How to play - The SunAmp Guessing Game

[ToughButterCup]

Roll up Roll up! There’s a new game in town - the SunAmp Guessing Game. No, I’d never heard of it either until I was forced to play it.

 

It goes like this.

• Install a SunAmp Uniq summat or other (14kWh - Ok, 13.7)
• Hitch it up to some solar panels
• Wait for the sun to kick the PV to life
• Watch the electrons being converted (via that Mr Eddi and Mr Solis) from this-to-that-to-the-other. (Very pretty little animation too)
• Look at the readout which tells you how many of those tortured electrons are sitting in your SunAmp waiting for you to
• Have a shower, wash the dishes, scrub grandchildren clean before their mother sees them

 

Easy innit? Well no. And thats the game. 

 

See, SunAmp hide vital information from you. Like how much ‘hot water’ is ‘left’ in the tank.

(Sorry nerds, can’t be arsed to describe it more accurately). 

 

Lets imagine the tank is full. Its been a lovely sunny day: full-speed charging of the SunAmp. And I take an 18l per minute shower (excessive I know but want, want, want). 10 minutes later I’ve got rid of a fair bit (say at least 160 litres - you can’t change the flow rate on the part of  my shower that I use [iBox])  SWMBO has a bath - say 50 litres. Both at an unknown temperature but  above 20.

 

How many kWh’s worth have I used? No, I’m damn well not gonna take a thermometer out and measure the temperature during my shower or in her bath.  So I can only guess how much ‘hot water’ is left. Anyway, couldn’t do the maths.

 

Interesting.  

 

Next question: 
In relation to tomorrow’s DHW needs,

• Boost or Not to Boost ? (shunt mains electricity into the SunAmp instead of PV)
• What hot water are we likely to use before tomorrow? 
• Some/any/nowt? Lets say nowt ....
• Well wassa weather forecast for tomorrow then?

 

Partly cloudy for NW Ingerland
Hmmmm, got enough water for our showers tomorrow ?

 

So how many kWh is that likely to be?

The only way I have solved this question (have we got enough hot water ‘left’ for tomorrow)  is empirically. 

 

And annoyingly, the answer to this ‘game’ depends on how much cloud there is locally.

Heavy clouds, easy, no cloud, easy. Partly cloudy: nightmare. Too little PV, I need to boost. Too much and PV generation goes into the grid. Sod that.

 

The problem becomes guessing:

• how much sunlight will get through on a partly cloudy day.
• where is the sun in its cycle
• how many leaves on the trees
• the local wind effect on cloud (we live within the coastal strip: ie. in the ‘cleaner’ air mass)

 

All because SunAmp can’t / won’t / CBA to give us normal users an indication of how much energy is left in the tank
 

[SteamyTea]

13 minutes ago, ToughButterCup said:

All because SunAmp can’t / won’t / CBA to give us normal users an indication of how much energy is left in the tank

That is because they don't know it accurately enough.

The trouble is that the phase change temperature is a constant.

The only way to get it fairly accurate would be to measure the electrical input, measure the thermal output, factor in standing losses, then do the sums.

Only needs a cheap thermal energy logger, a simple processor unit and some time.

If the flow rate is constant i.e. just showers, no need for a flow meter. 

[MikeSharp01]

10 minutes ago, ToughButterCup said:

All because SunAmp can’t / won’t / CBA to give us normal users an indication of how much energy is left in the tank

Actually not heard you can get this with a normal hot water tank does Sunamp actually know how much is left? Interesting problem none the less. So you would need to know how much flow you had taken through and the temperature of it as it went through, it would still be somewhat error prone depending upon accuracy / resolution of the measuring devices.

[MikeSharp01]

 

3 minutes ago, SteamyTea said:

The only way to get it fairly accurate would be to measure the electrical input,

Guess the Sunamp must know when it is full! So you only need to measure outflow of energy and use that to determine top up regime / requirement.

[ToughButterCup]

Yes lads. 

You two have forgotten more science than I'll ever know. 

 

First class opportunity for intelligent bods like you two to come up with a nice little after-market gizmo to tell us plebs 

"Ow much 'ot wada's left then?

Edited June 7, 2022 by ToughButterCup

[Dan F]

Get yourself one of these?

 

[dpmiller]

what happened to the string of thermistors up the middle that worked like a fuel gauge?

[ProDave]

The problem is not much better with a conventional unvented hot water cylinder.

 

The ASHP uses the lower of the 2 thermostat pockets to measure the tank temperature.  Near the end of a sunny day like today it is reading69 degrees.  All that lovely heat courtesy of a bit of sun, some chemistry and some electronics.

