Geothermal Cooling
Kitep
idea I keep coming across is burying pipes under the ground and circulating
air or water through them. Then I read on
http://www.builditsolar.com/Projects/Cooling/Shading/NCSolarCenterCooling13coolng-1.pdf
EARTH TUBES
The earth tube, or earth cooling tube, was a concept that gained popularity
for a while in the late seventies and early eighties. It consists of pipes
buried several feet below ground, where temperatures are lower. Air is drawn
into the house through the underground tubes, which allow it to be cooled
before entering. Experience has shown earth tubes to be unfeasible in North
Carolina for several reasons. The chief problem is the fact that the air
introduced through the earth tubes is typically humid, with the result being
that the occupants of the house are frequently left less comfortable than
before due to the extra humidity. In some homes, they were found to be an
entry way for insects, vermin, and sometimes water during heavy rain storms.
Additionally, the fact that earth tubes increase the possibility of exposure
to radon and other unhealthful soil gases has led to their falling into
disfavor as public awareness of the dangers of these gases has grown.
I figure the insects, vermin, and water is due to poor installation, and not
due to the actual concept. But does it really introduce more humidity and
radon or other unhealthful gases?
For myself, I like the idea of buried PVC pipe laid horizontally,
circulating air. But alas, my yard is the size of a postage stamp. So if I
do anything, it'll probably be liquid-filled vertical pipes. Would that
make any difference to the above listed problems?
Gordon
news:482633cd$0$5107$4c36...@roadrunner.com:
> For myself, I like the idea of buried PVC pipe laid horizontally,
> circulating air. But alas, my yard is the size of a postage stamp.
> So if I do anything, it'll probably be liquid-filled vertical pipes.
> Would that make any difference to the above listed problems?
>
I would say that your biggest problem would be water collecting at the
bottom of the tubes and blocking air flow. To combat that, I would
would design a sump at the bottom of the tubes with a way to pump
them out. I would also investigate using an air/air heat exchanger
instead of trying to directly use the air from the tubes. That would
combat most of your vermin and humidity problems.
David Williams
-> for a while in the late seventies and early eighties. It consists of pipes
-> buried several feet below ground, where temperatures are lower. Air is drawn
-> into the house through the underground tubes, which allow it to be cooled
-> before entering. Experience has shown earth tubes to be unfeasible in North
-> Carolina for several reasons. The chief problem is the fact that the air
-> introduced through the earth tubes is typically humid, with the result being
-> that the occupants of the house are frequently left less comfortable than
-> before due to the extra humidity. In some homes, they were found to be an
-> entry way for insects, vermin, and sometimes water during heavy rain storms.
-> Additionally, the fact that earth tubes increase the possibility of exposure
-> to radon and other unhealthful soil gases has led to their falling into
-> disfavor as public awareness of the dangers of these gases has grown.
-> I figure the insects, vermin, and water is due to poor installation, and not
-> due to the actual concept. But does it really introduce more humidity and
-> radon or other unhealthful gases?
-> For myself, I like the idea of buried PVC pipe laid horizontally,
-> circulating air. But alas, my yard is the size of a postage stamp. So if I
-> do anything, it'll probably be liquid-filled vertical pipes. Would that
-> make any difference to the above listed problems?
If the tubes are well sealed, and just conduct heat though their walls,
then no moisture, radon, insects, etc., should be able to enter.
However, the *relative* humidity of the air will rise, simply because
it is cooled. Conceivably, it may get close to saturation, producing
dampness. You may have to include some sort of drying agent to take
care of this problem.
Radon is a very patchy problem. Some locations are prone to it, others
aren't. Generally, if the underlying rock is something like granite,
then it may release radon into the soil, which may then seep into
buildings. Other kinds of rock such as limestone don't release radon.
If there is radon in the soil, you can keep it out of the house by
sealing the basement well, and using plenty of ventilation to flush any
radon from inside the house to outdoors.
Vertical pipes should work okay, provided you have enough depth of
soil. But why fill them with liquid?
This kind of system works best if you use it in both directions, for
heating in winter and cooling in summer. That way, the heat you take
out of the soil in winter is replaced in summer. If you use it only for
heating, say, the soil will cool over several years, making the thing
useless.
dow
Kitep
"David Williams" <david.w...@bayman.org> wrote in message
news:1210470774.9...@bayman.org...
