Maximum demand calculation

mapj1: 
It may help to consider how much floor area are you serving - there is a limit to the number of kW anyone will dissipate in a small space for very long without overheating and turning things off - the 32A per 100m2 rule may be more realistic for domestic regardless of how many circuits  it is divided over.

That depends very much upon the insulation, but the likes of Grand Designs suggest that a few kW can be sufficient.

Let's not forget that the heat emitted by a cooker stays in the house one way or another, be it during cooking, whilst the food is on a plate, or even after being eaten. Same for your tea and coffee, and even when using a food mixer (a Kenwood as we used to say).

Of course if you don't pay for your heating directly, it is easiest to regulate the temperature by opening windows. ?

I can see two approaches, both of which may suggest that the supply will be adequate.

Firstly, most domestic socket outlet circuits are very lightly loaded most of the time, but a good design should allow for use of multiple portable electric heaters when the central heating breaks. In this case however an electric heat pump is proposed. That should provide sufficient heating so as not to need portable electric heaters. When it breaks, then it is NOT consuming anything, and the 28 amps that it would have used is available for perhaps three or four portable heaters.

Secondly, consider the calculated maximum demand WITHOUT the EV charger, is it less than 100 amps ? I suspect that it is. 

Now add the EV charger which is stated to incorporate load curtailment. Does this in fact add ANYTHING to the maximum demand ? Perhaps not, presuming that the load curtailment feature is actually fitted, works correctly, and is used.

This replacement of gas by a heat pump is mad, gas will always be cheaper whatever the alleged efficiency (COP) of the heat pump claims. However much we point out the illogical “Green” agenda is faulty, the more that people seem to believe it.

Realistically your 100A supply will be sufficient, until the day they realise that the gas shower has been replaced by an electric one of similar performance. Remember that a system that takes 100A is costing about £100 per day, and very few except perhaps Bill Gates can afford that for long! The socket circuits in a gas-heated house rarely have very much load, and 100A main fuse will pass 140A for quite a long time without failure. If there are many houses like this the substation will probably fail first! There is likely to be a 400A fuse protecting 80-100 houses if the area is not very modern, or perhaps 600A if it has failed a few times. This is the future to be expected soon.

Try this for domestic premises.

0.02 A per installed lamp.

0.5A per installed socket (double or single). 

32A for a kitchen +utility room.

13A for water heater.

32A Oven/hob

Multiply total by 0.66 above. Then add.  

32A for heat pump or preferably rating of heat pump.

13A for 3kW EV charger.

31A for 7.2kW EV charger.

For an all electric house you are highly likely going to need load curtailment/load shedding.

No doubt forum members will disagree with my back of an envelope calculation and want to tinker with my numbers but I would value your views. I think the above is more realistic than using the OSG method which for an all electric house is going to need a 3 phase supply. Why in the OSG does the number or rings the sockets are connected to matter?  Why does the load go up for the same number of sockets spread over multiple rings using the OSG calculation? 

Lights touch paper and retires!

JP

That will be at least as good as any other back of envelope method. 

The OSG is conservative and over-estimates the supply need, by a lot in some cases.  I might raise your current per socket to a whole amp if there are less of them - thinking older places with a socket or 2 per room and a tangle of 4 way loads under the table.  As above I like to also consider room area based loading - with a few limits, so we do not add in the  full area of any barn-like sheds with nothing in them, or the area of the lawn because there is a mower socket serving that area!

I'd be interested how you might add in an instant electric shower or 2, The OSG sort of assumes these run non-stop, but in reality this  is not as likely to be long duration as say a few hours on the EV charger.  Similarly OSG says that diversity does not apply the  the water heating in one property, but given the no. of 1 room flats that van be supplied from a 100A fuse (record seems to be about  6..)  each with water and heating to consider, perhaps with multi-occupant households, it could be assumed if  there is more than one water heater, they will not be on together very often..

Mike.