"IMM" wrote in message ...
"N. Thornton" wrote in message
om...
Mike Mitchell wrote in message
. ..
On 3 Aug 2004 01:37:23 -0700, (N. Thornton) wrote:

Now I'll offer my favoured system.

Outside air is hot in day and cool at night. Houses (brick, block, and
concrete ones) have a lot of thermal capacity. If ventilated heavily
at night, the whole structure is cooled, and day time temps stay much
lower. Biggest temp drop I ever achieved this way was 10C! All for the
cost of a couple of 12" fans.

Where were the fans? The attic? Blowing from where to where?

All I did to get upto 10C was put a 12" deskfan by an open window,
with a 2nd sash open for through draught. It was basically test setup
no 1. There was no attic venting there, and no automated control... do
it all properly for a better result. Note 10C was the max drop I got,
6C was more typical, just from that one measure.


The idea of a sash window (the Georgians had them up to the ceiling) is that
when both halves are opened, hot air in the room rises to the ceiling and
floats out of the window with cooler outside air coming in the bottom.

indeed - but that can be improved on. That original approach equalises
mid air indoor temp to outdor temp. Tops only approach equalises top
indoor air to outdoor air, thus giving you another 1-2C of benefit.


If the "earth tube" is slanting away from the house and the house is on an
incline condensation runs out.

if.... Even on a steep slope it wont all run out.


As with the earth tube, controls need to be in place to detect whether it is
worth drawing in outside air either for heating or cooling.

One thing I found was proper control makes a big difference.


Regards, NT

"N. Thornton" wrote in message
om...
"IMM" wrote in message
...
"N. Thornton" wrote in message
om...
Mike Mitchell wrote in message
. ..
On 3 Aug 2004 01:37:23 -0700, (N. Thornton)
wrote:

Now I'll offer my favoured system.

Outside air is hot in day and cool at
night. Houses (brick, block, and
concrete ones) have a lot of thermal
capacity. If ventilated heavily
at night, the whole structure is cooled,
and day time temps stay much
lower. Biggest temp drop I ever
achieved this way was 10C! All for the
cost of a couple of 12" fans.

Where were the fans? The attic?
Blowing from where to where?

All I did to get upto 10C was put a 12"
deskfan by an open window,
with a 2nd sash open for through
draught. It was basically test setup
no 1. There was no attic venting
there, and no automated control... do
it all properly for a better result. Note
10C was the max drop I got,
6C was more typical, just from that
one measure.

The idea of a sash window (the Georgians
had them up to the ceiling) is that
when both halves are opened, hot air in the
room rises to the ceiling and
floats out of the window with cooler outside
air coming in the bottom.

indeed - but that can be improved on. That
original approach equalises
mid air indoor temp to outdor temp. Tops
only approach equalises top
indoor air to outdoor air, thus giving you
another 1-2C of benefit.

If the "earth tube" is slanting away from
the house and the house is on an
incline condensation runs out.

if.... Even on a steep slope it wont all run out.

It will eventually. Gravity takes over.

Condensation in earth tubes is exaggerated. If there is air moving at a
decent rate inside the tube, the likelihood of condensation occurring is
negligible. Any condensation occurs mainly on the section near the air inlet
to the tube. Having perforated tube at this point will drain away any
condensation away to earth, if it ever forms in the first place.

If you have a "U" shaped tube length, down, along and up into the house, the
first bend at the first downward section maybe could be perforated. The
horizontal section could slope to this bend which is accessible from the
surface by cleaning rods. A small surface mounted pump could take away any
water that accumulates there. Not rocket science and a great benefit using
the tube.

In the UK you would probably find that the tube would give a constant 12-15C
out of the tube, which is ideal for cooling in summer. In winter if 10C air
is coming out of the tube this may be 10C higher than the ambient air
temperature. This piped into an air to air heat recovery heat exchanger
would make the whole system more efficient. If 22C is being exhausted from
the house, the 10C inlet air will be raised substantially and any in-line
duct heating battery will only require raising the inlet air a few degrees.
For most of the year let air, combined with the heat recovery heat exchanger
will probably deliver an air temperature that requires no purchased energy
to run.

An earth tube should have insulation over it and earth over that. It needs
to take its heat from the earth below which has a more stable temperature,
that the earth above which is influenced more from the ambient air.

As with the earth tube, controls need to
be in place to detect whether it is
worth drawing in outside air either for
heating or cooling.

One thing I found was proper
control makes a big difference.

