Diesel Generator Load Calculation For Buildings

As the scale of civil construction expands and building heights increase, power supply reliability has become a critical concern. According to regulations, Class I loads should be supplied by dual power sources, where a failure in one source should not affect the other. Normally, Class I loads are powered by the primary supply, with the backup supply activating during primary source failures to ensure uninterrupted power. For particularly important Class I loads, an emergency power source such as a diesel generator should be added besides dual power supplies. 500kW diesel generators are a simple, reliable backup/emergency power solution widely used today. This article explains diesel generator load calculation methods.

1. Diesel Generator Load Calculation Formula

The 2009 edition of "National Technical Measures for Civil Building Engineering Design – Electrical" provides a simplified formula for diesel generator capacity calculation:

Pe = K×Kx×Pn/η

Where:

·Pe = Rated power of generator set (kW)

·K = Reliability coefficient (1.1~1.2)

·Kx = Demand coefficient

·Pn = Total equipment capacity (kW)

·η = Parallel unit unevenness coefficient (0.9 for parallel operation, 1.0 for single unit)

The key to generator capacity calculation lies in determining the calculated load capacity (Pn value) that the generator must support.

2. General Requirements for Load Calculation

According to specifications, emergency generator load calculations must meet the following requirements:

(1)When the emergency generator solely powers particularly important Class I loads, the calculated capacity of these specific loads serves as the basis for generator selection.

(2)When the generator supplies both fire-fighting equipment and Class I loads, the sum of their calculated loads determines the required generator capacity.

(3)When the self-provided generator acts as the second power source (with a third source for critical Class I loads), and supplies fire-fighting loads, non-firefighting Class I loads, and particularly important Class I loads, the total combined calculated load of these three categories determines the generator capacity.

For requirements (2) and (3), note that non-essential non-firefighting loads must be automatically disconnected during a fire. Therefore, load calculations must consider both normal (non-fire) and fire emergency scenarios separately, as further explained in engineering design examples below. Generator sets must interlock with municipal power and are not allowed to operate in parallel with the mains supply.

Engineering Case Application

This project has a total construction area of 45,600 m², with 23 above-ground floors (roof height 98.7m) and 4 underground floors. Underground floors 1-4 house mechanical parking garages and auxiliary equipment rooms, while above-ground floors serve as office space. Two 10kV municipal power supplies are introduced based on project electricity demand and local supply conditions. To ensure reliability, a diesel generator is additionally installed as emergency power for fire-fighting and critical loads (main business/computer systems, security systems, electronic information equipment rooms, passenger elevators, etc.).

Normal Condition (Non-Fire) Load Calculation

The diesel generator starts only when both municipal power supplies fail, powering critical loads. Load calculation here is relatively straightforward, focusing on maintaining normal building operations and ensuring safe evacuation during power outages. With a diversity factor accounting for simultaneous operation, the calculated capacity = 466 kW.

Fire Emergency Load Calculation

For single office buildings, fire scenarios prioritize activating relevant fire-fighting equipment while evacuating all occupants, placing the entire building in emergency mode.

Dingbo Power was founded in 1974 and is one of the earliest manufacturers of generators and diesel generator sets in China. If you want get more information, please feel free to send email to [email protected] we will pay highly attention on your question.