[Greenbuilding] Solar Water Heater architecture

[Keith Winston]

Hi Corwyn,

I personally wouldn't do a dye in the tank, since then you have a big 
mess when one dye leaks into the other. Propylene glycol is a food-grade 
additive (most people on this list probably ate some yesterday... well, 
maybe not this list...) and typically comes pre-dyed. With your 
arrangement you'll see the solar loop leaking into the tank. Just 
pressure test your domestic circuit every year or so, it's at positive 
pressure and will cause your tank to overflow if it leaks anyway (and 
for the same reason won't pick up much/any tank water anyway).

A fairly simple tank approach can be: a round aluminum, steel, or other 
material tank constructed of a sheet bolted or riveted to itself. No 
bottom. Rest it on level concrete. Fill the inside & bottom with foam, 
say 4" polystyrene (240C melt) or polyisocyanurate (400C melt) board, 
cut it right (say 4" wide pie slices in a roughly 5' diameter tank) and 
it will be very tight. Line the inside with EPDM (temp limit: 250F), 
Either folded so no seams, or carefully seamed (I'd fold, I don't know 
about the glue at high temps, but it's on my research list). All coils 
and fittings enter from the top (there's a cover, also, of course). This 
is much like the tank you can buy through Tarm, which is a nicely-built 
tank from a shop in PA called STSS (no website, but googlable). A 
not-very-useful picture/description can be had here:

http://www.woodboilers.com/heat-storage-tank.asp

If you want a professional liner built for your tank, you can contact 
these folks:

http://www.flexi-liner.com/tank_linings.htm#watertank

They can build it out of anything, including PTFE with a working temp of 
500F (and a price-tag to match).

You could build a drain pan around it that drains to a, well, drain, if 
you wanted to help assure you'll never flood your basement.

When you talk about "movement of heat", I guess you're using this for 
space heating too. Depending on what else is in the loop (multiple 
radiant floor loops, etc.) consider using a primary/secondary loop 
plumbing approach: near infinite flexibility for control, and future 
modification. As for controllers, you're stuck with a computer in the 
loop if you really want total control. But there's some pretty flexible 
control options that can be built out of PLC's and the like. Here's a 
relatively cheap option for a self-built highly flexible (16 I/O + 8 I) 
embedded controller system:

http://www.onsetcomp.com/Products/Product_Pages/Tattletale_pages/2363_TFX_11.html

Remember you might need interfaces for any temperature sensors.

Warmly, Keith


> Open questions for me remain:
> Can I get dyes that can be detected for both kinds of leaks?
> Best method of building the tank (and ensuring that failures don't 
> result in a flooded basement?
> Control systems?  I would like to be able to control movement of heat 
> based on tank temperature, house temperature, time of day, outdoor 
> temperature, season, occupancy level (and probably some others I can't 
> think of right now).
> Cost?
>
> Thank You Kindly,
>
> Corwyn
>
>   

-- 
Keith Winston
Earth Sun Energy Systems
3927 Madison St.
Hyattsville, MD 20781
301-980-6325
keith at earthsunenergy.com
www.EarthSunEnergy.com