"Robert Gammon" wrote in message
. net...
daestrom wrote:

wrote in message
...
daestrom wrote:

The GFX does well with its small surface...

OK, GFX doesn't help with heat recovery for a bath, but great for hot
showers, dishwashing, clothes washing.

...60% is not "great," IMO.

For a total surface area of just (4 in)*pi *60 in /144 = 5.24 ft^2, 60%
is
pretty 'great'.

It might be 3 vs 4", but it's still poor overall performance.

How much surface area does your setup require?

There's no requirement... 300' of 1" pipe is a convenient design choice.


Guess again. If your setup was restricted to just 5 feet long, would its
performance be anywhere near as good as the GFX??? And that's the point.
To get performance on par with GFX, you have to resort to something
several tens of feet long.

Heck, If I had someone build a GFX that was 100 feet tall, I'm sure it's
performance would put your setup to shame. But who has space for 100' of
4" pipe (vertical, coiled or otherwise).

The issue with a 100 foot tall GFX is the required size of the potable
water tubing and the pressure required to get a reasonable flow rate thru
the 100ft stack.

I wasn't seriously recommending a 100' GFX. Just pointing out that 100' of
any sort of piping takes considerably more space than a 5' GFX.


As it is on a 60 inch GFX, manifolding is performed to limit pressure loss
(coil height is about 27 inches each) with the base of each coil tied to
the inlet water, and the top of each coil tied to the outlet.


Yes, that is exactly how mine is constructed. The problem with piping the
freshwater side in parallel is that the two coils form a sort of
series-parallel flow heat exchanger. One heat exchanger cannot heat its
outlet as much because it only receives already-cooled greywater from the
other heat-exchanger. So when it's cooler freshwater outlet water mixes
with the warmer water from the upper one, there is a reduction in overall
efficiency. I can detect this when someone is in the shower by touch alone
on the two coil outlets.

This is the same sort of thing that multiple-pass conventional
heat-exchangers suffer from. Less than ideal, but a compromise of
heat-transfer performance versus hydraulic performance (pressure drop).

I've toyed with the idea of restricting the flow through the lower coil to
improve on this. Would increase the pressure drop some, but not as bad as
the full series model. Some weekend project I may put a throttle valve in
series with the lower coil and play around with different settings.

The engineering drawings on gfxtech's web site clearing indicate an
asymptotic behavior. Adding additional length brings lower and lower
incremental benefit. Still with two S4-40s in series, pressure loss is
about 2.5psi on a 2 gal/hr flow rate. and 80 inches of gfx recovery will
get efficiency up another 5-10% over a 60 inch model and a 40inch height
is easier, in many cases, to find a spot for.

True, but you would need two 40inch heights, or a pumping arrangement.
Since mine is installed in the main waste line for the entire house, pumping
blackwater did not seem very attractive.


daestrom is doing us a great service by pointing out the issues with the
home brew system. I too do not believe that the home brew system proposed
will work as well as a 60 inch GFX to recover waste heat from grey/black
water and pump that heat to DHW and cold side showers.


It could perform rather well. And if I know Nick at all from his postings
over the years, it will cost less than my GFX did, even though I installed
in myself. I'm just trying to keep Nick 'honest' by not letting him apply
steady-state calculations to a transient system. But it does require more
space to install, and may have some maintenance issues.

Hopefully when Nick is done building it, he'll post his performance numbers
(good or bad). Direct measurements and experimentation are always better
than theory.

daestrom
"In theory, theory and practice are the same. In practice, they're
different"