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.

[dguzzi]

You might check Belimo brand valves, you can get them configured so power on is open and power off close by a spring. Also available with extra benefit of modulation to control flow (that requires control circuit) Very durable and cost effective.
We used them for years on centrifuge systems in machine shop settings in order to prevent over pressure in the feed system. I have a couple open/close to prevent floods if water is sensed on my basement floor.

[NiHaoMike]

Originally Posted by Piwoslaw

This summer I reworked the heat trap plumbing on the hot side, extending it first barely above the top of the tank (can't go higher due to low ceiling) then down almost to the cold input:

Hoping this shape, plus the weighted flap of the swing valve, would be enough to stop heat escaping when the pump is not working.

Now that heating season has started I see it didn't stop, the pump and plumbing are still warm/hot, even after a few hours

Only closing the manual valve next to the pump stops the flow, I am afraid that the only solution here might be a mechanical gizmo to open/close the valve whenever the pump is/not powered. I was hoping to avoid that, as I wanted this as simple and passive as possible.

As a test, what happens if you direct a fan over the pipe rising from the low bend to cool it down? Maybe why it's not working is because the pipe never manages to cool down enough for the trap to work.

[Piwoslaw]

Originally Posted by NiHaoMike

As a test, what happens if you direct a fan over the pipe rising from the low bend to cool it down? Maybe why it's not working is because the pipe never manages to cool down enough for the trap to work.

Well, technically, I'd be losing more heat then, at least until it cooled enough to stop the flow

In fact, it is insulated pretty well, so a fan wouldn't do much.

I read here that good insulation of the loop/bend is one of the requirements for a trap to do its thing.

I also read there that a similar heat trap on the return might also be needed, so I have prepared all materials (including a second additionally weighted flap valve), just waiting for a day off with warmer weather, to turn off heating for a few hours.

[Piwoslaw]

I added the heat trap and flap valve to the return from the house:


The additional resistance is evident from the sound/load of the circulation pump. When the pump is in 2nd speed I can hear the flap (with additional weight) bobbing up and down.

Tonight I left the pump off for the whole night to see whether heat is still escaping, and unfortnately it is - supply plumbing was warm to hot (30-40C next ot the pump, basement temp is <10C)

So the dual heat traps + weighted flaps add resistance when the pump is on, but do not hinder the loss of heat when it is off.
So much for keeping this system passive.