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Excessive heat build-up

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Posted by Alan on February 24, 2006, 8:28 am
I've got a radiant floor system in an "open-loop" design, meaning that
the fresh water intake circulates through the radiant floor before
entry into the natural gas fired tank water heater.  The radiant and
DHW are both heated by the water heater.  But, I'm interested in
pre-heating the water from a roof top vacuum tube type solar system.
I'd rather skip the expense of a sizeable second water tank, for which
I have no room really, a tank that could also become stagnant and prone
to Legionnaires bacteria build-up.  I'd also like to skip the expense
of the glycol and heat exchanger option.  I want maximum winter solar
heat for the floor, but in the summer California sun could easily
produce more heat than even the hot water heater could handle.  I also
want to avoid the complication and expense of a heat dump system.  Does
anyone know about designing some kind of automatic awning that would
shade the solar system on the roof, effectively shutting down the solar
heat, when the temperature in the hot water tank gets too high?  It
seems to me that a retractable awning system shouldn't be mechanically
difficult to design, or is it?

Posted by nicksanspam on February 24, 2006, 1:59 pm

Perhaps you can just turn off the pump...


Posted by louie on February 24, 2006, 2:56 pm
 Nick wrote:

I'm certainly no expert on solar panels, but wouldn't that allow the
panel to build up too much heat?  I thought you have to either shade
them or dump the heat somewhere.  Especially vacuum tube panels, since
they're pretty efficient at gathering heat; they could theoretically
get hot enough to boil the water contained in them.  Of course, maybe
there are panel/tube designs that take this into account.

Posted by Alan on February 24, 2006, 3:53 pm
nicksanspam@ece.villanova.edu wrote:

Well that's another option, I suppose and certainly a cheaper one.  I
wonder though what will happen to the system on the roof.  Some Chinese
built evacuated vacuum tube systems have a small secondary tank on the
roof with a pressure release valve, but if the releave valve opens then
hot water and air are lost, right?  Isn't that bad for the system and
the water supply?

Posted by nicksanspam on February 24, 2006, 7:58 pm

How about an unpressurized tank with supply and return pipes underwater
and a small hole above the water line to allow a slow draindown?


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