Thursday, June 9, 2016

Solar hot water system mantenance

        Installed in August of 2005 my SDHW system has been a learning experience. After storing 2 salvaged flat plate collectors from a 1970's system and reading up on several system designs in Home Power magazine I made the leap. After building a tube within a tube heat exchanger that was featured in Home Power I was ready to go. Second, I say second because it took me two times to learn that the domestic side water loop would require a bronze circulating pump to survive the high lime content in my non  softened water supply. Then everything ran like clockwork and provided over 50% of my hot water needs (100% during the summer months)for the next 10 years.
       Year after year all was well until around November of 2015 and I noticed that the system was not pumping. Thinking that the problem was with the anti freeze filled solar loop I did not want to mess with this until warmer spring weather. So I waited until last week. Then I noticed that there was a small black burn mark on the circuit board where a relay for the differential temperature controller was. After replacing the relay still no go. Now I had the problem zeroed in as a locked pump that allowed high current to fry the relay. The plan was to replace the hot side loop antifreeze side and pump.

After draining the system I was ready to replace the pump and refill however the pump was just fine.
So I want ahead and refilled the system and bled off any trapped air. So far so good.

Now would have been a good time. I was a bit fuzzy on remembering the system details and how all the pieces, pumps, check valves, loops, air vents expansion tanks, etc, etc. fit and work together. But, I plunged ahead. Shutting off the water supply and removed the domestic loop pump. Locked solid just as I suspected. Even the bronze pump could only last 10 years.
Here is where things got ugly. The picture shows the correct stack up with the compression plate behind the pump cartridge flange. For some odd reason on the first try I put it on the other side. A total failure to seal the water and when I turned on the main, in the basement, water shot out all over before I got upstairs! And back down!! I had a lot of time while cleaning up the spillage to THINK!

After replacing the pump cartridge with a new bronze one I also installed a flow indicator in the domestic side. There is just something about seeing the flow in the system that gives me piece of mind.

And in a few short minutes of operation the pressure was up and the solar loop was hot. That heat was being transferred by the heat exchanger to the domestic water. There would be a solar shower tonight!

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