solar thermal pumps [RE-wrenches]

[Jeffrey Wolfe, Global Resources]

Our experience with glycol (we've standardized on DowFrost / DowTherm at 
60%) is that is DOES slush, but that the March pumps we've been using will 
pump it when the day warms up. The hardest part to get moving can be the 
underground piping (no sunshine on it), but the underground in our systems 
has always received heat from the house basement, so the worst pipes are in 
the spaces behind the collectors.

I believe that pushing this cold slush does wear the brushes faster, 
resulting in more maintenance.

If a DC pump must be used, seriously look at Windy's. If you must go 
brushless (and I understand...) then you really must go AC.

The advantage of PV direct seems to fad on the larger systems. As the size 
increases, having one controller doesn't seem like a big added complexity.

Pipe all the collectors in parallel as Smitty says. They'll give you more 
BTU. Otherwise you're heating progressively hotter water in each collector, 
cutting efficiency in each one.

Provide some means to balance the system. Parallel piping loops can create 
sections that get no flow. Arrange the collectors in say two banks of 3 
collectors, with globe valves on the return from each section. Set these 
return valves so that you get equal temperatures from each collector set 
(therefore equal flow).

The piping should be minimum 1". The 3/4" would be good up to MAYBE 3 
gallons per minute, but that's high with glycol. The bigger pipe does have 
the disadvantage of more fluid, longer travel time, etc., but that can be 
overcome with a little extra insulation. (Insulation is cheap, collectors 
are expensive.) So run 1" out to the panel location, then feed each bank of 
3 collectors with 3/4".

Bury the pipes in an oversized smooth wall drain pipe. Pitch this pipe back 
to an open drain. Buried piping either costs about $200 PER FOOT, or it 
gets water in it. Since ours always costs less than $200 per foot, we give 
the water some place to go, rather than sitting in the pipe and insulation.

Good luck.

Jeff
----------
From: 	Smitty[SMTP:smitty at aaasolar.com]
Reply To: 	RE-wrenches at topica.com
Sent: 	Tuesday, August 21, 2001 11:38 AM
To: 	RE-wrenches at topica.com
Subject: 	Re: solar thermal pumps [RE-wrenches]

Kurt, for what it's worth, Richard Lane and I have conducted some tests
of various pumps moving glycol and water at the large Packerland system
(R.I.P.) in Green Bay. I am assuming this system is going to be in
northern Wisconsin. What we found is that in the dead of winter, with
very low temps, the glycol will start slushing and even become a
semisolid ice plug, but not enough to pop anything. At daylight the
panels tend to thaw out, but the glycol in the insulated above ground
plumbing remains semi frozen or very thick. The DC pumps we tested had a
very tough time with this. Sorry Dan, but the El Cid just didn't cut it
with semi frozen glycol. The Hartell did a bit better but in the final
analysis I would use an AC pump and a differential controller if
possible. A few days of the year, we would even have problems with the
Packerland system, and that was with 6"-14" pipes and many 10 hp pumps
(5000 collectors). If you go DC, I would oversize the PV panel to
accommodate morning incident angle, so it at least it has chance of
getting the glycol moving.

The panels should be plumbed in parallel.

The smaller a pipe is, the more frictional wall loss there is. 3/4" is
the smallest I would use. Hope this helps. Smitty.

Kurt Nelson wrote:

> Greetings all (and Smitty?), I'm doing a solar thermal system/in-slab
> hydronics, and though I have done a number of SDHW systems, I'm new to
> moving fluid through larger arrays. The collector is 5  (possibly
> six), 4x8 Solar Kings ground mounted about forty feet from the house.
> I would like to run the pump(s) PV direct and it would seem that there
> is a shortage of pumps to choose from here.  I was thinking two Hartel
> HEH-10's (did I get the model numer right) and would welcome other
> suggestions.  Also, .... 1 - Is it best to plumb (pipes) them in
> series, or parallel?2- Is it best to wire them each to individual
> 18-22 watt panels (my guess) or both to a single 38 to 44 watt panel.3
> - The burried and insulated piping from the array to the house....  go
> with 3/4 inch pipe (or even larger) to accomidate flow, or 1/2 inch to
> reduce heat loss from piping surface area AND the increased time the
> heat transfer fluid spends in the pipe? Thanks in advance for thoughts
> and suggestions.Kurt NelsonSOLutions
>
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