# Emergency Generator with shared fuel tank



## mshields (Jul 9, 2013)

I'm working on a project where we are going to replace a very old (1975) 55kW diesel generator with new.  The generator presently serves Emergency loads only.

It get's it's diesel fuel from a fuel tank whose primary purpose is for the Diesel Boiler for the building.

Is this shared source permissible for an Article 700, Emergency generator?

Thanks,

Mike


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## cda (Jul 9, 2013)

what kind of occupancy or high rise or?


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## chris kennedy (Jul 9, 2013)

Can you be absolutely sure the fuel tank will ALWAYS have enough fuel to serve genny AND the boiler for not less than two hours? 700.12(B)(2)

Can the ATS shed the boiler control load? You would still have to guarantee the tank never falls below the 2 hr level for the genny. Sounds like a crappy idea to me.


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## mark handler (Jul 9, 2013)

| Classifying generator power sources | Consulting-Specifying Engineer

 The amount of on-site fuel should be sufficient to provide a minimum of 2 hours of run time.

A rough rule of thumb for diesel consumption by a generator is 7 gal/hour for every 100 kW of generator capacity. In many cases where generators used, the desired run times are much longer. It is not unusual to see 8, 24, or even 72 hours of fuel needed for some mission critical facilities. In these cases, the engineer will need to carefully examine where to store the fuel. “Belly tanks” under the generator are common, as are separate fuel tanks. The size of these storage tanks can be very significant, and the use of belly tanks may notably elevate the generator and require catwalks for access. NFPA 110 7.9.5 specifies a maximum of 660 gal diesel storage inside or on the roof of a structure.


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## jar546 (Jul 9, 2013)

chris kennedy said:
			
		

> Can you be absolutely sure the fuel tank will ALWAYS have enough fuel to serve genny AND the boiler for *not less than two hours? 700.12(B)(2)**Can the ATS shed the boiler control load?* You would still have to guarantee the tank never falls below the 2 hr level for the genny. Sounds like a crappy idea to me.


2 reasons right off the bat why you make the big bucks and I volunteer


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## jar546 (Jul 9, 2013)

mark handler said:
			
		

> *|*Classifying generator power sources*|*Consulting-Specifying Engineer The amount of on-site fuel should be sufficient to provide a minimum of 2 hours of run time.
> 
> A rough rule of thumb for diesel consumption by a generator is 7 gal/hour for every 100 kW of generator capacity. In many cases where generators used, the desired run times are much longer. It is not unusual to see 8, 24, or even 72 hours of fuel needed for some mission critical facilities. In these cases, the engineer will need to carefully examine where to store the fuel. “Belly tanks” under the generator are common, as are separate fuel tanks. The size of these storage tanks can be very significant, and the use of belly tanks may notably elevate the generator and require catwalks for access. NFPA 110 7.9.5 specifies a maximum of 660 gal diesel storage inside or on the roof of a structure.


What if he installs new high efficiency spark plugs in the diesel generator to ensure 2 hours?


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## mark handler (Jul 9, 2013)

jar546 said:
			
		

> What if he installs new high efficiency spark plugs in the diesel generator to ensure 2 hours?


a minimum of 2 hours of run time. that works


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## jar546 (Jul 9, 2013)

mark handler said:
			
		

> a minimum of 2 hours of run time. that works


Even when I am joking you seem to find code compliance information....


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## TheCommish (Jul 9, 2013)

use a day tank fed from the  main supply to ensue there is enough fuel for 2 hours


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## Dr. J (Jul 10, 2013)

Are you required to meet NFPA 110 as well (you would in Healthcare)?  There is more direction on shared fuel sources there

From 2005 NFPA 110

5.5 Energy Converters — Fuel Supply.

5.5.1  The fuel supplies specified in 5.1.1(1) and 5.1.1(2) for energy converters intended for Level 1 use shall not be used for any other purpose. (For fuel system requirements, see Section 7.9.)

5.5.1.1  Enclosed fuel tanks shall be permitted to be used for supplying fuel for other equipment, provided that the draw-down level always guarantees the quantity needed for the EPSS.

5.5.1.2  Vapor-withdrawal LP-Gas systems shall have a dedicated fuel supply.

5.5.2*  A low-fuel sensing switch shall be provided for the main fuel supply tank(s) using the energy sources listed in 5.1.1(1) and 5.1.1(2) to indicate when less than the minimum fuel necessary for full load running, as required by the specified class in Table 4.1(a), remains in the main fuel tank.

5.5.3*  The main fuel tank shall have a minimum capacity of at least 133 percent of either the low-fuel sensor quantity specified in 5.5.2 or that specified in Table 4.1(a) (class).


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## Builder Bob (Jul 10, 2013)

Beware of special requirements fo generators for health care in seismic areas..... this may blow the two hour requirement out of the water.


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## mark handler (Jul 10, 2013)

Builder Bob said:
			
		

> Beware of special requirements fo generators for health care in seismic areas..... this may blow the two hour requirement out of the water.


Bob I do not believe Plymouth, MA is in a seismic area....assuming the post location is the project location....


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## Dr. J (Jul 10, 2013)

Healthcare is minimum 24 hours, perhaps more by State regs.

However, rereading the OP, @ 55kW - it's unlikely it is healthcare.

BTW, a typical method of assuring generator fuel in a shared tank is to have separate suction lines or submersible pumps where the generator suction/pump is lower than the boiler suction/pump so the boiler runs out first, leaving the legally required amount of fuel for the generator.

I also like the day tank idea if NFPA 110 is not involved.  Note that NFPA 110 references the "main tank" needing the required amount of fuel.


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