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Ditching gas, going electric immersion only, a wee project

edited 4 August at 7:31PM in Green & ethical MoneySaving
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SolarchaserSolarchaser Forumite
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edited 4 August at 7:31PM in Green & ethical MoneySaving
I think this fits within the green and ethical section of MSE.

This is an ongoing project to replace my gas combi boiler with water tanks heated by immersion. (Hopefully finished In next couple of weeks)

A common question would be why not use a heat pump, and there are two reasons for this.
1. It would have to run all day, and I plan to use only cheap rate electric of 3-4 hours of octopus go/faster.
2. Wife says NO, heat pumps are ugly, and thats that.

This project has evolved somewhat over time.
Initially I was going with a thermal store in loft and a buffer under the house, that changed to two tanks under the house, this was my thread in another section of MSE 

https://forums.moneysavingexpert.com/discussion/6349403/heating-engineers-going-electric

I had looked a while at sunamp, tepeo and warmstone instead of storage of water, as all seemed to have in impressive lack of heat loss, but 1 by 1 they were crossed off for various reasons from conversion losses, lack of ability to take heat in a short time, and amount of space (and weight(and wait)) required.

I had 1meter of headroom under the house, so I could only have horizontal tanks and these are much less common.

I eventually decided on telford tempest cylinders, and found they had a bespoke service which i used to spec a tank with twin coils, 1 for hot water and 1 for central heating.
After a bit of back and back and forward I agreed on this design.


A fairly standard water tank, with heat coils for solar and a combi to be used to heat the tank. 
The coils give 25kw of heat transfer each, so not too dissimilar to the 28kw combi boiler they are replacing.

However my plan was always to use it in reverse.
Instead of the potable water flowing through the tank heated by the coils, instead, like a thermal store the water in the tank would always remain there (and  remain hot) and the water for DHW and for CH would run through the coils to be heated by the tank water.

I was initially going to buy two identical 500L tanks, however they were coming in at over £3200 due to them being custom made.
So instead I opted for 1 custom tank and one off the shelf 300L tank which happened to have a small "solar" coil in it. The two combined came to around £2600.
This reduced my total literage to 800, from the 1000L I wanted, but I'm hoping this will be enough.

My 15 year old combi was in its death throes which was a good nudge to get me to move on this, and it was the right time of year, May/June meant plenty of excess solar to heat the tanks at no cost and a few months of messing about to get it optimised, so that when winter comes around I know it will work.

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West central Scotland
4kw sse since 2014 and 6.6kw wsw / ene split since 2019
24kwh leaf, 75Kwh Tesla and Lux 3600 with 20Kwh useable storage
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  • SolarchaserSolarchaser Forumite
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    So why immersion /electric?

    Like alot of people who get solar panels, it started to annoy me how much I exported during the day, to then buy it back in the evening,  so I got batteries, great.
    But in the brighter months I still export around 2Mwh, and at the same time, buy gas to heat water for the taps, and central heating.

    I also have 10kw showers which means any evening showers and I'm importing electricity. 

    I could switch to thermostatic showers, but with combi hot water, the pressure is garbage so what's the point. 

    So I could get a hot water tank and heat it from solar in summer and gas in the winter, but that will mean the combi being off for 5-7 months at a time, and then relying on it to work right during winter... but it's 15 years old, and a replacement is going to be around the £3k mark.

    This had been my thinking for a couple of years.

    Then something interesting happened,  between March 21 and March 22 my gas price almost tripled, which meant that in my cheaper electric periods, gas was actually more expensive than electric, this was the push I needed to do it this year.
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 20Kwh useable storage
  • edited 4 August at 8:26PM
    SolarchaserSolarchaser Forumite
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    edited 4 August at 8:26PM
    First question is, does it work?
    Yes, it works.
    Does it provide central heating heat?
    Yes it does and at roughly the same temperature as the combi did.

    How long does it last?
    That I don't know, and won't really until we get into winter.

    The more technical stuff.
    The 500L tank Is the main tank.
    It has 2x3Kw elements to heat the tank.
    300L tank is the secondary and also has 2x3kw elements. 

