

I gotta disagree Len with a PAHS house not being partially underground... that's the whole idea.  To use the thermal properties of the soil's mass and reflect it back into the house... Ok, maybe if you dig under the house initially and put a thermal barrier there - is that what you're implying?

Thick adobe wall do this (straw bale doesn't + cob doesn't) because the thick adobe has mass... straw doesn't. In my own experience I find that granite rocks have a nice 'give and take' and do well in thermal dampening of temperature extremes.

RMi's  (www.rmi.org) headquarters in Snowmass does the same thing.. uses heat from the summer and fall way into the winter... and Amory Lovins (PhD physicist) has a lot of data to prove it as he grows his bananas in the winter.

winsol3 wrote:
There's two parts to a PAHS house... the contained thermal storage of the soil, and the long tube air circulation... both of which are totally static.. in that there is no auxiliary energy required... just intelligent design

yup.

I gotta disagree Len with a PAHS house not being partially underground... that's the whole idea.  To use the thermal properties of the soil's mass and reflect it back into the house... Ok, maybe if you dig under the house initially and put a thermal barrier there - is that what you're implying?

Feel free to disagree I notice there are lots of different thoughts on this and different (working) designs too. The umbrella needs to be there. The house needs to be thermally well connected to the large earth mass (rock is good... sand no so good) but I don't think The house itself has to be below ground level. I also think the house needs to incorporate a lot of mass in it's design. As has been pointed out, having part of the house below level leads to water infiltration.... I don't know though, I see lots of houses with basements which seem to be very dry.

In the 70's one of the dominant solar home themes was gravel bed thermal storage where the entire 'basement' was filled with 3/4 - 1" gravel and the air pockets in between would store tremendous amount of heat/cool... that went the same way as trombe walls and water filled culverts...

dry basements are perhaps a urban phenom where pavement and stormwater runoffs are plentiful.  rural and some suburban homes usually have elaborate sump pumps and drain pits to get rid of subsurface water.

Hi Len:  I hope you're still active in this forum.  I'm working on a project in the tropics right now (indonesia) where we need to design and build a 'cool room' to store cheese and milk only for just a few days.  I'd like to do total passive cooling in a super insulated room (about 4'x8') with earth tubes and then use available river water going through some car radiators to further cool (if needed) the space. I was thinking of your root cellar and sidewalk snow melter in reverse...  bringing cold up from below.

Any thoughts? suggestions?

Len wrote:
thankyou for starting the new thread
The heat transfer fluid has to be liquid down to below -10C(14F?). In my area I may be able to get away with salt water as I don't think it gets down to -18C air temp and the ground even 4 inches down will be warmer. I don't know if the salt would settle out at all or stratify with fresh(er) water on top. I could make it saltier than seawater of course.

But I don't want to avoid freezing temperatures, I want to use them... The coldest temperatures will do me the most good. Avoiding freezing temperatures in this set up would be like avoiding heat in a solar heater 

The first purpose of this set up, is to keep my root cellar cooler, the heating of side walks would be just a bonus... permaculture principle.... try to make any change do more than just one thing (the Len paraphrase). Anyway, the height difference should be around 36 inches, so thermo-siphon should work... and be the least complex. The tube(s) from the lower tank to the top would be straight. I may put a valve in to stop heat penetration in the summer.... but a steel valve would conduct heat just as well as the fluid... hopefully cooling the earth around the lower tank will make up for that.... and the coolest fluid should fall too. I need to find the smallest pipe that will still work to join the two tanks.

Depends on altitude, sky view, cloudiness... maybe latitude too. Even surface colour affects this.

winsol3 wrote:
Hi Len:  I hope you're still active in this forum.  I'm working on a project in the tropics right now (indonesia) where we need to design and build a 'cool room' to store cheese and milk only for just a few days.  I'd like to do total passive cooling in a super insulated room (about 4'x8') with earth tubes and then use available river water going through some car radiators to further cool (if needed) the space. I was thinking of your root cellar and sidewalk snow melter in reverse...  bringing cold up from below.

