Specific gravity as glycol mix indicator [RE-wrenches]

[Geoff Greenfield]

A glycol direct thermal customer had some -4F weather, his pressure shot up
to 40 psi and he had no typical temp differential on his supply and return
(and the pump was getting really hot).  He couldn't get a hold of me and was
about to leave town, so he dumped his glycol mix into buckets and turned
things off.  He couldn't blow air through (he has a low point in
unconditioned attic space) and concluded that he had frozen pipes.

We used a 50/50 mix of dowfrost HD that should be good for freeze protection
down to -30.

Does anyone know of a formula or chart where I can calculate the
%concentration based on specific gravity?  The measured SG of the solution
is 1.027 (at 66F - I can have the customer remeasure at 60 if need be).  The
dowfrost literature says 1.053-1.063 at 60F.  Water is 1.  Is this a linear
thing where I should expect a 50-50 mix to be the average of those two?
(1.0265-1.0315).

Any guidance/feedback would be great.  I did look in Tom Lane's book and
read (page 55)that (counter-intuitively) a greater concentration than 50% of
glycol would have less freeze protection, so I don't just want to tell him
to add more glycol!

For a brighter energy future,

Geoff Greenfield
NABCEP Certified PV Installer

"Clean Energy, Expertly Installed"

Third Sun Solar & Wind Power Ltd.
340 West State Street
Athens, OH 45701
www.third-sun.com <http://www.third-sun.com>

(740) 597-3111   ( Fax: 1548)



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