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Sizing a Generator for a building

Apostolos

Good afternoon

I would like to ask if anyone is aware of any BS standard that provides any guidelines on how to size a generator set

We currently have a big hotel that has life safety systems (fire fighting lift, smoke ventilation, sprinkler system...etc)

Is there anything in the British Standards about this or we go by the common sense?

At this stage I have to say that in the past I have heard the following rule:

'It has to be able to start the biggest motor (highest starting current) while everything else is operating'

However in this very project its the first time the sprinkler subcontractor asked us to size the generator based on 1 sprinkler pump at locked rotor and the standby pump starting. So after this if I add all the rest (smoke vent panel, fire fighting lifts, car park smoke vent etc) this leads to a huge total current so I am starting this discussion in case someone know of any official guidelines or any other help is appreciated

Thanks

Parents

  • Good Morning

    Your starting point would be BS 7671 Chapter 56 then BS 9991, BS 9999, BS 8519. The Fire Strategy for the building etc.

    The generator must be able to pick up the load presented to it without stalling. You will need to get the data sheet for your chosen generator to verify what load it can pick up with a "crash transfer" normally something around 60% of the maximum output of the generator.

    Fire pumps for hydrant mains are a big problem as fire engineers do not like variable speed drives as they contain electronics and they will want star delta starters for reliability. They come in pairs controlled by a panel which does the changeover and starting. If one has a locked rotor condition, bearing failure or the pump trying to digest a chunk of ice or half a house brick the fusing the pump fuses will operate before the supply fuses. If necessary the pumps have to be able to run to destruction. 

    The fuel supply capacity has to meet the requirements for the Fire Strategy.

    The Fire Engineer and the mechanical engineers have to do their design before you can put finger to keyboard.

    JP

     

  • in reply to John Peckham

    BSEN 12845 (Commercial) sprinklers and wet riser fire mains pumps don't have starters, just DOL contactors and then, as you say,  run to destruction. A generator may have support the full locked rotor current of one pump motor and then start the other DOL. Also support the full building load unless there is any form of load shedding.

    The sprinkler supplier will have to tell you the locker rotor current and the maximum starting currents (effectively the same value) of the motors. It has to do this until the stalled motor burns out, so they will also have to tell you the burn out times for the motors, if they haven't already done so (they usually do).

    Typically for a 10 storey building the current will be 800-1200A, so you would need a 1000kVA generator. For this reason it is usually more practicable to have a diesel motor on the secondary pump. The pump engine only has a single load to start and is far smaller than the generator would be.

    regards, burn

  • in reply to burn

    Star delta starting for electric sprinkler pumps

  • in reply to John Peckham

    Thanks. One question. What is a 'crash transfer' ?

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