Stop, Thief!!

[hiccup]

Hi

Now that I've got some rudimentary logging working, I've spotting something stealing our stored solar energy!   

Notice the two black arrows - both tank top and bottom sensors drop by about 10C - and at night when we're all asleep.

First thought was the washing machine, but no not on those nights, but wait, why both top and bottom, the DHW coil is at the top of the tank and I can see when HW is used because the top temp drops on its own.
No, this is something else...

Doh! 

The nights are a bit cold and the frost stat on the oil boiler in the garage has been kicking in so a big slosh of cold water is entering the tank at the bottom and my nice hot solar water is being sucked out to the garage, at which point the stat thinks the frost has gone and stops the pump. The boiler doesn't even get a chance to make up for the loss.

I've tweaked the frost stat down to a safe minimum (I hope) and so far no more night time thievery!

Might help others.

Hic!

[KLD]

HIc

Why do you think you see the top sensor moving? If iy was a relatively small amount of cold being pushed into the tank bottom section, then the top temp should drop no further then a section a few inches down, if you see what I mean. But it seems to go as far down as the bottom temp was before the boiler pump started ?
You seem to loose 9°C for your entire 288L store, that's 3kWh in one pop!

What I also don't understand is how the solar heat is deposited into the cylinder. The panel temperature seems to follow the top of the cylinder instead of the bottom. Do you have a (retrofit-)coil installed such that you heat the top first?

What d'you reckon is the late afternoon shoulder in the panel traces?

Klaus

[KenB]

Hic,

I may be wrong, but I wouldn't be too certain that it was your frost stat.  It seems to come on at approximately the same time.

I'd look at your timestamps and see when it happens and for how long. Then I'd look back at your boiler controller.


Ken

[hiccup]

Hi Ken

No, the last two occurrences were at 6:01 and then the next day at 6:44

If it was the HW stat calling for heat, the boiler/pump would stay on for a while until the stat was satisfied. There is no sign of the tank temp going up after the drop.

It is going to be cold again tonight so we'll see what happens.


Hic!

[KenB]

Hic,

Put a max/min or datalogging thermometer in your garage, and perferably another temperature sensor on the pipe to the pump. 

Wire a loud stereo system across the boiler circulation pump - you'll know then if it comes on or not (So will your neighbours) ;-)



Ken