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Old 11-05-09, 12:41 PM   #6
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Default Various Methods of Hydronic Floor Installs...

Originally Posted by Daox View Post
Wow, that would indicate that in slab would be MUCH more efficient. Especially in a heat pump situation I'd imagine.
As I mentioned, the hydronics guy is referring to conditions around here, and the weather is much milder here than in many parts of the country and world (must remember we have an international audience here!). The feed temps would be higher in areas where the heating demands are greater, but the ratios would stay pretty close.

Nicolas Léonard Sadi Carnot

Heat pumps, in their present state of development, have difficulty making feed water temperatures much over 120. And the Carnot theorem indicates that efficiency is increased as Delta T is decreased. So heat pump + staple up hydronic heating is not a good match.

Here's a table of Thermal Conductivity of common materials...

The reason a slab is more efficient is that concrete is a pretty good conductor (k=0.42 to 1.7), at least compared to wood or MDF (k=0.12 to 0.17), etc. Another reason favoring concrete and gypcrete (AKA: 'the wet system') is that the slab is poured over and around the PEX, so conduction from the PEX to the concrete is assured. The aluminum (k=250) plate idea , even with a U-bend in them are not in 100% contact with the PEX... conduction needs contact.

But weight is a big factor with the slab on a suspended floor, and I have been working and testing and researching this problem for nearly a year. I think I may have come up with a way to keep cost and weight down and performance at an acceptable level.

Stay tuned...


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diy, heat pump, hydronic, pex, radiant

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