http://www.builditsolar.com/Projects/GreyWaterHE/gwinbarrel.htm
I would use a cylindrical plastic drum with close fitting lid...
Where would you find one? Plastic would help preserve stratification...
The lid needs to be large enough to allow putting the pipe coils inside,
and airtight to avoid horrible odors in the house. Our steel lid has a
thermostat and a 1500 W electric immersion heater installed vertically
through it for a planned standalone water heater, which might have a
cylindrical 50' soft copper vs plastic pipe coil in the upper 6" of the
drum. We'd like to have all the holes in the lid, with none in the drum.
Bolt-ring drums are widely available and often free, if not new.
and have the outlet on the side 10% from the top to cope with any
greywater pressure - the water just rises up into the 10% space above.
That would be more difficult to fit in a basement with a drainpipe near
the ceiling, even with a strong pedestal. With 2' of head, our current
version would push up the drum lid with about 400 pounds of force.
These can be close to 100% efficient, vs 50% for parallel flow.
I can, but I said "A flat coil near the top of the water line in the drum
would transfer more heat as hot water rises." That is:- pipes come in
coils, the spiral being fitted horizontal - have the heat exchanger (coil of
pipe) in the hottest part of the drum. A coil in the bottom section of the
drum can coiled, as in the pictures, which preheats, with it connected to a
horizontal spiral near the top water line - all common sense.
Fresh water flows in through a bottom cylindrical coil like ours, then
through a flat horizontal spiral top coil? There isn't much room for that
spiral in our present design, since all the fittings go through the top. Got
any dimensions, areas, flow rates, temperature or effectiveness estimates?
Have the heat exchanger in the mass of water which is hottest for more
efficient heat transfer - all common sense.
Seems OK, if fresh water flows from bottom to top. One web description of
a greywater system in a Manitoba house contains a gloomy flat statement
that it can recover 50% of the heat at best, partly because there's a
plastic film layer between the greywater and the copper pipe coil, in
clean water, but also, they don't encourage stratification, so their
simulations show decreasing effectiveness with increasing greywater volume,
vs a system that allows a large slug of cold greywater to drop to the bottom
and slide out a dip tube without disturbing the warmer water above it.
We want this to be simple, low-cost, and efficient. We planned on external
drum insulation, but now it seems it might all be inside, with beveled kerfs
inside 1" foil-faced "R7.2" foamboard instead of flat open kerfs taped on
the outside. If the average temp in the upper part of the drum is 90 F, with
R10 insulation inside (counting the foil), it would lose 24h(90-60)15ft^2/R10
= 1080 Btu/day to a 60 F basement, small compared to a typical day's 50K Btu
hot water usage. Fiberglass insulation over the lid might be useful.
Nick