> Radon is a very patchy problem. Some locations are prone to it, others
> aren't. Generally, if the underlying rock is something like granite,
> then it may release radon into the soil, which may then seep into
> buildings. Other kinds of rock such as limestone don't release radon.
> If there is radon in the soil, you can keep it out of the house by
> sealing the basement well, and using plenty of ventilation to flush any
> radon from inside the house to outdoors.
Hereabouts, we tend to have a bunch of clay. Not much of a radon problem.
I just wasn't sure if vertical pipes would bring it up from the depths :) I
don't think it'll be a problem, and if it is, I imagine a closed system
would keep it from passing into the house.
> Vertical pipes should work okay, provided you have enough depth of
> soil. But why fill them with liquid?
I thought that was how it was done.
I suppose that with the horizontal air-filled one, I read that you could
have a slope in it, so that any condensation will drain into a conveniently
place bucket where the return enters the house. Obviously, an open system.
With a vertical air system, water would accumulate at the bottom of the
vertical tubes - leading to mold, or other problems. Liquid filled would
avoid this problem. Of course, I'm still learning and am open to new
information.
> This kind of system works best if you use it in both directions, for
> heating in winter and cooling in summer. That way, the heat you take
> out of the soil in winter is replaced in summer. If you use it only for
> heating, say, the soil will cool over several years, making the thing
> useless.
Good point. I mostly need it for cooling, as with an average 80% relative
humidy in the summer, a swamp cooler won't cut it. But I do use more
heating than cooling, so I may have to supplement it with some solar
collectors.
Kitep
"Gordon" <go...@alltomyself.com> wrote in message
news:Xns9A9ABF99C218...@199.45.49.11...
> I would say that your biggest problem would be water collecting at the
> bottom of the tubes and blocking air flow. To combat that, I would
> would design a sump at the bottom of the tubes with a way to pump
> them out. I would also investigate using an air/air heat exchanger
> instead of trying to directly use the air from the tubes. That would
> combat most of your vermin and humidity problems.
The water collecting would be a problem. That's why I assume liquid filled
tubes would be better for vertical. I hadn't thought of the sump idea. I'm
guessing several solutions exist, I just need to figure out which would be
the best :)
nicks...@ece.villanova.edu
>-> ... Experience has shown earth tubes to be unfeasible in North Carolina
>-> for several reasons. The chief problem is the fact that the air introduced
>-> through the earth tubes is typically humid
Raleigh has an average wo = 0.0035 #H20/#air humidity ratio on an average
38.9 F January day with a 28.8 min and wo = 0.0149 on a 78.1 F average July
day with a 68.1 daily min. The deep ground temp is 59.3. A tight house won't
need much cooling, but it needs dehumidification. With 80 F and wi = 0.0120
indoors and 30 cfm, it would need 24hx60mx30cfmx0.075lb/ft^3(0.0149-0.0120)
= 9.4 pints per day.
>If the tubes are well sealed, and just conduct heat though their walls,
>then no moisture, radon, insects, etc., should be able to enter.
>However, the *relative* humidity of the air will rise, simply because
>it is cooled...
Concrete stores about 1% of its weight in water as the RH rises from 40
to 60% (its "sorption isotherm") which makes for a low RH in January, if
we don't let the tubes get too cold. Psat = 0.522 "Hg at 100% RH at 60 F,
and w = 0.0035 makes Pa = 29.921/(1+0.62198/w) = 0.167 with 100Pa/Psat
= 32% RH. If the concrete reaches 70 F at 0.0120 (77% RH) in July, it can
store about (77-32)/(60-40) = 2.25% of its weight in water. If we only
need dehumidification in July, we might store 31x9.4 = 291 pounds of water
in 13K pounds of concrete, eg a 4'ID x 13' earth tube with 6" walls, or
smaller tubes with the same weight and more surface.
>This kind of system works best if you use it in both directions, for
>heating in winter and cooling in summer. That way, the heat you take
>out of the soil in winter is replaced in summer.
We might solar heat a house and just use the tubes for dehumidification
and cooling, with a passive thermal chimney and a 1-way passive flapper
valve at the tube inlet that lets outdoor air flow up through the chimney
until the start of the cooling season, then circulate air through the tubes
during the cooling season, then start cooling them with winter air again.
