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Originally Posted by SDMCF
Thinking about it later I don't understand why the pressure relief valve did not activate. Either it is faulty or there I have made a design error in the layout..
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My guess is that the pressure relief valve was faulty. Ether that or it was specified for activation on bigger pressure than your system is able to produce when overheated.
Yes, I'd say that this is very important point. One that could maybe be simulated when installing the system (dunno if the glycol can be reused after?)
Your example is why I want to go with drainback solar system design, instead of standard pressurized closed loop with glycol that everybody and their mom has. When public electric power is off, to address the glycol overheating problem some kind of backup power for the pump is needed, but sometimes it's possible that power will be off longer than the backup capacity (UPS with inverter, or something like that). And than you will have the same (big) problem.
That's the beauty of drainback system, when public electric power is off - the exchange fluid (destiled water in this case, instead of glycol) will simply drainback down in the drainback water tank. Yes, the collectors themselves will be exposed to much increased heating - but the rest of the system is safe.
Quote:
Originally Posted by SDMCF
It could be a good idea to design in a method of losing any excess heat produced when your tank temperature gets up to your required maximum. If the power is on I have 2 possibilities. One is to lose the heat into my central heating system and the other is to send the heat to my front steps which I keep clear of snow using solar heat in the winter. Not sure how much heat the steps can take but the central heating can certainly take anything the panels can produce. Neither of these options is effective if the power is off though. Think about that in your system design.
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You need some kind of a heat dump for overheating protection. But when the public electric power is off, I don't think it will be the boiler that will overheat - only the heat exchange fluid (glycol I guess) in the upper part of the tubing. Not sure how corrosive glycol is, but it will for sure be quite hot (and not funny for anybody using your steps at the time).