 

BUT from watching what happens next, there is "room for improvement"

 

Someone takes a long shower (far longer than necessary, but they blame the duration on the amount of products needed to be applied to their long hair, a problem I do NOT have).  The water at the top of the tank is still coming out piping hot, but what has happened is the hot water in the tank has all just "moved up a bit" and at the bottom replaced by cold.  As soon as the hot / cold transition gets above that lower thermostat pocket, the ASHP thinks the tank is cold and fires up, and I am there shouting at it saying why the b****y hell do you want to come on?

 

If I were designing this system again, I would specify a whole row of thermostat pockets up the tank, and I would specify an extra tank tapping near the bottom of the tank, not far above the cold inlet tapping, and I would have a circulating pump that could come on to stir up the hot water in the tank to even it;s temperature out a bit, and hopefully avoid the ASHP coming on when not really needed.  but I can't see a way to retro fit that with no tank tapping low down to circulate the water to.

 

[joe90]

1 hour ago, ProDave said:

and I would have a circulating pump that could come on to stir up the hot water in the tank to even it;s temperature out a bit, and hopefully avoid the ASHP coming on when not really needed. 

But if you did this then someone halfway through a shower would get warm water not hot 🤔. What we need is a “fuel gauge “ like on a petrol tank, come on bods design us something (that’s not complicated because I am a Luddite 🤷‍♂️)

[ProDave]

2 minutes ago, joe90 said:

But if you did this then someone halfway through a shower would get warm water not hot 🤔. What we need is a “fuel gauge “ like on a petrol tank, come on bods design us something (that’s not complicated because I am a Luddite 🤷‍♂️)

What I am talking about is something to stir up the water in the tank so instead of having 70 degrees in the top half and say 30 degrees in the bottom half, it mixes it around a bit when it senses a large stratification like that and ends up all at say a nice even 50 degrees.

 

Thermostatic mixers ensure nobody notices a change in water temperature.

 

To make an accurate "fuel gauge" for an UVC you would need several thermometers all the way up the tank, hence if I were ordering again, I would have got at least say 5 thermostat pockets evenly spaced up the tank.

[joe90]

10 minutes ago, ProDave said:

What I am talking about is something to stir up the water in the tank so instead of having 70 degrees in the top half and say 30 degrees in the bottom half, it mixes it around a bit when it senses a large stratification like that and ends up all at say a nice even 50 degrees.

But as I have no PV (yet) and I only heat DHW to 48’ i would end up with Luke warm water 🤔

[ProDave]

25 minutes ago, joe90 said:

But as I have no PV (yet) and I only heat DHW to 48’ i would end up with Luke warm water 🤔

Yes, my idea is aimed at how to mix the very hot water from surplus PV heating around a bit.

 

What I find, is when I get this temperature step thing and the ASHP comes on because the bottom of the tank is cold but the top is still piping hot, is the ASHP does not run for very long, less time than you might expect.  I am convinced that once it starts heating, this sets up convection currents within the tank that draws the top hot layer down and helps with the mixing process.  Just speculation.

[SteamyTea]

4 hours ago, ProDave said:

I would have a circulating pump that could come on to stir up the hot water in the tank

Have often thought this is a good idea to get an extra kWh or 2 in a cylinder.

I am currently running my cylinder with just the top element (on a timer to get the E7 rate).

Water temperature is 20°C higher than it used to be, but a lot less volume and much less mixing.

So saving between 1 and 2 kWh/day.

Usually have enough hot water for the after work shower.

[SteamyTea]

4 hours ago, dpmiller said:

what happened to the string of thermistors up the middle that worked like a fuel gauge?

I think they are probably more to do with making sure all the phase change material becomes liquid while heating. Convection currents will tend to even the temperature out, but an off set to cater for distance from element could be easily established with experimentation.

 

I do not know the product well enough, but as it knows it is full (element turns off), it would not be too hard to program something to make it take a charge after use.

I think it has to treated like a car with a very small fuel tank on a long, unknown, journey.  You take every opportunity along the way to fill it up as you go along.

[ToughButterCup]

11 hours ago, SteamyTea said:

...

but as it knows it is full (element turns off), it would not be too hard to program something to make it take a charge after use.

I think it has to treated like a car with a very small fuel tank on a long, unknown, journey.  You take every opportunity along the way to fill it up as you go along.

 

Exactly right. 

But sometimes the fuel cost is pre-paid (upfront purchase, and maintenance costs ) or import from the grid. And when - by accident - (I try hard to self-consume) 'my ' power I export it , it makes me cross

( @SteamyTea's right, I get cross about loads of stuff these days)

 

Today is an excellent case in point. Fully loaded yesterday evening : then 1 bath, and 1 shower - at a guess 10kWh's worth of PV self-consumption . So, there's a bit left in the tank  (13.7 - 1 [heat loss o/n] - 10 = say 2kWh)

 

Have I got enough left in the tank to have a shower this morning using PV alone?  

