Bare Tube & Conduction Plates

Mike T., Swampeast MO

[This is under another active post--but it's so long and bizarre that most probably won't see.]

The output of two radiant floors in my house has really troubled me.

Nearly everything between the two (including surface temperature) is nearly identical yet one puts out at least twice the number of BTUs as the other.

Have been tearing myself up trying to figure out why. Think I found the answer and it is extremely simple.

The heat transfer is HIGHLY CONDUCTION based. Copper in thermofin attached to underside of floor.

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Think of an electrical wire conducting electricity. Just because it might be capable of flowing 40 amps does not mean that it IS flowing 40 amps.

The amount that is conducted through depends on the load!

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The amount of conduction through my system VARIES WITH MEAN RADIANT TEMPERATURE!!!! More importantly, this variance is PREDICTABLE AND AUTOMATIC!!!

Were this a suspended bare tube system, this WOULD NOT HAPPEN!!! Such might work--but certainly not in the same way and with the same results!

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Comments/criticisms please! I honestly believe this is HIGHLY important to designing comfortable, efficient and responsive systems!

Boilerpro_3

Hmmmmm?

Are the two floors in identical environments and how are you determining the Btu outputs. I beleive you're right about the MRT. If you've got cold walls and lots of cold glass heat transfer from the surface of the floor will increase until the heat transfer from the tube to the floor is outrun....I suspect it doesn't matter how the heat is getting into the floor from the tube. The floor is acting as the radiator into the room, not the tube under the floor. Oh course, it appears conduction from direct contact will get you the most btu's at a given water temp, so its harder to outrun a conduction heated floor instead of a convection or radiantly heated one.

BP

Mike T., Swampeast MO

One floor has exposure (double window and exterior wall), other has no exposure (internal). Same amount of tube, same amount of plates, same number of bends in tubes, both connected (reverse return) to same supply/return headers.

Output difference as evidenced from delta-t, yet both have nearly the same surface temperature at the floor.

Radiation/convection are both driven by difference in temperature. I don't see how it would be possible to get this sort of output difference if the heat didn't have a direct route of conduction from water through to the floor.

Boilerpro_3

I don't see what you see

I don't see the connection between how energy is delivered into the floor versus how it is delivered from the floor. Once the floor recieves energy it's temperature rises and it begins to release energy to any surface or material that has less energy. It can recieve the energy from any source, hot air blowing across it, radiation from a higher energy source, from direct contact with a higher energy source, or by passing electricity through the material. I suspect that if you ran the same test using another energy source with a different mix of energy transfer characteristics to the floor, you'd still see the same output characteristic.... higher output for a floor in a space with a lower MRT (and probably more convection air current due to air washing down off the cold surfaces). You'll probably see higher water temps, though, in order to keep up with the output of the floor.

Afraid I'll have to sign off now, heading out of town for a couple weeks. I'll catch you later.



BP

Mike T., Swampeast MO

Wait for the book

If I can make it ¾ as understandable as "Pumping Away" I've more than succeeded.

It may yet become "Understanding Heat in All of It's Motions" without turning into "War and Peace".