Load diversity allowance?

[cyriousn]

Hello to all. I am currently sizing a generator to backup an entire residence.
Owner wants EVERYTHING on emergency. The following are rough load breakdowns.

HVAC, water systems: 50kva
Built in appliances (kitchen, laundry): 45kva
Lighting (Lutron): 22kva
Receptacles at 180W per: 20kva
Steam Baths (3): 18kva
Spas (2): 22kva
Other loads: 20kva

Total: 197kva

Design occupant load: 10-15 People

Are there any good rules of thumb for these types of loads? It's looking like a diesel to LP conversion, 120/240V. It's on the beach so diesel tanks are looked down upon and no natural gas line is available.


Thanks to all.

 

[gobblerhuntr]

The easiest way I can think of is to put a recorder on and record the load for a period of time when it is occupied and see what the current draw is. Do you know what size transformer the poco is feeding it with? What size is the main service?

 

[cyriousn]

Service size

Service size

The poco has a 100kva there as of now and they are looking to replace it soon with another 100 or a 167. Service size is 800 amps.

 

[steve66]

Some of the generator manufacturers have sizing calculations online. Try Caterpillar or Generac, or Cummins.

You may have to size the generator based on the starting current of the air conditioning compressor.

Steve

 

[coulter]

Coulter's rule for multi-million dollar villas on the beach: Don't make anything marginal.

This is not a "residence". It's five residences, or a small commercial.

You are looking at 200kw- why skimp. I'd guess the customer is far more interested in seamless operation, and flawless reliability.

I know there is a large following for gen mfg sizing programs. I have never trusted them as anything other than a poor guide. Personal opinion is these programs are designed to sell the generators they have, not necessarily meet the customers needs.

Sizing this gen is is up to you - not some salesman. Discuss with the customer the level of PQ while on generator. The utility is possibily installing a larger xfm cause the level of flicker is too high. Probably a good idea to ask why.

Don't forget, there is likely a caretaker that has to be able to run/exercise it. Controls will have to be up to what ever level the caretaker needs.

Fuel tanks would not be high on my list of worries. For a 100kw average load you are looking at 10 - 12gph. A 660gal double-wall tank, suitable for installation inside the gen house, is good for 50 hours. If they need more than that, service station contractor have been burying 6000g, double-wall, fiberglass tanks for 20+years - that should get them 500hrs.

UG LP tanks take a vault and have significant classified areas. Workable, just more stuff to take care of.

I'd say my biggest concern would be where am I going to find a single-phase, 120/240, 200kw gen set. You are likely looking at a 250kw, 3ph, 208V, 12 lead, reconnected for single phase.

good luck - let us know how it comes out.

carl