[RE-wrenches] Heat dump or Stagnate?

Carl Emerson freepower at freepower.co.nz
Thu Apr 30 02:54:47 PDT 2009


Hi Gang,

 

We are installing our first "steam back" system with a German roof
integrated array 51 SqM (flat plate) from the Wagner Company.
http://www.wagner-solar.com

 

The system is pressured to approx 2 to 2.2 bar.

 

At approx 120 to 125 degrees the glycol/water fluid starts to go from liquid
to gas and the pressure increases.

An expansion vessel starts to compensate for the pressure.

The temperature increases up around 155 to 160C until all the fluid is in
gas form.

The right volume of expansion vessel, and a larger 'pre vessel' and right
pressures are critical to guarantee that the medium is not going to crack
(become acidic) and safely transition back to its original state on cooling.

 

The Wagner company stands behind this approach and we no longer need a
backup UPS as for a standard closed loop system to keep things running
safely during a power failure. Nor do we need to worry about the pH of the
medium.

 

Hope this helps,

 

 

Carl Emerson

Free Power Ltd.

Auckland NZ

 

 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of August Goers
Sent: 25 April 2009 6:47 a.m.
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Heat dump or Stagnate?

 

Hi Troy -

 

We've installed a good deal of Schuco systems with Slim V collectors which

are supposed to utilize steam back. Being a mechanical engineer, I still

have my doubts about the steam back principle but I don't have any real

world data proving it does or doesn't work. I can't say anything bad about

it, however.

 

Our installed systems are all relatively new so it is hard to say how

they'll hold up in the long term. Our first Schuco systems were installed in

2006. We routinely check the glycol ph and haven't found it going acidic yet

although I've noticed the color (Schuco's glycol is pink) is turning a bit

brown. We've also revamped a large system where we disassembled the copper

piping and found quite a bit of dark pink sediment in the rooftop pipes.

 

The bottom line is that the more times the system overheats the faster the

glycol inhibitor is going to degrade in any system. Since all these systems

are so new it is hard to say how long this will take. The danger I see is

that it is easy to forget older systems and before you know it they start

failing. 

 

On another note, Heliodyne is also packaging closed loop glycol systems and

they aren't touting the steam back principle. Their system operates at

higher pressures and use Dowfrost HD. Dow's website indicates that HD is

good up to 325 deg F which is cooking - I doubt flat plate collector

stagnation temps will reach that high at least in our area. See spec sheet

here:

 

http://www.dow.com/PublishedLiterature/dh_0040/0901b80380040bd2.pdf?filepath

=heattrans/pdfs/noreg/180-01315.pdf&fromPage=GetDoc

 

I guess I better get back to work... Anyone else have experience with

degrading systems?

 

Best, 

 

August

 

 

August Goers

 

Luminalt Energy Corporation

O:  415.564.7652

M:  415.559.1525

F:   650.244.9167

www.luminalt.com

august at luminalt.com

 

 

-----Original Message-----

From: re-wrenches-bounces at lists.re-wrenches.org

[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Troy Harvey

Sent: Thursday, April 23, 2009 11:10 AM

To: RE-wrenches

Subject: Re: [RE-wrenches] Heat dump or Stagnate?

 

Apparently this is the "modern" design method used in many european  

systems. It scares me too. But from several sources, this seems to be  

considered one of the most reliable design methods for closed loop  

systems (ie. it works even without electronic controls working, power  

outages, etc).

 

Standard glycol. The main point seems to be the design of the pipes  

and collectors need to facilitate collector draining from the steam  

pushing the fluid back into the expansion tank, so the collectors  

empty themselves.  Its closed loop, but effectively becomes a  

"pressurized drainback" in over heating conditions.

 

Here is a couple of links:

     http://www.aee-intec.at/0uploads/dateien48.pdf

     http://www.suterconsulting.com/CISBAT.pdf

 

I'm hoping to find someone with experience with this kind of system to  

overcome my fears

 

Troy Harvey

---------------------

Heliocentric

801-453-9434

taharvey at heliocentric.org

 

 

On Apr 23, 2009, at 11:04 AM, Dana wrote:

 

> I have only seen boiled glycol turn to a cola like syrup that had to  

> be

> purged and removed.

> 

> What kind of system & glycol is this?

> Where would you expand that much?

> 

> Can you provide a link to this paper?

> 

> We use heat dumps.

> 

> 

> 

> 

> Dana Orzel

> 

> Great Solar Works, Inc

> www.solarwork.com

> E - dana at solarwork.com

> V - 970.626.5253

> F - 970.626.4140

> C - 970.209.4076

> "I'd put my money on solar energy. I hope we don't have to wait 'til  

> oil and

> coal run out before we tackle that."

> -Thomas Edison, in conversation with Henry Ford and Harvey  

> Firestone, March

> 1931

> 

> -----Original Message-----

> From: re-wrenches-bounces at lists.re-wrenches.org

> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Troy  

> Harvey

> Sent: Thursday, April 23, 2009 10:43 AM

> To: RE-wrenches

> Subject: [RE-wrenches] Solar Combi-systems: Heat dump or Stagnate?

> 

> I'm wondering how many of you out there have installed medium sized

> solar hot water systems (6-8 panel) that were designed to stagnate

> during summertime over production as opposed to diverting to a heat

> dump or radiator? The International solar agency has a couple of

> papers that show a properly designed system should be able to stagnate

> in a way that the boiling glycol mix vapors in the panels, purge the

> panels of fluid, turning off the system without degrading the glycol.

> 

> That doesn't seem to be a typical way to design systems in the U.S. ,

> we've usually gone to a heat dump. Does anyone have experience with

> this?

> 

> 

> Troy Harvey

> ---------------------

> Heliocentric

> 801-453-9434

> taharvey at heliocentric.org

> 

> 

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