The sun, our Eddi and my SunAmp: keepin' me guessin'

[ToughButterCup]

SunAmps linked to PV supply make you guess, don't they? ' Course, if you don't wanna guess, you press Boost on yer Eddi (a PV diverter) . But that's the coward's choice. The game is get the maximum out of the sunlight available to make sure that TwinkleToes bath is as warm as she wants.

 

We've a 12kW Sunamp, a bath and a couple of showers. Normal hotwater use for two old fuddy duddies.

Decent drop of sunshine recently: time to build up a 'feel' for how much power our Eddi shunts to our SunAmp. And then there's how much water we've used . Take one from the other and you've cracked it

 

A bath a day is about 5kW (right @SteamyTea ?) A shower, 3kW or so: that makes 11kW a day - two showers one bath. Plus a kilo Watt to scrub a grandchild half way clean.  12kW. Bingo.

 

So, if our Edward ( or, Eddi - why can't they spell it right ?) tells me that SunAmp's up to temperature, all will be well in the ToughButterCup family. But life ain't like that is it?

 

Why oh why oh why cant SunAmp tell us how much power is left and available to heat the PCM in the SunAmp eh? I mean, it can tell Eddi that it cant take any more PV power, so why not tell us how much is left?

I mean a SunAmp - any bloody SunAmp - ain't cheap now is it?

Disgusted of Lancashire

 

 

[SteamyTea]

12 minutes ago, ToughButterCup said:

We've a 12kW Sunamp

No you don't.

 

 

The main reason it cannot tell you how much is left inside, is because it does not know.

 

A normal storage cylinder could just use 3 or 4 temperature sensors at different heights and a simple calculation based on those temperature differences.

A Sunamp basically only has one temperature, the phase change temperature.

 

You could put a heat meter on it, then ditch the crappy built in controller, and just pump in the appropriate amount of energy.

 

Edited May 10, 2021 by SteamyTea

[ToughButterCup]

Ahhhh, my mistake then ... do explain.....

[SteamyTea]

kW is the power, kWh is the energy.

Think of it as how fast your car can go, and how much fuel is in the tank. They are different things.

 

Edited May 10, 2021 by SteamyTea
Is anyone else have trouble typing replies on an Android phone. Seems worse since the upgrade

[ProDave]

3 minutes ago, ToughButterCup said:

Ahhhh, my mistake then ... do explain.....

kWh 

[ToughButterCup]

ah, but for an 'h' ......?

[SteamyTea]

Just now, ToughButterCup said:

ah, but for an 'h' ......?

Why we should use the MJ, megajoule, as a unit of energy.

[MikeSharp01]

18 minutes ago, SteamyTea said:

You could put a heat meter on it,

How?

[SteamyTea]

9 minutes ago, MikeSharp01 said:

How?

Only a flow meter and a couple of temp sensors.

Then:

E = SHC x Mass Flow Rate x Time x ∆T.

Calculate that number, then turn on the inbuilt heater for the appropriate amount of time.

 

Or junk the overpriced lump and fit a basic vented or unvented system.  You can easily store excess energy by upping the store temp when the sun is shining (though you may export more PV the next day).

 

Edited May 10, 2021 by SteamyTea

[MikeSharp01]

1 hour ago, SteamyTea said:

Only a flow meter and a couple of temp sensors.

Then:

E = SHC x Mass Flow Rate x Time x ∆T.

Calculate that number, then turn on the inbuilt heater for the appropriate amount of time.

So you are effectively measuring consumption and assuming it was topped up at the start. Wonder how their gizmo does it? 

[SteamyTea]

16 minutes ago, MikeSharp01 said:

 Wonder how their gizmo does it? 

Think we have a thread on it somewhere.

It may sense the fusion temperature, plus and minus a degree or two.

Which may account for it not being able to be charged up untill it is 75% depleted. That bottom 25% may be the energy it can take when the magic wax is fused.

 

 

[dpmiller]

don't they have a string of thermistors down the middle, or am I imagining reading that?

[SteamyTea]

23 minutes ago, dpmiller said:

don't they have a string of thermistors down the middle, or am I imagining reading that?

I seem to remember reading something like that.  But they will not be able to do much with a solid.

[ToughButterCup]

Okay  folks, explain this then...

 

Our Uniq12 was refusing PV yesterday evening ( it reported via the Eddi- 'Max Temperature Reached') . In other words it had reached its heat storage capacity  (14 kWh)

 

This morning- bright sun, one shower, (3 kWh) max, the  SunAmp is accepting power from the diverter.

 

It cannot have been 75% depleted. No other hot water was used overnight. 

 

 

 

[SteamyTea]

16 minutes ago, ToughButterCup said:

Okay  folks, explain this then

No idea.

But it could be the inbuilt software misreporting.

How much charge did the SA accept, 3 kWh?

[jack]

3 hours ago, ToughButterCup said:

Okay  folks, explain this then...

 

Our Uniq12 was refusing PV yesterday evening ( it reported via the Eddi- 'Max Temperature Reached') . In other words it had reached its heat storage capacity  (14 kWh)

 

This morning- bright sun, one shower, (3 kWh) max, the  SunAmp is accepting power from the diverter.

 

It cannot have been 75% depleted. No other hot water was used overnight. 

 

The way phase change materials (PCMs) work is that they start as a solid below a transition temperature. Heat gets added and the temperature rises until it reaches the transition temperature (note that there's really a temperature transition range, partly due to material properties and partly due to imperfect heat transfer within the material). At that point, extra heat energy no longer raises the temperature, but instead goes into changing the phase from solid to liquid.

 

In general, this phase change takes a lot of energy. That's why a relatively small volume of PCM can store a lot more accessible energy than can be achieved by heating something like water while it stays within its liquid phase.

 

Once the PCM has all been converted to liquid, adding further energy will start to increase the temperature. At some point, the PCM's maximum operating temperature is reached, and no more energy can be added.

 

One difficulty with PCMs is that you can't determine from temperature alone how much energy it's storing when it's at its transition temperature. With water, if you know the temperature, you can estimate how much hot water you have. With PCMs, once you reach the transition temperature, there's no significant temperature change until the PCM has all liquefied.

 

This means that if the temperature is below or above the transition temperature, you can estimate total energy based on temperature, but you're somewhat in the dark while at the transition zone. Estimating the energy while the PCM is at the transition temperature is what's been discussed above.

 

However, once you go above the transition temperature, you can again determine how "full" the energy store is. So if your Sunamp was completely full, then used a small amount of energy, that would have resulted in a temperature change that the Sunamp controller can interpret as meaning that capacity again exists. So the Sunamp knows when it's full, and in theory knows (or could know) how much capacity it has left as long as its PCM temperature is above the transition temperature. It's when it's at the transition temperature that it's ignorant of how much energy it's actually storing.

 

Of course, the vast majority of the energy stored by the Sunamp is available at the transition temperature, so the ability to determine energy capacity based solely on temperature (beyond "nearly full" or "nearly empty") doesn't exist.

 

I'm completely ignorant of how Sunamp actually program their controllers, but something like the above could be happening in terms of allowing the immersion diverter to operate even if only a small amount of power has been taken from the store from when it was full.

 

[ToughButterCup]

@jack  , thanks very much indeed.  Took three  readings of your post to understand most of it (possibly).

I'm sure I'll come back to it once in a while for a refresher.....