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

snip
But on the other hand, you need less energy without any sort of hx for
that shower than the energy I need even *with* a GFX heat-exchanger.

All true, in the Sunbelt (I'm on the fringes as we are wet and hot,
whereas the main body is dry and hot), the energy recovered from a GFX,
GFX Star, Nick's, or PowerPipe is much lower than will be seen in cooler
climates. Still, if we raise inlet water temps to the hot water heater to
about 90F, getting to 140F from 90F is EASY compared to getting from 50F
or 40F to 140F First hour ratings and recovery times are all about
raising water temp 90F above incoming cold temp With only a 50F increase
in feed water temp to meet the 140F spec, tank less, LP, NG, or electric
will spend comparatively little energy maintaining the tank regardless of
application.

Yes, to recover dish/clothes washer heat, we need a pump in the loop and
we may also need a storage tank. The issue with the storage tank is
legionella. However, whenever water warmer than the water in the coils
goes down thru the heat exchanger, whether that is shower drain, sink
drain, toilet flush, dishwasher, clotheswasher, the pump turns on and
circulates warm water thru the storage tank/coils and does so at a
relatively high rate (10-15gph).

Careful, in the control you need to consider if the greywater inlet
temperature is lower than the tank temperature. Just looking at coil
temperature could result in some adverse operation. Maybe not in your
specific circumstance, but in some common situations. For example, for me
in the winter, the coil (located in the basement) is cooler than the living
space. So flushing the toilet with 70F water from its tank, while the coil
is 55F, would start the pump and circulate 140F water from the tank to the
coil. And that would actually end up *heating* the greywater.

So the controls may need to be a bit 'smarter' and also consider the
hot-water tank's drain temperature. Just so you don't start the pump when
the tank bottom drain is warmer than the greywater.


With any hot water demand, the cold supply from city/well flows thru the
coils and into the storage tank. So filling a bath runs 70-75F water into
the bottom of the coils, and about 90F out at the top. Draining the bath,
starting a shower, emptying a hot clothes wash cycle, emptying the dish
washer will start the pump, and we get a blended mix of fresh (70-75F) and
storage water (85-90F). What is the ratio?? If it is 50:50, then water
enters the coils at about 80F and exits the top at near 90F.

And yes the payback period is 6-8 years for me. However, the payback
could be MUCH shorter, depending on what energy prices do over the next
decade. Are we going to see gas prices under $2.00/gal, will
electricity prices go back under $0.10 KWH, will Propane prices go back
under $1.00........... If the trend of the last few years continues, the
payback period even for me, could be 3-4 years.


Well this is certainly true. Energy prices certainly seem to be rising
faster than general inflation, and that means payback on energy conserving
devices of all sorts have better payback.

And one of my goals with this is to take the risk out of sink use. We
sometimes, not often, but sometimes pour boiling water (200F+) down the
drain (i.e. pasta, boiled corn....) That is verboten for a septic tank.
Having a GFX Star in place protects the septic tank as the grey water will
exit the heat exchanger well below the dangerous temps for the bacteria in
the septic tank. i.e.greywater temp, we HOPE will drip below 125 on this
trip thru the heat exchanger.

That's a question for you/ Dr V. Model 200F greywater inlet temp, 70F
cold water inlet to heat exchanger, what is the exiting greywater temp?

If we go with the GFX-star setup, and assume we are not drawing off any
water (hot or cold) while dumping this boiling hot water down the drain, we
could *assume* the pump start will circulate about 4 gpm. But how fast does
the water flow when you dump a large pot of pasta through a collander into
the sink drain?

This is the sort of question we could spend quite a long time trying to
figure out. After all, the sink drain is probably a 1 1/2 pipe, that leads
some distance to the main drain. There is perhaps 1 lbm of cold water
sitting in the P-trap under the sink. Your home may have a 'master trap'
that contains another 4 lbm or so of water. Your sink could be metal. The
piping from the house to the tank are probably 70F (same general ground
temperature as your water supply). The factors are many and various.

But looking at the GFX alone, a G4-60 model has about 110 turns of 1/2" Cu
pipe with a mean turn diameter of 4 1/2 inches. That holds about 11 lbm of
freshwater. And the whole thing weighs in at 40 lbm of Cu when dry. So I
don't think you have much to worry about. Take a *large* pot of boiling
water holding 2 1/2 gallons (20.8 lbm) of 212F water. Mix that with 1 lbm
P-trap water at 70F, and 11 lbm of 70F water in the GFX, and 40 lbm of Cu
(equivalent capacitance as 40 lbm *(0.90 / 1.00) = 36 lbm) at 70F and you
get a mixture at...

(11lbm*70F + 1lbm*70F + 36lbm*70F + 20.8lbm*212F) / (11lbm + 1lbm + 36lbm +
20.8lbm) = 112.9F

Now, the 'pasta water' isn't in contact with the GFX long enough to reach
equilibrium with it, but it will lose a lot of its energy just flowing
through a GFX style heat-exchanger. Combine this with the other factors I
mentioned, and I don't think your septic tank will receive any water over
120F. And considering the volume of a septic tank versus the 2 1/2 gallons
of 'no-longer-boiling-hot' water, I wouldn't be concerned unless you making
pasta for an army and dumping pots of water down the drain every ten
minutes.

daestrom