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Dry stagnation temps in drainback thermal can be damaging?
Over the past few weeks I've been reconditioning some old Solaron collectors. The collectors were originally installed atop a university building in Kansas, I believe in the 1970s. I don't know all the details of the system but it was 200+ collectors. It never worked properly and was removed a couple years ago when the roof needed repair. I assume the collectors have been allowed to stagnate for years. Some of them showed signs of previous leak repairs, others I had to repair due to physical damage. The absorbers are copper tube on copper sheet, soldered where the tubes lay in formed channels on the sheet. When I had them apart I noticed the solder looked like it had melted and actually dripped in some places. It was ugly but I thought they must have been manufactured that way. There still seemed to be a decent mechanical and thermal bond so I didn't think much of it.
Last week I got some of the collectors up on the roof. Within an hour or two they were at 380 degrees and still climbing. I didn't expect they would ever get that hot. I took a sample of the solder from a spare collector and it seems to be normal 60/40 with a melting point of 370. So now I know why the solder on the absorbers looked like it had been dripping, it was. At this point there's not much I can do. I had been under the impression that dry collectors would not be damaged by overheating, one of the advantages of a drainback system. I sized the system for my winter space heating load, assuming that the collectors could sit dry for most of the summer without damage.
I guess I'm just looking for any comments or suggestions. Any damage to the collectors has already been done, and was surely done years ago. It just doesn't seem right to have the solder in the collectors becoming liquid every day when the sun comes up.