Sizing generator

[alphabraxon]

I need help sizing a generator. System is 208/120V 3 ph 4 wire 60 hz.

Full connected load [ this is an office building] is about 115 kVA. Biggest load is Air Con. Three 12.5 Ton units. Two of them package one split unit. Each unit is about 21kVA. Package units come with twin compressors, split has one compressor. I will time delay them. I can further time delay the second comp of the package units.

Now heres the rub, my genset supplier sent me a load analysis sheet where he shows the motor loads, and tells me I need a 450kVA set!

Any suggestions?

 

[hardworkingstiff]

I need help sizing a generator. System is 208/120V 3 ph 4 wire 60 hz.

Full connected load [ this is an office building] is about 115 kVA. Biggest load is Air Con. Three 12.5 Ton units. Two of them package one split unit. Each unit is about 21kVA. Package units come with twin compressors, split has one compressor. I will time delay them. I can further time delay the second comp of the package units.

Now heres the rub, my genset supplier sent me a load analysis sheet where he shows the motor loads, and tells me I need a 450kVA set!

Any suggestions?

Do you trust the genset supplier as being more knowledgeable than you?

Who takes the liability if it is sized smaller and can't handle the loads on startup?

What size do you think you need?

 

[BAHTAH]

Sizing Gen

Sizing Gen

There are several factors that effect generator sizing ( altitude, type of fuel used, air cooled or water cooled etc.) Most generator manufactures have sizing programs available for you to use on the internet or through their rep's. You need to provide as much information as possible with respect to the loads you have ( time delay starting etc.) the more information the better you will be able to size the unit. If you just provide a list of loads the manufacture will take the worst case. Try and be more detailed with your supplier and ask what can be done to allow for a smaller unit if possible. At least you will better understand the process when all is done.

 

[bsh]

Also consider the starting sequence of the loads. If most loads are on and a large motor starts it may trip the gen. Most gen manufacturers have sizing programs which take starting sequence into account