Emergency Generators or Diesel Engine Driven Pumps
Fire pumps have been used to supply water and pressure to fire protection systems for over a century. A fire pump can be used in cases where flow and pressure or both are lacking. For example, a ground-mounted suction tank can provide a sufficient amount of water, but without the fire pump to move that water to a fire protection system, the stored water is of little value. Therefore, the fire pump can be considered to be providing flow in this case. In other situations, such as in a high-rise building, a city water supply usually lacks sufficient pressure to move water to the higher floors. In this case, the fire pump is used to supplement the available pressure.
To run a fire pump, a reliable driver is needed. Both electric motor and diesel engine are proven to be reliable drivers of a fire pump.
Electric motors used to drive fire pumps are required to withstand severe changes in operating conditions and should be arranged to accommodate large electric loads that might cause the motor to be destroyed. This strategy is contrary to the design and arrangement of most other electric motor applications. However, the reliability of the fire pump is the primary concern. The fire pump must continue to operate during a fire emergency for as long as is necessary.
When an electric motor is considered as a driver, the power supply to the motor becomes utmost important and must be from a reliable source. Power supplies that can be compromised due to maintenance, load shedding, storms, fires, or other accidents can leave electric motors without power and render the fire pump useless. Where reliable sources cannot be secured, backup supplies such as an emergency generator or diesel engine are considered.
Properly installed and maintained emergency generators increase the reliability of an electric motor driven fire pump. However, there are significant differences between the requirements of a diesel engine to drive a fire pump and an emergency generator. The requirements of a Diesel engine to drive a fire pump is covered under NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection and the requirements of a Diesel engine to drive an emergency generator are covered under NFPA 110, Standard for Emergency and Standby Power Systems.
The below table highlights the key differences and provides a comparison of requirements for diesel engine drivers for fire pumps and emergency generators.
|Diesel Engine to Drive Fire Pump
|Diesel Engine To Drive Emergency Generator
|Two Battery Sets
|Single Battery Set
|Two Battery Chargers
|Single Battery Charger
|Engine Cranking Time – 90 Sec
|Engine cranking time – 45 sec (continuous)/75 sec Cycle Crank
|Design Concept: Run to self-destruction to mitigate emergency
|Design Concept: Interlocks to save the engine.
|Engine Shuts down only on overspeed otherwise runs till its destruction.
|Engine shuts down on overspeed, high engine temperature, low lube oil pressure and optional shutdown at low coolant level.
|Only diesel engines are allowed as they are considered more reliable
|Spark Ignition engines are also allowed.
|Fuel Supply is exclusively for driving fire pump diesel engine only.
|Fuel Supply is shared for other loads as well
|Diesel Engine is fully dedicated to drive fire pump only
|Can supply multiple loads
|Design concept of fuel storage tank shall be a capacity for 8 hr.
|Fuel tanks are sized to accommodate the specific EPS Class. The minimum can be as low as 5 mins.
|Design Concept: 10% reserve power
|No concept of reserve power
|Testing frequency is Weekly
|Testing frequency is monthly
|Must be Listed
|Listing not mandated.
|Coolant Heater must for quick starting of engine
|No coolant heater requirement.
|Annual Test with pump @ full flow, max. load.
|No requirement to test pump @ full flow max. load powered by emergency generator.
Diesel engine to drive fire pumps seems to be a more viable and reliable option than using electrical motor driven by emergency generator.
Whitepaper Authored By:
Eng. Redentor Ymballa:
Facility Incharge at Sffeco Global:
30+ year of Experience in Industry
Eng. Dilbagh Singh:
Engg. R&D Manager at Sffeco Global
BSc., BE (Fire), DIIS,
15 year of Experience in Industry