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Re: GFX vs home brew - Page 17

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Posted by Robert Gammon on April 22, 2006, 11:29 am
daestrom wrote:

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 $.00/gal, will
electricity prices go back under $.10 KWH, will Propane prices go back
under $.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?

Posted by nicksanspam on April 22, 2006, 12:54 pm

Wrong again.


Posted by Robert Gammon on April 22, 2006, 3:00 pm
 nicksanspam@ece.villanova.edu wrote:

Ok, I stand corrected.

Some long term users of septic tanks were told LONG ago NOT to pour
boiling water down the drain, it hurts the bacteria in the tank.  

While this is true, it is unlikely in the extreme that you could put
enough boiling water down the drain to raise 1000 gallons of waste in
the septic tank by more than a degree or two.

Posted by nicksanspam on April 22, 2006, 3:13 pm

If your 1000 gallon tank were 60 F and perfectly insulated inside
the concrete and you added a gallon of 200 F water, the new temp
would be (200x1+999x60)/1000 = 60.14 F. And bacteria love heat.
Every time you raised tank temp by 10 F (if you could do that),
the digestion rate would double, up to about 130 F.

How can you be so wrong so often? :-)


Posted by Robert Gammon on April 23, 2006, 2:02 am
 nicksanspam@ece.villanova.edu wrote:

Well ground temps are around 70-75 so getting towards 80 and some of
them die off.

I will aim for a larger than 1000 gal tank just to be sure.  And a
larger than normal drain field as this will be a 2.5 acre lot.

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