Ditching gas, going electric immersion only, a wee project

Heedtheadvice · 2 November 2022 at 1:01PM

Sad to hear of your PID results. It is probably down to tuning of the PID controller functions as it should perform much better than straight on off control.

Not so easy to tune in an operational system but, if you can and wish to progress, suggest manual tuning at lower temperature set point and then increasing temp once you have it sussed. A lot about PID on WickieP a fair way through article comes to tuning with much maths to ignore if you wish

Solarchaser · 2 November 2022 at 7:56PM

Hi Michael's, yeah If stat on bottom element is at 75,C you can guarantee the top will be significantly hotter than that.

Heedtheadvice, I watched a load of you tube videos and did several searches where people had done multiple stages of optimisation of the PID's and gotten good results, but I guess what they excell at is providing a stable temperature over an extended period of time with the optimised cycling, however what I really need is just to heat full power and then cut out when it reaches the temperature I specify, I dont really expect them to come back on after having cut off during the 3 hours of heating.

The other part is, I'm kinda done/over the messing about stage, I just want it to do as I instruct, and I swear I've put 10 years on my knees over this last 6 months, so I'm trying to avoid multiple visits to the tanks.... cos, well it hurts!!
And so the optimisation isn't floating my boat right now.

I dont disagree I'd potentially end up with a better result, and perhaps next summer I'll view things differently, but for now I just want it to work as a blunt instrument rather rhan a precise one.... I feel a little sad even saying that.

The truth is the tanks themselves were a good amount of time as a project, but having to rip out the main bathroom to be able to fit thermostatic showers, removing all the wiring for the electric showers, all the plumbing involved, it's a good size or project on its own, plus having to fix a car unexpectedly....

Oh man, I feel myself turning into a grumpy old man 😂😂😂

On a lighter note, due to removing the thermostats in the tanks, I've had 3 controllers running 3 elements, and the Eddi controlling the last... but with no temperature control as the relay board has been out of stock.
It's been a few weeks away since the start of MAY!!!!
I found a relay board in stock on ebay, so I should have one of those in the next couple of days, the difference that will make is being able to set a stop temperature that I can depend on, but also I will be able to see the temperature from the App which for a lazy bum will be great.

Heedtheadvice · 3 November 2022 at 10:32AM

You have done a power of work and that should not be underestimated for a lone person. You may wish to tweak it in time but progress so far seems excellent and you can enjoy the fruits of your labours.....and now give your knees a rest. Internal embrocation recommended!

I expect for virtually all readers of this thread 'lazy' could be the last thing that comes to mind

Solarchaser · 9 November 2022 at 2:07AM

Very kind of you to say, thanks 😊

Came to a decision about my overflowing small tank, I've blocked the overpressure/over temperature safety.
I know, I know, but it was leaking at 82C, which the small tank was hitting most nights, and dumping a load of water I'd paid to heat🤬
My thinking is there are 2 fail reasons
1. Overtemperature, well I now have PID's and Eddi Controlling temperature, both more accurate than what I assume is a bimetallic strip/valve

2. Overpressure, well the tanks are linked together, the tanks are built for 7 bar, I'm running a max of 2 bar, and if there is an overpressure situation then the main tank will vent/dump.

I'm generally dead against removing safety measures, but I feel this is all I can do with this.
Having researched a bit into these dual safety 7bar /95C they nearly all state a 10% tolerance, so 95c is maybe 85c or 105c. So I feel its not worth the faff getting another one, as the main tank has a working one, which lifts around 93-94c so hopefully I can run a 90C limit

The eddi relay board arrived yesterday and so I finally got to plug in the pt1000 sensors, which is great as I'm never too trusting on pt100 sensors or ntc's that I've had monitoring the tanks.
PID K types are within half a degree of the pt1000's though, so I know they are good.👍

Eddi has a configurable hysteresis , with standard of 5C, and I think that's a good figure for me.

The weather has turned a bit colder these last weeks and noticing that as I approach the off peak rate the tanks are down in the low 50's or even high 40's due to the heating running for longer periods, and the lack of half decent solar to give a mid day top up.

So far struggling to get to 80C in the main tank during the off peak time, partly I guess due to the central heating being on in the evening, sucking some of the heat away, and partly due to 1-2 of the heaters cutting out as the top of the tank is 25c hotter than the mid point on the smaller tank, so not getting the full 36kwh of heat.

