"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