[Greenbuilding] PEX location in concrete slab

Mon Oct 2 01:03:01 CDT 2006

These documents have some informative thermal images of radiant floors
followed by articles and research papers on tube depth and spacing.

http://www.flirthermography.com/media/2004-003-Amhaus%20FINAL.pdf
Infrared Applications for Post Construction Radiant Heating Systems,
Eric G. Amhaus and Edward L. Fronapfel, Professional Investigative
Engineers 

http://www.fh-brandenburg.de/~piweb/projekte/thermo_pics/12a_ir_thermo.j
pg

http://www.maverickinspection.com/in-floor%20heating.jpg

http://www.closerlookinspection.com/images/therma1.jpg

http://www.nachi.org/gallery/details.php?image_id=424&mode=search&sessio
nid=48e399068173a3f4b0cd3439c71985dd

http://www.healthyheating.com/downloads/Radiant%20Heating%20Cooling.pdf
Slide four of this presentation has an infrared comparison of four
different sub floor systems.

Useful Research Paper

ASHRAE Research Project 1036, Develop Simplified Methodology to
Determine Heat Transfer Design Impacts Associated with Common
Installation Alternatives for Radiant Tube Spacing and Depth 
http://www.ngml.ksu.edu/research/project_archive/project_archive_publica
tions/ashrae/1036_final_report.pdf#search=%22the%20effect%20of%20radiant
%20tube%20spacing%20and%20tube%20depth%22

Useful Articles:

Depth Perception, by John Siegenthaler, P.E. May 18, 2000 The depth of
hydronic tubing can affect the performance of a heated concrete slab. 
http://www.pmmag.com/copyright/67c66155b6fc7010VgnVCM100000f932a8c0____?
view=print

Is 2 Foot Too Far? By John Siegenthaler P.E. , January 31, 2001, Some
radiant installation can afford to push the envelope.
http://www.pmmag.com/copyright/575d4e5a59fc7010VgnVCM100000f932a8c0____?
view=print

My offices (7000 sf main plus second floor 1500 sf on Q Deck ), both
floors insulated, wwm, tubes on top and pulled into the middle have no
appreciable differences on start up - or should I say no one has
complained or cares. At home I have heated floors and walls. In the case
of the floors, tubes are right on the insulation, counterflow pattern
and I can't tell you where the pipes are by touch during or after start
up.

As a side note: NRCan should also have (fingers crossed) thermal images
from the Ottawa test home this winter comparing forced air to radiant.
Though it doesn't study concrete floors specifically nor tube depth or
spacing it will show thermal patterns, hot and cold spots on start up
and in a steady state condition.

Not sure if this stuff is useful to readers of greenbuilding...if its
too much - let me know.

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Speireag
Alden
Sent: Sunday, October 01, 2006 6:17 PM
To: greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] PEX location in concrete slab

Sgrìobh Chris Green:

>I am now wondering if the aluminum on the top of the foil covered 
>under-slab insul  might be functioning as a heat sink, drawing the 
>heat from the warmer regions under the PEX to the less warm areas 
>between the runs, and thereby helping to 'average out' the 
>concentrations of heat a bit?

     It is certainly doing that to some extent, but I doubt that the 
effect is measurable, and I strongly doubt that it's perceptible.

     The rebar, on the other hand, being right up against the pipe, 
reasonably thick in comparison to the foil, and criss-crossing all 
over the place, is probably doing a dandy job of helping distribute 
the heat.

     I know that a radiant floor will have hotter and colder spots, 
because I've felt them in mine.  However, I have only felt them when 
looking for them with my hand.  I have never noticed them just 
walking around barefoot, except right at the start of the season, 
when the slab is coming up to temperature.  Certainly I've never felt 
them in socks or shoes.

     My floor is rarely actually perceptibly warm at all, even with 
the heat running.  It's just not cold.  An efficient house should 
never require so much heat that the floor can get warm enough to be 
noticed specifically.  The whole house just gradually warms up, and 
unless you investigate, you don't notice the source.

     If I had it to do over again, there are things I would do 
differently, but I would not spend any extra effort or money trying 
to even out the perceived floor temp.

-Speireag.

-- 
Leaves starting to turn
Anticipation shivers
Me as winter comes

-Speireag.

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