DTT: Cooling: Radiant

[Toby Anderson <anderstc@nv.doe.gov>]

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Design Topic Thread (DTT): Cooling: Radiant
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Initial Lister:  Toby Anderson  anderstc@nv.doe.gov
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last updated: 01/29/97

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 other listers:
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Purpose:
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This "paper"  will describe passive and non-passive, 
radiant-cooling methods for inexpensively (through 
energy savings) cooling a  strawbale house.

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Table of  Contents:
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0. Listers Opinions
I. Pipes in the slab scheme
   A. Problems with pipes in the slab scheme
   B. Solutions to problems for pipes in the slab
II. Water over a tiled wall scheme (2 sections)
III. Underground heat exchange for pipes

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0. Lister's Opinions
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Because of thier super insulation properties, strawbale houses offer an
unprecedented chance to use passive or really inexpensive solutions in
energy savings for cooling your house. This paper deals with radiant
cooling methods. From the discussion, this basically means cooling using
flowing, cool water, and heat exchangers.

The list's opinion is that condensation on the floor will pose a big problem
when the water pipes are in the concrete slab, altho, some possible
solutions were suggested.

Another promising solution is to have an interior "water wall". The water
would run down the face of say a tiled wall, into a catch basin. The drain
of the catch basin could be attached to a tube. The water in the tube
could be cooled in any and several of several methods. The tube could
be run to a heat exchanger (like a radiator), run underground (at least 10
feet below the surface with possibly cool evaporate air blowing across
it, run through an underground well and thus cooled by ground water, or
run through the cool water of a nearby stream or pond. In death valley at
a tourist trap called Scotty's castle which was build in the 1920's, such a
totally passive cooling wall was built using water from a nearby stream -
it is still being used today.

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I. Pipes in the slab scheme

I've seen some discussion on this mailing on radiant heating systems.
Particularly those with water in pipe in the floor.
What about running cooled water thru the tubes in the Summer to
facilitate  cooling?

I'm in Texas where heating is fairly easy (most of the time), but cooling  in
the Summer is the real problem.  

Any ideas as to whether this would work?
Condensation may be the biggest problem since our humidity is generally
fairly  higi (>80%).

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A. Problems with pipes in the slab scheme

Actually that should be the other way around. If the cooled water
temperature drops below the dew point temperature of the air then you
risk damp floors, moldy baseboards, car problems and bad hairdos.

Mark you answered the question yourself, condensation is a problem. If
the dew point temperature drops below the cooled water temperature
then you run the risk of damp floors and moldy baseboards. 

I am presently installing a hydronic radiant floor heating system in a two
story house with garage below and living quarters above. The owner
wanted to cool the living area so I have come up with a plumbing layout
that will circulate the water from one floor to the other in the cooling
mode. That way the warmer upper floor can loose heat to the cooler slab
floor below. I don't know how much of an effect this will have but will
see this summer.

+++++++++++++++++++++++++++++++++++++++++++
Tim    Chamberlain

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B. Solutions to problems for pipes in the floor

Michael Perry wrote:
I like the idea of using the same "basic" system to heat and cool the
house. This cuts down on costs of installation and maintenance. A
number of years ago, I heard of plans to just pump water through tubes
buried
10' under the back yard of a house. While this has been done using air
chambers to cool incoming air, I haven't heard if it was successful for
cooling water.  I think it was a dairy that successfully used a large pond
to provide cool water in their processing plant, but that wouldn't be
practical for most of us.

You have a good point when raising concerns of humidity, though. If you
experience 80% humidity at 100 degrees, then the dew point would be
of major concern, if inside air were dropped to 75 degrees, and a
dehumidifier would be necessary, and, of course, one of the more
efficient dehumidifers around is simply to run an A/C (heat pump) unit, at
least as a backup unit. In full time use, an A/C unit will take TOO much
humidity out of the air, in many climates.

BTW, I really liked the article. It seems to me that, properly designed, a
large tank of water could be chilled at night, when A/C units work
efficiently, then pumped through the house during the day... in effect
increasing the thermal mass of the home. To control humidity, a
humidistat could be hooked into the same system. When the cooler is
running, the inside air could be circulated through the same system.

