Non coincident peak represents the sum of individual zone or circuit maximum demands when those peaks occur at different times rather than simultaneously. Adding separate peak loads that do not occur together overestimates actual instantaneous demand on the building’s central systems. Non coincident peak calculations establish upper theoretical limits but do not reflect real operating conditions.
Calculation Method
Non coincident peak results from summing Zone A’s 2 PM peak (50 tons) plus Zone B’s 4 PM peak (40 tons) to reach 90 tons total. This method assumes both zones operate at maximum simultaneously, which rarely happens in practice. Building schedules, solar patterns, and thermal mass cause zone peaks to distribute throughout the day rather than cluster. Non coincident peak calculations often exceed actual coincident peak by 15 to 30 percent in commercial buildings. ASHRAE standards recognize this distinction when sizing equipment.
Practical Application
Non coincident peak calculations serve as conservative sizing benchmarks for electrical service and central plant equipment when actual coincident peak data is unavailable. Designers use non coincident peak for preliminary estimates before detailed hourly simulation confirms actual peak conditions.
Comparison to Coincident Peak
The difference between non coincident and coincident peak quantifies the diversity factor value. Using non coincident peak for equipment sizing wastes capital investment, while using only coincident peak risks inadequate capacity during actual simultaneous peaks.