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??
daestrom wrote:
"Robert Gammon" wrote in message
. com...
daestrom wrote:
"Robert Gammon" wrote in message
. net...
wrote:
Robert Gammon misunderstands again:
snip
Goto www.gfxtechnology.com/GFX-STAR.html and click on Application
Notes and click on the link to Retrofit of an existing Solar Hot
Water Heater.
You sir, need to READ first, before you make accusations that you
cannot back up with facts.
In there he describes a patent pending application of GFX Star in
an industrial process control application.
The models of what happens to the efficiency of his product with
changing potable water flows thru the equipment are there for all
to see.
Okay, *I* read the documents. It is clear that you must have a
separate storage tank for the GFX-star setup to work 'as
advertised'. Only by using a *cooler* separate storage tank is the
setup able to capture the waste heat from 'batch' drains. Once the
storage tank reaches the temperature of the greywater (or exceeds it
in the conventional heater storage tank), performance will drop off.
Well in the Solar Heater Retrofit, HE DOES NOT USE A SEPARATE TANK!!!
Still seems messed up. The water going into the bottom of the GFX is
a mixture of say 2gpm cold water (flow rate set by the shower head),
and 4-5 gpm hot/warm water from the heater bottom (flow set by the
pump). In my book that means the water going into the GFX is *warmer*
than the non-pump setup. And that means the improvement in
heat-transfer you get from the higher flow rate is offset by the
higher temperatures in the freshwater side. Warmer freshwater going
in means warmer greywater going down the drain. And that's a bad thing.
If the circulating pump runs at 4 gpm and the shower at 2 gpm, then it
is crucial to know the tank bottom drain temperature. Using the
application note...
http://www.gfxtechnology.com/GFX-STAR.pdf we see that we can expect
the efficiency to rise from 57% to 67%. But that is based on the
Tcold going into the bottom of the heat-exchanger. So if Tdrain-in is
still our same 100F, and the bottom of the tank temperature at the
recirc pump suction is a warm 90F instead of 55F, then
Without pump
57% = (100F - Tdrain-out) / (100F - 55F)
Tdrain-out = 74.4 F
Tfreshwater out = (100 - 74.4)*2gpm / 2gpm + 55 = 80.6
Total energy gained by freshwater (2gpm*8.33 lbm/g)*(80.6-55) = 426.5
Btu/min
Withpump, first find Tcold into hx...
Tcold = (4gpm*90F + 2gpm*55F)/6gpm = 78.3F
Then repeat calculation for 67% efficiency and new Tcold...
67% = (100 - Tdrain-out) / (100 - 78.3)
Tdrain-out = 85.5F
Tfreshwater out = (100 - 85.5)*2gpm/6gpm + 78.3 = 83.13F
Total energy gained by freshwater (6gpm*8.33 lbm/g)*(83.13-78.3) =
241.5 Btu/min
In this situation, leaving the pump off results in a lower CDR
(efficiency), but more energy recovered from the greywater. Isn't
life just full of wondrous things :-)
To get at least the same energy recovery performance with the pump
running, we would need to be sure the coil inlet temperature is at
least down to...
0.67 = (100 - 74.4) / (100 - Tcold)
Tcold = 61.8F
And to get that with 2 gpm shower flow and 4 gpm pump flow, the pump
suction from the tank bottom must be at or below...
61.8F = (2*55F + 4*Tbottom) / 6
Tbottom = 65.2 F
But the tank bottom temperature is probably going to be close to the
heat-exchanger's fresh-water outlet temperature (that is after all
where the return water to the tank is coming from). So unless the
freshwater exiting the heat exchanger is no warmer than 65.2F, it's a
losing proposition. But if the freshwater out is that low, then
you're losing anyway.
Now, I have no idea what the *real* tank bottom temperature is in this
situation. But if its warmer than 65.2F, then leave the pump off
while showering. Running the pump is still a great way to recover
'batch process' energy and move it into the freshwater system. And
this is still a significant advantage. Perhaps a timer controlled in
the bathroom that inhibits the pump while someone is in the shower
would be the way to go. Then other 'batch' uses can automatically
start the pump on the differential temperature setup.
Improving 'efficiency' but at the sacrifice of temperature
differential isn't always a winning proposition. Beware of salesmen
and their numbers :-(
daestrom