    They are plumbed together in that both mid tank plugs are connected together with a tee piece that goes up to a central heating pump I'm using as a destrat pump, this then connects to the tops of both tanks, though for the 300L tank it first hits a motorised valve so that if the 300l tank is not hot, then it doesn't get destratification, and purely the 500L does.
    The idea being its better to have 1 hot tank than 2 warm ones, less heat loss for a start.
    The motorised valve is controlled by a 40C 301 N/O temperature switch (or will be when I get to it).

    In terms of water flow, cold water first of all goes through the 300L solar coil, this acts as a preheat, then goes through a flow switch (to operate the destrat pump after a timed delay) and onto the 500L tank and the main coil, from here it travels into the house around 65C at the moment and hits a thermostatic blend valve which blends it down to 45C for the house hot water.
    The great thing about this is after around a 10 second delay, you get consistent high flow rate hot water, not the cold, warm, hot, cold, hot you get with a combi.

    For the central heating, the radiator circuit is connected to the other coil on the 500L tank.
    Pump on one side, and magnetic filter on the other, I also have them teed together above the coil with gate valve which I will adjust to get the best blend.
    I dont want to turn on heating and get the radiators sitting at 80C, but I also don't want them to take 30 mins to heat up.

    I was too focused on my lack of room between the top of the tank and the bottom of my floor that i stupidly mounted the central heating pump directly on the tank, for reasons unknown completely forgetting about thermosyphon,  and so of course the entirety of this pump is hot all of the time, as is quite a bit of the central heating piping under the house. Idiot!
    so I need to remove the pump, create a U, and fit a check valve to stop the thermosyphon, both at the supply end and at the return.

    Anyway it's powered by the same system as used to tell the combi to switch on, a timed control linked to a thermostat in the hall.
    The thermostat is good for 2A and the Central heating pump draws less than 100w or less than a 1/4 of an amp.
    This is great because it means no-one in the house has to learn anything new, if they want heating they turn the dial up as before,  or press the boost button etc, only difference is the silent running pump rather rhan the huff and puff of the combi kicking to life.
    I will also link the pump control to the timer for the destrat pump so that I don't end up with a situation where one side of the 500L tank Is cold due to the central heating drawing out all the heat, yet the other side is still warm.

    I have a doubke resetting timer circuit made up and tested for this, just need ro wire it in.

    What's been my biggest problem?
    In short, myenergi.
    The zappi I had installed has impressed me so much, the way the app works, the data from it, how smooth it all goes, it's been great, so i decided I would get a couple of myenergi Eddi's and they would become the computer that was to run everything. 
    You can get a relay board which will run two relays separate from the actual diverter, these can activate other heaters in cheap leccy periods, or destrat pumps or both, in my theory.
    They can also take 2x temperature sensors each, so I can monitor both tanks, CH and DHW temperature from the app in theory.

    The problem is... well its not myenergi fault, the Eddi is in backlog due to global chip shortage apparently. 
    I ordered two at the start of May and they are not here yet. Hopefully two weeks time... we shall see.

    So for the moment I have a timer switch running 1 x 3kw element for 4 hours a day, and I've been lucky that it's still been fairly sunny, but as we get further into the year I will need two diverters to run all 4 heaters (sequentially in solar, together in cheap rate winter) without my input.

    A secondary problem which I didn't realise as I've never had an immersion heated tank, is that most immersion heaters cut off around 70C and have an overheat cutout at 80C which has to be manually reset, this means you can't insulate the entire tank, you need the immersion heater to have air circulate around it, it also means if you have 2 immersion heaters at the bottom of one tank and two at the top of another, if water is circulating between both, the two at the top can hit their overheat cut out without ever having being powered on.

    My calculations on kwh of heat storage relied on the heaters being able to heat to around 90-95C, so I need high temperature thermostats for all 4 immersion heaters or come winter, I'm going to be buying alot of expensive electricity. 
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 20Kwh useable storage
  • michaelsmichaels Forumite
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    Will read in more detail but highly pertinent to us.

