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Originally Posted by Mikesolar
AC, It is all great to understand how turbulent and laminar flow affects heat transfer but there is something you forgot to mention. If you increase the diameter, your flow will become more laminar and the reynolds number will drop.
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I think I did address that when I indicated that extra pumping would be required, and I indicated that the increased volume could be achieved with less power (linear increase rather than quadratic increase).
It was after that section that I included my statements on reynolds number, as it needs to be re-calculated. If I failed to make that connection clearly, let me know and I will re-edit.
Quote:
Originally Posted by Mikesolar
The increase in heat transfer is not as great as you may think and you must think of the whole package (tubing, flow rate, concrete....and it ability to transfer the heat) including whether you need to use that heat. Not in this case. Drake is at the low end of the scale and the tubing choice is due to it being free (otherwise I would use 1/2"). He will never need to pump fast enough to get turbulence in the tubing.
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NEVER?
I think this is where the kind of thinking that is needed for Low-Temperature Heating departs from conventional thinking that has worked so well in the past.
Fortuitously, I came across
THIS_PAPER just today, that addresses certain aspects of Low-Temperature Heating. Here is a segment that talks about the need for increased flow rates when using low-temp heating.
I ran into Low-Exergy Heating and this whole different way of thinking when I was researching the possibility of heating my house with solar, in Western Oregon, where I live, where direct winter sun is rarely available. It turns out that even on an overcast day, a solar collector can produce 80 degree F water. So I started researching if it would be possible to do that. I learned that first of all it was necessary to drastically reduce the heating load (this is where Passive House ideas are so useful), and also the heating system itself would need to be substantially different from conventional designs.
So I pursued radical radiant floor designs, and began computer modeling them to see if 80F feed temp (or less) would work. This lead me the the LowEx consortium, and their work. It was during this phase that I was spending a lot of time with the RadiantWorks hydronic modeling program, to see if the physics of radiant floors would allow me to achieve my goal.
It turns out that really close spacings (<= 6") are key. RadiantWorks was not designed to go narrower than 6", so I called one of their Tech Reps on the issue and he said that narrower spacings were required and that
flow rates would need to be increased above what is commonly used, to make it happen.
The interesting thing to me is that the radical approaches to heating with low temperature sources will also have a tremendously positive effect on conventional fuel sources, because far less of them will be required.
Who knows, maybe less of Canada would need become a Sacrifice Zone if we designed heating systems as if the availability of fossil fuels could someday decline.
-AC