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Solar assisted radiant floor heating system - Page 12

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Posted by Gary on January 16, 2007, 3:52 pm
 
nicksanspam@ece.villanova.edu wrote:

Is this some kind of trick question Nick :)

The sun conditions and temperatures for each category are defined on each
collectors report page.
2000 BTU/sf-day for sunny, ...
Ti - Ta = 90F for category D, ...

Or am I missing something?

It seems to me these ratings the SRCC provides are very useful, but very much
underused?

Gary


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Posted by Ecnerwal on January 16, 2007, 10:38 pm
 


There are also multiple sets of data at the SRCC site. Nick may be
looking at the "simplified" or whatever set that does not include the 5
different ranges (A-E) (I think it just reports range C). He's an adult,
he can look for it.

--
Cats, coffee, chocolate...vices to live by

Posted by Alan on February 10, 2007, 7:12 am
 I did exactly what you are planning, and it has worked out fine during
the past two years.  What you are planning is referred to as a
"suspended slab" by the radiant floor company that has a big web site
devoted to this.  What I did was lay 3/4" thick rigid foam with a
vapor barrier on it, NOT bubble wrap, below the tubing and between
treated 2x4 sleepers that were glued and bolted to the original
concrete slab.  If you have a basically dry concrete slab, then as I
do, then I don't see why the cheap stuff at Home Depot, the white
styrofoam junk, won't work.  The foam will hold the pressure.

It was difficult, but I zig-zagged the tubing between the sleepers to
get maximum tube to floor area exposure, and then held the tubing in
place temporarily with strips of rigid foil flashing.  Since I used
300 foot tubes for three zones, I had to try a number of
configurations to get things just right, as I recall.  You want the
tubes to be very much the same length for equal water pressure.  I ran
my system to test it thoroughly.  Then, I mixed a very thick, just
enough water to make it like a thick dough for molding, cement, and
laboriously handpacked over the tubes, and between the sleepers,
carefully removing the temporary strips of aluminum when I knew the
tubes couldn't buckle.  After the cement patching was complete, and
the cement dry, I tested the system again to ensure that the cement
was indeed dry.  Then, I layered plastic sheeting over everything to
prevent any possible moisture from coming into the room.  Given my
treated/glued sleepers and rigid foam, moisture from the original slab
itself is much reduced, but the plastic sheeting provides cheap
insurance against any type of mold problem.

Over that, one can nail down hardwood directly to the sleepers, but I
wanted tile for the heat storage value, so I took two somewhat
controversial extra steps.  I was worried about expansion/contraction
cracks along where the wood sleeper meets the concrete, and since I
live in California, I wanted further separation from the slab before
laying tile.

To resolve these concerns, I screwed thin OSB sheeting to the
sleepers, the same thin stuff used on roofs.  As a subfloor, the roof
sheathing isn't as supporting as flooring, of course, but I didn't
really need complete support due to all that was below.  I just wanted
a continuity of surface material.  In reality, this OSB does provide
considerable support though across 16" on center sleeper spacing
though, helping to minimize concerns that foot traffic might
eventually compress the rigid foam buried below the concrete.   As
insurance against wood rot, I painted the top of the OSB with the
green copper stuff.  I made sure that I marked exactly where the
sleepers were, because over the OSB I put hardibacker for the tile.
Then, I tiled in a normal manner.

My system works well.  I have good room heating, but very little heat
loss between the intake and return manifold temperature gauges.  On
start up in the fall, the system is more responsive than an in-slab
hydronic heat, and the OSB seems to diffuse the heat so that I don't
have "heat streaks".

Good luck...


(the) water heater.

conservation, but also because I want to make a serious

material down, then a snake pattern of PEX tubing, and

using a commercial)floorsystem like that.

avoid more that 10 or 20% of the heat to disappear

submerge in a hard thermally conductive compound ?


Posted by Rob Dekker on February 10, 2007, 7:39 am
 Alan,

Thanks for sharing your experience !
Interesting that I also just posted my findings (elsewhere in this thread) after
3 weeks of this NG tread being dormant...

I have a few questions on your system :
First : How thick is it (including the tile) ?
I count the 1 3/4 inch for the 2x4's, plus 1/2 inch (?) OSB, plus tile mat (?)
plus tile.. That should be close to 3 inch total over
the slab..
Didn't you have problems with your (interior and exterior) doors ?
How about kitchen countertops going up 3 inch, coming up over a window or so...
Was none of that a problem ?

