<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.6002.18332" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial size=2>It's drainback, draindown systems have largely been
abandoned because the valves that were supposed to allow household water to
drain out of the panels typically failed, and the panels plumbing froze and
broke. I agree completely that solar water heating is cost effective, especially
DIY. My PV pumped closed loop glycol system has been producing most of our hot
water for 20 years now, built from an early 80's collector, locally built heat
exchanger tank, and a Zomeworks matched PV panel and pump. <A
href="http://www.builditsolar.com/Projects/WaterHeating/DougsSolarWater.htm">http://www.builditsolar.com/Projects/WaterHeating/DougsSolarWater.htm</A> Since
I sized panel to tank to usage well, no heat dump is needed. An easy way to dump
excess heat, assuming the typical situation where the storage tank is below the
collector, is to use a "vacation bypass valve". Closed loop systems in the
configuration I described above have a check valve to prevent nightime
thermosyphoning, losing tank heat to the night sky. Just plumb in a full flow
valve around the check valve, and the need for solenoids and running heated
water down a drain is eliminated. Doug</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>
<DIV><FONT face=Arial size=2><A
href="http://www.builditsolar.com/Projects/SolarHomes/Doug/DougsProjects.htm">www.builditsolar.com/Projects/SolarHomes/Doug/DougsProjects.htm</A></FONT></DIV><FONT
face=Arial size=2><A
href="mhtml:{CA288A34-4824-4A3B-B831-4C742FE39715}mid://00000471/!x-usc:http://www.builditsolar.com/Projects/SolarHomes/Doug/DougsProjects.htm"><FONT
face="Times New Roman" size=3></FONT></A>
<DIV><BR><BR><A
href="http://www.youtube.com/user/sundug69">http://www.youtube.com/user/sundug69</A></DIV>
<DIV> </DIV></FONT></DIV>
<DIV><FONT face=Arial size=2><FONT face="Times New Roman"
size=3></FONT></FONT> </DIV>
<DIV><FONT face=Arial size=2><FONT face="Times New Roman" size=3>Date: Fri, 7
Jan 2011 11:42:52 -0600<BR>From: Lawrence Lile <</FONT><A
href="mailto:LLile@projsolco.com"><FONT face="Times New Roman"
size=3>LLile@projsolco.com</FONT></A><FONT face="Times New Roman"
size=3>><BR>To: "Environmentally-preferable design, construction,
building<BR> elements"
<</FONT><A href="mailto:greenbuilding@lists.bioenergylists.org"><FONT
face="Times New Roman"
size=3>greenbuilding@lists.<WBR>bioenergylists.org</FONT></A><FONT
face="Times New Roman" size=3>><BR>Subject: Re: [Greenbuilding] one more
pleasure (or not) of heating<BR> with
wood<BR>Message-ID:
<<WBR>AC254829C2A6324CB4DF94CED1DB37<WBR>FB6638A0656E@exchange><BR>Content-Type:
text/plain; charset="us-ascii"<BR><BR>Lynelle,<BR><BR>Greetings from Missouri,
where we are treated to a month of clouds in a typical November. Solar
pre-heat can be one of the most cost-effective solar installations if done
right, even here.<BR><BR>Good solar panels can boil water! I've seen this
happen, it is real. They can definitely produce higher temperature water
than you need under the right conditions.<BR><BR>There are two ways to get rid
of excess heat in the summer, if you don't have the luxury of a hot
tub:<BR><BR>1. Don't make excess heat. Use a drainback (or is it
draindown? I can never keep these two terms straight) system that leaves
the collectors dry when heat is not required. The water drains into a tank when
not needed. This uses a more complex controller, but eliminates need for
antifreeze in your collectors, even in Ontario. This is really a very
straightforward solution. If I built another solar water heater this is
what I would do.<BR><BR>2. Have a heat-dump circuit. In a glycol
(antifreeze) collector, the controls can be really simple - a little pump run by
a solar cell. Size the system so that in the summer it matches your
typical usage, and it won't overheat under normal conditions. But if it
does overheat, then you will need a solenoid valve and a little control that
dumps domestic hot water on the hot side of your solar tank straight down the
drain. If your system is sized correctly, this will almost never be used,
so it is not a big waste. Dumping 10 gallons will cool off your solar storage
tank a lot, and the heat was free anyway. I've wasted more than ten gallons
trying to wash my dog.<BR><BR>3. Throw a tarp over the collectors when you are
going on vacation, as I did before I installed the heat dump. There is no
good reason to do this except for desperation born of poor
planning.<BR><BR>There are arguments pro and con for each system.<BR><BR>You
always need a tempering valve after a solar water preheater to eliminate any
risk of sending scalding water to someone in a shower.<BR><BR>If you can
generate all of your hot water in the summer, and then 30% or 50% in the winter,
you probably have a system that has the optimum payback.<BR><BR><BR>--Lawrence
Lile, PE, LEED AP, CEM</FONT><BR><BR></DIV></FONT></BODY></HTML>