wrote in message
ups.com...
***Responding to things that I believe warrant a response.***


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.

As long as the combustion mixture is ideal, it doesn't matter what the
flame size is.

From a chemical reaction/combustion pov, correct.
From a *heat transfer* pov, absolutely incorrect. Flame size is directly
proportional to gas velocity, which is inversely proportional to transfer
time, and therefore inversely proportional to heat transfer per unit fuel.
Thus, a system capable of pumping out 200,000 btu, to keep the same heat
transfer efficiency, would have to be substantially larger in dimension than
my 70,000 btu system, to accommodate 3x the combustion rate.

Thermodynamically, on-demand is *necessarily* less efficient than
quasi-static (small flame) systems.
Unless the system is made really large.
Then, you are back to square one, cuz you now have so much volume of boiler
HW, that you wind up with the same insulation losses you were trying to cure
in yer HW heater!!


As you comment below, this is nothing more than a fancy heat
exchanger. Good engineering (can't believe I just said that) using a
counterflow heat-exchanger does a good job of extracting energy into
the water.


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* a
3-syllable word), and one *long-assed* coil of copper tubing around sed
long-assed chiminey, for heat reclamation.

Whoa! think about this Heat rises, copper coils surrounding a vertical
chimney do diddly!
The chimney is warm with continuous use. Horizontal mounting allows
some of that heat to warm the chimney and escape into the room.

The only device I claim to be 100 % efficient is the fan coil.

Yeah, but this is a trivial 100%, one step removed from where the relevant
heat transfer problems exist, that is, between the combustion gas/water
interface. You still have that inefficiency (shared with all heating
plants), and then put the coil in hot water--really no different than steam
boilers with an immersed HW coil--which in fact is an "on demand" system,
around for ages, in virtually all apartment buildings.



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
*considerable*.
Virtually the same itty bitty circulating pump feeding the fan coil in
your
system could feed the whole house!

The article was to emphasize a system that could easily integrate into
what most homes have: forced air.

But with questionable benefits. See above. The coil is just one step
removed from the same heat transfer vicissitudes of all gas/oil fired
systems.

I whole-heartedly agree that the same pump could be used for infloor
heating, which is mentioned in the article.


And, you seem willing to take the manufacturers' word on their numbers.
Manufacturers are lying sacks of ****. 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.

All manufacturers lie. But that lie has to be based on something --
ideal conditions, most likely.
Consider that some lie and quote 95 % efficiency but others can only
quote 80 % efficiency for their systems. If they all exagerate by 20
%, the ODHW is still on top.
Price doesn't change; the ODHW is still half the price.

I don't see why it would be that much cheaper.
I got my sears 50 gal HW gas heater for $180.
On sale, of course.


You in particular could probably well envision the experimental setups
required to test all the explicit/implicit assertions in this system.

As I write this sentence, I have developed a procedure to test the
efficiency with a few thermometers and flow meters. It even includes
several redundancy factors and checks. Now, who has money to fund it?

Not that hard. I did it, way back when.
Not with air, tho, but the same principle.
E = m c delta T


But, sheeeit, Jethro, take shorter showers!

You don't have teen-agers, do you?

Well, not post-pubescent boys, who spend 20-30 minutes masturbating, on my
HW dime. Thank gawd....
Must cost a fortune....



A 5-ton A/C can easily produce 50 gallons/day of near-pure
condensate, on a humid day.

It picks up what is in the air, in a mechanical room being blown over
the coils. Wouldn't call that near-pure.
And near-pure water is GREAT for bacterial growth. Just ask any
chemistry lab with a deionizer.

Well, purer than lake/well water, fergodsake.



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 OnDemand, 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.

THANKS! This is exactly what I was looking for. Will post an updated
version shortly.

Looking forward to it. Suggest crossposting to alt.hvac.
Some smart experienced guys over there, but none too flush with manners.
But I'm sure this would generate an, uh, energetic thread.
--
------
Mr. P.V.'d (formerly Droll Troll), Yonkers, NY

Stop Corruption in Congress & Send the Ultimate Message:
Absolutely Vote, but NOT for a Democrat or a Republican.
Ending Corruption in Congress is the *Single Best Way*
to Materially Improve Your Family's Life.
The Solution is so simple--and inexpensive!

entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie,
all d'numbuhs




Roy Jensen