As a phys chemist, you know about Carnot efficiency, reversible processes,
and alladat, and from virtually all thermodynamic considerations, the less
quasi-static a process is, *necessarily*
the less efficient it must be.
Now, you can do thermodynamic damage control, of course, but all other
things being equal, you have *hurt your efficiency*
merely by dint of the
higher instantaneous energy input req'd for on-demand!
Probably equal to the insulation losses of stored hot water. :)
Now, Carnot does not really apply here, as this is simple heat transfer and
not a heat engine, but the same principles of quasi-staticness apply, in the
form of transfer time.
Thus, it is possible, in a simple heat transfer process, to get 100% heat
But that requires a flue gas whose temperature is *ambient*
How does one do that?
Well, with *small*
flames, low combustion gas velocity, long-assed transfer
times, etc. *All inconsistent with On-demand.*
And, with one *long-assed chiminey*
, jack (and yes, chiminey *is*
3-syllable word), and one *long-assed*
coil of copper tubing around sed
long-assed chiminey, for heat reclamation.
Which then creates draft problems, S02 problems (depending on the fuel), and
just overall complexity.
However, for on-demand situations, ELECTRIC energy would in fact be
near-100%, as there are no flue losses.
You just have to factor in the generally higher cost of electricity.
The only thermodynamic consideration for electric on-demand might be the
additional IR drop from high current surges.
And likely shorter filament life, etc.
Note that your system here is sort of the *inverse*
of the more traditional
system where a hot-water tank (or coils), are driven by a hot-water or steam
Here, your "furnace" is driven by the hot water heater.
Which means you might have a considerably larger water mass in your HW
heater than necessary for HW itself--didn't check the details.
Imo, if you are going to pump HW to a heat-transfer coil, those coils might
as well be baseboard units in a room!
Forced air is a pita, AND the losses from those big-assed blower fans are
. Noisy, too.
Mine is 10 effing amps, running all the goddamm time. Convert DAT to btus,
bro, and calc THOSE losses!!
Yes, you can argue that that energy becomes a part of the heat sent to the
house, but it is "low-quality" heat, in the literal entropic sense, but
moreso in the "sensible" sense, where you need heat beyond a certain
temperature to create a comfort range--esp. in a low-mass/low specific
medium such as effing air.
So the current draw of a blow is not a total loss, just not the best use of
the intended energy. imo.
Virtually the same itty bitty circulating pump feeding the fan coil in your
system could feed the whole house!
Wonderfully quiet, efficient, elegant.
Indeed, you got more initial plumbing, but the overall efficiency, from
zoning as well, proly more than makes up for it.
And, you seem willing to take the manufacturers' word on their numbers.
Manufacturers are lying sacks of shit. This is like thermodynamic law.
Just look at mfr's EPA claims for mpg's, and Consumer Reports' numbers.
20-30% difference, across the board.
You in particular could probably well envision the experimental setups
required to test all the explicit/implicit assertions in this system. Do
you really think these effing mfr's go thru the trouble?
Of course they don't. They fukn wing it, at your/our expense.
It's called marketing.
Marketing don't give a flying fuck about facts or experiments.
Not saying this system is not worthwhile, but I think it overlooks more
important HVAC/thermodynamic fundamentals than simple insulation losses of a
It's selling point, is, I think, that it is a little different.
With the nice feature that theoretically you can never run out of HW.
But, sheeeit, Jethro, take shorter showers!
Baseboard hot water heating can also double as chilled water-A/C, with a
drain system built in to collect all the condensate and perhaps recycle
that. A 5-ton A/C can easily produce 50 gallons/day of near-pure
condensate, on a humid day.
Large housing complexes indeed use this system.
Super quiet, efficient, infinitely zonable.
Previous snippy comments aside, actually a very good and interesting post,
altho a little hard to follow, as, first of all, you mixed too entirely
different concepts, that of On Demand, and that of using the HW supply as
the domestic heat source.
Second, imo, I think with anything related to thermo/HVAC, you need to more
clearly state the various premises, how they differ from tradition, and move
along in more bite-sized conceptual increments.
Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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