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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
    An electric boiler will be virtually 100% efficient, where else can the electrical input go, except into heating the water ?

    It still represents a substantial extra load if heating was formerly by gas.


    For a relatively small number of flats, only a very little diversity may sensibly be applied. Consider a block of say 30 flats, 10 per phase, and all fitted with 10KW electric boilers. It might be overly pessimistic to assume that every one will operate at the same time, but I would certainly allow for 8 out of 10 operating simultaneously.

    10 flats, each using say 5 amps for lighting and small appliances, and 8 of 10 flats each using 45 amps for the boiler. I make that a total loading of over 400 amps per phase.


    Over a larger area, with diverse types of dwellings and inhabitants, a much lower average load figure is a reasonably safe assumption. With only modest numbers, the risks of simultaneous operation increases.
  • Former Community Member
    0 Former Community Member
    I stand corrected!
  • 0
    Hi folks,


    Just called an electric heating manufacturer to get an idea of instantaneous demand of a typical system. In fact they do supply up to a 14kWatt system for heating and hot water.  The size depends on the heat loss of the flat (no surprises there) but also on water flow rate. If you have a bath then you'll need a sizeable system to cope with the water flow. 


    Now, it transpires that in order to add, say, the 14kWatt device (large flat, 4 bedroom with bath, say), their requirement is a 100 Amp supply at the flat.  Furthermore, the recommended procedure is to install an 80 Amp isolator and run 16mm cable to the boiler.  No small job for one device!  


    From my experience with this particular building all of the flat supplies are 60 Amp fused and their supply cables are 16mm.  So that sets a limit to begin with.  Smaller systems, 9kWatt for example, might be more feasible.


    This, of course, brings us to Mike's latest comment on why we are looking at this as a solution at all.  Well, it seems that one resident has been looking at it and discussed with others.  This travels through the community and we end up with the management committee worried about the power consumption rising to the point where they'll have to pay UK Power Networks extra for fuses and an eventual cable upgrade.  Then I get the call. I'm doing this study pretty much for no charge so far and a general update and education on fuel alternatives is not on my agenda.  That said, if a good critique comes out of this post, I'll be able to go back to them with a better informed opinion.
  • 0
    Hi Amanda


    I didn't really take in the kWatt ratings of these systems!   I haven't installed one so I had to take a look around.  In the end I called the tech advisory people of a major electric heating company.


    Seems they do combi boilers at 9, 12 and 14.4 KWatt!
  • 0
    Hi broadgage


    Bit slow in refreshing the page so I missed your most recent post.


    Now, I think we are talking.


    Yes, small amount of diversity with the electric boilers and add to that the diversity total of the other appliances in a typical flat.


    You've also reminded me to check on how many flats run off each phase for these buildings of which there are three x 12 flat blocks each with a 3-phase supply.


    Presumably UK Power Networks will be able to tell me what the capacity of the cables and fuses are?


    donf
  • Former Community Member
    0 Former Community Member
    I'd assumed that you wouldn't have one that drew more than 40A single phase in a domestic setting, but you know what they say about assuming! 


  • 0
    It's an interesting question because at some stage gas boilers will become a thing of the past.


    I don't know how the efficiency of gas and electric compare, but if you point out that the cost of heating will treble, the residents may well lose interest.
  • 0

    pay UK Power Networks extra for fuses and an eventual cable upgrade.



    That might be a little optimistic - the DNO will probably want paying for all the costs incurred - if it's a substantial increase (e.g. moving from a  maximum demand per flat form say 1kW to 7kW) then the impact might be not only the fuses in your installation and the cables into the building, but the cables running down the street and the transformer too. Then you really are into serious money. The demand on the distribution system has in general been growing for many years and there often isn't much slack left in some places. If you're very unlucky the HV side supplying the transformer might need reinforcing too.

        - Andy.
  • 0
    The beginnings of a methodology..


    Estimate power demand per flat.


    Assume, say, a 10kWatt electric boiler, low diversity per building - concurrent boiler running in 70% of the flats during peaks.


    Use the IET Electrical Installation Design Guide to calculate power demand of a typical flat, including the electric boiler.


    Then use the same guide to calculate the load for 22 flats. In particular I'm referring to Figure 3.4 (IET Guide Nov 2008) which is a graph providing estimate values for demand factors for the calculation of power demand for a number of dwellings.  The top curve (a) provides for a high coincidence of loads.  Might need to add a bit for the electric boilers but not sure yet)


    Calculate final power demand for a block.


    Check with UK Power Networks to agree on a suitable figure for their purposes.


    Because the flats are generally high-end residences, in my survey (so far) I'm finding the following


    Gas combi-boiler system.


    Double oven, hob (a number are induction hobs  - any thoughts on diversity for them??), kettle, toaster, fridge, freezer, microwave, TV, in a number of case plasma screens, incandescent lights, vaccuum cleaners, some IT equipment, second TV, dishwasher, clothes dryer, washing machine and other equipment.
  • 0
    Hi Andy


    "the DNO will probably want paying for all the costs incurred - if it's a substantial increase (e.g. moving from a  maximum demand per flat form say 1kW to 7kW) then the impact might be not only the fuses in your installation and the cables into the building, but the cables running down the street and the transformer too. Then you really are into serious money."


    Precisely!


    And that's why I need to be careful about where this leads.  No point in panicking the residents' committee if I overestimate demand.  So assumptions will be key.


    donf

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