    Just switched to a 4.5p/45p electric tariff, 13p gas.  Will obviously use the 4.5p period to fill the immersion tank to 70 degrees and set the gas thermostat to 45 degrees as a back up.  Reason for this is that our daily hot water demand is twice what our 180l tank can provide.

    (Aside, iboost dumps PV into the tank in the day at lowest priority after filling the car V2H etc)

    Am thinking of adding a second tank in series with an immersion so I can double the volume of hot water and do the whole day demand at 4.5p. (Another 200kg in the loft of course is a question but I think it is ok).

    It would be nice to store enough to do heating as well but in winter that means probably 3x more storage again - ie another 1000-1200 litres for 1400 - 1600 total plus would need a different set up perhaps like the one you have.

    But getting to the point, that does give one thing that perhaps you have not thought about, at my old house I had a horizontal cylinder configured as a heat store for hot water and heated the water via a mains fed plate heat exchanger, obviously this requires a pumped circuit but avoids a coil.

    In fact I don't see why you need coils at all, couldn't you just use the hot water in the tank as your hot water supply and a single coil or indeed plate heat exchanger to heat the heating circuit which might be a much cheaper solution?
    I think....
  • SolarchaserSolarchaser Forumite
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    I specifically don't want to use the whole tank, there is a much larger chance of stagnant water, giving rise to bacteria growth, that's why I've went with coils, plus it should be the case that everything in the coil is too hot for any chance of legionella, and means the hot water should be just as potable as cold, if the kids want to use hot water doing their sensitive teeth etc.

    It also reduces any contamination /corrosion coming into the tank as I can put inhibitors in the water and don't have any water coming in.

    No cost involved now, they have been installed under the house giving hot water for over a month 🙂
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 20Kwh useable storage
  • 70sbudgie70sbudgie Forumite
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    Slightly related in that it can reduce your hot water requirement, but check out Eco camel showerheads. I bought one, perhaps a decade ago. It has a flow limiter, but uses vacuum syphon theory to increase the pressure with air, so it feels like a power shower (perhaps a slightly gentler one). I loved it so much, I bought another for a second shower. The original is still going, but I did have to replace the faceplate earlier this year, about 20% the cost of a new showerhead.

    I also plan to fit flow limiters on all our taps (we have blender taps), so when the children turn the tap on full it doesn't steal all the water (hot or cold). I only have the two most popular taps fitted with them so far - they were free from my water company.
    Longi 360W panels: 2.52kW ENE, 1.8kW WSW, Solis Dual 3.6kW inverter. 41kWh Zoe. 540W Ripple Kirk Hill. Cheshire
  • michaelsmichaels Forumite
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    I specifically don't want to use the whole tank, there is a much larger chance of stagnant water, giving rise to bacteria growth, that's why I've went with coils, plus it should be the case that everything in the coil is too hot for any chance of legionella, and means the hot water should be just as potable as cold, if the kids want to use hot water doing their sensitive teeth etc.

    It also reduces any contamination /corrosion coming into the tank as I can put inhibitors in the water and don't have any water coming in.

    No cost involved now, they have been installed under the house giving hot water for over a month 🙂
    Would potability be a concern if you used the tank for hot water and just a single coil for the central heating.  Or if you wanted the separation and ability to use inhibitor could you have put the tank direct into the heating loop (with a suitable blender valve) and used a single coil for the hot water - or as mentioned above a plate heat exchanger rather than a coil?

    You have got me thinking about whether rather than just adding a hot water tank to support our whole daily usage we could add a tank in the garage to support the central heating too.

    Starting to think about the 100A main fuse now though.  Potentially we will be charging the battery at 5kw and the car at 2.5kw.  Add on the existing hot water tank and possibly a second hot water tank and that is another 6kw.  Now add on 6 more kw to store central heating heat and we are up to 19.5kw or about 85A.  Then we of course plan to run the dishwasher and washing machine overnight (max 6kw if they are heating at the same time?) and we are at 110A!!

