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What iis best for low temperature solar?

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Posted by AstickfortheMULE on July 28, 2006, 2:43 am
 
Radiant floors, staple up or hot air?   Trying to take as much
advantage of my large volume, low temperature collector and storage.

Probably going with Energie Solair ES roof system, unglazed.  5,000
gallon tank.


Posted by Jeff on July 28, 2006, 11:30 am
 
AstickfortheMULE wrote:

Here's the way it looks to me.

Operating temperatures for radiant will be lower than for forced air.

For staple up, look at the thermal resistance going up. Lower thermal
resistance going up means a lower temperature gradiant for the same
number of BTUs, that means a lower operating temperature and more
extractable BTUs from your sytem before your heat store is too cool.

   All that implies wide contact for the heat spreader. The conductivity
for even a thin sheet of aluminum will be much higher than the wood decking.

   Softwood ~ .75 BTU/(ft2 (T/inch))
   Hardwood ~ 1.2 BTU/(ft2 (T/inch))


   Aluminum ~ 1500 BTU/(ft2 (T/inch)), so for .032" flashing that's
about 4 BTUs/F ft for each inch (at 7" away you still have over a half
BTU). Note that I'm referring to heat spreading *horizontally* from the
pex for a single side. It looks to me that you can use such a thin heat
diffuser, thermal expansion/contraction noise is another issue.

   For US, this looks a good pex supplier:

<URL: http://www.blueridgecompany.com/radiant/hydronic/453  />

   Jeff





    Trying to take as much


Posted by Jeff on July 28, 2006, 9:32 pm
 Jeff wrote:

I meant radiant floor. Radiant radiators require much higher temps to
generate rated BTUs, and forced air is essentially air passed through a
radiator.



Posted by Steve Shantz on July 29, 2006, 6:15 pm
 AstickfortheMULE wrote:

I am about 1/2 way finished installing a staple-up system in my
quad-level house.  Two of the levels have unfinished ceilings, so this
is a feasible project, but not easy to do physically, with all of the
wires and pipes.

I already have hot water baseboard heat, so the basics were all in
place.  The first level that I finished was under my Kitchen, Living
room, Dining room.  This level of the house has too few baseboard
heaters, and so it was cool, especially when very cold outside, or cold
and windy.  To make matters worse, the thermostat was in this area.  My
furnace would go up to 180F (high limit), and the area was still
quite cool.  The other levels of the house would be toasty warm.  After
installing the staple-up under this area, I was able to set an upper
limit of 140F for the water temperature, and could leave the
baseboard heaters out of the loop for all but the very coldest of
nights.  This part of the house has old carpet over about 5/6 of the
floor (not ideal), and linoleum in the Kitchen.  Eventually we want to
remove the carpet and replace with hardwood or ceramic, either of which
should improve the performance.

I'm very pleased with the results.  My furnace is 21 years old, but
even it should run more efficiently at 140 vs. 180F water
temperature.  My longer term goal is to replace the furnace with a
condensing furnace, and save some significant money.

For the staple up system, I used continuous aluminum panels (for
optimum heat transfer), 1/2" PEX, with two runs between each joist, and
reflectix stapled to the joists.  I had turned on the system before the
reflectix was installed, and one could feel the heat radiating down
into the basement.  After the reflectix was installed, I can honestly
say that I cannot feel any heat coming down.  Now this is not an
objective measure of the effectiveness of reflectix, but I can say that
the difference is very noticable.

In my unheated crawl space under the lower mid level, I'm putting the
reflectix about 2" from the top of the joist (stapled to the side...
not particularly easy to do), and 3 1/2" fiberglass bats stapled to the
bottom of the joists.  I think this will be a very effective way to
keep the heat up.

As for the original question (staple-up or hot air), the answer seems
like a no brainer to me.  Radiant floors require lower temperature
water, which works better for solar or for high efficient gas furnaces.

We use a setback thermostat and when I get up in the morning the house
is aoubt 60 F, but the furnace has been running for about 15 minutes
alreadly.  The feeling of a warm floor under my feet when I get up in
the morning is wonderful.  Hot air will NEVER give you a warm floor,
especially first thing in the morning!

Steve


Posted by AstickfortheMULE on July 30, 2006, 1:53 am
 What type of PEX did you use?  What aluminum heat transfer plates did
you use?

Eric


Steve Shantz wrote:


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