My water heater overheating sensor!

[Christophe]

1) My planar sensor has blocked dozens and dozens of times (on the De Dietrich model that I have, there is a safety that stops the circulator if the temperature difference between the panel's high probe and the probe low of the preparator exceeds 50 °, so when in full sun, you make a large draw, the bottom temperature can fall quickly from eg 35 ° to 12 ° - cold water temperature).

I do not understand the physical logic of this security? What does it protect?

If I understand what you say, the system goes off from a certain delta T, so when there is the most power / solar energy to recover? And this, on the contrary for me, therefore leaves the panels with risk of overheating when it should dissipate this energy (some solar systems have a heat sink in the cellar but quite rare)

And what do you mean by blocked?

[netshaman]

I did not say that the circuit was in the cellar: I have no cellar!
No the circuit goes through the attic (not amenages) and leads directly into the habitable zone a little lower (it goes through the ceiling).
From the tank to the panel there is a distance of about 5 m and 2 m about vertical.
So it is strange that there is so much pressure indeed!
On the pressure gauge of the valve the red arrow indicates 5 bars: is the valve taree at this pressure?
I inspected the pipes (not obvious below), I saw nothing except a place where the glass wool was stuck on the insulating foam over a distance of 50 cm => is the leak there?
If this is the case there should have been traces on the ground (a big stain) no?
Or is it vaporised?
But suddenly the wool should have colored no?

[Christophe]

Ah yes inevitably in this configuration it empties more easily ... but not entirely either if the ball is under the panels ...

Usually the red zone is "adjustable" by hand by rotating the edge of the pressure gauge since most safety valves are adjustable.

What is on it is that there was never need of 3 bars in your configuration! 0.2 bar height + anti cavitation safety pressure (0.3 to 0.5 bars) would have been enough without worries! In short 1.0 bars it was good ...

But no regret to have: nothing says that it would have avoided the accident ... maybe it would have delayed a little ...

[Did67]

1) My planar sensor has blocked dozens and dozens of times (on the De Dietrich model that I have, there is a safety that stops the circulator if the temperature difference between the panel's high probe and the probe low of the preparator exceeds 50 °, so when in full sun, you make a large draw, the bottom temperature can fall quickly from eg 35 ° to 12 ° - cold water temperature).

I do not understand the physical logic of this security? What does it protect?

If I understand what you say, the system goes off from a certain delta T, so when there is the most power / solar energy to recover? And this, on the contrary for me, therefore leaves the panels with risk of overheating when it should dissipate this energy (some solar systems have a heat sink in the cellar but quite rare)

And what do you mean by blocked?

1) By blocked I mean "no circulator working". I no longer know the maximum temperatures reached up there: 150 ° (order of magnitude) !!!

2) This system is poorly designed (well, it has 11 or 12 years, my installation).

It must, in the spirit of its design, avoid a "thermal shock".

Power failure = "up" temp rises; the temp in the balloon does not move; the delta exceeds 50 °; the current returns, the circulator does not send the "cold" liquid, which had plenty of time to cool down to the temperature of the balloon while it was not running.

That's good!

Except that under "normal" circumstances, the following happens from time to time:

a) full sun around solar noon; sensor temp 70 °

b) the circulator, the water that arrives at 65 ° from the flask comes out at 45 ° (it loses between 15 and 20 ° max).

c) the bottom of the balloon is eg at 25 °

d) the bottom of the balloon / top of the panel is 45 °, it is in the nails

e) but someone in the family decides to take a shower and since the weather is nice, do not think to save; the cold front is rising; the bottom probe is drowned in freshly arrived cold water [I do it on purpose!], eg at 12 °; the temperature at the top of the sensor has hardly moved; so we have a gap that exceeds the 50 ° ...

It is a "functioning" that the engineers had not foreseen. When it works in equilibrium, there is always an adjustment: the return temp to the panel goes down, so the top temp of the panel also goes down, the liquid circulates at a lower temp, the delta T remains constant.

But when it is done suddenly, it "gets stuck".

NB: the small samples, like rinsing the dishes, are not sensitive enough. It's really the showers the problem!

[netshaman]

On my regulation there is this function too.
When a certain time is reached, everything stops.
But I've settled the binz so that it never goes into operation.
In fact, I have set the balloon time to 60 just like that with the function of refreshing the sensor, the balloon can go up to 90 (never arrives) while refreshing the sensor from time to time as soon as a set temperature is reached.

[Christophe]

It must, in the spirit of its design, avoid a "thermal shock".

Ok I thought about it without daring to write it ... never heard ...

[Cuicui]

The water which arrives at 65 ° from the balloon, for example, comes out at 45 ° (it loses between 15 and 20 ° max).

I am surprised, because in my installation that has been running for more than 30 years, the difference in temperature between the inlet and the outlet of the balloon does not exceed 5 °.
And what is this heat shock story? What is the disadvantage?
In my opinion, a solar thermal system is made to store the maximum calories before the sun goes down. Cutting the circulator during the day seems like a mess. If by chance the temperature is very high, it is advantageous to install a larger balloon or to add a second, so as to have the largest reserve of hot water possible.

[Did67]

1) The delta of time between the start of the ball and the return to the ball depends on the capacity of your panel (I have two, almost 5 m²) and the flow ...

Normally, it is recommended in the manual of my system to adjust the flow so that this delta is close to 15 °...

Above, you lower the yield because your panels are warmer and capture less well / lose more ...

Below, your circulator mill for nothing and you consume electricity for tails ... cherry!

Nevertheless, in solar full sun, in very clear weather, I can be a little beyond.

I put the figures as an indication and memory ...

2) Thermal shock: it is in case abnormal stop of the circulator by power failure, in daylight. You then have your panel at the top which goes up to 150 ° and your liquid which is at the temperature of the balloon at the bottom (eg 25 °). If the pump start again [the current returns without warning], this makes, at the level of the panels a sudden passage from 150 ° to 25 ° in a few seconds ... Here is the risk of "shock"!

Now I don't know any more. They are surely engineers who "invented" that !!!

This unfortunatly does not play in normal operation, where, in fact, I have high temps of 70 or 80 and departures at the balloon exit of about 15 ° less ...

In normal operation, the temperatures change constantly depending on the sun and the temperature in the balloon ... but this is done in minutes or tens of minutes, not in seconds, on smaller gaps. So this normal operation is not the problem.

[Did67]

But I've settled the binz so that it never goes into operation.
.

Alas, on my regulator, this function is not configurable. I usually miss a few degrees for it to pass! So if I could put 60 instead of 50, it would be good .. No doubt even 55!

I can not disable the function either!

[Cuicui]

Normally, it is recommended in the manual of my system to adjust the flow so that this delta is close to 15 °...
Below, your circulator mill for nothing and you consume electricity for tails ... cherry!
2) Thermal shock: it is in case abnormal stop of the circulator by power failure, in daylight. You then have your panel at the top which goes up to 150 ° and your liquid which is at the temperature of the balloon at the bottom (eg 25 °). If the pump start again [the current returns without warning], this makes, at the level of the panels a sudden change from 150 ° to 25 ° in a few seconds ... Here is the risk of "shock"

I developed a system of self-draining: in case of power failure the sensors are empty. If the current comes back, it is 30 years that I shocks gaily my self-built sensors without ever seeing any damage. It's crazy how engineers are trying to complicate a simplistic technology.
Normally, the difference between the entry and the exit of the balloon is 3 °, so as to store the least calories. At home, it's a little higher (5 °) because the circulator has a modest power: 120 W for 40 m2 sensors.