How do you size a diesel generator for a facility?
Accurate sizing begins with a power audit: measure peak and running loads, including motor starting currents, and review historical energy bills. Estimating 5-10 watts per square foot for lighting and HVAC loads can provide a baseline. After summing all running and starting loads, add about 25% reserve capacity to accommodate future expansions and derating for high altitudes or extreme temperatures.
Proper sizing is critical. An undersized generator can’t handle peak loads (leading to voltage drops and overheating), while an oversized unit will run inefficiently at light loads (causing issues like wet stacking). Generator suppliers, electricians and engineers can perform detailed load analysis and recommend appropriate capacity.
Related Questions
How do you calculate total power requirements?
Sizing begins with a power audit. Measure the peak and running loads of all equipment you plan to power. This can involve:
- Using a clamp-on ammeter to measure current draw at the service panel during peak operation.
- Reviewing historical utility bills to identify maximum demand.
- Estimating wattage per square foot for lighting and HVAC loads (e.g., adding 5-10 watts per square foot).
- Considering starting currents of motors and compressors; large motors can require 3-7 times their running amperage when starting.
What is reserve capacity and why is it needed?
After calculating total running and starting loads, add 25% reserve capacity. Reserve capacity accommodates unplanned future loads, prevents the generator from constantly operating at maximum output and compensates for derating due to altitude or extreme temperatures.
Is oversizing or undersizing harmful?
Yes. Undersized generators cannot handle peak loads, leading to voltage drops, overheating and premature wear. Oversized units operate at low load and experience wet stacking, wasting fuel and causing carbon buildup. Selecting the right size ensures efficient operation and long life.
Who can help with sizing calculations?
Generator dealers, electrical contractors and professional engineers can perform detailed load analysis, recommend appropriate sizing and assist with installation. Depco’s team offers consultation and can match you with the right diesel generator for your facility based on application, load profile and budget.
