Quote:
Originally Posted by Mikesolar
But the question is......do you need it? A typical 1/2" tube on 8" spacing with 110F water can give 50 btu/ft2. I'll bet Drakes home won't need more than 10-15btu max. There is no need to try to get the most heat out of a tube when it will only make your feet uncomfortable.
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There's a very different way to look at this...
If you make the radiant surface as efficient as possible (closer tubes, larger diameter, turbulent flow, increased volumetric flow, better thermal conduction, etc) you can satisfy your heating requirements with lower temperature (lower exergy) water.
This equates to substantial gains in efficiency, especially if you are using a heat pump. In fact, with a heat pump, linear reductions in feed temperature will result in exponential increases in heat pump efficiency.
With fossil fuels, I think that linear decreases in required feed temp will result in linear increases in efficiency. Still a good thing.
This low temperature heating thing is really phenomenal... who would have guessed that you can use cold air to make your house warm... or cold dirt, or cold water.
And unlike fossil fuels, of which there is an ultimately vanishing supply, there is a vast amount of cold air, and cold dirt, and cold water... the supply is unimaginably large.
Low-Exergy (AKA: low delta-T) techniques really do open up completely new opportunities.
-AC