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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

  • How 'huge' is the current involved for the locked sprinkler calc ? That one sounds quite sensible. - maybe in a fire  other loads are dropped (cookers water heaters etc may not be needed. )
    Realise  that most gensets, unless specially designed with larger flywheels (which slows start up time) will stall if there is a load step of more than perhaps 1/3 to 1/2 of the full load. (unlike the normal mains that just dips a bit more than the 10% but keeps supplying current, unless the ADS trips )

    Or how big is the mains supply you are trying to emulate?

    Mike.

  • in reply to mapj1

    I have 270A locked rotor plus 71A to start the other pump

    Then add to that various smoke vent control panels, fire fighting lifts, lift sump pump....another good 100A

    I just struggle to believe there is a scenario where all the above life safety services will be working at the same time and one sprinkler pump will lock rotor and start the second.

    I think more along the lines of diversity however I dont know if I am allowed to apply any diversity

    Thats why I am looking to see if there is any BS Standard that mentions generator sizing for life safety systems

    Cheers

Reply
  • in reply to mapj1

    I have 270A locked rotor plus 71A to start the other pump

    Then add to that various smoke vent control panels, fire fighting lifts, lift sump pump....another good 100A

    I just struggle to believe there is a scenario where all the above life safety services will be working at the same time and one sprinkler pump will lock rotor and start the second.

    I think more along the lines of diversity however I dont know if I am allowed to apply any diversity

    Thats why I am looking to see if there is any BS Standard that mentions generator sizing for life safety systems

    Cheers

Children
  • in reply to Apostolos

    I can't remember which standard says it, but no, you can't allow diversity as such for life safety systems. You have to refer to the Fire Strategy, or ask the Fire Engineer. They risk assess it and usually only allow for a single fire in a building at any one time, meaning not all the systems will be needed simultaneously. This allows you to design for just the most onerous case.

    There may be a BS for guidance but generators of a given size can have differing starting capabilities so you have to ask your specific manufacturer.

    burn

  • in reply to Apostolos

    well a 500kVA  machine is not so big .....

    Mike.

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