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Old 11-17-09, 01:10 PM   #22
AC_Hacker
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Default Thermal Transmisivity Testing...

I have been considering Maxis' method of making a hydronic floor, by building it up, using layers of Sheetrock as the thermal mass material that is between rows of PEX piping. As I understand it, Maxis grouted the channel, under, around and over the PEX to insure maximum thermal conduction.

I like the idea for more than one reason...
  • Lower weight of floor - Definitely a factor for me with my house that was built in 1892 (or earlier).
  • Ease of installation - I haven't worked with cement much and the idea of pouring wet cement onto a floor sounds very challenging.
  • Ease of un-installation - If results are not as positive as I would hope, I want to be able to return the floor to something that resembles its present state.

So, I have been considering the variables, and the physical and thermal characteristics of the mass material seems to me to be a variable worthy of attention.

I really like Maxis' idea of utilizing sheet rock that was left over from previous remodeling, it's a brilliant way to save money and material.

In my case, however I'll be buying my material new, so the choice of material is open. I tried to find values on-line of the thermal transmissivity, or K value. I found that the K values given in various product literature, varied all over the map, and it all made my brain start to ache.

So, I have been doing some initial testing of various wall-board and concrete board products. Here is a photo of my test setup...




This was all just thrown together, so I could get some idea if there was enough of a difference to even worry about.

I decided if there was a significant difference, I would refine my testing.

So the method I followed was to use a heat lamp as the heat source, placed the same distance from my test samples in all tests. The temperatures were measured each second by three thermistors placed 1 inch apart, using my DIY Datalogger. I ran each test for exactly 10 minutes using my Eco-Experimenter's Test Box. The readings for each measurement period were averaged together.


The ambient temperature was measured to be the same for all tests, my mini split does a good job of providing an even temperature. All of the test samples were stored in the same location (my living room), with 'breathing room' around each one. I kept the samples in this room for for four days, so that if there were any unusual temperature or humidity differences, they would even out.

So here I have a graph of the results so far...


This graph is useful only for ranking which material is a better thermal conductor than another, it is not useful for calculating how much better.

The horizontal axis is the "time' axis, the vertical axis is the temperature axis, no scale is implied, however, beginning temperatures were about 70 F and ending temperatures were as high as 145 F. The time duration of the test was about ten minutes. The time shown in the graphic is about eight minutes.

It is clear that in this test, Durock is the best conductor of heat then Wonderboard, and that Sheetrock (both white face and green face, anti mold) has the lowest thermal conductance of the materials tested.

I'll be repeating the tests, and adding other materials that seem appropriate.

Stay tuned...

-AC_Hacker
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Last edited by AC_Hacker; 11-17-09 at 06:28 PM.. Reason: include link to Eco-Experimenter's Test Box
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