This has been on my mind for quite some time. Use black poly-ethelene or possibly it's modified variant PEX, but I don't think the temps would be that high. The idea is pipe suspended from the rafters, the volume of water would be around 10 gallons, but legionella, and condensation seem like issues. Anyone actually tried this, or have any other simmilar poor-man (read cheap guy) solar ideas?
TS
Hi,
This comes up quite a bit, and I think its workable, but maybe not just by hanging a coil in the open attic.
The attic varies quite a bit over the day in temperatures, and can get pretty cool even on summer nights -- this is the log of attic temps in my house in SW MT:
http://www.builditsolar.com/Experimental/Attic/AtticTemps.htm so, in some seasons, an open coil might loose quite a bit of the temperature it gains during the day to cooler attic air at night?
I think (but never tried it) that putting the coil of pipe in an insulated box in the attic, and having a temperature controlled fan (like an attic vent fan) blow hot attic air through the insulated box when the attic hot, but not when the attic is cold might make this scheme work pretty well for three seasons, but probably not in the winter except for a mild climate.
You do need to think about freezing, but the coil in an insulated box might be pretty resistant to freezing.
Given that this makes the whole thing more complicated, I'm not sure it would not make more sense to just pull hot air down from the attic via a duct and blower and use it to heat a coil of pipe (or metal tank) when the attic air is hot. That has the advantage that you can put the coil in a non-freezing location.
Randy uses such a scheme to pull hot air from his attic for clothes drying:
http://www.builditsolar.com/Experimental/AtticToDryer/AtticToDryer.htm
Here is a scheme to use solar heated air over the outside of a metal tank for heating water -- I guess the solar heated air could come from at attic:
http://www.builditsolar.com/Projects/WaterHeating/SolarAirWaterHeater.pdf
The attic air is not likely to get the water up to as high a temperature as a regular solar thermal collector, but that does not mean its not worthwhile -- if warms the water from 50F up to 80F or so, that cuts your water heating energy in half.
If you do this, would love to get some pictures.
Gary