Depends on how much PV is generated between dawn and .... when I get back. Doesn't look too good does it?

 

Off to the gym now, so I'll tell ya wot happened when I get back...... 

 

[SteamyTea]

2 kWh should be enough.

I had 2 showers and ran my house on that amount yesterday.

[MrMagic]

15 hours ago, ProDave said:

What I am talking about is something to stir up the water in the tank so instead of having 70 degrees in the top half and say 30 degrees in the bottom half, it mixes it around a bit when it senses a large stratification like that and ends up all at say a nice even 50 degrees.

 

I think the EDDI has an option for a de-strat pump - pg50/51 of the user manual - 

Quote

The water in the cylinder (3) is heated via the immersion heater (4) with surplus power until the thermostat has opened, then eddi will run the pump (8) for up to five minutes. This pushes some of the hot water from the top of the cylinder (3), down to the bottom, thus pulling the cooler water up to the region that can be heated via the immersion heater (4). As the cooler water is drawn up, the thermostat will close again and eddi is able to resume heating the water

 

[TW9]

On 07/06/2022 at 17:02, dpmiller said:

what happened to the string of thermistors up the middle that worked like a fuel gauge?

I assume you mean whatever is triggering the lights on the front of the Sunamp that show how full it is? They're still there... at least they are on ours. There are only four of them so it doesn't give a detailed view of how charged it is but it's better than nothing.

 

They're only on the electrically heated Sunamp. For the others you have no way of knowing how charged they are.

[Radian]

23 hours ago, ProDave said:

What I find, is when I get this temperature step thing and the ASHP comes on because the bottom of the tank is cold but the top is still piping hot, is the ASHP does not run for very long, less time than you might expect.  I am convinced that once it starts heating, this sets up convection currents within the tank that draws the top hot layer down and helps with the mixing process.  Just speculation.

 

I think that's very interesting indeed. Could it be that chopping the solar divert power into bursts (over a period of several minutes to illustrate my thinking) could kick off turbulence? Some experimentation is in order!

[SteamyTea]

1 hour ago, Radian said:

 

I think that's very interesting indeed. Could it be that chopping the solar divert power into bursts (over a period of several minutes to illustrate my thinking) could kick off turbulence? Some experimentation is in order!

Or recrystallization

[Radian]

1 hour ago, SteamyTea said:

recrystallization

Breaking bad style?

[SteamyTea]

17 minutes ago, Radian said:

Breaking bad style?

 

[Ferdinand]

Hmmm.

 

As I see it this may be practically unknowable.  Gre-mattering:

 

Problem 1: Hot water runs out unpredictably because I do not know how much heat is left in the Sunamp.

Problem 2: This is likely to be unfixable without a fair amount of technology. As part of the heat in a Sunamp is stored as phase change, and part if stored as rising temperature. So it is difficult to measure - measuring the % of phase change material which is liquid / solid perhaps being the most awkward aspect.

 

Plan A: Partial solution: install a shower heat recovery device, which should mean that the heat required from the Sunamp is a little less due to the recovered heat, which should mean that the heat you have lasts longer than it would otherwise.

 

So your shower should go cold less frequently.

 

(This does not help with a bath, as you do not continue running it whilst water is running out.)

 

Plan B: Take a shorter *&^% shower.

 

Sidenote for @ToughButterCup.

 10 minutes later I’ve got rid of a fair bit (say at least 160 litres - you can’t change the flow rate on the part of  my shower that I use [iBox])  SWMBO has a bath - say 50 litres. Both at an unknown temperature but  above 20.

 

Are you sure about that 50l bath?

 

In a normal bath (estd at .8-1 sqm in area in the hole say) that is approx 50-60 mm of depth. 2 inches and a bit.

 

Really?

 

Ferdinand

 

 

[SteamyTea]

10 minutes ago, Ferdinand said:

Plan A: Partial solution: install a shower heat recovery device

Where will use that saving on a short shower, say 2 or 3 minutes.

I think the problem with these devices is they need a relatively long time to start recovery processes.

Energy scavengers, which these devises are, are rarely worth it in practice.

[Ferdinand]

1 minute ago, SteamyTea said:

Where will use that saving on a short shower, say 2 or 3 minutes.

I think the problem with these devices is they need a relatively long time to start recovery processes.

Energy scavengers, which these devises are, are rarely worth it in practice.

 

They are about to become a much needed product for LLs needing 2 more points on their EPC to avoid committing a criminal offence by renting out a substandard property.

 

And hopefully soon for owner-occupiers if NoGoBoJo gets off his fat butt and starts imposing some regulation of Energy Efficiency on OO house, with reasonable incentives for noncompliance (say an extra Council Tax band).