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"Food Grade" propylene glycol?

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Posted by Nolan Tucker on September 22, 2005, 7:48 pm
 
I have recently replumbed my 2 panel DHW system from a serial setup to
parallel.  Wow! What a difference!  I am now achieving 160 degrees on clear
sunny day.  I suspect the solar man mantaining the system switched this
years ago, before I bought the house.

My questions are related to MY maintenance.   I used a propylene glycol I
got from the autoparts store.  It looks just like the ethylene glycol -
green.  How does this differ from the food grade propylene glycol I'm
reading about on this site?  Where would I find the food grade type?

At what pressure should I be maintaining the anti-freeze closed loop?



Posted by Ecnerwal on September 23, 2005, 12:53 am
 


Check the pump manual. If you don't have a pump manual, guesstimate 15
lbs or so. The pump manual (or interpretations thereof) will tell you
the minimum system pressure that the pump will be happy with, for
various conditions. 15 lbs is typically plenty, or more than plenty, but
it's not overly much. Well, come to think of it,  it may also depend
where you are measuring the pressure and how much vertical distance the
loop covers - If there are collectors on the roof of a two-story
building, and the pressure gauge is in the basement, you may need a bit
more than 15 PSI to keep it all happy...

--
Cats, coffee, chocolate...vices to live by

Posted by Solar Flare on September 23, 2005, 1:01 am
 Just like atmospheric pressure.  15lb will lift 34 feet until it begins to
siphon back down and then 34 feet for the pump and 34 feet for the vacuum
(atmospheric pressure)



Check the pump manual. If you don't have a pump manual, guesstimate 15
lbs or so. The pump manual (or interpretations thereof) will tell you
the minimum system pressure that the pump will be happy with, for
various conditions. 15 lbs is typically plenty, or more than plenty, but
it's not overly much. Well, come to think of it,  it may also depend
where you are measuring the pressure and how much vertical distance the
loop covers - If there are collectors on the roof of a two-story
building, and the pressure gauge is in the basement, you may need a bit
more than 15 PSI to keep it all happy...

--
Cats, coffee, chocolate...vices to live by



Posted by Nolan Tucker on September 23, 2005, 1:24 am
 The pump in the closed loop is a Grundfos model UP26-64F 1/12 HP that can
handle a max 145 psi.  It is located in the basement of a two story, so the
panels are actually 30 ft overhead on the roof.  The system is currently at
40 psi and drops to 30 when the pump runs - the pump is just past the
pressure gage.  I'm looking for the recommended operating pressure for the
aluminum lines and Reynolds 4x12 collectors.  I have no documentation for
the system.  I don't know if running at this pressure is asking for trouble.




Posted by Ecnerwal on September 23, 2005, 1:59 am
 

Well, a Grundfos manual covering that pump is available online as a PDF,
and states that the minimum pump inlet pressure (for the whole series)
is a function of temperature, as follows: 140F - 1.3 psi, 190F - 4.0
PSI, 230F - 15.6 psi.

If we guess that your system will be in the 190F regime, figure that you
need about 15 PSI to have the system full (30 feet, rounded up), with
perhaps another 5 so the top part of the loop is reasonably pressurized
(cold). Pressure will bump up a bit at operating temperatures, and if we
guess that your 10PSI differential is not too dependent on overall
system pressure, you'd have 20 PSI static, and 10 while pumping on the
inlet side of the pump, which is still twice minimum at that
temperature. Take the static pressure up to 30 if you think it might get
hotter. I can't see any reason you'd need 40 static with the system you
describe...

--
Cats, coffee, chocolate...vices to live by

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