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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










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  • 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

Reply
  • 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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