Please explain how methods have improved for heat distribution in energy-efficient structures
I have looked at the marvelous improvements in insulating walls, and the changes in glass performance in windows is spectacular, What I have not seen is a marked improvement in heat distribution. It’s like people watering the garden, the heating industry is still wanting to use impulse sprinklers from the 30’s and what is needed is drip irrigation where the water / Heat is put right where it is needed.
Another example of how important this distribution is to a proper functioning structure is coming on the market with the new surface 4 Low E. The attribute of this product is it gives a really low U value by reflecting IR back into the room. In an example of be careful you might get what you wish for this reflection will restrict the ability of the glass in the window to get heat from the room, therefore it will tend to drop below the dew point, result weeping windows.
The quick and dirty solution for the occupant once they have lowered the humidity to the point it is painful is to put fans to bath the window glass in room air to dry and warm up the inner glass surface.
So with people blindly following the energy path what is or can be done to insure that all inside building surfaces can be kept above the dew point. I do not believe it is reasonable to do this with humidity alone.
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Charlie,
There have been several discussions of the "Surface 4 low-e coating" issue already here on GBA. Here is a link to one of the previous discussions: Surface 4 low-e condensation issues.
The best innovation in heat distribution has probably been focusing on heavy insulation and airtightness. With a great building shell, distribution really becomes a secondary concern unless the layout is like a maze.
I suggest we devote this thread to heat distribution, and refer the surface 4 discussion to the thread Martin linked.
On heat distribution, Nate is right--once the envelope is ~R30, it's hard to maintain a sign a large difference in temperature between rooms, so heat distribution becomes much less of an issue.
As far as innovations, one thing that has greatly improved is that you can now get hydronic equipment with low electric consumption: ECM pump motors like the Grunfos Alpha that use as little as 5 W vs. 80 W or so for conventional pumps, and zone valves from Taco that only use a watt or so vs. 5 to 10 W for the conventional ones.
You could also consider mini-splits an innovation in distribution, as they avoid the need for ducts. They generally rely on the fact that a good envelope makes heat distribution using fewer sources work OK.
Phun phacts with physics: When condensation occurs on a low-E surface as in the surface 4 low-E glass case, the emissivity of the surface soars to that of liquid water.
So while surface fogging may occur, it's inherently self-limiting, not so much a copious-condensation problem, since the surface is no longer reflecting room radiation once it is fogged with a thin film of water. When that condensation occurs it reduces the performance of the window, and the enhanced comfort benefit recedes until it re-evaporates. Surface-4 low-E glass is really variable-emissivity, since it varies with the amount of condensation on the surface.
Raising the temperature of the glass with fans would fix the fogging issue, but that also cuts into performance, since it increases the delta-T across the window. But it would preserve the comfort-factor at temps that might otherwise condense. Expending blower power to achieve that end is likely to reduce net efficiency.