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IDNO Loads

HI All


Just come across the attached - a snippet from an IDNO's documentation about loads for residentials.


Loads a lot lower than I am used to - what are peoples thoughts on this?


I would not be comfortable going down that low - e.g. an all electric flat with panel rads and a 3kW cylinder - don't see how you could drop down so much.


i tend to see 4.5 to 5.5 kVA for all electric flats, lowerend being for single bed units and 5.5 for two bed

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  • The published figures are reasonable as an average over a large number of dwellings. 1Mw for 333 houses each electrically heated is reasonable.

    Not applicable to small numbers though.

    If two dwellings each have an electric shower, both might be used at the same time, if hundreds of dwellings have electric showers only a small number will be used at the same time.

    Out of say 200 houses, 15% might be empty and consuming almost no electricity (5% awaiting sale, and another 5% on holiday, and a third 5% out during the peak hours for pleasure or shift work)

    Another few might have had wood stoves or oil heating added despite being planned as all electric.


    And of course DNOs get away with pushing cables and transformers far beyond "normal" ratings due to cold weather and to short term loading.
  • I agree - they take into account diversity across a large number of homes - they're no use at all for sizing an individual supply.


    If you think about it the National Grid rarely generates more than 50GW - and as there are about 20 million homes - the average demand per home even during peak times can't be more than about 2.5kW - and probably a lot less than that as industry and commerce will be drawing a not insignificant amount.


      - Andy.
  • Thanks broadgage


    I am in agreement and the doc does not reference smaller jobs. 


    Even your example is 3 kW in comparision to their 2 kW. 


    I have most commonly worked on sub 100 and for that scale would not go less than 5 kW usually. 


    As an example a colleague of mine is being pressured to revise his load calc for 47 flats from 5 to 4.5 kW to fit inside an available 222 capacity. Even doing that would be about 211 without landlord power. I am not comfortable about that personally as these are a mix of 1 and 2 beds (panel heaters) 


    Thing is if a client comes across those figures it becomes a pain to explain to them. 


  • I can't see how diversity applies for electric heating. On a really cold winter's morning, nearly every house in the estate will have its electric heating whacked on.


    Also I don't understand why a heat pump system is higher than electric heating. Surely a heat pump is supposed to have a COP > 1?
  • An electric rad with thermostat would cut concurrent power draw wouldn't it. 


    The ASHP is weird though I would agree. 



  • I can't see how diversity applies for electric heating.

    Actually you  do not need as much diveristy on a cold winter day, if the transformer is also outside and cold, it will be able to take 100% overload - it too is rated based on temperature rise, depending where these figures are for, there may be this sort of assumption n hidden.

    Of course it goes horribly wring for indoor substations, and ones that are supposed to be fan cooled but the air intake fills with snow.
  • Also I don't understand why a heat pump system is higher than electric heating. Surely a heat pump is supposed to have a COP > 1?

    I'd guess that traditional all-electric heating would have a large thermal storage component (e.g. storage heaters or stored water heated by immersion heater) - so would draw a large bulk of its power during off-peak tariffs - while I suspect ASHP are more likely to run on demand - so a much greater chance of it coinciding with other (peak) loads, pushing the max demand up even though the overall energy usage might still be lower.


       - Andy.
  • In my view, diversity can not be applied to electric space heating within any one dwelling. On a cold day the occupiers might well turn it all on.

    Some diversity can however be applied over a large estate, some homes will be empty, either continually, or during the evening peak. Other homes will have been occupied all day, and therefore be up to temperature with most of the heaters turned off by thermostats or by hand.

    3kw is a fair bit of heat in a small and well insulated modern home, especially as it might be nearer 4kw after allowing for a few empty homes, and for a bit of overloading in cold weather.


    The price of the homes if compared to others in the same area is also IMO indirectly relevant. A relatively low purchase price implies relatively less well of customers who will tend to spend less on electricity.

    A higher price implies a potentially greater fuel use.


    Flats tend to use less per square meter than houses, due to less heat loss, and a lot less in absolute terms due to the smaller area.
  • There are many assumptions in these numbers, and most of them are to do with cost, which is being minimised. If these were modern houses the heating requirement most of the time might well be low, say 3kW, but British weather being what it is we have snow and -20C temperatures (particularly up north or Scotland) much more often than is often realised. This means the heat pump will struggle and additional heating will also be needed. Then there are the electric vehicles, which if we all have one will need a great deal of charging power unless typical usage can also be controlled (which I hope it never can be). Then there is the cooker, washing machine etc. These figures have been pared to the absolute minimum, and I assume that load shedding will become common.
  • An electric vehicle charging at every home is not possible, the idea that many homes may have two is laughable. EV's charging is not an issue at present, because there is so few of them, but a massive switch to EV's is impossible.


    Andy B.