Any thoughts? suggestions?

Some questions   :

a) What temperature do you envision this cool room being?
b) What is the yearly average temperature at ground level? This is what ground temp will be 20 feet down.
c) what is the temperature of the water from the river?

If a is lower than both b and c.... you need to be looking for other alternatives.

If b is lower than a, then just building the cool room low enough in the earth may be good enough... no insulation under and lots on top.

If c is lower than a but b is higher than a, then the room needs to be insulated all around but may still need more on top.

In any case, shade will help in the form of either a roof or trees. An air space under the roof (the roof being white or at least light colour) so the air can move and not collect heat is recommended (by me )

If your elevation is high enough and your nights get as low as 10C you may be able to use night time radiation to cool a heat transfer fluid. Sort of like a solar water heater but opened only at night with exposure to as much sky as possible. Mirrors can be used to expand sky view if there are trees or building to the side. It is possible to freeze water so use some kind of antifreeze (even salt). I do not know if thermo syphoning will work fast enough or if pumping would help. I would prefer no pump so that if I got up late to close the lid I would not be pumping hot water to my under ground water tank

If this is a pretty dry place, then evaporative cooling may work if all else fails. I am not sure how easy it would be to do with out power but the zeer pot seems to work in some pretty hot places. There are "outback fridges" based on the same principle to look at too. My sense is that scale may improve this technology. That is, bigger is better. A room cooled by this technique may take some time to get cool, but once cool the centre of the room would not need to be cooled just the outside. Adding mass in rocks or water tanks would help too... although they would also make it take even longer to get cool in the first place. The one thing I see is that it will be used to lower the temperature of relatively high mass things like milk and cheese which will start at around 27C (coming out of a cow). The mass in the cool room needs to be higher (10x would be nice). However one works with what they have.

Hi Len:  That is really GREAT advice - thanks!  I knew you'd be keen on this!

A lot of the issues you point out lead me to think we may need an external cooling source-- which may even be as simple as an ice chest inside the cold box. 

I do wonder why you say that the 20' down temp will be same as the average surface ground temp?  I would say that 20' down temp is fairly consistent at 50-60F anywhere in the world?  I believe there's some science to back that up. 

I wish we could do night time radiance... but alas, there's heavy cloud cover almost 24/7... or so it seems.  I'm still trying to find some weather station data on cloud cover somewhere.  We did install a weather station and have some on-site data logging going on.

Are there any limitations on the surface area (size) of the zeer, clay-in-clay pots? 

Thanks again Len!

Len wrote:
Some questions   :

a) What temperature do you envision this cool room being?
b) What is the yearly average temperature at ground level? This is what ground temp will be 20 feet down.
c) what is the temperature of the water from the river?

If a is lower than both b and c.... you need to be looking for other alternatives.

If b is lower than a, then just building the cool room low enough in the earth may be good enough... no insulation under and lots on top.

If c is lower than a but b is higher than a, then the room needs to be insulated all around but may still need more on top.

In any case, shade will help in the form of either a roof or trees. An air space under the roof (the roof being white or at least light colour) so the air can move and not collect heat is recommended (by me )

If your elevation is high enough and your nights get as low as 10C you may be able to use night time radiation to cool a heat transfer fluid. Sort of like a solar water heater but opened only at night with exposure to as much sky as possible. Mirrors can be used to expand sky view if there are trees or building to the side. It is possible to freeze water so use some kind of antifreeze (even salt). I do not know if thermo syphoning will work fast enough or if pumping would help. I would prefer no pump so that if I got up late to close the lid I would not be pumping hot water to my under ground water tank

