Tnx AC, and wow - a reply from the author of the famous "
The Homemade Heat Pump Manifesto"
Quote:
Originally Posted by AC_Hacker
...I have not heard of solar collectors failing from the stagnant phase.
I was under the impression that the drain-back cycle would kick in at night, and also protect the collectors from freezing.
-AC
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Yes, but drain back phase could also occur at daytime, depending on the system dimensioning. Namely, one could aim to design the whole system so that collector power is such that on the perfect sunny conditions, the water in the drainback tank does not get above 175-195F (80-90C). When the conditions are not as good, drainback tank water temperature would be lower - and that is good compromise to live with, considering the alternatives and costs of
heat dump part of the system.
But still even when designing to avoid heat dump, one should aim to be close to 175-195F (80-90C) temperature range. With the certainty of some water evaporating eventually, there could be possibilities of daily occurrences of the drain back (stagnant ) phase.
I'd very much like to hear some
do's and don'ts on designing Drain Back Solar Hot Water Systems. Yours are excellent advices AC, shame that you don't have experience with drainback systems. But hopefully somebody else can help.
If the thread does go in that direction, maybe admins or moderators could rename this thread.