So I'm pretty delighted to finally have the destrat wired up to come on for 10 minutes, 3 times during the heating period to spread the heat around the tanks, that should stop the heaters cutting out, and that should mean I'll get the full 36kwh of heat in my 3 hours of off peak.🤞

Last night I seen 24.6kw on the in house display, 7kw charging batteries, 12kw on the tanks, the dishwasher running and the wife plugged in her car.
Only lasted one 10 second cycle though, as I set the max amperage on the zappi to 96a, so when it seen I was over that amperage it reduced power to the eddi, which was pretty cool to watch it react, and certainly instills confidence in the myenergi kit, which I have to say I really do like.... and yes especially now I can see temperatures in the app 😁😁
And track them all day like a proper saddo 😂

So as a general round up for the last couple of weeks, since we no longer have electric showers and are using thermostatic utilising the hot water from the tanks, I'm noticing that I've generally got around 20-25% more in the batteries than I'd expect for this time of year.

I guess this is due to not having them trying to cover the showers.
This should mean a decrease in peak import, which was unavoidable before, so hopefully a saving there.

I'm using significantly more electricity than before, which is hardly a surprise, averaging around 300kwh / week just now, but on an upward trend as you would expect with the weather turning colder.

I think even getting the full 36kwh into the tanks, I'm going to struggle to maintain good temperature in the tanks over the course of a harsh winters day, in fact I think it will be pretty impossible.
My average winters day was 50kwh of gas, plus around 6kwh of electric showers, so covering 56kwh with 36kwh I suppose was on a hiding to nothing.... or let's go with optimistic 🤪

Maybe I'm being a little defeatist here, let's see how it runs the next week with a full 36kwh every night, and now I'm done messing about I can finally insulate around the tanks, which should help too.

Heedtheadvice · 9 November 2022 at 12:39PM

You have probably already looked at this topic but would it be worth your while reviewing individual room heating times and set temperatures.......just 1 degree cooler and......you may freez......no, save a bit!

Solarchaser · 12 November 2022 at 8:37PM

Hi Heedtheadvice, I can't say I've specifically looked at that to be honest.
More generally I'd say that it's been noted different rooms in the house are warmer or colder, and so for instance the back room was cold for my daughter, and so when ripping it all out and redoing it last year I added some more insulation above the room and the wife decided on a much larger flat panel radiator for her room, and so controlled by thermostatic valves, it's now at a temperature she is happier with. On the flip side of that, the front room was always too warm, so simply turning down the thermostatic valve and the lockshield on that one has helped, also while redoing it at the start of this year, I added sound deadening insulation to it for two reasons, 1 to reduce noise from son playing xbox and 2 for reduction of heat loss from livingroom below.

I can't really say I've optimised for a set temperature more I've optimised the temperatures for the people in the rooms, and generally the household seems happier with this.

I appreciate you are looking from the point of view of optimising temperatures for potential costs savings, I guess I'm viewing more in terms of optimising the house for its inhabitants comfort levels first, and savings next as long as they don't affect the comfort levels.

Since my last post predicting a struggle to reach top temperature, of course the tanks have both topped out every single night 🙈
The destratification during the heating cycle is both spreading the heat much better in the tanks, but also meaning the heaters can be on pretty constantly throughout and have reached max temp within the first 2 hours of the 3 hour cycle.
Milder temperatures have obviously helped too.

Solarchaser · 14 November 2022 at 6:35PM

So inspired by Freeposts block diagram of the proposed system, I figured I should really do one myself of my system as it sits.
I figure I'll do it over two posts, this one being the plumbing , and the next one the electrical.

Hopefully it's fairly self explanatory, bit i'll prattle on a bit anyway.

There are 3 fluidic circuits.

First circuit is the generation of hot water, cold water comes in, and is connected to an expansion vessel (EV) to try and reduce water hammer both through the various machine valves (washing and dishwasher etc) as well as shock to the internal coils of the tanks from when the taps are turned on and off.
From there water goes through a pressure reducing valve (PRV) the main reason for this, apart from bringing the 3.5bar mains down to 3 bar, is to balance the system so that both hot and cold are at the same pressure, this should ensure the thermostatic showers are predictable and consistent.

Cold water goes from here to the mixer for potable hot water.
For the hot water, it goes first through the coil on the smaller tank acting as a preheat, and then through the main coil and out to the mixer.

