[RE-wrenches] 29 year old propylene glycol - keep going?

[Aladdin Solar]

9/23/2012

Wrenches:

We did some maintenance on a 29 year old solar thermal system in South Dakota last week -- 468 sq feet of water heating collectors and 300 gallons storage. This is a drainback system and the entire 300 gallon tank works as the drainback tank. The system owner pays very close attention to the system and it has been running every day since 1983. The area's record low the past 50 years is in the neighborhood of -25 F.

The propylene glycol mix (not ethanal) is 29 years old and measures -8F freeze/slush protection with the refractometer. The PH measures 7.8. He still has an unlabeled container with a couple of gallons of the original stuff (manufacturer unknown)--it also measures -8F freeze protection but a with 8.4 PH (or higher, 8.4 is the top of the litmus paper scale we had).

We would normally insist that it's time to clean out and replenish the solar fluid but for a 300 gallon drainback tank we're talking $3000 for just for the glycol!

What are the risks of continuing to use the existing mix? Since it is a drainback system, should be little chance of burst pipes. The PH is a little low although we don't really know what it started at since the old unused glycol may have changed some having sat for 29 years. Should we insist that the mix must be changed out immediately or can he continue to watch it carefully and keep going? If he does keep going, what is the indicator to watch for that will tell him he absolutely must change it out?

Thanks in advance for your opinions!

Charlie Pickard
NABCEP Certified Solar PV Installer ®
Aladdin Solar
952-401-7073
cpickard at AladdinSolar.com
www.AladdinSolar.com




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