Run time requirement for diesel generator for legally stand by power for elevator

zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
Hi guys, here is my questions:

How many hours are diesel generator required to operate for legally stand by power for the elevator of a 5-story residential building? I can only find a requirement in NEC 701.12(B) (2). An onsite fule-supply shall be provided with an on-premises fuel supply sufficient for not less than 2 hours of full-demand operation of the system. Is there any other code that has a requirement for the run time? I am in Philadelphia.

Another interesting question: I am curious that how do you refill the diesel generator tank on the roof? Is it like using a fuel hose from the truck connecting to the fuel inlet on the tank (50' above the ground) and pump the diesel to the tank? That's gonna be a tough work...I can't imagine how much more cost will need for maintenance, refill if you install a diesel generator on the roof...
 

steve66

Senior Member
I'm not sure what else might affect the required run time.

But if the generator is on the roof, there is usually a day tank at the generator that holds x hours of fuel. Then there is also a bulk tank down at grade (or below grade). A fuel pump fills the day tank when it gets down to a certain point. So the delivery truck just has to fill the bulk tank.

I know of a recent generator install on the second floor, and the techs were complaining about how many gallons of oil they had to carry up one flight of stairs just to do an oil change. If I remember right, there were 3 generators, and each one required about 50 gallons of oil.
 

Russs57

Senior Member
IMHO Steve is right. You need to be looking at a ground level tank with pump and fuel lines (and monitoring system/etc.) feeding a generator day tank. Given what your needs are I think you will come out much cheaper having a generator with skid mounted tank at ground level and running conduit/wire to load on roof.

I work at a hospital and our run times are more stringent. In your case I'm not sure you are legally required to have the elevator on generator power.....just have a battery backup system that will return it to the ground floor. Very cheap and easy with a hydro elevator.
 

zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
Why not use propane, or natural gas?
Hi norcal, yes the owner also considers the natural gas generator. But in the Philadelphia area, the gas pressure of low pressure gas can't reach the requirement of the Generac generator. The high-pressure gas has safety hazards. What we do is to use a gas booster pump and an ups power for the booster pump to have the gas pressure.
The owner wants to compare the cost of diesel and gas generator w/ gas booster pump and ups package.
 

zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
Hi guys. Thanks for your reply!

They want to place the generator on the roof because they don't have an outdoor space on-site at ground level. What do you think the cost of installing an indoor diesel generator at ground or basement comparing with installing it w/ day tank on the roof and storage tank and pump at the ground? I think the indoor diesel generator must have a more strict requirement for ventilation and some other issues?
 

junkhound

Senior Member
Location
Renton, WA
Back in my Minuteman days, we ran DG sets for half hour every 2 weeks IIRC. Studies showed that this was the optimum for best power availability and engine life.

Do you have any power availability requirement number to meet vs. 'we have a generator and it almost always runs when started?

10 years ago or so our local hospital had to evac patients after a power outage when the DG failed (a rotating diode in generator of all things.)
A fortnightly test regime would have caught that before an actual outage occurred.
 
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