[XCSSA] Solar and Green events in SA

[xcssa@xcssa.org]

On Jul 3, 2007, at 12:01 AM, xcssa-admin@xcssa.org wrote:

> On Tue, May 15, 2007 at 02:27:31PM -0500, xcssa-admin@xcssa.org wrote:
>> I think there ought to be "thermal
>> dumping" capacity (such as a really big outdoor heat exchanger)
>
> There's a tiny Austin company who makes a system - I think it's a heat
> pump system - that uses the water mains as a heat dump.  Basically
> they're buried, and water can carry a lot of heat away (compared to
> air), and so it just exchanges heat with a pipe containing mains
> water, but doesn't actually touch the water, and then lets it go back
> into the mains (theoretically not accruing any water usage costs).

By the way, after talking with a solarthermal water installer at the  
solar fair, I am convinced that I could get a thermal dumping system  
that I would consider satisfactory (if not the best imaginable).  I  
was given three options and three heat dump manufacturers.  The  
typical approach used is a buried system, which might not be the best  
for the always-shifting and cracking clay soil in San Antonio.  But  
there are also air dumpers, though they rely on fans (which could  
fail) and I'd rather have a massive passive air heat dumper.

The installer said they always add heat dumping when they have a  
system designed to provide 100% of the hot water needed from solar heat.

The more usual, and cheaper, approach is to design the system for  
only 70% of needed hot water, then let heat leakage deal with excess  
heat when it arises.  (Of course, that means there's lots of  
temperature variation, which gets pushed to the limit when there is  
maximum solar heat and minimum hot water usage.  The water  
temperature rises until the heat leakage and heat input are in  
equilibrium.  There is a pressure relief valve to handle the worst  
cases.  I don't like this approach because I think it reduces system  
reliability.)

Another trick used is to put the heat transfer fluid into a special  
"fast" mode in which it doesn't pick up or deliver as much heat.   
(That's much better than a "stationary" mode in which the heat  
transfer fluid simply cooks in place.  Though I'm not exactly sure  
how much better.)  Also, you could drain the fluid for a long  
absence.  In fact, the fluid is supposed to be drained and replaced  
every 5 years.  The evacuated tube collectors themselves are said to  
be unaffected by being empty.

So, I think I *could* get what I want, though it's not the usual way  
of doing things.    What I'd probably do is go for a system which  
*could* get away without any heat dumping, and then add air dumpers.   
That way, even if the fans were to fail, I'd still be in the safety  
zone, and never have to rely on the pressure relief valve.


>
> Also, Eneco has a semiconductor technology they're working on that
> does direct conversion of heat to electricity (heat isn't always
> unusable energy, as a steam engine or our demand for fossil fuels
> shows).

Well, that's interesting, thanks.

Charles