Choice of intelligent switches ?

EricMears

zeupater wrote: »

. . . considering the number of days where generation must be far in excess of the thermal capacity of a standard build cylinder (#327)

Luckily, I don't have a 'standard' cylinder.

My Heatbank cylinder is big (300litres I think) and the immersion is trying to get to 95 deg C (but usually failing - I very seldom see the "HOT" message). Today wasn't a brilliant day - I've only generated 18.9 kWh - but MyImmersun is telling me that I've generated 19.5 kWh & diverted 10.4 of that to Heatbank. Apparently I've used 20.6 kWh but around half of that was to charge the car last night.

My donation to the grid was 0.8kWh.

danesol

zeupater wrote: »

Only in very good months, so anyone considering that the saving would be for a typical month and therefore multiply the figure by 12 and use that figure as a typical saving, well they should consider that as being ... <cough> ... Bulls**t ... <cough> ...

Notably, there was no response to .... "So you're diverting somewhere around 1000kWh/year to the DHW then ?" .... logic check needed .... orrery has stated a saving based on around 1100kWh/year reduction in gas usage and our dedicated solar thermal averages 'diverts' somewhere around 1400kWh but this is limited more by usage than collection, So, when taking DHW heating (only) gas system efficiencies at (say) ~66% (?) with gas at (your) 3.45p/kWh, diversion of 1000kWh would likely displace ~1500kWh of gas, which would cost £51.75 (1500x0.0345) .... at orrery's diversion (say 660kWh diverted) call it ~£40 and at ours ~£75 .... we would save a little more due to very long primary circuit 28mm pipe runs, but those figures would probably describe a typical bracketed range for decent proportional-diversion annual savings from a ~4kWp array as being £40 to £75 ... of course, depending on a number of obvious factors, there's scope for more and the risk of less, but .....

HTH
Z

Correct only in good months and if you review what i said initially 7 x 12 = 84, LOL I didn't mention duration as that simply is conditional to surroundings given I am assuming not everyone maybe in the UK

I didn't respond to your previous statement purely as I don't know as with the way these units work, they make clamp meters act strangely and they do not record correctly

The recordings I do know which are accurate and meaningful are the following;

1. DNO meter reading every month ie How much I import

2. Reading of generation taken each month ie. How much I generate

The others are either assumption, via calculation or mis-readings due to the issue surrounding the SolarImmersion circuitry which calculates free excess electric, which does work as I regularly check for a stationary meter

My calculations are merely stating the obviously, I know roughly now or I did back then, how much it costs to heat a tank of water up, if doesn't need great brain power to know that if the boiler is switched off for several months - that is your ULTIMATE saving .... lol


Are you always this argumentative/subjective ? :rotfl:

danesol

orrery wrote: »

I've got the solarImmersion and I can't get a handle on the savings because things have changed so much since (new boiler, revised C/H system, electric car etc) that I can't make any 1:1 comparison.

I can say that for about 3 months of the year (last year was longer, but this year is proving a bit lacking) we get our daily hot water for free (a bath and a shower plus a bit spare) for free.

However ...
In making all these statements we need to be careful to advise that you do need the right immersion heater - a short 12" top-mounted immersion isn't going to deliver the savings. I've had a 30" fitted, and a bottom mounted immersion would be better.

My best shot is that I now use about 17 cu meters of gas over the 4 best months (I use the gas if the previous day has been shockingly bad, or we have visitors for the weekend) and I used 130 cu meters the year before I had the solarImmersion. So a rough estimate is 100 cu meter = 1100kWh of saving or about £38 per year. Of course, there is contribution in the other months too, but I'm ignoring this as the comparison is with an older less efficient boiler.

So, proper payback would take about 8 years but I'm well happy as I wake up with a free tank of hot water and that is a really great feeling.

Completely agree with this, but I will add that its a subjective situation depending on multiple factors and I have noticed with surprise sometimes how this unit works outside the normal Feb to Oct period, given you have the right conditions outside to cause an excess the unit can utilise.

Unfortunately unless a future unit records the absolute diversion of energy to loads 1 and/or 2 you merely dont realise its full potential, only what its obvious.

With associated methods or technologies to aid this, I have held myself back in most cases even the longer immersion heater as when I really think about it unless I need a replacement due to a fault, it simply isnt worth ROI especially in the short time.

zeupater

pinnks wrote: »

Don't get me wrong, I am more than happy to play with maths but sometimes the modelling needs factors which are difficult to estimate.

Anyway, the displaced amount looks about right for my system (sorry, can't find the energy today to pull out the actual numbers) but my diversion is only about 750kwh per year over the 3 years it's been in (2250kWh since 25 June 2013).

The difference on top of boiler (in)efficiency? Losses I assume in the 20m plus round trip of unlagged 28mm/22mm pipes between boiler and tank, which is less easy to model.

Hi pinnks

Then the question revolves around the overall efficiency. Using your supplied figures as an example, a £100 saving from diverting 750kWh values the gas at 13.3p/kWh which represents a boiler/system efficiency at somewhere close to 25% (3.45/13.3). It is interesting to note that 750kWh diverted is pretty much in line with orrery's assessment of 1100kWh of displaced gas, both being from proportional diversion and both are roughly in line with the BRE's assessment of solar contributions to DHW demand referenced earlier in this thread.