Second circuit is the central heating circuit, the pump (P) pulls water through the trap (which should filter out the crud) in through a one way valve, through the internal coil where its heated and out through the next one way valve.
Some of the water will be pulled through the valve before the coil which acts as a mixer valve, this stops the radiators being at 80C, I'm averaging around 56C at the moment, which seems about right, though even at 40C the radiators appear to be happy keeping the rooms warm.
After the pump the easiest route for the water appears to be through the pex loops (floor coil) I used to make a rudimentary under floor heating at the back of the livingroom, and straight back to the coil, however as its pex, the inner diameter of the tubes is quite a bit smaller than the 22mm copper running to the radiators, and so this seems to work pretty well at distributing heat everywhere.

The third circuit is the recirculation of the water within the tanks.
This water doesn't go anywhere and can be seen as dirty water.
The Pump (P) pulls the water from the middle of one side of the tanks through two one way valves and pumps up to the top of the tanks and over to the other side.
Unfortunately I've only just realised when I drew this out, I put the motorised valve (MV) on the wrong tank 🤦‍♂️
The motorised valve is actually on the connection to tank two not tank one as my diagram shows.

So when the pump draws the water from the right side of the tanks and pumps it up to the left side of the tanks, if the second tank is cold, then the water is only pumped around the 1st tank.
If the water in the second tank is above 40C then the motorised valve is open and the water mixes in both tanks.

Solarchaser · 14 November 2022 at 7:07PM

Now for the electrical diagram, I think this will take a bit more explaining, but I'll give it a go.

I think it's best to think about this as a couple of different modes.
In summer mode the 1st 16a trip powers the EDDI, which in turn powers Tank 1 Element 1 by a variable power based on solar energy.
If tank 1 reaches its max during summer heating then two things happen.
1. The Eddi switches to its second heating element Tank 2 Element 1 (T2E1), this goes through relay 1 NC and out through Com
2. The Eddi relay 2 activates which then powers the Destratification pump for 15 mins.

For those who don't know relays, they are basically electric switches.
Usually they have 3 contact ports (though you can have more)
(NO) Which is normally open, or normally not active, which means that when the relay is not switched, this port is disconnected from the rest of the relay
(NC) which is normally closed, or normally connected to the circuit when the relay isn't switched.
(COM) Common is the port which is connected to the circuit.

So if the relay isn't powered there will be connectivity between NC and Com, but nothing between NO and Com.
If the relay is powered then there will be connectivity between NO and Com and nothing between NC and Com.
There will not be connectivity between NC and NO at any point with the relays I'm using.

So when relay 2 on the Eddi activates, the NO part is connected to the Com part, this Is power from the 6a trip and so power is given to the destrat pump.
If the 2nd Tank is below 40C then the 40C NO switch will not give power to the motorised valve and the water will only circulate in the 1st tank.
If the 2nd tank is above 40C then the 40C NO switch will be activated and so will give connectivity to the Motorised valve, which opens and allows the water to circulate between both tanks.

In winter mode for the Eddi, on a timer set in the Eddi relay 1 switches over at the same time Eddi gives 3kw to T1E1, so when it switches over, the NO is connected to the Com and T2E1 is powered by the second 16a trip.
This is used for the off peak charging and means I can heat two elements with a total of 6kw on off peak tarriffs.

In winter mode for the other two elements, a timer activates during my off peak, this gives power to both the PID controllers and the Destrat timer.

The destrat timer makes the destrat pump come on for 10 mins every hour, it does that by powering the destrat relay (DR) coil causing it to switch from NC to NO and so taking power from the 6a right hand trip, this takes the power to eddi R2 which is set to NC and so power simply runs right through it and down to the destrat pump.
As before if the 2nd Tank is below 40C then the 40C NO switch will not give power to the motorised valve and the water will only circulate in the 1st tank.

If the 2nd tank is above 40C then the 40C NO switch will be activated and so will give connectivity to the Motorised valve, which opens and allows the water to circulate between both tanks.

The PID controllers monitor temperature and give power to the solid state relays (SSR) which are similar to relays, essentially just electronic switches, when powered they allow the current from the 32a trip (two individual lines, one to each SSR) to T1E2 and T2E2
If the preset PID temperature is reached in either tank, its corresponding SSR is switched off and power is removed from the element.

So that's all the heating of the tanks, the only thing left to explain is the central heating portion.

