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Electric boilers - effect on power demand of a block of flats

donf
Hello there.


I would like to  know if anyone on the forum has done a study of or knows about an existing study of the impact on power demand of introducing electric boilers to block of flats. 


I have been tasked with estimating the impact of a gradual migration to electric boilers for central and water heating in a modern block of flats. Nearly all of the flats currently use gas fired combi boilers.


I then have to present this information to UK Power Networks so that they can asses whether or not an increase in capacity to the building supply might be needed in future.  Finally I need to put any recommendations to the owners' management board.


Clearly electric boilers will have some impact on power demand.


I can start with an estimate of current power demand (worst case) for a typical flat.  To that end, I'll be doing a survey of about 25% of the flats to come up with a figure.


I can then apply the IET Electrical Installation Design Guide diversity calculations for a typical flat and then the building as a whole using figure 3.4 (IET Electrical Design Guide Nov 2008 page 33).


I can then do a second power consumption exercise adding the demand of a typical electric boiler per flat and then the whole building.


However, it's not clear to me if this approach will be suitable for a massive migration to electric boilers.  I need to be sure of my ground if I approach UK Power Networks with a demand figure.


If we look at the usual peak use of heating demand (morning and evening) a building full of electric boilers, to me, could add a significant load to existing street fuses and possibly even cable capacity.


I would be grateful for any suggestions and experience people could bring.


Kind regards


donf










  • 0
    Broadage I`m pretty much ditto you (no wood burner though and a few storage heaters). In the good old days we had coal fires, loose fitting sash windows plenty of ventillation and we did not suffer all these colds and illness like being cooked up and stiffled. Winter mornings were best, off to t`coil oil (coal place) for a hod of coal, brr it were cold, ooh and outside lavs (they were a bit grim). That was normal.


    Take a glimpse of real life

    https://www.youtube.com/watch?v=RwJQQyF0yy0


  • 0

    ebee:

    In the good old days we had coal fires, loose fitting sash windows plenty of ventillation and we did not suffer all these colds and illness like being cooked up and stiffled.




    But if you lived in a city, you had smog and the bronchitis to go with it.

  • 0
    I am sure you have seen that the Government want to ban wood burning and they are very against coal too. We could go back to cold houses but can you imagine the wallflower generation going to the cold cinema or whatever dress in the full winter kit? I can't. Also employers are now forced to heat workplaces fully by law, even if they are partly open sheds, and whilst this may improve productivity it needs a great deal of energy. Remember that all these changes to carbon zero, and taking all the estimates as real temperature rises, we (UK) can only make 30-40 thousandths of a degree of difference! See the Savoy Place virtual club forum for more.
  • 0
    I remember going to cinema in the South Wales valleys (Abercynon) in the early 80s which was not heated but they served hot soup in the interval to warm you up. It was also the only cinema I have been to where the film stopped and a black dot appeared in the middle followed by the film burning.


    Best regards


    Roger
  • 0
    Some people happily stand outside pubs and other places throughout the year in all weathers to have a fag, some people also make a point of wearing shorts all through the year even in the depths of winter.


    Are these people also heating their entire home to the same cosy temperature even though there’s rooms that are only used for part of the day?


     Replacing existing controls will probably bring more benefits in the short term than replacing the entire system or boiler.


    Andy Betteridge
  • 0

    donf:


    I have been tasked with estimating the impact of a gradual migration to electric boilers for central and water heating in a modern block of flats. Nearly all of the flats currently use gas fired combi boilers.


    I then have to present this information to UK Power Networks so that they can asses whether or not an increase in capacity to the building supply might be needed in future.  Finally I need to put any recommendations to the owners' management board.


    Clearly electric boilers will have some impact on power demand.















     




    It seems obvious to me that unless heat store cylinders are installed be able to utilise an off peak tariff to charge cylinder with heat overnight there will have to be a massive upgrade to the DNO and BNO installations.


    Presumably in addition to the massive increase in demand for electric space and water heating there will also be a request from the tenants for electric vehicle charging points to be installed and some tenants need to swap from gas the electric cooking appliances.


    There is going to have to be an expensive upgrade to the DNO and BNO installations that someone has to pay for, unless heat store cylinders or storage heaters are a viable option.


    Andy Betteridge 

  • 0
    I did the calculations for a brand new block of flats in Malvern a few years ago, the cost difference of having an electric supply installed with or without gas central heating and cooking hobs to get the main fuse down to 40-amps was £64,000.


