daestrom wrote:

"Robert Gammon" wrote in message
. com...
Your figures below are very interesting, particularly so for my
application.

65F cold water inlet is darn near IMPOSSIBLE here, much less 55F This
thing, Nick's, and Power-Pipe ALL work MUCH better in cold climates
than warm climates.

So the efficiency does drop with rising cold water inlet temps, and
Dr V admits to the same in his notes on the web site. The
comparisons of different regions of North America illustrate that fact.
Hot side out with balanced flow of coil and waste water will have a
peak temp out of near 90F with cold side at 65F per his web notes.
I am likely to have cold water in closer to 70F or even 75F, so the
storage tank and coil temp should rise to near 90F with a long shower
and/or clothes/dish washer in simultaneous operation.

Waste water will only fall to then about 85-90F on exit from the heat
exchanger. that's good for a septic tank as that is what we will be
using. Boiling water 200F or greater going down the drain will kill
the bacteria in the septic tank.
Hot water out of the dishwasher is/is not hotter than incoming hot
water, correct?? Internal heaters raise the temp to above 140F don't
they??


I think that's an individual washer issue. Many do have internal
heaters to heat water up to 140F. I've seen a couple that recommend
120F hot-water feed, then boost it internally to 140F. But those with
an internal heater often have various cycles and one is an 'energy
saver' mode that inhibits the water-heater. But remember, plain GFX
won't recover any of that. Only a GFX-star or Nick's system would
recover energy from a 'batch' process like a dishwasher that fills and
drains at different times.

For your climate, with very warm inlet water temperatures, it's a
double-edged sword. Yes, it makes these sorts of heat-exchangers less
efficient overall, and they recover less energy from the greywater.
But on the other side, it takes less energy to heat the water in the
first place from 70F to 120F than it would from 55F to 120F (in the
winter where I'm at, cold water inlet runs about 35F-38F).

So the economics of such a system for you is probably not as
attractive as it is for one of us in the 'great white north' ;-)
After all, a 2gpm shower where I am in the winter, without a
heat-exchanger, the greywater is carrying away energy at....

2gpm*8.33 lbm/g * (100-35) = 1083 Btu/minute

For you, it would run more like....

2gpm*8.33 lbm/g * (100-70) = 500 Btu/minute

So my GFX heat-exchanger running at just 50% recovers about 541
Btu/min and can pay for itself in avoided energy costs in under three
years. Your's, even if it runs at 67% can only recover 334 Btu/min.
If it cools greywater outlet to 87F, that means greywater is now
carrying away...

2gpm*8.33 lbm/g *(100-87) = 217 Btu/minute

And you'd be recovering (500-217) = 283 Btu/minute. Makes the payback
analysis a lot worse for your situation than in mine.

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).

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.

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?