Reducing the guesswork involved with a SunAmp

[ToughButterCup]

Owning a SunAmp , for me, is a bit like a Guess-The-Weight-Of-The-Baby competition. You've had a rubble of your own babies, looked after God knows how many other ones, so you've got a good 'feel' for how much the little tike weighs. Oooops, a bit less now - sick down the back of your shirt. You know the routine. 

 

Same routine with a SunAmp: it makes you guess how much  (be gentle @SteamyTea) energy (?) is left in the bloody thing after SWMBO has had one of her bath-of-the-century incidents, and the daughter has run the shower for gaud knows how long.... ( ask @ProDave, he knows the score ?)

 

Mine's (SunAmp) a 13.7 kW machine. And up to today, I've assumed that the average bath gets rid of about 5kW, and a shower 3kW. Roughly.

 

But today I thought I'd try a bit of slewthing.

When the SunAmp's full, you see this on the Eddi thingy that shunts energy to the SunAmp

 

From this image I can see that its taken 3.38 kWh to heat the PCM from what it was to 'Full' ( hmmmm waasat mean?)

 

Quick sprint to the shower, play with my ducks and have rub down with the Sports News. A bit later that day (today) - no other hot water used

 

 

Another 2 and a half kWh or more have been sucked into the SunAmp.

 

Does that mean the shower I took earlier today consumed 5.82 - 3.38 kWh's worth of energy? Or am I missing something? 

Put differently, is my assumption that one of our showers consumes about 3kWh's worth of energy per average shower correct?  (We have a quite powerful HansGrohe 'rain' head)

 

Edited July 8, 2021 by ToughButterCup

[SteamyTea]

3 minutes ago, ToughButterCup said:

Does that mean the shower I took earlier today consumed 5.82 - 3.38 kWh's worth of energy? Or am I missing something? 

Put differently, is my assumption that one of our showers consumes about 3kWh's worth of energy per average shower?  (We have a quite powerful HansGrohe 'rain' head)

Measure the flow rate, the output temperature on the hot pipe and the input temperature on the cold pipe.

Then do the sums.

[ProDave]

A typical "good" electric shower uses 10kW and a typical lady shower is at least 15 minutes so that's 2.5kWh.  Yours will use more than that as with a decent rainfall head you are probably getting twice the flow rate than from an electric shower.

 

I think the other issue, is the sunamp does not seem very good at determining itself when it is "full" and has a lot of hysteresis, so won't accept any more input until if thinks it has some spare capacity.

 

To a lesser extent I see this with my ASHP and cylinder.  The temperature probe is in the lowest pocket, about 1/3 from the bottom of the cylinder.  So the ASHP does not even know you have used any hot water until you have used 1/3 of it.  Or put it another way, my 300L tank might have only a little over 200L of hot water when the epic showering starts, and then you have the potential for a "ran out of water" situation.

[ToughButterCup]

30 minutes ago, SteamyTea said:

Measure the flow rate, the output temperature on the hot pipe and the input temperature on the cold pipe.

Then do the sums.

 

Ok.

Can I ask you for a formula that I can apply to those numbers, please?

I know that the HansGrohe is pre-set at 40 , and the input temp is about 18ish....... Flow rate  is 18 litres a minute or thereabouts....

[Dan F]

3 minutes ago, ToughButterCup said:

 

Ok.

Can I ask you for a formula that I can apply to those numbers, please?

I know that the HansGrohe is pre-set at 40 , and the input temp is about 18ish....... Flow rate  is 18 litres a minute or thereabouts....

 

0.46kWh/min I think.  Which would mean your 2.4kWh shower earlier today was about 5.3 minutes?

 

https://www.omnicalculator.com/physics/specific-heat?c=GBP&v=equation:0,c:4181.3!jkgk,substance:1543850775,m:18!kg,T:22!C

[Temp]

I'm not very familiar with Sunamp but I know they store energy in the latent heat of fusion (aka phase change, aka melting) rather that in the materials specific heat capacity (aka temperature change/rise). Phase changes normally occur at a constant temperature so to work out how full it is you really need to know how much of the magic wax (or whatever they use) has melted and how much is still solid. If you keep adding heat once its all melted the temperature would start rising again so they can decide that its full when a certain maximum temperature is reached. Likewise if the temperature falls below some minimum they can assume its empty. So full and empty are probably easy to work out but anywhere in between is tricky. 

 

Its a bit like the difference between lead acid batteries and lithium. With lead acid the voltage is a reasonable measure of the state of charge but with  Lithium the voltage curve is a bit too flat to be a reliable measure of how full they are. Modern Battery management systems measure how much energy has gone in and out so they can work out how much is left in the battery since it was last fully charged. With the Sunamp its easy to work out how much electricity has gone in but I suspect they don't measure how much is taken out? 

 

Hence i agree with...

 

1 hour ago, SteamyTea said:

Measure the flow rate, the output temperature on the hot pipe and the input temperature on the cold pipe.

Then do the sums.

 

Once you have input an output data you could (with the help of a computer prog) calculate how much is still in the Sunamp without waiting to see how much you have to put back in to fill it up.

 

 

[ToughButterCup]

15 hours ago, Dan F said:

....

Which would mean your 2.4kWh shower earlier today was about 5.3 minutes?

 

You 'bin lookin' while I wuz ablutin' ? 

Edited July 9, 2021 by ToughButterCup

[Triassic]

So how much is a Sunamp nowadays? Was it worth the extra over a cylinder setup?

Edited August 2, 2021 by Triassic

[Russdl]

@Triassic obviously depends on the model, the largest is around the £3300 mark from Midsummer  

[ToughButterCup]

@Triassic, the issue for us is space. The SA fits neatly in   a little nook next to our bathroom. So, yes is the answer.

[willbish]

5 hours ago, Triassic said:

Was it worth the extra over a cylinder setup?

Installed mine this week. Piece of cake. Definitely a labour saving to be made over a cylinder which might be a consideration for you. 

[Oz07]

14 minutes ago, willbish said:

Installed mine this week. Piece of cake. Definitely a labour saving to be made over a cylinder which might be a consideration for you. 

Respect to all you hubbers who have no fear playing around with electricy magic boxes. Changing a fuse is my limit. 

[Triassic]

20 hours ago, Russdl said:

@Triassic obviously depends on the model, the largest is around the £3300 mark from Midsummer  

Then there's the ASHP price on top.

[ToughButterCup]

Just for the sake of completeness, our diverter needed a set of tweeklets to cope with the SA's characteristics: they are well known and simple to set up. EDDI's phone support is excellent. 

[Russdl]

@Triassic I’ve got the all electric Sunamp so no ASHP in the equation for me but plenty of solar PV.
 

Works a treat, but I suspect our first full winter of occupation (which seems to be fast approaching) will highlight how little the sun will play a part in our master plan.