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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
    Regret no specific data, but I would expect a very substantial increase in load. Unless the existing supply is unusually generous, then a supply upgrade will almost certainly be needed.


    One possible source of data might be the existing gas consumption, though remember that will give an average and not the peak hour loading on a winter evening.
  • Former Community Member
    0 Former Community Member
    I would speak to the DNO first, they should be able to tell you what the current actual usage of the building is, and what the maximum capacity of the incomer is. When doing an initial estimate of load for apartments I use a figure of 3.4kW per apartment, which is what ENW allow for an electrically heated apartment. Then refine this when equipment is selected.
  • 0
    I do not have a simple answer for you I'm afraid, but will make it more complex. Electric boilers generally are not an efficient use of electricity, compared to say heat pumps, and so are not good news for the building energy rating. Certainly for rented flats at least, the Lot 20 rules and EPC rating requirements combine to make a very confusing mix - off peak storage heating being cheapest to run of course if you have no gas, but electric vehicle charging is set to eat into that.


    I caution that a simple exchange of all gas boilers to electric in an existing building is unlikely, even if keeping the radiators and so on looks attractive to begin with, as the economic drivers both for owner occupiers and sub-letters are not in that direction - though in 5 years they may be of course.


    They also tend to be lower rated, so maximum water flow and heat up times are all poorer -  a combi boiler may be 30kW on gas ,and yet the largest electric model that does not need a 3 phase supply will be lucky if it is half of that. A small one for a bedsit may be more like 4 to 6kW.


  • 0
    As a sanity check you might do a thermal heat loss calculation for a typical flat - like heating engineers do - surface area of external walls, U-value (depending on construction and whether it's been insulated and so on) and likely worst case temperature difference. That should give you a reasonable estimate of maximum heating demand - at least when averaged over say a day or so. Then add a bit for domestic hot (tap) water, if the boiler is to feed that too.


    Next question is how will the boiler be used - just 'on demand' like a combi boiler on a normal 24-hour tariff would be horribly expensive. Run together with some kind of thermal storage, with the bulk of heating done off-peak should be somewhat cheaper to run - but might increase the maximum instantaneous load somewhat as much of the load would be 'bunched' into the overnight period, plus the added cost of dual-tariff supply.


    If the flats are well insulated, so the space heating demand is small, you might be better with a few individual space heaters and heat the water separately - either storage tank and immersion (powered off-peak) or instantaneous water heaters at point-of-use (better for showers than baths perhaps).


       - Andy.

  • 0
    Diversity isn't really going to apply. On a really cold winter's day its quite possible that all boilers in all flats will be going flat out for many hours.
  • 0
    Hi to you all,


    Many thanks indeed for your comments so far.

    This study is trying to look 4-5 years down the road so technology may have changed/improved by then.

    As for broadgauge I would expect a large increase in building load if people used electric boilers for on-demand heating of water for radiators and hot water.

    Thank you Amanda, it will be a good idea to check in with the DNO which I plan to do.  Just to clarify, does that 3.4kWatt apply for dwellings with space heaters?  In the case of an electric boiler, I’d probably have to add quite a bit more for peak demand.

    Agreed Mike, electric boilers won’t be better than heat pumps.  However their installation cost and the architectural impact of the exterior condensers would likely be vetoed by the building management committee.  From what I lifted from a brief Internet search, 13kWatt is a typical example of the instantaneous consumption of an electric boiler, confirming your observation that they have about half the heating capacity of a gas boiler.  (Not sure about efficiency without further reading)

    Andy, the building heat loss should be low.  The building is modern and all windows and exterior doors are double-glazed. The loft is well insulated and only the perimeter flats would have a slightly higher heat transfer to the exterior.

    On the subject of how the boilers will be used, from a behavioural point of view, most of the residents are retired people who like to stay warm. Their daily habits appear to be regular so I would expect instantaneous heating demand to peak in the mornings and evenings.  

    At this point, then I have to return to the point that if, at any time, we had more or less simultaneous switch-on of a number of electric boilers (in this case, 12 flats per building, each building with its own supply cables and fuses) we are likely to see much greater peak demand than for a standard flat scenario.

    As wallywombat mentions, there won’t be much diversity in those peaks.

    I remain open to further debate!



    donf
  • Former Community Member
    0 Former Community Member
    Your not going to get a 13kW single phase boiler though. Agree with above poster that you will probably be better off replacing with space heaters. 

  • Former Community Member
    0 Former Community Member
    Sorry didn't answer your question, its just a general 'electric heating' figure (with non electric heated apartments estimated at 1kW). When you speak to UKPN they may well have similar figures they use for estimating residential loads.
  • 0
    Single phase electric boilers are available upto about 14KW
  • 0
    UKPN will probably refer you to their tables of  After Diversity, Maximum demands P.19  as a first assumption.

    Note how depressingly far down the list of ascending demand they think an electric boiler ought to be...

    I agree however, older folk are not out at work during the day, and are likely to take more heating than the average.

    At the risk of being nosey - why are you looking at this one option, and are you or others also looking at all the other possible fuel futures?

    Actually looking how far wind generation has come in the last 5 years and what naysayers were expecting back then,  I wonder how many of the now apparently

    'hare brained' futures may actually occur  (I know that for example this trial of hydrogen in the gas is coming on pretty much as well as anyone dared hope.)

    Of course right now the UK does not make anything like enough to do this nationwide, and if we did, until we get electrolysis working at scale ,

    we'd still have CO2 to capture,  just as we do now, but at the H2 plant, not at the power stations.

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