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II. Water over a tiled wall scheme

I share your both your home state and (not coincidentally) your interest in
radiant cooling.  You might be interested in an article that I found at:

http://eande.lbl.gov/CBS/NEWSLETTER/NL4/RadiantCooling.html

I too have questions regarding dew point/condensation problems for
which I have not heard definitive answers.  It seems to me that radiant
heating works particularly well in part because the temperature of the
circulated water is only slightly higher (10-15 degrees F) than the
temperature of the room. It seems to my sun-baked brain that running
water that is 10-15 degrees cooler than room temp would tend to reduce
condensation problems, but I'm willing to be corrected by someone who
knows which numbers to run.  It's pretty obvious to me that cooling tubes
in a humid enviornment right up against straw would probably not be a
good combination, unless you really want to do some hands-on research
in Fetid Goo.  

I've also heard of baseboard-type systems that are run at the top of the
wall (I would say crown molding, except that mold is one thing that we're
trying to avoid here) with a condensate pan running below the cooling
pipes.  I don't know about the maintainence part of that kind of a system -
It sounds like it would be destined for eventual failure: clogging or leaking
of the pan, etc.  

It seems to me that a "radiantly cooled" interior wall of some thermal
mass may work.  Then again, we might think in terms of working _with_
the phenomenon, instead of battling against it, and see where that leads
us.  What if we were to design a system that is _supposed_ to
condense moisture from the air _and_ provide radiant cooling?  Any
ideas on that?  

Create a water wall.  It works sort of like a fountain, and not only could it
be functional for cooling, it could also serve as a really nice aesthetic
touch.  

The ones I've seen are vertical walls, tiled (often with 1ft or bigger
marble or granite tiles).  Water enters a trough at the top of the wall, and
spills over, running down the tiles.  Kind of like your own personal
waterfall.  Toss a few plants around for that jungle effect.  

Now cool the water - either directly, by running it through some type of
heat exchange, or by cooling the wall.  So what if it condenses there? 
No big deal, it's supposed to be wet. 

Ok you number crunchers - How big/cool would the water wall have to
be to act as a heat sink for a reasonably sized, very well insulated home
(this is still the SB list, after all) when the outside air is averaging August
in Texas temps?   Let me know if you need real numbers for temps,
humidity, etc to play with, and i'll track them down.  

Bill Christensen
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II. Water over a tiled wall scheme

re:  It seems to me that a "radiantly cooled" interior wall of some thermal
mass may work.  Then again, we might think in terms of working _with_
the phenomenon, instead of battling against it, and see where that leads
us.  What if we were to design a system that is _supposed_ to
condense moisture from the air _and_ provide radiant cooling?  Any
ideas on that?  

unquote

This is the way I would pursue.  Whenever looking at moving energy
around, I get very interested  when there is a phase change somewhere
in the equations.  The liquid/vapour transition point represents 520 more
BTU's/deltaT than direct conduction/convection systems.  This can lead
to designs that yeild useful earth based cooling response even in
greenhouse environments.  If there was some way of directing
evaporative cooled air to subterranean zones *before* entering the
building, then you could concievably have cool *dehydrated* air for use
in the space - no moisture problems there.  The Age Old cooling method
still works too if there is enough mass in the building - open everything
up at night, and keep it closed during the day.

John Cruickshank 

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III. Underground heat exchange for pipes

mperry@efn.org mentioned a heat exchange system that uses
circulation pipes buried 10+ ft underground, or in a pond.   Since the
temperature of the earth
10' below the surface remains essentially constant year round (65
degrees here in central texas, 55 degrees in Iowa, and probably a heck
of a lot colder in Rob Tom Land), there is the added efficiency advantage
of pumping the heat from your home into a cool place, rather than the 110
degree in the shade outside air.  Or conversely, pumping heat out of 60
or so degree thermal mass in the winter, instead of trying to use a heat
pump against cold winter air.  ("perversely" in the case of Rob Tom).  

The basic formula that I've heard is 200 ft of 1" tubing for each ton of
heat exchange.  There are several installations in my area that have
used this kind of a system, drilling a series of 200' wells, slipping a loop 
 of heavy polyethylene tubing in, and backfilling.  I haven't heard a whole
lot about relative cost benefits.  

Bill Christensen

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