"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.

daestrom