To remove 291 pounds of water with an average w = 0.060 inside the tubes,
we need to move about 291/(0.075(0.060-0.035)) = 155K ft^3 of January air,
eg 5K ft^3/day (3.5 cfm :-) for 31 days, with a 3.5/(16.6sqrt(8(65-38.9))
= 0.015 ft^2 x 8' tall chimney :-) Or a larger chimney, for more cooling.
Simulating lots of 4' tubes and 2 1' rings of soil surrounding them using
hourly local TMY2 weather data, I see a 3-month phase shift with a 2-day
time constant for the soil rings. It looks like a 2'-diameter x 24'-tall
chimney will work.
Nick
Morris Dovey
I've been warned that an "open" air cooling system will, sooner or
later, become a mold source and produce an unhealthy environment. I'd
suggest doing a bit of research in this direction before doing much
spending.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
David Williams
-> bottom of the tubes and blocking air flow.
Yes. In summertime, the ambient air is both warm and humid. If this air
is passed through the cold tubes, condensation will almost certainly
occur. Also, the cool air coming out from the tubes into the house will
be at 100 percent humidity, which won't be very pleasant. So you'll
have to put some sort of dryer, maybe using calcium chloride, somewhere
in the system. I would suggest putting it into the flow *before* the
warm air goes into the tubes. This would make condensation in the tubes
much less likely.
dow
Morris Dovey
> I've been trying to learn about various solar/alternate energy schemes.
Here's another that's a favorite of mine: Use solar radiation to power a
Stirling engine (not a big deal, you can buy "toy" Stirling engines that
come with a parabolic dish) - and use the mechanical energy produced by
that engine to drive a second Stirling engine. The second Stirling
engine can produce below freezing temperatures.
I bought one of the toy engines. When I aimed the dish at the sun it
cranked at over 1500 RPM. When I drove the same engine at 600 RPM with a
hand drill on a summer day, the head immediately acquired a thick
coating of frost. I read later that Stirlings are used in some labs to
produce cryogenic (extreme cold) temperatures.
Now I'm working on a solar-powered fluidyne, which is a Stirling cycle
engine whose only moving parts are air and water. The first application
won't be cooling because that's not where my primary interest lies, but
it will be the second application.
This is yet another approach that you might direct your attention.
daestrom
"Morris Dovey" <mrd...@iedu.com> wrote in message
news:48271471$0$89879$815e...@news.qwest.net...
> Kitep wrote:
>
>> I've been trying to learn about various solar/alternate energy schemes.
>
> Here's another that's a favorite of mine: Use solar radiation to power a
> Stirling engine (not a big deal, you can buy "toy" Stirling engines that
> come with a parabolic dish) - and use the mechanical energy produced by
> that engine to drive a second Stirling engine. The second Stirling engine
> can produce below freezing temperatures.
>
> I bought one of the toy engines. When I aimed the dish at the sun it
> cranked at over 1500 RPM. When I drove the same engine at 600 RPM with a
> hand drill on a summer day, the head immediately acquired a thick coating
> of frost. I read later that Stirlings are used in some labs to produce
> cryogenic (extreme cold) temperatures.
>
Quite right. One application I've seen in industry is 'reclaimers' for
cryogenic storage tanks. A small Stirling cycle machine, driven by an
electric motor is used to re-liquify the gas.
daestrom
Kitep
> I've been warned that an "open" air cooling system will, sooner or later,
> become a mold source and produce an unhealthy environment. I'd suggest
> doing a bit of research in this direction before doing much spending.
My plans exactly. I spent last night learning about heat flow equations.
It's so much nicer to know the actual numbers instead of having to rely on
"people say...." :)
Kitep
<nicks...@ece.villanova.edu> wrote in message
news:g06m2j$k...@acadia.ece.villanova.edu...
> Raleigh has an average wo = 0.0035 #H20/#air humidity ratio on an average
> 38.9 F January day with a 28.8 min and wo = 0.0149 on a 78.1 F average
> July
<much more message clipped>
Thanks. I don't understand most of the numbers in your post yet, but I
saved it so I can test my understanding later, and apply it to my own
city/house.
Guess I'll have to see how a solar chimney works...
Kitep
> Yes. In summertime, the ambient air is both warm and humid. If this air
> is passed through the cold tubes, condensation will almost certainly
> occur. Also, the cool air coming out from the tubes into the house will
> be at 100 percent humidity, which won't be very pleasant. So you'll
> have to put some sort of dryer, maybe using calcium chloride, somewhere
> in the system. I would suggest putting it into the flow *before* the
> warm air goes into the tubes. This would make condensation in the tubes
> much less likely.