If this is a pretty dry place, then evaporative cooling may work if all else fails. I am not sure how easy it would be to do with out power but the zeer pot seems to work in some pretty hot places. There are "outback fridges" based on the same principle to look at too. My sense is that scale may improve this technology. That is, bigger is better. A room cooled by this technique may take some time to get cool, but once cool the centre of the room would not need to be cooled just the outside. Adding mass in rocks or water tanks would help too... although they would also make it take even longer to get cool in the first place. The one thing I see is that it will be used to lower the temperature of relatively high mass things like milk and cheese which will start at around 27C (coming out of a cow). The mass in the cool room needs to be higher (10x would be nice). However one works with what they have.

winsol3 wrote:

I do wonder why you say that the 20' down temp will be same as the average surface ground temp?  I would say that 20' down temp is fairly consistent at 50-60F anywhere in the world?  I believe there's some science to back that up. 

Only way to find out is measure. I got my info from all the pages that deal with PAHS. Basically, heat travels through earth at about 1.5 feet per month from hot to cold. When the air temp/ solar absorption heats the earth surface higher than ground temp, that heat starts to travel down at that speed. Of course when the surface is cooler it radiates heat and the heat moves up. Anyway, the temp below the surface of the earth moves up and down with the season until 20 feet below the surface where the two things balance out. It may even be a lot less than 20 feet where the temp swing is less than the US midwest where most of the testing was done.

As I say, the only way to test this is measure for your self. One of those 3 foot compost thermometers might give you some good info if the ground is not too hard. Otherwise digging is the way to go. If you have two years or so, forgo the digging and waterproof and insulate a 20foot circle... after two years the ground level should be close to what it is 20 feet down if the insulation is good enough. I don't get the idea there is that much time available.

After all is said and done, I have not taken my own measurements except our basement only ever seems to get down to 12C unheated. I am only passing on what I have read. Site evaluation would give a better answer.


I wish we could do night time radiance... but alas, there's heavy cloud cover almost 24/7... or so it seems.  I'm still trying to find some weather station data on cloud cover somewhere.   We did install a weather station and have some on-site data logging going on.

Are there any limitations on the surface area (size) of the zeer, clay-in-clay pots? 

Thanks again Len!

I use the CERES data from NASA... http://eosweb.larc.nasa.gov/PRODOCS/srb/table_srb.html

They have almost too many raw metrics, but it's rocknroll empirical data used by all solar developers... has more info on cloud cover and surface temp than you need... just be sure to read their parameters... we haven't figured out yet how to measure low-cloud cover. 

But here on the Indonesia project where I've had to use if for the first time becuase of constant overcast (hey in California there's hardly any clouds for 9 months! )  and it seems to intuitively match.  i've been amazed at the amount of energy solar PV systems get through these thick clouds.

Another think I just learned:  I think is true but deeply hidden in western countries:  indonesia subsidizes it's electricity from 40c production cost to 10c delivery cost.  So ANYTHING renewable is a slam dunk on the production side.  if the government ever lifted that subsidy and seel electricity at the true cost: there'd be instant riots in the streets.

House ventilation is benefited by use heat reclaimers or heat exchangers, (buried or unburied). Time may tell which type proves best.


http://www.heatingandair.com

just a thought on mass storage.. for heat. Have read in several places about using 2 liter bottles filled with water.. the bottles are placed in spaces as high as one can get them near the ceilings so that they can absorb and release heat in a thermal cycle(thermal flywheel effect). Absorbing heat during the day then releasing it at night. Due to the weight it is important to have supporting wall under the bottles. Remember heat rises so the thermal mass is always best near the ceiling.

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

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

Manu nice ideas.. to bad the laws of thermodynamics dont let it work that way.

please, where can i read about the reasons you point?

i'm interesting in it.

i just thought that if pahs works with one storage zone, splitting it in two specialiced ones would be better.


thankyou very much

Manu

just another idea, would it be useful to have an earth tube just for heating the earth?

for instance, one opening within a solar collector, the exit forming a solar chimney (maybe both outside the house) and the Middle forming many "S" in the storage zone.


