⚡ Understanding Diversity and Demand in Electrical Design
- MTS DNC ENERGY CONSULTANTS LIMITED
- Oct 27
- 3 min read
Updated: Nov 2
In electrical engineering, the actual operating load of a system rarely equals the sum of all installed loads. Why? Because not all equipment runs simultaneously or at full capacity. This is where diversity and demand factors come into play — essential concepts for designing efficient, safe, and cost-effective electrical systems.
🔍 What Is Diversity in Electrical Systems?
Diversity refers to the variation in load usage across a system. It recognizes that different devices operate at different times and intensities. For example:
Lighting: Controlled by daylight sensors or occupancy, many lights remain off in unused areas.
Office Equipment: Devices like photocopiers and hand dryers are used intermittently.
Motors: Often run below their rated capacity due to variable mechanical loads.
Cyclic Loads: Pumps, compressors, and lifts operate in cycles, not continuously.
Rarely Used Equipment: Fire safety pumps or emergency systems activate only during tests or emergencies.
Cooking Equipment: Draw full load briefly, then cycle to maintain temperature.
These patterns mean the total connected load is not a reliable indicator of actual demand.
📐 Diversity Factor vs Demand Factor
Two key metrics help engineers assess realistic operating conditions:
Factor | Definition | Formula | Insight |
Diversity Factor | Ratio of sum of individual demands to maximum system demand | Diversity = ∑Demands / Max Demand | Always ≥ 1; higher values mean more staggered usage |
Demand Factor | Ratio of maximum demand to total connected load | Demand = Max Demand / ∑Connected Load | Helps size equipment appropriately |
🔧 Example: Imagine a conveyor system with 6 motors, each rated at 4 kW. When a motor is actively carrying material, it draws 2 kW. When idle but still running to keep the belt moving, it draws 0.5 kW.
🧮 Load Breakdown
At any given moment, only one motor is actively carrying material. The rest are idling.
Active motor load: 2 kW
Idle motor load: 0.5 kW × 5 = 2.5 kW
Total operating load at any moment: 2 kW + 2.5 kW = 4.5 kW
🔢 Demand and Diversity Calculations
Connected load: 4 kW × 6 motors = 24 kW
Maximum demand: 4.5 kW
Sum of individual demands: 2 kW × 6 = 12 kW
Diversity Factor
Diversity Factor=∑Demands/ Maximum Demand=12/4.5=2.67
Demand Factor
Demand Factor=Maximum Demand/ Connected Load=4.5/24=0.1875
📈 What This Means
The diversity factor of 2.67 shows that not all motors operate at full load simultaneously.
The demand factor of 18.75% helps engineers size equipment more accurately, avoiding overspecification.
If the conveyor speed increases and all motors carry material simultaneously, the maximum demand would rise to 12 kW, reducing the diversity factor to 1 and increasing the demand factor to 0.5.
💡 Application in Building Services
Lighting
Even in commercial buildings, not all luminaires are active. Local switching and daylight linking reduce simultaneous usage, introducing diversity.
Small Power Loads
Designers often overestimate the number of devices in office spaces. Real-world data shows demand grows slower than connected load. Accurate assessments help avoid oversizing HVAC systems, which can lead to poor control and overcooling.
Power Factor
Different loads have varying power factors. For initial analysis, working in real power (kW) simplifies calculations, but total system load must consider reactive components.
Electric Heating
Heating loads should be added independently to demand calculations. In air-conditioned buildings, heating and cooling rarely peak together — another layer of diversity to consider.
🧠 Why It Matters
Understanding diversity and demand ensures:
Proper sizing of electrical infrastructure
Efficient HVAC design
Reduced energy waste
Lower installation and operational costs
Improved system reliability
📞 Need help designing your next project with diversity and demand in mind? Our team of electrical engineers can guide you through load assessments, HVAC integration, and power factor optimization.
Disclaimer: The content shared in these posts is intended for informational purposes only and should not be interpreted as design advice, specifications, or a calculation template. For professional guidance or design services, please contact us through our contact form.
