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GEM Electrics

Sanity Check Required

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GEM Electrics

Have you designed hotel electrical systems?  I am in the mids of such a design but am finding that, even with diversity applied where possible, the total load is cumming up as 1400Amps for this 80 room hotel.  From your experiance is this reasonable?

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Sharpend

what are you basing the use per room on?

electric showers?

 

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GEM Electrics

No, hot water is by gas.  The figure per room is taken from a respected study (can't remember the name off hand) and works out to 2.3 to 2.9 amps per room with diversity applied.  The big guzlers are the kitchen with oven at 90Amps dishwasher at 30Amps and three toasters at 12Amps each, thats 156Amps just for those three and I don't think I can claim diversity on any of them at 8am.  Then the Air Con at 465Amps.  It might be said that they will not pull full power until maybe 3pm, could I off set them against the kitchen?

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Sharpend

this is a 3ph supply?

 

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Evans Electric

Gotta be I'd think Sharpie . 

GEM Electrics  can I ask ,  are you  basically a sparkie  like most of us on here  and if so  I'm wodering why you are doing design on such a project ?     No offence  implied . 

 

I know if you try to do calcs for a block of flats its scary  ,   but  the DNO will put in no more than a 500A   Three Phase supply .....it works  but not on paper .   

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Andy™
Just now, Evans Electric said:

 

I know if you try to do calcs for a block of flats its scary  ,   but  the DNO will put in no more than a 500A   Three Phase supply .....it works  but not on paper .   

 

iirc they use (or used to) 4-6a per house. so a street of 80 houses would be 160a per phase. not much...

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Evans Electric
3 hours ago, GEM Electrics said:

From your experiance is this reasonable?

No  its not  .  The kitchens may be a constant at differing times of day but even the top design engineers  cannot  estimate how many guests  will book in at any given time  and if they will be in or out at any particular time  or boiling a kettle at any particular time .  

 

You say 80 rooms  , lets say its full and theres one person in each room .   Some will be boiling a kettle ,  some will be taking a dump , some will be gazing out of the window  , some will be walking to the bar , some returning from the bar ,  some will be in the lift , some walking down the stairs etc etc .  

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Evans Electric
Just now, Andy™ said:

4-6a per house. so a street of 80 houses would be 160a per phase. not much...

Exactly  ,  reading my meters last week , I tried  my clamp meter  as I thought the wheel was turning a bit fast ,   reading was 1Amp  ,  obviously we wern't cooking  or showering  but then a shower lasts 10 mins  say  and cooking , the stats keep cutting in & out on hobs & ovens .   

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kerching

It's  interesting if you look at the Bullrush charts and see what a 100A fuse WILL actually carry and for how long.  Obviously it's going to get sick of being overloaded and go "moody" at the most inconvenient time, but nonetheless interesting al, the same

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Evans Electric

You're right  ,  theres always this thing in the back of your mind that it will blow at 100 A  immediately  when its not the case at all .  

 

Bit like a printer we looked after , they suddenly  decided to add  a 5 colour  Hiedelberg  to the two  already  running , we ran the supply but warned them to  run only two at a time  as they were near the limit on their 300A supply.  

But they needed all three working and  the mains coped well ....again a case of  yes all three running but the time characteristics  of the mains fuses  copes with the overload  ...then as the fuses are warming up  , say ,  one print run is over , current drops .    

 

The DNO networks function in the same way .     The proverbial commercial break during Coronation Street used to cause a surge as  kettles switched on all over the UK  but all over in 10 mins .  

Edited by Evans Electric

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GEM Electrics

Thank you all for your comments.  I am well aware of the need to apply diversity, but this is the first hotel design I have done and the figures did supprise me.  That is why I asked for anybody with hotel design experiance to give me a sanity check.

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Geoff1946

I've stayed in an all-electric hotel. Can't remember which now, but a Travel Lodge, Premier Inn, or similar budget place. The rooms had kettles and convector heaters and the water was always hot when we used the shower, morning or night. I did wonder quite how the power was organised.

Thinking: Most people come in late afternoon, turn up the heating and put the kettle on.

Everyone gets up between 7.00 and 8.00am and wants a shower or bath, just as the kitchen switches everything on for breakfast.

I  dare say the early day water will be off-peak storage, but even so I wondered how it was all done.

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Tony S
5 hours ago, Geoff1946 said:

I  dare say the early day water will be off-peak storage, but even so I wondered how it was all done.

 

Large water tanks gently heated over a long period. Our plant’s bath house had two 500 gallon tanks, even then the hot water would run out.

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