The air system has to be thought out properly.

On Thu, 5 Aug 2004 10:47:21 +0100, "IMM" wrote:

An earth tube should have insulation over it and earth over that. It needs
to take its heat from the earth below which has a more stable temperature,
that the earth above which is influenced more from the ambient air.

Are these earth tubes actually manufactured, or is this all just a
utopian possibility and nothing more? Because they sound amazing and
we should all try it wherever possible.

MM

"Mike Mitchell" wrote in message
...
On Thu, 5 Aug 2004 10:47:21 +0100, "IMM" wrote:

An earth tube should have insulation over it and earth over that. It
needs
to take its heat from the earth below which has a more stable
temperature,
that the earth above which is influenced more from the ambient air.

Are these earth tubes actually manufactured,

Well the pipes are manufactured, you have to join them together and do the
digging.

or is this all just a utopian possibility and nothing
more?

Many earth tubes are in operation. The USA has 100s of them. A google will
bring up many examples and the performance.

Because they sound amazing and
we should all try it wherever possible.

I fully agree.

I did a google: Google in the groups on "Air / Earth Tubes" as the subject
for the whole thread.


I read a number of discussions about earth tubes here and elsewhere. Since
Spring is officially here I thought you might enjoy an update on the air
tubes I had experimented with this Winter.

Background: while installing some electrical and water pipes for an animal
corral I had a trench open so I installed an experimental air tube to bring
fresh air into our house. The
goal was to warm it with the earth's heat since our outdoor air temps are so
low. We heat with wood so our wood furnace chimney acts as an exhaust stack
that draws in the fresh air through the earth air tubes (and any other
cracks in the house .

The air tubes consist of four 4" smooth walled drainage pipes 70' long with
one right angle and a slight bend near the other end. Only one is currently
in use, the other three are reserved for the greenhouse when I rebuild it.
The one that is in use comes in through the cellar wall near the wood
furnace. The intake end of the air tube out in the field is about 5' (?)
below the output side of the pipe in the cellar. The pipes are laid in a bed
of gravel for drainage and perfed pipe was used for the last 20' which
slopes strongly to prevent condensation from pooling in it. The soil depth
of the pipes vary from about 1' to about 4' sloping away from the house.
Above the pipes there is a 3' wide by 2" to 4" thick foam insulation. The
insulation is worth far more than the soil for stopping the cold from coming
down (Soil 1" = R0.1, Foam 1" = R5.0). One interesting note is that in most
places around here the frost depth is several feet. The frost depth here is
only a few inches because we get snow so early and it stays keeping the
ground warm. I have been told that this is typical of high altitude
locations like ours that gets early snows. With deeper frosts the top
insulation would be even more important. We also had a 4' deep pack of snow
that insulated the soil and pipes.

This was a colder than usual winter with the temperature almost never
getting above 0F for January, February and the first half of March. On the
other hand it never got as cold as it has some years (-55F?) The low
temperature was -37F at our house and we had extended weeks of -20F. This
past week (end of March) it finally broke the 32F mark and we've actually
got some bare patches of ground now. Today we got our first rain. So this
has been a good cold test of air warming properties of the air tubes.

The soil temperature never dropped below 39F around the tubes and most of
the time it was up around 45F or warmer. The air temperature dropped to a
low of 32F during the extreme cold period but that was still a lot warmer
than the -37F air outdoors that was being drawn in through the air tube.
Most of the time the air tube air stayed at about 39F to 42F. The air
being brought in from outside was being warmed 20F to 70F degrees which
likely cut our wood consumption considerably. I think it also made the house
feel less drafty since the air for the furnace had an easy time getting in
through the air tube rather than the walls and window cracks.

The tube's insides have remained bone dry of course since this was Winter
and the incoming air lacked humidity and was being warmed. I'll see how it
does and how my drains and slow work come Summer. In a more southern climate
I have read that humidity and condensation within the air tubes can be a
serious problem leading to mold growth.

The research I had read on them suggested using much larger tubes (up to
about 18" diameter) but even the single 4" tube brought a lot of fresh air
into the house. Almost all of the research also suggested much longer pipe
lengths and deeper pipes were required but like one person's notes I had
read I found that even this short length of pipe made a significant
difference in tempering the air. One significant factor may be that I
insulated above the pipes.

One problem we had was snow depth. I did have to dig out the ends of the air
tubes several times because the area I had put them drifted to about 7' of
snow depth which covered the tubes and stopped the air flow.

