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Old 02-27-11, 09:52 AM   #81
mrd
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The units conversion is a little confusing. Let's try it this way, with known values to test:

R = t/k
R: Thermal resistance
t: thickness
k: thermal conductivity coefficient

This lists foamed plastic insulation with k=0.03

we are looking for R-value per inch, so t in meters = 1/39.37 = 0.0254
R = (0.0254 m)/(0.03 W/m*K) = 0.847 m^2*K/W

to convert this SI R-value to US R-value, we multiply by 5.682
0.847 x 5.682 = US R-value of 4.81/inch of foam plastic.
This appears correct. Now we just need some k-values of soil to calculate with.

The same page lists dry & wet soil with a range from 0.15 to 4. This is a huge range, dependent on soil moisture. Let's first check these values, in units of US R-value per foot.

thickness, t, of one foot in meters: t = 12/39.37 = 0.3048
R = t/k = (0.3048 m)/(0.15 W/mK) = 2.03 x 5.682 = 11.5 US R-value/ft, best case
R = t/k = (0.3048 m)/(4 W/mK) = 0.076 x 5.682 = 0.43 US R-value/ft, worst case

Can we narrow our range of likely k-values?

IEEE 442-1981, Guide for Soil Thermal Resistivity Measurements
See Figure 3 on page 9. The Y-axis is in units of degreeC*cm/W. We can convert to k-value = 100/y.

I'm going to select two values, 200 and 80.
k = 100/200 = 0.5
R = (0.3048 m)/(0.5 W/mK) = 0.61 x 5.682 = 3.47 US R-value per foot
k = 100/80 = 1.25
R = (0.3048 m)/(1.25 W/mK) = 0.24 x 5.682 = 1.36 US R-value per foot

Now if we look at data listed here, units of thermal conductivity in Figures 5 & 6 are in Btu/(hr ft F), the reciprocal will give us R-value per foot..
1/0.52 = 1.92 US-R/ft for loam
to 1/0.96 = 1.04 US-R/ft for saturated silt/clay
to 1/1.44 = 0.7 US-R/ft for saturated sand

Soil type & moisture will make or break it..


Last edited by mrd; 02-27-11 at 09:59 AM.. Reason: Fixed my calculations, again..
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Old 02-27-11, 10:27 AM   #82
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Hi guys I am new here and only skimmed thru some of these pages. When we built our 2100' house in 06 I put in one 400' length of 1/2" oxygen barrier tubing in the post tension slab just under the kitchen, dining and master bath with ceramic tile. The tubing is 100' too long so it has about 23' of head at 1.5 GPM. I tested it in real conditions very accurately. I overcame it with a bigger pump. I am getting about 1'3 GPM. It is working really good though. It will transfer 9K btu with 100 degree water going in and the house is at 62 degrees which is warm enough for us. It feels more like 68 in here. The floor is spotty though cause my runs are not strait enough. The floor temps run 75 to 81 wich feels good on bare feet. The tile where there is no heat will be about 57 degrees. We only used about 5 gallons of propane and that was when it was 13 below 0 with record lows here in Oklahoma the first week of Feb. I also used very little supplement from our master br water to air geothermal heat and air. We used a total of 1600 KWH in Jan. All elec except the range. And I have two saltwater aquariums. One 70 gallons and one 45. They are running at 80. They use alot of energy with bright coral growing lights. The smaller one has some insulation on it. On top of that we open the BR window at night sometimes. We like to sleep at 52 to 60 degrees. That master bath floor heat migrates into the BR and wil make it too warm. Some times we turn on the Mater only AC! Pobably 20 days in Jan. we did one or the other to keep it cool in there. Our elec is cheap here in Ok. Our bill was 117. The other two BR's are cool, they get no direct heat. Empty nesters. Videos are on YT search StriperEd08. Will add some pics later. Don't have much for the tubing before concrete pour though.
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Old 03-01-11, 12:30 AM   #83
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Quote:
Originally Posted by okpiddler View Post
Videos are on YT search StriperEd08...
If you just paste the URL of your YT page in here on an empty line, the blog will take care of the rest... very handy.

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Old 03-01-11, 12:44 AM   #84
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Quote:
Originally Posted by mrd View Post
Soil type & moisture will make or break it..
Good analysis...

Much of the hydronic lore I have encountered, suggests that foundation insulation is a must and that insulating with foam at least under the outer portion of the heated floor is a good idea. But I think that the cost of energy really tilts the playing field even beyond that.

When figuring payback, I think that it's wise to remember that energy prices are not a static thing, and that they are moving up, not down.

I think it's not unrealistic to estimate that they will be moving up much faster than one might be comfortable with, especially since virtually every major oil field in the world is now in decline.

Also the cost per BTU from Canadian oil sands is very much higher than from conventional oil wells.

I say insulate very well, much better than you think you need, and do it now.

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Old 03-01-11, 08:31 AM   #85
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http://www.youtube.com/my_videos?feature=mhum
I did not isulate the edges of my slab, just unter the tubing. I do not think a whole lot of heat is lost there just by taking readings near the outer walls with IR thermometer. I had taken a video and put it on DVD but am having trouble playing it back Sure wish I would have taken some pics too!
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Old 03-01-11, 11:18 AM   #86
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Default Radiant Precision...