Second : 1 1/2 inch 2x4 minus 3/4 inch foam leaves 3/4 inch space for the
'cement' radiators. 1/2 inch PEX tubing in that space
leaves the cement islands only 1/4 inch thick over the PEX. That's really
thin.... Didn't these things break right away if you put
some load on it (without the OSB).. ? Or when the PEX expands under the water
heat, up when the concrete expands and contracts with
the system on- and off-line ? And might they all be cracked right now ? Would
that be a problem (if they are cracked) ? Do you feel
that the OSB and the tile provide enough floor load support even if the cement
islands were nonexisting...?

Third : When you designed the system, did you consider the alu-fins (to
distribute the heat) instead of the cement islands ? If so,
what made you decide for the cement islands ?
I am very curious about all such trade-offs, since I'm really going to do this
thing !

Thanks

Rob



(the) water heater.

conservation, but also because I want to make a serious

material down, then a snake pattern of PEX tubing,

using a commercial)floorsystem like that.

avoid more that 10 or 20% of the heat to disappear

submerge in a hard thermally conductive compound ?


Posted by Alan on February 13, 2007, 8:07 am
 Rob,

Yes the calculations are more or less correct, although nominal 2x4s
in our area are actually 1-1/2" thick.  The foam simply stops downward
conduction, while the OSB, hardi-backer, and tile contribute to the
thermal store and radiant effect.  The pex is right under the OSB and
barely covered by cement, but once dry the cement hold it fast, and
due to the dry high portland cement mixture that I used, it was
solid.  I had no problems with cracking or the foam settling under the
weight.  Now, I was cautious about the concern you had until I had the
OSB screwed down.  But, really if may crack later, it's still not a
serious problem.  It won't likely break the pex that way.  Some people
use simply sand or granite, but I felt that the better grip of
concrete would make for better conduction from the Pex, and I found
that it does make for a solid floor, so that's why I used just the
7/16 OSB. The main challenge I had before the concrete was in place
was snaking and securing the pex such that I got an ideal use of the
300ft max each tubing pieces to/from the zone manifold, and put into
place without ANY kinks.  Some kinking can be fixed by warming the
tubing, but severe kinks aren't so generous.  I had to replace a
section of tubing because I screwed up and got a kink.  Fortunately,
in the scheme of things, Pex really isn't terribly expensive.  Your
concrete and lumber will cost more than the pex.  Also, be EXTREMELY
careful not to drive a screw through the Pex when laying the OSB or
hardibacker.  If you do, it's not the end of the world, but it will
mean chipping out a section of concrete with a hammer and using brass
couplings to put in a splice--not horrible but not ideal either--then
patching with cement.  Mark out the sleepers very carfully every step
of the way.


We have a split level house, where the lower level was on the slab
foundation while the upper level is on a raised foundation.  The lower
level was always stone cold in the winter no matter how we set the
thermostat.  But, we also tore out the perimeter wall of the
downstairs that faces to a patio area, and added on new and improved
foundation slab with more rebar and a deeper footing on the outside
edge.  So, I put in all new doors and windows anyway.  Reframing a
door and a couple of windows isn't a huge hassle though compared to
the work putting in the radiant floor, unless you have some kind of
weird siding that might be difficult to redo.  The result in our
situation was a slight threshold step down to the patio area (which is
actually protection against flooding) given the thickness of the
radiant floor.  We had 9 ft ceilngs in the original family room area
downstairs, so the loss of 3 inches was insignificant, and actually
made the steps up to the raise foundation part of the house more
leisurely.  I used steps near a double door acessway as the access for
distribution to/from the tank heater that's in a centrally located and
insulated closet.  Whatever cabinetry and furniture we have in this
room was removed and replaced on the flooring.  I looped tubing into a
small bathroom and around the toilet and sink, and back into the main
room, and looped away from an area where I knew I would put a beverage
refrigerator, and so on.  I might have missed the opportunity to
incorporate a heat exchanger from the fireplace.  There are units that
water can flow through to take the fireplace heat into the water,
reducing heat loss from the tank heater, but I was worried that such
could be a failing contraption further down the road.  I wanted to
keep things simple.

Hope this helps.  If you want to reply to my e-mail, feel free to do
so.


after 3 weeks of this NG tread being dormant...

plus tile.. That should be close to 3 inch total over

so... Was none of that a problem ?

'cement' radiators. 1/2 inch PEX tubing in that space

thin.... Didn't these things break right away if you put

heat, up when the concrete expands and contracts with

that be a problem (if they are cracked) ? Do you feel

islands were nonexisting...?

distribute the heat) instead of the cement islands ? If so,

thing !

(the) water heater.

conservation, but also because I want to make a serious

insulation material down, then a snake pattern of PEX tubing,

using a commercial)floorsystem like that.

to avoid more that 10 or 20% of the heat to disappear

? submerge in a hard thermally conductive compound ?


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