    That was to pay for running in a cable from a couple of streets away rather than the one in the foot path in front of the flats.


    Andy Betteridge
  • 0
    To be honest I think the idea is a complete and utter non-starter.


    A 15 kW single phase electric boiler draws 65-amps which may be above the current main fuse rating and the capacity of the distribution circuit from the intake to the flats if there is one without any other usage.


    If a 24 kW boiler is required then all the supply’s will have to be reinstalled as three phase and the DNO equipment and distribution within the building replaced, almost certainly along with upgrading the DNO network.


     I have just spent a few minutes considering the issues and the potential upgrades that will be required, as a contractor that’s all I would want to spend on this without getting paid. I certainly would not be offering a free design and quote.


    It comes under the heading of a tyre kicking exercise.


     Andy Betteridge.
  • 0
    “4 and 6kW units use single phase (230 Vac) electricity and can be connected to your existing circuit board. Always check if you have sufficient amperage available on the circuit fuse you’d like to connect to.  9kW and over require a 3-phase electricity, power current. “

    http://waterheaterstore.co.uk/index.php?route=product/product&product_id=529


    Other manufacturers make 15 kW single phase boilers.


    Andy Betteridge 


  • 0
    Hi all

    Just returned from a long and late working week hence my late input here.  Many thanks indeed for all of your comments.  I would like, at this point, to summarise, as well as I can, our collective thoughts and advice.

    Just to recap, I’ve been asked by the residents owners’ management board of a modern block of flats to give an opinion as to whether or not a migration to electric boilers would affect power demand to the extent where they would need to pay the DNO for an upgrade to the supply system.

    I plan to use the IET Electrical Installation Design Guide to calculate power demand of an average flat (worst case demand scenario) and then apply a demand factor for the block. (There are three blocks of 12 flats)

    On receiving your feedback, here is where I think we are:

     
    1. Before going too far, think about the energy performance of the flats.  This will give an idea of the amount of energy that will be needed by any heating system.  As I found by calling the technical people of a well-known electric heating company, the thermal performance could make a difference between selecting a 14kWatt, 12kWatt or a 9kWatt system!  In fact, most of the flats in this complex have an energy performance of C with potential to go to B.  They are two to three bedroom, generally well-insulated with double glazed windows and exterior doors.


     

    1. Diversity for electric boilers is questionable.  I’m much inclined to agree with a number of you that given the power demand of electric boilers and that fact that many could well run concurrently, any de-rating factor for a block (as in the IET design book) may not be relevant. As broadgage mentioned you could have a scenario where, for 10 flats equipped with these boilers, 8 out of 10 could be using them in peak time.  Also, building-wise, double-check the distribution of flats per phase. 


     

    1. If a mass migration to electric boilers is done without thought to installing a heat store system power demand is very likely to increase to the point where a DNO supply upgrade becomes necessary.


     

    1. Single-phase electric boiler systems are available up to 14kWatt (from what I’ve seen so far).  Clearly these will require suitable supply points.  As was evident when I phoned an electric boiler supplier, a larger capacity system would require a distribution board of 100 Amp capacity to which you add an 80 Amp switch fuse for the boiler itself.


     

    1. Installation costs.  Quite apart from the cost of an electric boiler system you need to consider what you are using it for and whether or not you have existing electric water heating systems such as electric showers.  For example, I was told by the tech people at the electric boiler company that extra provisions need to be made when you have electric showers and when you have such things as baths where large volumes of hot water have to be supplied on demand. 


     

    1. Impact of the installation of the flat itself.  In the buildings in question, most of the existing gas boilers in the flats are some distance away from the distribution boards which are usually situated in a modestly-sized hallway cupboard near the entrance.  Supply to the DBs is 16mm twin + earth from an isolator and cable head in the lobby outside the front doors of the flats.  The supply fuse is 60 Amp.  Even if we could upgrade to 100 Amp, somewhere we’d need to add an 80 Amp switch-fuse and run large cables from the DB to the boiler – across a finished and decorated high-quality flat.  That’s going to be an interesting conversation with the residents...


     

    1. Having completed some sort of power demand estimation, as Amanda recommended, discuss with the DNO and show them how we calculated it.  Get their input.



    You’re right Andy, there’s a certain amount of tyre kicking going on here. But given that the client concerned is an important one I’m happy to have the debate!  The proviso in this study is that it is an opinion, not an actual design.  If they want a full study that’s another matter.


    donf

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