glycol and drainback systems [RE-wrenches]

[Travis Creswell, Ozark Solar]

Hello Bill,  

Thanks for your comments.  I don't think there would be damage to the
collector if a controller or thermistor failed in such manner to keep the
pump running.  As you are likely aware this failure would cool the storage
tank off which would then cause back up heater to kick on and heat the
collector.  Hopefully the customer would notice this soon as that would be
pretty expensive, especially if it happened in the winter. 

I've installed and serviced about a hundred SHW systems in the last 14 years
plus lived with SHW for most of that time.  I've never seen a failure cause
the pump to not shut off.  I'm sure it's happened.  Has anyone personally
seen this?  Inquiring minds want to know.

I think we all know the difference from ethylene and propylene but thanks
for pointing that out anyway.

We have SHW customer who is a retired chemist.  We once had a discussion
about ethylene vs. propylene and he assured me propylene was toxic albeit
far less then ethylene.  Yet its FDA approved and found in all sorts of
cosmetics and even used as a food additive.  Go figure.

I still see no compelling reasons to use glycol in a closed loop drain back
system.

Best,

Travis Creswell
Ozark Energy Services




-----Original Message-----
From: Bill Loesch, Saint Louis Solar [mailto:bill_loesch at compuserve.com] 
Sent: Friday, September 23, 2005 6:37 AM
To: INTERNET:RE-wrenches at topica.com
Subject: RE: glycol and drainback systems [RE-wrenches]

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Travis,

Like you said, 25 years with the same glycol is truly impressive. Reduced
maintenance and fewer components are also big advantages of the drainback
philosophy. 
And how does the glycol drainback achieve this reduced maintenance? By
being able to _effectively_ high limit the glycol fluid _not_ just the
storage tank.

The downside is a bigger pump to overcome static head pressure _every_ time
the system starts and correspondingly higher electrical consumption for the
life of the system. The situation of relatively cold fluid being pumped up
to an already hot collector is a sourse of thermal shock in the drainback
scenario. 

Tell me, Travis, what happens when a pump controller fails or a thermistor
fails in the drainback? If there is a proper glycol mixture is the system,
it would be hard to have freeze damage.

Lastly, I would hope that you are using proplene glycol rather than
ethylene glycol in your systems. The difference? The  first is _non_ toxic,
the second _is_ toxic.

Thanks for asking, I'm sure there are folks out there that also did not
understand and also did not ask.

Bill Loesch
Solar 1 - Saint Louis Solar