The issue here is that the 25% is most likely down to the way the DHW was being heated by gas before the proportional diversion was in place. If your summer demand isn't particularly high compared to the stored DHW volume the heat replacement demand will be low and this will have a disproportion negative effect on the overall heating cycle efficiency - ie you could be expending more energy heating the 'system' than the water ... this is what you seem to be describing and I agree, but 25% efficiency is still extremely low, much worse than we had from our huge 25 year old floor-standing boiler before it was replaced and certainly about half of what we currently achieve even with our long pipe runs ...

There is a solution to the issue described above. If the DHW stored is sufficient to cover a number of days of usage and is well insulated, then why fire-up the boiler every day? - just do it when it's required and the efficiency will improve substantially - all that's needed here is a higher specification GCH timer/controller and a little forethought ... this is effectively what we do between late Autumn and late Winter when the solar thermal input to our (huge) cylinder becomes anywhere near the point where shower temperatures reach MrsZ's moan-zone, but it equally applies to anyone, completely independently of whether solar is in place, or not .... it's simple energy/money saving ....

HTH
Z

zeupater

EricMears wrote: »

.. My donation to the grid was 0.8kWh ...

Hi Eric

Although, as should be apparent, the figure actually represents a daily net energy balance to the grid and in no way represents a 'monetary' position ...

Z

pinnks

Hi Z,

I agree your reasoning. We get all of the hot water from diversion for the summer months and when the central heating goes back on then it powers DHW to, of course, but only once a day in the evenings to ensure that the max available is taken from PV. On the rare occasion when we have really bad day in summer, such that the water does not show hot on the diverter, I tend to give a short burst of 3kW immersion to finish the job rather than firing up the boiler. Probably did that a handful of times over the past 12 months.

When it is time to replace immersion and/or tank I may well go slightly larger and of course better insulated but until something breaks will struggle on with what I have...

zeupater

danesol wrote: »

Correct only in good months and if you review what i said initially 7 x 12 = 84, LOL I didn't mention duration as that simply is conditional to surroundings given I am assuming not everyone maybe in the UK

I didn't respond to your previous statement purely as I don't know as with the way these units work, they make clamp meters act strangely and they do not record correctly

The recordings I do know which are accurate and meaningful are the following;

1. DNO meter reading every month ie How much I import

2. Reading of generation taken each month ie. How much I generate

The others are either assumption, via calculation or mis-readings due to the issue surrounding the SolarImmersion circuitry which calculates free excess electric, which does work as I regularly check for a stationary meter

My calculations are merely stating the obviously, I know roughly now or I did back then, how much it costs to heat a tank of water up, if doesn't need great brain power to know that if the boiler is switched off for several months - that is your ULTIMATE saving .... lol


Are you always this argumentative/subjective ? :rotfl:

Hi

So, in summary - you seem to have absolutely no idea what you're diverting but are confident on what's being saved ...

Regarding "Are you always this argumentative/subjective ?" ... well, considering the paragraph above, by utilising mathematical modelling I'm obviously trying to bring an objective viewpoint to claims which seem to be purely based on subjective interpretation ....

Pretty simply, a typical domestic cylinder (~114litres) would need to consume approximately 7kWh of electricity to heat from completely mains temperature cold to around 70C. Considering that most cylinders wouldn't be completely cold at the start of the heating cycle then probably less would be common ... so a sanity check based on a (say) 5kWh daily diverted energy provision to a mostly depleted typical DHW store, every day - month by month, summer & winter - totally independent of weather conditions and daylight hours gives what ? ... 1825kWh (5x365) ... this is almost almost spot on with the 1800kWh/year calculated as the likely diversion required to achieve a claimed £94.90 annual saving as calculated in post #500 earlier on this thread ..... sanity check therefore suggests that the claim would be pretty hard to achieve, after-all there are plenty of days where our 4kWp system doesn't achieve an excess which would allow diversion of 5kWh to thermal storage, some of those even being within the past couple of weeks ...

HTH
Z

EricMears

zeupater wrote: »

Hi Eric

Although, as should be apparent, the figure actually represents a daily net energy balance to the grid and in no way represents a 'monetary' position ...

Z

No monetary position was implied. One can donate may things : money certainly but also flowers, chocolates, books, clothes or - as in this instance - electricity.

zeupater

pinnks wrote: »

Hi Z,

I agree your reasoning. We get all of the hot water from diversion for the summer months and when the central heating goes back on then it powers DHW to, of course, but only once a day in the evenings to ensure that the max available is taken from PV. On the rare occasion when we have really bad day in summer, such that the water does not show hot on the diverter, I tend to give a short burst of 3kW immersion to finish the job rather than firing up the boiler. Probably did that a handful of times over the past 12 months.

When it is time to replace immersion and/or tank I may well go slightly larger and of course better insulated but until something breaks will struggle on with what I have...

Hi

I seem to remember discussing adding further insulation (DIY jacket) a couple of years ago (?) ... have you done this yet ? .... I've just checked back on an improvements spreadsheet from the '90s and providing an additional (and thicker!) insulation jacket to double insulate our cylinder at the time cost ~£6, which reduced the standing (replacement fuel) heat-loss from 5.5kWh to 2.1kWh/day, so a providing pretty reasonable payback ....

HTH
Z

zeupater

EricMears wrote: »

No monetary position was implied. One can donate may things : money certainly but also flowers, chocolates, books, clothes or - as in this instance - electricity.

.... on the subject of chocolates or flowers, should we consider sending some virtual ones to Amber Rudd to celebrate/commiserate the demise of DECC .... OUTSTANDING (sorry for shouting) result, I'm almost starting to like TM already (maybe not though - it's still early) .... or should we simply write & donate a book ... something like 'The Palace of Westminster Dummies Guide to Energy Efficiency' ? ....

Z