glycol and drainback systems [RE-wrenches]

[Bill Loesch, Saint Louis Solar]

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Fellow RE-wrenches,

Tom Lane asked me to forward these comments about drainback hot water systems.

Thanks,

Bill Loesch, Solar 1 - Saint Louis Solar

-------------Forwarded Message-----------------

From:	"Tom Lane", INTERNET:tom at ecs-solar.com
	
Date:	9/21/2005 10:18 AM

RE:	glycol and drainback systems

 
The lack of information about drainback systems is common. The use of glycol 
with drainback systems has been common for 25 years.  First, a tilt of 23 
degrees or more results in almost all fluid draining back in the reservoir. 
Second, at zero pressure a 50% solution of water/glycol starts vaporizing at 
130 degrees F.-a 40% solution of water/glycol starts vaporizing at 120 
degrees F. The vaporizing of any fluid in the collectors well below 160 
degrees F. results in a fluid film vaporizing out of the collector into the 
reservoir. Glycol/water completely boils at 216 degrees. (-30% glycol 
solution) to 222 degrees F.(50% glycol solution).  I have examined (during reroofing) 20 to 25 year 
old thermal collectors which were using a glycol/water mixture and the 
absorber headers all looked brand new. All pressurized anti-freeze systems 
that old when examined revealed erosion of the copper walls.  
Brandon Levett at Solar Service Inc., has been installing commercial and residential
 drainback systems in the Chicago area since 1977. Their website,www.solarserviceinc.com 
provides photographs of large commercial drainback systems that have been glycol drainback
50% solution for over 25 years.


p.s.I would 
definitely NOT use a anti-scald valve as a diversion valve for any PV driven 
system, you are asking for vapor lock of the system. 

Gator Tom
======================================
Tom Lane @ tom at ecs-solar.com
Energy Conservation Services / www.ecs-solar.com

"Your Florida Solar Solutions Provider"

6120 SW 13 Street 
Gainesville FL 32608
352 377-8866 work
       338-0056 fax
       591-0234 home
======================================


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