Maximum Demand Calculation Official

For an electrical engineer or facility manager, performing a maximum demand calculation involves four key steps:

| Load | Connected (kW) | Demand Factor | Contribution (kW) | |-------|----------------|---------------|-------------------| | Lighting | 4.0 | 0.8 | 3.2 | | HVAC | 6.0 | 0.8 | 4.8 | | Elevator | 7.5 | 0.6 | 4.5 | | Sockets | 10.0 | 0.3 | 3.0 | | Pumps | 4.4 | 0.7 | 3.08 | | Total MD | | | 18.58 kW |

| Feature | Manual Spreadsheet (Excel) | Dedicated Software (e.g., SIMAR, DIALux, ETAP) | | :--- | :--- | :--- | | Accuracy | Moderate (Human error prone) | High (Automated diversity) | | Speed | Slow for >50 circuits | Instant once loaded | | Future-proofing | Poor (Static) | Good (Scenario analysis) | | Best for | Small shops, houses | Hospitals, high-rises, industrial |

Winner: Software, but only if the user understands the logic. Garbage in = garbage out. maximum demand calculation

Before diving into calculations, one must understand the "why." There are three primary drivers:

Reviewed by: Senior Electrical Engineer Subject: Application of AS/NZS 3000 / IEC 60364 & Load Estimation Software

| Load Type | Demand Factor | | :--- | :--- | | General Lighting (first 3 kVA) | 100% | | General Lighting (remaining) | 35-50% | | Receptacles (office) | 50% for first 10 kVA, 25% remainder | | Electric Clothes Dryers | 70% | | Kitchen Equipment (restaurant) | 80% | | Motors (continuous duty) | 125% of full-load current | For an electrical engineer or facility manager, performing

Several subtleties often trip up practitioners. First, coincident vs. non-coincident peaks: A single consumer’s MD is non-coincident (their own highest interval). But the utility’s system peak is coincident—when all consumers happen to be high simultaneously. A consumer who shifts load away from the system peak reduces both their own MD and the utility’s stress.

Second, the effect of harmonics: Non-linear loads (variable frequency drives, LED lighting, computers) produce harmonic currents that increase RMS current without contributing useful real power. These harmonics artificially inflate kVA demand, a factor increasingly addressed by “true RMS” metering in MD calculations.

Third, temperature compensation: For conductors, the heating effect—and thus the safe MD—varies with ambient temperature. Some advanced calculations derate MD limits based on seasonal temperature averages. Before diving into calculations, one must understand the

Finally, the rise of Internet of Things (IoT) and real-time analytics has transformed MD calculation from a retrospective billing tool into a predictive operational lever. Modern energy management systems can forecast MD for the next 15 minutes and automatically shed non-critical loads to prevent exceeding a target threshold—a practice known as “peak shaving” or “demand limiting.”

A facility with a real demand of 400 kW at PF=0.7 has an MD of 571 kVA. Correcting to PF=0.95 reduces MD to 421 kVA. At $10/kVA, that's a monthly saving of $1,500.

Capacitor Bank Calculation: [ Q_c = P (\tan(\cos^-1PF_old) - \tan(\cos^-1PF_new)) ] Using above: 400 kW old PF=0.7 (angle=45.6°), new PF=0.95 (angle=18.2°) [ Q_c = 400(\tan45.6° - \tan18.2°) = 400(1.02 - 0.33) = 276 \text kVAR ]