I have come across references to a book called "radiant Precision" by John Siegenthaler.


It's not cheap, but it is available here.

However, I did find a series of Powerpoints that are meant to accompany a CD audio lecture, and they are located here:
Lots of good info, and the price is right.

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Old 03-02-11, 03:56 PM   #87
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Default Update to: Radiant Floor Infra-Red Photos...

Please note that I updated this posting: Radiant Floor Infra-Red Photos... to include Thermal Imaging photo of a continuous aluminum radiant floor product called Warmboard. Although the image was made by a different photographer and with a different camera, the uniformity of the temperature gradient is apparent.

The uniformity of the temperature gradient has pronounced implications for low temperature heating systems (AKA: low exergy), such as heat pumps and solar heating. It is the average temperature of the heat source that heats the room in question and the lower the temperature gradient, the lower the required feed temperature, thus the greater the efficiency.

* * *

Here are some diagrams from Warmboard technical literature that illustrate some principles that I have come to understand, but are not so easy to explain. Please note that I think that company-supplied sales and technical literature should be viewed with a certain suspicion. But since these diagrams illustrate an important principle I am presenting them not to endorse a product, but to illustrate a concept.

Here is a diagram from warmboard technical literature that illustrates the principle of even distribution of heat over the surfaced of a floor:


The diagram implies that smaller heat differences over the surface of a floor will favor lower feed temperatures.

Here is another diagram, also from Warmboard technical literature, that illustrates the impact of feed temperature on heat pump (ASHP or GSHP) efficiency (AKA: COP):


When the feed temperature is lower, the heat pump doesn't need to do as much work (lower lift) and efficiency is increased.

Here is a diagram used to illustrate the effects that floor coverings have on radiant floor performance, and thus feed temperature and thus efficiency. "Rv" means the thermal resistance (R-value) of the floor covering:


If anyone has trouble figuring this chart out, let me know and I'll edit to clarify.

And here is a general graphical summation of the above information:


So am I a Warmboard fan? Not quite yet, but it is the best commercially available product of its kind I have found so far. But I think that manufacturing concerns and pricepoints, leave plenty of room for DIY folks to do even better.

* * *

I have also been doing some research into graphite as a heat transfer medium. I have actually come across studies that conclude that in certain cases, graphite can be a better thermal conductor than copper or aluminum.

Check out this patent and also this brochure and the thermal imaging video below.


Regards,

-AC_Hacker

* * *
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Old 03-06-11, 11:18 AM   #88
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Looking at AC_Hacker's post about hydronic floors makes me wonder....
Could a DIYer just lay down sheets of copper, put 1/2" copper tubing on it,
then allow the tile guys to come in and put down tile?

Not sure, perhaps the tubing could be soldered to the copper plate.
What I don't know is if the tile guys would work without sleepers
to bring the subfloor up to the top of the tubing.

Maybe that's a very naive question.

Likewise the thought, could you do the opposite?
Cut grooves in the subfloor and then prepare copper sheets
with copper tubes soldered to them, and invert them into the grooves?


Does someone make products that do this?
Warmboard looks (from the brief post) like a system including
a subfloor. (But the subfloor for the kitchen is in.... :-)

I'm going to show AC_Hacker's post to the builder
so he understands what I am trying to do.
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Old 03-06-11, 01:36 PM   #89
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Copper doesn't remain the first choice for radiant floor tubing anymore. Cost and some corrosion possibilities have made PEX tubing favorite. So many soldier joints unless one used soft copper. Copper plates would require same amount of contact with piping as Alum/pex I would think. For tile top surface a rough coat would be needed to cover tubing and let dry before tiling should be done if tubing not imbedded in subfloor channels.
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Old 03-10-11, 11:22 AM   #90
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Default Thermal Imaging photos of Radiant Flooring...

Gary over at Build It Solar recently got a Thermal Imaging camera and he sent me some photos he took of his radiant flooring project.

He was interested to actually "see" the effect that 0.018 inch thick plates made to heat radiation patters of a hydronic floor.

Comments

"All the pictures are taken looking down the radiant floor -- there is an about 3/8 thick engineered lumber floor between the camera and the tubes. So, you are seeing the temperatures on top of the laminate floor with the tubes under the laminate."

"The FloorLoopsNS pic #1 is just PEX tube and no heat spreader. The tags on the pictures give temperatures -- so, its 80.2F right over the tube and 75.4F between the tubes."



"The other two show areas where I put the spreader plates in. It's clear that the spreader plate does carry the hotter zone out further. These are the 0.018 inch thick plates.

It looks like the area between plates does drop down significantly, but when you compare it to the area well away from the tubes (the 74.6F spot), the plates apparently do help the floor to run a bit hotter even when you get beyond the plate edge."




(photo below is a detail of the effect of the aluminum spreader plate)



Huge 'Thank You' to Gary for getting a Thermal Imaging camera and sharing this information with the DIY community. We all benefit from this.

Best Regards,

-AC_Hacker

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