In the article I read, the dehumidifying was one of the selling points. In
my town, "hot & humid" is basically one word :) The article did mention
that you don't want water to puddle several times, and made it clear that
for a horizontal air tube you should make sure it slopes downward in the
direction of airflow. That way, the water won't puddle, and the air helps
to push it along. You would collect the water in a bucket/drain where the
return tube enters the house.
Though the more this group responds, the better a closed system sounds.
Kitep
> Kitep wrote:
>
>> I've been trying to learn about various solar/alternate energy schemes.
>
> Here's another that's a favorite of mine: Use solar radiation to power a
> Stirling engine (not a big deal, you can buy "toy" Stirling engines that
> come with a parabolic dish) - and use the mechanical energy produced by
> that engine to drive a second Stirling engine. The second Stirling engine
> can produce below freezing temperatures.
>
<snip>
> This is yet another approach that you might direct your attention.
Still on my to-learn list. I did watch a nice little you-tube video the
other day, which showed a solar powered stirling engine cranking away. I
didn't realize they could produce freezing temperatures themselves.
The thing that bothers me though, is that if this was a good way to go, why
does it seem like no one's doing it? When I google solar cooling, it's all
about evaporative cooling (no good in my humid town), with some "earth
tubes" thrown in too. Maybe it's because stirling engines are buried in
reference 8349...
Morris Dovey
> "Morris Dovey" <mrd...@iedu.com> wrote in message
> news:48271471$0$89879$815e...@news.qwest.net...
>> Kitep wrote:
>>
>>> I've been trying to learn about various solar/alternate energy schemes.
>> Here's another that's a favorite of mine: Use solar radiation to power a
>> Stirling engine (not a big deal, you can buy "toy" Stirling engines that
>> come with a parabolic dish) - and use the mechanical energy produced by
>> that engine to drive a second Stirling engine. The second Stirling engine
>> can produce below freezing temperatures.
>>
>
> <snip>
>
>> This is yet another approach that you might direct your attention.
>
> Still on my to-learn list. I did watch a nice little you-tube video the
> other day, which showed a solar powered stirling engine cranking away. I
> didn't realize they could produce freezing temperatures themselves.
Yuppers - these are fascinating devices. The Stirling cycle is
reversible: If you provide the engine with a temperature differential,
it'll produce mechanical energy. If you provide it with mechanical
energy, it'll produce a temperature differential.
> The thing that bothers me though, is that if this was a good way to go, why
> does it seem like no one's doing it? When I google solar cooling, it's all
> about evaporative cooling (no good in my humid town), with some "earth
> tubes" thrown in too. Maybe it's because stirling engines are buried in
> reference 8349...
Fulton's "Claremont" was /almost/ fitted with a Stirling engine, but it
would seem that engineers consider Stirlings a bit magical for their
liking. I'm not an engineer, but I like things that /work/ and I don't
mind getting my hands dirty.
People don't change established patterns until their pain threshold has
been sufficiently exceeded...
(perhaps $250/bbl?)
...and at that point I'd expect much more widespread use of the
technology. :-)
Kitep
> Kitep wrote:
>> The thing that bothers me though, is that if this was a good way to go,
>> why does it seem like no one's doing it? When I google solar cooling,
>> it's all about evaporative cooling (no good in my humid town), with some
>> "earth tubes" thrown in too. Maybe it's because stirling engines are
>> buried in reference 8349...
>
> Fulton's "Claremont" was /almost/ fitted with a Stirling engine, but it
> would seem that engineers consider Stirlings a bit magical for their
> liking. I'm not an engineer, but I like things that /work/ and I don't
> mind getting my hands dirty.
>
> People don't change established patterns until their pain threshold has
> been sufficiently exceeded...
So very very true.
Jeff
There's some old threads on solar desiccant cooling in this group.
Roughly it is a swamp cooler with the humidity removed by a desiccant (a
brine), the desiccant is recharged by solar heat. Eventually I'll try
that here.
Jeff
David Williams
-> Roughly it is a swamp cooler with the humidity removed by a desiccant (a
-> brine), the desiccant is recharged by solar heat. Eventually I'll try
-> that here.
-> Jeff
Good idea.
You should try to avoid condensation in tubes through which air passes
that you will eventually breathe. Some really nasty organisms can grow
in such places, including the one that causes "legionnaire's disease"
which is often fatal.
dow