just thinking

best regards

Manu

think of a thermos if it is hot it keeps it hot if it is cold it keeps it cold.. that is the earth.. that is what it does. The deeper the tubing is buried the closer the air exchange is to the AVERAGE temperature.. Most tubes need to be buried near 6 to 8 ft deep. One can go to 20 foot but that makes digging very difficult. Working in a pit 20 foot deep one really has to worry about cave in ... not good

The shallower the pipe is buried the longer it takes for the ground to recharge from the change of heat from the tube to the earth.. basically because it is closer to the seasonal or even as much as daily temperature. Using tubing as you had suggested where you draw air from outside with an open end also increases the time for the ground to recharge getting back to the outside air temperature. Having a chimney is a great idea because it helps to keep the house fresh with air changes.. but it does not take as much as one might think.

I have been dreaming on this.. and think that a combination of both sealed and open end is likely a good thing so you get natural air convection along with real cooling or heating added via the closed loop portions of the earth tubes.

Best to just think straight lines as ridged piping is straight.. s curves dont do much other than slowing the flow of air.. and one needs as little restriction as you can get. Remember you are talking each tube the size of a bathroom vent pipe 4 inches.. and as you add more pipe loops.. they all are just 4 inch pipe... two things working here.. the optimal size for the pipe and cost for that pipe. Going up to larger pipe has a couple of disadvantages.. one heat exchange between the pipe and the ground.. larger pipe means more surface area.. but you suck the heat or coolith out of the ground to rapidly and then the pipe looses its abilty to to exchange as the ground is no longer acting as a heat sink till it re stabilizes at average ground temp. The other part is cost.. the price of pipe goes up dramatically with each two inch increment.. Around here 4 inch pipe is $7 a length currently.. and the fittings are 3- 5 each.. move to 6 inch and you can expect that to go up to 20 a section.. and 15 to 20 per fitting.. so you have a double negative thing going on..

As to only using the pipe for heating.. that is fine.. it just means you will use it during the winter

Hello again.

First of all, thank you for your kind reply.

There is something I don't understand. When we put an insulation umbrella and a house above it, we modify the "average" temperature at a given depth, tipically raising it from the air average. In PAHS, the house (its exaust gases) and the earth tubes are "used" (among other uses) to modify it, from one season to the next.

So for instance in summer, we extract coolness from the earth by direct contact and through the air crossing the tubes, thus at the same time, heating a little bit the storage zone for the next winter.

The idea is if we have an isolated hot storage zone, we can try to heat it "to the maximun", more than a house would need or be comfortable, (thus the dedicated earth tubes with solar collector and chimney outside the house). Of course similar in winter and a cold storage zone.

This way I think it would be easier to get the balance between summer cooling and winter heating, because you can heat or cool those storage zones independently (to some extend) from the house temperature.

A kind of control system.

Just a thought

Best regards.

Manu

the ground under the umbrella is going to eventually find its new equilibrium.. the idea is that it takes tiime heating and cooling the ground to find the is balance point. but you are always either charging the ground with heat (summer time) or removing heat (winter time)

ONE really simple way of keeping water out of a sub surface house like a pahs structure seems to elude people. Water wants to go to the place of least resistance.  So give it a place to go.  As simple as this sounds people do not install french drains correctly.. 99% of the time they put the gravel and pipe at the same level as the foundation floor.  If one wants to do this you will always be fighting with it.. If you take the french drain and sink it down where the top of the drain field is below the level of the foundation.. it works a lot better.. Think about it.. water runs down hill. so the water is not going to seep UP but will stay below the foundation level.  obviously the drain tile and field must run down the same way that plumbing for dwv pipe has a 1/4 inch drop per foot.. so if you start level with the bottom of the foundation.. that is the high point.. must continue to drop from there.  

The second note is to run a second drain tile about half way up the wall With correct drainage from the pahs umbrella the drain tiles should never show any water flowing out of them.  Remember the idea of this system is you have three layers to shed water from a 20 ft perimeter to the house.  if you did not do this the system likely will fail as the water will wick away any heat that is stored under the umbrella