Demand factor is the ratio of actual simultaneous demand to total connected load, expressed as a percentage or decimal. This factor accounts for the reality that not all equipment operates at full capacity simultaneously. A lighting system with 100 kW connected capacity operating at 0.75 demand factor requires only 75 kW actual power supply. Demand factor differs from diversity factor by comparing actual use to connected capacity rather than comparing peak times.
Application in HVAC Systems
HVAC demand factors recognize that not all terminal units, fans, pumps, and compressors run at full load simultaneously. Electrical service, gas supply, and chilled water distribution systems are sized using demand factors rather than connected loads to achieve economical infrastructure. Typical HVAC demand factors range from 0.50 to 0.90 depending on system type, controls, and occupancy patterns. Variable speed drives and smart controls lower demand factors by modulating equipment output to actual requirements. National Electrical Code (NEC) and ASHRAE standards provide demand factor tables for different equipment categories.
Load Distribution
Diversity among multiple zones, units, and operating schedules creates demand factor reductions. A building with numerous small zones and distributed occupancy shows higher demand factors (0.80 to 0.90), while concentrated loads show lower factors (0.50 to 0.70).
Design Calculation
Applying accurate demand factors optimizes infrastructure investment while ensuring adequate capacity. Oversizing based on total connected load wastes capital and increases operating costs, while undersizing risks inadequate performance during actual demand conditions.