Heat accumulator

[Piwoslaw]

Originally Posted by Solar Mike

Makes you wonder how long a heat trap is required, perhaps duplicate what you have and place two next to each other; or add another flapper check valve in the cold line entry into the tank.

Wondering about the following: In all diagrams of heat traps, the water at the top of the trap is as hot as in the top of the tank, and its temperature goes down as you get lower, so that in the part that starts ascending again the water is cold.
Now, if my pump just turned off, then of course the whole heat trap will be filled with hot water, but it will cool down to the distribution described above.
But what if:
a) The heat trap is insulated exceptionally well, so the cooling is very slow?
b) The hot water in the parts of the heat trap farther out is trying to climb to the rest of the house, pulling more hot water out of the top of the tank. At the same time, cooler (=heavier) water from the house above wants to go down, into the bottom of the tnk, pushing the hot water out of the top.
It looks like once this is set in motion, there will be gravitational circulation for a long time - until the tank cools down. And this indeed is what I have observed - the heat trap only hinders gravitational circulation when it is "cooled off", but not when it is fully warm

Originally Posted by Solar Mike

Simple solution seems to be getting more complicated. Because you have a powered pump, a simple solenoid valve that is activated whenever the pump is running may be the easiest to implement.

I read about some solenoid valves, and they all seem to have 1 hour time limit for being powered on, apparently to prevent the electrics from overheating (some have an optional additional heat radiator extending this to 2h). This does not really suit my set up, as in the deep of winter the system may be on for 2-4h at a time.

So I also read about motorized ball valves. These seem to need additional electrical controls, as they do not close by themselves after being powered off.
Also, they take appr. 15 seconds to open, not sure how the pump would handle the additional load and pressure while the valve takes its sweet time to open? Might not be an issue, as it would on be a few seconds.
What would be an issue is when the valve fails to open at all after the pump starts up. That would ruin it, unless I invest in additional protection.