Addition Solar Heating Update

Well, it’s been 3 weeks since we got our solar water heating system up and running in our new addition. First off, it definitely works — Yay! But it is also definitely a complicated setup.

I have been testing and tweaking the various controller settings. The system manual, as so many are, is very poorly written. Here is a fine example, as no doubt translated from the original Chinese:

If hot water in tank isn’t used for long time, then the capacity that solar system absorbs solar energy reduces, when tank temperature rises to its preset maximal temperature, solar circuit pump is ceased compulsively even the temperature difference is satisfied. then when more solar irradiation shines in, as a result collector temperature will rise continuously, temperature of collector maybe rise up to the evaporated temperature of heat fluid, this phenomenon names collector – overheat, it should be avoided.

And I have, indeed, and as I suspected, had this “phenomenon” happen. With the recent warm and sunny weather, the heat wasn’t going on. The big 211 gallon tank reached it’s max (145°F) by noontime so the pump “ceased compulsively” and the collectors overheated — I saw it at 303°F; that’s why it uses stainless steel pipe, not pex — and the 50/50 glycol/water mix evaporated into the pressure tank as designed. This is OK once in a while, but having it happen on a regular basis causes the fluid to acidify over time. So, yes, “it should be avoided”.

Bumping the tank max up to 160°F helped a little, but not enough. I could go up 175°F, but that would not likely solve the problem and is also a bit too close to the 180°F rating of the pex piping. After sorting through the various system settings and the creative prose in the manual, I have settled on a solution of using the “BYPR Bypass function (high temperature)” to trigger a solenoid valve to dump hot water when the collectors are near overheating until the system cools down a bit. We are fortunately blessed with an over-abundance of well water, and we put in an extra conduit running down to the spring house during construction so we can use that for the cool-down dump. I ordered the parts I need — the last ones are arriving today — this includes the solenoid valve and another mixing valve (since I really do not want to run 160+°F into my floor). Meanwhile, I have been manually dumping hot water, as well as running the heat on whatever cool nights I can. We have some cool and rainy weather coming in a couple of days, that will be a good time for me to drain the big tank and readjust the plumbing with the new parts. I am using SharkBite put-to-fit connectors, which are a breeze to remove and reposition, so it should go pretty smoothly (he says, inviting the wrath of the easily-irked Gods of Plumbing).

Here is the updated system schematic; not really all that complicated, right? Right?


Click to embiggen [Updated 20 May2017 to reflect final as-built]

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