[Greenbuilding] [BULK] Re: Solar Water Heater architecture

[Lawrence Lile]

Thanks, Kieth

>I would stay away from ethylene glycol. Toxic. Yuck. Also, how much less
expensive? Also, I've never heard that ethylene glycol never needs
replacement, but that may be because no one uses it anymore, so I don't
hear anything about it. I've always assumed it degrades like propylene
glycol in similar circumstances (i.e. system stagnation).

>You can get good solar-quality propylene glycol for $12/gallon, and then
you dilute it 1:1. 

Last price I found was $16/gallon.  If you know of a cheaper source, I'm all ears. I'm thinking of a system that should use about a quart of propylene glycol, versus the 25 gallons of it I was planning with the earlier design.  

>Also, check how much that tank is going to cost you
to make, at the current cost of copper. 

$200 for a 60' roll of 3/4" copper, and climbing.   $14 for an HDPE food grade 50 gallon drum with a removable lid.  $50 for some fittings and so forth, and then some insulation.  HDPE is good for 110C, way hotter than I can achieve with this system.  A little armaflex ont he outside for insulation.  

>Unfortunately, if anything your
estimate of the cost of a pre-made double-coil tank is probably also
low. which tanks are you thinking of, the only ones I know that are
readily available (sort of) are Vaughn (I hate their heat exchangers,
though I like their tanks) and Stiebel-Eltron (expensive, standard
glass-lined tanks, but well-made and good company). I can't remember any
others right now (except some open-loop tanks like Trendsetter, or the
one that Tarm sells). How big a tank are you talking about?

I am thinking about hacking a tank/heat exchanger out of a 50 gallon plastic drum and two coils of copper pipe.  Michael Hackleman would be proud. 


>PV pumps often won't work too well in drainback systems, since they
don't have much power, and a drainback system has to overcome the
vertical head/friction of the system all day every day, whereas a closed
system doesn't (the fluid coming down counterbalances the fluid going
up: the pump only needs to overcome the pipe & fitting head/friction of
the system).


So it's true.  Looks like a closed loop system is going to be the way to go. I'm going with 1" pipe most of the way, which has negligible pressure drop at 3GPM, the capacity of my pump.  


>As to your icemaker scenario, it depends a lot on your collectors, how
well insulated they are and how much thermal mass they have. But it is a
colorful scenario.


Thank you.  It is much more fun to write about things in a colorful way.  

Generally, what I am envisioning is a rather low-efficiency solar collector system, but low cost.  The collectors were free, I'm repairing them in the driveway as we speak.  They are not-too good quality flat plate collectors, with single glass covers, but with all copper pipe and absorber plate (copper was cheap in the 1980's when my father in law was playing around with these).  With a low-efficiency system, you are trying to harvest the low hanging fruit.  The system may not work at all in the winter, but could produce all our hot water needs in the hottest part of the summer.  

I'm going to rough it in so that a better system could be installed later, if I decide to upgrade.  

 

--Lawrence