Ideally I would have more of a slope to work with so that I could get more
thermo siphon and protection from drifting snow.

I was pleased with the results of the air tubes. The house smelled less
smokey, it was less drafty, the fire had a better draw and the air was less
stuffy. Possibly related or not, we
all noticed our skin felt less dry this year and we had fewer colds (1) than
in any previous year and they were less severe which might be attributed to
the fresher air.

This is only one winter of experience, there are still more season's to see
it operating in. Worst case for the summer is I may simply plug it to stop
air draw during the period when
it would be drawing in humidity and depositing it in the pipes. Time will
tell.


another:


Sorry for the confusion there. I meant that there was a gain in the range of
20F to 70F, not that the air was 70F. Rereading it I see how that looked
odd. Maybe this states it better:

1. Typically the air tube air, measured in the cellar coming out of the air
tube, stayed about 39F to 42F;

2. The air going into the tube was typically in the -0F for most of this
winter and varied from a low of -37F with extended periods of -20F;

3. Thus the air was being warmed from the outside temp (#2) to a temp of
about 40F. That makes a rise in temperature of as much as about 70F
( -37F - 32F = 69F I rounded to about 70F). Alternatively, early in the
season, when the ground temps were higher, the gain was only about 20F.
This was limited to the fact that the ground couldn't raise the temp more
than its own temp. e.g., When the outdoor air temp was +25F and the
ground temp was +45F the air coming into the house out of the air tube was
about ground temp (+45F) which was a 20F gain.

Of course, I would love it if the incoming temp were 70F!!! That would
make our house quite cozy. In reality our house is only about 45F to 65F
(depending on the room you're in) in the winter. We sometimes joke about
living in an icebox. But then there is never any problem with food
getting left out and going bad... Butter on the counter stays rock hard!

The time that we got the biggest efficiency and gain from the ground (that
is to say largest difference between input air temp and output air temp) was
when the outdoors air temp was lowest. Since the ground temp probe never
dropped below 32F this suggests to me that we never froze the soil around
the pipe. I had wondered if that might happen.

By the way, I forgot to mention that all temp readings were for about 7am.
That makes a differences some days, especially in March when things started
to warm up. In Jan and Feb it often stayed cold all day. In Nov, Dec and
March the outdoor temp varies significantly if the sun maked it through the
clouds and it wasn't too windy.

Aldo des anyone know what climate not to use an earth tube in? High
rainfall? etc?

I would think that all climates could benefit from air tubes if they are
properly designed to handle the humidity and condensation problems that
would occur in warm wet climates. I have read of some installations in warm
climates, both failed and succeeding. Drainage seems a big issue. I designed
and built for good drainage, possibly over engineered (my tendancy).

I have a collection of links from my reading last fall that I can try and
organize and post if there is interest. This is something I have been
interested in trying for decades. Now that I have a backhoe it becomes
easier to play with ideas. One of my brothers is building a house nearby
this summer (?) and plans to do air tubes so that will provide some more
interesting experience.

"Mike Mitchell" wrote in message
...
On Thu, 5 Aug 2004 10:47:21 +0100, "IMM" wrote:

An earth tube should have insulation over it and earth over that. It
needs
to take its heat from the earth below which has a more stable
temperature,
that the earth above which is influenced more from the ambient air.

Are these earth tubes actually manufactured, or is this all just a
utopian possibility and nothing more? Because they sound amazing and
we should all try it wherever possible.

also see:
http://www.thenaturalhome.com/earthtube.htm

"IMM" wrote in message
...

An earth tube should have insulation over it and earth over that. It
needs
to take its heat from the earth below which has a more stable temperature,
that the earth above which is influenced more from the ambient air.

How is the temperature of the earth below the tube any different to that
15mm higher above the tube ?

On Fri, 6 Aug 2004 23:27:18 +0100, "G&M"
wrote:


"IMM" wrote in message
...

An earth tube should have insulation over it and earth over that. It
needs
to take its heat from the earth below which has a more stable temperature,
that the earth above which is influenced more from the ambient air.

How is the temperature of the earth below the tube any different to that
15mm higher above the tube ?

Hi,

The deeper you go the more stable the temperature is, the temperature
on the surface will follow the air temperature and the temperature
deep below would be near the average.

Even last August, when temps peaked at 38.5°C the average temperature
was still only 17.7°C:

http://www.metoffice.com/climate/uk/2003/august.html

cheers,
Pete.