[permaculture] any biologists out there?

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Sun Dec 20 06:04:46 EST 2009

paul wheaton wrote:
> Well, a year ago I would have never thought to ask about any of this.
> And when I brought it up before a solar hot water demo about three
> months ago, I was sorta shamed into shutting up.  Reasoning was:  A)
> The gub'mint is always trying to take away our liberties and I must
> have been brainwashed by the gub'mint, and B) Lots of folks have been
> using this sort of thing for years and not a one has ever complained
> about anything of the sort.
> I ain't sore about it.  I just wanna figure out what it takes to do
> the super simple approach that everybody else is doing without getting
> sick.
> Now we're learning that there are very real things to be concerned
> about.  And the information appears to suggest that a lot of people
> are getting sick, but they don't know that it is related to this.
> I'm glad that we're having this discussion!  Powerfully educational!
> Once we get our heads wrapped around the particulars, we might be able
> to figure out solutions so that existing simple systems can work
> safely.
>> Sometimes simple isn't the right solution. The various water borne
>> diseases are a serious matter. Personally, I would not necessarily take
>> a chance with the popular simple solutions unless I could come up with
>> mods that ensured safety of use. Not to say that they wouldn't be safe
>> as designed and used. HS Tarm wood Danish fired boilers send very hot
>> water into a huge tank for long term storage. Into this is immersed a
>> heat exchanger with cold i and hot out ports for clean DHW. I think
>> contamination from pathogen growth occurs when the system is stagnant
>> for long periods or successive short periods. during which the microbes
>> can incubate and propagate.

Man, you sure know how to keep discussion alive! It is a lot of work 
sometimes. Now, to figure out how to make best use of this forum and 
permies.com to move this discussion forward toward toward maximum 

As for the approach described in your first paragraph I choose to ignore 
those types who seem not particularly creative or interested in relating 
to the rest of the back to the land community.

Example: the HS Tarm system. large hot water storage unit with heat 
exchanger supplying DHW.

Simple system solution:
1) inexpensive conventional hot water heater with cold in and hot out 
plumbing; this is where the DHW will be stored that will be used in the 
house for washing and bathing
2) buy a big plastic cistern (often used for water storage these days)
3) run plumbing from collector 1) solar or/and 2) coiled black pvc lines 
in compost pile to the plastic cistern; add circulation pump, backflow 
preventer and cleanout drain valve - this probably should go in through 
the top of the tank
4) also through the top of the tank, drop your heat exchanger into the 
middle of the tank, attached at the top to its plumbing (cold in, hot 
out and insulated) which is run to the house and into hot water heater 
(no pump needed, relies on line pressure for circulation, on demand). 
This line should be hot water type PEX, 3/4" diameter.
5) The heat exchanger consists of 4 foot lengths of 1" straight copper
water line all connected with simple 90degree elbows and 4-6" straight 
sections for the turns; you make and connect together enough of these 
sections to make a circular "column" of copper tubing; inlet and outlet 
are at the top, connected to your plumbing to house. The copper heat 
exchanger should probably be coated with a water resistant durable paint 
or epoxy to prevent it from being etched by acidic water or undergoing 
other surface damage from the hot water; using black paint will help 
with heat exchange. Of course, there may be leaching of copper from the 
exchanger into the hot water but that might be preferable to bathing in 
hot water that has passed through hot pvc pipe, a known problem with 
toxics given off by pvc at high temperatures. You're probably stuck with 
copper because of its thermal properties. I would not use aluminum but 
that is a remote option. Of course black steel pipe can be used too with 
lower thermal transmission qualities.
6) Spray weather-resistant foam insulation all over the tank for at 
least R30 insulation or if the tank is indoors use any other type of 
insulation you choose or put the tank in an insulated closet. Put a 
blanket of insulation around the plumbing (4 pipes) coming out of the
top of the tank (usually 1-2 feet wide); seal the top to keep dirt out.

Compare the cost of this with that of the system without the heat 
exchanger and consider the longevity of the former, convenient 
maintenance issues and the security of knowing you have clean DHW.

The factors affecting the vulnerability of the cheaper system to 
contamination by pathogenic microbes should be considered with an eye to 
designing and building the more expensive system with the HE; i.e. avoid 
obvious mistakes and pitfalls with the better system. Standing water in 
the cheap system undergoing wide temperature swings and remaining 
stagnant for periods of time may be what creates the environment 
favorable for the pathogenic microbes to incubate and propagate. With 
the better system you have water only in the 3/4" lines and what is in 
the hot water heater which likely presents no more risk for 
contamination than normal use of that type of heater using an electric 
element or natural gas - plus you could hook it up to an energy source 
for backup DHW source.


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