Power Conversion Guide
Master power conversions with practical examples for electrical systems, motor sizing, HVAC equipment, and industrial applications.
⚡ Electrical Systems & Load Analysis
Residential Electrical Planning
Circuit Breaker Sizing
Electric water heater: 4,500W, 240V
Current:
Continuous load:
Breaker size: Next standard = 25A
Wire size: 12 AWG (20A rating)
Use 25A breaker, 12 AWG wire
Load Center Capacity
Household loads analysis
HVAC: 5,000W
Water heater: 4,500W
Range: 8,000W
General outlets: 3,000W
Total:
At 240V:
Need 100A service minimum
Commercial Power Systems
Three-Phase Load Analysis
Office building: 480V, 3-phase system
Lighting: 50 kW
HVAC: 200 kW
Equipment: 75 kW
Total: 325 kW
Current:
Transformer:
Need 400 kVA transformer
Demand Factor Calculation
Restaurant electrical load diversity
Kitchen equipment: 80 kW × 0.8 = 64 kW
HVAC: 40 kW × 1.0 = 40 kW
Lighting: 15 kW × 1.0 = 15 kW
Outlets: 20 kW × 0.5 = 10 kW
Total demand: 64 + 40 + 15 + 10 = 129 kW
Connected load: 155 kW
Demand factor: 83%
🔧 Motor Sizing & Applications
Industrial Motor Selection
Conveyor Belt Motor
Belt speed: 100 ft/min, load: 500 lbs
Power required:
Friction force:
Speed:
Mechanical HP:
Motor size (90% eff):
Select 0.75 HP motor
Fan Motor Analysis
Centrifugal fan: 10,000 CFM, 4" SP
Air power:
Fan efficiency: 65%
Shaft power:
Motor efficiency: 92%
Motor input:
In kW:
Select 15 HP motor
Pump Motor Applications
Water Pump Sizing
Centrifugal pump: 800 GPM, 120 ft TDH
Water HP:
Pump efficiency: 78%
Brake HP:
Motor efficiency: 94%
Motor HP:
In kW:
Select 40 HP motor
VFD Energy Savings
Pump runs at 80% speed with VFD
Full speed power: 25 HP = 18.7 kW
VFD power:
VFD losses:
In kW:
Savings:
47% power reduction
❄️ HVAC Power Systems
Cooling System Power
Chiller Power Analysis
300-ton water-cooled chiller
Cooling capacity:
In kW:
Chiller COP: 6.0
Compressor power:
Pumps & fans: 45 kW
Total input:
System efficiency: 4.8 kW/ton
RTU Power Consumption
25-ton rooftop unit analysis
Cooling:
Compressor: 18 kW
Supply fan: 3.5 kW
Condenser fans: 2.8 kW
Total cooling:
Electric heat: 15 kW
Max power:
Unit efficiency: 0.97 kW/ton
Heating System Power
Boiler System Analysis
Commercial hot water boiler
Heat output: 2.5 MMBtu/hr
Boiler efficiency: 85%
Gas input:
Burner power: 150 kW equivalent
Pump power: 7.5 kW
Fan power: 3.5 kW
Electrical load:
Gas rate: 2,940 ft³/hr
Heat Pump Performance
Air-source heat pump: 5 tons
Heating capacity:
COP at 47°F: 3.2
Power input:
Aux heat strips: 10 kW
Total at 17°F:
COP with aux:
Cold weather COP: 1.13
🌞 Renewable Energy Systems
Solar Power Systems
Residential Solar Sizing
Home uses 1,200 kWh/month
Daily usage:
Peak sun hours: 5.5 hrs/day
System size:
Panel rating: 400W each
Panels needed:
System size:
Install 7.6 kW system
Solar vs Grid Power Cost
7.6 kW system analysis
Annual generation:
Grid rate: $0.12/kWh
Annual savings:
System cost: $20,000
Federal tax credit:
Net cost:
Payback: 8.1 years
Wind Power Analysis
Small Wind Turbine
10 kW rated turbine performance
Rated wind speed: 11 m/s (25 mph)
Cut-in speed: 3 m/s (7 mph)
Average wind: 7 m/s (16 mph)
Power at 7 m/s:
Capacity factor: 30%
Annual generation:
Average output: 3.0 kW
Wind Power Economics
Commercial wind farm analysis
Turbine rating: 2.5 MW
Capacity factor: 35%
Annual output:
Power price: $0.04/kWh
Annual revenue:
O&M costs: $45,000/year
Net income:
ROI: $261K annually
❌ Common Power Conversion Mistakes
Mistake #1: Confusing Power and Energy
Wrong: "This motor uses 10 kWh" (per what time?)
Right: "This 10 kW motor uses 240 kWh/day"
Power is rate (kW), Energy is total consumption (kWh)
Mistake #2: Ignoring Power Factor
Wrong: P = V × I (for AC loads)
Right: P = V × I × cos φ (include power factor)
Inductive loads (motors) have power factor < 1.0
Mistake #3: Wrong Horsepower Type
Wrong: All HP are equal (746 W)
Right: Mechanical HP ≠ Electrical HP ≠ Boiler HP
Boiler HP = 33,475 BTU/hr, much larger than mechanical HP
🎯 Professional Power Analysis Tips
Electrical System Design
- Safety factors: Size conductors 125% of continuous load
- Voltage drop: Keep under 5% for branch circuits
- Load diversity: Not all loads operate simultaneously
- Future expansion: Size panels 25% larger than calculated
Motor Selection Guidelines
- Service factor: 1.15 SF allows 15% overload
- Starting current: 6-8× full load amps typical
- Efficiency class: Premium efficiency saves energy
- Variable speed: VFDs save energy on variable loads
HVAC Power Considerations
- Seasonal variation: Heating vs cooling loads differ
- Part-load efficiency: Equipment efficiency varies with load
- Simultaneous operation: Size electrical for peak demand
- Auxiliary equipment: Include pumps, fans, controls
Cost Analysis Methods
- Operating costs: kWh × rate × hours/year
- Demand charges: Often 30-60% of commercial bills
- Time-of-use: Rates vary by time of day
- Lifecycle costs: Include maintenance and replacement