max demand and diversity

[james KEI]

hi all

just wanted to get some opinions. got a place being converted in to two flats and everything will be electric! new edf supplie(s) to go in and so need to know what max demand in kva is for edf to evaluate.

just one flat

electric shower 10kw

electric oven/hob 8kw

electric water htr 3kw

storage heaters for main heating 3x 2.5kw & 1x 3.4kw

and then the usual couple of rings and lighting circuits.

using the onsite guide for diversity values I come out at 176A

even with a g factor of 0.8 (playing it safe) it's still 140A. customer is thinking there wont be a economy 7 supply so it'll all be on one supply.

not had much experience where everything is electric so looking for some views from people that have and what the scenario has been to get over the large load. 3phase seems a bit ott?? is there a larger supply available than 100A single phase although then i guess DB's etc aren't rated high enough. i realise that in real life it shouldn't pull near to 140a but thats what it is coming out at on paper and if it went wrong with me saying less than 140A i'd cop the blame which i don't want.

thanks for any help

 

[Sidewinder]

Total load x0.4

 

[Doc Hudson]

Economy 7 normally all comes up the same supply cable, but as the storage heaters take most power at night when most other appliances are off they are not all additional to things like showers and cookers.

Doc H.

 

[Technician]

Read the posts...very interesting.

But what is the "g" factor?

Where would I find it or others?

 

[james KEI]

Hi

Thanks for the replies. Sidewinder-can you tell me why you say to use 0.4? In the designers guide there's a graph (don't have it to hand) and it gives you the g factors depending on the possible coincidence all all loads. As there's to be NO economy 7 and the storage heaters will be off the general supply (the only supply) I chose a high coincidence which came out at 0.8.

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Thanks for the replies

 

[Doc Hudson]

Storage heaters by their very nature store up heat over one period of time then release that heat over another period of time. Irrespective of if they are paying economy 7 rates or not, I would think that storage heaters will be on during the night and outputting heat during the day. I can't imagine anyone switching them on to store during the day and release heat at night? Are the definitely storage heaters? or are they combined storage and radiant heater?

Doc H.

 

[james KEI]

Hi doc

It's planning for a house to be converted in to two flats so nothing there as yet. True, but as there is no eco7 there's nothin to stop them turning them on in the day. Unless I introduce my own version with a time clock and contactors.

Has noone come across this situation before?

Thanks

 

[Sidewinder]

IF you are going to allow for true 24hr electric heating then you cannot allow diversity on that at all.

"Officially".

However, you said storage heating in your op.

 

[Technician]

James, can you put the name of the publication in a post?

I have never heard the term "coincidence factor" but I can

imagine exactly how it might be used.

 

[Doc Hudson]

Hi docIt's planning for a house to be converted in to two flats so nothing there as yet. True, but as there is no eco7 there's nothin to stop them turning them on in the day. Unless I introduce my own version with a time clock and contactors.

Has noone come across this situation before?

Thanks

Why would someone want to turn a storage heater on during the day, as they are not an instantaneous heat source? The logic of such usage would be similar to using an electric shower to fill a bath, very long winded and inefficient. A person wanting to turn heat on/off during the day would not opt for storage heaters. I would suggest a reassessment of exactly what is needed by the client to ensure the correct type of heating is installed. Once you have verified the correct type of heating the max demand can be reassessed. Dimplex do a good range of heaters capable of supplying daytime operation at lower power ratings.

Doc H.

 

[james KEI]

Table 3.4 g factors table pg34

Figure 3.4 coincidence g factor graph pg33

In the electrical installation design guide

 

[Doc Hudson]

Table 3.4 g factors table pg34Figure 3.4 coincidence g factor graph pg33

In the electrical installation design guide

Do you mean this book James? Electrical Installation Design Guide: Calculations for Electricians and Designers: Amazon.co.uk: Paul Cook: Books I would be interested to hear how many of our members have actually ever used that book or have access to a copy of it?

Doc H.

 

[james KEI]

Yes that's the one! I did my 2391-20 (old 2400) last year so we needed it for that