When central heating is powered then power goes to NO port of Timed Relay 2 (TR2), but goes nowhere as its NO.
Power also goes to the right hand NC port of TR1, it goes through the relay and comes out of the Com port and activates the timed coil on TR2.

After 10 mins of continuous power, (if power is removed at any point then timer returns to zero) TR2 switches and power goes from the NO port to the Com port which then goes to the left hand NC port of TR1 and out through its Com port. (TR1 timed coil is also powered)
From here it goes through the NC and Com ports of DR and the NC and Com ports of Eddi R2 coming down and powering the destrat pump.
As before if the 2nd Tank is below 40C then the 40C NO switch will not give power to the motorised valve and the water will only circulate in the 1st tank.
If the 2nd tank is above 40C then the 40C NO switch will be activated and so will give connectivity to the Motorised valve, which opens and allows the water to circulate between both tanks.
If after an additional 5 minutes have passed power is still present from the Central heating, the timed coil on TR1 will switch, this will disconnect power from the TR2 coil which will reset it back to NO and so the destrat pump will stop.

This will cycle continuously like this until the central heating power is removed, so off for 10 mins, on for 5, purely to ensure movement of water around the central heating coil in the main tank.

Any questions, ask away and I'll try to explain without confusion

Solarchaser · 2 December 2022 at 2:52AM

a minor update.
The weather has taken a colder turn again and I believe I finally have the answer to the question of will the hot water tanks do the job of central heating, yes, they definitely will.

Will 36kwh of electric heated water replace 56kwh of gas heated water, unfortunately not.

The 56kwh is a figure based on 6kwh of previously electric showers and 1500kwh of gas over 30 days which makes up November, February and March. So 50kwh/day.
I've mucked up with December and January which actually average 55kwh/ day, not 50 as I'd previously thought/stated/ based my calculations on, so that will be 61kwh required in the coldest months.

My findings of the past 3 weeks are that having an average usage figure doesn't necessarily help, if the weather is milder, then 36kwh is more than enough, if the weather is colder, 36kwh is not enough, and by that I mean the tanks are down in the mid to low 40's C while still being required to provide heat, lowest I've seen on the main tank is 42C.
This still provides adequate heat, but is not so good for showers, don't get me wrong, they arnt cold, fine for me as I like about 36C, but the wife likes 40C and that isn't achieved with 42C tanks.

Between 50C and 90C is about 4.5kwh for every 100L and so with 800L I have 36kwh useable.
With 3 hours of cheap rate and 12kw of heating elements I have about 36kwh of heat I can apply.

As was always suspected/wondered/feared, I need more of both.

I think around 39kwh is enough *average* to replace my previous 56kwh average, I've taken this based on the last two weeks where I've added 3kw to the second tank midday as a top up, hoping to grab as much available solar as possible, that's why midday.
So over those two weeks adding 39kwh each day I've averaged ~50C just before the heating cycle.
But what does an average really mean? It means some days I've had 60C at that point, and some I've had 45C or lower.

What I'm driving at, is an average day was the wrong way for me to approach this, I should with hindsight approached it with a reasonable worst day of storage with maybe an average days consumption.
So if for instance I had 50kwh of storage, but 39kwh of heat each day, that would give me a buffer to absorb the odd colder days.
And if I had the ability to add the heat in over a longer period of time, then I'd have the ability to add more heat that average to the week of several days lower than average.

I was always constrained by my 3 hour go faster window, and I think that I said at the start that I'd probably need more than this 3 hours, and I do.

What this means is that come spring I'm gonna have to hire a skip and dig more of under the house out to accommodate another tank.
By my calculations if I add another 300l tank, I'll have 51kwh of storage between 50C and 90C.
When I renew my tarrif in February I will likely opt for a 5 hour tarrif instead of 3, giving a potential 60kwh of heatand I'm confident that with the experience gained so far, this will provide more than enough heat with a good size buffer both in terms of heat supply and heat storage, this will also let me reduce the current draw per hour off peak as I can charge the batteries on less power per hour to achieve the same charge level.

As an aside and to share a graph, I've found that destratification for 5 mins every 30 mins is the best way to regulate the tank heat, here is the 2nd tank showing the 1 hour of heat midday as well as the step downs from central heating in the morning and afternoon/evening of a cold day (yesterday) and on the right side the destratification pump coming on during its heating