    Also would we be able to store enough energy?  Our highest ever month of gas usage was 5,500 kwh = 183kwh per day, to pull all that in in 5 hours would be 36kw!!  So basically we would still need gas so couldn't also factor in the savings of going boiler and standing charge free.
    I think....
  • 70sbudgie70sbudgie Forumite
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    michaels said:
    I specifically don't want to use the whole tank, there is a much larger chance of stagnant water, giving rise to bacteria growth, that's why I've went with coils, plus it should be the case that everything in the coil is too hot for any chance of legionella, and means the hot water should be just as potable as cold, if the kids want to use hot water doing their sensitive teeth etc.

    It also reduces any contamination /corrosion coming into the tank as I can put inhibitors in the water and don't have any water coming in.

    No cost involved now, they have been installed under the house giving hot water for over a month 🙂
    Would potability be a concern if you used the tank for hot water and just a single coil for the central heating.  Or if you wanted the separation and ability to use inhibitor could you have put the tank direct into the heating loop (with a suitable blender valve) and used a single coil for the hot water - or as mentioned above a plate heat exchanger rather than a coil?

    You have got me thinking about whether rather than just adding a hot water tank to support our whole daily usage we could add a tank in the garage to support the central heating too.

    Starting to think about the 100A main fuse now though.  Potentially we will be charging the battery at 5kw and the car at 2.5kw.  Add on the existing hot water tank and possibly a second hot water tank and that is another 6kw.  Now add on 6 more kw to store central heating heat and we are up to 19.5kw or about 85A.  Then we of course plan to run the dishwasher and washing machine overnight (max 6kw if they are heating at the same time?) and we are at 110A!!

    Also would we be able to store enough energy?  Our highest ever month of gas usage was 5,500 kwh = 183kwh per day, to pull all that in in 5 hours would be 36kw!!  So basically we would still need gas so couldn't also factor in the savings of going boiler and standing charge free.
    I have looked at it from the point of view that in the future, I would like to replace my gas boiler with ASHP. Any effeciencies I can make now will reduce my gas costs, but may also mean that the size of HP I would need could be reduced, with the relative savings.
    Longi 360W panels: 2.52kW ENE, 1.8kW WSW, Solis Dual 3.6kW inverter. 41kWh Zoe. 540W Ripple Kirk Hill. Cheshire
  • edited 6 August at 3:11PM
    SolarchaserSolarchaser Forumite
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    edited 6 August at 3:11PM
    I looked at it in terms of gas usage in the dead of winter.
    I'm 50kwh of gas, which I take to be 75% efficient meaning I need about 37kwh of heat.
    4x 3kw elements running for 3 hours of octopus go faster is 36kwh, so pretty close.

    I'm saving around £90/ year in gas standing charges so if it costs me another pound or two a day through winter that would be OK.

    As well I have an issue that should be resolved by the new system.
    The hall is wherevthe thermostat is, but the living room is where most of the family is most of the time. (Wife doesn't want stat moved)
    It has a large radiator at both ends.
    10 years ago the wife decided she wanted to remove the back window and fit patio doors, and one of those large radiators was removed too.
    So we tend to find the rest of the house is warm before the livingroom.
    With mounting the tanks under the floor at the back of the livingroom gave me the chance to put together a cheap heated floor in the form of pex pipe in loops fed by the central heating system, this should mean the livingroom heats up first, and so the central heating should be on less heating the rest of the house before livingroom 
    Seems to work

    though won't know for sure until winter I guess.
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 20Kwh useable storage
  • 70sbudgie70sbudgie Forumite
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    We have underfloor heating in the kitchen and master bedroom. I love it. I particularly like the heat gradiant with my feet warmer than my head. But I realise that is a personal thing.

    The one thing I noticed when it was being installed is that there was a lot of insulation below the heating to make sure the heat all goes up into the room (and isn't wasted warming the floor).
    Longi 360W panels: 2.52kW ENE, 1.8kW WSW, Solis Dual 3.6kW inverter. 41kWh Zoe. 540W Ripple Kirk Hill. Cheshire
  • michaelsmichaels Forumite
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    That is not a lot of gas compared to us and a pretty low assumed efficiency.

    If you remove gas altogether then you are potentially using peak rate leccy to make up any shortfall days.
    I think....
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