Thoughts on using a pressure switch in a closed loop system?

[Stringpark]

So I'm slowly restoring a closed loop solar thermal system that I was given for the effort of de-installing. When taking the system down, the loop was already completely dry. Later, I found a few pinholes in the manifold of one of the collectors. The Wilo pump was also seized, with a bunch of solidified gunk in the back housing that appears to have built up and warped the cartridge. I'm just guessing that this happened to the pump after it continued to run without actually moving any fluid (having lost pressure in the loop due to the pinholes).

If this assumption is accurate, then one would think that a pressure switch in the loop (that would turn off the pump if pressure was lost) would be a normal practice. However, in all of my research on these systems over the last few months, I haven't come across any mention of anyone doing this and I also haven't been able to find a switch for this purpose marketed for solar thermal.

So if no one is doing this, then there must be a reason it is not needed. Perhaps my guess on what happened to the pump is wrong. Any thoughts?

[Solordabber]

I think a pressure switch is a good idea because it can't be too hard to install.

I based my closed loop system on a book I liked written by Ramlow and I don't recall a system with a pressure switch in there. In the two years I've had my system I had only one failure when an old 1980's vintage automatic air vent suddenly began leaking on the roof. Luckily I caught it on the day of the failure when I became alarmed when I had no hot water. Having the pump at the very bottom of the loop helped a lot too. I replaced the automatic vent with a ball valve and now manually vent the system.

I got the two 1980's vintage Alten 3' x 8' solar thermal panels off the Craiglist Free section by being the first to respond to the ad. The guy posting the panels said they were made of copper to peak the interest of recyclers in order to get them to haul them away but I think they're mostly aluminum. He had hundreds of inquiries. Imagine some guy coming along and using them the make hot water!

[Stringpark]

Lol, using them for what they’re made for, go figure! Thanks for the input and the comment about the auto vent. This setup had two purg-o-mats in it. One was toast and I was trying to decide on whether to use the other or not. The top side sensor well has a manual vent built in, so I think I’ll just skip the auto vent. Anyway, guess I’ll also do some more digging for a pressure switch and try to incorporate it.

[LucMan]

So I'm slowly restoring a closed loop solar thermal system that I was given for the effort of de-installing. When taking the system down, the loop was already completely dry. Later, I found a few pinholes in the manifold of one of the collectors. The Wilo pump was also seized, with a bunch of solidified gunk in the back housing that appears to have built up and warped the cartridge. I'm just guessing that this happened to the pump after it continued to run without actually moving any fluid (having lost pressure in the loop due to the pinholes).

If this assumption is accurate, then one would think that a pressure switch in the loop (that would turn off the pump if pressure was lost) would be a normal practice. However, in all of my research on these systems over the last few months, I haven't come across any mention of anyone doing this and I also haven't been able to find a switch for this purpose marketed for solar thermal.

So if no one is doing this, then there must be a reason it is not needed. Perhaps my guess on what happened to the pump is wrong. Any thoughts?

The gunk in the pump is probably cooked glycol. If there are pinholes they were caused by the the lack of heat transfer fluid maintenance. Heat eventually breaks down the glycol and makes it acidic and it can leave a coating on all the internal piping affecting heat transfer. I suggest that the system is flushed with vinegar to try to remove the build up within the system, or try Rydelyme if the vinegar doesn't work. Some are so far gone that they are only good for scrap.
No need for a pressure switch just complicates the system , just remember to perform regular maintenance or convert the system to drain back using plain old water.

[Stringpark]

Thanks LucMan! All the pipes look they they could use a good cleaning. I’ll try the vinegar idea. What ratio do you recommend?

In this case, I believe the pinholes were due to excess condensation within the collectors which drained down and kept the insulation surrounding the bottom manifold constantly wet. The absorber plates on all the collectors were corroded in that area, even on the collectors without any leaks. These are the original Stiebel-Eltron Sol 25’s, which I’ve read were bad for that.