21-0519 Diesel as Back-up Generator for High-Rise Residential Project


400 Westlake  - ILFI requirement for no combustibles in building Per May 2017 Energy Petal Handbook, Net Positive Energy, no combustion is allowed for emergency power systems. 

The project is a high rise that contains multiple elevators, multiple stair and elevator pressurization fans, a 200hp fire pump, and egress lighting. Battery backup for these loads is not practical or feasible. The total anticipated load required for emergency to be on the generator is approximately 497.2kVA. 

The current design is for a single 600kW diesel generator with 8 hours of fuel storage (driven by NFPA 20 – Standards for the Installation of Stationary Pumps for Fire Protection). Natural gas generators were studied but natural gas generators are not deemed a reliable source of power in this region since the gas lines could break or be shut off in a seismic event. 

Propane generators were also studied and two 335kW Propane generators would be required to provide the same capacity as the single 600kW diesel generator. The propane generators consume 15,747 liquid gallons of propane per hour and assuming one unit will support the emergency system and its 2-hour run time requirement (31,494 Liq Gal) and the other will support the fire pump and its 8-hour run time requirement (117,976 Liq Gal) and the fact that the tanks are only filled to 80% for expansion, a tank with a capacity of 186,838 Liquid Gallons of propane would be required. Based on SFC 6104, there does not seem to be a location where the propane tank could be situated given proximities to other buildings. 

Storing this much liquid propane is both impractical and seemingly very dangerous. Due to the nature of the loads served, a diesel generator seems to be required. The project team has studied what is required to operate on the generator and optimized the design of the systems connecting to it to the extent possible. The project will utilize regenerative power for elevators and will only connect things required for emergency and proper building function during an extended outage. This equipment includes the fire pump, elevators, pressurization systems, emergency lighting, the sewage and sump pumps, the toilet flushing system, access control and surveillance, building controls, and the fire alarm system. 

The project team respectfully asks for a review and a variance to allow the use of a diesel generator for emergency power.


The project team has done their due diligence to understand what back-up systems would have the least amount of impact while creating the most resiliency for their residents by exploring battery, natural gas, and propane back-up options. ILFI understands that a diesel generator is the only feasible solution for their large-scale back-up needs and therefore is issuing a project-specific pathway for the team to apply Exception I06-E13 Critical Infrastructure and Life Safety - Emergency Power. All loads required by code and/or related to life safety (e.g. elevators, egress lighting) may be backed up by the diesel generator. However, all LBC resiliency strategies (e.g. phone charging, refrigerators) should be moved to a battery-powered back-up system. The team must document all effort was made to minimize the amount of power backed up on the diesel generator.

Still need help? Contact Us Contact Us