Solar system - Frozen antifreeze

When I re-filled the collector loop last fall, I started with about 3 gallons of propylene glycol antifreeze (DowFrost HD) that I had available. I mixed this with water in a 5 gallon bucket and pumped it into the collector loop. Well, I forgot that my loop takes more than 5 gallons now (since adding 2 collectors last year). So I kept adding water to the bucket until the loop was full. I ended up with a mixture that was less than 40% antifreeze. I figured that this would be OK.

Well, this morning my collector loop froze - no circulation - even in full sun! The ambient temperature dropped below -13F last night. The high for yesterday was no more than 9F. I checked the specs for DowFrost and found that a 42% mixture only protects to -10F. Oops!

I made a quick run to the local plumbing supply and got a 5 gallon pail of Hercules Cryo-Tek -100. By using my fill pump to aggressively push the ice around in my plumbing I eventually got the collectors un-frozen. The collectors themselves were stagnating at 130F while the shaded and insulated return pipe was well below freezing! I drained a few gallons from the collectors and dumped it outside, (remember this stuff is non-toxic) then I pumped in a couple of gallons of the Cryo-Tek.

It's interesting that the DowFrost that I used originally looked like green Gatorade, while the Cryo-Tek looks like fruit punch! The mix is an ugly brownish color. But hey -- it works! I'm good to -40F now.

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