Max Demand Calculation < 2025-2027 >

Maximum Demand is the highest average load (in kW, kVA, or A) that an electrical installation draws over a specified time interval (typically 15, 30, or 60 minutes) within a billing period.

| Time | Instant kW | Avg over last 15 min | |------|------------|----------------------| | 13:00 | 100 | 100 | | 13:05 | 300 | 200 | | 13:10 | 500 | 300 | | 13:15 | 200 | 275 (13:00–13:15) | | 13:20 | 400 | 350 (13:05–13:20) ← | | 13:25 | 100 | 300 | max demand calculation

(not the 500 kW spike). 5. Software & Tools Review | Tool | Type | Best for | Accuracy | Cost | |------|------|----------|----------|------| | Excel (manual) | Spreadsheet | Simple estimates, learning | Low | Free | | ETAP / DIgSILENT | Professional power system | Complex industrial MD & load flow | High | $$$ | | Ecodial (Schneider) | Free tool | LV installation & MD estimation | Medium | Free | | PowerLogic ION Setup | Meter configuration | Real MD from meters | Very high | Varies | | OpenDSS | Open source | Distribution ADMD studies | High | Free | Reviewer note: For most facility managers, the best tool is already inside your energy meter (e.g., Schneider PM5500, Siemens PAC4200, or simple utility meter). Learn to read its MD registers. 6. Common Mistakes & Pitfalls | Mistake | Consequence | |---------|--------------| | Using instantaneous peak instead of averaged demand | Oversized equipment, higher capital cost. | | Ignoring power factor | MD in kVA may exceed kW MD – paying for reactive power. | | Wrong demand interval | 30 min vs 15 min changes MD significantly (shorter = higher). | | Not updating diversity factors | Older buildings have different load patterns today. | | Forgetting seasonal variation | Summer MD (AC) vs winter MD (heating) can differ 2x. | 7. Real-World Case Study Problem: A hotel had monthly demand charge of $18/kW. Their MD was 450 kW (metered). Energy manager staggered pool pumps, laundry, and kitchen exhaust fans. Maximum Demand is the highest average load (in

It is the instantaneous peak (which could last milliseconds), but a sustained peak that actually stresses supply equipment. Example: A factory starts a 500 kW motor for 2 seconds – that’s not MD. But if it runs 400 kW for 20 minutes – that likely sets the MD. 2. Why Is Max Demand Calculation Important? | Purpose | Explanation | |--------|-------------| | Utility billing | Many commercial/industrial tariffs charge a demand charge (e.g., $15/kW of MD per month) plus energy (kWh). | | Transformer & cable sizing | Prevents undersizing (overheating/trips) or oversizing (wasted capital). | | Generator selection | Ensures backup power can handle the highest sustained load. | | Power factor correction | High MD in kVA indicates poor PF – correction reduces MD charges. | | Load scheduling | Stagger large loads to shave MD and save costs. | 3. Common Methods for Max Demand Calculation A. Diversity Factor Method (Design/Estimation) Used when meters aren’t installed. Software & Tools Review | Tool | Type