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Drainback design questions
I am doing my best to design a new drainback solar hot water
system to provide domestic hot water and help heat the 1500sq ft concrete radiant floor in my
house in central Virginia. I know that it will not entirely heat our very insulated passive solar house but I am looking to reduce my fire wood consumption. I want to avoid summer overheating so a
drainback system seems like the best choice.
I have room for (8) 4’x8’ AET 32 panels mounted flat on my 5/12 pitch
south facing roof and am looking to install a 120 gal solar storage tank with
an integrated heat exchanger. Sadly I
don’t have room for a larger tank. I am
hoping to set it up to automatically send the excess heat to the radiant floor
during heating months. For safety I
want to make the currently open radiant floor system a closed system which will
add an extra pump and heat exchanger.
For non heating months I will simply turn off the controller that kicks
heat to the floor so that the system will drain back when the tank hits its max
temp. I am attaching an image of how I
see the system and would appreciate any advice.
A few Questions:
1. is 1" copper the correct sizing for feeding 8 panels or should I save a bundle and use 3/4" pipe
2. It looks like most 120 gal tanks have a 20sq ft internal
coil heat exchanger. Is this enough to handle the heat from 256sq foot of
3. should I add a pressure tank and pressurize the drainback
system to reduce the chance of steam if
the system turns on mid-day and runs fluid through 8 super hot panels
4. is the Taco 009 the correct pump for only 9’ of vertical
head? I calculate a total head of 19’
(9' ft vertical head + 50’ of 1” copper pipe + the heat exchanger + a safety of 4’)
5. any advice on sizing the flat plate heat exchanger for
6. I currently have an I link SP-81 pump controller for the
floor pump and would like to pair it with an aquastat that would kick the floor
pumps on when ever the 120 gal tank hits 140* and off when it drops to
130* any recommendations?
Ok that is enough in the question department for now. Thanks for any advice!